Explain the working principle of a regulated power supply. What is the role of Zener diode in it ?

Asked by pratikbharadia | 30th Dec, 2009, 11:51: AM

Expert Answer:

Hi dear,

There are many types of power supply. Most are designed to convert high voltage AC mains electricity to a suitable low voltage supply for electronics circuits and other devices. A power supply can by broken down into a series of blocks, each of which performs a particular function.

For example a 5V regulated supply

Each of the blocks is described in more detail below:

  • Transformer steps down high voltage AC mains to low voltage AC.
  • Rectifier- converts AC to DC, but the DC output is varying.
  • Smoothing smooths the DC from varying greatly to a small ripple.
  • Regulator- eliminates ripple by setting DC output to a fixed voltage.


Zener diode regulator

For low current power supplies a simple voltage regulator can be made with a resistor and a Zener diode connected in reverse as shown in the diagram. Zener diodes are rated by their breakdown voltage Vz and maximum power Pz (typically 400mW or 1.3W).

The resistor limits the current (like an LED resistor). The current through the resistor is constant, so when there is no output current all the current flows through the Zener diode and its power rating Pz must be large enough to withstand this.

Answered by  | 30th Dec, 2009, 01:39: PM

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