The diode tester circuit, which can be used for a variety of purposes, is available for download here. Utilizing this circuit also enables one to verify the functionality of a zener diode. The transistors and resistors that make up this diode tester's circuit layout are rather straightforward components. Because there is no IC of any sort utilized in this circuit, it will be simple for those who are just starting out in the field of electronics to comprehend how the diode tester in this circuit actually functions.

Resistors R1=2.2K; R2=10K; R3=680 Ohm; R4=1.2 K; R5=10K , 0.5W TRANSISTORS T1 equals BC147B, while T2 is 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 Description of the circuit The 12-0-12 step-down 500mA power transformer was utilized for this purpose. The output of the transformer is sent into the bridge rectifier, which is comprised of the diodes D2, D3, D4, and D5, and is used to convert the alternating current supply into the direct current supply. The DC output is filtered by capacitor C1, which serves in this capacity. The capacitor that we used was 470 F, but you can use any value. The higher the capacitance value, the purer DC that can be obtained. As a bleeder, the resistor R2 has a value of 2.2K. You can see that the transistors T1 [BC147B] and T2 [SL100] are being used for the regulator compressor here. These transistors get the DC output through their connection. T1 acts as a series pass driver or a current regulator. Resistor R2 with a value of 10k serves as a base bleeder, while capacitor C2 with a value of 1 F filters base potential. The base bias for transistor T1 is obtained from the supply by way of resistor R3, which has a value of 680 ohms. When the test probe is completely open and there is no connection to the zener, the base potential of transistor T1 is approximately 32V, which is measured across resistor R4 or capacitor C2. The net DC voltage equivalent to the potential of the base of transistor T1 (which is fed to the voltmeter) is provided by the transistor T2 (which serves as a series pass regulator) and is supplied by the transistor T1 (BC147B), which supplies the base potential.

With no zener diode attached across the probe, the voltmeter is currently reading somewhere about 30V. When a zener diode is put across the test probe, the base potential of transistor T1 drops until it reaches the level at which the zener diode breaks down. As a result of this, the base potentials of the transistors T2 and T1 are brought into parity with one another. The meter is now displaying the real voltage produced by the zener. By moving the needle using the zero-adjustment screw on the meter, it is possible to make a modification to the scale of the meter that is 0.6 V in magnitude.

Resistors (all of them are 14 watt, less than 5% carbon). R1 = 100 KΩ; R2 = 39 KΩ; R3 = 2.2 KΩ; R4 = 680 Ω; R5 = 100 Ω; VR1 = 4.7 KΩ; VR2 = 10 KΩ Capacitors C1 = 27 KPF (273); C2, C4 = 2.2 µF/16 V; C3 = 22 µF/16 V; C5, C10 = 100 µF/16 V; C6 = 10 µF/16 V; C7 = 100 KPF (104); C8 = 47 KPF (473); C9 = 220 µF/16 V Semiconductors T1 is a BC147B, and IC1 is an LM386. Both are power amplifiers. Miscellaneous L1 equals the pick-up coil on the speaker 8.

SW1 is the switch for on and off.