I want to drive the IRF9530 P-Channel FET with 5V PIC microcontroller. My load is 3.2A. schemtic shows one row in my LED matrix. Scanning @ 1/16th rate, so peak current per LED will be 64mA and the average will be 4mA. When one or two LEDs light up in a row, they are bright. However when more LEDs light up inthe same row, they are dimmer.
- Can the FET can supply require current with the given gate voltage?
- Is there any simple modification to be done within the given hardware, to supply the required current?
I cannot use another driving transistor to drive the FET (because I have a PCB). Also I cannot find logic level MOSFETs in my area.
Minor changes will be preferred.
Best Answer
Can the FET can supply require current with the given gate voltage?
Not really, you do not have a lot of voltage margin left.
From the left plot I can see that at \$I_D\$ = 3 A and \$V_{gs}\$ = -5 V the FET's \$V_{DS}\$ will be about -1 V.
That leaves 5 V - 1 V = 4 V for the LEDs + series resistor. If the LEDs actually have a 3 V forward voltage then this might just work but often LEDs do have a higher forward voltage especially White LEDs.
You could try to decrease the 27 ohms resistors such that you do get the required current. That will still not eliminate the 1 V drop across the MOSFET though.
This MOSFET is really better suited to a much higher \$V_{GS}\$ like 10 V as then the drop would be about 0.5 V, that's still a lot!
Also note that if you manage to get the 3 A and the MOSFET drops 1 V it will dissipate 3 W so it will get hot! It will need a heatsink!
You really need to consider using a "better" MOSFET with a much lower \$R_{DSon}\$, for example the AO3401. Since the 3.2 A is on the edge for this device I'd use 2 of them and let each power half of the LEDs.