Introduction:
A firing circuit is used to control the output of a DC power supply. It is responsible for initiating the firing of the thyristors or transistors that control the output voltage or current. The firing circuit ensures that the thyristors or transistors are triggered at the desired phase angle of the input waveform, allowing for precise control of the output.

Schematic Diagram of Firing Circuit:
The firing circuit typically consists of the following components:

1. Transformer: The input voltage is stepped down using a transformer to a suitable level for the circuit.

2. Rectifier: The AC input is converted to DC using a rectifier circuit. This provides a stable DC voltage for the firing circuit.

3. Triggering Circuit: This circuit generates the required signal to trigger the thyristors or transistors. It typically consists of a pulse generator, timing circuit, and gate drive circuit.

4. Pulse Generator: The pulse generator generates a pulse signal with the desired phase angle. It can be implemented using various techniques such as a microcontroller, timer IC, or a dedicated pulse generator IC.

5. Timing Circuit: The timing circuit determines the duration of the pulse signal. It is usually implemented using resistors and capacitors to control the charging and discharging of the timing capacitor.

6. Gate Drive Circuit: The gate drive circuit amplifies and shapes the pulse signal to provide the necessary gate current to trigger the thyristors or transistors. It may include level shifting, amplification, and isolation components.

7. Protection Circuit: A protection circuit is often included to ensure the safe operation of the firing circuit and prevent damage to the power supply. It may include overvoltage protection, overcurrent protection, and short-circuit protection.

Working Principle:
The firing circuit works by generating a pulse signal with the desired phase angle and duration. This pulse signal is then amplified and shaped by the gate drive circuit to trigger the thyristors or transistors.

1. The AC input voltage is stepped down using a transformer and converted to DC using a rectifier circuit.

2. The pulse generator generates a pulse signal with the desired phase angle based on the input waveform.

3. The timing circuit controls the duration of the pulse signal.

4. The pulse signal is amplified and shaped by the gate drive circuit.

5. The amplified pulse signal is applied to the gate of the thyristors or transistors, triggering them and controlling the output voltage or current of the DC power supply.

Conclusion:
The firing circuit plays a crucial role in controlling the output of a DC power supply. It generates a pulse signal with the desired phase angle and duration to trigger the thyristors or transistors. By controlling the firing angle, the output voltage or current can be precisely regulated. The schematic diagram of the firing circuit includes a transformer, rectifier, triggering circuit, pulse generator, timing circuit, gate drive circuit, and protection circuit.