Test a Diode | Zener Diode

Here you can get the diode tester circuit for general purpose using diode. You can also test a zener diode by the use of this circuit too. The circuit diagram of the diode tester here is made of simple Transistors and resistors. Any kind of IC is not used in this circuit so it will be easy for the electronics beginners for understanding the working principal of diode tester in this circuit.

PART LISTS

RESISTORS

R1	2.2K
R2	10K
R3	680 Ohm
R4	1.2 K
R5	10K , 0.5W

TRANSISTORS

T1	BC147B
T2	SL100

CAPACITORS

C1	470μ 35V
C2	1μ 40V

DIODES

D1	LED
D2 -D5	1N4001

OTHERS

S1	ON/OFF Switch
X1	12V-0-12V Transformer
Volt Meter	30V
Probe	2 pieces

 

CIRCUIT DESCRIPTION

Here we used the 12-0-12 step-down 500mA power transformer. The output of the transformer is supply to the bridge rectifier made of D2 , D3, D4, D5 which is use to convert the Ac supply to the DC supply. Capacitor C1 is used as a filter the DC output. We used  470 μF capacitor  but you can used any. More the value of capacitor more pure DC can be obtained. Resistor R2 of 2.2K is used as bleeder. Here you can see the transistor T1 [BC147B] and transistor T2 [SL100] are use for regulator compressor. The DC output is fed to these transistors. T1 acts as a series pass driver or a current regulator. Base bias for transistor T1 is achieved from the supply through resistor  R3 of 680 ohms  as resistor R2 of  10k is a base bleeder and capacitor C2 1 μF  filters base potential. When the test probe is fully open with no zener connected, the base potential of transistor T1 is around 32V that is across resistor R4 or capacitor C2.

Transistor T1 [BC147B] provides the base potential for transistor T2 [SL100] which acts as a series pass regulator, providing the net DC voltage equivalent to T1 base potential which is fed to the voltmeter.