2018-08-22 12:27 PM
I am connecting my GPIO pin of STM32F4 of discovery board to gate of N channel MOSFET and drain of this N channel drives gate of P channel Mosfet and source of P channel Mosfet with turn on my 5VDC devices. I have also connected 2K pull up resistor to Gate of P-channel and N channel other end of resistor is connected to 5VDC. I am using DMC2038LVT for P-channel and N-Channel Mosfet.
But I am unable to get 5VDC at output source of P channel. Please find GPIO initialization below.
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOB, ENABLE);
GPIO_InitStruct.GPIO_Pin = GPIO_Pin_5 ;
GPIO_InitStruct.GPIO_Mode = GPIO_Mode_OUT;
GPIO_InitStruct.GPIO_OType = GPIO_OType_PP;
GPIO_InitStruct.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_NOPULL;
GPIO_Init(GPIOB, &GPIO_InitStruct);
GPIO_ResetBits( GPIOB, GPIO_Pin_5);
Can someone help as to find why I am unable to get 5 V at source of P channel Mosfet
2018-08-22 03:45 PM
Do your fets open at 3.3V. That is what you get from STM32F. And do the other voltages make sense.
Besides, P-channel fet source must be at + (5V?) voltage and drain goes to devices using that voltage.
2018-08-22 04:01 PM
You would set the port pin with pull down resistor.
You would pull it hi to turn on the N-Channel,
The NChannel would pull down a 10K pullup connected to 5V
that same pin would drive the gate of the PChannel.
Yes, @LIM2 is correct, seems that you may have the Source and Drain reversed.
2018-08-23 09:09 AM
@LM12, you are right, my source of P channel Mosfet is connected 5VDC and drain is connected to all the devices that requires 5V.(Sorry I mentioned it as "SOURCE" in my earlier post) But is my initialization for GPIO pin is correct?