MOSFETs for switching application

Discussion in 'The Projects Forum' started by verydexter, Jul 25, 2014.

  1. verydexter

    Thread Starter New Member

    Jul 25, 2014
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    I have generated two signals using fpga and want to drive MOSFET switches using these signals such that the output generated is a single signal with the first signal having voltage level +10V and the second signal -10V.
    I have attached the picture of the signals and the circuit I have designed. As I have never used MOSFETs before in any circuits, I want you guys to help me with this. Please tell me whether the way NMOS and PMOS have been connected is right or not and also, how should their gates be driven (Should I use a high side and low side driver and give the fpga outputs to them and which one would guys suggest)?
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Below is a circuit that does what you want, if I understand your requirements. I used two BJTs to generate the proper gate polarity signals for the two MOSFETs.

    You didn't mention the pulse width of the signal or the output load, so I just guessed on that. You showed an input pulse voltage of 1.2v min. so that's what I used. The circuit values shown are for a relatively low speed circuit. You just need to pick the MOSFET for the load current and supply voltage (at least 3 times the supply or 30V). Note that there can be a significant shoot-through current when both transistors switch. You may want to put a small resistors in series with the source or drain of one of the MOSFETs to minimize this.

    Driver.gif
     
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  3. Experimentonomen

    Member

    Feb 16, 2011
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    20k pulldowns, UGH those fets are not gonna last long.
     
  4. crutschow

    Expert

    Mar 14, 2008
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    Depends entirely on his pulse rate and load, which he didn't specify.
     
  5. verydexter

    Thread Starter New Member

    Jul 25, 2014
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    This circuit wont be used for driving any huge loads as such. I am just going to connect a resistor as load and it can be as low as 100 ohm. Plus the frequency of the signals is going to be in multiples of 1k Hz.
     
  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Just make sure there is a small period (~10us) after Signal1 turns off before Signal2 turns on..
     
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  7. Experimentonomen

    Member

    Feb 16, 2011
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    Yup, called deadtime.
     
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  8. verydexter

    Thread Starter New Member

    Jul 25, 2014
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    @crutschow : Thank you for the circuit! Because I have been looking for drivers for a long time now. Can I just use an already available high side and low side driver for driving the MOSFETs? I want to know your views about drivers?
     
  9. crutschow

    Expert

    Mar 14, 2008
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    Typically the drivers are used with a single positive power supply. I don't know of any that are designed to drive from a negative supply with a positive signal.
     
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