Voltage Regulation Circuits

Voltage Regulation Circuits (Voltage Regulators):

Voltage regulation in the circuit means zener diode will come in our mind. But it is not the universal solution for the voltage regulation..
In this short post we will discuss in brief about various voltage regulator circuits....
It is recommended to read about How zener diode will provide the Voltage Regulation in the Circuit before proceeding further....

Zener Diode Based Voltage Regulator:

We can make a simple voltage regulator using zener diode as shown in the below figure.
As we had already discussed in detail about the voltage regulation using zener diode, we will see the constraints/limitations here.

  1. The output voltage VOUT is not adjustable to the precise value.
  2. The zener diode will provide only moderate protection against ripple voltages.
  3. When load impedance varies zener diode regulator does not work effectively.
  4. To meet the large load variations zener diode with huge power rating should be used. It will be expensive.

Voltage_Regulator_using_zener_diode
Transistor Based Voltage Regulator: Circuit # 1

The below circuit shows the voltage regulator using transistor.
Comparing with the zener voltage regulator, it will provide better regulation.
This circuit provides the voltage regulation with wide load variations.
In addition to that, it will provide high current output with better stability.voltage_regulation_using_BJT

This circuit is similar to the preceding circuit, except that the zener diode is connected to the base of a npn transistor.

  • The zener diode is used to regulate the collect to emitter current.
  • The capacitor(C) is incorporated to reduce the noise from the zener diode.
  • Combining with the resistor (R), It also forms an RC filter which is used to reduce the ripple voltages.
  • The BJT is used in Emitter-Follower configuration.
    ie, the emitter will follow the base.
  • The zener diode is used to regulate the base voltage which leads to regulated emitter voltage.

Note that in a transistor the current required by the base is only 1/hFE times the emitter to collector current. So a low power rated zener diode can regulate the base voltage of the BJT that can pass a huge current through it.

BJT Based Voltage Regulator: Circuit # 2

  • In some cases, the zener diode connected to the base of transistor will not provide enough base current.
  • To solve this problem, an additional transistor is used as shown in the following circuit.
  • This extra transistor acts as an amplifier.
  • It amplify the current sent to the base of the upper transistor (ie, base current of upper BJT).voltage_regulation_using_transistor

Thanks for reading about the Voltage Regulation Circuits...

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