p channel mosfet with n channel mosfets

[qwertyqwq]

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

Many kinds.

 

[kubeek]

Not possible. What exact circuit are you trying to hack?

 

[qwertyqwq]

It 's a reverse voltage protection circuit.

 

[kubeek]

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

 

[qwertyqwq]

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 ..

 

[DerStrom8]

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

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

 

[gophert]

Like this one ..
View attachment 120081

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

 

[crutschow]

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]

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]

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]

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]

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.

 

[rjenkinsgb]

It will if the supply is connected with reverse polarity. The whole point of the circuit is reverse-polarity protection.

Doh... I was confusing it with the "low voltage shutdown" thread & not paying attention to the actual details.