Auto cut-off power for Overcurrent draw on USB Device

Discussion in 'Electronics Resources' started by Bongski1515, Jan 10, 2013.

  1. Bongski1515

    Thread Starter New Member

    Jan 10, 2013
    I have a device that drawing a ~460mA while streaming in PC and it momentarily spikes above 500mA during turn ON (Should not last more that 1/2-second) which is normal.
    I am using a normal multimeter/ammeter to monitor the current reading.

    Any suggestion on what equipment/device that I could use to monitor the current reading? But a requirement of: should remain under 500mA while it is streaming in the PC and will automatically cut off the power once excessive current detected, but will able to allow momentary spike during turn-ON of the USB device.

    Thanks very much in advance.
  2. vortmax


    Oct 10, 2012
    Is this something you expect to happen frequently, or is it a 'something went very, very wrong' type of ordeal.

    If it is something you don't plan on happening frequently, you need something like a fuse or a breaker. A PTC might actually serve you well. The trick is to read the data sheets and look at the tip time. Not all fuses/breakers are made equally. Some are fast trip, and will pop in milliseconds, while other "slow trip" or "long burn" fuses will permit over current for longer periods of time. The data sheet will at least list a characteristic trip time, but good ones will have charts.

    If this is something that can happen often, you will need to look into an active current limiting circuit which is more involved.
    Bongski1515 likes this.
  3. Bongski1515

    Thread Starter New Member

    Jan 10, 2013
    Thanks vortmax for the reply.

    As I'm doing the current measurement in a electronics manufacturing site, yes, it is something that can happen frequently.
    I need to interface a device to monitor the current reading of the Unit Under Test.
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    Search DigiKey or Mouser for PTC Fuse / Poly fuse for one that holds at 450mA, trips at 750mA (what is the peak you want to allow?) Or the range you are looking for. They are self-resetting.

    Finding one with a hold current very close to trip current will be difficult, especially in a non-surface mount form. A standard slow blow 500mA fuse may be the best fit there, but may get expensive if tripped often.