A device for testing any transistors

This is another article dedicated to a novice radio amateur. Checking the functionality of transistors is perhaps the most important thing, since it is a non-working transistor that causes the failure of the entire circuit. Most often, novice electronics enthusiasts have problems checking field-effect transistors, and if they don’t even have a multimeter, then it is very difficult to check the transistor for functionality. The proposed device allows you to check any transistor, regardless of type and conductivity, in a few seconds.



The device is very simple and consists of three components. The main part is the transformer. You can take any small-sized transformer from switching power supplies as a basis. The transformer consists of two windings. The primary winding consists of 24 turns with a tap from the middle, the wire is from 0.2 to 0.8 mm.



The secondary winding consists of 15 turns of wire of the same diameter as the primary. Both windings wind in the same direction.




Light-emitting diode connected to the secondary winding through a 100 ohm limiting resistor, the power of the resistor is not important, polarity LED too, since an alternating voltage is generated at the output of the transformer.
There is also a special attachment into which the transistor is inserted, observing the pinout. For direct conduction bipolar transistors (type KT 818, KT 814, KT 816, KT 3107, etc.), the base goes through a base 100 ohm resistor to one of the terminals (left or right terminal) of the transformer, the middle point of the transformer (tap) is connected to the power plus, the emitter of the transistor is connected to the power minus, and the collector to the free terminal of the primary winding of the transformer.



For reverse conduction bipolar transistors, you just need to change the power polarity. The same is true with field-effect transistors, it is just important not to confuse the pinout of the transistor. If after feeding Light-emitting diode starts to glow, it means the transistor is working, if not, then throw it in the trash, since the device provides 100% accuracy in checking the transistor. These connections need to be made only once, during assembly of the device, the attachment can significantly reduce the time of checking the transistor; you just need to insert the transistor into it and apply power.
The device, in theory, is a simple blocking generator. The power supply is 3.7 - 6 volts, just one lithium-ion battery from a mobile phone is perfect, but you need to remove the board from the battery in advance, since this board turns off the power; current consumption exceeds 800 mA, and our circuit can consume such current in peaks.
The finished device turns out to be quite compact; you can place it in a compact plastic case, for example, from tic-tac-type candies, and you will have a pocket device for testing transistors for all occasions.