How to test a germanium transistor. Basic methods for testing a transistor. Case and layout

Being engaged in the repair and design of electronics, you often have to check the transistor for serviceability.

Let's consider a method for checking bipolar transistors with a conventional digital multimeter, which almost every novice radio amateur has.

Despite the fact that the method for checking a bipolar transistor is quite simple, novice radio amateurs can sometimes encounter some difficulties.

The features of testing bipolar transistors will be discussed a little later, but for now we will consider the simplest testing technology with a conventional digital multimeter.

First you need to understand that a bipolar transistor can be conditionally represented as two diodes, since it consists of two p-n junctions. A diode, as you know, is nothing more than an ordinary p-n junction.

Here is a schematic diagram of a bipolar transistor that will help you understand the principle of verification. In the figure, the p-n junctions of a transistor are shown as semiconductor diodes.

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

As you know, bipolar transistors are of 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 composed of diodes. We will need this figure for the next check.

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

The essence of the method is to check the integrity of these same p-n junctions, which are conventionally shown in the figure in the form of diodes. And, as you know, The diode only allows current to flow in 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 the opposite, 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 during the check it turns out that the p-n junction passes current in both directions, then it means that it is “broken”. If the p-n junction does not pass current in any of the directions, then the junction is in a "break". Naturally, if at least one of the p-n junctions breaks down or breaks, the transistor will not work.

Please note that conditional scheme of diodes is necessary only for a more visual representation of the method for testing the transistor. In reality, the transistor has a more sophisticated device.

The functionality of almost any multimeter supports diode testing. On the multimeter panel, the diode test mode is displayed as a conditional image that looks like this.

I think it is already clear that we will check the transistor just with the help of this function.

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

Why am I talking in such detail about how to connect test leads to a multimeter? Yes, because the probes can be simply confused and connect the black probe, which is conditionally considered “negative” to the socket to which you need to connect the red, “positive” probe. As a result, this will cause confusion, and, as a result, errors. Be careful!

Now that the dry theory is set out, let's move on to practice.

What multimeter will we use?

First, we will test a domestic-made silicon bipolar transistor KT503. It has a structure n-p-n. Here is his pin.

For those who do not know what this incomprehensible word means pinout, I explain. The pinout is the location of the functional pins on the body of the radio element. For a transistor, the functional outputs will respectively be a collector ( TO or English- WITH), emitter ( E or English- E), base ( B or English- IN).

Connect first red (+ ) probe to the base of the KT503 transistor, and black(-) probe to collector outlet. This is how we check the operation of the p-n junction in direct connection (that is, when the junction conducts current). The breakdown voltage value appears on the display. In this case, it is equal to 687 millivolts (687 mV).

As you can see, the p-n junction between the base and the emitter also conducts current. The display again shows the value of the breakdown voltage equal to 691 mV. Thus, we checked the B-C and B-E transitions with direct connection.

To make sure that the p-n junctions of the KT503 transistor are working, we will check them in the so-called reverse inclusion. In this mode, the p-n junction does not conduct current, and the display should show nothing but " 1 ". If the display unit " 1 ”, this means that the resistance of the transition is high, and it does not pass current.

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

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

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

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

Breakdown of the P-N transition of the transistor.

If any of the junctions (B-K or B-E) are broken, then when checking them on the multimeter display, it turns out that in both directions, both in direct connection and in reverse, they show a non-breakdown voltage of the p-n junction, but resistance. This resistance is either zero "0" (the buzzer will beep), or it will be very small.

Open P-N junction of the transistor.

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

Checking bipolar transistors of the p-n-p structure is carried out in a similar way. But at the same time polarity needs to be reversed connecting measuring probes to the transistor terminals. Recall the drawing of a conditional 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 take a domestic silicon transistor KT3107 p-n-p structures. Here is his pin.

In the pictures, the transistor test will look like this. We check the B-K transition with direct connection.

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

We do the same for the B-E transition.

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

Now let's check the health of the transitions in the opposite direction - for the presence of a "breakdown" of the transition.

Transition B-K when reversed…

Transition B-E when reversed.

In both cases, on the display of the device - one " 1 ". The transistor is correct.

Let's summarize and write out a brief algorithm for checking a transistor with a digital multimeter:

Determination of the pinout of the transistor and its structure;

Checking B-C and B-E transitions in direct connection using the diode test function;

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

When checking, it must be remembered 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 "linear"), etc.

All of them 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 verification using this technique. Therefore, before checking a transistor unknown to you, it is advisable to familiarize yourself with the documentation for it (datasheet). I talked about how to find a datasheet for a specific electronic component or microcircuit.

