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Old 9th March 2007, 01:28 PM   #1
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Default How to use P- and N-channel Mosfet as switches

hello everybody,

im my amplifier I want to use mosfet to disconnect the powersupply lines in case of an error, this error could be DC-fault, temp fault etc. I have an ATmega which will be controlling the Amplifier.

Normally this would be done with relays but i don't like the "clicking noise" they make.

So i would like to try a different approach by using mosfets as a switch.

Click the image to open in full size.

can someone please tell me how i should connect them? What i would like is that A and B will be replaced with a mosfet + additional components ( level shifter etc)

which mosfet needs to be where and how do i connect them?

Best Regards Fixation
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Old 9th March 2007, 01:35 PM   #2
Did it Himself
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Either use n-channel for both and isolated gate drivers, or p-channel in the +ve line and n-channel in the -ve line and refer the gate drive to ground.
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Old 9th March 2007, 04:14 PM   #3
CBS240 is offline CBS240  United States
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I would think you want to choose fets with lowest Rds on, and placed in the circuit after the filter caps. Totem pole driven N-channels? IRFZ44 is a cheapie, used in low voltage(hi current) SMPS switch.

All the trouble I've ever been in started out as fun......
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Old 9th March 2007, 04:15 PM   #4
ilimzn is offline ilimzn  Croatia
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...remembering that the maximum gate potential is 20V for most MOSFETs. Working as a swuitch comes naturally to MOSFETs
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Old 9th March 2007, 04:51 PM   #5
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You can use something like this although you will have to change the values to real-world
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Old 9th March 2007, 06:05 PM   #6
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I think i will go with the n-channels with isolated gate drivers.
If i would put another small transformer in my amplifer which could power an MAX621 which power for example an IRF540

.. does that mean that it is isolated from the rest of the circuit?

Could i use the MAX621( High side driver ) for +ve line?
and do i need to get a Low side driver for the -ve line? or could i use a High Side driver here aswell?

the mosfet will be placed after the capacitator bank as CBS240 said

@jackinjj: Your circuit looks good but it uses 2 mosfet. the problem is that I want to use this circuit for 7 channels.. which means that i should use 28 mosfet....

i'd rather go with a solution that uses some IC's
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Old 9th March 2007, 07:43 PM   #7
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All that solution isn't so easy, how do you think...probably will arise something, which will be more comlicated than " guarded " amp...
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