Which transistor is connected in parallel with feedback capacitor for termination of each ramp

Q.  Which transistor is connected in parallel with feedback capacitor for termination of each ramp at a prescribed level in a Voltage Controlled Sawtooth Oscillator(VCO)?
- Published on 26 Oct 15

a. BJT
b. FET
c. MOSFET
d. PUT

ANSWER: PUT
 
Programmable Unijunction Transistor (PUT) is a switching device adopted by Op-amp integrator in VCO, which is generally connected in parallel to feedback capacitor so as to allow the termination of each ramp by adjusting reset conditions of the circuit. Thus, PUT comprises three terminals like an anode, a cathode and a gate where the biasing level of gate is supposed to be positive corresponding to the cathode.
An extravagant increase in an anode voltage as compared to gate voltage can be figured out by approximately 0.7 V. As a result, the PUT gets turn ON and starts operating like diode in forward biased stipulation. Thus, PUT gets turned OFF due to decrease in value of anode voltage below this level.

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