Device for testing transistors (betnik). A device for testing any transistors. Diagrams of devices for testing high-power transistors.

When assembling simple structures, it is necessary to ensure the functionality of the transistors installed in them. At the same time, it is often completely insufficient to simply verify their integrity by ringing their transitions. It will be much more reliable and effective to test them, for example, in generation mode.

Transistor tester

Below is a very simple transistor tester circuit for beginner radio amateurs.

Transistor tester

(Second profession of household dosimeter)

The article describes how to complete a household dosimeter and turn it into a transistor tester, allowing you to measure some of their parameters.

LED probe for testing transistors

A very good circuit for a transistor tester, allowing you to determine the pinout of an unknown specimen, with display on a sign-synthesizing indicator.

Simple probes, attachments, meters (retro)

The transistor, as an amplification device, is the basis for building a wide variety of electronic devices. Accordingly, there is a need to be sure of its serviceability, as well as to evaluate its quality indicators, which is discussed below.

To check the serviceability and functionality of the transistor itself, it turns out that you can use a radio point. Moreover, by the volume of the sound emitter used, you can estimate the gain of a particular instance. Well, a generator circuit based on the transistor being tested is the standard method for testing it. In addition, using a generator circuit for testing semiconductor devices, you can roughly determine the gain of triodes in order to select the best specimens.

For a specific measurement of the static gain of a transistor, you will need to make a tester and even a meter thereof. Although in reality its circuit may not be much more complicated than a probe. The only thing that will need to be calibrated is the scale of the measuring device. And for this, of course, a model tester may be required. Or you can use the tester itself as an indicator))).

There are simple attachments with which you can also measure such a transistor parameter as the reverse collector current.

All these designs are applicable in conjunction with low-power transistors. To check and test medium-power transistors and high-power transistors, other attachments will have to be made. Of course, you can use these same devices by simply adding additional switching elements. But this is what spoils the matter. It is easier and more convenient to make meters separately for powerful transistors.

Separately, it should be noted that the static current transfer coefficient (gain) and the reverse collector current are the main indicators of the amplifying properties of the transistor. But in the practice of a novice radio amateur, it is often enough to simply verify the serviceability and functionality of a particular instance.

Transistor Test Probe

The advantage of the proposed probe circuit is that in many cases it allows you to check the serviceability of transistors without removing them from the structure.

It is advisable to have a tester for medium and high power transistors in the measuring laboratory of a radio amateur. It is especially necessary when selecting pairs of transistors for the final push-pull stages of audio amplifiers with a power of more than 0.25 W.

Using the proposed device, you can test the collector junction of a transistor for breakdown, measure the static current transfer coefficient h21e, and check the stability of the transistor. Tests are carried out when the transistor is turned on according to a circuit with a common emitter. The indicator is a milliammeter with a current of 1 mA. The power source is a rectifier that provides a constant voltage of 12 V at a current of up to 300 mA. The reverse current of the Irbo collector junction is not measured, since it can range from several microamps to 12...15 mA for different transistors, and this parameter has virtually no effect on the selection of pairs of transistors for operation in a power amplifier.

The schematic diagram of the device is shown in Fig. 1. The VT transistor being tested is connected to the terminals of the electrodes to the corresponding terminals of the device. Switch SA1 sets the structure of the transistor. In this case, a power source is connected to the transistor in a polarity corresponding to its structure. Next, the transistors are checked, observing the following order: check the collector junction for breakdown; set the base current Ib equal to 1 mA; measure the static current transfer coefficient h 21e

Measurements of these parameters of medium and high power transistors are illustrated by the circuits shown in Fig. 2.

The collector junction is tested by pressing the SB2 Breakdown button. In this case, resistor R4 and milliammeter RA1 are included in the collector circuit of the transistor being tested VT, the negative terminal of which is connected to the power source, and resistors Rl - R3 are connected in parallel to the collector junction (Fig. 2, a).

At this time, the sliders of the variable resistors R2 and R3 should be in the right (according to the diagram) position. The current flowing through the chain of resistors Rl - R3 does not exceed 50 μA, which practically does not affect the readings of the milliammeter. Resistor R4 limits the current through the milliammeter to 1 mA, thereby preventing its needle from going off scale in the event of a breakdown of the collector junction of the transistor.

