RIGOL Technologies (test equipment) - RF Cafe
Berkeley Nucleonics Academy RF Boot Camp - 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 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:

AirplanesAndRockets.com

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 App Notes Calculators Education Engineering magazine articles Engineering software Engineering smorgasbord RF Cafe Archives RF Cascade Workbook 2018 RF Symbols for Visio - Word Advertising RF Cafe Homepage Thank you for visiting RF Cafe!
everythingRF RF & Microwave Parts Database (h2) - RF Cafe

Resistor combos - 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. If the folks at phpBB would release a version with integrated sign-in from the major social media platforms, I would resurrect the RF Cafe Forums, but until then it is probably not worth the effort. 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
-- Anecdotes, Gripes & Humor
-- Antennas
-- CAE, CAD, & Software
-- Circuits & Components
-- Employment & Interviews
-- Miscellany
-- Swap Shop
-- Systems
-- Test & Measurement
-- Webmaster

Guest
Post subject: Resistor combos
Unread postPosted: Sat Jan 01, 2005 10:57 am

I need to combine a couple 1% resistors to make a nonstandard value. For power dissipation in the resistors, is it best to use series resistors or parallel resistors? Thanks.

:lol:


Top


garylsmith2k
Post subject: Resistor power dissapation
Unread postPosted: Sun Jan 02, 2005 4:09 pm
Offline
Captain

Joined: Sun Oct 31, 2004 3:01 pm
Posts: 5
Location: N/A
Parallel.

_________________
Cheers,
Gary Smith


Top
Profile

Guest
Post subject:
Unread postPosted: Wed Jan 05, 2005 7:24 am

no, Smith answer is wrong because it is incomplete.

In general it does not matter whether you use a series or parallel circuit, but you need to use resistors that are equal or almost equal to obtain an equal distribution of the total power over all components. This is alo the best strategy to obtain optimal tolerance improvement.


Top


Kirt Blattenberger
Post subject:
Unread postPosted: Wed Jan 05, 2005 9:41 am
Offline
Site Admin
User avatar

Joined: Sun Aug 03, 2003 2:02 pm
Posts: 308
Location: Erie, PA
Total power dissipation in the series/parallel resistor combinations is going to be the same for a given equivalent resistance. The only difference is how the power dissipation will be distributed between the resistors. Depending upon the combination(s), one resistor can dissipate nearly all the power while the other(s) dissipate very little. Using values as close to equal as possilbe will keep the power distribution nearly equal.

Based on Ohm's Law, power dissipation is proportional (or inversely proportional) to resistance, so in a series combination, the power dissipation in the larger resistor will be greatest (same I through all resistors and P=I^2*R, so larger R dissipates higher power), and in a parallel combination the power dissipation in the smaller resistor will be greatest (same voltage across all resistors and P=V^2/R, so smaller R dissipates greatest power).

One last comment. With series combinations, the closest you can get to some exact non-standard value is equal to the number of significant places in the nominal resistance value and the available stanrd values. For instance, if you need exactly 37.5 ohms, then for 5% values the closest you can get with a series combination is within +/0.5 ohms (22+15=37, 22+16=38 ). Using a parallel combination of two 75 ohm resistors gets you right on. Theoretically, any degree of precision can be obtained with enough parallel resistors, but not with series.

- Kirt Blattenberger :smt024



Posted  11/12/2012
RF Superstore (RF Components) - RF Cafe
withwave microwave devices - RF Cafe
Axiom Test Equipment - RF Cafe
 

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

These Are Available for Free