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In the process of repairing electronics, it is often necessary to check the functionality of the most common radio components - transistors.

There is a device specially designed for this - R/L/C/Transistor-meter, but it is not always available.

Therefore, it is useful to know how to test transistors, which will be discussed below.

A transistor consists of materials with special electrical properties - semiconductors. The latter are of two types:

with n-conductivity (electronic);
with p-conductivity (hole).

The simplest representative of semiconductor elements is a diode containing one p-n junction.

Transistors are more complex. There are two types of them: bipolar and field.

Bipolar

Also divided into two subgroups:

with n-p-n junction;
with p-n-p junction.

The components of a bipolar transistor are called emitter, collector and base. If we imagine this element in the form of two connected diodes, then the base will be their junction point.

To check a bipolar device, you need to recognize its type (n-p-n or p-n-p) and determine the purpose of the terminals (base, emitter and collector).

Field

Also divided into two types:

n-channel;
p-channel.

In a field-effect transistor, the resistance of the current-carrying section is regulated by the electric field.

The components of the element are called source, drain and gate. The current moves from source to drain, regulation is carried out by the gate.

The design of modern field-effect transistors is supplemented by a diode installed between the source and drain.

Determining the base (gate) output

The easiest way to determine the purpose of the transistor's terminals (pinout) is to download the documentation for it. The search is carried out using markings on the body. This alphanumeric code is typed into the search bar and then “datasheet” is added.

If the documentation cannot be found, the base and other terminals of the bipolar transistor are recognized based on its features:

pnp transistor: opens by applying negative to the base;
npn transistor: opens by applying a positive voltage to the base.

They work like this:

Set up the multimeter: the red probe is connected to the connector with the “V/ Ω " (positive potential), black - to the COM connector (negative potential), and the switch is set to the "continuity" mode or, if this is not the case, to the resistance measurement sector (icon " Ω ") to the top position (usually "2000 ohms").
Define the base. The red probe is connected to the first terminal of the transistor, the black one - alternately to the others. Then red is connected to the second terminal, black again in turn to the 1st and 3rd. A sign that the red one is connected to the base is the same behavior of the device when the black probe comes into contact with other terminals. The device beeped both times or showed a certain final resistance on the display - the transistor is of the n-p-n type; The device was silent both times or displayed “1” on the display (no conductivity) - the transistor belongs to the pnp type.
Collector and emitter recognition. To do this, connect a probe corresponding to the type of conductivity to the base: for an n-p-n transistor - red, for a p-n-p transistor: black.

Design field effect transistor with a control p-n junction and an n-type channel a) with a gate on the substrate side; b) with diffusion seal

The second probe is alternately connected to the other terminals. When contacting the collector, the display shows a lower resistance value than contacting the emitter.

The terminals of the field effect transistor are usually marked:

G: shutter;
S: source;
D: drain.

If there is no marking, the gate is detected using the same circuit as that of a bipolar transistor.

Field effect transistors are sensitive to static electricity. Because of this, their terminals are short-circuited with foil during storage, and before starting manipulations, wear an antistatic bracelet or at least touch a grounded metal object (instrument cabinet) to remove the static charge.

Checking the transistor with a multimeter

If the purpose of the terminals is known, the bipolar transistor is checked as follows:

Prepare the multimeter as described above: the switch is moved to the “2K” position in the “ Ω "(resistance measurement) or in continuity mode, the black probe is plugged into the "COM" connector, the red one into the "V/ Ω ».
Connect the probes to the emitter and collector, then swap them. Normally, in both cases the device does not produce a signal and displays “1”. Some terminal resistance indicates a breakdown.
Connect a probe corresponding to its type of conductivity to the base: “hole” base (n-p-n type transistor) - red probe, “electronic” (transistor p-n-p type) - black.
The second probe is connected in turn to the emitter and collector. Test results: the multimeter emits a signal, the display shows a resistance from 500 to 1200 Ohms - the transistor is working; there is no signal and the display shows one - an open circuit.
Another probe is connected to the base, and the second one is short-circuited in turn with the emitter and collector. Results: no signal, “1” on the display – the transistor is working; the device beeps, the display shows a certain final resistance value - the transistor is broken.

