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I have put together a variable pulsed DC signal using a 555 timer IC. I want to control an IRFP460 MOSFET so that I can drive high-current loads. I have found a circuit for a MOSFET driver in one of GreatScott's videos; the circuit is at 9:55.

my 555 varible ic controller

The 555 timer needs to:

  • have a variable frequency of 1 to 80 Hz;
  • be able to control the duty cycle from 10% to 50%.

All the videos on YouTube and posts on forums are about switching a MOSFET at 50 kHz or more. I was wondering if I need a gate driver circuit for the low-frequency task that I have.

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2 Answers 2

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So i was wondering do i need a gate driver circuit for low frequency task that i have

Probably not at 80 Hz.

If you are switching some very high load or are chasing very high efficiency, it might be needed. But with moderate load and no strict efficiency requirement, it is likely that the 555 output is fully sufficient to drive the MOSFET gate.

You should add a series resistor to the gate to limit the inrush-current though, so you don't damage the 555 output with the fairly high input capacitance of the IRFP460.

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  • \$\begingroup\$ Mosfet needs to switch 100V - 350V and up to 7A of current \$\endgroup\$ Feb 5, 2022 at 14:40
  • \$\begingroup\$ @WannaBeEngineer With 7A load, the MOSFET might get somewhat warm. I'd recommend you to simply try. If the MOSFET gets too hot, you could add a heatsink or in worst case, add proper gate driving. But since 555's typically can drive like 200 mA, the switching time won't be terribly long anyways so I'm guessing it won't be any problems. \$\endgroup\$
    – Klas-Kenny
    Feb 5, 2022 at 14:46
  • \$\begingroup\$ Ok i will try with 200ohm resistor between output of 555 timer and gate with a zener diode between gate and ground and 10k Ohm resitor as pull down \$\endgroup\$ Feb 5, 2022 at 15:00
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Mosfet needs to switch 100V - 350V and up to 7A of current

I think you may need to have a good think about your choice of MOSFET: -

enter image description here

At 7 amps, it will drop about 1.7 volts between drain and source and dissipate nearly 12 watts of heat. This will cause it to warm (even on a heatsink) and, as it warms, the volt-drop increases. Here's what the volt drop might be around 150°C: -

enter image description here

At this high limit of temperature, the device will be dissipating about 29 watts so, you definitely need a substantial heatsink if you are to avoid it warming up to it's limiting temperature.

And, bear in mind that the junction temperature will be significantly higher than the case temperature and it is the junction temperature limit of 150°C that is to be avoided. That fact and the thermal resistance from junction to case imply to me that you need quite a sizable heatsink.

For instance, if we draw a line between the 12 watt power dissipated at 25°C and the 29 watts at 150°C then we might expect it to have to dissipate 20 watts at around a case temperature of 90°C.

So, given that the local ambient temperature around the heatsink may rise up to around 50°C, the heatsink itself will have to have a thermal resistance that is better than (90 - 50)/20 °C per watt. That equals 2 °C/watt.

So I was wondering do I need a gate driver circuit for low frequency task that I have

It's unlikely that you will need one but, that isn't your big problem as far as I can tell.

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  • \$\begingroup\$ Andy Aka thank you for your answer. I am not concerned abaut heat because i have designed a very good water cooled system. \$\endgroup\$ Feb 5, 2022 at 15:12
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    \$\begingroup\$ @WannaBeEngineer Still, I wonder why you're using an IRFP460 instead of something like a UF3C065040, or something else with significantly lower on resistance. You're wasting a lot of power in your transistor here. \$\endgroup\$
    – Hearth
    Feb 5, 2022 at 15:27

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