Are you sure the pins are connected to the correct signals and voltages? Check the board for shorts.

 

i checked it many times but couldnt find out the mistake... i will make the comparator part tomorrow...i am thinking about voltage follower and a resistor between comparator output and bjt base...what should be the value of the resistor and which opamp should i use as a voltage follower...thank you all..

 

Hello,

You can only proceed when the comparator is giving the PWM signal.
Can you make a complete drawing upto the comparator (with collector resistor) ?

Greetings,
Bertus

 

Check if the other op amps work first and then come to the comparator. Start to check each part of the circuit, ensure it works and then proceed to another part check.

 

That illustration I provided will make a good output driver. However, since the chip has got hot there is a good chance you have fried that one. Wookie is right, you have a wiring error somewhere, it may not be on the chip directly, but on somethey connected to the chip.

For trouble shooting purposes, try feeding a variable DC level into the comparitor and watching the output of the chip. It should vary between two levels on the output that are easily measureable.

 

Bill,
Your suggested circuits will not work at the frequency and current required to charge/discharge the MOSFET gates.

Until our OP can get the correct output signal from the comparator, no progress can be made.

If our OP has not disconnected the output from the bjt (transistors) bases, he will not get an output from the comparator.

This has to be a step-by-step process, as our OP has not as of yet obtained a suitable output from the comparator.

Since our OP is experiencing excessive heating from the comparator, I suspect that they may still have a connection to the bases of the bjt's; in particular the PNP transistor.

It won't work if the OP won't follow instructions.

 

Hello,

I think the comparator is fried.
At first it was used with pin 4 to gnd, the input signals could go negative, this probably burnt the comparator.
Replace the comparator and keep pin 4 to - 9 Volts.
Try to measure the PWM signal.

Greetings,
Bertus

 

I think the comparator is fried.
At first it was used with pin 4 to gnd, the input signals could go negative, this probably burnt the comparator.
Replace the comparator and keep pin 4 to - 9 Volts.

I can see why you would think this, but that LM392 opamp/comparator is rated for 50mA maximum current on the inputs, and a TL082/LF353 can only source a maximum of around 20mA @ 0°C, less at room temperature.

However, it's quite possible that the LM392 was already damaged prior to installation, or a wrong connection caused high current through it, and it is now destroyed.

 

Baggio2,

Check all the circuit step by step, then come here and write your results to see what is going wrong.

 

thanks a lot guys..it worked...

 

What was the problem?

 

We'll never know...

 

Trying to get info from our OP is like trying to pull teeth.

 

it was becos of my board's comparator part....i guess there was a voltage attenuation on comparator's feed path..i made a new layer for comparator...thank you all

 

If you guess how did you solve it? !!
What do you mean by new layer?

 

i mean part of comparator was wrong...i made a new board for comparator and added it to the circuit..

 

Wiring error, in other words. Easy to do, even for the most experienced.

 

And it is a very annoying fault Bill

 

yes so annoying...thank you all guys for ur help

 

Just a quick blurb about the MOSFETs our OP selected (I finally was able to read the numbers):
IRF9530 - P-ch (Vdss=-100, Rdson=0.3,Id=12, Qg=38nC)
IRF540 - N-ch (Vdss=100, Rdson=0.077,Id=28, Qg=72nC)
They're poorly matched, and have a rather large gate charge requirement (Qg), in particular the IRF540 at 72nC.

Trying to charge/discharge that gate at 100kHz is going to take a LOT of current!

could you advice me some complementary mosfets?