The field device is checked as follows:

Static electricity is removed from the element.
Set up the multimeter according to the usual scheme: black probe - into the “COM” port; red - to port “V/ Ω "; switch - to position “2K” of sector “ Ω "(resistance measurement).
Check the resistance between drain and source: normally the tester displays 400 - 700 Ohms.
The source and drain are short-circuited in order to reset the junction capacitances, after which the polarity is changed and the measurements are repeated. If the transistor is working properly, the readings change up or down by about 10% (40 - 70 Ohms). An infinitely high resistance between the source and drain (the display shows “1”) indicates a malfunction of the device.
Check for one-way continuity between source and gate, then between drain and gate. With one polarity of measurements, the multimeter will show a resistance of 400 - 700 Ohms, with the other - unity. Which probe is connected to the gate depends on the type of transistor (n-channel or p-channel). If the conductivity on the drain-gate or source-gate lines is two-way, that is, the device displays a certain final resistance value at any polarity, the transistor is broken.
When checking an n-channel field switch, the black probe is connected to the drain, the red probe to the source. The channel resistance value is recorded.
The red probe is connected to the gate, which will lead to a partial opening of the transition.
Return the red probe to the source and measure the channel resistance. If the transistor is working properly, the resistance will decrease (due to partial opening).
The black probe is connected to the gate, which will close the transition.
Return the black probe to the drain and measure the resistance. If the transistor is working, it acquires original meaning which was recorded.

Transistor test circuit

Check points 6 - 10 for a p-channel field-effect transistor are performed with the opposite polarity - swapping the red and black probes.

To open power transistors The voltage generated by the multimeter is not enough. In this case, a 12 V power supply is used, connected through a resistor with a resistance of 1500 - 2000 Ohms.

Testing without soldering

A bipolar transistor can be checked without soldering if the circuit is not shunted with low-resistance resistors. Otherwise, instead of a resistance of 500 - 1200 ohms, the multimeter will show only a few tens or even units. Then it is required.

Field-effect transistors are almost always bypassed, so they have to be desoldered before testing.

Gain Determination

When a device fails, another one with a similar gain is selected to replace it. To determine this parameter, you need a multimeter with a transistor testing function. On the switch panel of such a device there is a sector marked “hFE”. It has two rows of ports of three each, which are designated as follows:

n-p-n;
p-n-p.

Field effect transistor testing circuit

This is a type of bipolar transistor that needs to be connected to a given row of ports. The purpose of each port is judged by its letter designation:

B: base;
C: manifold;
E: emitter.

By connecting the transistor leads to the corresponding ports of the appropriate row, the user sees the gain value on the display.

Checking a Composite Transistor

A compound transistor includes two conventional bipolar transistors, and sometimes more. The standard method of checking with a multimeter is not applicable to it. It is necessary to assemble an electrical circuit powered from a constant 12 V power source. “Plus” is connected through a light bulb to the collector, “minus” - to the emitter. The base is connected through a resistor to a switch, which allows you to apply either “plus” or “minus” to it.

The resistor resistance is calculated using the formula:

R = U x h21E /I,

U- input voltage, IN;
H21E - minimum gain of this transistor;
I - load current, A.

Consider the following example:

tested composite transistor: KT827A (h21E = 750);
lamp power: 5 W.

The load current will be: I = 5 / 12 = 0.42 A.

Then the resistor resistance: R = 12 * 750 / 0.42 = 21600 Ohm, take R = 21 kOhm.

The verification is carried out in two stages:

Using a switch, “plus” is supplied to the base. If it is working properly, the light will come on.
The switch short-circuits the base to minus.

If it is working properly, the light will go out.

Even the simplest multimeter, which is not equipped with a function for determining the parameters of semiconductor devices, will help check the performance of the transistor. If you need to select an equivalent one instead of a burnt-out transistor, you will have to look for a tester model with the mentioned function.

