Bipolar transistors are made of alloyed materials and can be of two types - NPN and PNP. The transistor has three leads known as the emitter (E), base (B), and collector (K). The figure below shows an NPN transistor where, in the main modes of operation (active, saturation, cutoff), the collector has a positive potential, the emitter is negative, and the base is used to control the state of the transistor.

The physics of semiconductors will not be discussed in this article, however, it is worth mentioning that a bipolar transistor consists of three separate parts, separated by two pn junctions. A PNP transistor has one N region separated by two P regions:

An NPN transistor has one P region enclosed between two N regions:

Joints between the N and P regions are similar to transitions in, and they can also be forward and reverse biased pn junction. These devices can operate in different modes depending on the type of displacement:

• Cutoff: work in this mode also occurs when switching. There is no current flowing between the emitter and the collector, practically “open circuit”, that is, “contact open”.
• Active mode: the transistor works in amplifier circuits. In this mode, its characteristic is almost linear. A current flows between the emitter and the collector, the magnitude of which depends on the value of the bias (control) voltage between the emitter and the base.
• Saturation: works when switching. There is practically a "short circuit" between the emitter and the collector, that is, the "contact is closed".
• Inverse active mode: as in active mode, the transistor current is proportional to the base current, but flows in the opposite direction. Very rarely used.

In an NPN transistor, a positive voltage is applied to the collector to create current from the collector to the emitter. In a PNP transistor, a positive voltage is applied to the emitter to create current from emitter to collector. In NPN, current flows from the collector (K) to the emitter (E):

And in PNP, the current flows from the emitter to the collector:

It is clear that the directions of current and voltage polarity in PNP and NPN are always opposite to each other. NPN transistors require positive supply with respect to common terminals, while PNP transistors require negative supply.

PNP and NPN work in much the same way, but their modes are different due to polarities. For example, to transfer NPN to saturation mode, U B must be higher than U K and U E. Below is a brief description of the operating modes depending on their voltage:

The basic principle of operation of any bipolar transistor is to control the base current to regulate the current flowing between the emitter and the collector. The principle of operation of NPN and PNP transistors is the same. The only difference is the polarity of the voltages applied to their N-P-N and P-N-P junctions, that is, to the emitter-base-collector.

Polyneuropathy (PNP) is a common, common disease of the peripheral nervous system (PNS). It is manifested by changes in sensitivity, a decrease in strength, pain in the arms and legs, and trophic disorders. PNP brings a lot of suffering, difficult to treat, often chronic, progressive
flow.
What is the Peripheral Nervous System?

PNS is a part of the nervous system, which is formed by long ocanes of nerve cells (neurons). Theirbodies are in nucleispinal cord and in the brain stem. Once the processes leave the dura mater, they are considered peripheral nerve fibers. Autonomic fibers are attached to these long fibers, they intertwine and form peripheral nerves (PNS).

With polyneuropathy (PNP), distant areas of the peripheral nerves are affected. Accordingly, there is a change in the distal parts of the lower and upper extremities. They are affected diffusely, symmetrically (left and right).

Symptoms of polyneuropathy

Polyneuropathy manifests itself in a complex of sensory, motor and autonomic problems. Symptoms can be isolated, but more often, they are in various combinations and have a degree of severity - from minor to pronounced.
The main manifestations of PNP include pain, loss or decrease in reflexes, weakness in the arms and legs, changes in sensitivity in the limbs, and autonomic disorders.

With the flow, the process is acute, subacute and chronic.
Depending on the etiological origin, PNP is divided into 2 groups - primary and secondary.

Primary ones result from direct damage to the nerves. These PNPs are traumatic, hereditary and of unknown cause (idiopathic).
Secondary polyneuropathies are much more common than primary ones. They are formed as a result of diseases, the pathogenesis of which is not associated with the nervous system. Or due to various intoxications, infections.

Diseases in which secondary polyneuropathies develop include diabetes mellitus (most often), diffuse connective tissue damage, and oncological processes.
Intoxication can be alcoholic (most often), medicinal, caused by exposure to various toxic substances, heavy metals, with infectious nerve damage.

