Question

1. If the circuit shown in Fig 3.3, where to be configured as a Class B amplifier, what would be
an appropriate value for the resistance R1 with respect to R2?

2. Explain the need for opto-isolation in AC control using thyristors.

3. Why is a thyristor not ideal for AC power control?

Answer 1

1: please provide figure to answer this.

2: Opto isolation are used for switching electronic devices like transistors or to provide electrical isolation between low voltage control signal and high output signal.In general these are used in AC or DC power control , computer communication ,and for regulation of power supply.

The noise and voltage spikes of AC power supply can be easily isolated.These opto isolation circuit makes high electrical isolation between input and output voltage.

3:As we know that AC power reverses the polarity periodically and therefore thyristor used in AC circuit will automatically be reversed biased causing it to turn OFF during one half of each cycle.

Once thyristor start to conduct it continues to conduct even with no gate signal , untill anode current decreases below the device holding current I_{​​​​​​H} and below this value it automatically gets turn OFF , therefore in AC circuit the current has to be reduced by separate switch or turn off switch.

This the reason thyristor are not ideal for AC power control.