Zener Diode Voltage Regulator

Here it is show how to build voltage regulator design with Zener diode. A voltage regulator produces regulated power supply of particular voltage and current from unregulated power supply. The 7805 IC(Integrated Circuit), LM7806, LM7809, LM7812, LM317, LM7905, LM7912, LM117V33, XC6206P332MR are examples of voltage regulator that is used in electronics project. However with few inexpensive zener diodes, transistors and passive components we can build voltage regulator that can be used in electronics projects. For example, a motor may need a voltage regular with specific power and voltage rating. 

A zener diode works like an ordinary diode, but can also work in the reverse breakdown region without heating and burning out. That is they are designed to work in the reverse breakdown region of the IV characteristic curve. The voltage at which at which breakdown occurs is called zener breakdown voltage or just zener voltage. At the zener voltage the zener diode acts like a constant voltage source.

Zener diode are rated with voltage like 1V, 2V, 5.1V and with power rating like 0.5W, 1W, 5W and so on. With this we can find out the maximum current(P = I*V so Imax = P/V) that the diode can handle and not exceed that current value.

Here the 1N5242B Zener diode is used as an example zener diode. The following is one way of making a simple voltage regulator with a 1N5242B Zener diode. 

simple voltage regulator with zener diode

Here the zener diode is build in simple shunt regulator configuration. The resistor is used to limit the current into the zener diode so that it does not burn out. The power handling capacitor of the resistor must be such that it can handle the current through it.

The rated zener voltage of 1N5242B is 12V. The following shows the current voltage characteristics curve of 1N5242B.

1N5242B IV curve

Here we assume the AC power supply source with 60Hz, 120V rms sinusoidal signal. This signal is fed into step down transformer with turn ratio of 10. The down converted ac signal passes through a half wave rectifier and capacitor input filter. 

This circuit converts a sinusoidal wave to square wave. The voltage of the output signal from this zener regulated circuit is the zener diode which is 12V. The above simple zener diode voltage regulator does not give precise output voltage, does not have good protection for voltage ripple and the regulator does not work properly when the load impedance changes.

One way to improve this zener voltage regulator is to add transistor and capacitor as shown in the following circuit diagram.

The input signal is 500Hz, 120V signal and the output signal waveform is shown below.

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