Milliammeter readings of less than 1 mA indicate the serviceability of the collector junction, and if there is a breakdown, the milliammeter needle will always be set to the rightmost scale division. In the event of a break between the terminals of the collector and base electrodes, the device will only show the current passing through resistors Rl - R4.

The base current /b, equal to 1 mA, is set with resistors R3 Rough and R2 Precisely with the SB2 button pressed. In this case, an insignificant initial collector current flows through the milliammeter (Fig. 2, b) and a current flows through resistors Rl - R3, which, when measuring the coefficient h21e, will be the base current Ib of the transistor being tested.

The static current transfer coefficient is measured by pressing the SB4 h21e 300 button or, with a small numerical value of this parameter, the SB3 h21e 60 button. In this case, the button contacts connect the transistor emitter to the positive (or negative, if the transistor is of a p-p-p structure) conductor of the power source, and parallel to the milliammeter is a wire resistor R5 (or R6), expanding the measurement limit (Fig. 2, c). The collector current of the transistor being tested will approximately correspond to its static current transfer ratio. The error arising from simplifying the switching of device circuits does not affect the selection of pairs of transistors for the output stages of powerful AF amplifiers.

When testing transistors of the p-p-p structure, a milliammeter is connected to the circuit of its emitter,

The design of the device is arbitrary. Resistors R1 and R4 are type MLT-0.5, R2 and R3 are type SP-3. Resistors R5 and R6 are made from wire with high resistivity with a diameter of 0.4...0.5 mm. Switch SA1 - toggle switch TP1-2, push-button switches SB1 - SB4-KM2-1. Power-on indicator HL1 - switch lamp KM24-90 (24 Vx90 mA).

By selecting resistor R4 with the collector and base terminals short-circuited and the SB2 button pressed, the milliammeter needle is set as accurately as possible to the rightmost division of the scale.

To adjust the resistances of resistors R5 and R6, you will need a standard milliammeter for a current of 300...400 mA and variable wire resistors with a resistance of 51...62 and 240...300 Ohms. Connect in series a standard milliammeter, a transistor tester milliammeter, resistor R5 and a variable resistor of 51....62 Ohms. Having turned on the power source, use a variable resistor to set a current in the circuit equal to 300 mA, while simultaneously making sure that the milliammeter needle of the device does not go off scale. After this, by adjusting the resistance of resistor R5, the milliammeter needle of the device is set to the rightmost scale division. Then the variable resistor is replaced with a resistor with a resistance of 240...300 Ohms, resistor R5 with resistor R6, and in the same way the current in the circuit is set to 60 mA, and the milliammeter needle of the device is set to the far right mark of the scale.

When the SB4 button is pressed, the deviation of the tester's milliammeter needle to the full scale corresponds to the static current transfer coefficient of the transistor 300, when the SB3 button is pressed - 60.

To judge the suitability of a transistor for a particular device, it is enough to know two or three of its main parameters:

1. Reverse collector-emitter current with the emitter and base terminals closed - Ікек-current in the collector-emitter circuit at a given reverse voltage between the collector and emitter.
2. Reverse Collector Current - IQ current through the collector junction at a given reverse collector-base voltage and an open emitter terminal.
3. Static base current transfer coefficient - h21e - the ratio of direct collector current to direct base current at a given constant reverse collector-emitter voltage and emitter current in a common emitter (CE) circuit.

The easiest way to measure the current Ikek is in a circuit simplified in Fig. 1. Node A1 on it summarizes all the parts included in the device. The requirements for the unit are simple: it should not influence the measurement results, and in the event of a short circuit in the tested transistor VT1, limit the current to a value that is safe for the dial indicator.

Measuring Ikbo is not provided for by the instruments, but this is not difficult to do by disconnecting the emitter terminal from the measurement circuit.

Some difficulties arise when measuring the static transmission coefficient h21e. In simple devices, it is measured at a fixed base current by measuring the collector current, and the accuracy of such devices is low, since the transmission coefficient depends on the collector (emitter) current. Therefore, h21e should be measured at a fixed emitter current, as recommended by GOST.

