Controller for active power correction. With low starting current: power factor correctors from STM

To date, there are two approaches to building power supplies that provide a stable output voltage or current at the output - power supplies with parametric and pulse stabilization.

In linear sources, the stabilization of the output parameter is carried out at the expense of a non-linear element. Pulse - work on the principle of energy control in an inductor using one or more switching keys.

The advantage of the former is the low level of high-frequency noise, which is important for analog equipment. Behind the pulsed sources are higher powers and a better power-to-size ratio. In addition, they have a higher efficiency. The questions of complexity or simplicity of circuitry are very controversial, because. modern industry offers a wide range of solutions, including single-chip ones, for any application.

But for a network, linear and switching power supplies are a non-linear load - the shape of the consumed current will differ from a sinusoidal one, which will lead to the appearance of additional harmonics, and therefore to the appearance of a reactive power component, additional heating and losses in power lines. In addition, other power consumers have to take additional measures to protect against mains interference - especially in the case of high power switching units operating under load. Restrictions on permissible interference in the network from a working device are regulated by the relevant international and national standards. There is no doubt that Russian standards in this area will become tougher and approach the world standards. As a result, it is those companies that master the techniques for reducing network interference that will gain a significant advantage over competitors.

To reduce the influence of the current consumer on the network, active or passive correctors are used. Passive correctors are chokes, most often used in low power devices and non-critical in terms of overall dimensions. In other cases, it is advisable to use active high-frequency correctors, often called power factor correctors (PFC or PFC - Power Factor Correction). The main tasks of the KCM include:

• Giving the current consumed from the network a sinusoidal shape (reducing the harmonic coefficient);
• Output power limitation;
• Short circuit protection;
• Undervoltage or overvoltage protection.

In fact, PFC can be considered as a kind of buffer cascade (circuit) that reduces the mutual influence of the mains and power supply.

A typical structure of a power corrector is shown in Figure 1.

Rice. one.

PFC can be implemented not only on discrete elements, but also with the help of specialized microcircuits - PFC controllers (PFC-correctors). The main manufacturers of power factor corrector controllers include:

• STMicroelectronics- L4981, L656x;

• Texas Instruments UCx854, UC28xx;

• International Rectifier - IR115x;

• ON Semiconductor- MC3x262, MC33368, NCP165x, NCP160x;

• Fairchild Semiconductor- FAN48xx, FAN69x, FAN7527;

• Linear Technology Corporation- LTC1248.

PFC controllers STMicroelectronics

STMicroelectronics offers several series of high-performance PFC controllers capable of providing various modes of device operation. Additional options simplify the construction of switching power supplies, taking into account energy saving standards and requirements for the level of distortion introduced into the supply network.

Table 1. Power Factor Corrector Controllers STMicroelectronics

Chip	Frame	Working mode	Voltage power, V	Consumption current, mA active / starting (low consumption)	Note
L4981	PDIP 20; SO-20	SSM	19,5	12/0,3	Soft start; over voltage, over current protection
L6561	DIP-8; SO-8	TM	11…18	4/0,05	Surge protection
L6562A	DIP-8; SO-8	TM, Fixed Off Time	10,5…22,5	3,5/0,03	Surge protection
L6562AT	SO-8	TM, Fixed Off Time	10,5…22,5	3,5/0,03	Surge protection
L6563H	SO-16	TM, tracking boost	10,3…22,5	5/0,09
L6563S	SO-14	TM, tracking boost	10,3…22,5	5/0,09	High voltage start; protection against overvoltage, open loop, inductor saturation
L6564	SSOP 10	TM, tracking boost	10,3…22,5	5/0,09	High voltage start; protection against overvoltage, open loop, inductor saturation

Power Corrector Controller IC L4981 allows you to build high-performance power supplies with a sinusoidal current consumption. The power factor can be as high as 0.99 with low harmonics. The microcircuit itself is implemented according to BCD 60II technology and operates on the principle of average current control (CCM), maintaining a sinusoidal current consumption.

L4981 can be used in systems with supply voltages of 85…265 V without an external power switch driver. The "A" series for the PWM controller uses a fixed frequency; the "B" series additionally uses frequency modulation to optimize the input filter.

The microcircuit also includes: a precision reference voltage source, a mismatch amplifier, a blocking circuit for operation during a critical voltage drop, a current sensor, a soft start circuit and overvoltage and overcurrent protection. Current protection trip level for L4981A set using an external resistor; to improve the accuracy in series L4981B an external voltage divider is used.

Key features:

• Boost-PWM with power factor up to 0.99;
• Current distortion no more than 5%;
• Universal input;
• Powerful output stage (bipolar and MOSFETs);
• Voltage sag protection with hysteresis and programmable turn-on threshold;
• Built-in reference voltage source with an accuracy of 2% (accessible from the outside);
• Low start current (~0.3mA);
• Soft start system.

Series L6561 is an improved version of the PFC controller L6560(fully compatible with it). Main innovations:

• Improved analog multiplier that allows the device to operate over a wide input voltage range (85 to 265V) with excellent harmonic distortion (THD) performance;
• Starting current reduced to a few milliamps (~4mA);
• Added operation enable output to ensure low power consumption in standby mode ( stand by).

Key features embodied in BCD mixed technology:

• Ultra-low starting current (~50µA);
• 1% built-in voltage reference;
• Programmable surge protection;
• Current sensor without external low-pass filter;
• Small quiescent current.

The output stage is capable of driving power MOS or IGBT switches with control currents up to 400 mA. The microcircuit operates in the transitional mode of operation of power factor correctors - Transition Mode (TM) - an intermediate mode between continuous (CCM) and intermittent (DCM). The L6561 is optimized for ballast power supply circuits for gas discharge lamps, mains adapters, switching power supplies.

KKM controller L6562A/L6562AT also operates in transient mode (TM) and is pin-to-pin compatible with the L6561 and L6562 predecessors. Its highly linear multiplier features special circuitry to reduce input AC mismatch, allowing it to operate over a wide range of input voltages with low harmonic content under various loads. The output voltage is controlled by an operational amplifier with a high-precision voltage reference (up to 1% accuracy).

The L6562A/L6562AT in idle mode has a consumption of about 60 μA and an operating current of only 5 mA. The presence of an on/off control input facilitates the creation of end devices that meet the requirements of Blue Angel, EnergyStar, Energy2000 and several others.

An effective two-level overvoltage protection system works even in the event of an overload at the time of starting the corrector or in the event of a load break during operation.

The output stage is capable of providing an output current of up to 600 mA and an input current of up to 800 mA, which is sufficient to drive high power MOSFETs or IGBT switches. In addition to the above features, the L6562A can operate in a proprietary fixed off time mode ( Fixed Off Time) - Figure 2.

Rice. 2.

Series of KKM controllers L6563, L6563S, L6563H, L6564 built according to the scheme of a typical power factor corrector operating in TM mode with a number of additional features.

L6563, L6563S have a Tracking boost mode of operation, a bidirectional voltage lead input, an operation enable input, a precision reference voltage source (accuracy at 25 ° С within 1 ... 1.5%). In addition, the microcircuit is integrated with: overvoltage protection circuits with an adjustable threshold, feedback loop break (microcircuit off), inductor saturation (microcircuit off); programmable AC voltage drop detector. Maximum current consumption L6563x is no more than 6 mA in active mode, the starting current is less than 100 μA.

