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 Engineering smorgasbord RF Cafe Archives RF Cascade Workbook 2018 RF Symbols for Visio - Word Advertising RF Cafe Forums Magazine USAF Radr Shop Sponsor RF Cafe RF Electronics Symbols for Visio RF Electronics Symbols for Office Word RF Electronics Stencils for Visio Thank you for visiting RF Cafe!
Copper Mountain Technologies (VNA) - RF Cafe
Windfreak Technologies Frequency Synthesizers - RF Cafe
 

About RF Cafe

Kirt Blattenberger - RF Cafe Webmaster

Copyright: 1996 - 2024

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 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 typing 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:

AirplanesAndRockets.com

RIGOL Technologies (test equipment) - RF Cafe

Topspice simulation - experts advice needed - RF Cafe Forums

RF Cafe Forums closed its virtual doors in 2012 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.

-- Amateur Radio

-- Antennas

-- CAE, CAD, & Software

-- Circuits & Components

-- Employment & Interviews

-- Systems

-- Test & Measurement

balajisu
 Post subject: Topspice simulation - experts advice needed
Posted: Wed Aug 23, 2006 1:50 pm 
 
Colonel
User avatar

Joined: Wed Jul 06, 2005 5:54 pm

Posts: 31

Location: Germantown,MD

Simulating a Voltage Regulator spice model - Performing Transient analysis with Voltage regulator loaded with current source set with 20KHx pulse input. Voltage regulator is a fixed 5V regulator.

When I measure the regulator output after the simulation it seems to be stable.

When i load the regulator with a LPF and then run a similar simulation I see the regulator output to be ringing?

can anyone throw some light on whats happening in this situation?

Any help in this regard would be much appreciated

Thanks


 
   
 
fred47
 Post subject: TopSPICE & VR output ringing
Posted: Mon Aug 28, 2006 11:03 pm 
 
General
User avatar

Joined: Wed Feb 22, 2006 3:51 pm

Posts: 119

Hi!

There are two common structures for voltage regulators. In one, the output comes from the emitter of a transistor (NPN for a positive voltage, PNP for a negative voltage). In the other, the output comes from the collector of a transistor (PNP for a positive voltage, NPN for a negative voltage). The first one is more widely used, but the second is the structure of choice for LDO's (Low DropOut voltage regulators). These two behave rather differently, because feedback is more local for the emitter output, and more global (read "slower") for the collector output.

So it's important to know which style of regulator you have.

BJT's are often the active element of choice, due to die size considerations.

Also, just as in RF, the input impedance of your LPF (the one whose connection leads to ringing) is important - is it capacitive or inductive at the ringing frequency?

The oscillating emitter follower is a famous and rather widespread problem, so the simulator is probably not lying.

So let us hear more from you!

Good Luck,

Fred


 
   
 
balajisu
 Post subject:
Posted: Tue Aug 29, 2006 9:43 am 
 
Colonel
User avatar

Joined: Wed Jul 06, 2005 5:54 pm

Posts: 31

Location: Germantown,MD

Thanks Fred for all the inputs.

The regulator model that I have been using is a UA7805 fixed positive voltage regulator from TI. I believe it is a emitter follower. Not sure about the input impedance of the filter. Shall get back to you on this one.

Can you throw some light on why oscillations occur in a emitter follower?

Thanks for your time

Best regards

Balaji


 
   
 
balajisu
 Post subject:
Posted: Tue Aug 29, 2006 11:18 am 
 
Colonel
User avatar

Joined: Wed Jul 06, 2005 5:54 pm

Posts: 31

Location: Germantown,MD

Fred

The oscillation frequency of the ripples were at 25 - 30 MHz.

I looked at the S11 for the Filter ( 1MHz to 100 MHz), At the lower end it was inductive and moved over to capacitive. @ the oscillation frequency its looks like an open. Its more like a crossover point from being inductive to capacitive.

Looking forward for your feedback

regards

Balaji


 
   
 
fred47
 Post subject: Emitter Follower Oscillation
Posted: Fri Oct 20, 2006 2:57 pm 
 
General
User avatar

Joined: Wed Feb 22, 2006 3:51 pm

Posts: 119

Hi again!

Sorry for the delay - I got swamped at work.

Here's the best discussion I've found so far:

http://www.analogzone.com/col_1017.pdf

Let me know what you think!

Good luck,

Fred

Posted  11/12/2012

everythingRF RF & Microwave Parts Database (h1) - RF Cafe

RF Cafe Visitor Comments on News, Articles, System, Design, Components, etc.

Please e-mail your comment to me (Kirt B.), and I will post it here for you - no computers involved!

1 - Your participation will be greatly appreciated. - Kirt B.

KR Electronics (RF Filters) - RF Cafe
Windfreak Technologies Frequency Synthesizers - RF Cafe
 

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

These Are Available for Free