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Zener Diode Voltage Tester
The circuit was designed to provide a means for measuring the operating voltage of zener diodes before applying on a circuit.
- 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
- 2N5363 – a low power N-channel junction field effect transistor (JFET) used for general purpose device types enclosed in a TO-72 package
- Digital Voltmeter – an instrument used for measuring the potential difference between two points in an electric circuit with a special type of analog to digital converter known as integrating converter
The purpose of using Zener diodes is the due to their capability of regulating the voltage across an electric circuit. There are circuits that would require the use of Zener diodes which makes them very essential in the market. It is just proper to be aware of their actual and operating voltage rating to prevent any unwanted faults during operation. Because of this, Zener diodes have to be tested physically by not just looking at what is written on its casing. In this circuit, the half wave rectification system is composed of 1N4002 diode D1, 470 uF capacitor C1, and 230 VAC/12 VAC transformer T1.
The use of push button switch S2 is to pass DC current from the current limiter Q1 and the Zener diode DZ that is being tested. The current is being stabilized by Q1 to the value of 10 mA without reference to the Zener voltage that is attached to connector J1. The other connector J2 will be connected to the voltmeter which will show the voltage on the digital voltmeter. The circuit can be measured to a maximum of 25 Volts. For Zener diodes, a low voltage measurement will be likely 0.8 V which would signify the breakdown voltage. If the diode is connected in reverse, changing the polarity can be done. No reading will show in the case of reversed probe. An indication of having leakage or shorted Zener diode is when two readings are showing in the result.
This circuit is mainly used for quality-testing by performing a rough check of the breakdown voltage of Zener diode. This testing would ensure a precise amount of voltage produced by a Zener diode that is required for a circuit. A good working Zener diode will have 20 ohms to 50 ohms resistance for 6.8 V Zener diode while 13K ohms for a 13 V and above value. To do this, the black probe of the digital voltmeter is in the anode while the red probe to the cathode. The circuit can be checked by comparing a good Zener diode with a shorted one, which can be obtained from a component’s rack. When replacing a Zener diode, a higher wattage or the same and exact voltage is preferred.