In this case, it is enough to measure the base current and judge from it the value of h21e. Then the scale of the dial indicator can be calibrated directly in the transmission coefficient values. True, it turns out to be uneven, but all the necessary values ​​fit on it (from 19 to 1000).

Such devices have already been developed by radio amateurs (see, for example, the article by B. Stepanov, V. Frolov “Transistor Tester” - Radio, 1975, No. 1, pp. 49-51). However, they quite often did not take measures to fix the collector-emitter voltage. This decision was justified by the fact that h21e depends little on this voltage.

However, as practice shows, this dependence is still noticeable in the OE circuit, so it is advisable to fix the collector-emitter voltage.

Rice. 1. Circuit for measuring collector-emitter reverse current.

Rice. 2. Scheme for measuring the static current transfer coefficient.

Based on these considerations, in the radio circle of the KYuT of the Pervouralsk New Pipe Plant, Evgeniy Ivanov and Igor Efremov, under the leadership of the author, developed a measurement scheme, the principle of which is illustrated in Fig. 2. The emitter current ls of the transistor under test is stabilized by a stable current generator A1, which removes most of the requirements for the power source G1: its voltage can be unstable, almost only a current of 1 e is consumed from it. The collector-emitter voltage of the transistor is fixed, since it is equal to the sum of the stable voltages on the zener diode VD1, the emitter junction of transistor VT1 and the dial indicator PA1. Strong negative feedback between the collector and the base of the transistor through a zener diode and a dial indicator keeps the transistor in the active mode, for which the following relationships are valid:

where Ik, Ie, Ib are the current of the collector, emitter, and base of the transistor, respectively, mA.

To construct a direct reading scale, it is convenient to use the formula:

The above formulas are valid only in the case of a very low ICBO current, characteristic of silicon transistors. If this current is significant, for a more accurate calculation of the transmission coefficient it is better to use the formula:

Now let's get acquainted with the practical designs of devices.

Low-power transistor tester

Its circuit diagram is shown in Fig. 3. The transistor under test is connected to terminals XT1 - XT5. The stable current source is assembled using transistors VT1 and VT2. Switch SA2 can be used to set one of two emitter currents: 1 mA or 5 mA.

In order not to change the h21e measurement scale, in the second position of the switch, resistor R1 is connected parallel to the PA1 indicator, reducing its sensitivity fivefold.

Rice. 3. Schematic diagram of a low-power transistor tester.

Switch SA1 selects the type of work - measuring h21e or Ikek. In the second case, an additional current-limiting resistor R2 is included in the measured current circuit. In other cases, in case of short circuits in the tested circuits, the current is limited by a stable current generator.

To simplify switching, a rectifier bridge VD2 - VD5 is introduced into the base current measurement circuit. The collector-emitter voltage is determined by the sum of the voltages on the series-connected zener diode VD1, two rectifier bridge diodes and the emitter junction of the transistor under test. Switch SA3 selects the transistor structure.

Power is supplied to the device only during the measurement by push-button switch SB1.

The device is powered from a GB1 source, which can be a Krona battery or a 7D-0D battery. The battery can be recharged periodically by connecting the charger to sockets 1 and 2 of the XS1 connector. The device can be powered from an external DC source with a voltage of 6...

15 V (the lower limit is determined by the stability of operation in all modes, the upper limit is determined by the rated voltage of capacitor C1), connected to sockets 2 and 3 of connector XS1. Diodes VD6 and VD7 act as isolation diodes.

Rice. 4. Converter PM-1.

It is convenient to use the PM-1 converter (Fig. 4) from electrified toys to power the device from the mains. It is inexpensive and has good electrical insulation between the windings, ensuring safe operation.

The converter only needs to be equipped with the pin part of the XS1 connector.

The device uses an M261M type dial indicator with a full needle deflection current of 50 μA and a frame resistance of 2600 Ohms. Resistors - MLT-0.25. Diodes VD2 - VD5 must be silicon, with the lowest possible reverse current. Diodes VD6, VD7 - any of the D9, D220 series, with the lowest forward voltage possible.

Transistors - any of the KT312, KT315 series, with a static transmission coefficient of at least 60. Oxide capacitor - any type, with a capacity of 20...100 μF for a rated voltage of at least 15 V. Connector XS1-SG-3 or SG-5, clamps XT1 - XT5 - any design.