Before you assemble any circuit or start repairing an electronic device, you need to make sure that the elements that will be installed in the circuit are in good condition. Even if these elements are new, you need to be sure of their performance. Such common elements of electronic circuits as transistors are also subject to mandatory verification.

To check all the parameters of transistors, there are complex devices. But in some cases, it is enough to conduct a simple check and determine the suitability of the transistor. For such a check, it is enough to have a multimeter.

Various types of transistors are used in technology - bipolar, field-effect, composite, multi-emitter, phototransistors and the like. In this case, the most common and simple ones will be considered - bipolar transistors.

Such a transistor has 2 p-n junctions. It can be represented as a plate with alternating layers with different types of conductivity. If hole conductivity (p) prevails in the extreme regions of a semiconductor device, and electronic conductivity (n) prevails in the middle region, then the device is called a p-n-p transistor. If vice versa, then the device is called an n-p-n type transistor. For different types of bipolar transistors, the polarity of the power sources that are connected to it in the circuits changes.

The presence of two junctions in the transistor makes it possible to represent in a simplified form its equivalent circuit as a series connection of two diodes.

At the same time, for a p-n-p device, the cathodes of the diodes are connected to each other in the equivalent circuit, and for the n-p-n device, the anodes of the diodes.

In accordance with these equivalent circuits, the bipolar transistor is checked for serviceability with a multimeter.

The procedure for checking the device - follow the instructions

The measurement process consists of the following steps:

• checking the operation of the measuring device;
• determining the type of transistor;
• measurement of direct resistances of emitter and collector junctions;
• measurement of reverse resistances of emitter and collector junctions;
• transistor health assessment.

Before you check the bipolar transistor with a multimeter, you need to make sure that the measuring device is working. To do this, you first need to check the battery indicator of the multimeter and, if necessary, replace the battery. When checking transistors, the polarity of the connection will be important. It should be borne in mind that the multimeter has a negative pole at the “COM” output, and a positive pole at the “VΩmA” output. For definiteness, it is desirable to connect a black probe to the “COM” output, and a red one to the “VΩmA” output.

In order to connect the multimeter probes of the correct polarity to the transistor terminals, it is necessary to determine the type of device and the marking of its terminals. For this purpose, you need to refer to the reference book or find a description of the transistor on the Internet.

In the next test step, the multimeter's operation switch is set to the resistance measurement position. The measurement limit is set to "2k".

Before you check the pnp transistor with a multimeter, you need to connect the negative probe to the base of the device. This will allow you to measure the direct resistance of the transitions of the radio element of the p-n-p type. The positive probe is connected in turn to the emitter and collector. If the junction resistances are 500-1200 ohms, then these junctions are OK.

When checking the reverse resistance of the transitions, a positive probe is connected to the base of the transistor, and the negative probe is connected in turn to the emitter and collector.

If these transitions are serviceable, then in both cases a large resistance is fixed.

Checking the npn transistor with a multimeter follows the same method, but the polarity of the connected probes is reversed. According to the measurement results, the health of the transistor is determined:

1. if the measured forward and reverse transition resistances are large, then this means that there is an open circuit in the device;
2. if the measured forward and reverse junction resistances are small, then this means that there is a breakdown in the device.

In both cases, the transistor is faulty.

Gain Estimation

The characteristics of transistors usually have a large spread in magnitude. Sometimes, when assembling a circuit, it is required to use transistors that have a similar current gain. A multimeter allows you to select such transistors. To do this, it has a switching mode "hFE" and a special connector for connecting the outputs of transistors of 2 types.

By connecting the outputs of the transistor of the corresponding type to the connector, you can see the value of the h21 parameter on the screen.

conclusions:

1. Using a multimeter, you can determine the health of bipolar transistors.
2. To carry out correct measurements of the forward and reverse resistances of transistor junctions, it is necessary to know the type of transistor and the marking of its terminals.
3. Using a multimeter, you can select transistors with the desired gain.

Video on how to test a transistor with a multimeter

Field-effect transistors are semiconductor devices in which the control of transients, as well as the magnitude of the output current, is carried out by changing the magnitude of the electric field. There are two types of these devices: with (in turn, they are divided into transistors with a built-in channel and with an induction channel) and with a controlled transition. Field-effect transistors, due to their unique characteristics, are widely used in electronic equipment: power supplies, televisions, computers, etc.

When repairing such equipment, for sure, every novice radio amateur was faced with the following question: how to check a field effect transistor? Most often, checking such elements can be encountered when repairing switching power supplies. In this article, we will tell you in detail how to do it right.

