Today it is not uncommon to see people throw away computer power supplies. Well, or the PSUs are just lying around idle, collecting dust.
But they can be used on the farm! In this article I will tell you what voltages can be obtained at the output of a conventional computer power supply.
A small educational program about the voltages and currents of a computer PSU
First, do not neglect safety precautions.
If at the output of the power supply we are dealing with voltages that are safe for health, then there are 220 and 110 Volts at the input and inside it! Therefore, follow the safety precautions. And make sure no one else gets hurt by the experiments!
Secondly, we need a voltmeter or multimeter. With it, you can measure voltages and determine the polarity of the voltage (find plus and minus).
Thirdly, on the power supply you can find a sticker that will indicate the maximum current that the power supply is designed for, for each voltage.
Just in case, subtract 10% from the written figure. This way you will get the most accurate value (manufacturers often lie).
Fourthly, the ATX type PC power supply is designed to form constant supply voltages +3.3V, +5V, +12V, -5V, -12V. Therefore, do not try to get an alternating voltage at the output. We will expand the set of voltages by combining the nominal ones.
Well, did you get it? Then we continue. It's time to decide on the connectors and the voltages on their contacts.
Connectors and voltages of a computer power supply
Color coding of computer power supply voltages
As you can see, the wires coming out of the power supply have their own color. It's not just like that. Each color represents voltage. Most manufacturers try to adhere to one standard, but there are completely Chinese power supplies and the color may not match (which is why a multimeter is helpful).
In normal PSUs, the wire color markings are as follows:
- Black - common wire, "ground", GND
- White - minus 5V
- Blue - minus 12V
- Yellow - plus 12V
- Red - plus 5V
- Orange - plus 3.3V
- Green - On (PS-ON)
- Gray - POWER-OK (POWERGOOD)
- Purple - 5VSB (maintenance).
Pinout of AT and ATX power supply connectors
For your convenience, I have selected a number of pictures with the pinout of all types of power supply connectors today.
To begin with, let's study types and types of connectors(connectors) of a standard power supply.
The motherboard is powered by a 24-pin ATX connector or a 20-pin AT connector. It is also used to turn on the power supply.
For hard drives, CDROMs, card readers and other things, MOLEX is used.
A rarity today is a connector for floppy disks. But on old power supplies you can meet.
The 4-pin CPU connector is used to power the processor. There are two of them or even dual, that is, 8-pin, for powerful processors.
The SATA connector has replaced the MOLEX connector. Used for the same purposes as MOLEX, but on newer devices.
PCI slots are most often used to supply additional power to different kind PCI express devices (most common for video cards).
Let's proceed directly to the pinout and marking. Where are our cherished tensions? And here they are!
Another picture with pinouts and color coding of voltages on the PSU connectors.
Below is the pinout of the AT type power supply.
Here you go. We figured out the pinout of computer power supplies! It's time to move on to how to get the necessary voltages from the power supply.
Obtaining voltages from the connectors of a computer power supply
Now that we know where to get the voltages, let's use the table that I have given below. It should be used like this: positive voltage + zero = total.
| positive | zero | total (difference) |
| +12V | 0V | +12V |
| +5V | -5V | +10V |
| +12V | +3.3V | +8.7V |
| +3.3V | -5V | +8.3V |
| +12V | +5V | +7V |
| +5V | 0V | +5V |
| +3.3V | 0V | +3.3V |
| +5V | +3.3V | +1.7V |
| 0V | 0V | 0V |
It is important to remember that the final voltage current will be determined by the minimum value of the ratings used to obtain it.
Also do not forget that for high currents it is desirable to use a thick wire.
The most important!!! The power supply is started by shorting the wires GND and PWR SW. Works as long as these circuits are closed!
REMEMBER! Any experiments with electricity must be carried out with strict observance of electrical safety rules !!!
Connector add-on. Clarification of pinouts for PCIe and EPS connectors.
Modern form factors: ATX and SFX
On the following pages, we will take a closer look at the form factors of power supplies used in modern PCs. ATX is by far the most common of these, but if you have different types of PCs in your line of work, then you will most likely encounter other types of PSUs, which we will discuss here.
ATX/ATX12V
In 1995, Intel discovered that the existing power supply design was literally running out of steam to handle the increasing load. The problem was that the existing standard used two connectors with a total of 12 wires that provided power to the motherboard, controllers soldered on it and the processor. In addition, the connector plugs were equipped with ill-conceived latches, wrong connection which led to damage to both the motherboard and power supply. To solve these problems, in 1995, Intel took the then-popular LPX (PS / 2) form factor as a basis and simply modified the power circuits and connectors implemented in it, while maintaining the same dimensions and physical design of the power supply. Thus, the ATX standard was born.
Intel introduced the ATX specification in 1995, and in 1996 this form factor began to gain popularity among desktop systems based on Pentium processors and Pentium Pro, capturing 18% of the market in the first year. Since 1996, ATX-based form factor options have dominated both motherboards and PSUs, replacing the earlier Baby-AT/LPX standards. ATX12V power supplies are also used for motherboards of the more recent BTX standard, which was intended to replace ATX, ensuring that ATX power supplies can be used in the next few years. The ATX12V specification defines the physical or mechanical shape power supply, as well as the configuration of the connectors that are used to power the computer components.
From 1995 to 2000, the ATX form factor was defined as part of the ATX motherboard specification. However, in February 2000, Intel took the then-current ATX 2.03 motherboard/chassis specification as a basis and created a separate power supply form factor specification, ATX/ATX12 version 1.0, while adding an additional 4-pin connector. +12 V (power supplies with this connector comply with the ATX12V specification). The +12V connector became a requirement for version 1.3 of the ATX standard, introduced in April 2002, after which only the ATX12V standard remained. The ATX12V 2.0 standard (February 2003) lost the 6-pin auxiliary connector, the main connector became 24-pin, and the presence of Serial ATA power connectors became mandatory requirement. The current version of ATX12V 2.2 was introduced in March 2005 and contains only minor improvements regarding previous versions such as the use of Molex High Current System (HCS) contacts on plugs.
