Probe for testing field-effect transistors. Scheme, description

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Probe for testing field-effect transistors. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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This probe (Fig. 1) is designed to quickly check the performance of field-effect transistors. With it, you can check field-effect transistors of the KP103, KP302, KP303, KP305, KP307 series and others with an initial drain current that is different from zero.

Probe for testing field-effect transistors

An amplifying stage is assembled on transistor VT1, the DC mode of which is set by resistor R3. Resistor R2 increases the resistance of the device to self-excitation at high frequencies.

Field-effect transistors are connected to the sockets of the XS1 connector: with a p-channel - to the top three according to the scheme, with an n-channel - to the bottom three. Through the capacitors C2, C3, C4, an alternating voltage feedback is carried out, through the resistors R4, R5, the supply voltage is supplied to the drain of the field-effect transistors. Resistors R6, R7 provide a direct current connection between the gate and the source.

Without the field-effect transistor being tested, the transistor VT1 is open, current flows through it, the HL1 LED lights up continuously. When a field effect transistor is connected, a capacitively coupled multivibrator is formed. If the field-effect transistor is working, generation will occur at a frequency of several hertz and the LED will flash at this frequency.

The device can be powered from a mains power supply, including an unstabilized one, as well as from a battery of batteries or galvanic cells with a voltage of 9 ... 12 V. The consumed current does not exceed 40 mA.

In the device, in addition to that indicated on the diagram, any transistor of the KT312, KT315 series, LED - any other with a working current of 10 ... 20 mA can be used. Polar capacitors - K50-6, K50-16, non-polar - K10-17a, resistors - MLT, S2-33. It is permissible to use any suitable contacts as sockets of the XS1 connector, for example, from a chip board.

All parts are placed on a printed circuit board (Fig. 2, 3) made of one-sided foil fiberglass.

Probe for testing field-effect transistors

Establishment comes down to selecting a resistor R3 of such a resistance in order to obtain a voltage on the collector of the transistor 2 ... 3 V.

To check the operability of the device, several known-good field-effect transistors of various types must be connected to it.

Author: I. Nechaev, Kursk

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