Howcheck the field effect transistor with an ohmmeter

First of all, in order to start checking the field-effect transistor, it is necessary to deal with its “pinout”, that is, with the pinout. To date, there are many different versions of such elements, respectively, the location of the electrodes they have is different. You can often find semiconductor transistors with signed contacts. For marking use the Latin letters G, D, S. If there is no signature, then you need to use the reference literature.

So, having dealt with the marking of the contacts, let's consider how to check the field-effect transistor. The next step is to take the necessary safety measures, because field devices are very sensitive to static voltage, and in order to prevent failure of such an element, it is necessary to organize grounding. To remove the accumulated static charge, it is common to wear an antistatic grounding wrist strap on the wrist.

We should also not forget that it is necessary to store field-effect transistors with closed terminals. After removing the static voltage, you can proceed to the verification procedure. To do this, you need a simple ohmmeter. For a serviceable element between all terminals, the resistance should tend to infinity, but there are some exceptions. Now we will look at how to test an n-type field effect transistor.

We apply the positive probe of the device to the gate electrode (G), and the negative probe to the source contact (S). At this point, the gate capacitance begins to charge and the element opens. When measuring the resistance between source and drain (D), the ohmmeter will show some amount of resistance. In different types of transistors, this value is different. If you short-circuit the transistor terminals, then the resistance between the drain and the source will again tend to infinity. If this does not happen, then the transistor is faulty.

If you ask how to test a P-type field effect transistor, the answer is simple: repeat the above procedure, only change the polarity. It should also not be forgotten that modern powerful field-effect transistors between the source and drain have a built-in diode, respectively, it “rings out” only in one direction.

Checking the field effect transistor with a multimeter

If you have a "multimeter" device, you can check the field effect transistor. To do this, we set the diodes to the “ringing” mode and enter the field element into saturation mode. If the transistor is N-type, then touch the drain with the negative probe, and the gate with the positive probe. A good transistor in this case opens. We transfer the positive probe, without tearing off the negative one, to the source, and the multimeter shows some resistance value. After that, we lock the transistor: without removing the probe from the source, touch the gate with a negative and return it to the drain. The transistor is off and the resistance tends to infinity.

Many radio amateurs ask: "How to check the field effect transistor without soldering?" We will immediately answer that there is no one hundred percent way. To do this, a multimeter with an HFE socket is used, but this method often fails, and a lot of time can be wasted.

Experienced electricians and electronics engineers know that there are special probes for a complete check of transistors.

With the help of them, you can not only check the health of the latter, but also its gain - h21e.

The need for a probe

The probe is really a necessary device, but if you just need to check the transistor for serviceability, it is quite suitable.

transistor device

Before proceeding with the test, it is necessary to understand what a transistor is.

It has three terminals that form diodes (semiconductors) among themselves.

Each pin has its own name: collector, emitter and base. The first two conclusions pn transitions are connected in the base.

One p-n junction between base and collector forms one diode, the second p-n junction between base and emitter forms a second diode.

Both diodes are connected in a circuit opposite through the base, and this whole circuit is a transistor.

We are looking for a base, emitter and collector on a transistor

How to find a collector

To immediately find the collector, you need to find out what power the transistor is in front of you, and they are of medium power, low power and powerful.

Transistors of medium power and powerful are very hot, so heat must be removed from them.

This is done using a special cooling radiator, and heat is removed through the collector terminal, which in these types of transistors is located in the middle and is connected directly to the case.

It turns out such a heat transfer scheme: collector outlet - housing - cooling radiator.

If the collector is defined, then it will not be difficult to determine other conclusions.

There are cases that greatly simplify the search, this is when the device already has the necessary designations, as shown below.

We make the necessary measurements of direct and reverse resistance.

However, all the same, the protruding three legs in the transistor can lead many novice electronics engineers into a stupor.

How do you find the base, emitter and collector?

You can't do without a multimeter or just an ohmmeter.

So let's start searching. First we need to find the base.

We take the device and make the necessary measurements of the resistance on the legs of the transistor.

Take the positive probe and connect it to the right terminal. Alternately, the negative probe is brought to the middle, and then to the left conclusions.

Between the right and middle, for example, we showed 1 (infinity), and between the right and left 816 Ohm.

These testimonies do not give us anything yet. We take measurements further.

Now we move to the left, we bring the positive probe to the middle terminal, and with the negative probe we successively touch the left and right terminals.

Again, the middle one - the right one shows infinity (1), and the middle left 807 Ohm.

It also does not tell us anything. We measure further.