Due to numerous reasons, axial cylinders of peripheral fibers suffer from polyneuropathy. This is the main part of the nerve. They are long outgrowths of neurons in the spinal cord. The processes are called axons and dendrites. Some axons are very long - up to one meter. The axial cylinder contains axoplasm. An axoplasmic current (impulse) flows through it. Many metabolic and toxic ANPs are associated precisely with violations of the axoplasm and this axoplasmic current.

But, not less often, due to polyneuropathy, myelin sheaths also suffer. They are formed by Schwann cells. These cells contain a substance called myelin. A separate Schwann cell twists around the axon, enveloping it, like the insulating material of an electric wire.

There are areas between the cells that are not protected by them, not myelinated. An unmyelinated stretch is called a Ragged Intercept. The current along the axon spreads "jumps" from one interception to the next. Due to the spasmodic flow, a very high speed of its advance is achieved.

Disruption of the myelin sheath with PNP leads to impaired conduction of impulses. Promotes movement and sensory disorders.
With polyneuropathy, there is, most often, a combined lesion of both the nerve trunk itself and its sheath.

Pain syndrome

Pain is the main symptom of polyneuropathy, frequent and significant. It becomes the predominant complaint of patients and significantly affects the quality of life. Polyneuropathic pain is poorly treated and is often resistant to traditional analgesics.
By its nature, pain can be varied, depending on the severity of the process, the caliber of the affected fibers. She has a burning, persistent character. It starts at the feet (soles), then spreads in the proximal direction (up the shins).

The pain occurs spontaneously (independently), or is caused in response to various stimuli. And it is called, respectively - spontaneous or evoked.
Spontaneous appears at rest, intensifies at night, disrupts sleep.

Induced is formed by external stimuli. This is hyperalgesia. A weak painful stimulus with hyperalgesia is accompanied by an intense painful response that is inadequate to the stimulus.
Also, with PNP, allodynia may occur. It is characterized by the fact that non-painful stimuli - touch, stroking, light pressure, normal movement, a slight temperature effect cause an intense pain reaction and also bring enough suffering to a person.
Hyperalgesia and allodynia can reach such a degree of intensity that the patient can often hardly bear the touch of a blanket or even a sheet.

But, subsequently, hypesthesia (decreased sensitivity) begins to progress. It also develops from the distal parts of the feet and hands. Areas of hyperalgesia (increased pain sensitivity) with the development of reduced sensitivity move up (proximally). And hypesthesia spreads along the traces of the territory of the former painful zones.
In chronic polyneuropathies, as the process progresses, with the expansion of the zone of other symptoms (sensitive, trophic, motor), pain may regress, but not always.

Conventionally, neuropathic pain is divided into 2 main groups:
superficial, burning, burn-like skin, accompanied by hyperalgesia (with damage mainly to thin fibers)
deep, breaking pain, sometimes it has a crump-like (type of convulsions) character - when thick fibers are involved in the process.

In isolation, these types of pain are rare. One kind of her usually just significantly prevails over the other.
For long-term pain, it is characteristic and dangerous that, due to increased impulses from the suffering nerves, a functional restructuring of neurons occurs at the level of the spinal cord and brain stem. This process is associated with the special plasticity of the nervous system.

Therefore, PNP pain may not be relieved by the use of conventional analgesics. This creates certain difficulties in its treatment.
The mechanisms of this process have not yet been fully understood.

Transthyretin familial amyloid polyneuropathy

This is a rare, progressive, genetically determined, degenerative polyneuropathy. It occurs against the background of a mutation of the protein transthyretin, which carries vitamin A and thyroid hormones.

In the early years of the disease, the manifestations of neuropathy are insignificant, have little effect on the quality of life, but, from year to year, gradually increasing, lead to severe motor, sensory and autonomic disorders.
Therefore, it is important to diagnose at an early stage of the disease and start treatment as early as possible.

To clarify the diagnosis, DNA analysis is performed. You can make it free of charge at the Center for Molecular Genetics in Moscow. Get a referral from your doctor.

Restless legs syndrome


In middle and old age, there is a condition associated with unpleasant pain in the legs. Pain occurs - in the feet and legs.

