I am building a basic bldc controller, using tc4427 as mosfet driver. I some how ended up burning the IC and now I am planing to control the mosfet from bc547 transistor. It worked perfectly fine for N channel mosfet (IRFZ44N), but it is not working as expected for P channel mosfet (IRF9540). I have attached the circuit of bc547. The problem is P channel mosfet never turns off, there is drop of 4 voltage ( 12v at source, 8 volt at gate of mosfet, when bc 547 turned off that is 0v at base) at the collector terminal of bc547 which is making VGS of mosfet negative and it will always be on. Can anyone suggest me a solution...?? ( I am using Arduino as microcontroller)

 

The problem is P channel mosfet never turns off, there is drop of 4 voltage ( 12v at source, 8 volt at gate of mosfet, when bc 547 turned off that is 0v at base)

The MOSFET gate voltage should obviously be equal to the supply voltage (12V) when the bc547 is off, so there appears to be a circuit wiring error somewhere.

Double-check all the connections, especially that the MOSFET package pinout is correct.

 

Thanks for the reply, I drew the diagram and attached it...and I also varified the wire connection but the problem remains the same..
I found the similar problem here https://forum.arduino.cc/t/p-channel-mosfet-is-always-on/696417

 

What happens is you remove the BC547 completely?

 

The problem is P channel mosfet never turns off, there is drop of 4 voltage

Sounds like the mosfet or BC547 is installed incorrectly. You can change the base resistor to 4.7K on the BC547.

 

When the pins on a transistor are reversed then the turned off transistor conducts like an 8V zener diode.
American 2Nxxxx little transistors have ouns EBC but European BCxxx little transistors are CBE.

 

Sounds like the BC547 transistor is the wrong way round, what happens if you remove the BC transistor and just pulse the gate down to ground and let it stand alone with the resistor across the G and S terminals?

 

Sounds like the BC547 transistor is the wrong way round, what happens if you remove the BC transistor and just pulse the gate down to ground and let it stand alone with the resistor across the G and S terminals?

I think the 12v applied at the source will burn out the microcontroller I am using....

 

I think the 12v applied at the source will burn out the microcontroller I am using....

You're not understanding me, we're try to work out why your fet is not turning off, so as a temporary measure just wire the fet up without the BC transistor and no microcontroller, and see if it turns off, then you can add the BC transistor the right way round.

 

You're not understanding me, we're try to work out why your fet is not turning off, so as a temporary measure just wire the fet up without the BC transistor and no microcontroller, and see if it turns off, then you can add the BC transistor the right way round.

Yeah I tried it...and MOSFET works as expected..it turned off

 

Yeah I tried it...and MOSFET works as expected..it turned off

So this proves that the BC transistor is in the wrong way..