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p channel mosfet with n channel mosfets

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qwertyqwq

Member
hello there .

Is there any specific method to make a p type mosfet with using n type mosfets(like IRF520 ) ?
Running low with p types :D

Many kinds. :)
 

qwertyqwq

Member
You can use an N-fet in the negative rail, and mirror the rest of the circuit. But better to post here the schematic.
Like this one ..
index.png
 

DerStrom8

Super Moderator
As kubeek said, you can use an N-channel on the negative rail to do the same thing:

120087

C9 is not strictly necessary, it's just there for protection.
 

crutschow

Well-Known Member
Most Helpful Member
Your p-channel mosfet is installed (drawn) backwards. Source pin should be on the positive rail.
Nope.
The MOSFETs used for reverse-polarity protection normally conduct in the reverse direction, (the direction of the substrate diode) since MOSFETs conduct equally well in both directions when biased ON, and block when the polarity is reversed (MOSFET biased in the normal direction).

Make sense?

Note that as long as the supply voltage is less than the Vgs(max) value (typically 20V), you don't need the Zener from source to drain.
 

DerStrom8

Super Moderator
Nope.
The MOSFETs used for reverse-polarity protection normally conduct in the reverse direction, (the direction of the substrate diode) since MOSFETs conduct equally well in both directions when biased ON, and block when the polarity is reversed (MOSFET biased in the normal direction).

Make sense?

Note that as long as the supply voltage is less than the Vgs(max) value (typically 20V), you don't need the Zener from source to drain.
Correct. If the source was connected to the positive rail then the intrinsic body diode of the FET would conduct in the reverse direction and render the reverse-polarity protection useless.
 

gophert

Well-Known Member
Most Helpful Member
Nope.
The MOSFETs used for reverse-polarity protection normally conduct in the reverse direction, (the direction of the substrate diode) since MOSFETs conduct equally well in both directions when biased ON, and block when the polarity is reversed (MOSFET biased in the normal direction).

Make sense?

Note that as long as the supply voltage is less than the Vgs(max) value (typically 20V), you don't need the Zener from source to drain.

I missed post 3. Thanks.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Your p-channel mosfet is installed (drawn) backwards. Source pin should be on the positive rail.

Gophert is correct - the way that circuit is drawn, the anode of the FET body diode is connected (via the load or resistor and zener) to battery positive.

It will never turn anything off, just vary the voltage drop slightly.
 

alec_t

Well-Known Member
Most Helpful Member
It will never turn anything off
It will if the supply is connected with reverse polarity. The whole point of the circuit is reverse-polarity protection.
 
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