Voltage Rating Tester for Zener Diode

Overview

The circuit has been constructed to test and measure the voltage rating of zener diodes.

Terminology

• 555 Timer – an 8-pin electronic device used in several mixtures of applications involving multivibration and timing
• Zener Diode – a special kind of diode that permits the flow of current in just one or forward direction as a normal diode, but will also allow in the reverse direction if the voltage is above or larger than a certain value of the breakdown voltage
• LT700 – a miniature audio transformer that has a frequency of 1 kHz
• 1N4004 – a general purpose plastic rectifier with reverse voltage from 50 Volts to 1000 Volts and forward current of 1.0 Ampere

Circuit Explanation

To be able to test the voltage rating of a zener diode up to 50 VDC, a small transformer and a single 555 timer IC would be required to produce a high voltage. In this event, the 555 timer functions in the astable mode in which it operates as an oscillator or in a free running mode, thereby producing square waves. The small audio transformer is being driven by the output in pin 3. This transformer is the type of LT700 which can weigh around 0.02 kg and a dimension of 16 X 16 X 20 mm. The impedance of 8 ohms is rated on the secondary coil while an impedance of 1K ohm is center tapped on the primary winding. The unloaded voltage is about 120 VDC as the transformer operates in reverse. The 1N4004 diode rectifies the unloaded voltage while the 2.2 uF capacitor flattens it to reach the rate of 150 VDC. 1N4004 provides high forward surge current capability, guaranteed high temperature soldering and low forward voltage drop or reverse leakage.

A multimeter set to DC voltage is used during the test of zener diode. The zener diode can be tested at 1 mA or 2 mA DC with the aid of the load current switch. These values are the rectified DC load. A properly working zener diode will show a good reading in the multimeter.

Application

This circuit will have a straight forward use in the testing of zener diodes. Zener diodes are normally used to regulate the voltage across an electric circuit. When the 555 timer is operating in astable mode, it may be utilized in pulse position modulation, security alarms, tone generation, logic clocks, pulse generation, lamp flashers, and light emitting diode.

Source:www.zen22142.zen.co.uk/Circuits/Testgear/zenertest.htm