Content:

In electronics and radio engineering, not only the correct assembly of the circuit, but also the subsequent verification of its performance is of great importance. The entire device or its individual elements can be checked. In this regard, the question quite often arises of how to check a transistor with a multimeter without disturbing the circuit. There are various methods that apply individually to each type of element. Before starting such verification and testing, it is recommended to study general device And .

Basic types of transistors

There are two main types of transistors - bipolar and field-effect. In the first case, the output current is created with the participation of carriers of both signs (holes and electrons), and in the second case - only one. Testing the transistor with a multimeter will help determine the malfunction of each of them.

Bipolar transistors are essentially semiconductor devices. They are equipped with three pins and two pn junctions. The operating principle of these devices involves the use of positive and negative charges - holes and electrons. Flowing currents are controlled using a specially dedicated control current. These devices are widely used in electronic and radio engineering circuits.

Bipolar transistors consist of three-layer semiconductors of two types - “p-p-p” and “p-p-p”. In addition, the design has two pn junctions. The semiconductor layers are connected to external terminals through non-rectifying semiconductor contacts. Middle layer is considered a base that is connected to the corresponding pin. Two layers located at the edges are also connected to the outputs - the emitter and collector. In electrical circuits, an arrow is used to indicate the emitter, showing the direction of current flowing through the transistor.

IN different types In transistors, holes and electrons - carriers of electricity - can have their own functions. The most common type is p-p-p due to the best parameters and technical characteristics. The leading role in such devices is played by electrons, which perform the main tasks of ensuring all electrical processes. They are approximately 2-3 times more mobile than holes, and therefore have increased activity. Qualitative improvements in devices also occur due to the collector transition area, which significantly more area emitter transition.

Each bipolar transistor has two pn junctions. When testing a transistor with a multimeter, this allows you to check the performance of the devices by monitoring the resistance values of the transitions when direct and reverse voltages are connected to them. For normal operation p-p-p-device, a positive voltage is applied to the collector, under the influence of which the base junction opens. After the base current occurs, the collector current appears. When appearing in the database negative voltage, the transistor turns off and the current flow stops.

The base junction in pnp devices opens when exposed to negative collector voltage. Positive voltage causes the transistor to turn off. All the necessary collector characteristics at the output can be obtained by smoothly changing the current and voltage values. This allows you to effectively test the bipolar transistor with a tester.

There are electronic devices in which all processes are controlled by the action of an electric field directed perpendicular to the current. These devices are called field-effect or unipolar transistors. The main elements are three contacts - source, drain and gate. The design of the field-effect transistor is complemented by a conductive layer that acts as a channel through which electric current flows.

These devices are represented by modifications of the “p” or “p”-channel type. Channels can be located vertically or horizontally, and their configuration can be volumetric or near-surface. The latter option is also divided into inversion layers containing enriched and depleted ones. The formation of all channels occurs under the influence of an external electric field. Devices with near-surface channels have a metal-insulator-semiconductor structure, which is why they are called MOS transistors.

Checking a bipolar transistor with a multimeter

The functionality of the bipolar transistor can be checked using a digital multimeter. This device measures direct and alternating currents, as well as voltage and resistance. Before starting measurements, the device must be properly configured. This will allow you to more effectively solve the problem of how to test a bipolar transistor with a multimeter without desoldering.

Modern multimeters can operate in a special measurement mode, which is why a diode icon is displayed on the body. When the question of how to check a bipolar transistor with a tester is decided, the device switches to the semiconductor testing mode, and one should be displayed on the display. The device terminals are connected in the same way as in resistance measurement mode. The black wire is connected to the COM port, and the red wire is connected to the output that measures resistance, voltage and frequency.

Older multimeters may not have a diode and transistor test feature. In such cases, all actions are carried out in the resistance measurement mode set to maximum. The multimeter battery must be charged before use. In addition, you need to check the serviceability of the probes. To do this, their tips are connected to each other. The squeak of the device and the zeros shown on the display indicate that the probes are working properly.

