Motor Control with P-Channel MOSFET

Using Arduino Motors, Mechanics, Power and CNC
1

Hello,

I recently started learning about electronics and have been doing some tutorials to further my knowledge.

I have a setup as in the following picture.

I used a TIP120 and a IRF9520 with the same resistor values.

The circuit works and I can control the motor but I can't get the potential between the gate and source to go to 0v. It goes down to about 0.15v when i activate the TIP.

Can someone shed some light on this and offer suggestions to improve the circuit?

Thanks

2

Yes, that's VCE - You can't get absolute 0.
You may get closer to Gnd using a FET in place of Q1.

or more base current (a value lower than 10K between PIC signal and Base)

3

Ok so basically the TIP120 when open has a bit of resistance which is dividing the voltage at the gate?

Can I add a restistor in paralell with the IRF9520 to divide the voltage there and make Vgs negative?

4

straycurrent:
Ok so basically the TIP120 when open has a bit of resistance which is dividing the voltage at the gate?

When the transistor is on, it doesn't go perfectly to a no resistance state. When it's off, it's not infinite ohms, but a very high resistance.

You should try a 2N3904 instead of the TIP120, you don't need a Darlington to trip a FET gate.
Try 1k - 5k for the base resistor.

[I think that you should have some low-value resistor between the Gate and the transistor, too (100?).]

Optimally, you should look for a FET Driver (MIC4426, et al.)

5

Thanks for the help. I also used a BC547 transistor in place of the TIP120.

What would be a good way of lowering the voltage to the IRF9520 source?

I want to try to add another motor controlled by an M-channel MOSFET and use the same control signal the P-channel MOSFET is using so the motors in opposite states when switched. I tried doing this already but because the gate voltage only goes to 0.15v the other motor stays on the whole time as I alternate the control signal from 0v to 5v.

6

You're bandying about terms and such inaccurately, I think.
Please sketch out what it is you're doing.
(Pencil to paper, take a picture of that, post/attach it.)