Drive P Channel Mosfet Using 8051

[gauravkothari23]

Hi all.
I am trying to Drive a 5V Solonied using 8051
Circuit Attached.
The gate of the Mosfet is not getting low. when i keep the mosfet OFF, it shows 5V at gate, but when i try to ON the mosfet using microcontroller 89S52, the voltage hardly drops to 3V, due to which my solonied does not gets active.

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I am using 2 NPN Transistors to drive the Mosfet, because i need to invert the data.
when the system reset initially, all the port pins of microcontroller get high, so i dont want the solonied to get active at this stage.

 

[KlausST]

Hi.

My recommendations:
* use low side switching (easiest. Logic level N-CH)
* or use high side power switch
* or use one of the countless proven circuits given here in this forum and even more in the internet.

your circuit:
* no need to invert nor for a third transistor. Just use a pullup at the port pin.
* show (supply) voltages in the schematic
Every voltage measurement needs two points. When no other informatin is given then the voltage is meant to refer to GND.
Thus I assume when you say "gate voltage" you mean "gate to GND voltage".
But this is not how a MOSFET works. It switches ON/OFF by the value of "gate to source voltage"

Drawing a schematic:
* signal (information) flow is left to right
* top are positive (supply) voltages
* bottom are negative and GND voltages
* add all informations for the function to the schematic (like supply voltage)
This makes schematics more easy to read... and no need to switch between text and picture.

Klaus