As the specification of the ATX standard PSU has been improved, the orientation of the cooling fan and the design of the PSU have also changed. Initial specs assume an 80mm fan mounted on the inside power supply, from where it can force air out of the back of the case, directing airflow along the motherboard. In other words, such a fan works in the opposite direction than most fans currently in use, which divert hot air from accessories. The idea is to redirect the air flow inside the case in such a way that you can get by with just one fan per PSU, eliminating the mandatory use active cooling of the CPU heatsink.
Scheme of an ATX12V 2.x standard power supply with a main 24-pin power cable, a 4-pin additional +12V connector, as well as additional power connectors for video cards connected to PCI bus Express
In a reverse flow ATX system, air is forced into the chassis and the only entry point for dust into the system is the air filter located in front of the fan. For computers that operate in environments that are not too clean room(for example, in stores) this method of cooling allows you to keep the inside of the case relatively clean.
Although this method of cooling seems to be very convenient in terms of domestic use PC, it should be noted that it involves the use of a more powerful fan, which should work effectively together with the installed filter and, at the same time, pump excess air pressure into the case. In addition, when using a filter, it must be serviced periodically, that is, it must be cleaned of dust and dirt several times a week. It should also be noted that already warm air is supplied from the power supply to the processor cooler, which reduces the overall cooling efficiency.
Processors have evolved, become more productive and as a result began to warm up more than their predecessors. As a result, it took more efficient system cooling and the option with overpressure inside the case ceased to correspond to the task. That is why subsequent versions of the ATX specification have been rewritten to allow for both positive pressure and negative pressure cooling systems. But it was emphasized that it was the second option, which involves the creation of negative pressure due to the fan power supply blower and a powerful fan directly above the processor is the best solution.
Because the standard system cooling with negative pressure inside the case provides the most efficient for a given fan power and airflow strength, in practice all modern models PSUs made in the ATX form factor use exactly this approach to cooling. Most of them are equipped with an 80mm fan, which is mounted on the back wall and works for blowing. But in some models, a fan with a diameter of 80 to 140 mm is fixed on the top or bottom surface power supply inside the case, driving air through the PSU to the outlets on the rear wall. But in any case, the idea is to take hot air out of the case and throw it out through the back of the PSU.
ATX Form Factor solved several problems that were relevant to the previous PC / XT, AT and LPX form factors. One of them was that PC/XT/AT boards were equipped with only two connectors for power cables. If you connected the cables incorrectly or confused them, as a rule, both the power supply and the motherboard burned out! Most responsible manufacturers have tried to come up with a special key that would only allow these cables to be connected in the correct sequence. However, most manufacturers that offered cheap systems did not include such protection on power supplies or boards. ATX form factor includes motherboard sockets and connectors power supply designed by default to be "fool-proof" - that is, they can only be connected in the right way. In addition, a low-voltage ATX +3.3 V line has appeared among the connectors, which reduces the need for desoldering additional voltage regulators directly on the board for those components that use this voltage.
The new +3.3V connectors on ATX power supplies have a different set of outputs that are usually not noticeable on a standard PSU. The set includes the Power_On (PS_ON) and 5V_Standby (5VSB) outputs, which we talked about a little earlier and which are responsible for the Soft Power mode (software power management). They provide features such as Wake on Ring or Wake on LAN, that is, when the signal from the modem or network can be used to wake the computer from sleep mode or automatically turn on to perform scheduled tasks. These signals can also be enabled through the specific power buttons found on most modern keyboards. In particular, the option to turn on using a button on the keyboard or via the network is available even when the computer is turned off but connected to a power source, since the 5V_Standby line is always energized. The advanced power management features themselves can be enabled or disabled via the BIOS.
SFX/SFX12V
Intel introduced the microATX form factor motherboard in December 1997. At the same time, the power unit reduced size - Small Form Factor (SFX). Despite this, most microATX chassis still used a standard ATX power supply. But then in March 1999, Intel introduced the FlexATX addition to the microATX specification for miniature motherboards used in budget desktops and industrial PCs.
Since that time, SFX-standard enclosures have been used in many compact desktop systems. Unlike most power supply specifications that specify physical dimensions, the SFX standard describes five different physical shapes for power supplies, some of which cannot be replaced as separate module. In addition, there have been changes in the set of PSU connectors, as the specification has changed. Thus, when buying power supply SFX/SFX12V standard, you need to make sure you choose the right type of block that will physically fit in the case and also has the right connectors for connecting to the motherboard.
The number and type of connectors have changed over the course of the evolution of the SFX standard. The original power supply specification includes one 20-pin motherboard connector. An additional 4-pin +12 V connector for independent CPU power appeared as an option in the revision 2.0 specification introduced in May 2001, and became mandatory in revision 2.3 (April 2003), so that in the end only the SFX12V specification was developed further. In SFX12V version 3.0, the main power connector was transformed from 20-pin to 24-pin, and Serial ATA connectors appeared among the requirements. At the moment, version 3.1 is considered relevant, which was introduced in March 2005 and contains minor differences, in particular, the use of Molex High Current System (HCS) contacts in the connectors.
SFX12V has several physical options layouts, one of which is called PS3.
Standard power unit The SFX/SFX12 is equipped with a 60mm fan located inside the power supply facing the inside of the computer. The fan draws hot air into the PSU from the case and exhausts it through back panel. The location of the fan in this location is for noise reduction reasons and retains the standard type of negative pressure cooling system inside the case. The system can also use additional fans to cool the processor and chassis, independent of the power supply.
Standard SFX/SFX12V PSU with 60mm internal fan
Fan version available for compact systems requiring more cooling bigger size- with a diameter of 80 mm - fixed on the top of the PSU. Such a system is more powerful and efficient in terms of cooling and is used if the computer has a productive filling, despite its size.
Standard SFX/SFX12V PSU with more powerful 80mm fan mounted on top panel
Another version of the SFX12V standard also uses a "reinforced" 80mm fan on the top panel, but the case itself power supply unfolded, resulting in an increase in the occupied space in width and a decrease in depth, as shown in the diagram two paragraphs below.