Rice. b. Appearance of a low-power transistor tester.

Rice. 6. Indicator reading scale.

The device parts are assembled in a housing measuring 140X 115X65 mm (Fig. 5), made of plastic. The front wall, on which the dial indicator, push-button switch, switches, clamps and connector are mounted, is covered with a false panel made of organic glass, under which colored paper with inscriptions is placed.

In order not to open the dial indicator and not to draw a scale, a stencil was made for the device (Fig. 6), duplicating the reading scale. You can simply create a table in which, for each scale division, indicate the corresponding value of the static transmission coefficient.

The above formulas are suitable for compiling such a table.

Setting up the device comes down to accurately setting the currents 1e 1 mA and B mA by selecting resistors R3, R4 and selecting resistor R1, the resistance of which should be 4 times less than the resistance of the dial indicator frame.

Power transistor tester

The diagram of this device is shown in Fig. 7. Since the power transistor tester is subject to lower accuracy requirements, the question arises: what simplifications can be made compared to the previous design?

Powerful transistors are tested at high emitter currents (0.1 A and 1 A are selected in this device), so the device is powered only from the network through a step-down transformer T1 and a rectifier bridge VD6 - VD9.

Rice. 7. Schematic diagram of a power transistor tester.

It is difficult to build a stable current generator for these relatively large currents, and there is no need - its role is played by resistors R4 - R7, diodes of the rectifier bridge, and the transformer winding. True, a stable emitter current flows only at a stable mains voltage and the same collector-emitter voltage of the transistor under test.

The matter is made easier by the fact that the last voltage is chosen to be small - usually 2 V, in order to avoid heating the transistor. This voltage is equal to the sum of the voltage drops across the two diodes of the bridge VD2 - VD5 and the emitter junction of the transistor under test.

It was expected that the difference in voltage drops across the emitter junctions of the germanium and silicon transistors would have a noticeable effect on the emitter current, but the expectation was not confirmed: in practice, this difference turned out to be very small. Another thing is the instability of the mains voltage; it causes even greater instability of the emitter current (due to the nonlinearity of the resistances of semiconductor diodes and the constancy of the collector-emitter voltage of the transistor under test).

Therefore, to increase the accuracy of h21e measurements, the device should be connected to the network through an autotransformer (for example, LATR) and the supply voltage of the device should be maintained at 220 V.

The next question is about rectified voltage ripples: what amplitude is permissible? Numerous experiments comparing the readings of a device powered from a source of “pure” direct current and from a source of pulsating current have revealed virtually no difference in the readings h21e when using a dial indicator of a magnetoelectric system.

The smoothing effect of the device's capacitor O appears only when measuring small currents Ikek (up to about 10 mA). Silicon diode VD1 protects the dial indicator PA1 from overloads. Otherwise, the device circuit is similar to the previous device.

Transformer T1 can be from the PM-1 converter, but it is not difficult to make it yourself. You will need a USH14X18 magnetic circuit. Winding I should contain 4200 turns of PEV-1 0.14 wire, winding II - 160 turns PEV-1 0.9 with a tap from the 44th turn, counting from the top one in the output diagram. Another ready-made or home-made transformer with a voltage on the secondary winding of 6.3 V at a load current of up to 1 A will do.

Resistors - MLT-0.5 (Rl, R3), MLT-1 (R5). MLT-2 (R2, R6, R7) and wire (R4), made of wire with high resistivity. Lamp HL1 - MNZ,5-0.28.

The dial indicator is M24 type with a full needle deflection current of 5 mA.

Rice. 8. Appearance of a tester of power transistors.

Rice. 9. Indicator reading scale.

The diodes may be different, designed for rectified current up to 0.7 A (VD6 - VD9) and 100 mA (others). The device is mounted in a housing with dimensions 280 X 170x130 mm (Fig. 8). The parts are soldered on the switch terminals and on a circuit board mounted on the dial indicator clamps.

As in the previous case, a stencil was made for the device (Fig. 9), duplicating the reading scale.

Setting up the device comes down to setting the specified emitter currents by selecting resistors R4 and R5. The current is controlled by the voltage drop across resistors R6, R7. Resistor R1 is selected such that the sum of its resistance and the indicator PA1 is 9 times greater than the resistance of resistor R2.