Checking a bipolar transistor with a multimeter is performed in the following order:

First of all, you need to correctly connect the leads of the multimeter and the transistor. To do this, you need to determine exactly where the base, collector and emitter are located. To determine the base, a black probe is connected to the first electrode, which is presumably considered the base. Another red probe is alternately connected first to the second and then to the third electrode. The probes are swapped until the device detects a voltage drop. After this, the bipolar transistor is finally checked with a multimeter and the pairs are determined: “base-emitter” or “base-collector”. The emitter and collector electrodes are determined using a digital multimeter. In most cases, the voltage drop and resistance at the emitter junction are higher than at the collector junction.
Definition of a base-collector pn junction: the red probe is connected to the base, and the black probe is connected to the collector. This connection operates in diode mode and allows current to flow in only one direction.
Definition of a base-emitter pn junction: the red probe remains connected to the base, and the black probe must be connected to the emitter. Same as in previous case, with such a connection, current flows only when connected directly. This is confirmed by checking the NPN transistor with a multimeter
Definition of an emitter-collector pn junction: if this junction is in good working order, the resistance in this section will tend to infinity. This is indicated by the unit shown on the display.
The multimeter is connected to each pair of contacts in two directions. That is, transistors p-p-p type checked by connecting back to the probes. In this case, a black probe is connected to the base. After measurements, the results obtained are compared with each other.
After checking the pnp transistor with a multimeter, the performance of the bipolar transistor is confirmed when, when measuring one polarity, the multimeter shows the final resistance, and when measuring the reverse polarity, one is obtained. This test does not require desoldering the part from the common board.

Many people are trying to solve the question of how to test a transistor without a multimeter using light bulbs and other devices. This is not recommended, since the element is highly likely to fail.

Checking the functionality of the field-effect transistor

Field-effect transistors are widely used in audio and video equipment, monitors and power supplies. The functioning of most electronic circuits. Therefore, in case of any malfunctions, these elements are checked in various ways, including checking transistors without desoldering them from the circuit with a multimeter.

A typical field-effect transistor circuit is shown in the figure. The main terminals - gate, drain and source - can be located differently, depending on the brand of transistor. If there is no marking, it is necessary to clarify the reference data regarding a particular model.

The main problem that arises when repairing electronic equipment with field-effect transistors is checking the transistor with a multimeter without desoldering. As a rule, faults concern high-power field-effect transistors, which are used in power supplies. In addition, these devices are very sensitive to static discharges. Therefore, before deciding how to test a transistor on a board with a multimeter, you should wear a special antistatic bracelet and familiarize yourself with the safety rules when performing this procedure.

Checking using a multimeter involves the same steps as for bipolar transistors. A working field-effect transistor has an infinitely large resistance between the terminals, regardless of the test voltage applied to it.

However, solving the question of how to ring a transistor with a multimeter has its own characteristics. If the positive probe of the multimeter is applied to the gate, and the negative probe to the source, then in this case the gate capacitance will be charged and the junction will open. When measuring between the drain and the source, the device shows the presence of a small resistance. Sometimes electrical engineers, in the absence of practical experience, may consider this a malfunction, which is not always true. This may be important when testing a horizontal transistor with a multimeter. Before testing the drain-source channel, it is recommended to short-circuit all terminals of the field-effect transistor to discharge the junction capacitances. After this, their resistance will increase again, after which you can re-test the transistors with a multimeter. If this procedure does not give a positive result, then this element is inoperative.

In field-effect transistors used for high-power switching power supplies, internal diodes are often installed at the drain-source junction. Therefore, during testing, this channel exhibits the properties of a conventional semiconductor diode. Therefore, in order to exclude an error, before checking the serviceability of the transistor with a multimeter, you should make sure that the internal diode is present. After the first check, the multimeter probes need to be swapped. After this, a unit will appear on the screen, indicating infinite resistance. If this does not happen, there is a high probability of a malfunction of the field-effect transistor. Using the device, you can not only check, but also measure the transistor with a multimeter.

