PROJECT: Capacitor ESR & Leakage Tester

General description:

Capacitor leakage and ESR tester 3V... 100V with voltage feedback control. Can be also used for electrolytics reforming. Analog scale readout 0-100 uA / 0-1000 uA full scale. ESR readout 0-25 ohm with zero calibration potentiometer. Function ESR/ leakage can be selected by a DPDT switch.

Function description:

9-volt DC supply voltage is fed to midpoint of a step-up transformer primary through a pass transistor. 4047 provides a constant 100 kHz 50% duty cycle to drive the primary winding halves. After rectification of secondary voltage, a feedback voltage is selected by the rotary switch JP1 (Common pole= pin 12). Feedback voltage is compared against a fixed 1.2V reference in error amplifier IC2, which output drives the pass transistor's base current thus regulating the output.

ESR test voltage is generated by a 74HC14 schmitt trigger oscillator. Test frequency is about 100 kHz. Circuitry consists of an oscillator, AC-coupled transistor amplifier stage, DC clamp, buffer op-amp and a peak detector stage.


4047 astable multivibrator

2x9V/230V step-up transformer

TIP 120 transistors

LF356N op amp error amplifier

uA-meter 0-100 uA

Software: None


Schematic leakage

Schematic ESR

PCB leakage


Photo1, Photo2, Photo3