Corrector controller chip
power factor L6562A

Areas of application for the KKM controller include:

• Switching power supplies that meet the requirements of IEC61000-3-2 standards (TVs, monitors, computers, game consoles);
• AC/DC converters/chargers up to 400W;
• Electronic ballast;
• The input layer of servers and web servers.

The key features of the L6562A are:

• Proprietary multiplier solution;
• Customizable surge protection levels;
• Ultra-low starting current - 30mkA;
• Low quiescent current - 2.5mA;
• Powerful output stage for power switches control - -600,800mA.

Chips are available in compact eight-pin DIP-8 and SO-8 packages. The block diagram of the L6562A is shown in Figure 3.

Rice. 3.

The inverted input of the error amplifier shares the functions of the chip enable pin. When the voltage on it is below 0.2 V, it turns off the microcircuit, thereby reducing its power consumption, and when the threshold of 0.45 V is exceeded, the microcircuit goes into active mode. The main purpose of this function is to control the PFC controller, for example, it can be controlled by the next PWM controller of the voltage converter. An additional capability provided by the Shutdown function is automatic shutdown in the event of a voltage-to-ground fault in the output divider's low-resistance resistor or an open divider circuit.

The output signal of the error amplifier is fed to its inverse input through compensating feedback loops. In fact, the operation of these circuits determines the stability of the output voltage, high power factor and low harmonics.

After the rectifier, the main supply voltage is fed to the input of the multiplier through a voltage divider and serves as a source of a reference sinusoidal signal for the current loop.

The voltage from the measuring resistor in the power switch circuit is fed to the input of the PWM comparator, where it is compared with the reference sinusoidal signal to determine the moment of opening the key. To reduce the influence of impulse noise, a delay of 200 ns from the pulse front is implemented in hardware. On the negative edge of the inductor demagnetization pulse, the power switch closes.

An example of an L6562A switching circuit is a 400V step-up voltage source (Figure 4).

Rice. 4.

The second example is the use of the L6562A as part of a power supply for LED lamps (Figure 5).

Rice. five.

The L6562A has dedicated circuitry to reduce the effect of transients around zero AC input voltage when the diodes in the rectifier bridge are still off and there is zero current through the bridge. To combat this effect, the built-in circuit forces the PFC controller to pump more power at the moment the mains voltage crosses zero (the time interval for the power switch to open increases). As a result, the time interval during which the energy (current) consumption of the circuit is insufficient is reduced, and the filter capacitor after the bridge is completely discharged. A low reference voltage value allows the use of a lower resistance resistor to measure the current in the power switch circuit, and the power dissipated on it is correspondingly reduced (less power dissipation ® less heating ® lower requirements for the cooling and ventilation system). The low input currents of dynamic surge protection allow the use of a high-resistance top resistor in the voltage divider of the voltage feedback loop without increasing the effect of noise. As a result, the current consumption of the circuit in standby mode is reduced (important due to the requirements of energy saving standards). Table 2 shows the main parameters of the L6562A PFC controller.

Table 2. Main operating parameters L6562A

Parameter	Meaning
On/off thresholds, V	12,5/10
Dispersion of values ​​of a threshold of switching off (max), V	±0.5
Chip current before starting (max), µA	60
Multiplier Gain	0,38
Reference voltage value, V	1,08
Response time to current change, ns	175
Dynamic switching current of the OVP circuit, μA	27
Thresholds of the detector of zero, off / operation / hold, V	1,4/0,7/0
Chip on/off thresholds, V	0,45/0,2
Voltage drop on the internal driver of the key, V	2,2
Delay relative to the front of the pulse in the current sensor, ns	200

All of this makes the L6562A an excellent low cost solution for UPSs up to 350W that are compliant with EN61000-3-2 standards.

Applications and calculation methods for typical assemblies for circuits based on the L6562A/AT are given in the application guides; a list of key documents is given below.

AN3159: STEVAL-ILH005V2: 150 W HID electronic ballast - built-in block of electronic ballast with power up to 150 W.

AN2761: Solution for designing a transition mode PFC preregulator with the L6562A — examples of building a preliminary regulator with PFC in transitive mode based on L6562A.

AN2782: Solution for designing a 400 W fixed-off-time controlled PFC preregulator with the L6562A - An example of the development of a 400-watt PFC pre-regulator based on the L6552A in fixed time off mode.

AN2928: Modified buck converter for LED applications - Modified buck converter for LED lighting.

AN3256: Low-cost LED driver for an A19 lamp - LED driver for A19 lamps at a low price.

AN2983: Constant current inverse buck LED driver using L6562A - Constant current LED driver on L6562A.

AN2835: 70 W HID lamp ballast based on the L6569, L6385E and L6562A — Scheme of electronic ballast for gas-discharge lamps.

AN2755: 400 W FOT-controlled PFC pre-regulator with the L6562A - 400-watt pre-regulator based on the L6562A in fixed-off-time mode.

AN2838: 35 W wide-range high power factor flyback converter demonstration board using the L6562A — Demonstration board of a 35-watt wide-range high power factor converter based on the L6562A.

AN3111: 18W single-stage offline LED driver - Standalone single level 18W LED driver.

AN2711: 120 VAC input-Triac dimmable LED driver based on the L6562A — Thyristor adjustable LED driver on L6562A 120W.

Demo boards offered by STMicroelectronics allow you to quickly understand the various modes of operation of microcircuits, as well as see how the devices behave in different operating conditions. In addition, debugging tools serve as device prototypes. At the time of this writing, the following set of debugging tools is offered for familiarization with the L6562A - table 3.

Table 3 Debugging tools for L6562A

Pay	Appearance	Description
STEVAL-ILL027V2		18W standalone LED driver
EVL6562A-TM-80W		Evaluation board for 80-watt power factor corrector in TM mode
STEVAL-ILL013V1		Adjustable Standalone PFC and Power Adjustable LED Driver Based on L6562A
EVL6562A-LED		L6562A Constant Current LED Driver Demo Board
STEVAL-ILL016V2		Thyristor standalone LED driver on L6562AD and TSM1052
STEVAL-ILL019V1		35W standalone LED driver for HB RGGB quad LED sources
STEVAL-ILL034V1		A19 LED driver based on L6562A (targeted for the US market)
EVL6562A-400W L6562A		Pre-voltage regulator with power factor correction in fixed-off-time mode

PFC controllers STMicroelectronics series L6563S/H

In addition to the standard features and capabilities, the L6563S/H series power factor controllers (Figure 6) have a number of options that improve the performance of the end devices based on them.

Rice. 6.

Among the distinguishing features:

• Ability to work in tracking boost mode;
• 1/V 2 -correction;
• Protection against overvoltage, open circuit feedback, saturation of the inductor.

Highly linear multiplier with correction of step distortions of the main current allows microcircuits to work in a wide range of input AC voltage with a minimum level of non-linear distortions even at heavy loads.

The output voltage is controlled by an error amplifier and a precision voltage source (1% at 25°C). The stability of the feedback loop is monitored by voltage feedforward (1/V 2 -correction), which in this microcircuit uses a unique proprietary technique that can significantly improve transient processes on the line during drops or surges in the mains voltage (the so-called bidirectional communication - “bidirectional ").

The L6563H PFC controller has the same feature set as the L6563/L6563S with the addition of a high voltage trigger source. This feature is in demand in applications with stringent energy saving requirements, as well as in cases where the PFC controller operates in master mode.