How to test a compound transistor with a multimeter

A compound transistor or Darlington transistor is a circuit that combines two or more bipolar transistors. This allows you to significantly increase the current gain. Such transistors are used in circuits designed to operate with high currents, for example, in voltage stabilizers or output stages of power amplifiers. They are necessary when it is necessary to provide a large input impedance, that is, total impedance.

The general conclusions of a composite transistor are the same as those of bipolar model. The NPN transistor is checked in exactly the same way with a multimeter. In this case, a technique similar to testing a conventional bipolar transistor is used.

Testing semiconductor devices is the most important stage in diagnosing faults in electronic equipment. Some defective solid-state electronic components show themselves as burnt housing, darkening, etc. If there are simply no such indications of malfunctions, then it’s time to learn how to identify faulty diodes and transistors using a tester. In this article we will look at how to test the simplest rectifier diodes, diode assemblies, as well as bipolar transistors using simple equipment. Diodes and bipolar transistors can be checked using a Chinese multimeter.

Regardless of what device you have, you can definitely test any diode and transistor. The main thing is the presence special regime, which is indicated by a diode icon. This mode is intended for dialing, as well as for testing semiconductor devices. The multimeter probes must be connected in the same way as in the resistance measurement mode: the black probe to the COM port, the red probe to the resistance, voltage and frequency measurement port. If you have an outdated analog device with a dial indicator of the measurement result, then, probably, such a mode may simply not be there. For such devices, you can use the resistance measurement mode by setting the switch knob to the highest measurement limit.

How to check a diode and diode assemblies made on their basis?

As you know, a diode has 2 working electrodes - a cathode and an anode. A working diode passes current only in the forward direction if you connect the red probe of the device to the anode, and the black probe to the cathode. Connecting the wires in reverse causes the diode to turn off, and its resistance increases almost to infinity. When connecting the multimeter directly, we will notice that the device will indicate the presence of a certain voltage drop. As a rule, this value is several hundred millivolts. Reverse switching is expressed in the absence of any indication of the device. The diode can have only two faults: 1 – open, 2 – short circuit. In the first case, the device will not show any voltage drop in both forward and reverse connection. In the second case, there is infinitesimal forward and reverse resistance. If the device has a sound indication, then the device will beep both in forward and reverse switching on. Four diode rectifier assemblies are tested by testing each of the four diodes in the bridge rectifier.

How to test a semiconductor bipolar transistor?

Before you start testing, you need to determine exactly what type of transistor you are currently testing. In addition to bipolar transistors, there are a great many other types of transistors, which need to be tested in a completely different way. Within the framework of this article, testing of bipolar type transistors will be considered. A bipolar transistor can be represented as an arrangement of 2 diodes. These diodes are connected into a half-bridge using electrodes of the same name. At the output of the transistor there are 3 electrodes, conventionally designated as base, collector and emitter. Depending on the polarity of the diode connection, NPN and PNP bipolar transistors are distinguished. The base-emitter junction is a control junction, and the collector-emitter junction is a driven junction. The transistor is designed in such a way that a small current signal, which is supplied to the base-emitter junction, with the correct ratio of resistors in the circuit of the collector, base and emitter junction, causes a higher current signal at the collector-emitter junction.

How to determine where the base, collector, emitter are?

First of all, we note that in any analog tester or digital device, the negative probe is black, and the positive probe is red. Correctly installing the probes, as well as setting the device mode, is very important points. If everything is configured and connected correctly, then determining the pinout of the bipolar transistor will be as easy as shelling pears.