The low profile version of the SFX12V was designed for cases as thin as 50mm and is equipped with a 40mm fan as shown in the diagram below.
Finally, the most recent implementation of the SFX is the so-called PS3 form factor, which is defined in the SFX12V specification in "Appendix E" (Appendix E). Although this form factor is defined as a subset of the SFX12V specification, it is actually a smaller version of the ATX12V and is typically used in chassis for microATX boards and motherboards that require more high power than can be provided by more compact Power supplies, presented in variations of the SFX standard.
PSU in SFX/SFX12V form factor deployed in width and equipped with a "reinforced" 80mm fan on the top panel
Low profile SFX/SFX12V PSU with 40mm fan
PS3 PSU (SFX/SFX12V variant) with 80mm fan
SFX12V power supplies are designed specifically for miniature systems that contain a limited set of components and are limited in upgrade options. Most SFX PSUs are designed to deliver between 80 and 300W of power under constant load and have four power lines: +5V, +12V, -12V, and +3.3V. power supply is sufficient for a compact system equipped with a processor, graphics card AGP or PCI-E x16, up to four expansion card slots, as well as three internal drives, such as hard drives and optical drives.
Although Intel created the SFX12V power supply specification with microATX and FlexATX motherboards in mind, SFX is a motherboard-independent power supply form factor that can be used with other motherboards just as well. In particular, power unit The PS3 version of the SFX12V standard can be used as a full-fledged replacement for the ATX12V PSU due to the fact that the connectors for these two standards are identical. The SFX power supply uses exactly the same 20-wire or 24-wire connectors as defined in the ATX/ATX12V standard specification and includes Power_On and 5V_Standby lines. The SFX12V power supply includes an additional 4-pin +12V connector to power the CPU, just like the ATX12V standard. Whether to use an ATX or SFX power supply in a given system depends more on the case or chassis than on the motherboard. Each form factor has the same power connectors, with the main difference being the physical layout and dimensions.
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Introduction
An integral part of every computer is the power supply. It is as important as the rest of the computer. At the same time, the purchase of a power supply is quite rare, because. A good PSU can power several generations of systems. Given all this, the purchase of a power supply must be taken very seriously, since the fate of a computer is directly dependent on the operation of the power supply.
To implement galvanic isolation, it is enough to make a transformer with the necessary windings. But to power a computer, you need a lot of power, especially for modern PCs. To power a computer, a transformer would have to be made, which would have not only big size but also weighed a lot. However, with an increase in the frequency of the supply current of the transformer, to create the same magnetic flux, fewer turns and a smaller cross section of the magnetic circuit are needed. In power supplies built on the basis of a converter, the frequency of the transformer supply voltage is 1000 or more times higher. This allows you to create compact and lightweight power supplies.
The simplest switching power supply
Consider a block diagram of a simple switching power supply, which underlies all switching power supplies.
Block diagram of a switching power supply.
The first block converts the AC voltage to DC. Such a converter consists of a diode bridge that rectifies the alternating voltage, and a capacitor that smooths out the ripple of the rectified voltage. This box also contains additional elements: mains voltage filters from pulse generator ripples and thermistors to smooth out the current surge at the moment of switching on. However, these elements may be omitted in order to save on cost.
The next block is a pulse generator that generates pulses at a certain frequency that feed the primary winding of the transformer. The frequency of the generating pulses of different power supplies is different and lies in the range of 30 - 200 kHz. The transformer performs the main functions of the power supply: galvanic isolation with the network and lowering the voltage to the required values.
The alternating voltage received from the transformer is converted by the next block into direct voltage. The block consists of voltage rectifying diodes and a ripple filter. In this block, the ripple filter is much more complex than in the first block and consists of a group of capacitors and a choke. In order to save money, manufacturers can install small capacitors, as well as chokes with low inductance.
The first switching power supply was a push-pull or single-cycle converter. Push-pull means that the generation process consists of two parts. In such a converter, two transistors open and close in turn. Accordingly, in a single-cycle converter, one transistor opens and closes. Schemes of push-pull and single-cycle converters are presented below.
Schematic diagram of the converter.
Consider the elements of the scheme in more detail:
X2 - circuit power supply connector.
X1 - connector from which the output voltage is removed.
R1 - resistance that sets the initial small offset on the keys. It is necessary for a more stable start of the oscillation process in the converter.
R2 is the resistance that limits the base current on the transistors, this is necessary to protect the transistors from burning.
TP1 - The transformer has three groups of windings. The first output winding generates the output voltage. The second winding serves as a load for the transistors. The third one forms the control voltage for the transistors.
At the initial moment of switching on the first circuit, the transistor is slightly ajar, because. A positive voltage is applied to the base through resistor R1. A current flows through the ajar transistor, which also flows through the second winding of the transformer. The current flowing through the winding creates a magnetic field. The magnetic field creates voltage in the remaining windings of the transformer. As a result, a positive voltage is created on winding III, which further opens the transistor. The process continues until the transistor enters saturation mode. The saturation mode is characterized by the fact that as the applied control current to the transistor increases, the output current remains unchanged.
Since the voltage in the windings is generated only in the event of a change in the magnetic field, its growth or fall, the absence of an increase in current at the output of the transistor, therefore, will lead to the disappearance of the EMF in the windings II and III. Loss of voltage in the winding III will lead to a decrease in the degree of opening of the transistor. And the output current of the transistor will decrease, therefore, the magnetic field will also decrease. Reducing the magnetic field will create a voltage of opposite polarity. The negative voltage in winding III will begin to close the transistor even more. The process will continue until the magnetic field disappears completely. When the magnetic field disappears, the negative voltage in winding III will also disappear. The process will start repeating again.
A push-pull converter works on the same principle, but the difference is that there are two transistors, and they open and close in turn. That is, when one is open, the other is closed. The push-pull converter circuit has the great advantage of utilizing the entire hysteresis loop of the transformer's magnetic conductor. Using only one section of the hysteresis loop or magnetization in only one direction leads to many undesirable effects that reduce the efficiency of the converter and degrade its performance. Therefore, basically, a push-pull converter circuit with a phase-shifting transformer is used everywhere. In circuits where simplicity, small size, and low power are needed, a single-cycle circuit is still used.