A. Aristov.

Aristov Alexander Sergeevich- head of the radio circle of the club of young technicians of the Pervouralsk New Pipe Plant, born in 1946. At the age of twelve, he built receivers, measuring instruments, and automation devices. After graduating from school, he led a radio club, working at a factory and studying at a technical school. Since 1968, he devoted himself entirely to teaching young radio amateurs. The leader described the designs of the circle members in three dozen articles published in domestic and foreign magazines, on the pages of the VRL collection. The work of the circle members was awarded 25 medals “Young Participant of VDNKh”, and the work of the leader was awarded three bronze medals of VDNH of the USSR.

For transistors of the p-p-p structure, the switching polarity of the supply battery GB and the measuring device PA must be reversed.

The reverse collector current Ikbo is measured at a given reverse voltage at the collector pn junction and the emitter is turned off (Fig. 57, a). The smaller it is, the higher the quality of the collector junction and the stability of the transistor.

The parameter h21e, which characterizes the amplifying properties of the transistor, is defined as the ratio of the collector current Ik to the base current IB that caused it (Fig. 57, b), i.e. h2le ~ Ik/Iv. The higher the numerical value of this parameter, the greater the signal amplification that the transistor can provide.

To measure these two main parameters of low-power bipolar transistors, it can be recommended to make an attachment in a circle to the homemade avometer described above. The diagram of such an attachment is shown in Fig. 58, a. The transistor V under test is connected with the electrode leads to the corresponding terminals “E”, “B” and “K” of the attachment connected (via terminals XI, X2 and conductors with single-pole plugs at the ends) to the milliammeter of the avometer, switched on to the measurement limit of “1 mA”. Switch S2 is preliminarily set to the position corresponding to the structure of the transistor being tested. When checking a transistor of a p-p-p structure with the “Common” socket The avometer is connected to terminal XI of the attachment (as in Fig. 58, a), and when checking a transistor of the p-p-p structure, to clamp X2.

By setting switch S1 to the “I KBO” position, first measure the reverse current of the collector junction, and then, by moving switch S1 to the “h21e” position, measure the static current transfer coefficient. Deviation of the instrument needle to the full scale when measuring parameter I KB0 will indicate a breakdown of the collector junction of the transistor being tested.

The h21e parameter is measured at a fixed base current, limited by resistor R1 to 10 μA. In this case, the transistor opens and a current proportional to the coefficient h21e flows in its collector circuit (including through the milliammeter). If, for example, the device detects a current of 0.5 mA (500 μA), then the coefficient h21e of the transistor being tested will be 50 (500: 10 = 50). A current of 1 mA (deviation of the instrument needle to the final scale mark), therefore, corresponds to a coefficient h21e equal to 100. If the instrument needle goes off scale, the milliammeter of the avometer must be switched to the next current measurement limit - “10 mA”. In this case, the entire scale of the device will correspond to a coefficient h21e equal to 1000, and every tenth of it will correspond to 100.

Resistor R2, which limits the current in the measuring circuit to 3 mA, is needed to prevent damage to the measuring device due to breakdown of the transistor being tested.
A possible design of the attachment is shown in Fig. 58, b. For a front panel measuring approximately 130X75 mm, it is advisable to use sheet getinax or textolite with a thickness of 1.5-2 mm.

Clamps “E”, “B” and “K>” for connecting the terminals of the crocodile-type transistor. Measurement type switch S1 - toggle switch TP2-1, transistor structure S2 - TP1-2. The power battery GB1 - 3336L or composed of three 332 elements is mounted on the panel below, and limiting resistors R1 and R2 are also mounted there. The clamps (or sockets) for connecting the attachment to the avometer are placed in any convenient place, for example, on the back side wall of the box. Brief instructions for working with the measuring attachment are pasted onto the top of the panel. You can check the performance and evaluate the amplification properties of medium and high power transistors using a simple device, the diagram of which is shown in Fig. 59. The transistor V being tested is connected to the terminals corresponding to its electrodes. In this case, ammeter RA1 is connected to the collector circuit of the transistor for the full deflection current of the arrow 1A, and one of the resistors R1-R4 is connected to the base circuit. The resistances of the resistors are selected so that the current in the base circuit of the transistor can be set to 3, 10, 30 and 50 mA. Thus, the transistor is tested at fixed currents in the base circuit, set by switch S1. The power source is three 373 elements connected in series, or a low-voltage rectifier providing a voltage of 4.5 V at a load current of up to 2A.

