Zener Diode Tester Circuit - Engineering Projects

One of the most important uses of the zener diode is in making the constant voltage power supply. Its works are based on the fact that in the reverse breakdown (Zener) region, a small change in voltage across the zener diode produces a very large change in current through the circuit but the voltage across the Zener remains constant. In this article, we have posted two different circuits to test the zener diode i.e. general Zener diode tester circuit and modified Zener diode tester circuit

Here, is a circuit that is used to test the voltage of the zener diode and also whether the zener diode is good or not. With the help of a voltmeter (or multimeter in voltmeter mode), it directly reads the voltage of the zener diode which is under test.

Circuit Description of Zener Diode Tester Circuit

The circuit is built around variable voltage regulator IC (LM317), IC LM317 is used to supply a definite amount of current to the zener diode under test (Figure 1). The value of this current is determined by resistor R₂ and does not dependent on Zener breakdown voltage.

When the zener diode to be tested is connected across probes, a voltage is developed across resistor R₁. The voltage developed across resistor R₁ triggers transistor T₁ as a result it provides base current to transistor T₂. When transistor T₂ is on, the relay RL₁ gets energized and the voltmeter gets connected across the zener diode through the N/O (normally open) contact of the relay.

The voltmeter connected to the relay shows the Zener breakdown voltage of the diode under test. When the diode is taken off the probe or diode is open circuit, the voltage across resistor R₁ is not developed, and as a result, both transistors (T₁ and T₂) will be turned off.

You can also use a multimeter instead of a voltmeter but at first, a multimeter is set in a suitable voltage range.

The circuit Zener Diode Tester is simple and advantageous as it provides quick and easy testing of the Zener diode.

Check out other various electronic component tester circuits posted in bestengineeringprojects.com

Advantage of Zener Diode Tester Circuit

As this circuit uses a regulated supply it does not damage the zener diode under test.
For better reliability and accuracy, a relay is used in this circuit.
The circuit does not draw any current when the probes are left free.

PARTS LIST OF ZENER DIODE TESTER SHOWN IN FIGURE 1.

Resistor (all ¼-watt, ± 5% Carbon)

R₁ = 150 Ω

R₂ = 220 Ω

R₃, R₄ = 10 KΩ

Semiconductors

IC₁ = LM317T

T₁ = BC177

T₂ = SL100

D₁ = 1N4001

Miscellaneous

RL₁ = 24V relay

M₁ = Voltmeter or multimeter in voltmeter mode

The above circuit can be modified by eliminating some components as shown in figure 2. One extra push switch SW₁ is connected which is pressed while testing the zener diode. This circuit works satisfactorily and is more economic in comparison to the circuit shown in figure 1.

PARTS LIST OF SIMPLE ZENER DIODE TESTER SHOWN IN FIGURE 2.

Resistor (all ¼-watt, ± 5% Carbon)

R₁ = 220 Ω