First, you need to determine where the base is. Regardless of whether the experimental transistor has a PNP or NPN structure, we can make the assumption that the base junction is the first electrode. We connect the black probe of the multimeter to the first electrode, and the red one, alternately, to the second and third electrode. Continue searching the base until you find a location where the meter begins to indicate a certain voltage drop, expressed in millivolts. Having noticed an indication of a voltage drop on a certain pair of electrodes, we can say with confidence that either a base-emitter pair or a base-collector pair has been found. Then you need to find the location and polarity of the remaining second pair. Basically, you have to find a pair of diodes whose common electrode is the base. The base can have a negative polarity in the case of a PNP structure, as well as a positive polarity in the case of a PNP polarity. You can check the operation of the transistor already at this stage, because the faulty element will have one of the transitions shorted or broken.

Secondly, when you have already decided on the base electrode, it remains necessary to determine where the emitter is located and where the collector is. Either using the semiconductor test mode on a digital device, or using the resistance measurement mode on an analog device, it is necessary to determine which of the junctions biggest drop voltage and resistance. We connect the measurement of base-emitter and base-collector diodes in direct connection. We write down the values and compare. As a rule, the difference is not large, but in fact the junction with the emitter electrode turned on will have a slightly higher resistance and voltage drop. Finally, we note that the correctness of the determination of the electrodes can be checked by connecting the transistor to the socket for measuring the parameters of bipolar transistors. If the device shows parameter h21e close to that, which is indicated in the datasheet, then finding the location of the electrodes can be considered correct.

When repairing and designing electronics, you often have to check the transistor for serviceability.

Let's consider a technique for testing bipolar transistors with a conventional digital multimeter, which almost every beginning radio amateur has.

Despite the fact that the technique for testing a bipolar transistor is quite simple, beginning radio amateurs can sometimes encounter some difficulties.

The features of testing bipolar transistors will be discussed a little later, but for now let’s look at the most simple technology check with a conventional digital multimeter.

First you need to understand that a bipolar transistor can be conventionally represented as two diodes, since it consists of two p-n junctions. And a diode, as you know, is nothing more than regular p-n transition.

Here is a schematic diagram of a bipolar transistor that will help you understand the principle of testing. On p-n figure The transistor junctions are depicted as semiconductor diodes.

Bipolar transistor device p-n-p The structure using diodes is depicted as follows.

As you know, bipolar transistors come in two types of conductivity: n-p-n And p-n-p. This fact must be taken into account when checking. Therefore, we will show the conditional equivalent of an n-p-n structure transistor made up of diodes. We will need this drawing for subsequent testing.

Transistor with structure n-p-n in the form of two diodes.

The essence of the method comes down to checking the integrity of these same p-n junctions, which are conventionally depicted in the figure as diodes. And, as you know, A diode allows current to flow in only one direction. If you connect plus ( + ) to the anode terminal of the diode, and minus (-) to the cathode, then the p-n junction will open and the diode will begin to pass current. If you do it the other way around, connect the plus ( + ) to the cathode of the diode, and minus (-) to the anode, then the p-n junction will be closed and the diode will not pass current.

If suddenly, when checking, it turns out that the pn junction passes current in both directions, then it means it is “broken”. If the p-n junction does not pass current in any direction, then the junction is in an open circuit. Naturally, if there is a breakdown or break in at least one of the p-n junctions, the transistor will not work.

Please note that conditional diagram of diodes is necessary only for a more visual representation of the transistor testing technique. In reality, the transistor has a more sophisticated design.

The functionality of almost any multimeter supports diode testing. On the multimeter panel, the diode test mode is depicted in the form of a symbolic image that looks like this.

I think it’s already clear that we will be checking the transistor using this function.

A little clarification. The digital multimeter has several sockets for connecting test leads. Three, or even more. When checking a transistor, you need a negative probe ( black) connect to the socket COM(from the English words common– “general”), and the positive probe ( red) into the slot marked with the letter Omega Ω , letters V and possibly other letters. It all depends on the functionality of the device.

Why do I talk in such detail about how to connect test leads to a multimeter? Yes, because the probes can simply be mixed up and you can connect the black probe, which is conventionally considered “negative,” to the socket to which you need to connect the red, “positive” probe. This will ultimately cause confusion and, as a result, errors. Be careful!

Now that the dry theory has been outlined, let's move on to practice.

What multimeter will we use?

