DC voltage regulators
The main property of the DC voltage regulator is, if there is any change in the I/P voltage, the O/P of the voltage regulator will be constant. And further we can adjust the O/P voltage according to our requirements.
There are two main types of DC voltage regulator.
- Series voltage regulator
- Shunt voltage regulator
1. Series voltage regulator
The block diagram of basic series DC voltage regulator is shown in figure, which is consisting of four stages.
a:) Sampling unit:
The sampling unit takes a sample from the o/p voltage and feed to the error detector stage. In the error detector stage compare the o/p voltages with reference voltages and give the error signal to the control element, which control the o/p voltage.
b:) Reference voltage
This stage provides reference voltages to the error detector stage for the comparison. In the reference voltage stage normally the zenar diodes are used because, if there is any change in the i/p, the o/p will be constant.
c:) Control Element
The control element of the series voltage regulator is used and amplified signals to keep o/p voltage constant.
d:) Error Detector
This stage gets a sample from the sampling unit, compare it with the reference voltage and give the error signal to the control element for controlling the o/p voltage.
Operation of basic op-amp series voltage regulator
In the figure of basic op-amplifier series voltage regulator , the op-amp is used as comparator . Resistor R1 and R2 is the voltage divider network which is used to sense any change at the o/p. The change sensed by the divider network is applied at the inverting i/p of the comparator, while the reference voltage hold by the zenar diode is applied at the non-inverting i/p of the comparator is applied at the base of transistor “Q”.
When the o/p voltage decreases because of the decrease in i/p voltage , the voltage drop across R1,R2 decreases and so this error voltage (-ve) is sensed by the divider network which is applied at the inverting i/p of the comparator. The comparator compare the reference constant voltage and the –ve error voltage and provide the difference (+ve) of the two voltages at the o/p as i/p at the base of transistor . The transistor conduct according to the forward bias voltage at the base and so, the o/p voltage remain constant. When the o/p voltage tries to increase, the voltage sensed by the divider network is increased . This is applied at the inverting i/p of the comparator. The comparator provide the difference (-ve) of the two voltage at the i/p of Q1 and so, the conduction of transistor decreases to the constant (required) voltage level.
2. Shunt voltage regulator
The shunt voltage regulator is connected parallel to the load. In the shunt voltage regulator, the reference voltage unit produces constant voltage to the error detector stage. The sampling unit takes a part from O/P voltage and feed to the error detector where it compares with the reference voltage. If there is any change in the O/P voltage, the sampling unit detects this change in the O/P voltage and provides to the error detector stage, the net change is provided to control element, which control the O/P voltage nearly at constant level.
Circuit diagram of shunt voltage regulator
The 2nd basic type of linear voltage regulator is the shunt voltage regulator. In the series voltage regulator the controlling element (Q) is connected in series but in shunt regulator the transistor is connected in parallel. The reference voltage is applied at the inverting I/P of the op-amp and the O/P of sampling unit is applied at non-inverting I/P of the op-amp as shown in the figure.
The transistor is connected in parallel with the load, when the O/P voltage tries to decrease due to the change in I/P voltage or load current. This decrease in O/P voltage sensed by the R3, R4 resistors and applied to the voltage on op-amp non-inverting I/P in result of which the o/p of op-amp decreases and base current of transistor is also decreases due to which collector current is also decreases, which increases its collector to emitter resistance (RCE) is also increases and the o/p voltage is back to its normal level.
When o/p voltage is increases, it increases also the signal which is applied at the non-inverting I/P of op-amp due to which the blazing voltage increases , the emitter to collector resistance decreases and so the transistor do conduction according to the base blazing voltage. In this way the increasing voltages are grounded through the transistor and keep the o/p voltage constant.
The change in the o/p voltage is controlled by the conduction of the transistor through which the voltage is grounded.