Build Your 12Hz Transistor Tester Circuit Diagram

Circuit diagram

This straightforward circuit has proven invaluable in numerous situations. It facilitates the assessment of transistors, measuring a resistance of approximately 40 ohms across the collector-base or base-emitter connections. Furthermore, it is capable of evaluating power transistors within amplifier configurations.

555 Timer (IC1)

The 555 timer (IC1) is configured as a 12Hz astable multivibrator. The signal generated on pin 3 drives the 4027 flip-flop (IC2). This flip-flop divides the input frequency in half, generating complementary voltage outputs at pins 15 and 14. These outputs are then connected to LED1 and LED2 via current-limiting resistor R3. When the voltage polarity across the circuit shifts, only one of the LEDs will illuminate, and the other will turn off. Without a transistor connected to the tester, the LEDs will flicker alternately. The 555 timer is a versatile integrated circuit used for timing applications, providing a stable pulse output. It is commonly found in oscillators, timers, and pulse generators due to its adjustable frequency and duty cycle.

4027 Flip-Flop (IC2)

The 4027 flip-flop (IC2) is a digital logic integrated circuit employed to generate complementary output signals. It divides the input frequency from the 555 timer by two, producing a distinct set of outputs on pins 15 and 14. This functionality is crucial for creating a switching circuit that toggles between two states. The 4027 is often utilized in digital circuits for creating binary logic gates and memory elements. It's a fundamental component in various digital systems.

Circuit operation is as follows. The 555 timer ( IC1 ) is set up as a 12hz multi vibrator. The output on pin 3 drives the 4027 flip-flop (IC2). This flip-flop divides the input frequency by two and delivers complementary voltage outputs to pin 15 and 14. The outputs are connected to LED1 and LED2 through the current limiting resistor R3. The LED's are arranged so that when the polarity across the circuit is one way only one LED will light and when the polarity reverses the other LED will light, therefore when no transistor is connected to the tester the LED's will alternately flash. The IC2 outputs are also connected to resistors R4 and R5 with the junction of these two resistors connected to the base of the transistor being tested. With a good transistor connected to the tester, the transistor will turn on and produce a short across the LED pair. If a good NPN transistor is connected then LED1 will flash by itself and if a good PNP transistor is connected then LED2 will flash by itself. If the transistor is open both LED's will flash and if the transistor is shorted then neither LED will flash.