Pain has a daily rhythm of its occurrence. She appears in the evening, at rest, when a person is already ready for sleep. The condition is relieved and pain is relieved by moving the legs. Patients bend, unbend limbs, rub them, massage them, walk around the room, cannot sleep.
Therefore, this condition is figuratively called "restless legs syndrome" (RLS). By morning, the pain disappears, a person can forget about it, but, before going to bed, the problem arises again and again. C "restless legs syndrome" often begins Parkinson's disease , but a significant part of his cases are associated with polyneuropathies of various etiologies.

Thus, polyneuropathy is a complex problem, has many reasons for its occurrence, more often it is of a chronic progressive nature, requires a mandatory visit to a doctor at the initial stage of its onset.
Treatment of polyneuropathy

Many of you have probably run into the situation - you downloaded and installed a free program, then opened your browser and found a strange bar, a modified default search engine and a different home page. You just picked up a Potentially Unwanted Program (PUP).

Usually, this program is packaged in an installer of common programs, more often free, but sometimes even found in commercial products. They usually change browser settings in an attempt to redirect traffic to resources that generate income for the creators of unwanted software. They can also track your online behavior and then resell that data to advertisers.

Preventing the installation of PUPs

Although the programs are unwanted, they are not malicious in nature and are often undetectable by antivirus software. The best defense against them is attentiveness and caution.

Always carefully read each step of the program installation and disable the checkboxes that are responsible for installing additional programs, toolbars and extensions. If you are offered a normal and custom installation, then select Custom - there are often hidden switches for installing hidden software. The program can help you remove unnecessary checkmarks in the installers and warn you about an attempt to install an unwanted program.

The free Unchecky tool monitors software installations and automatically disables checkboxes that lead to third-party software installations. On our site is available on the use of the utility.

Sometimes, when you install freeware, PUPs are an integral part of the offering and you cannot disable their installation. When you come across a license agreement for a program, it is very tempting to click the "Next" button, because reading the document can take a lot of time. However, sometimes it is better to review the agreement to find out that the program comes with a bunch of unnecessary “friends”. In this situation, the best solution would be to close the installer and look for another program that does not impose additional modules.

It may be worth looking for a portable version of the program - they do not need to be installed, which means they do not have an installer containing third-party software.

To check a suspicious installer, you can use the sandbox - in this case, unwanted software will not gain access to files on the real system. You can use a virtual machine like VirtualBox or VMware to install applications on a separate OS.

You did your best to avoid PUPs, but your browser was hacked, panels appeared, page and search engine changed. If your antivirus doesn't find the culprit and you can't remove the unwanted extension from your browser, try Malwarebytes Free.

Malwarebytes can scan the system for PUPs and remove them. The product can safely work in conjunction with an antivirus, it can be configured to detect PUPs and treat them like normal malware, i.e. suggesting deletion.

In addition, you can use free adware and PUP removal utilities - AdwCleaner, Junkware Removal Tool and Ultra Adware Killer.

Have you ever encountered a PUP? How did you fix them? Let us know in the comments!

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The term "PNP"

PNP is an abbreviated name for the bottomhole formation zone. Bottom-hole formation zone is a section of the formation that is adjacent to the wellbore and within which the filtration properties of the productive formation change during the construction, operation and workover of the well. The reasons that lead to a change in the characteristics of the bottomhole formation zone include the following - redistribution of stress in the near-wellbore part of the well, various physicochemical effects of various process fluids, as well as various processes that are caused by operating modes and conditions. The dimensions, configuration, and hydrochemical properties of the bottomhole formation zone change during the entire period of the well's existence. They affect the hydraulic connection of the well with the EOR and very often affect its productivity.

The configuration of the zone of the formation with changed characteristics in the near-wellbore part of the well does not have any geometric shape. Its morphology is very diverse and complex, especially for fractured-porous and fractured reservoirs. Thanks to hydrodynamic testing of wells, it is possible to obtain a quantitative, qualitative assessment of the properties of the bottomhole formation zone, as well as to determine the hydraulic resistance. In the course of such studies, data is obtained on the size of the equivalent, rather than the actual, circular zone. So, the size of the reservoir zone is measured from fractions to several tens of meters. Sometimes it is possible to observe the separation of the formation and the well both during construction, as well as during repair, operation. As a result, when tested, such objects may not produce products. To prevent a decrease in the filtration properties of the bottomhole formation zone, a number of measures are carried out that reduce the pressure on the formation during drilling, as well as when casing and repairing wells. Process fluids or formulations that are compatible with the formation rock or fluids saturating it can also be used. When exposed to the bottomhole zone by different methods, its filtration properties are increased or restored. The maximum effect can be achieved with a complex effect on PNP.

