Electronics World articles Popular Electronics articles QST articles Radio & TV News articles Radio-Craft articles Radio-Electronics articles Short Wave Craft articles Wireless World articles Google Search of RF Cafe website Sitemap Electronics Equations Mathematics Equations Equations physics Manufacturers & distributors Engineer Jobs LinkedIn Crosswords Engineering Humor Kirt's Cogitations RF Engineering Quizzes Notable Quotes Calculators Education Engineering Magazine Articles Engineering software RF Cafe Archives RF Cascade Workbook 2018 RF Symbols for Visio - Word Advertising RF Cafe Forums Magazine Sponsor RF Cafe RF Electronics Symbols for Visio RF Electronics Symbols for Office Word RF Electronics Stencils for Visio Sponsor Links Saturday Evening Post NEETS EW Radar Handbook Microwave Museum About RF Cafe Aegis Power Systems Anritsu Alliance Test Equipment Amplifier Solutions Anatech Electronics Axiom Test Equipment Berkeley Nucleonics Bittele Centric RF Conduct RF Copper Mountain Technologies Empower RF everything RF Exodus Advanced Communications Innovative Power Products ISOTEC KR Filters Lotus Systems PCB Directory Rigol RF Superstore San Francisco Circuits Reactel RFCT TotalTemp Technologies Triad RF Systems Windfreak Technologies Withwave LadyBug Technologies Wireless Telecom Group Sponsorship Rates RF Cafe Software Resources Vintage Magazines Thank you for visiting RF Cafe!

P channel Power MOSFET - RF Cafe Forums

RF Cafe Forums closed its virtual doors in 2010 mainly due to other social media platforms dominating public commenting venues. RF Cafe Forums began sometime around August of 2003 and was quite well-attended for many years. By 2010, Facebook and Twitter were overwhelmingly dominating online personal interaction, and RF Cafe Forums activity dropped off precipitously. Regardless, there are still lots of great posts in the archive that ware worth looking at. Below are the old forum threads, including responses to the original posts.

NOTICE: The original RF Cafe Forum is available again for reading, and the new RF Cafe Blog is an active board.

-- Amateur Radio

-- Anecdotes, Gripes, & Humor

-- Antennas

-- CAE, CAD, & Software

-- Circuits & Components

-- Employment & Interviews

-- Miscellany

-- Swap Shop

-- Systems

-- Test & Measurement

-- Webmaster


Post subject: P channel Power MOSFET Posted: Wed Jun 10, 2009 12:32 am


Joined: Mon May 04, 2009 6:47 pm

Posts: 22

Hi, there. Can someone suggest a p channel power mosfet I need such one to switch +28VDC rail max current of 2A. The MOSFET is controlled by a open drain output comparator, which is 5VDC powered. As I can see, the max IGS of the MOSFET needs to be larger than +/- 25VDC. I have checked onsemi and found nothing meet my requirement.




Post subject: Re: P channel Power MOSFETPosted: Fri Jun 12, 2009 2:20 pm


Joined: Mon Apr 20, 2009 2:04 pm

Posts: 14


I don't think you'll find a MOSFET with such a high gate punch through, but that's not the end of the world, you just need to modify the circuit slightly.

I'd send you a picture, but I don't know how to get it across... SO, here goes a way to describe what you need:


1. (1) Q1, MMBT3906 (or other NPN)

2. (1) Q2, FDD8685 (or similar P-MOSFET)

3. (1) R1, 2.2K, 1/10W, 5%

4. (1) R2, 2.7K, 1/10W, 5%


R1, Comparitor_out, NPN_Emitter

Q1, (E)NPN_Emitter, (B)+5V, (C)MOSFET_Gate

R2, MOSFET_Gate, +28V

Q2, (S) +28V, (G) MOSFET_Gate, (D) Switched_28V

I hope this isn't too much a mess, communicating it by net list. Also, this circuit is only valid for slow switching. If you need something in the kHz, this won't get it because the MOSFET turns on & off very slowly.

If you need something fast, post it, and I'll give you something a little more complicated + faster.

- Mike



Post subject: Re: P channel Power MOSFETPosted: Fri Jun 12, 2009 6:27 pm


Joined: Mon Apr 20, 2009 2:04 pm

Posts: 14


Q1 should be MMBT 3904 (the NPN version!)


R2 should be 4.7K

I plead old age....



Post subject: Re: P channel Power MOSFETPosted: Tue Jun 16, 2009 9:39 pm


Joined: Mon May 04, 2009 6:47 pm

Posts: 22

Thanks a lot, Mike. This is a good solution but the logic is reversed to my application so a NOT gate is needed to fix the logic, or maybe connect comparator output to base and emitter to GND.

Is it possible to control P-channel MOSFET gate by a N-channel FET? I found some N-channel FEt with 30VDC VDS however max VDG is not specified . I wonder why VDG is not important.

Posted  11/12/2012

Anatech Electronics - RF Cafe
Holzworth RF Synthesizers
Amplifier Solutions Corporation (ASC) - RF Cafe
TotalTemp Technologies (Thermal Platforms) - RF Cafe
Copper Mountain Technologies (VNA) - RF Cafe

Please Support RF Cafe by purchasing my  ridiculously low−priced products, all of which I created.

These Are Available for Free


About RF Cafe

Kirt Blattenberger - RF Cafe Webmaster

Copyright: 1996 - 2024


    Kirt Blattenberger,


RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.

My Hobby Website: