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UPdated circuit

This circuit is intended to use a 1-10Hz PWM signal as input and produce a 1-10kHz 10A PWM output. It will be used for controlling the speed of a water pump: GP1352 The PCB will be ordered with (only) SMB components pre-assembled and will be potted once the SW has been commissioned. Thus keeping the heat low is important. I can only order the PCB with 1oz copper so heat from the traces is a concern as well. Therefore I am using 4 MOSFET's even though 1 should be able to power the pump alone. This way I plan to spread the heat generation out across the board to avoid hot spots. (The potting will be as thin as possible to allow the greatest heat transfer) The desire for low heat goes hand in hand with driving the pump to its full capacity as well.

I could explain the calculations and data sheet lookups I've used to arrive at this design, but the question would get very long and I think my intentions are clear from the description and the schematic. If anything was unclear I will elaborate in the comments.

So, how can I modify this circuit to better achieve my goal?

PS: This is my first electronic circuit design. Apologies in advance for the newbness, I'm doing my best.

Schematic updated 20191001 based on input from Brian Drummond and The Photon.

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  • \$\begingroup\$ 3 questions : 1) Why are you using a high side switch? 2) Why choose NMOS devices for your high side switch? 3) How do the gate drivers generate the correct drive voltage for an NMOS high side switch with no bootstrap connection? \$\endgroup\$ – Brian Drummond Sep 30 at 15:59
  • \$\begingroup\$ On a lot of PICs the RA3 pin is input-only: this may be the case on your MCU, too. Be sure to check it. \$\endgroup\$ – anrieff Sep 30 at 16:01
  • \$\begingroup\$ @anrieff Thanks, you're right. I had the datasheet for the 220 instead of the 320 for some reason. On the 220 it was RA2 \$\endgroup\$ – K0ICHI Sep 30 at 16:11
  • \$\begingroup\$ Another possible issue: depending on the type of motor in the pump, running it at reduced voltage might be bad for operating life. But I don't know anything about pumps and what kind of motors are used in them. \$\endgroup\$ – The Photon Sep 30 at 16:12
  • \$\begingroup\$ @Brian Drummond 1) 2) That was a mistake. I meant to make it a low side NMOS. Does that answer 3) also? \$\endgroup\$ – K0ICHI Sep 30 at 16:14
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One major problem: IRS44273L is a low-side gate driver IC, but you are trying to use it to drive high-side FETs. Your chip doesn't have any boost circuit to provide a gate drive above VCC like you need for an efficient high-side drive.

However, as other comments point out, there doesn't seem to be any reason you shouldn't control your pumps with a low-side switch instead of high-side.

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