Power supplies ATX form factor without power factor correction
The converters discussed above, although they are finished devices, are inconvenient to use in practice. Converter frequency, output voltage and many other parameters "float", change depending on the change: supply voltage, converter output load and temperature. But if the keys are controlled by a controller that could carry out stabilization and various additional functions, then you can use the circuit to power devices. The power supply circuit using a PWM controller is quite simple, and, in general, is a pulse generator built on a PWM controller.
PWM - pulse width modulation. It allows you to adjust the amplitude of the signal of the passed low-pass filter (filter low frequencies) with a change in the duration or duty cycle of the pulse. The main advantages of PWM are high value efficiency of power amplifiers and great opportunities in application.
Scheme simple block power supply with PWM controller.
This power supply circuit has a low power and uses a field-effect transistor as a key, which allows you to simplify the circuit and get rid of the additional elements necessary to control the transistor switches. In power supplies high power The PWM controller has control elements ("Driver") for the output key. IGBT transistors are used as output keys in high-power power supplies.
The mains voltage in this circuit is converted into a constant voltage and fed through the key to the first winding of the transformer. The second winding is used to power the microcircuit and generate voltage feedback. The PWM controller generates pulses with a frequency that is set by the RC circuit connected to pin 4. The pulses are fed to the input of the key, which amplifies them. The duration of the pulses varies depending on the voltage on pin 2.
Consider real scheme ATX power supply. It has many more elements and it contains more additional devices. The red squares of the power supply circuit are conditionally divided into main parts.
ATX power supply circuit with a power of 150-300 watts.
To power the controller chip, as well as to generate a standby voltage of +5, which is used by the computer when it is turned off, there is another converter in the circuit. In the diagram, it is designated as block 2. As you can see, it is made according to the single-cycle converter circuit. The second block also has additional elements. Basically, these are surge absorption circuits that are generated by the converter transformer. Chip 7805 - voltage regulator forms duty voltage+5V from rectified converter voltage.
Often, low-quality or defective components are installed in the standby voltage generation unit, which causes the frequency of the converter to decrease to the audio range. As a result, a squeak is heard from the power supply.
Since the power supply is powered by AC 220V, and the converter needs power constant voltage, the voltage needs to be converted. The first block performs rectification and filtering of the alternating mains voltage. This block also contains a blocking filter against interference generated by the power supply itself.
The third block is the TL494 PWM controller. It performs all the basic functions of the power supply. Protects the power supply from short circuits, stabilizes the output voltage and generates a PWM signal to control transistor switches that are loaded on the transformer.
The fourth block consists of two transformers and two groups of transistor switches. The first transformer generates a control voltage for the output transistors. Since the TL494 PWM controller generates a low power signal, the first group of transistors amplifies this signal and passes it to the first transformer. The second group of transistors, or output ones, are loaded on the main transformer, which forms the main supply voltages. Such more complex scheme output key management is applied due to the complexity of managing bipolar transistors and protection of the PWM controller from high voltage.
The fifth block consists of Schottky diodes that rectify the output voltage of the transformer, and a low-pass filter (LPF). The low-pass filter consists of electrolytic capacitors of considerable capacity and chokes. At the output of the low-pass filter there are resistors that load it. These resistors are necessary so that after turning off the capacitance of the power supply, they do not remain charged. There are also resistors at the output of the mains voltage rectifier.
The remaining elements that are not circled in the block are chains that form “serviceability signals”. These chains carry out the work of protecting the power supply from short circuit or monitoring the health of output voltages.
200W ATX power supply.
Now let's see how the elements are located on the printed circuit board of the 200 W power supply. The figure shows:
Capacitors that filter the output voltages.
Place unsoldered output voltage filter capacitors.
Inductors that filter output voltages. The larger coil not only plays the role of a filter, but also acts as a ferromagnetic stabilizer. This allows you to slightly reduce voltage distortions with uneven loading of various output voltages.
Chip PWM stabilizer WT7520.
A radiator on which Schottky diodes are installed for voltages + 3.3V and + 5V, and ordinary diodes for voltage + 12V. It should be noted that often, especially in older power supplies, additional elements are placed on the same radiator. These are voltage stabilization elements + 5V and + 3.3V. In modern power supplies, only Schottky diodes are placed on this radiator for all basic voltages or FETs, which are used as a rectifier element.
The main transformer, which performs the formation of all voltages, as well as galvanic isolation from the network.
A transformer that generates control voltages for the output transistors of the converter.
Converter transformer that generates standby voltage + 5V.
The radiator, on which the output transistors of the converter are located, as well as the transistor of the converter that forms the standby voltage.
Mains voltage filter capacitors. They don't have to be two. To form a bipolar voltage and form a midpoint, two capacitors of equal capacity are installed. They divide the rectified mains voltage in half, thereby forming two voltages of different polarity connected at a common point. In single supply circuits, there is only one capacitor.
Network filter elements from harmonics (interference) generated by the power supply.
Diode bridge diodes that rectify the AC voltage of the network.
350W ATX power supply.
The 350 W power supply is equivalent. Immediately striking is the large board, enlarged heatsinks and a larger converter transformer.
Output voltage filter capacitors.
A heatsink that cools the diodes that rectify the output voltage.
PWM controller AT2005 (similar to WT7520), which performs voltage stabilization.
The main transformer of the converter.
A transformer that generates a control voltage for the output transistors.
Standby voltage converter transformer.
A radiator that cools the output transistors of the converters.
Mains voltage filter from power supply interference.
diode bridge diodes.
Mains voltage filter capacitors.
The considered scheme has long been used in power supplies and is now sometimes found.
ATX format power supplies with power factor correction.
In the considered schemes, the network load is a capacitor connected to the network through diode bridge. The charge of the capacitor occurs only if the voltage on it is less than the mains. As a result, the current is pulsed, which has many disadvantages.
Bridge voltage rectifier.