Now we move even more to the left, we bring the positive probe to the leftmost conclusion, and the negative probe sequentially to the right and middle.

If in both cases the resistance will show infinity (1), then this means that the base is the left terminal.

But where the emitter and collector (middle and right conclusions) will still need to be found.

Now you need to measure the direct resistance. To do this, now we do everything the other way around, the negative probe to the base (left terminal), and the positive one is connected in turn to the right and middle terminals.

Remember one important point, the resistance of the base-emitter p-n junction is always greater than the base-collector p-n junction.

As a result of measurements, it was found that the resistance base (left terminal) - right terminal is equal to 816 Ohm, and base resistance - average output 807 Ohm.

So the right pin is the emitter and the middle pin is the collector.

So, the search for the base, emitter and collector is completed.

How to check the transistor for serviceability

To check the transistor with a multimeter for serviceability, it will be sufficient to measure the reverse and forward resistance of two semiconductors (diodes), which we will do now.

There are usually two junction structures in a transistor p-n-p And n-p-n.

P-n-p- this is an emitter junction, you can determine this by the arrow that points to the base.

The arrow that goes from the base indicates that this is an n-p-n transition.

The P-n-p junction can be opened with a negative voltage applied to the base.

We set the multimeter operation mode switch to the resistance measurement position at the mark " 200 ».

The black negative wire is connected to the base terminal, and the red positive wire is connected in turn to the emitter and collector terminals.

Those. we check the emitter and collector junctions for operability.

Multimeter readings ranging from 0,5 before 1.2 kOhm they will tell you that the diodes are intact.

Now we swap the contacts, connect the positive wire to the base, and connect the negative wire in turn to the emitter and collector terminals.

The multimeter settings do not need to be changed.

The last reading should be much larger than the previous one. If everything is normal, then you will see the number "1" on the display of the device.

This indicates that the resistance is very large, the device cannot display data above 2000 ohms, and the diode junctions are intact.

The advantage of this method is that the transistor can be checked directly on the device without unsoldering it from there.

Although there are still transistors where low-resistance resistors are soldered into p-n junctions, the presence of which may not allow correct measurement of resistance, it can be small, both at the emitter and collector junctions.

In this case, the conclusions will need to be soldered and measurements taken again.

Signs of a Transistor Fault

As noted above, if the measurements of direct resistance (black minus on the base, and plus alternately on the collector and emitter) and reverse (red plus on the base, and black minus alternately on the collector and emitter) do not correspond to the above indicators, then the transistor is out of order .

Another sign of a malfunction is when the resistance of p-n junctions in at least one measurement is equal to or close to zero.

This indicates that the diode is broken, and the transistor itself is out of order. Using the above recommendations, you can easily check the transistor with a multimeter for serviceability.

Checking transistors is an important point in electronics and radio engineering. Try to figure out for yourself how to check the transistor with a multimeter without soldering. This is a fairly simple procedure that can be performed in various ways. The most practical option is to check the transistor with a multimeter. It is this method that will be discussed in this article.

General information

To date, there are two types of transistors - bipolar and field. In the first case, the output current is created with the participation of both charges in the form of holes and electrons, and in the other version, only one of the carriers is involved.

Bipolar transistor test

The specified procedure for bipolar transistors It starts with proper instrument setup. The device is switched to the semiconductor test mode, the unit should be displayed on the display. The outputs are connected by analogy with the resistance measurement mode. A black wire is connected to the COM port, and a red wire is connected at the output for measuring voltage, resistance and frequency. If the multimeter does not have the appropriate mode, then the process should be carried out in the resistance measurement mode when set to maximum.

It is also important that the multimeter battery is fully charged and the probes are working. When connecting the tips, the squeak of the device and zeros on the screen testify to the serviceability. The procedure in this case goes according to the following steps:

As a result, it will not be necessary to solder the element for its serviceability. If you would like to use for checking light bulbs and other items, then it is not recommended to do this, since there is a risk of completely ruining the bipolar type transistor.

Field device test

Procedure for such elements similar to bipolar. However, there are some features here:

Due to these moments, it is possible to carry out a qualitative check of field devices without using desoldering. If you have a composite device, then the test is similar to the technique for bipolar devices.

Advantage of the method

Checking a transistor using a multimeter is advantageous in that there is no need to solder the element, and it is quite accurate. The methodology for testing bipolar and field devices is similar, but it is necessary to take into account a number of points and nuances that contribute to the improvement of the methodology. Proper setting of the multimeter and the ability to work with various elements will allow you to make the most accurate and high-quality check of the health of devices of any kind.