HOME  |  NEWS  |  BLOGS  |  MESSAGES  |  FEATURES  |  VIDEOS  |  WEBINARS  |  INDUSTRIES  |  FOCUS ON FUNDAMENTALS
  |  REGISTER  |  LOGIN  |  HELP
Feature
Electronics & Test

Measure Efficiency Quickly in Switching Power Supplies

NO RATINGS
1 saves
Page 1 / 3 Next >
View Comments: Newest First|Oldest First|Threaded View
William K.
User Rank
Platinum
Considering the noise, as well
William K.   10/14/2013 8:33:36 PM
NO RATINGS
This is an interesting and useful posting. But sometimes the readings from a noisy supply will be inacurate because of the noise on top of the DC output, and possibly on top of the input as well. An easy solution is to add filtering and read the voltage outside the filters. Usually the output voltage will be different with the noise filtered out, either higher or lower. Likewise the current, although it will usually be lower. This does reflect that noisy supplies are not as good as quieter ones.

ChuckMahoney
User Rank
Gold
non linear loads
ChuckMahoney   10/14/2013 11:06:32 AM
NO RATINGS
This article seems to ignore the fact that most (those without active PFC) AC-DC power supplies are non-linear loads, and therefore the traditional concept of power factor doesn't apply. Current drawn by a typical SMPS (like a computer power supply) is in phase with the voltage since the bulk filter caps charge at the peak of the voltage waveform. The resultant waveform is severly distorted however. This is not the case if the SMPS uses active power factor correction. 

For non-linear loads, make sure to use a wattmeter designed to measure distorted waveforms. You can check for distortion by measuring the Crest Factor of the waveform using a DMM that has a peak capture mode and can measure true RMS. A pure sinewave will have a crest factor (Peak/RMS ratio) of 1.414. Any variation greater or lower indicates distortion. Typical SMPS current draw waveforms will have a very high crest factor, generally around 5. This indicates the typical "peaky" current waveform when caps charge at the peak of the voltage waveform. [voltage waveform distortion - especially in SMPS - tend to have crest factors less than 1.414 due to voltage flattopping]

An SMPS with active PFC will have sinusoidal (well, very nearly sinusoidal) voltage and current waveforms, and they will be in phase so input power is simply VrmsxIrms.

j-allen
User Rank
Gold
Power supply efficiency
j-allen   10/14/2013 9:25:15 AM
NO RATINGS
If you need a wattmeter, an excellent and economical choice is the Weston 310 series.  These are the "Lab Standard" instruments in the mahogany cases rated at 1/4% accruacy.  Since they are electrodynamometers they measure true watts and they have no permanent magnets that can change strength over time.  You can check their calibration with DC using an accurate voltmeter and ammeter on the potential and current terminals, respectively, but it is best to flip polarity to check both ways.  

These instruments were very expensive when new (>$1000), but are now available quite cheaply on the used market.  And they are real works of art. 

Rob Spiegel
User Rank
Blogger
Efficiency always
Rob Spiegel   10/11/2013 10:48:49 AM
NO RATINGS
This is just one more example of increased efficiency in power supplier. It will be interesting to see the cumulative effect of efficiency gains in so many areas.

Partner Zone
Latest Analysis
A Frost & Sullivan study finds that increased cyber attacks are prompting a flurry of innovative protection tools.
Devices and interconnected systems are finding a foothold not only in our homes but in mainstream organizations. Here are three tips to mitigate the risk.
What makes this movie stand out from the typical high school sports story is that the teenagers are undocumented immigrants, and the big game is a NASA-sponsored marine robotics competition. Like many other Hollywood movies, however, Spare Parts only tells part of the story. What the film shows -- and doesnít show -- raises important issues affecting STEM education in the US.
Instead of sifting through huge amounts of technical data looking for answers to assembly problems, engineers can now benefit from 3M's new initiative -- 3M Assembly Solutions. The company has organized its wealth of adhesive and tape solutions into six typical application areas, making it easier to find the best products to solve their real-world assembly and bonding problems.
Load dump occurs when a discharged battery is disconnected while the alternator is generating current and other loads remain on the alternator circuit. If left alone, the electrical spikes and transients will be transmitted along the power line, leading to malfunctions in individual electronics/sensors or permanent damage to the vehicleís electronic system. Bottom line: An uncontrolled load dump threatens the overall safety and reliability of the vehicle.
More:Blogs|News
Design News Webinar Series
2/25/2015 11:00 a.m. California / 2:00 p.m. New York
12/11/2014 8:00 a.m. California / 11:00 a.m. New York
12/10/2014 8:00 a.m. California / 11:00 a.m. New York
3/31/2015 11:00 a.m. California / 2:00 p.m. New York
Quick Poll
The Continuing Education Center offers engineers an entirely new way to get the education they need to formulate next-generation solutions.
Mar 30 - Apr3, Getting Hands-On with Cypressí PSoC
SEMESTERS: 1  |  2  |  3  |  4  |  5  |  67


Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.
Learn More   |   Login   |   Archived Classes
Twitter Feed
Design News Twitter Feed
Like Us on Facebook

Sponsored Content

Technology Marketplace

Copyright © 2015 UBM Canon, A UBM company, All rights reserved. Privacy Policy | Terms of Service