Explain the operation of shunt mode power supply with circuit diagram. Give its merits also.

Operation of Shunt Mode Power Supply with Circuit Diagram

A shunt mode power supply, also known as a shunt regulator, is a simple voltage regulator circuit that operates by shunting current away from the load to control the output voltage. It uses a variable resistance in parallel with the load to maintain a constant output voltage by diverting excess current.

Step-by-Step Operation:

1. Voltage Reference: The shunt regulator starts with a stable voltage reference, which could be a Zener diode or a bandgap reference. This reference sets the desired output voltage level.

2. Comparison: The output voltage is continuously compared to the reference voltage. This can be done using an operational amplifier or directly through the Zener diode's junction.

3. Control Element: The control element, which is typically a transistor, responds to the difference between the actual output voltage and the reference voltage.

4. Shunting Current: If the output voltage rises above the reference voltage, the control element allows more current to flow through it, effectively shunting current away from the load and dropping the excess voltage across the shunt regulator.

5. Stabilization: Conversely, if the output voltage drops below the reference voltage, the control element reduces the current flowing through it, allowing more current to flow to the load, thus increasing the output voltage.

6. Feedback Loop: This process is a feedback loop that maintains the output voltage at a constant level despite changes in the input voltage or load conditions.

Circuit Diagram:

Here's a basic circuit diagram of a shunt mode power supply:

Input Voltage
+ ----|Vin|----------------+
                          |
                         .-.  Reference
                         | |  Zener Diode
                         | |  (Vref)
                         '-'
                          |
                          |
                         \|/
Output Voltage           /|\  Control
+ ----|Vout|----+----| BJT |----+
                 |               |
                 |               |
                 |               |
                 |               |
                 +----| Load |---+
                 |               |
                 |               |
                 |               |
Ground           +---------------+

In this diagram:

• Vin is the input voltage.
• Vout is the output voltage across the load.
• The Zener diode sets the reference voltage (Vref).
• The BJT (Bipolar Junction Transistor) acts as the control element.

Merits of Shunt Mode Power Supply:

Merit	Explanation
Simplicity	Shunt regulators are simple in design and easy to implement with a minimal number of components.
Low Cost	Due to their simplicity, they are also cost-effective for many applications.
Fast Response	Shunt regulators can respond quickly to changes in load or input voltage, which is beneficial for certain applications.
Low Noise	They can provide a low-noise output voltage, which is useful in sensitive electronic circuits.
Good for Low Power	Shunt regulators are suitable for applications where the load current is relatively low.

Example:

Consider a shunt regulator designed to maintain a 5V output. A Zener diode with a breakdown voltage of 5V is used as the reference. If the input voltage is 9V and the load requires 10mA, the shunt regulator will shunt the excess current to maintain the output voltage at 5V. If the load changes and only requires 5mA, the shunt regulator will adjust and shunt more current to maintain the 5V output.

Conclusion

Shunt mode power supplies are a basic form of voltage regulation that are best suited for low power applications where simplicity and low cost are important. They are not as efficient as series regulators for high current applications, but they offer advantages in terms of noise and response time for the right applications.