Electronic Fuse for DC Circuit

Discussion in 'General Electronics Chat' started by rainyday101, Apr 16, 2010.

  1. rainyday101

    Thread Starter Member

    Sep 24, 2009
    I thought this was a nifty circuit at first.
    http://electroschematics.com/2923/dc-electronic fuse

    I would be using one of these on the output side of a 7805 power supply at .6 amps and one on the output side of a 7824 power supply at 1.6 amps. The problem is that resistor RS would have to quite a large wattage rating in both cases. The 7805 power supply will be supplying an arduino controller, 4n25 optocouplers and ms2222a transistors and the 7824 will be supplying external I/O components. I just thought this would be nifty instead of traditional fusing. Can anyone recomend a fusing circuit or small device other the the good old glass fuse?
  2. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    kingdano likes this.
  3. rainyday101

    Thread Starter Member

    Sep 24, 2009
    Thanks Robert, I ordered some and will give them a try.
  4. Norfindel

    Senior Member

    Mar 6, 2008
    They don't need to be of high wattage. The maximum voltage drop over the RS resistor is only about 0.7v.

    0,7v / 0.6A = 1.16 ohms. 0,7v * 0.6A = 0.42 watts.
    0,7v / 1.6A = 0.44 ohms. 0,7v * 1.6A = 1.12 watts.

    The problem with this approach is that the resistor is not on the regulator feedback loop, so the output voltage will be lower than 5v and 24v, and regulation will suffer.

    Did you taken a look at the LM723? It's a voltage regulator with current limit that is designed to use an external pass transistor for high current over what the IC can handle. It's not a fuse, however, it's a current limit.