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I have a circuit which is used to control dc motor. PWM is configured to work with 10 kHz frequency. Each time when the duty cycle is set to 100%, the transitor is rather cold, but any other configurations like duty cycle set to e.g. 80% makes transistor very hot. I'm wondering is it something usual and using radiator will be enough to dispate heat? Or maybe I'm doing something wrong?

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  • \$\begingroup\$ Please add a freewheeling diode across your motor. \$\endgroup\$
    – winny
    Commented Jun 25, 2020 at 7:50
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    \$\begingroup\$ At 100% the transistor is never switching. \$\endgroup\$
    – user16324
    Commented Jun 25, 2020 at 9:23

2 Answers 2

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Why have you left pin 6 of the TC4420 disconnected? Data sheet circuit: -

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Your circuit: -

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My addition in red shows that you need to have a reverse diode across the motor to prevent back emfs from damaging Q1.

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  • \$\begingroup\$ I added diode and now it works perfectly. \$\endgroup\$
    – bielu000
    Commented Jun 25, 2020 at 8:09
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Put a reverse biased diode across the motor to dissipate the inductive flyback spike. The transistor is doing that at the moment and that could be leading to your heating problem.

The transistor is not designed to do this and it could lead to failure of the transistor.

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  • \$\begingroup\$ I added diode and now it works perfectly. Thank you :) \$\endgroup\$
    – bielu000
    Commented Jun 25, 2020 at 8:09

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