Types of Voltage Regulator

Basic Voltage Regulator

The basic voltage regulator in its simplest form consists of,

1. Voltage reference, V_R

2. Error amplifier

3. Feedback network

4. Active series or shunt control element

The voltage reference generates a voltage level which is applied to the comparator circuit, which is generally error amplifier. The second input to the error amplifier is obtained through feedback network. Generally using the potential divider, the feedback signal is derived by sampling the output voltage. The error amplifier converts the difference between the output sample and the reference voltage into an error signal. This error signal inturn controls the active element of the regulator circuit, in order to compensate the change in the output voltage. Such an active element is generally a transistor. 

Review Question

1. What are the blocks of basic voltage regulator ?

Types of  Voltage Regulator

Depending upon where the control element is connected in the regulator circuit, the regulators are basically classified as,

1. Series voltage regulator

2. Shunt voltage regulator

Each type provides a constant d.c. output voltage which is regulated.

1. Shunt Voltage Regulator

The heart of any voltage regulator circuit is a control element. If such a control element is connected in shunt with the load, the regulator circuit is called shunt voltage regulator. The Fig. 5.5.1 shows the block diagram of shunt voltage regulator circuit.

The unregulated input voltage V_in, tries to provide the load current. But part of the current is drawn by the control element, to maintain the constant voltage across the load. If there is any change in the load voltage, the sampling    circuit provides a feedback signal to the comparator circuit. The comparator circuit compares the feedback signal with the reference voltage and generates a control signal which decides the amount of current required to be shunted to keep the load voltage constant. For example if the load voltage increases then the comparator circuit decides the control signal based on the feedback information, which draws the increased shunt current I_sh. Due to this the load current I_L decreases, hence the load voltage decreases to its normal value.

Key Point Thus the control element maintains the constant output voltage by shunting the current, hence the circuit is called shunt voltage regulator. 

2. Series Voltage Regulator

If in a voltage regulator circuit, the control element is connected in series with the load, the circuit is called series voltage regulator circuit. The Fig. 5.5.2 shows the block diagram of series voltage regulator circuit.

The unregulated d.c. voltage is the input to the circuit. The control element, controls the amount of the input voltage, that gets to the output. The sampling circuit provides the necessary feedback signal. The comparator circuit compares the feedback with the reference voltage to generate the appropriate control signal.

For example, if the load voltage tries to increase, the comparator generates a control signal based on the feedback information. This control signal causes the control element to decrease the amount of the output voltage. Thus the output voltage is maintained constant.

Key Point Thus, control element which regulates the load voltage based on the control signal with the load and hence the circuit is called series voltage regulator circuit.

Review Question

1. Explain the shunt and series voltage regulators.