3
\$\begingroup\$

I'm looking to control a 12v/2A circuit from a Raspberry Pi but I'm a little lost on what I need to get to operate it.

I was looking at the following but with a IRLZ44NPBF transistor and a in4004 diode from CPC as I can't find the right PN2222 or in4003 in the UK.

enter image description here

Would I be along the right lines?

\$\endgroup\$

2 Answers 2

1
\$\begingroup\$

Yes, that should work, except that you can lose R1 since MOSFETs are voltage-controlled, not current controlled. Just make sure you get the drain-source polarity right, due to the parasitic diode. And since RPi GPIOs are push-pull outputs, you can probably lose R2 as well (although this will increase turn-off time and power usage just a bit).

The diode change is not a problem either, since the new diode will only have a higher voltage rating as its primary difference.

\$\endgroup\$
3
  • \$\begingroup\$ Perfect! Thanks very much. It's all new to me so it's nice to hear that will work. \$\endgroup\$
    – MrNorm
    Oct 14, 2013 at 11:23
  • 1
    \$\begingroup\$ +1, but isn't IRLZ44NPBF too powerful and with too big gate capacitance in order to be controlled by a uC output? For 2A@12V some less powerful MOSFET IMO is better. \$\endgroup\$
    – johnfound
    Oct 14, 2013 at 11:27
  • \$\begingroup\$ Well, you'd need a slightly lower PWM frequency, but the gate capacitance is still only about 2nF. \$\endgroup\$ Oct 14, 2013 at 11:29
1
\$\begingroup\$

This will most probably work.

Note that the performance (RDSon) of an IRLZ44 is specified at 5 and 4 Volt. The RaPi I/O pins are at 3.3 V. With some allowance for the output buffers and the resistors you could assume 3V at the gate. At the low (for an IRLZ44) current level of 2A this won't be a problem (check fig. 1 in the datasheet) but don't try a gate level this low with higher currents.

Definitely keep R2, otherwise your FET might be fried when the RaPi pin is high-impedance (= configured as input, as it is at startup).

\$\endgroup\$
1
  • \$\begingroup\$ OK thanks. Better to be safe than sorry. I'll get that ordered up also. I don't have the rep to vote this up but when I do I will come back :) \$\endgroup\$
    – MrNorm
    Oct 15, 2013 at 7:10

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.