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Why not directly drive only with the low-pass filter? (FYI, this circuit is for constant current load)

enter image description here

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  • \$\begingroup\$ This question is related to Arduino Nano's PWM pin with driving power MOSFET. What's the problem with u @Juraj? \$\endgroup\$
    – user58029
    Commented Jan 20, 2019 at 7:56
  • \$\begingroup\$ Origin: instructables.com/id/DIY-Adjustable-Constant-Load-Current-Power Answer: youtu.be/VwCHtwskzLA?t=334 \$\endgroup\$
    – Jot
    Commented Jan 20, 2019 at 8:06
  • \$\begingroup\$ @Jot , Thanks for ur reference but there's no answer for PWM in those links, FYI. \$\endgroup\$
    – user58029
    Commented Jan 20, 2019 at 8:09
  • \$\begingroup\$ you can use the IRLZ44N instead, it work at 3.3v... \$\endgroup\$
    – dandavis
    Commented Jan 22, 2019 at 17:35
  • \$\begingroup\$ @dandavis , Thanks for ur info, but IRLZ44N has a bit of inferior characteristics compared to IRFZ44N. And I already concluded that in this case TC4420 is not required in driving IRFZ44N. Plz refer to my comment on the following Jot's post. \$\endgroup\$
    – user58029
    Commented Jan 26, 2019 at 8:15

2 Answers 2

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A mosfet driver is often required, but in this case it is not needed. Without the mosfet driver and with other values for the RC-filter it will also work.

The gate of a mosfet act as a capacitor. For PWM signals a mosfet driver can put enough current into the gate, so the mosfet turns on and off very fast. That reduces the heat dissipation of the mosfet.

Most mosfets are turned completely on with a voltage of about 9 V at the gate. The Arduino boards can not output that voltage. A mosfet driver can be used for higher voltages for the gate of the mosfet.

For Arduino projects, often "logic level" mosfets are used. They are already turned on at 5 V or even at 3.3 V. A resistor from the Arduino board to the gate of the mosfet should be used to limit the peak currents (because the gate acts as a capacitor).

The project of GreatScott! does not need to turn the mosfet fast on and off. The gate voltage is altered very slowly. The IRFZ44N mosfet is not a "logic level" mosfet, but the mosfet driver uses the low voltage of 5V, the same power voltage as the Arduino Nano.

The mosfet driver can be removed. The 10 Ω of the RC-filter is too low for the Arduino Nano, but a RC-filter with 470 Ω and 10 µF will do the same in my opinion. To protect the Arduino board, the 10 A fuse has to move to the high side (at VCC).

Because of the high currents of this project, the mosfet might blow. The mosfet driver provides extra protection in case that happens. The fuse is slow.

The "DIY Adjustable Constant Load (Current & Power)" project of GreatScott! at instructables: www.instructables.com/id/DIY-Adjustable-Constant-Load-Current-Power/
His explanation in the video about the mosfet driver: youtu.be/VwCHtwskzLA?t=334

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  • \$\begingroup\$ @user58029 I was still editing my answer, I have added the "extra protection" paragraph. Perhaps it is possible to put two mosfets parallel in case it blows too fast. \$\endgroup\$
    – Jot
    Commented Jan 20, 2019 at 8:47
  • \$\begingroup\$ So you mean that the intermediate mosfet is there for the extra protection in case of IRFZ44N's failure? \$\endgroup\$
    – user58029
    Commented Jan 20, 2019 at 8:47
  • \$\begingroup\$ Even though IRFZ44N blows, what's bad for arduino? \$\endgroup\$
    – user58029
    Commented Jan 20, 2019 at 8:48
  • \$\begingroup\$ @user58029 If a mosfet blows, anything can happen. Perhaps a high voltage will be pushed into the gate. I think that GreatScott! planned to use the mosfet driver with 12v, but later changed it to 5v, but kept it because his rc filter has a low value for the resistor. Perhaps splitting the resistor of the rc-filter into two, and with two clamping diodes, it offers the same protection as the mosfet driver. \$\endgroup\$
    – Jot
    Commented Jan 20, 2019 at 8:53
  • \$\begingroup\$ Can I have his phone number? I would like to ask him about his true intention for this intermediate mosfet. \$\endgroup\$
    – user58029
    Commented Jan 20, 2019 at 9:01
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I looked the .pdf file of this driver. The TC4420CPA driver output is Push-Pull. You do not need pull up or pull down the MOSFET gate when using it. Also has Latch-UP and ESD protection.

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