First, we will check a domestically produced silicon bipolar transistor KT503. It has structure n-p-n. Here is its pinout.

For those who don't know what this means unknown word pinout, I’ll explain. Pinout is the location of the functional pins on the body of the radio element. For a transistor, the functional terminals will be the collector ( TO or English- WITH), emitter ( E or English- E), base ( B or English- IN).

First we connect red (+ ) probe to the base of the KT503 transistor, and black(-) probe to the collector terminal. This is how we check work p-n junction in direct connection (i.e. when the junction conducts current). The breakdown voltage value appears on the display. IN in this case it is equal to 687 millivolts (687 mV).

As you can see, the p-n junction between the base and emitter also conducts current. The display again shows the breakdown voltage value equal to 691 mV. Thus, we checked the B-K and B-E transitions when connected directly.

To make sure that the p-n junctions of the KT503 transistor are in good condition, let’s check them in the so-called reverse switching. In this p-n mode the junction does not conduct current, and the display should show nothing other than " 1 " If the display shows " 1 ", this means that the junction resistance is high and it does not allow current to pass through.

To check the p-n junctions B-K and B-E in reverse connection, we change the polarity of connecting the probes to the terminals of the KT503 transistor. We connect the negative (“black”) probe to the base, and the positive (“red”) probe first connects to the collector terminal...

...And then, without disconnecting the negative probe from the base output, to the emitter.

As we can see from the photographs, in both cases the display showed one “ 1 ", which, as already mentioned, indicates that the p-n junction does not pass current. So we checked the transitions B-K and B-E in reverse switching.

If you carefully followed the presentation, you will have noticed that we tested the transistor according to the previously outlined method. As you can see, the KT503 transistor turned out to be working.

Breakdown of the P-N junction of the transistor.

If any of the transitions (B-K or B-E) are broken, then when you check them on the multimeter display, you will find that they are not broken in both directions, both in direct connection and in reverse p-n voltage transition, but resistance. This resistance is either equal to zero “0” (the buzzer will squeak) or will be very small.

Broken P-N junction of the transistor.

In the event of a break, the p-n junction does not allow current to pass either directly or indirectly. reverse direction– the display in both cases will show “ 1 " With this p-n defect the transition, as it were, turns into an insulator.

Checking bipolar transistors p-n-p structures is carried out similarly. But at the same time polarity needs to be changed connecting measuring probes to the terminals of the transistor. Let us recall the drawing of a conventional image of a p-n-p transistor in the form of two diodes. If you forgot, then look again and you will see that the cathodes of the diodes are connected together.

As a sample for our experiments, we will take a domestic silicon transistor KT3107 p-n-p structures. Here is its pinout.

In the pictures, checking the transistor will look like this. We check the B-K transition when connected directly.

As you can see, the transition is correct. The multimeter showed the breakdown voltage of the junction - 722 mV.

We do the same for the B-E transition.

As you can see, it is also working properly. The display shows 724 mV.

Now let’s check the serviceability of the transitions in the opposite direction - for the presence of a “breakdown” of the transition.

Transition B-K when switched back on...

Transition B-E during reverse switching.

In both cases, the device display shows one “ 1 " The transistor is OK.

Let's summarize and describe a short algorithm for checking a transistor with a digital multimeter:

Determination of the transistor pinout and its structure;

Examination transitions B-K and B-E in direct connection using the diode test function;

Checking the B-K and B-E transitions in reverse connection (for the presence of a “breakdown”) using the diode test function;

When checking, it is necessary to remember that in addition to conventional bipolar transistors, there are various modifications of these semiconductor components. These include compound transistors (Darlington transistors), “digital” transistors, line transistors (the so-called “line transistors”), etc.

They all have their own characteristics, such as built-in protective diodes and resistors. The presence of these elements in the structure of the transistor sometimes complicates their testing using this technique. Therefore, before checking a transistor unknown to you, it is advisable to read the documentation for it (datasheet). I talked about how to find a datasheet for a specific electronic component or microcircuit.