Additionally, the L6563H has the ability to operate in rise tracking mode ( tracking boost operation) - the output voltage changes in response to changes in the mains voltage.

The L6563H can be used in power supplies up to 400W in compliance with EN61000-3-2, JEITA-MITI standards.

The L6564 is a smaller version of the L6563S in SSOP-10 package - it has the same driver, voltage reference and control system. The L6563A series does not have inductor saturation protection.

Just like the L6562A, the L6263x PFC controllers can operate in fixed off time mode ( Fixed Off Time). In addition, the controller status outputs allow you to control the PWM controller of the DC / DC converter, fed by the preliminary regulator of the PFC controller in emergency situations (feedback break, inductor saturation, overload). On the other hand, it is possible to turn off the PFC controller if the DC/DC converter is operating at a low load. Unlike the L6562x series, there are separate controller control inputs, which makes the control quite flexible.

AN3142: Solution for designing a 400 W fixed-off-time controlled PFC preregulator with the L6563S and L6563H - 400-watt PFC regulator on L6563S and L6563H in fixed-off-time mode.

AN3027: How to design a transition-mode PFC pre-regulator with the L6563S and L6563H - Development of a TM PFC controller using L6563S and L6563H.

AN3203: EVL250W-ATX80PL: 250W ATX SMPS demonstration board - 250W ATX power supply demo board.

AN3180: A 200 W ripple-free input current PFC pre-regulator with the L6563S 1 — The power factor corrector on the L6563L is free from input current noise.

AN2994: 400 W FOT-controlled PFC pre-regulator with the L6563S - 400-watt PFC controller on L6563S in fixed-off-time mode.

AN3119: 250 W transition-mode PFC pre-regulator with the new L6563S — 250-watt PFC controller on L6563S in transition-mode.

AN2941: 19 V - 75 W SMPS compliant with latest ENERGY STARR criteria using the L6563S and the L6566A - 19V 75W switching power supply compliant with the latest Energy Starr standard.

AN3065: 100 W transition-mode PFC pre-regulator with the L6563S — 100-watt PFC controller on L6563S in transition-mode.

Demo boards for L6563S/L6564 are shown in Table 4.

Table 4 Debugging tools for L6563S/ L6564

Name	Appearance	Description
EVL250W-ATX80PL		250W PSU ATX Board
EVL6563S-250W		250-watt pre-regulator with PFC based on L6563S in TM mode
EVL6563S-100W		100W L6563S PFC Pre-Regulator in TM Mode
EVL6563S-200ZRC		Power factor corrector on L6563S free from input current noise (200W)
EVL185W-LEDTV		185W PFC Standby Power Supply for LED TVs based on L6564, L6599A, and VIPER27L

Additionally, at the request of the developer, software products can be provided to automate the development and calculation of circuits on the L6563S, L6564 in TM and fixed-off-time modes.

Component Selection Guidelines
for KKM controller

For the correct operation of microcircuits of PFC controllers, stable operation of the device and its compliance with the requirements of standards, it is necessary to select the appropriate operating mode.

As a rule, for powers less than 200 W, L6562A/3S/3H/4 PFC controllers are switched on in TM mode. For devices operating with powers of more than 200 W, the L4981 chip is used (its operating mode is CCM). It is also possible to use the L6562A/3S/3H/4 series in Fixed-Off-Time or Reeple-Steering modes.

The power MOSFET switch and rectifier diode for the power part of the power corrector or power supply can be easily selected from STMicroelectronics products.

For low power devices (up to 100 W), power keys of the SuperMesh3 family, for example, the STx10N62K3 series, are suitable. For medium power (100 ... 1000 W) - the MDMesh2 family of the STx25NM50M series. And for powerful sources operating with powers of more than 1 kW - the MDMesh5 family of the STP42N65M5 series.

Conclusion

Despite the relatively small range of offered PFC controllers in terms of the number of series, STMicroelectronics products, thanks to a number of successful circuit solutions and a variety of possible operating modes, cover almost the entire range of applications for switching energy converters - step-up / step-down power supplies, LED lamp drivers, power factor correctors.

In addition, for the entire range of applications, information and technical support is provided to the developer - from application recommendations and programs for calculating blocks and nodes to debug and demonstration boards.

Obtaining technical information, ordering samples, delivery - e-mail:

About ST Microelectronics

Hello again!..
Unfortunately, my article was delayed, because. an urgent work project arose, and there were also interesting difficulties when implementing the power factor corrector ( further KKM). And they were caused by the following - in our production, to control the KKM, we use a “custom” microcircuit, which Austria, especially in 1941, friendly, especially in 1941, produces for our tasks and, accordingly, cannot be found on sale. Therefore, the task arose to remake this module for an accessible elementary base, and my choice fell on a PWM controller chip - L6561.
Why is she? Banal accessibility, or rather found it in "Chip & Dip", I read the datasheet - I liked it. I ordered 50 pieces at once, because. cheaper and in my amateur projects I already have a few tasks for her.

Now about the main thing: in this article I will tell you how almost from scratch I recalled the design of single-cycle converters ( it would seem what are they doing here), why he killed a dozen keys and how you can avoid it. This part will tell the theory and what happens if you neglect it. The practical implementation will be released in the next part, as I promised along with charger, because they are essentially one module and they need to be tested together.
Looking ahead, I’ll say that for the next part I have already prepared a couple of dozen photos and videos, where my memory is not for long "retrained" first to the welding machine, and then to the power supply for "goat". Those who work in production will understand what kind of animal it is and how much it consumes to keep us warm)))

And now to our sheep...

Why do we need this KKM at all?

The main thing misfortune The "classic" rectifier with storage capacitors (this is the thing that turns 220V AC into + 308V DC), which operates from a sinusoidal current, is that this very capacitor is charged (takes energy from the network) only at the moments when the voltage is applied more to him than to himself.

In human language, faint of heart and with scientific degrees, do not read

As we know, the electric current completely refuses to go if there is no potential difference. The direction of current flow will also depend on the sign of this difference! If you freaked out and decided to try to charge your mobile with a voltage of 2V, where the Li-ion battery is designed for 3.7V, then nothing will come of it. Because the current will be given by the source that has a higher potential, and the one with the lower potential will receive energy.
Everything is like in life! You weigh 60 kg, and the guy on the street who came up to ask you to call is 120 kg - it's clear that he will distribute pizdyuly, and you will receive them. So here - a battery with its 60 kg 2V will not be able to give current to a battery with 120 kg 3.7V. With a capacitor in the same way, if it has + 310V and you apply + 200V to it, then it will refuse to receive current and will not charge.

It is also worth noting that, based on the “rule” described above, the time allotted for the capacitor to charge will be very small. In our case, the current changes according to a sinusoidal law, which means the required voltage will be only at the peaks of the sinusoid! But the capacitor needs to work, so it gets nervous and tries to recharge. He knows the laws of physics, unlike some, and “understands” that time is short and therefore begins to consume just a huge current at these very moments when the voltage is at its peak. After all, it should be enough to operate the device until the next peak.

A little about these "peaks":

Figure 1 - Peaks in which the capacitor is charged

As we can see, the piece of the period in which the EMF takes on a sufficient value for the charge (figuratively 280-310V) is about 10% of the full period in the AC network. It turns out that instead of constantly taking energy smoothly from the network, we pull it out only in small episodes, thereby we “overload” the network. With a power of 1 kW and an inductive load, the current at the time of such “peaks” can calmly reach values ​​​​of 60-80A.

