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Zener diode tester using LM317

This circuit diagram project can be used for testing zener diode , we can measure the value of an unidentified Zener diode. This zener diode tester circuit it's centered around a common LM317 voltage regulator. The current is set to under 5mA, being calculated by the formula I = 1*25V/R, and this flows through the Zener diode being tested.
A voltmeter connected in parallel with the Zener its show the Zener voltage .
By adjusting potentiometer VR1, it is possible to vary the voltage on transistor TR1 emitter , which provides an adjustable voltage to the current limiter. VR1 is then adjusted until the LED D10 illuminates to indicate that current is flowing, when the test voltage may be read.
To measure diodes up to, say, 33V DC, it is normally to use a transformer of 30V AC output, but if you use a voltage trebler circuit, based around diodes D1 and D2 and capacitors C1 and C2,we can use a lower secondary voltage ( 10V AC).

Zener diode Tester circuit diagram

Zener diode Tester pcb circuit
Zener diode Tester

Notatie Valoare/Descriere
R1
R2
Rv1
C1,C2,C3
C4,C5
U1
D1,D2,D3
D4,D5
D6-D9
Q1
680 ¼ Resistor
270 ¼ Resistor
22k ¼ Potentiometer
1000µF pol
10µF pol
LM317
1n4004
Zener 18 V
1N4148
2N1711

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