Why the pulsed train triggering is preferable than the single pulse triggering?

It reduces gate dissipation and power demand from the trigger circuit. It is also convenient for coupling to the thyristor gate with a pulse transformer, to achieve the rewuired galvanic isolation.

Why pulse triggering of SCR is preferred over single or DC triggering?

For thyristors pulse triggering is preferred than dc triggering because: The DC gate voltage and current increase losses in the SCR. Pulsed triggering is to reduce gate losses. The pulsed gate drive can easily be passed through isolation transformers to isolate SCR and the trigger circuit.

Why is a pulsating DC voltage needed to trigger the SCR?

A momentary pulse to the gate will cause the SCR to conduct and current will flow across the device until the value changes. If this happens, the gate needs to be pulsed again to cause conduction to resume; otherwise no current will flow across the device.

What is pulse triggering?

The term pulse-triggered means that data are entered into the flip-flop on the rising edge of the clock pulse, but the output does not reflect the input state until the falling edge of the clock pulse.

What are the necessary conditions for turning on of an SCR?

The first and most important condition is that, SCR must be forward biased. This means that the anode voltage should be more than the cathode voltage. In other words, anode voltage should be positive with respect to cathode voltage. Gate pulse width must be more than the SCR turn-on time.

Why pulse trigger method is preferred?

Pulse triggering is preferred higher than RC triggering because of its following advantages: The SCR has small turn ON time ie, upto 5uS. Hence a pulse of gate drive is sufficient to turn on the SCRs. Once the SCR turns ON, there is no need of gate drive.

Why gate pulses are preferred than continuous gate signal?

To reduce gate power dissipation, SCR firing circuits generate a single pulse or a train of pulses instead of a continuous DC gate signal. This allows precise control of the point at which the SCR is fired. In addition, it is easy to provide electrical isolation between the SCR and the gate trigger circuit.

Why are pulse transformers used in thyristor circuits?

Pulse transformers are often used to couple a trigger pulse generator to a thyristor in order to obtain electrical isolation between the two circuits. In some cases where high noise levels are present it may be necessary to load the secondary of the transformer with a resistor to prevent false triggering.

What is the purpose of an SCR?

SCRs are mainly used in devices where the control of high power, possibly coupled with high voltage, is demanded. Their operation makes them suitable for use in medium- to high-voltage AC power control applications, such as lamp dimming, power regulators and motor control.