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How does a shunt regulator work?

Latest Updated:11/01/2007

Question:

How does a shunt regulator work?

Answer:

A shunt regulator detects output voltage variation via external resistors by using an error amplifier and controls a transistor connected in parallel to the load to keep the output voltage constant. In other words, the characteristic of a shunt regulator is to minimize current variation of power supply (operation in the direction of minimizing variations) even if the load fluctuates. However, as a basic limitation of shunt regulators, they can not tolerate more fluctuations of current flowing in the load than the difference between the min. level and the max. level of the current flowing in the transistor.
The basic operation of a shunt regulator is described below using a simplified circuit.




When the output voltage drops due to a variation of the load, the voltage applied to resistors R1 and R2 drops. This then lowers the voltage of V1, which is the output voltage divided by R1 and R2. In other words, the input voltage of the error amplifier's non-inverted pin (+) is also lowered (below the internal reference voltage). As a result, the error amplifier causes the voltage applied to the base of transistor TR to drop, which suppresses the current flowing to the TR collector. This in turn raises the output voltage, stabilizing it.

Conversely, when the output voltage rises due to a variation of the load, V1 also rises, causing the error amplifier to raise the voltage of the TR base. This in turn increases the current flowing to the TR collector, which lowers the output voltage, stabilizing it. In other words, the shunt regulator operates to ensure that V1 is always equivalent to the internal reference voltage.
Suitable Products
CMOS comparators
bipolar comparators
Shunt Regulators