High AC & LOW AC tripping not working

Discussion in 'The Projects Forum' started by asimraufawan, Dec 26, 2009.

  1. asimraufawan

    Thread Starter Member

    Jul 4, 2008
    Hi Everyone,

    The Attached circuit diagram is used in inverter for High AC & Low AC tripping using LM339 configured as window comparator.

    When the circuit test individually it works fine when the high AC 250 VAC detected & Low AC 180 VAC detected ,the output of the LM339 pin number 13 goes low after 20 second due to timer circuit.

    But when the circuit integrates with inverter as shown in the block diagram & when the voltage increases or decreases with the limit ,
    then PIN nimber 2 for high or pin number 1 for low goes low,but the pin number 13 does not goes low & when i check the voltage across C6
    it shows 1 VDC which is below the reference limit which is 2.5VDC.

    Kindly help me out.

  2. asimraufawan

    Thread Starter Member

    Jul 4, 2008
    Here is the schemetic
    • WC.JPG
      File size:
      51 KB
  3. SgtWookie


    Jul 17, 2007
    That schematic really doesn't make much sense.

    You do know that LM339 comparators have open-collector outputs, and need to have pull-up resistors on them so that you can see an output? They are limited to around 6mA sink current, so size your resistors accordingly.
  4. asimraufawan

    Thread Starter Member

    Jul 4, 2008
    LM339 input volt is 5v, i have pull up all the outputs of LM339 but the result is still same ,the driver IGBT card PSHI 2012 recommemnds pull resistor to error pin should be (Rc > Vc/6mA).i have pull up this pin using 4.7K.
  5. asimraufawan

    Thread Starter Member

    Jul 4, 2008
    Kindly help me out ,its very urgent for me.
  6. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    I agee. His diagram looks somewhat similiar to the block diagram of the PSHI-20.
  7. BillB3857

    AAC Fanatic!

    Feb 28, 2009
    If I understand your circuit correctly, A1 is your analog signal representing the voltage being measured. I can only assume that it has been properly rectified, filtered and scaled to match your circuit. Potentiometers R14 and R15 adjust the trip levels for the two comparators. Pin 1 or Pin 2 of the LM339 going low represents one of the limits has been reached and an error exists. R22 provides the pull-up function through diodes D12 and D13. R22 also provides forward bias for Q1 when no error exists.

    I do notice that there are two 1K resistors that go to connector pins labeled HI and LOW. What do these lines feed. Is it possible that there is a voltage there that cannot allow the LM339 to pull all the way to ground, therefore not allowing sufficient reduction of forward bias to Q1?

    I think the key to solving your problem will be to look at the bias voltage on Q1 while connected to the inverter and in what should be a failed condition. The fix may be as simple as putting a diode in the emitter lead of Q1 to require a higher bias voltage for turn on.