A PNP transistor is an electronic device, in a sense, the opposite of an NPN transistor. In this type of transistor design, its PN junctions are opened with voltages of reverse polarity with respect to the NPN type. In the device legend, the arrow, which also defines the emitter pin, this time points to the inside of the transistor symbol.

Device design

The structural diagram of a PNP-type transistor consists of two regions of p-type semiconductor material on either side of an area of ​​n-type material, as shown in the figure below.

The arrow defines the emitter and the generally accepted direction of its current ("inward" for a PNP transistor).

The PNP transistor has very similar characteristics to its NPN bipolar counterpart, except that the directions of currents and polarities of voltages in it are reversed for any of the three possible switching schemes: with a common base, with a common emitter and with a common collector.

The main differences between the two types of bipolar transistors

The main difference between them is that holes are the main current carriers for PNP transistors, NPN transistors have electrons in this capacity. Therefore, the polarities of the voltages supplying the transistor are reversed, and its input current flows out of the base. In contrast, the NPN transistor has base current flowing into it, as shown in the diagram below for both common base and common emitter types.

The principle of operation of the PNP-type transistor is based on the use of a small (like the NPN-type) base current and negative (unlike the NPN-type) base bias voltage to drive a much higher emitter-collector current. In other words, for a PNP transistor, the emitter is more positive with respect to the base as well as with respect to the collector.

Consider the differences between the PNP-type in the connection diagram with a common base

Indeed, it can be seen from it that the collector current I C (in the case of an NPN transistor) flows out of the positive pole of battery B2, passes through the collector terminal, penetrates into it and must then exit through the base terminal to return to the negative pole of the battery. In the same way, looking at the emitter circuit, you can see how its current from the positive pole of battery B1 enters the transistor at the base pin and then penetrates into the emitter.

Thus, both the collector current I C and the emitter current I E pass through the base output. Since they circulate along their circuits in opposite directions, the resulting base current is equal to their difference and is very small, since I C is slightly less than I E. But since the latter is still larger, the direction of flow of the differential current (base current) coincides with I E, and therefore a PNP-type bipolar transistor has a current flowing out of the base, and an NPN-type transistor flowing in.

Differences PNP-type on the example of a switching circuit with a common emitter

In this new circuit, the base-emitter PN junction is opened by battery voltage B1 and the collector-base junction is reverse biased by battery voltage B2. The emitter pin is thus common to the base and collector circuits.

The total emitter current is given by the sum of the two currents I C and I B; passing along the output of the emitter in one direction. Thus, we have I E = I C + I B.

In this circuit, the base current I B is simply “branched off” from the emitter current I E, also coinciding with it in direction. In this case, the PNP-type transistor still has a current I B flowing out of the base, and an NPN-type current flowing in.

In the third of the known circuits for switching on transistors, with a common collector, the situation is exactly the same. Therefore, we do not present it in order to save space and time for our readers.

PNP transistor: connecting voltage sources

The voltage source between base and emitter (V BE) is connected negative to base and positive to emitter, because the PNP transistor operates with negative base bias in relation to the emitter.

The supply voltage to the emitter is also positive with respect to the collector (V CE). Thus, in a PNP-type transistor, the emitter terminal is always more positive with respect to both the base and the collector.

The voltage sources are connected to a PNP transistor as shown in the figure below.

This time, the collector is connected to the supply voltage V CC through a pull-up resistor, R L, which limits the maximum current flowing through the instrument. The base voltage V B, which bias it in the negative direction with respect to the emitter, is applied to it through resistor R B, which is again used to limit the maximum base current.

