UJT relaxation oscillator circuit
(With variable and selectable frequency)
UJT is acronym of uni junction transistor. It’s a thyristor device and It has only one junction. It’s a 3 terminal device and its 3 terminals are emitter, base 1 and base 2. It’s mostly used in high frequency switching applications and its one of the prime application is relaxation oscillator circuit. UJT relaxation oscillator generates very short duration positive and negative spikes at low as well as at high frequencies. It is widely used in triggering of other thyristor devices like SCR or TRIAC. Its can be used in AC / DC chopper circuit that generates variable AC/DC. I
The circuit can be built with the help of few components only and can be built on breadboard also. Here is the circuit diagram followed by description and working and operation of the circuit.
Description : UJT 2N2646 is used in the circuit along with few other components resistors, capacitors and one pot.
• Base 1 terminal of UJT is connected to Vcc through resistor R2 of 220E
• Base 2 terminal is connected to ground through resistor R3 of 50E
• Emitter terminal is connected to junction of pot RV1 (47 K) and 3 capacitors
• One fix value resistance R1 of 1K5 is connected in series with pot RV1
• 3 capacitors C1, C2 and C3 are connected to emitter through 3 SPST switches
Here is the snap of circuit built on bread board