Therefore, our task is to ensure a uniform selection of energy from the network so as not to overload the network! It is KKM that will allow us to implement this task in practice.

Who is this KKM of yours?

Power corrector- This is a conventional step-up voltage converter, most often it is single-ended. Because we use PWM modulation, then at the time of the open key, the voltage across the capacitor is constant. If we stabilize the output voltage, then the current taken from the network is proportional to the input voltage, that is, it changes smoothly according to a sinusoidal law without the previously described consumption peaks and jumps.

Circuitry of our KKM

Then I decided not to change my principles and also relied on the datasheet of the controller I chose - L6561. Company engineers STMicroelectronics have already done everything for me, and more specifically, they have already developed the ideal circuitry for their product.
Yes, I can count everything from scratch and spend a day or two on this business, that is, all my own and so rare weekends, but I ask why? To prove to myself that I can, this stage, fortunately, has long been passed)) Here I recall a bearded anecdote about the area of ​​red balls, they say a mathematician applies a formula, and an engineer takes out a table with the area of ​​red balls .... So it is in this case.

I advise you to immediately pay attention to the fact that the circuit in the datasheet is designed for 120 W, which means we should follow it adapt to our 3 kW and extreme operating stresses.

Now some documentation for the above:
Datasheet on L6561

If we look at page 6, we will see several diagrams, we are interested in a diagram with a signature Wide Range Mains, which means from Basurman "for operation in a wide range of supply voltage" . It was this “mode” that I had in mind when speaking of extreme stresses. The device is considered universal, that is, it can operate from any standard network (for example, in the states 110V) with a voltage range of 85 - 265V.

This solution allows us to provide our UPS with the function of a voltage stabilizer! For many, this range will seem redundant and then they can make this module taking into account the supply voltage of 220V + - 15%. This is considered the norm and 90% of devices in the price category up to 40 thousand rubles are completely devoid of cash registers, and 10% use it only with the calculation of deviations of no more than 15%. This undoubtedly allows you to somewhat reduce the cost and dimensions, but if you have not forgotten, then we are making a device that must compete with ARS!

Therefore, for myself, I decided to choose the most correct option and make an indestructible tank that can be pulled out even in the country, where there is a welding machine or a pump in the well 100V in the network:


Figure 2 - Standard circuit solution offered by ST

Adaptation of standard circuitry to our tasks

a) When I look at this scheme from LH, the first thing that comes to mind is you need to add a common mode filter! And rightly so, because at high power, they will begin to "crazy" electronics. For currents of 15 A or more, it will have a more complicated look than many are used to seeing in the same computer PSUs, where there are only 500-600 watts. Therefore, this revision will be a separate item.

B) We see capacitor C1, you can take a tricky formula and calculate the required capacitance, and I advise those who want to delve into it to do it, remembering electrical engineering 2 courses from any polytechnic in one. But I will not do this, because. according to my own observations from old calculations, I remember that up to 10 kW this capacity grows almost linearly relative to the increase in power. That is, taking into account 1 uF per 100 W, we get that for 3000 W we need 30 uF. This container is easily collected from 7 film capacitors of 4.7 uF and 400V each. Even a little with a margin, because The capacitance of a capacitor is highly dependent on the applied voltage.

C) We need a serious power transistor, because. the current consumed from the network will be calculated as follows:


Figure 3 - Calculation of the rated current for PFC

We got 41.83A. Now we honestly admit that we will not be able to keep the temperature of the transistor crystal in the region of 20-25 ° C. Rather, we can overpower it, but it will be expensive for such power. After 750 kW, the cost of cooling with freon or liquid oxygen is eroded, but so far this is far from it))) Therefore, we need to find a transistor that can give 45-50A at a temperature of 55-60 o C.

Given that there is inductance in the circuit, then I prefer IGBT transistor, for the most tenacious. The limiting current must be chosen for the search, first about 100A, because this is the current at 25 ° C, with increasing temperature, the limiting switched current of the transistor decreases.

A little about Cree FET

I literally received on January 9 a parcel from the States from my friend with a bunch of different transistors for a test, this miracle is called - CREE FET. I won’t say that this is a new mega technology, in fact, silicon carbide-based transistors were made back in the 80s, they just brought it to mind why only now. I, as the original materials scientist and composite engineer, am generally scrupulous about this industry, so I was very interested in this product, especially since 1200V was declared at tens and hundreds of amperes. I couldn’t buy them in Russia, so I turned to my former classmate and he kindly sent me a bunch of samples and a test board with forward.
I can say one thing - it was my most expensive fireworks!
8 keys flickered so that I was upset for a long time ... In fact, 1200V is a theoretical figure for the technology, the declared 65A turned out to be only a pulsed current, although the nominal one was clearly written in the documentation. Apparently there was a "rated impulse current" well, or whatever else the Chinese come up with. In general, it's still bullshit, but there is one BUT!
When I did it all CMF10120D corrector for 300 W, it turned out that on the same radiator and circuit it had a temperature of 32 ° C versus 43 for IGBT, and this is very significant!
Conclusion on CREE: the technology is raw, but it is promising and it definitely SHOULD be.

As a result, after looking through the catalogs from the exhibitions I visited (a handy thing, by the way, ala parametric search), I chose two keys, they became - IRG7PH50 And IRGPS60B120. Both are at 1200V, both are at 100+A, but upon opening the datasheet, the first key was eliminated immediately - it is able to switch a current of 100A only at a frequency of 1 kHz, which is disastrous for our task. The second key is 120A and a frequency of 40 kHz, which is quite suitable. See the datasheet at the link below and look for a graph with the dependence of current on temperature:

Figure 4.1 - Graph with the dependence of the maximum current on the switching frequency for IRG7PH50, let's leave it on the frequency converter

Figure 4.2 - Graph with operating current at a given temperature for IRGPS60B120

Here we observe the cherished figures that show us that at 125 ° C both the transistor and the diode can easily handle currents slightly more than 60A, while we can implement the conversion at a frequency of 25 kHz without any problems and restrictions.

D) Diode D1, we need to choose a diode with an operating voltage of at least 600V and a current rated for our load, that is 45A. I decided to use those diodes that I had at hand (not long ago I bought them to develop a welder under the "oblique bridge") this is - VS-60EPF12. As can be seen from the marking, it is 60A and 1200V. I put everything with a margin, because. this prototype is made for myself and I feel so much calmer.
You can actually put a 50-60A and 600V diode, but there is no price between the 600 and 1200V version.

E) Capacitor C5, everything is the same as in the case of C1 - it is enough to increase the value from the datasheet in proportion to the power. It’s only worth considering that if you are planning a powerful inductive load or a dynamic one with rapid power increases (like a 2 kW concert amp), then it’s better not to save on this item.
I will put in my version 10 electrolytes at 330 uF and 450V, if you plan to power a couple of computers, routers and other trifles, then you can limit yourself to 4 electrolytes of 330 microfarads and 450V.

