Describe the operation of PUT as relaxation oscillator.

Ans:

PUT Relaxation oscillator:

 Waveforms of PUT relaxation oscillator

Operation: 

• As the biasing voltage Edc is applied to the circuit , capacitor starts charging towards Edc voltage through resistance R.

• As soon as capacitor voltage reaches up to peak point (Vp) voltage, the PUT turns on & the capacitor discharges. A positive going pulse is produced across Rs resistor as amplitude of the pulse is slightly lower than the capacitor peak voltage due to anode cathode ‘ON’ voltage of 1V. 

•  The peak point voltage (Vp =Vg+ 0.5) is set by the voltage divider consisting of the two resistors R1 & R2. 

•  The voltage at gate remains at Vg volts, the potential on the capacitor reaches the peak point voltage, PUT turns ON Vg drops to approximately zero and the capacitor discharges. 

•  When the discharging current of capacitor falls below the valley current PUT turns OFF & gate voltage returns to Vg volt.