Thank you for visiting RF Cafe! Electronics World Cover,TOC,and list of posted Popular Electronics articles QST Radio & TV News Radio-Craft Radio-Electronics Short Wave Craft Wireless World About RF Cafe RF Cafe Homepage RF Cafe in Morse Code Google Search of RF Cafe website Sitemap Electronics Equations Mathematics Equations Equations physics Manufacturers & distributors Engineer Jobs Twitter LinkedIn Crosswords Engineering Humor Kirt's Cogitations Engineering Event Calendar RF Engineering Quizzes AN/MPN-14 Radar 5CCG Notable Quotes App Notes Calculators Education Magazines Software,T-Shirts,Coffee Mugs Articles - submitted by RF Cafe visitors Simulators Technical Writings RF Cafe Archives Test Notes Wireless System Designer RF Stencils for Visio Shapes for Word Search RF Cafe Sitemap Advertising Facebook RF Cafe Forums RF Cafe Homepage Thank you for visiting RF Cafe!

Switching Negative Supply Line Using Positive Control - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement


jom
Post subject: Switching Negative Supply line using Positive control Posted: Mon Aug 27, 2007 4:52 pm

Captain


Joined: Fri Jan 26, 2007 2:40 am
Posts: 14
OK, I've got this problem where I have to turn be able to control power to sections of my board during TX or RX mode. For example lets say I've got a +5V supply that runs to some Op Amps. Some are used in TX mode and some are used in RX mode but that they aren't on all at the same time. We've used a control line (coming from a PIC, 0 to 3 V) to drive a NMOS Fet which in turn drives current thru a gate resistor of a PMOS device to either open or short the PMOS to connect the +5V line to the Op Amps. We repeat this circuit for TX and RX.

That works fine for a +5V but what about the -5V? The first problem is the control line, which is too high a voltage to switch a Fet. I obviously have to level shift but I can't seem to get any fet to drive completely ON since I also have the problem in that I don't have access to a voltage lower than -5V.

I've tried to run a search on the net for this but I keep coming up with "Switching power supplies" or some such. Any idea what this kind of problem is called? That might help my search.

Thanks

jom


Top

madengr
Post subject: Posted: Tue Sep 11, 2007 5:14 pm

Captain


Joined: Fri Feb 02, 2007 5:22 pm
Posts: 5
Location: Overland Park, KS
How about 3V uC drives gate of open collector inverter or buffer.

Buffer drives gate of PMOS. Drain of PMOS is at 5V. Gate of PMOS pulled to drain via 1k.

Source of PMOS tied to gate of NMOS. Source of NMOS tied to -5V. Gate of NMOS pulled down to source via 1k. Drain of NMOS drives load.

I have used this configuration to gate-switch large GaAs FETs and it works well.









Posted  11/12/2012

RF Cafe Software

   Wireless System Designer - RF Cafe
Wireless System Designer

RF & EE Symbols Word
RF Stencils for Visio
Calculator Workbook
RF Workbench
Smith Chartâ„¢ for Visio
Smith Chartâ„¢ for Excel

About RF Cafe

Kirt Blattenberger - RF Cafe WebmasterCopyright
1996 - 2022
Webmaster:
Kirt Blattenberger,
 BSEE - KB3UON

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 Internet was still largely an unknown entity at the time and not much was available in the form of WYSIWYG ...

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:
 AirplanesAndRockets.com

Try Using SEARCH
to Find What You Need. 
There are 1,000s of Pages Indexed on RF Cafe !

height-line