This article will present, in my opinion, the simplest, but no less effective circuit of Field Mice (field-effect transistors). I think this circuit will rightfully take one of the leading positions on the Internet in terms of simplicity and reliability of assembly. Since there is simply nothing to shake or burn here... The number of parts is minimal. Moreover, the circuit is not critical to the ratings of the parts... And can be assembled practically from rubbish, without losing its functionality...

Many will say, why some kind of probe for transistors? If everything can be checked with a regular multimeter... And to some extent they will be right... To assemble a probe you need to at least have a soldering iron and a tester... To check the same diodes and resistors. Accordingly, if there is a tester, then a probe is not needed. Yes and no. Of course, you can check a field-effect transistor (field-effect mouse) for functionality with a tester (multimiter) ... But it seems to me that this is much more difficult to do than checking the same field-effect mouse with a probe ... I will not explain in this article how a field-effect mouse (field-effect transistor) works. So, for a specialist this has all been known for a long time and is not interesting, but for a beginner everything is complicated and complicated. So it was decided to do without boring explanations of the principle of operation of a field mouse (field-effect transistor).

So, the probe circuit, and how they can test a field-effect mouse (field-effect transistor) for survivability.

We assemble this circuit, even on a printed circuit board (the seal is attached at the end of the article). At least mounted installation. Resistor values ​​can differ by about 25% in either direction.

Any button without locking.

The LED can be either bipolar, two-color, or even two back-to-back parallel. Or even just one. If you plan to test transistors of only one structure.. Only N channel type or only P channel type.

The diagram is assembled for field mice of the N channel type. When checking P channel type transistors, you will have to change the polarity of the circuit power supply. Therefore, another counter LED was added to the circuit, parallel to the first one.. In case you need to check a field mouse (field effect transistor) P channel type.

Many will probably immediately notice that the circuit does not have a power polarity switch.

This was done for several reasons.

1 No such suitable switch was available.

2 Just so as not to get confused in what position the switch should be when checking the corresponding transistor. I get N channel transistors more often than P channel ones. Therefore, if necessary, it is not difficult for me to simply swap the wiring. To test P channel field mice (field effect transistors).

3 Just to simplify and reduce the cost of the scheme.

How does the scheme work? How to test field mice for survivability?

We assemble the circuit and connect the transistor (field mouse) to the corresponding terminals of the circuit (drain, source, gate).

Without pressing anything, connect the power. If the LED does not light up, it is already good.

If at correct connection transistor to the probe, power supply and the button NOT pressed, the LED will light up... This means the transistor is broken.

Accordingly, if the button is pressed, the LED does NOT light up. This means the transistor is broken.

That's the whole trick. Everything is brilliantly simple. Good luck.

P/S. Why in the article do I call a field-effect transistor a field mouse? It's very simple. Have you ever seen transistors in a field? Well... Simple. Do they live there or grow there? I think not. But there are field mice... And here they are more appropriate than field-effect transistors.

And why are you surprised by the comparison of a field-effect transistor with a field-effect mouse? After all, there is, for example, the site radiokot or radioskot. And many other sites with similar names.. Which have nothing to do directly with living creatures... So.

I also think that it is quite possible to call a bipolar transistor, for example, a polar polar bear...

And I also want to express my deep gratitude to the author of this probe circuit, V. Goncharuk.

There is probably no such radio amateur who would not profess the cult of radio engineering laboratory equipment. First of all, these are attachments for them and probes, which for the most part are made independently. And since there are never too many measuring instruments and this is an axiom, I somehow assembled a transistor and diode tester that was small in size and had a very simple circuit. It’s been a long time since I’ve had a multimeter that’s not bad, but in many cases I continue to use a homemade tester as before.

Device diagram

The probe designer consists of only 7 electronic components + printed circuit board. It assembles quickly and starts working absolutely without any setup.

The circuit is assembled on a chip K155LN1 containing six inverters. When the leads of a working transistor are correctly connected to it, one of the LEDs lights up (HL1 when N-P-N structure and HL2 at P-N-P). If faulty:

1. broken, both LEDs flash
2. has an internal break, both do not ignite

The diodes being tested are connected to terminals “K” and “E”. Depending on the polarity of the connection, HL1 or HL2 will light up.

There are not many components of the circuit, but it is better to make a printed circuit board; it is troublesome to solder the wires to the legs of the microcircuit directly.

And try not to forget to put a socket under the chip.

