pc power box circuit schematic

PC Power Box with E-fuse

This little circuit will help you to remove all surplus small ac mains adaptors from your desktop. The circuit is nothing, but a smart dc power box directly powered by the smps of your desktop personal computer. Regulated, clean and protected +12VDC is available at the output of this unit. In addition, a USB power port is provided to re-charge portable devices including cellphones and music players, etc.

How does the pc power box works

All you need is to open your system box and connect an unused 4-pin drive power connector from the system smps to this circuit. +12V (Yellow wire) from the smps is processed by a resettable electronic fuse built around components T1, T2 and T3 and feed to the output terminal. Similarly the +12V is down converted to stable +5V by fixed 3 pin regulator IC1.

As a result, +12V (500 -750mA max, based on the electrical characteristics of T2 used) and +5V (1A max) DC supplies are available for external use, without affecting the normal pc functions. Switch S1 is the power on/off cum reset switch. Resistor R3 sets the maximum allowable output current rate and T1 disables the output power switch T3, when output load current exceeds the set value.

Smart dc power box circuit schematic

pc power box circuit schematic


Join the conversation!

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  • C.Mitra

    This circuit can be simplified to a large extent without sacrificing any features. The components R1,R2,T1, T2 and T3 can be simply omitted, and the 12V power can be directly drawn from the 12V pin of the SMPS. All standard PC power supplies have very robust built-in current limiting, so there is no need for all those extra components. It will give us the added advantage of a much higher current, not just 500-750 mA! Somebody please correct me if I am wrong.

  • rcweber55

    Nice little circuit with resettable electronic fuse.
    2 points if I may. Both T1 and T2 carry a max of about 5ma at any point, therefore T1 could be any small PNP (eg BC307). The max output current is determined by the size of the darlington transistor T3 (remember heatsink!).
    Best regards

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