High side switch or low side switch

Discussion in 'General Electronics Chat' started by bug13, Jul 20, 2013.

  1. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
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    38
    hi guys

    I want to switch a mini RC servo off when it is not use in order to save power, should I use a high side switch or low side switch? I have tried low side switch, and haven't tried high side switch (as I don't have a P MOSFET at the moment).

    the low side switch seen to do weird thing. I haven't given much thought about these two different switch until I need to use it. Do I do something wrong here?

    Thanks guys!

    edit: according to the datasheet, at 3.3V gate voltage, the mosfet should give enough current to the for the servo.

    [​IMG]
     
  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    The low side is easier. But you have 6V available, why not use a driver and turn on a logic level mosfet fully? When you get away from the rated Vgs you will need a bigger heatsink for the mosfet. Because it will be operating in the resistive/linear region.
     
  3. bug13

    Thread Starter Well-Known Member

    Feb 13, 2012
    1,208
    38
    So function wise, there is no different for my application here(high side or low side)? My circuit works fine until I added a low side switch, and the servo seen to do weird thing that I don't expect it to do.

    I think I can get away without a heatsink but a reasonable copper pour, as my servo will only operate for 4-5 seconds then it will be at idle/switched off, that's my ideal anyway, is there any flaws?

    The reason that I don't want to use a mosfet driver is I want to maximize standby time/minimize standby current consumption. Do I still better off adding a mosfet driver? My goal is to have a standby current < 1mA.
     
  4. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    A high side switch definitely needs a driver of some sort. It needs to supply Vgs and drain voltage to work. A driver uses very little 'standby' current. Have a look at driver data sheets, there are many out there.
     
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