P-Channel MOSFET for logic level drive

[Andrew Holme]

Can anyone recommend a small P-channel MOSFET suitable for 5V logic level
gate drive?

This is for an RS232-port-powered RS232 data output signal from a PIC.
Source will go to +5V, gate to a PIC output, and the drain is resistively
pulled-down to a negative rail. I did this years ago, but I can't remember
what MOSFET I used. Farnell don't seem to specify any of their P-channel
MOSFETs as being for logic level drive.

TIA
Andrew.

 

[Winfield Hill]

Andrew Holme wrote...

Can anyone recommend a small P-channel MOSFET suitable for 5V logic
level gate drive?

This is for an RS232-port-powered RS232 data output signal from a
PIC. Source will go to +5V, gate to a PIC output, and the drain is
resistively pulled-down to a negative rail. I did this years ago,
but I can't remember what MOSFET I used. Farnell don't seem to
specify any of their P-channel MOSFETs as being for logic level
drive.

There aren't many logic-level p-types to choose from. Supertex
has a few. Spehro Pefhany suggested the IRF7425, which has 13
mill-ohms Rds(on) (max) at -2.5V, 8.5 mill-ohms at 4.5 volts.
It's in an SO-8 package, about 85 cents US in 100's.

What are you looking for?

 

[Chris Carlen]

Can anyone recommend a small P-channel MOSFET suitable for 5V logic level
gate drive?

This is for an RS232-port-powered RS232 data output signal from a PIC.
Source will go to +5V, gate to a PIC output, and the drain is resistively
pulled-down to a negative rail. I did this years ago, but I can't remember
what MOSFET I used. Farnell don't seem to specify any of their P-channel
MOSFETs as being for logic level drive.

TIA
Andrew.

Fairchild FDV304P comes to mind.


--
_______________________________________________________________________
Christopher R. Carlen
Principal Laser/Optical Technologist
Sandia National Laboratories CA USA
[email protected]
NOTE, delete texts: "RemoveThis" and "BOGUS" from email address to reply.

 

[Spehro Pefhany]

Can anyone recommend a small P-channel MOSFET suitable for 5V logic level
gate drive?

This is for an RS232-port-powered RS232 data output signal from a PIC.
Source will go to +5V, gate to a PIC output, and the drain is resistively
pulled-down to a negative rail. I did this years ago, but I can't remember
what MOSFET I used. Farnell don't seem to specify any of their P-channel
MOSFETs as being for logic level drive.

TIA
Andrew.

Why don't you want to use a PNP BJT?

The BSS84 is one p-channel part spec'd at 5V.


Best regards,
Spehro Pefhany

 

[Joerg]

Hello Spehro,

Why don't you want to use a PNP BJT?

Yes, less cost.

The BSS84 is one p-channel part spec'd at 5V.

One of my favorite parts but only if it really has to be a FET.

Regards, Joerg

 

[Andrew Holme]

Andrew Holme wrote...

There aren't many logic-level p-types to choose from. Supertex
has a few. Spehro Pefhany suggested the IRF7425, which has 13
mill-ohms Rds(on) (max) at -2.5V, 8.5 mill-ohms at 4.5 volts.
It's in an SO-8 package, about 85 cents US in 100's.

What are you looking for?

It's a one-off hobby project (GPIB-->RS232 using PIC16F84). Up to a few
ohms would not be a problem for Rds(on), since the pull-down will be at
least 1k. Package wise, I would prefer not to go surface mount, but I can
handle them if necessary. I'll look at the IRF7425. Thanks.

 

[Andrew Holme]

Why don't you want to use a PNP BJT?

Yes, I could do. I was thinking of saving the base current, but then I
suppose it'll only be micro-amps.

The BSS84 is one p-channel part spec'd at 5V.

Thanks, I'll look at that part.

 

[Joerg]

Hello Andrew,

It's a one-off hobby project (GPIB-->RS232 using PIC16F84). Up to a few
ohms would not be a problem for Rds(on), since the pull-down will be at
least 1k. Package wise, I would prefer not to go surface mount, but I can
handle them if necessary. I'll look at the IRF7425. Thanks.

Then Spehro's suggestion (BSS84) should be the ticket. It's cheap.

Regards, Joerg

 

[Luhan Monat]

Can anyone recommend a small P-channel MOSFET suitable for 5V logic level
gate drive?

This is for an RS232-port-powered RS232 data output signal from a PIC.
Source will go to +5V, gate to a PIC output, and the drain is resistively
pulled-down to a negative rail. I did this years ago, but I can't remember
what MOSFET I used. Farnell don't seem to specify any of their P-channel
MOSFETs as being for logic level drive.

TIA
Andrew.

Screw the MOS Fet, use a 2n3906 pnp transistor...

http://members.cox.net/berniekm/spydar.gif

(See rs232 circiut in lower left)

 

[Chris Carlen]

It's a one-off hobby project (GPIB-->RS232 using PIC16F84). Up to a few
ohms would not be a problem for Rds(on), since the pull-down will be at
least 1k. Package wise, I would prefer not to go surface mount, but I can
handle them if necessary. I'll look at the IRF7425. Thanks.

Zetex also makes some PMOS in TO92 with <5V thresholds.


Good day!



--
_______________________________________________________________________
Christopher R. Carlen
Principal Laser/Optical Technologist
Sandia National Laboratories CA USA
[email protected]
NOTE, delete texts: "RemoveThis" and "BOGUS" from email address to reply.