We list these shortcomings:
- currents introduce higher harmonics (interference) into the network;
- large amplitude of consumption current;
- a significant reactive component in the consumption current;
- mains voltage is not used during the entire period;
- The efficiency of such schemes is of little importance.
The new power supplies have an improved modern circuit, it has one more additional unit - a power factor corrector (PFC). It performs power factor improvement. Or more plain language removes some of the shortcomings of the mains voltage bridge rectifier.
Formula full power.
The power factor (KM) characterizes how much of the total power of the active component and how much of the reactive. In principle, one can say, why take into account reactive power, it is imaginary and does not benefit.
Power factor formula.
Let's say we have a certain device, a power supply, with a power factor of 0.7 and a power of 300 watts. It can be seen from the calculations that our power supply has full power (the sum of reactive and active power) is greater than indicated on it. And this power should be given by a 220V power supply network. Although this power is not useful (even the electricity meter does not fix it), it still exists.
Calculation of the total power of the power supply.
That is, internal elements and network wires should be rated at 430 watts, not 300 watts. And imagine the case when the power factor is equal to 0.1 ... Because of this, the City Network forbids the use of devices with a power factor of less than 0.6, and if any are found, the owner is fined.
Accordingly, the campaigns were developed new power supply circuits that had KKM. At first, a large inductance choke included at the input was used as a PFC, such a power supply is called a power supply with PFC or passive PFC. Such a power supply has an increased KM. To achieve the desired KM, it is necessary to equip the power supplies with a large choke, since the input resistance of the power supply is capacitive due to the installed capacitors at the rectifier output. Installing a throttle significantly increases the mass of the power supply, and increases the KM to 0.85, which is not so much.
400 W power supply with passive power factor correction.
The figure shows a 400W FSP power supply with passive power factor correction. It contains the following elements:
- Output ripple filter capacitors.
Rectified line voltage filter capacitors.
A choke that performs power factor correction.
Transformer of the main converter.
Transformer that controls the keys.
Auxiliary converter transformer (standby voltage).
Mains voltage filters from power supply ripples.
The radiator on which the output transistor switches are installed.
Radiator on which diodes are installed that rectify the alternating voltage of the main transformer.
Fan speed control board.
The board on which the FSP3528 PWM controller (analogous to KA3511) is installed.
Group stabilization inductor and output voltage ripple filter elements.
Turn on the throttle to correct the KM.
Due to the low efficiency of passive PFC, a new PFC circuit was introduced into the power supply, which is based on a PWM stabilizer loaded on a choke. This scheme brings many advantages to the power supply:
- extended operating voltage range;
- it became possible to significantly reduce the capacitance of the mains voltage filter capacitor;
- significantly increased CM;
- reduction in the weight of the power supply;
- increase the efficiency of the power supply.
This scheme also has disadvantages - this is a decrease in the reliability of the PSU and incorrect operation with some uninterruptible power supplies when switching battery / mains operating modes. The incorrect operation of this circuit with a UPS is due to the fact that the capacitance of the mains voltage filter has significantly decreased in the circuit. At the moment when the voltage disappears for a short time, the current of the KKM increases greatly, which is necessary to maintain the voltage at the output of the KKM, as a result of which the protection against short circuit (short circuit) in the UPS is activated.
Scheme of an active power factor corrector.
If you look at the circuit, then it is a pulse generator that is loaded on the inductor. The mains voltage is rectified by a diode bridge and supplied to the key, which is loaded with an L1 choke and a T1 transformer. The transformer is introduced for the feedback of the controller with the key. The voltage from the inductor is removed using diodes D1 and D2. Moreover, the voltage is removed alternately with the help of diodes, then from the diode bridge, then from the inductor, and charges the capacitors Cs1 and Cs2. Key Q1 opens and inductor L1 accumulates the energy of the desired value. The amount of accumulated energy is regulated by the duration of the open state of the key. The more energy stored, the more voltage the inductor will give. After turning off the key, the accumulated energy is returned by the inductor L1 through the diode D1 to the capacitors.
This operation allows you to use the entire sinusoid of the alternating voltage of the network, in contrast to circuits without PFC, and also to stabilize the voltage supplying the converter.
AT modern schemes power supplies, dual-channel PWM controllers are often used. One microcircuit performs the work of both the converter and the PFC. As a result, the number of elements in the power supply circuit is significantly reduced.
Scheme of a simple power supply on a two-channel PWM controller.
Consider a simple 12V power supply circuit using a dual-channel PWM controller ML4819. One part of the power supply generates a constant stabilized voltage + 380V. The other part is a converter that generates a constant stabilized voltage + 12V. KKM consists, as in the case considered above, of the key Q1, the inductor L1 of the feedback transformer T1 loaded on it. Diodes D5, D6 charge capacitors C2, C3, C4. The converter consists of two keys Q2 and Q3, loaded on the transformer T3. The impulse voltage is rectified diode assembly D13 and filtered by inductor L2 and capacitors C16, C18. With the help of the cartridge U2, the output voltage regulation voltage is formed.
GlacialPower GP-AL650AA power supply.
Consider the design of the power supply, in which there is an active KKM:
- Current protection control board;
- Inductor, which acts as a voltage filter + 12V and + 5V, and the function of group stabilization;
- Voltage filter choke +3.3V;
- Radiator on which rectifier diodes of output voltages are placed;
- Main Converter Transformer;
- Transformer that controls the keys of the main converter;
- Auxiliary converter transformer (forming standby voltage);
- Power factor correction controller board;
- Radiator, cooling diode bridge and keys of the main converter;
- Line voltage filters against interference;
- Choke power factor corrector;
- Mains voltage filter capacitor.
Design features and types of connectors
Consider the types of connectors that may be present on the power supply. On the rear wall of the power supply is a connector for connecting network cable and switch. Previously, next to the power cord connector, there was also a connector for connecting the monitor's network cable. Other elements may optionally be present:
- indicators of mains voltage, or the status of the power supply;
- fan control buttons;
- button for switching the input mains voltage 110 / 220V;
- USB ports built into the unit USB power supply hub;
- other.
