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Push Pull problem!!!

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pppopey

New Member
Hi everyone

Im facing a problem. I am not able to understand the push pull configuration in this schematic. When I make this circuit on the breadboard, the circuit works till the PWM generator and doesn't work after the BJT, mostly there is a SC in this circuit even if connected properly. If i remove the 3 BJTs and attach the PWM straight to the mosfet,. the circuit works. But i need to have a drive circuit for the Mosfet and I've been told that this push pull drive circuit is good.

Please tell me why it is not working and some solutions to improve this drive circuit or any other options, EXCEPT using a microcontroller.
 

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alec_t

Well-Known Member
Most Helpful Member
The push-pull circuit as shown works fine in a simulation. If the PNP and NPN transistors are swapped around, however, then there's a short circuit (as you would expect).
I think there must be a wrong connection somewhere on the breadboard. Have you confirmed the connections and pin-outs of the BJTs ?
 

SgtWook

New Member
Gee, we went through this circuit in a good bit of detail with you on the other site a week or two ago. I'm attaching an image of the simulation, but I replaced the timing cap with one that's 10nF to get the freq up to ~900Hz; 100nF was just too slow.

What are you using for the transistors? If you don't have 9012 and 9013's, you can use 2N2222 and 2N2907's.

Are you absolutely certain that you have identified the pins on the transistors correctly? This is a very common mistake for people to make. Some datasheets show the pins from the bottom of the package, which can lead to a great deal of confusion.

If you are uncertain, then tell us what is the actual part numbers of the transistors that you are using.
 

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