E) R6 - it is also a current shunt, it will save us from crooked hands and accidental errors, it also protects the circuit from short circuits and overload. The thing is definitely useful, but if we act like engineers from ST, then at currents of 40A we will get an ordinary boiler. There are 2 options here: a current transformer or a factory shunt with a drop of 75mV + op amp ala LM358.
The first option is simpler and provides galvanic isolation of this circuit node. How to calculate the current transformer I gave in a previous article, it is important to remember that the protection will work when the voltage on leg 4 rises to 2.5V (in reality, up to 2.34V).
Knowing this circuit voltage and current, using the formulas from parts 5 you can easily count the current transformer.

G) And the last point is the power choke. About him a little lower.

Power choke and its calculation

If someone carefully read my articles and he has an excellent memory, then he should remember article 2 and photo no. 5, it shows 3 hank elements that we use. I'll show you again:

Figure 5 - Frames and core for power winding products

In this module, we will again use our favorite pulverized iron toroidal rings, only this time not one, but 10 at once! And how did you want? 3 kW is not Chinese crafts for you ...

We have initial data:
1) Current - 45A + 30-40% for the amplitude in the inductor, total 58.5A
2) Output voltage 390-400V
3) input voltage 85-265V AC
4) Core - material -52, D46
5) Clearance - distributed

Figure 6 - And again, dear Starichok51 saves us time and considers it a program CaclPFC

I think the calculation showed everyone how serious it would be)) 4 rings, yes a radiator, a diode bridge, and IGBT - horror!
Winding rules can be read in the article "Part 2". The secondary winding on the rings is wound in the amount - 1 turn.

Throttle summary:

1) as you can see, the number of rings is already 10 pieces! This is expensive, each ring costs about 140 rubles, but what will we get in return in the following paragraphs
2) the operating temperature is 60-70 ° C - this is absolutely ideal, because many lay the operating temperature at 125 ° C. We lay 85 ° C in our production. Why this was done - for a restful sleep, I calmly leave home for a week and I know that nothing will flare up, everything icy will not burn out. I think the price for this at 1500r is not so deadly, is it?
3) I set the current density to a meager 4 A / mm 2, this will affect both heat and insulation and, accordingly, reliability.
4) As you can see, according to the calculation, the capacitance after the inductor is recommended to be almost 3000 microfarads, so my choice with 10 electrolytes of 330 microfarads fits perfectly here. The capacitance of capacitor C1 turned out to be 15 microfarads, we have a double margin - you can reduce it to 4 film conders, you can leave 7 pieces and it will be better.

Important! The number of rings in the main inductor can be reduced to 4-5, simultaneously increasing the current density to 7-8 A / mm 2. This will save a lot of money, but the current amplitude will increase somewhat, and most importantly, the temperature will rise to at least 135 ° C. I think this is a good solution for a welding inverter with 60% duty cycle, but not for a UPS that works around the clock and probably in a rather limited space .

What can I say - we have a growing monster)))

Common mode filter

To understand how the circuits for this filter differ for currents of 3A (the computer PSU mentioned above) and for currents of 20A, you can compare the schematic from Google on ATX with the following:


Figure 7 - Schematic diagram of the common mode filter

A few features:

1) C29 is a capacitor for filtering electromagnetic interference, it is marked "X1". Its value should be in the range of 0.001 - 0.5 mF.

2) The throttle is wound on on the core E42/21/20.

3) Two chokes on rings DR7 and DR9 are wound on any core from a spray and with a diameter of more than 20 mm. I wound on all the same D46 from -52 material before filling in 2 layers. There is practically no noise in the network even at rated power, but this is actually redundant even in my understanding.

4) Capacitors C28 and C31 of 0.047 uF and 1 kV and they must be set to class Y2.

According to the calculation of the inductance of the chokes:

1) Common mode inductance should be 3.2-3.5mH

2) Inductance for differential chokes is calculated by the formula:


Figure 8 - Calculation of the inductance of differential chokes without magnetic coupling

Epilogue

Using the competent and professional developments of ST engineers, I managed to produce, at minimal cost, if not perfect, then simply excellent active power factor correction with better parameters than any Schneider. The only thing you should definitely remember is how much you need it? And based on this, adjust the parameters for yourself.

My goal in this article was just to show the calculation process with the possibility of correcting the initial data, so that everyone, having decided on the parameters for their tasks, would already calculate and manufacture the module. I hope I managed to show this and in the next article I will demonstrate the joint operation of the KKM and the charger from part No. 5.

V.Dyakonov, A.Remnev, V.Smerdov

Recently, the market of household and office radio-electronic equipment (REA) increasingly appears equipment, the composition of the power sources which include new units - power correctors (KM). The article deals with the application of CM, the principle of their operation, diagnostics and repair.

Most modern REA power supplies are switching secondary power supplies with a transformerless bridge rectifier and a capacitive filter. Along with the advantages (high efficiency, good weight and size indicators), they have a relatively low power factor (0.5 ... 0.7) and an increased level of harmonics of the current consumed from the network (> 30%). The shape of the current consumed by such sources is shown in fig. 1 with solid lines.

The non-sinusoidal waveform of the current leads to the occurrence of electromagnetic interference, clogging the AC network, and the failure of other electronic equipment.

The above-described power supplies, being single-phase consumers, with a large amount of electronic equipment and its irrational connection to a three-phase supply network, can cause phase imbalance. In this case, part of the electronic equipment will operate at increased voltage, and the other at reduced voltage, which is always undesirable. To eliminate phase imbalance in a three-phase network, as a rule, a neutral wire is introduced, which equalizes the voltage in all phases. However, with the pulsed nature of the consumed current and a large number of its harmonic components, an overload of the neutral wire is possible. This is due to the fact that its cross section is usually 2 ... 2.5 times smaller than that of phase wires. For safety reasons, it is forbidden to protect this wire with fuses or circuit breakers. Obviously, under adverse conditions, the neutral wire may burn out and, as a result, the occurrence of phase imbalance.

In this regard, the requirements for electromagnetic compatibility of secondary pulse sources with the supply network are becoming more and more stringent and the level of higher harmonics of the current consumed from the network for all single-phase consumers is sharply limited. At present, the new European standards require improvement of the shape of the consumed current only at consumer powers over 200 W, and in the near future these requirements will be introduced for consumers with power up to 50...70 W.

Currently, passive and active current waveform corrections are used.

Passive correction circuits, consisting of inductances and capacitances, provide a power factor that shows the difference in the shape of the consumed current from a sinusoid (not worse than 0.9 ... 0.95). With structural simplicity and reliability, passive correction circuits have relatively large dimensions and are sensitive to changes in the frequency of the supply voltage and the magnitude of the load current.

More promising is the use of active CMs, which form a sinusoidal consumed current at the input of the switching power supply, which coincides in phase and frequency with the supply voltage. Such CMs have small dimensions due to operation with conversion frequencies of several tens of kilohertz and provide a power factor of 0.95 ... 0.99.

It is possible to generate a sinusoidal current at the input of the bridge rectifier of a switching power supply using one of the circuits of DC-to-DC converters using the principle of tracking high-frequency pulse-width modulation (PWM). In this case, step-up converters are most often used, which have the following advantages:
. the power transistor has a source connection with a common wire, which facilitates the construction of its control circuit;
. the maximum voltage across the transistor is equal to the output voltage;
. the presence of an inductance connected in series with the load provides filtering of high-frequency components.

Consider the principle of operation of an active CM implemented on a boost converter with a tracking PWM (Fig. 2).