PNP transistor stage operation

So, to cause the base current to flow in a PNP transistor, the base must be more negative than the emitter (the current must leave the base) by about 0.7 volts for a silicon device or 0.3 volts for a germanium device. The formulas used to calculate the base resistor, base current, or collector current are the same as those used for the NPN equivalent transistor and are presented below.

We see that the fundamental difference between NPN and PNP transistor is the correct biasing of the pn junctions, since the directions of currents and polarities of voltages in them are always opposite. So for the above circuit: I C = I E - I B, since the current must flow from the base.

Typically, PNP transistor can be replaced with NPN transistor in most electronic circuits, the difference is only in voltage polarity and current direction. Such transistors can also be used as switching devices, and an example of a PNP switch is shown below.

Transistor characteristics

The output characteristics of a PNP transistor are very similar to the corresponding curves of an equivalent NPN transistor, except that they are rotated 180 ° taking into account the reversal of the polarity of voltages and currents (base and collector currents, PNP transistor are negative). Likewise, to find the operating points of a PNP transistor, its dynamic load line can be plotted in the third quarter of the Cartesian coordinate system.

Typical characteristics of PNP transistor 2N3906 are shown in the figure below.

Transistor pairs in amplifier stages

You may be wondering what is the reason for using PNP transistors when there are many NPN transistors available that can be used as amplifiers or solid state switches? However, having two different types of transistors - NPN and PNP - offers great advantages when designing power amplifier circuits. These amplifiers use "complementary" or "matched" pairs of transistors (which are one PNP transistor and one NPN connected together as shown in the figure below) in the output stage.

Two corresponding NPN and PNP transistors with similar characteristics, identical to each other, are called complementary. For example, TIP3055 (NPN-type) and TIP2955 (PNP-type) are good examples of complementary silicon power transistors. They both have a constant current gain β = I C / I B matched within 10% and a high collector current of around 15A, making them ideal for motor control or robotic applications.

In addition, class B amplifiers use matched pairs of transistors in their power output stages. In them, the NPN transistor conducts only the positive half-wave of the signal, and the PNP transistor only conducts its negative half.

This allows the amplifier to drive the required power through the loudspeaker in both directions at a given power rating and impedance. As a result, the output current, which is usually in the order of several amperes, is evenly distributed between the two complementary transistors.

Transistor pairs in electric motor control circuits

They are also used in H-bridge control circuits for reversible DC motors, which make it possible to regulate the current through the motor evenly in both directions of its rotation.

The H-bridge circuit above is so named because the basic configuration of its four transistor switches resembles the letter "H" with the motor on the cross line. The transistor H-bridge is probably one of the most commonly used types of reversing DC motor control circuit. It uses "complementary" pairs of NPN and PNP transistors in each branch, acting as switches to control the motor.

Control input A allows the motor to run in one direction, while input B is used for reverse rotation.

For example, when TR1 is on and TR2 is off, input A is connected to supply voltage (+ Vcc), and if TR3 is off and TR4 is on, then input B is connected to 0 volts (GND). Therefore, the motor will rotate in one direction corresponding to the positive potential of input A and the negative potential of input B.

If the states of the keys are changed so that TR1 is off, TR2 is on, TR3 is on, and TR4 is off, the motor current will flow in the opposite direction, which will entail its reversal.

By using opposite levels of logic "1" or "0" on inputs A and B, it is possible to control the direction of rotation of the motor.

Determining the type of transistors

Any bipolar transistor can be thought of as consisting primarily of two diodes connected together back to back.

We can use this analogy to determine if a transistor is PNP or NPN by testing its resistance between its three pins. Testing each pair of them in both directions with a multimeter, after six measurements, we get the following result:

1. Emitter - Base. These leads should act like a normal diode and conduct current in one direction only.

2.Collector - Base. These leads should also act like a regular diode and conduct current in one direction only.

3. Emitter - Collector. These findings should not be held in any direction.

The values ​​of the resistances of the transitions of transistors of both types

Then we can define a PNP transistor as good and closed. A small output current and a negative voltage at its base (B) with respect to its emitter (E) will open it up and allow much more emitter-collector current to flow. PNP transistors conduct with a positive emitter potential. In other words, a PNP bipolar transistor will only conduct if the base and collector pins are negative with respect to the emitter.