555 pointer electronic megger circuit diagram

This megohmmeter uses an electronic boost circuit as the measurement power supply, with a measuring range of 0.5~1000M ohms.

IC1 (555) and R1, R2, C1 are connected to form an astable oscillation mode. The oscillation frequency is f=1.44/(R1+2R2)C1, which is about 15kHz. Transformer T is a step-up transformer. After the secondary induced voltage is rectified and filtered by D1, a DC high voltage of about 1000V is obtained as a voltage power supply for measurement. It is connected in series with the resistor under test through the current limiting resistor R5 and forms a measurement loop with the meter.

The corresponding current value label can be calculated from the dial reading by the following formula: I=V/(R+R5+Rg), where V is the voltage value on C5, Rk is the internal resistance of the meter head, and R is the dial reading. RP1 is used to shunt the 100uA meter, calibrated to 2mA full scale, and can measure low resistance from 0.5 to 10M ohms.