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I would like to drive a mosfet on and off with a waveform generator. Nevertheless I would like to estimate the time it takes for turning off and on the MOSFET. I did not find the output current capabilities of this device. I supposed the output current capabilites are low. Here is the datasheet.

If someone has an idea of what are the output capabilities of a waveform generator it would be nice.

JRE
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Jess
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  • Why my question has received a minus "-1" ? It may be unclear ? Not appropriate ? In any case, it would be nice to know :) – Jess Aug 17 '20 at 07:37
  • Thank you ! I did not notice as the datasheet that I found on this link is in english. I am sorry ! – Jess Aug 17 '20 at 08:12

2 Answers2

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According to the datasheet you linked to (see page 4,) the output impedance is 50 ohms:

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The MOSFET will act as though there were a 50 ohm resistor between the signal generator output and the gate. That is, you use the gate capacitance and 50 ohms to calculate how fast the MOSFET can switch.

This question and its answers give tips on calculating the switching time.

JRE
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  • So it means the output power capabilities are higher when the voltage output is higher ? So if I want to turn on quickly the mosfet, I should apply a high voltage waveform (the maximum Vgs that the mosfet can withstand). It means that if I set 10V i would have 200 mA. – Jess Aug 17 '20 at 09:45
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    You would have 200mA, if the gate started at 0V yes. As the gate charges, the voltage difference will (of course) change which also changes the current. – JRE Aug 17 '20 at 09:48
  • Thank you very much :) – Jess Aug 17 '20 at 09:56
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It takes almost "no" current to turn a MOSFET on. Your waveform generator will be able to control almost any MOSFET.

You need to know the turn-on (threshold) voltage of the MOSFET you have in mind. If you get a "logic level" device, you can probably skip this step.

The speed of turn on/off will depend on the MOSFET. You need to know its input gate capacitance. The bigger the capacitance, the slower the switching speed.

To pick a MOSFET, you need to have an idea of what your load is (current? Voltage?)

Kyle B
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  • Thank you for your answer :) The switching speed depends on the input capacity, but if I am able to charge faster the capacity, the time for turning on the mosfet will be reduced. In general, the input capacity is proportional to the size of the MOSFET and I am not able to reduce the size of the MOSFET, so I actually not able to change a lot the input capacity of my MOSFET. So it is interesting to know what is the output current capabilities of the waveform generator. – Jess Aug 17 '20 at 07:41
  • @Kyleb: The switching time depends on how fast you can charge or discharge the gate capacitance. How fast that happens depends on the impedance of the signal driving the gate. – JRE Aug 17 '20 at 08:36
  • @JRE Of course the output impedance matters. It's an RC circuit. But this is a fixed output impedance, yes? Because he's settled on the waveform generator. But hadn't settled on the MOSFET. So the the only "variable" in this particular RC circuit is the "C". And that's a characteristic of the MOSFET. And specifically there was no indication of current requirements so the nature of the MOSFET wasn't specified. – Kyle B Aug 17 '20 at 13:30