High side or low side?

Discussion in 'General Electronics Chat' started by gagakseto, Mar 19, 2011.

  1. gagakseto

    Thread Starter New Member

    Mar 19, 2011
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    Hello All,

    I'm new here so please be gentle:)
    My first question, what is the consideration in using MOSFET switching in high side switch or low side switch? is it depend on the load? what is the advantage or disadvantage. For example if I have a heater, both should be able to be PWMed using high side or low side config of MOSFET, which one is better? the other also solenoid it should be able both config, what should be considered here then?

    Many thanks
     
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    N-channel or P-channel? Have you studied the difference? P-channel is usually easier high-side; N-channel low-side.

    John
     
  3. nigelwright7557

    Senior Member

    May 10, 2008
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    Low side is usually easier to drive.
    High side usually needs a chip or transistors to translate the voltages.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    It's usually easier to switch on the low-side using an N-channel MOSFET.
    But, if you get into higher voltages (say, over 40 or so) you'd want to use an N-channel MOSFET on the high side with a high-side driver IC. That way, when the MOSFET is off, power is removed from the load instead of the ground.
     
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  5. gagakseto

    Thread Starter New Member

    Mar 19, 2011
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    Yes I know the difference. Which one better, hi-side or lo-side switching ? given that you aren't restricted to use N or P-channel nor the cost budget. Is the hi-side (with protection) safer for the load for example?
     
  6. jpanhalt

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    Jan 18, 2008
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    Tell us what you are doing. High-side can be very useful in applications where you have an airplane or car or accessories thereto with negative ground, for example.

    John
     
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  7. gagakseto

    Thread Starter New Member

    Mar 19, 2011
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    Thanks SgtWookie! your explanation enlighten me, it answers my question
     
  8. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    A high side switch is, when the load is between the mosfet and ground.

    A low side switch is, when the mosfet is between the load and ground.

    N-channel low side is the easiest to configure. All the gate needs to switch on is +10V or for logic level mosfet +5V.

    A N-channel high side has to have the gate at +10V or +5V for logic level above the source voltage when turned on.

    A P-channel has to be has to have a -10V signal to turn on.

    As long as your heater or solenoid has a + and - connection on it (two wires) it can be wired as a high or low side device. Some things only have a single wire connection(the body or frame is the negative/ground) They have to be wired as a high side. Unless the body or frame can be isolated from the rest of the circuit.
     
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  9. gagakseto

    Thread Starter New Member

    Mar 19, 2011
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    Doing nothing actually. Just wondering around some schematic of car heater. It is a low side switched. Could you please explain how useful high side with negative ground in car or airplane? thanks
     
  10. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    It only takes one wire to control the device. See post #8 too.

    In other situations, think of high-side as sourcing, low-side as sinking. Wiring an SCR with the gate switched low-side would be very difficult compared to switching it high side.

    John
     
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