On the rear wall, less and less fans are placed, pulling air from the power supply. All bowl fan is placed at the top of the power supply due to the larger fan installation space, which allows you to install a large and quiet active element cooling. On some power supplies, even two fans are installed both at the top and at the back.
Chieftec CFT-1000G-DF power supply.
A wire with a power connector for the motherboard comes out of the front wall. In some power supplies, modular, it, like other wires, is connected through a connector. The figure below shows the pinout of the pins of all the main connectors.
You can see that each voltage has its own wire color:
- Yellow color - +12 V,
- Red color - +5 V,
- Orange color - + 3.3V,
- Black is common or ground.
For other voltages, the colors of the wires for each manufacturer may vary.
The figure does not show the auxiliary power connectors for video cards, since they are similar to the auxiliary power connector for the processor. There are also other types of connectors that are found in brand-name computers from DelL, Apple, and others.
Electrical parameters and characteristics of power supplies
The power supply has many electrical parameters, most of which are not marked in the passport. On the side sticker of the power supply, usually only a few basic parameters are noted - operating voltages and power.
Power supply power
Power is often indicated on the label big print. The power of the power supply, characterizes how much it can give electrical energy devices connected to it (motherboard, video card, HDD and etc.).
In theory, it is enough to sum up the consumption of the components used and select a power supply unit with a slightly higher power for the reserve. To calculate the power, you can use, for example, the site http://extreme.outervision.com/PSUEngine, the recommendations indicated in the video card passport, if any, the thermal package of the processor, etc., are also quite suitable.
But in fact, everything is much more complicated, because. the power supply unit produces various voltages - 12V, 5V, -12V, 3.3V, etc. Each voltage line is designed for its own power. It was logical to think that this power is fixed, and their sum is equal to the power of the power supply. But there is one transformer in the power supply to generate all these voltages used by the computer (except for the standby voltage + 5V). True, it is rare, but you can still find a power supply with two separate transformers, but such power supplies are expensive and are most often used in servers. Ordinary ATX PSUs have one transformer. Because of this, the power of each voltage line can float: it increases if other lines are lightly loaded, and decreases if the other lines are heavily loaded. Therefore, the maximum power of each line is often written on the power supplies, and as a result, if they are summed up, the power will come out even more than the actual power of the power supply. Thus, the manufacturer can confuse the consumer, for example, by declaring too much rated power, which the PSU is not capable of providing.
Note that if an insufficient power supply is installed in the computer, this will cause non-root operation of devices (“freezes”, reboots, clicks of heads hard drive), up to the impossibility of turning on the computer. And if a motherboard is installed in the PC, which is not designed for the power of the components that are installed on it, then the motherboard often functions normally, but over time, the power connectors burn out due to their constant heating and oxidation.
Burnt connectors.
Permissible maximum line current
Although this is one of important parameters power supply, often the user does not pay attention to it when buying. But when the permissible current on the line is exceeded, the power supply turns off, because. protection is triggered. To turn it off, turn off the power supply from the mains and wait for a while, about a minute. It is worth considering that now all the most voracious components (processor, video card) are powered by the + 12V line, so you need to pay more attention to the values \u200b\u200bof the currents indicated for it. For high-quality PSUs, this information is usually placed in the form of a plate (for example, Seasonic M12D-850) or a list (for example, FSP ATX-400PNF) on the side sticker.
Power sources that do not have such information (for example, Gembird PSU7 550W) immediately cast doubt on the quality of performance and the conformity of the declared power with the real one.
The remaining parameters of the power supplies are not regulated, but no less important. It is possible to determine these parameters only by conducting various tests with the power supply.
Operating voltage range
Under the operating voltage range is meant the range of mains voltage values at which the power supply unit maintains its performance and the values of its passport parameters. Now more and more often power supplies are produced with AKKM (active power factor corrector), which allows you to expand the operating voltage range from 110 to 230. There are also power supplies with a small operating voltage range, for example, the FPS FPS400-60THN-P power supply has a range of 220 up to 240. As a result, this power supply, even when paired with a massive uninterruptible power supply, will turn off when the voltage drops in the network. This is because a conventional UPS stabilizes the output voltage in the range of 220V +/- 5%. That is, the minimum voltage for switching to the battery will be 209 (and given the slow switching of the relay, the voltage may be even lower), which is lower than the operating voltage of the power supply.
Internal resistance
Internal resistance characterizes the internal losses of the power supply when current flows. By type, internal resistance can be divided into two types: conventional for direct current and differential for alternating current.
The equivalent circuit of the power supply.
DC resistance is the sum of the resistances of the components that make up the power supply: wire resistance, transformer winding resistance, inductor wire resistance, circuit board track resistance, etc. Due to the presence of this resistance, the voltage drops with increasing workload of the power supply. This resistance can be seen by plotting the cross-load characteristic of the PSU. To reduce this resistance, power supplies work various schemes stabilization.
Cross-load characteristic of the power supply.
Differential resistance characterizes the internal losses of the power supply during the flow alternating current. This resistance is also called electrical impedance. Reducing this resistance is the most difficult. To reduce it, a low-pass filter is used in the power supply. To reduce the impedance, it is not enough to install large capacitors and high inductance coils in the power supply. It is also necessary that the capacitors have a low series resistance (ESR), and the chokes are made of thick wire. It is very difficult to implement this physically.
Output voltage ripple
The power supply is a converter that converts the voltage from AC to DC more than once. As a result, there are ripples at the output of its lines. Ripple is a sudden change in voltage over a short period of time. the main problem ripples is that if the circuit or device does not have a filter in the power circuit or it is bad, then these ripples pass through the entire circuit, distorting its performance. This can be seen, for example, if you turn the volume of the speakers to the maximum during the absence of signals at the output sound card. Various noises will be heard. This is the ripple, but not necessarily the noise of the power supply. But if there is no great harm in the operation of a conventional amplifier from ripples, only the noise level will increase, then, for example, in digital circuits and comparators, they can lead to false switching or incorrect perception of input information, which leads to errors or inoperability of the device.
The form of the output voltages of the block Antec supply Signature SG-850.