You can use the probe without installing it in the case, but if you spend a little more time on its manufacture, you will have a full-fledged, mobile probe that you can already take with you (for example, to the radio market). The case in the photo is made from the plastic case of a square battery, which has already served its purpose. All that was needed was to remove the previous contents and saw off the excess, drill holes for the LEDs and glue a strip with connectors for connecting the transistors being tested. It would be a good idea to “dress” the connectors with identification colors. A power button is required. The power supply is a AAA battery compartment screwed to the case with several screws.

The fastening screws are small in size, it is convenient to pass them through the positive contacts and tighten them with the obligatory use of nuts.

The tester is in full readiness. It would be optimal to use AAA batteries; four 1.2 volt batteries will give the best supply voltage of 4.8 volts.

And industrial devices with LEDs. Today they are found almost everywhere. LEDs are also starting to be used instead of the old tubular ones. fluorescent lamps, well, you can keep silent about incandescent lamps altogether. Due to the fact that there is a huge variety of diodes, to check them it will be useful to have a tester, or make one yourself.

Of course, some LEDs can be checked with a regular multimeter in dial mode. The LED should light up. But if it operates at a higher voltage than the multimeter outputs, the glow will be very weak or not at all.
For some white, yellow and blue LEDs, the voltage can reach 3.3V.

First of all, when testing an LED, you need to determine where its cathode is and where its anode is. Of course, this can be determined by examining the insides of the crystal, but this takes time, effort, nerves, and in general this is an unprofessional approach.

Among other things, the manufactured probe will help determine what operating voltage the LED has, and this is very important parameter. And finally, the device will help you trivially determine the serviceability of the LED.

Device diagram
According to the author, the device circuit is very simple. The homemade product is an attachment that plugs into the socket of a multimeter.


Materials and tools for homemade work:
- connecting block from a “Krona” type battery;
- working battery (needed to power the probe);
- a miniature button without locking (a clock button from a phone, tablet, etc. is also suitable);
- one 1 kOhm resistor for 0.25 W;
- quick-release connector for transistors (socket with a pitch of 2.54 mm, a total of 3 contacts will be needed);
- material for creating the body of the device (a plastic plate, etc. will do);
- four brass screws.

Homemade manufacturing process:

Step one. We prepare the necessary elements
First you need to prepare the contacts that will connect to the multimeter. The photo shows that the pins have threads, but it is best to get rid of them. The thread is needed only to screw the elements using nuts to the plastic body.

To attach the pins, you need to drill fourth holes in the plastic plate. Two are needed to install the connecting block through which the Krona battery is connected. And the second two are needed for mounting the contacts with which the device is connected to the multimeter.

To attach the microbutton and the connector for transistors, you will need to cut the board out of PCB.

Step two. Soldering the circuit
Now you need to solder the electronic parts, guided by the diagram presented above. You need to solder a microbutton, a transistor socket and a 1 kOhm 0.25 W resistor.

Step three. The final stage. Homemade assembly
Now the device is assembled into a common housing. The removed wires are connected to the power supply block for the Krona battery and to the plugs with which the probe is connected to the multimeter. On the PCB board near the connector, the author glued a circuit that allows you to avoid confusion when testing the LED. The red power wire is the “plus”, that is, the anode. Well, the black one with a minus sign is the cathode.

To test the LED, you need to plug it into the connector and connect the Krona battery to the socket. Now the multimeter switches to voltage measurement mode in the range 2-20V DC. If the diode is working and turned on correctly, it will light up.

As mentioned at the beginning, you can use a multimeter to determine the operating voltage of the LED, but if this is not necessary, a multimeter is not needed at all. That's all, the little helper is ready, now it will be much more pleasant and faster to assemble homemade products with LEDs or repair something.

In case of repair electronic devices, installed in the circuit, is not always possible, so you have to unsolder it from the circuit. Often such interference leads to damage to printed circuit boards, and sometimes to the transistors themselves. Therefore, it is very good if you have a device at hand that allows you to determine the health of the transistor without unsoldering it from the board. Schemes of such devices are given in this article.

The probe circuit is simple and is shown in Figure 1.

The basis of the circuit is a classic blocking oscillator. The output of such a generator produces short rectangular pulses. Naturally, to obtain a working blocking oscillator, a tested VT transistor should be supplied to connector XS1 of the probe. Oscillations are obtained due to positive feedback in transformer T1 through the coupling winding I. The optimal feedback value is selected by rotating the variable resistor R1. If knob R1 is equipped with a scale, then by the angle of rotation of the slider you can approximately judge the amplifying properties of the transistor.

