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In this schematic circuit is presented a very simple Zener Diode Tester circuit that require few external components to  be build . Zener Diode Tester Circuit diagram As you can see in the schematic circuit , the Zener Tester  project is based on a common 741 operational amplifier .The supply need only be as high a value as the zener itself . The variable resistor P can be calibrated ( in volts ) , so when the LED 1 lights the voltage on pins 2 and 3 of the 741 operational amplifier is nearly equal .

The circuit can be simply Q1 is connected as a current source. By D1, there is a constant voltage on the base, and it is worth considering the selected resistor in the emitter approximately 5.6 V. With an emitter resistor of 5K6 R2 will then 1mA through the transistor. With the chosen resistors in the circuit the current is approximately: 1mA, 2mA, 5mA, 10mA and 20mA. Great precision is not required. If meter is chosen here for a small DVM module. However, every other meter is applicable, provided that the input resistance is high enough. Construction: The circuit is simple to build on a piece of PCB holes. Note that the DVM module separate from the circuit galvanic isolated power supply needs. Using Connect the test zener diode between the terminal A and K. Start with a current of 2mA. This is a safe value for most type zener diodes. Depending on the type of zener diode, may be chosen for a greater current. Than the Zener voltage will vary slightly. Join the zener diode on backwards, ...