Voltage stability
Next, consider such a characteristic as the stability of the voltages produced by the power supply. In the course of work, no matter how ideal the power supply would be, its voltages change. An increase in voltage causes, first of all, an increase in the quiescent currents of all circuits, as well as a change in the parameters of the circuits. So, for example, for a power amplifier, increasing the voltage increases its output power. Some electronic parts may not withstand the increased power and burn out. The same increase in power leads to an increase in power dissipation. electronic elements, and, consequently, to an increase in the temperature of these elements. Which leads to overheating and / or change in characteristics.
Reducing the voltage, on the contrary, reduces the quiescent current, and also degrades the characteristics of the circuits, such as the amplitude of the output signal. When it drops below a certain level, certain circuits stop working. Hard drive electronics are especially sensitive to this.
Permissible voltage deviations on the power supply lines are described in the ATX standard and should not exceed ± 5% of the line rating on average.
For a complex display of the magnitude of the voltage drop, a cross-load characteristic is used. It is a color display of the voltage deviation level of the selected line when two lines are loaded: selected and +12V.
Coefficient useful action
Now let's move on to the coefficient of efficiency or abbreviated efficiency. Many remember from school - this is the attitude useful work to spent. Efficiency shows how much of the consumed energy has turned into useful energy. The higher the efficiency, the less you have to pay for the electricity consumed by the computer. Most high-quality power supplies have a similar efficiency, it varies in the range of no more than 10%, but the efficiency of power supplies with PKKM (PPFC) and AKKM (APFC) is much higher.
Power factor
As a parameter that you should pay attention to when choosing a PSU, the power factor is less significant, but other quantities depend on it. With a small value of the power factor, there will be a small value of efficiency. As noted above, power factor correctors bring many improvements. A higher power factor will result in lower currents in the network.
Non-electrical parameters and characteristics of power supplies
Usually, as for electrical characteristics, not all non-electrical parameters are indicated in the passport. Although the non-electrical parameters of the power supply are also important. We list the main ones:
- Operating temperature range;
- reliability of the power supply (time between failures);
- the noise level generated by the power supply during operation;
- power supply fan speed;
- weight of the power supply;
- length of supply cables;
- ease of use;
- environmental friendliness of the power supply;
- compliance with state and international standards;
- power supply dimensions.
Most of the non-electrical parameters are clear to all users. However, let's focus on more relevant parameters. Most modern power supplies are quiet, they have a noise level of about 16 dB. Although even a power supply unit with a nominal noise level of 16 dB can be equipped with a fan with a speed of 2000 rpm. In this case, when the load of the power supply is about 80%, the fan speed control circuit will turn it on maximum speed, which will lead to the appearance of significant noise, sometimes more than 30 dB.
It is also necessary to pay attention to the convenience and ergonomics of the power supply. There are many advantages to using modular power cable connections. This and more convenient connection devices, less occupied space in the computer case, which in turn is not only convenient, but improves the cooling of computer components.
Standards and certificates
When buying a PSU, first of all, you need to look at the availability of certificates and its compliance with modern international standards. On power supplies, you can most often find an indication of the following standards:
RoHS, WEEE - does not contain harmful substances;
UL, cUL - certificate for compliance with its technical characteristics, as well as safety requirements for built-in electrical appliances;
CE - a certificate that shows that the power supply complies the strictest requirements directives of the European Committee;
ISO - international quality certificate;
CB - international certificate of conformity to its technical characteristics;
FCC - compliance with the standards of electromagnetic interference (EMI) and radio interference (RFI) generated by the power supply;
TUV - Certificate of Compliance international standard EN ISO 9001:2000;
CCC - China certificate of safety, electromagnetic parameters and environmental protection.
There are also computer standards of the ATX form factor, which define the dimensions, design and many other parameters of the power supply, including the permissible voltage deviations under load. Today there are several versions of the ATX standard:
- ATX 1.3 Standard;
- ATX 2.0 Standard;
- ATX 2.2 Standard;
- ATX 2.3 standard.
The difference between the versions of the ATX standards mainly concerns the introduction of new connectors and new requirements for the power supply lines of the power supply.
When it becomes necessary to purchase a new ATX power supply, you first need to determine the power that is needed to power the computer in which this PSU will be installed. To determine it, it is enough to sum up the power of the components used in the system, for example, using the calculator from outervision.com. If this is not possible, then we can proceed from the rule that for an average computer with one gaming video card, a 500-600 watt power supply is enough.
Considering that most of the parameters of power supplies can only be found out by testing it, the next step is to strongly recommend that you familiarize yourself with the tests and reviews of possible contenders - power supply models that are available in your region and satisfy your requests at least in terms of power provided. If this is not possible, then it is necessary to choose according to the power supply modern standards(how more, the better), while it is desirable to have an AKKM (APFC) circuit in the power supply. When purchasing a power supply, it is also important to turn it on, if possible, right at the place of purchase or immediately upon arrival home, and see how it works so that the power supply does not emit squeaks, buzzes or other extraneous noise.
In general, you need to choose a power supply that is powerful, well-made, with good declared and actual electrical parameters, and also turns out to be easy to use and quiet during operation, even with a high load on it. And in no case should you save a couple of dollars when buying a power supply. Remember that the stability, reliability and durability of the entire computer mainly depends on the operation of this device.
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But there is still a way out. This is an ordinary, standard ATX from any, even the most simple and ancient computer. Despite the cheapness of such PSUs (a second-hand one can be found by companies and for 5), they provide a very decent current and universal voltages. On the + 12V line - 10A, on the -12V line - 1A, on the 5V line - 12A and on the 3.3V line - 15A. Of course indicated values not exact, and may vary slightly depending on specific model PSU ATX.
Just recently I did one interesting thing- a music center from and a case from a small speaker. Everything would be fine, but given the decent power of the bass amplifier, the current consumption of the center in the bass peaks reached 8A. And even an attempt to install a 100-watt transformer with a 4-amp secondary did not give a normal result: not only did the voltage drop by 3-4 volts on the bass (which was clearly noticeable by the attenuation of the backlight lamps of the front panel of the radio), but also I couldn't get rid of the 50Hz background. At least set it to 20,000 microfarads, at least shield everything you can.