The numerical value of the static current transfer coefficient of the transistor being tested is determined as the ratio of the collector current to the base current that caused it. For example, if switch S1 is set to a base current of 10 mA, and ammeter PA 1 records a current of 500 mA, then the coefficient h21e of this transistor is 50 (500: 10 = 50).

The design of such a device - a transistor tester - is arbitrary. It can be made as an attachment to an avometer, the ammeter of which is designed to measure direct currents up to several amperes.

It is necessary to check the transistor as quickly as possible, because already at a collector current of 250...300 mA it begins to heat up and thereby introduce errors into the measurement results.

At best, a similar console is hastily assembled, which I also used.

TRYING POWERFUL TRANSISTORS

But, faced with a serious selection of pairs of powerful germanium transistors, I am in the process of suffering with dozens of copies. I decided to make a separate complete structure in order to save time and nerves in the future. What prompted this was an excellent switching power supply unit with an output voltage of 7.5V and a current of 3A, purchased from the “bruises” back in the summer for a symbolic price.

The circuit of O. Dolgov’s meter (“Radio”, 1997, No. 1) was taken as a basis. This fairly typical circuit with a current source on a field-effect transistor was distinguished by simpler switching due to the use of two diode bridges and, in addition, had already been assembled by a radio amateur I knew. Since the reviews were only positive, I chose it.

Since I had already built a fairly good device for low-power transistors a long time ago, the circuit was tailored only for powerful devices with minor changes to the circuit: the field-effect transistor was replaced with a KP302 BM, only 4 fixed values ​​of the base current were left: 0.5, 1, 5 and 10 mA. , for greater convenience, KM1 buttons are used instead of a switch. Here is a fragment of the circuit with the resistor values ​​that I got.

The existing pulse generator had a removable U-shaped iron cover with many ventilation holes, which I decided to use: 4 brass stands with an internal threaded hole (like computer ones) were installed in the outer holes.

To fit the size, I quickly drew out a drawing of all the holes for sockets and switches in my favorite Sprint Layout and printed out 2 copies. on a piece of plain office paper. I glued one onto a piece of double-sided fiberglass and drilled it directly according to the sketch with a drill and bored out all the holes with a needle file and a round file.

Next, I thoroughly sanded the scarf with “zero” and carefully glued on the final version, on which all the inscriptions were made. Then I primed the “muzzle” paper in two steps with slightly diluted PVA glue and, after complete drying, coated the scarves in one layer (tea, not for exhibition) with transparent nitro varnish for strength. Then I installed all the buttons, terminals and toggle switches in their places.

Well, a few hours with smoke breaks for installation. Alas, nothing works out quickly, and the vision is not the same, and mother laziness...

The field worker decided to install it on a small radiator for reliability, the role of which was ideally played by the fixing sleeve from the PP3 wire trimmer. The transistor body was pre-coated with KPT-8 paste and pressed tightly into the bushing, which was glued to the board through a textolite gasket.

The output sockets are old and useless SG-5. They are convenient because plastic transistors in the TO-220 package fit right into them. For TO-3 and other metal-glass cases I made adapters with crocodiles at the ends. Well, for dust protection, I wrapped the whole mess around the perimeter with electrical tape. Here's what we ended up with:

I “played” with the GT703-GT705 for half an hour - it’s convenient!!! Just from a little practice, I note that the 10 mA range is quite sufficient; at higher currents, the transducers heat up noticeably and quickly. On the first two ranges it turned out to be very convenient to test composite transistors (Darlington). Three amperes at the output is too much; two would be enough. If you recalculate the resistors to a convenient coefficient, then by parallel pressing of two adjacent buttons you can further expand the measurement range. And one improvement, perhaps, definitely needs to be made: limit the current from the power source with a 4-5 Ohm resistor in case a transistor with a broken junction comes into contact. And so it turned out to be a very useful thing in our household, I recommend it!

Drawing file in SprintLayout format:

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