First, let's consider the operation of the KM circuit without multiplication nodes (UM) and load voltage sensor (LNS), the role of which is described below. The reference voltage of a sinusoidal form, obtained from the rectified voltage sensor (RVS), is supplied to one of the inputs of the control circuit (CS) by a power switch implemented on the MIS transistor VT. The second input of the control system receives a signal proportional to the current of the key. As long as the voltage with DVN is greater than the voltage generated by the current sensor (TS), the transistor is open and energy is accumulated in the inductance (Fig. 3a). Diode VD on this interval (Ti) is closed.

If the signals to the CS are equal, the key is closed and the energy accumulated in the inductance is transferred to the load. After the current in the inductor drops to zero during the time tP, the transistor turns on again. The switching frequency of the transistor is many times higher than the frequency of the supply network, which can significantly reduce the size of the inductor. In this case, for the half-cycle of the mains voltage, the envelope of the amplitude values ​​of the inductance current (Fig. 3 b) changes according to a sinusoidal law. The average value of the current changes similarly. As a result, the consumed current has a sinusoidal shape and is in phase with the supply voltage.

However, the magnitude of the voltage at the load depends significantly on changes in the input voltage and load current. To stabilize the load voltage, a feedback circuit for this voltage is additionally introduced into the control system. The possibility of obtaining a sinusoidal form of the consumed current with simultaneous stabilization of the load voltage is realized using analog multiplication (PA node) of the signals coming from the DVN and from the LNN.
The additional signal thus obtained in this case becomes the reference voltage for the control system.

The considered CM control principle is used at load powers up to 300 W. At high powers, it is necessary to form a smoother curve of the change in the consumed current. This can be done when the current in the inductor does not drop to zero (Fig. 3c and 3d). If in a CM of relatively low power, the transistor comes into operation when the inductance current reaches zero, then in powerful CMs, at a given value of this current.

Let's consider the work of CM on the example of a practical scheme presented in fig. 4. The control circuit is implemented on a specialized L6560 microcircuit, the block diagram of which is shown in fig. five,

And the purpose of the conclusions - in the table. one.

The DVN voltage, generated by the resistive divider R1 R2, is fed to the pin. 3 chips L6560. Capacitor C1 at the rectifier output performs the functions of an RF filter, and not a smoothing capacitor, as in traditional circuits. Therefore, its value does not exceed hundreds of nanofarads - units of microfarads at load powers of 100 ... 200 W. Additional filtering of RF interference on the pin. 3 is carried out by capacitor C2.
Resistor R5 acts as a key current sensor, the voltage of which, through the RF filter R4 C4, is fed to the pin. 4 chips. The power switch is controlled by a signal received from the pin. 7. Taking into account the peculiarities of the operation of the KM keys (large dynamic range of current amplitude values), MIS transistors are most often used as them. At high conversion frequencies characteristic of CM, these transistors have low dynamic losses and are easily controlled directly by microcircuits. To reduce the likelihood of excitation of the circuit, a low-resistance resistor is introduced into the gate circuit of the MIS transistor.

From the resistive divider R6 R7, the output voltage feedback signal is removed and fed to the pin. 1. To reduce the influence of impulse noise that occurs in the output circuit, between the pin. 1 and 2 microcircuits include an integrating capacitor C3, the capacity of which is hundreds of nanofarads.

When the CM is connected to the network at the first moment, the microcircuit is powered through the resistor R3. As soon as the CM enters the operating mode, the voltage is removed from the additional winding of the inductor L, which, on the one hand, is used as the supply voltage of the microcircuit, and on the other hand, is a signal for determining the zero current of the inductance.

A filter capacitor C5 is necessarily present at the output of the KM, since the energy is transferred to the load by pulses. The capacitance of this capacitor, as a rule, is determined at the rate of 1.5 ... 2 microfarads per 1 W of power in the load.

Recently, leading companies have produced a large number of integrated circuits for control systems of power correctors. Such a number of microcircuits is associated with additional functions that they are capable of performing, although the principle of constructing CMs on these microcircuits is almost the same. Additional features include:
. transient overvoltage protection;
. protection against occurrence of repeated starts;
. protection against damage when starting on a closed load;
. improvement of the harmonic composition during the transition through zero of the mains voltage;
. blocking at low supply voltage;
. protection against accidental surges of input voltage.

The power corrector, as a rule, is not an independent device, but is part of a switching power supply. To obtain the required levels and polarities of the output voltages, such power supplies contain converters. In this regard, microcircuit designers often combine two stages of control circuits in one package: for the CM itself, as well as for the voltage converter.

In table. 2 shows the main parameters of control microcircuits of various companies designed for secondary switching power supplies with power correction.

The main criterion for the operation of the CM is the level of the output voltage. With an alternating supply voltage of 220 V, the output voltage of the KM is constant and should be 340.360 V. If the voltage is less than 300 V, then this indicates a malfunction. An oscilloscope is needed to further check the CM. With its help, the oscillograms are checked in the characteristic nodes of the KM at a rated load, which can be connected to an equivalent resistor.

The voltage at the gate of the transistor. With a working microcircuit, its output voltage is a rectangular pulse of high frequency, much higher than the mains frequency. With a working MOS transistor, the difference in voltage at the output of the microcircuit and the gate of the transistor is practically zero. If the gate of the transistor is broken, there is a difference of these voltages of several volts.

The voltage at the source of the transistor, which is the voltage taken from the current sensor. During normal operation of the CM, the voltage waveform should be similar to the switch current waveform shown in Fig. 3. The difference will indicate a possible malfunction of the MIS transistor. The diagnosis of their malfunctions is detailed in.

Voltage on DVN. The shape of this voltage is a rectified sinusoid. With a normally operating rectifier, a resistive divider may fail.

To check the microcircuit itself, an additional constant voltage source is required with voltage regulation from 3 to 15 V. This voltage is supplied to the inputs of the microcircuit power circuit when the CM is disconnected from the network. When the voltage of the regulated source changes, the output voltage of the microcircuit is controlled. As long as the supply voltage is less than 12..13 V, the output voltage is zero. With a higher voltage at the output of the microcircuit, an output signal appears with a level that tracks the supply voltage. As the supply voltage drops below 7V, this output drops abruptly to zero. In the absence of such a pattern, it is very likely that the microcircuit is faulty.

Literature
1. V. V. Bachurin, V. P. D’yakonov, A. M. Remnev, and V. Yu. Circuitry of devices on powerful field-effect transistors. Directory. Moscow: Radio and communication, 1994.
2. V. Dyakonov, A. Remnev, V. Smerdov. Features of repair of units of radio-electronic equipment on MOS-transistors. Repair & Service, 1999, No. 11, p. 57-60.
[email protected]

The inclusion of non-linear loads in the AC network, for example, lamps with gas discharge lamps, controlled electric motors, switching power supplies, leads to the fact that the current consumed by these devices has a pulsed nature with a high percentage of high harmonics. Because of this, electromagnetic compatibility problems may arise when operating various equipment. It also leads to a decrease in the active power of the network.

In order to prevent such a negative impact on the supply networks in Europe and the United States, a standard IEC IEC 1000-3-2, which defines the norms for the harmonic components of the consumed current and power factor for power supply systems with a power of more than 50 W and all types of lighting equipment. Since the 1980s and to this day, these standards have been consistently tightened, which has necessitated the adoption of special measures and prompted equipment designers to develop various options for schemes that provide power factor improvement.

