How to use P- and N-channel Mosfet as switches

fixation · 9th March 2007, 01:28 PM

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.

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

richie00boy · 9th March 2007, 01:35 PM

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.

CBS240 · 9th March 2007, 04:14 PM

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.

ilimzn · 9th March 2007, 04:15 PM

...remembering that the maximum gate potential is 20V for most MOSFETs. Working as a swuitch comes naturally to MOSFETs

jackinnj · 9th March 2007, 04:51 PM

You can use something like this although you will have to change the values to real-world

fixation · 9th March 2007, 06:05 PM

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

Upupa Epops · 9th March 2007, 07:43 PM

All that solution isn't so easy, how do you think...probably will arise something, which will be more comlicated than " guarded " amp...

9th March 2007, 01:28 PM	#1
fixation diyAudio Member Join Date: Feb 2005 Location: Netherlands	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. 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

9th March 2007, 01:35 PM	#2
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	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. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

9th March 2007, 04:14 PM	#3
CBS240 diyAudio Member Join Date: Aug 2005 Location: K-town	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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9th March 2007, 04:15 PM	#4
ilimzn diyAudio Member Join Date: Feb 2005 Location: Zagreb	...remembering that the maximum gate potential is 20V for most MOSFETs. Working as a swuitch comes naturally to MOSFETs

9th March 2007, 06:05 PM	#6
fixation diyAudio Member Join Date: Feb 2005 Location: Netherlands	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

9th March 2007, 07:43 PM	#7
Upupa Epops diyAudio Member Join Date: Aug 2003 Location: Prague,Czech Republic	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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