And then, just for luck, it burned down old system manager at work. But the ATX power supply is still working. Here we will stick it for the radio. Although according to the passport the car radio and their amplifiers are powered by 12V, we know that it will sound much more powerful if 15-17V is applied to it. At least in my entire history, not a single receiver has burned out from an extra 5 volts.
Since the voltage of the 12-volt bus in the existing ATX power supply was only a little more than 10V (maybe that's why the system unit did not work? Too late.), We will raise it by changing the control voltage at the 2nd pin of the TL494. circuit diagram computer power supply, see here.
Simply put, we will change the resistor or even solder it to tracks of a different denomination. I put two kiloohms and now 10.5V turns into 17. Need less? - Increase the resistance. The computer power supply starts by shorting the green wire to any black one.
Since the places in the building of the future music center not much - we take out the ATX switching power supply board from the native case (the box will come in handy for my future project), and thereby reduce the dimensions of the PSU by half. And do not forget to solder the filter capacitor in the PSU to a higher voltage, otherwise you never know ...
And the cooler? - An attentive and quick-witted radio amateur will ask. We don't need him. Experiments showed that at a current of 5A 17V for an hour of operation of the radio at maximum volume (do not worry about the neighbors - two 4 Ohm 25 watt resistors), the radiator of the diodes was a little warm, and the transistors were almost cold. So such an ATX PSU will handle a load of up to 100 watts without problems.
Discuss the article SIMPLE ATX PSU
The main topic has already been voiced in the title, so let's get straight to the point. So what do we need? First, a working car stereo or car CD/MP3 receiver. I had a Panasonic CQ-DFX883N car CD/MP3 receiver in my hands.
Secondly, an AT or ATX format computer power supply. It's full now computer hardware from old PCs, including power supplies.
Where can I find it for free or for minimal money?
Pull out of your old PC, which is gathering dust in the closet;
Buy for a penny at a "flea market" - there are 100% of these on any radio market;
Repair and bring to mind a faulty computer PSU.
For my idea, I bought a "second-hand" power supply just at the "flea market".
Before connecting a computer PSU to a car radio, you need to check it and, if necessary, bring it to working condition. More on this later, but for now, how to connect the car radio to a computer power supply.
Connecting the car radio to a computer power supply.
The computer power supply (PSU) has a healthy harness with output connectors. Black wires are a negative or common wire. On yellow voltage + 12V is applied. We will not need the remaining wires - we will not use them. So we need to take only 12V from the power supply. To do this, take any of the connectors MOLEX or floppy connector. Next, we bite off the yellow wire (+ 12V) from it and the black wire - negative. Then we connect these wires to the power wires of the car radio.
It is worth noting that the +12V output channel is quite powerful and can "give" a current of 8-10 amperes to the load (with a PSU power of 200 - 300 W), which, in fact, is what we need. Typically, the maximum current drawn by a car CD/MP3 receiver is 10-15 amps. But this is the maximum!
In addition, you need to carry out a slight revision if you have an ATX format power supply. I'll talk about this a little later.
The car radio has 3 wires to which the power supply (voltage + 12V) is connected from the car's standard electrical network. The black wire is a minus (in other words, a common wire, "ground", Ground). The yellow wire is +12V (marked as Battery). These are the main wires for connecting power to the car radio.
But even if you connect these wires to a battery or power supply, we will not turn on the car radio - it will be in standby ("sleep") mode.
Therefore, we are looking for a red wire (marked ACC) at the car radio and twist it together with the yellow wire + 12V. Regularly, the red wire is connected to the ignition switch of the car.
As soon as the driver closes the ignition key electrical circuit, the car radio automatically switches from sleep mode to working mode - the backlight of the car radio display turns on. In this case, the red wire through the ignition switch is shorted to plus + 12V. We do this by forcibly connecting the yellow (+ 12V) and red wires.
In this case, the car radio will turn on immediately when power is applied.
The difference between AT and ATX computer power supplies.
AT format computer units do not have a standby power supply +5 (Standby) and output voltages of 3.3V. Therefore, when such a unit is turned on, voltage appears immediately at its outputs + 12V, + 5V, -12V, -5V.
ATX format power supplies have a standby power supply on +5V SB (Standby). It always works as long as the power supply is connected to the 220V network. In order for voltages +12V, -12V, +5V, -5V, +3.3V to appear on the output channels, you need to close the main output connector green and the black the wire.
If you want the output voltages to appear immediately after the PSU is turned on, then you can install a jumper between the green ( Power ON) and black wire. In this case, the power supply will exit the "sleep" mode immediately after applying 220V mains voltage to it.
Restoration of a computer power supply.
First, try to turn on the power supply. In most cases, used (used or "used") power supplies from a PC, as a rule, are working, but have some defects (lack of some output voltages, low voltage on one of the channels +12, -12, +5, -5 volts, etc.). Even if the power supply starts up - at the same time the fan starts to turn - it is worth opening the case of the power supply, removing all the dust from it, unscrewing the printed circuit board and inspecting the contacts for leaks. If necessary, correct defects.
Before carrying out any work, it is necessary to disconnect the power supply from the 220V network. Also, after that, it does not hurt to forcibly discharge the high-voltage electrolytic capacitors of the input rectifier (220-470 uF. * 250V). This can be done by connecting a 100-200 kΩ resistor for a few seconds in parallel with the capacitor contacts. Naturally, you should not hold the resistor with your fingers - otherwise you can get a slight electric shock.
This operation is necessary because residual the electric charge of capacitors is dangerous (in operating mode they are 200V!). If you accidentally touch the terminals of the capacitors, you can get a slight electric shock. The phenomenon is very unpleasant.
Particular attention should be paid to the condition of the electrolytic capacitors of the output rectifiers. If they are swollen, have a serif gap, then they need to be replaced with new ones.
More details about the design of AT format computer power supplies are described.
To make the power supply look more solid, you can paint it with aerosol spray paint (sold at any auto parts store).
