When applying power to large wound components there may be a large initial current surge, sufficient to trip the mains fuse. Equipment incorporating large transformers may suffer from this problem. This circuit, which appeared in a CT ham radio magazine, limits the input current for a couple of seconds after switch on, thus avoiding the tripped mains fuse syndrome. I built the board small enough to fit inside an existing commercial 35 Amp power supply unit, which occasionally tripped my mains fuse at switch on.



Component values shown permit connecting up to 600 VA appliances - this can be increased to 1.3 KVA by substituting D4-D6 for 6A diodes and Tri for a TIC226D with heatsink.

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