forward/reverse voltage

Discussion in 'General Electronics Chat' started by tgregor, Sep 28, 2008.

  1. tgregor

    Thread Starter New Member

    Sep 28, 2008
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    I have an optocoupler that has a max forward voltage of 1.65 and a max reverse voltage of 6.0 does this mean i can only apply a max of 1.65v to the collector? or can i apply 5v? I get confused about forward a reverse voltages.
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    The input to the opto-coupler is an LED so you will need a current limiting resistor to avoid exceeding the maximum current applied to the input.

    Applying a reverse voltage in excess of the rated 6V should be avoid also.

    hgmjr
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
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    The foreward voltage is the voltage necessary to place the internal LED into conduction. As long as there is that much voltage present, the LED will emit light. Then it's a matter of limiting current to less than the maximum rating with resistors.

    The reverse voltage is the greatest voltage the LED can withstand in reverse bias. More than 6 volts will send the LED into avalanche conduction and destroy it.
     
  4. tgregor

    Thread Starter New Member

    Sep 28, 2008
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    Thank you that makes sense to me, the textbook answer i got online did not make that much sense. So if I were to put a 5v signal from an AVR for no more then 2 seconds the chip can withstand it especially if i put a pull down resistor on it.
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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    If the voltage is in the reverse direction, then a resistor will not help. Add a diode in series with the LED to block the reverse voltage.
     
  6. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    What is the part number of your optocoupler?
     
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