6
\$\begingroup\$

The new processors are all 3.3V and dropping. So while I am used to 5V arduinos being able to power the gate of a MOSFET, at least most of the way, this is not going to be true any more. And for an IRF630, someone pointed out that I really need to drive the gate to 10V to get the rated on-resistance. So what's the canonical way to do this? Do I have a 10V power supply, and drop the voltage for the processor, have a charge pump that generates the 10V from 3.3V? The current will be very small, because the gate has massive impedance.

Finally, assuming the 10V power supply, what's a good way to switch that voltage to the gate? Do I have to use a small junction transistor because I don't have the voltage to switch a MOSFET?

The junction transistor is shown in this solution: Multiplying the voltage of an output pin on an Arduino board

I'm just asking if there is another way.

\$\endgroup\$
  • 1
    \$\begingroup\$ The general integrated solution to control power MOSFETs is a "mosfet driver", e.g. linear.com/product/LTC1156 (although that one isn't precisely suitable for you as it won't run on 3.3V) \$\endgroup\$ – pjc50 May 22 '16 at 9:56
  • \$\begingroup\$ You ask this as if there's one-size-fits-all solution to this. Well, there isn't. If there was no voltage but the 3.3 V I'd make a charge pump (possibly using one of the uC's outputs as a clock for that) to make the 10 V. Feed that 10 V with a resistor to teh MOSFET's gate. Use a small NMOS to short that gate to ground to switch it off. Control small NMOS's gate from uC. But this wil not work up to very high switching speeds. That's the price of a simple solution. \$\endgroup\$ – Bimpelrekkie May 22 '16 at 9:58
  • 1
    \$\begingroup\$ MOSFETs can have significant current into / out of the gate during switching, depending on the device (and a 10V gate drive requriement might well be associated with a power device). \$\endgroup\$ – Peter Smith May 22 '16 at 11:52
16
\$\begingroup\$

Three options.

  1. Use a mosfet with a VGS compatible with 3.3V. Typically known as a logic level mosfet.

  2. Use a simple npn transistor as a switch to drive the mosfet at a higher voltage. Logic would be inverted.

  3. Use a dedicated mosfet driver IC.

\$\endgroup\$
9
\$\begingroup\$

Assuming you only have 3.3V available, that your MCU can supply at least 1mA thru the gpios, and that your application does not require more than 10A, I would use a N mosfet compatible with 3.3V.

For example the PMV16XNR has an On-Resistance of only 20 mOhm when powering the gate at only 3V, and can source a bit more than 6A. There are many other compatible MOSFETS.

Just be careful to add a resistor from your gpio to the gate, so the current spikes when switching the mosfet are not too large. For the PMV16XNR I use 500 Ohm resistors before the gate so the spikes are 6mA and the maximum switching frequency is somewhere near 300 KHz.

If using this option remember also to put a large resistor from the gate to ground, so it is powered off if gpio is floating.

If you need a much bigger MOSFET, then a mosfet driver or a charge pump could be necessary.

If you tell us your application and more details, maybe we can help you better.

\$\endgroup\$
5
\$\begingroup\$

For P-channel FETs, another option is to use a combination N/P MOSFET device. These have both P and N FETs built into the same pacakge. The P can be used as the high-side switch and the N can be driven at 3.3V to turn the P on/off. For example, SI4559ADY-T1-E3.

\$\endgroup\$
1
\$\begingroup\$

I've been using the NPN MOSFET AO3400 with a Rds(at Vgs = 2.5V) < 52mΩ with good results. They can be bought cheaply (100 pieces for less than 3 dollars) online from aliexpress or ebay. There is also the PNP MOSFET AO3401 with Rds(at Vgs =-2.5V) < 85mΩ for high side switching. The AO3401 is also useful for reverse polarity protection.

\$\endgroup\$
  • \$\begingroup\$ that would be n-channel, and p-channel, right... \$\endgroup\$ – Dov Feb 14 at 20:31
  • \$\begingroup\$ Yes, since these are MOSFETs I should have said N-channel Enhanced and P-Channel Enhance. \$\endgroup\$ – tst Feb 18 at 16:30

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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