Up to what frequency can an N channel Mosfet turn something on and off?

Discussion in 'General Electronics Chat' started by kavkav, Jan 6, 2013.

  1. kavkav

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    Jan 1, 2013
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    I'm building a high frequency amplifier using a common emitter amplifer setup. I want to use an N channel Mosfet as my switch but I wan to know if it can handle a frequency range of 1MHz to 3MHz without sacrificing anything like duty cycle and etc. Thanks.
     
  2. bertus

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  3. crutschow

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    Mar 14, 2008
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    The speed of a MOSFET switch is usually limited by how fast you can charge and discharge the large gate capacitance to turn it on and off. The intrinsic speed of the MOSFET is quite fast. To ease your drive requirements use a MOSFET with a current rating no more than about 25% above you maximum switching current and look for one with the lowest total gate charge (which is the amount of charge you need to add or remove to turn the transistor on and off). But you will still need to use a high current gate driver circuit to minimize the switching speed.
     
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  4. kavkav

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  5. bertus

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  6. Ron H

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    Give us more details about what you're wanting to switch.
     
  7. SPQR

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    Nov 4, 2011
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    I'm asking this question out of ignorance.
    What type of signal are you amplifying?
     
  8. kavkav

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    Jan 1, 2013
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    Okay so your saying I have to add a capacitor at the gate and the switching speed depends on speed of charge and discharge of the capacitor. Does that mean I have to use the time ratio formula which is dependent on capacitance? Also, what would happen if I didn't add a capacitor, and just had my signal directly hitting the gate?

    You mention that I require high current for the gate in order to minimize switching speed. If I want a high switching speed does that mean a lower current would achieve this? Thanks
     
  9. kavkav

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    Jan 1, 2013
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  10. kavkav

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    Jan 1, 2013
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    I have an experiment that I've done on small scale. It worked and all is good but now I want to make the experiment on larger scale. The signal is a DC pulsed frequency ranging from 1MHz to 3MHz. I'm using a function generator to produce the pulse and to activate the gate of the mosfet.

    Now all I need is a 100 watt power supply or a couple high voltage batteries which I'm having trouble finding.
     
  11. Ron H

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    Your first post mentioned
    . Common emitter amplifiers are made using BJTs, not MOSFETs. Perhaps you meant "common source amplifier"?
     
  12. kavkav

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    Jan 1, 2013
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    This is the set up I was referring to. I guess I'm not quite sure what it's called. Basically, I want a transistor or anything suitable that would act as a switch by making its resistance zero or very high and controlling that "transistor switch" using a signal from my function generator allowing the high DC voltage from the circuit to pulse itself according to the signal from the function generator. This would be an amplified version of the pulse from my function generator. I am amateur with circuits so I'm all ears if there's an easier way to do this. Also as a side note, my amplified pulse will be one amp max but the lower the current the better as long as I have a minimum of 100 volts and at least 80 watts of power. I will then feed it to a step up transformer for very high voltage with negligible current.
     
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