Starting from the 80s of the last century, microcircuits began to be actively developed and used in the above-mentioned countries, on the basis of which simple power factor correctors for rectifiers and electronic ballasts can be easily created.

In the Soviet Union, and later in the Russian Federation, such restrictions were not introduced for consumers of electricity. For this reason, the issues of power factor improvement have not received sufficient attention in the technical literature. In recent years, the situation has changed somewhat, largely due to the presence of imported electronic components, the use of which makes it possible to create active corrector circuits that are reliable in operation and inexpensive in cost.

Distortion power and generalized power factor

The negative impact on the supply network is determined by two components: the distortion of the current form of the supply network and the consumption of reactive power. The degree of influence of the consumer on the supply network depends on its power.

The distortion of the current waveform is due to the fact that the current at the input of the valve converter is non-sinusoidal (Figure 1). Non-sinusoidal currents create non-sinusoidal voltage drops on the internal resistance of the supply network, causing distortion of the supply voltage waveform. Non-sinusoidal mains voltages are expanded in a Fourier series into odd sinusoidal components of higher harmonics. The first is the main one (the one that should ideally be), the third, the fifth, etc. Higher harmonics have an extremely negative impact on many consumers, forcing them to take special (often very expensive) measures to neutralize them.

Rice. one.

The consumption of reactive power causes the current to lag behind the voltage by an angle (Figure 2). Reactive power is consumed by rectifiers using single-operation thyristors, which delay the moment of switching on relative to the natural switching point, which causes the current to lag behind the voltage. But even more reactive power is consumed by asynchronous electric motors, which have a predominantly inductive nature of the load. This entails huge losses in useful power, for which, moreover, no one wants to pay - household electricity meters only count active power.

Rice. 2.

To describe the effect of the converter on the supply network, the concept of full power is introduced:

, where:

- effective value of the primary voltage,

- effective value of the primary current,

, - effective values ​​of the voltage and current of the primary harmonic,

Effective values ​​of voltages and currents of higher harmonics.

If the primary voltage is sinusoidal - , then:

,

,

ϕ 1 - phase angle between the sinusoidal voltage and the first harmonic of the current.

N is the power of distortion caused by the flow of higher harmonic currents in the network. The average power for the period due to these harmonics is zero, because the frequencies of the harmonics and the primary voltage do not match.

Higher current harmonics cause interference in sensitive equipment and additional losses from eddy currents in network transformers.

For valve converters, the concept of power factor χ is introduced, which characterizes the effect of reactive power and distortion power:

,

- coefficient of distortion of the primary current.

Thus, it is obvious that the power factor depends on the angle of delay of the current relative to the voltage and the magnitude of the higher harmonics of the current.

Power Factor Improvement Methods

There are several ways to reduce the negative impact of the converter on the supply network. Here are some of them:

Using multi-stage phase control (Figure 3).

Rice. 3.

The use of a rectifier with taps from the transformer leads to an increase in the number of ripples per period. The more branches from the transformer, the greater the number of ripples per period, the closer the shape of the input current is to sinusoidal. A significant disadvantage of this method is the high cost and dimensions of the transformer with a sufficient number of taps (to achieve the effect, there must be more of them than in the figure). The manufacture of a winding element of such complexity is a very difficult task, difficult to automate - hence the price. And if the source of secondary power supply being developed is small-scale, then this method is unambiguously unacceptable.

Rice. 4.

Increasing the phase of the rectifier. The method leads to an increase in the number of pulsations per period. The disadvantage of this method is the very complicated design of the transformer, expensive and bulky rectifier. In addition, not all consumers have a three-phase network.

Usage power factor correctors (PFC). There are electronic and non-electronic KKM. As non-electronic PFCs, electromagnetic reactive power compensators are widely used - synchronous motors that generate reactive power into the network. Obviously, for obvious reasons, such systems are unsuitable for the domestic consumer. Electronic KKM - a system of circuit solutions designed to increase the power factor - is perhaps the most optimal solution for domestic consumption.

The principle of operation of the KKM

The main task of PFC is to reduce to zero the lag of the consumed current from the voltage in the network while maintaining the sinusoidal form of the current. To do this, it is necessary to take current from the network not at short intervals, but over the entire period of operation. The power taken from the source must remain constant even if the mains voltage changes. This means that when the mains voltage decreases, the load current must be increased, and vice versa. Converters with an inductive storage and energy transfer in reverse are suitable for these purposes.

Correction methods can be conditionally divided into low-frequency and high-frequency ones. If the frequency of the corrector is much higher than the frequency of the mains, this is a high-frequency corrector, otherwise it is a low-frequency corrector.

Consider the principle of operation of a typical power corrector (Figure 5). On a positive half-wave, at the moment the mains voltage passes through zero, the transistor VT1 opens, the current flows through the circuit L1-VD3-VD8. After the transistor VT1 is turned off, the inductor begins to give off the energy stored in it, through the diodes VD1 and VD6 to the filter capacitor and the load. With a negative half-wave, the process has a similar character, only other pairs of diodes work. As a result of the use of such a corrector, the consumption current has a pseudo-sinusoidal character, and the power factor reaches a value of 0.96 ... 0.98. The disadvantage of this scheme is the large dimensions due to the use of a low-frequency choke.

Rice. five.

Increasing the frequency of operation of the PFC allows reducing the dimensions of the filter (Figure 6). With the power switch VT1 open, the current in the inductor L1 increases linearly - while the VD5 diode is locked, and the capacitor C1 is discharged to the load.

Rice. 6.

Then the transistor turns off, the voltage on the L1 choke unlocks the VD5 diode and the choke gives off the accumulated energy to the capacitor, while simultaneously supplying the load (Figure 7). In the simplest case, the circuit operates with a constant duty cycle. There are ways to increase the efficiency of the correction by dynamically changing the duty cycle (ie, by matching the cycle to the voltage envelope of the mains rectifier).

Rice. 7. Forms of voltages and currents of high-frequency PFC: a) with a variable switching frequency, b) with a constant switching frequency

Chips for building high-performance correctors from STMicroelectronics

Given the possibilities of the modern electronics industry, high-frequency PFCs are the best choice. The integral design of the entire power corrector or its control part has become, in fact, the standard. Currently, there is a greater variety of control chips for building PFC circuits produced by various manufacturers. Among all this variety, it is worth paying attention to the L6561/2/3 microcircuits manufactured by STMicroelectronics (www.st.com).

L6561, L6562 and L6563- a series of microcircuits specially designed by STMicroelectronics engineers to build highly efficient power factor correctors (Table 1).

Table 1. Power Factor Correction ICs

Name	Voltage power, V	Current switching on, uA	Current consumption in active mode, mA	Current consumption in standby mode, mA	Output bias current, μA	Power switch current rise time, ns	Power switch current decay time, ns
L6561	11…18	50	4	2,6	-1	40	40
L6562	10,3…22	40	3,5	2,5	-1	40	30
L6563	10,3…22	50	3,8	3	-1	40	30

Based on the L6561/2/3, an inexpensive but effective corrector can be built (Figure 8). Due to the built-in predictive control system, the developers managed to achieve high accuracy of output voltage regulation (1.5%), controlled by the built-in mismatch amplifier.

Rice. 8.

It is possible to interact with a DC/DC converter connected to the corrector. This interaction consists in turning off the converter by a microcircuit (if it supports such a possibility) in the event of adverse external conditions (overheating, overvoltage). On the other hand, the converter can also initiate the switching on and off of the microcircuit. The built-in driver allows you to control powerful MOSFET or IGBT transistors. According to the manufacturer, based on the LP6561/2/3, a power supply with a power of up to 300 W can be implemented.

Unlike analogs from other manufacturers, the LP6561/2/3 are equipped with special circuits that reduce the conductivity of input current distortion that occurs when the input voltage reaches zero. The main reason for this interference is the "dead zone" that occurs during the operation of the diode bridge, when all four diodes are closed. A pair of diodes operating on a positive half-wave turn out to be closed due to a change in the polarity of the supply voltage, and the other pair has not yet had time to open due to its own barrier capacitance. This effect is enhanced by the presence of a filter capacitor located behind the diode bridge, which, when the polarity of the supply is reversed, retains some residual voltage, which does not allow the diodes to open in time. Thus, it is obvious that the current does not flow at these moments, its shape is distorted. The use of new PFC controllers can significantly reduce the "dead zone" time, thereby reducing distortion.

In some cases, it would be very convenient to control the output voltage to the DC/DC converter using a PFC. L6561/2/3 allow for such control, called "tracking boost control". To do this, just install a resistor between the TBO pin and GND.

It is worth noting that all three microcircuits are pin-compatible with each other. This can greatly simplify the PCB design of the device.

So, we can distinguish the following features of the L6561 / 2/3 microcircuits:

adjustable overvoltage protection;

ultra-low trigger current (less than 50 µA);

low quiescent current (less than 3 mA);

wide input voltage limit;

built-in filter that increases sensitivity;

the ability to disconnect from the load;

the ability to control the output voltage;

possibility of interaction directly with the converter.

Conclusion

Currently, there are strict requirements for the safety and economy of modern electronic devices. In particular, when developing modern switching power supplies, it is necessary to take into account officially accepted standards. IEC 1000-3-2 is the standard for any high power switching power supply as it defines current harmonics and power factor requirements for power systems above 50W and all types of lighting equipment. The presence of a power factor corrector helps to meet the requirements of this standard, i.e. its presence in a powerful power supply is a simple necessity. The L6561/2/3 is the optimal choice for building an efficient and at the same time inexpensive power factor corrector.

Obtaining technical information, ordering samples, delivery - e-mail:

About ST Microelectronics

The development and widespread use of pulsed methods for converting electrical energy has led to the emergence of low-power household and industrial electrical appliances with a distorted shape or a non-zero phase shift of the current consumed from the network (fluorescent lamps, electric motors, televisions, computers, microwave ovens, etc.). A sharp increase in the number of such consumers affects their electromagnetic compatibility and power systems as a whole. In 2001, the IEC adopted the IEC-1000-3-2 standard, according to which any electrical product with a power of more than 200 watts connected to the AC mains must have an active input resistance, that is, the power factor () must be equal to unity.

For increase Currently, passive and active power factor correctors (PFCs) are used. The former are used at constant loads, by introducing compensating reactances (for example, capacitors for fluorescent lamps), the latter have a wider range of applications. Consider a simplified scheme of the active corrector, which is shown in Fig. 6.1.

Figure 6.1 - Simplified diagram of the active PFC

In this figure, R 1, R 2 - input voltage sensor (DN), R 3 - current sensor (DT). Inductance L, key VT1, diode VD1 and capacitor C 1 form a pulse boost voltage regulator. The operation of CMC is illustrated by diagrams in Fig. 6.1b. The closing of the transistor VT1 occurs at the moment when the voltage at the output of the current sensor DT becomes equal to zero (i.e., at zero current in the inductance L). The opening of the transistor VT1 occurs at the moment when the linearly increasing voltage from the current sensor becomes equal to the sinusoidal voltage from the voltage sensor DN. After the transistor opens, the current in the inductance begins to decline, the inductance is discharged to the load through the diode VD1, DT and the network. At zero current, the transistor closes again. Then the process is repeated. The key switching frequency exceeds the network frequency and amounts to tens ... hundreds of kilohertz. The average current i cf in the inductance and consumed from the network repeats the shape of the mains voltage. According to the high frequency of the key, the network is shunted with a capacitor C 2 (usually a fraction of a microfarad). You can additionally introduce feedback on the output voltage and provide preliminary stabilization. It is obvious that the operation of the PFC is possible if the amplitude of the input voltage is less than the voltage on the capacitor C 1 (taking into account deviations). For a mains voltage of 220V (amplitude 311V), the output voltage of the PFC is assumed to be 380 ... 400V.

6.2 Varieties of kkm

In the KKM scheme considered above, the so-called boundary control method is used. It is the simplest to implement, but the key is opened at a significant current, which is associated with significant power losses.

Other methods of key management in KKM are also known:

current peak control

discontinuous current method with PWM.

average current control.

The essence of these methods is illustrated by diagrams in Fig. 6.2 a, b, c, respectively.

Figure 6.2 - Key management in KKM

Peak current control (Fig. 6.2.a) is attractive for small reverse noise (to the network) and small current surges through the key, but there is a frequency change and hard switching of the power diode.

Discontinuous current control with PWM (Fig. 6.2.b). The implementation of this method is close to the boundary control method, but differs by a constant switching frequency. The advantage is a simple control circuit, but the discontinuous currents of the inductor become an additional source of interference. Control by the average current value (Fig. 6.2.c) is carried out at a constant frequency, and the presence of an integrator for averaging the current increases the noise immunity of the control system. Typically, the peak value of the inductor current ripple is within 20% of the average value, and it is this control method that is used in correctors with a power of more than 300 watts.

There are not only single-phase, but also three-phase power factor correctors. The power circuit of a three-phase KKM with one controlled key is shown in fig. 6.3, and in fig. Figures 6.4 and 6.5 show diagrams explaining the work.

Figure 6.3 - Power circuit of a three-phase PFC

Figure 6.4 - Diagrams of currents of reactors L1, L2, L3 of a three-phase CFC

Figure 6.5 - Diagrams of the main processes of a three-phase CMC

The key is controlled in the same way as a single-phase corrector.

In the considered PFC schemes, the latter passes all the load power. This is a serial corrector and its element base restrains an increase in output power. KKM can also be built according to the ampere-booster (Fig. 1.19) scheme - the inclusion of an active current filter in parallel with the load. In this case, the installed power of the active filter elements, designed to compensate only the power of distortion from the higher harmonics of the input current, will be at a level determined by the harmonic coefficient of this current (for example, 0.3 for a three-phase bridge circuit and 0.15 for a twelve-phase rectifier circuit) . The block diagram of such a CMC is shown in fig. 6.6. The principle of compensation of higher harmonics in the curve of the current consumed from the network is illustrated by diagrams in Fig. 6.7. For clarity, the shape of the load current is assumed to be rectangular. The corrector forms the difference between the mains current harmonic and the actual load current

(6.1)

where j is the phase index (A, B or C);

i J 1 is the first harmonic of the phase j current.

The corrector control scheme is usually based on pulse-width modulation.

Figure 6.6 - Structural diagram of a parallel three-phase PFC

Figure 6.7 - Compensation of higher current harmonics

As separate elements of electronic technology, corrector control circuits were first released in 1989 by Mikro Linear (LM 4812). Then Siemens, Motorola, etc. took up the development. Currently, there is an extensive family of ICs for controlling pulsed sources combined with PFC and implementing one or another control method.