High AC & LOW AC tripping not working

Thread Starter

asimraufawan

Joined Jul 4, 2008
29
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.

Thanks.
 

Attachments

SgtWookie

Joined Jul 17, 2007
22,201
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.
 

Thread Starter

asimraufawan

Joined Jul 4, 2008
29
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.
 

Attachments

BillB3857

Joined Feb 28, 2009
2,493
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.
 
Top