Power Soft Start

Power Soft Start

This circuit limits the current through the power line to 5.5A for approximately 1.5 seconds. After that, the relay closes, and the current is no longer limited. This is a particularly interesting circuit if you have a large toroidal transformer and large electrolytic capacitors connected to the power supply, as these capacitors act like a short circuit for a short period when they begin charging. This unit is a delay unit that can be directly connected to the mains power supply. Using it is not mandatory, but it is a good idea, especially if you have a large toroidal transformer greater than 300 VA. This unit has a delay circuit; during the delay time, the mains power is supplied through a power resistor, thus minimizing the inrush current caused by the large capacitors and large toroidal transformer in the power supply. When everything is stable, it short-circuits the power resistor and supplies mains power directly.

Parts list

R1, R2 470 kΩ 0.25W 1% Metallic Film

R3 220 ohms 0.25 watts 1% Metallic film

R4, R5, R6, R7 10 ohms 5 watts

C1 330 nanofa 250 volts (for direct AC connection)

C2, C3 470µF 40V electrolytic capacitors

B1 B250C1500

Re1 24V (250V-8A contact)

F1 depends on the amplifier