The probe is powered by three AAA galvanic cells or a “square” battery. Using switch SA1, you can change the power-on polarity, which allows you to test transistors of various structures, as shown in the figure.

Figure 1. Probe circuit for testing transistors

The occurrence of generation is indicated by LEDs VL1 VL2. When the polarity of the supply voltage changes, the polarity of the output pulses naturally changes, so you have to install two LEDs.

The blocking generator transformer is made independently on a Ш6*8 core, although, without changing the number of turns, the size of the iron can be slightly increased. Such transformers were used in Mountaineer receivers and similar ones. All windings are made with PEV1-0.2 winding wire. Feedback winding I contains 200 turns, output winding II 30 turns, collector winding III 100 turns of the same wire.

The transformer plates are assembled end-to-end, like a DC choke: W-shaped plates are inserted into the frame hole, and jumpers are inserted through a thin paper spacer on top of the W-shaped plates. When connecting the windings, you should pay attention to their polarity, indicated in the diagram by dots: if, when connecting a known-good transistor, the generator does not start, then you should swap the ends of one of the windings - the collector or base.

A similar circuit was part of a device for testing industrially manufactured PPT-5 transistors. It’s just that this particular part was borrowed by radio amateurs because it had proven itself to be good.

Figure 2.

The probe is powered from one galvanic cell with a voltage of 1.5V, type AA or AAA. Switch S2 changes the polarity of the device's power supply to test transistors of different conductivities, as indicated in the diagram.

The design of transformer S is shown right there in Figure 2. It is made on a ferrite ring of standard size K10*6*4 with magnetic permeability NM2000. The collector winding S contains 6 turns, and the base winding P contains only 2 turns made of PEV2-0.2mm wire. However, the diameter of the wire does not matter much, so to increase mechanical strength it can be increased slightly. The ring can also be taken with a slightly larger diameter.

Resistor VR sets the operating mode of the probe, exactly the same as in the previous circuit. The LED connection diagram is somewhat simplified; there is no additional winding. The LEDs are ignited by reverse voltage surges on the collector of the transistor under test at the moment it is turned off.

There are quite a lot of different circuits for testing transistors, but these two, perhaps, can be considered the most successful. Their only drawback is the need to wind the transformer.

This device, the circuit of which is easy to assemble, will allow you to test transistors of any conductivity without removing them from the circuit. The circuit of the device is assembled on the basis of a multivibrator. As can be seen from the diagram, instead of load resistors, transistors with conductivity opposite to the main transistors are included in the collectors of the multivibrator transistors. Thus, the oscillator circuit is a combination of a multivibrator and a flip-flop.

Circuit of a simple transistor tester

As you can see, the transistor tester circuit couldn’t be simpler. Almost any bipolar transistor has three terminals, emitter-base-collector. In order for it to work, a small current must be supplied to the base, after which the semiconductor opens and can pass a much larger current through itself through the emitter and collector junctions.

A trigger is assembled on transistors T1 and T3; in addition, they are the active load of the multivibrator transistors. The rest of the circuit is the bias and indication circuits of the transistor under test. This circuit operates in the supply voltage range from 2 to 5 V, and its current consumption varies from 10 to 50 mA.

If you use a 5 V power supply, then to reduce the current consumption of resistor R5 it is better to increase it to 300 Ohms. The multivibrator frequency in this circuit is about 1.9 kHz. At this frequency, the LED glow appears continuous.

This device for testing transistors is simply indispensable for service engineers, as it can significantly reduce the troubleshooting time. If the bipolar transistor being tested is working, then one LED lights up, depending on its conductivity. If both LEDs are lit, then this is only due to an internal break. If none of them lights up, then there is a short circuit inside the transistor.

The given figure printed circuit board has dimensions of 60 by 30 mm.

Instead of the transistors included in the circuit, you can use transistors KT315B, KT361B with a gain above 100. . Absolutely any diodes, but silicon types KD102, KD103, KD521. Any LEDs too.

Appearance of the assembled transistor probe on a breadboard. It can be placed in the case of a burnt Chinese tester; I hope you will like this design for its convenience and functionality.

The circuit of this probe is quite simple to repeat, but it will be quite useful when rejecting bipolar transistors.

A generator is made on the OR-NOT elements D1.1 and D1.2, which controls the operation of the transistor switch. The latter is designed to change the polarity of the supply voltage on the transistor under test. By increasing the resistance of the variable resistor, one of the LEDs lights up.

The conductivity structure of the transistor is determined by the color of the LED. Calibration of the variable resistor scale is carried out using pre-selected transistors.