Direct Current switching

Discussion in 'The Projects Forum' started by thavamaran, Aug 3, 2011.

  1. thavamaran

    Thread Starter Active Member

    Feb 21, 2008
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    0
    Hi guys. I recently posted to discuss on switching signals. I have resolved that.

    Now, Im trying to switch a DC voltage/current.

    Say Im supply a DC stable bias current of about 40 mA. If I want to switch it off at certain time interval, maximum of 40 us. Which means, the maximum pulsewidth of the control pulse will be 40 us.

    After 40 us, I don't want any direct current to go through the switch.

    Can anyone suggest a switching IC operates at this region? I googled it, and I dont seem to get a right answer.

    Any advice please?
     
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Would be helpfull to know voltages to be switched. Presume that there is a signal to indicate the start of the 40μ s, time delay which could trigger a 555 40μs one shot, the trailing edge to reset a flip-flop, the Q out controls a P-ch MOSFET. At power-up FF is set, 555 after 40μs resets FF. Source to supply, drain to load, & gate to 555.
     
  3. thavamaran

    Thread Starter Active Member

    Feb 21, 2008
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    0
    Thanks for your reply Bernard. I will supply a control pulse with 40 us pulsewidth. Which means, the rising edge should turn on the switch and falling edge should turn off, until the next rising edge comes, it should be turned off.

    The voltage would be around 2-4 V. Can you re-explain that please, I really dont get it.
     
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Thanks for the reply. Try using a 74C904, non- inverting buffer, rated minimum @ 5V VCC, at 9 mA [6 X 9 =54 mA ], @ 25 deg C; assuming there is a 5V supply available. Parallel inpute & outputs, use combined outputs for bias supply. If IC not available try invertor & PNP transistor, like 2N 3906. A logic level P- ch MOSFET might be be better if you could find one.
     
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