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The Importance Of Current Sense Resistor In Switch Mode Power Supply
Current sense resistor is usually located in the switch mode powersupply section. Newer version of monitor-the b+ (boost) circuitalso have this current sense resistor. If you repair electronicequipment especially the switch mode power supplies, the currentsensing resistor is connected to the source pin of power FET (fieldeffect transistor) and the other end to HOT GROUND. The value of current sense resistor is in the range of 0.1 ohm to about 1 ohm.The values are depends on the design of each power supply. In monitor power supply where pulse width modulation (pwm) ic UC3842are used. Pin 3 of this power ic is called I-sense which meanscurrent sense and this pin is connected to source pin of POWER FET.The purpose of this current sense circuit is for overcurrent protection.This circuit usually samples the voltage drop across a resistor in serieswith the switching fet transistor. If the current rises abnormally due tosome short circuit in the secondary side such as a shorted secondary diodeor horizontal output transistor (HOT), the voltage will exceed a referencelevel and shutdown the pulse generator which is the PWM ic. This circuitprovides protection to components in the event a problem occurs.In some cases where overload happen-the power section will blow and most of the time the components changed are fuse, power fet, pwm ic,zener diode and current sense resistor. Do you know that a small change in this current sense resistor valuehave a great impact on the secondary output? A little change in valuesay from 0.22 ohm to 0.44 ohm can caused your ouput voltage to dropinto half! I have seen a lot of repairer can't detect this type ofproblem (low output voltage) due to that they used analog or digitalmeter that don't have the low ohms range. You can't differentiate if the low ohms resistor has its value changed by using normal meters.I personally use the Dick Smith ESR Meter which have the capabilitiesto check resistor value down to 0.01 ohm! If you don't have this special meter you may just direct replace the current sense resistorto see if the generated secondary output will back to normal voltage. Another tip is that if the current sense resistor in the monitorB+ circuit have changed value it will caused the output in theboost circuit to become low and you will have a small width displayand of course the high voltage will become low as well. Instead of24Kv it becomes 15-18Kv. Jestine Yong is a electronic repairer and a writer. For more information on electronic repair please visit his website athttp://www.noahtec.com/electronic-repair-articles.htm
Latest News:Site: Yahoo! News Search Results for news JCDecaux in talks for News Outdoor Group in Russia (AP via Yahoo! News) French outdoor advertising firm JCDecaux SA said Thursday it is negotiating to buy Russian rival News Outdoor Group from global media company News Corp. JCDecaux and News Corp. in talks to combine outdoor ad groups (International Herald Tribune) The News Corp. chief executive, Rupert Murdoch, has recently expressed nervousness about investments in Russia, where News Outdoor generated the bulk of its revenue last year. News Corp tightens grip on Premiere with new CEO (Reuters via Yahoo! News) Rupert Murdoch tightened his grip on German pay-TV broadcaster Premiere by appointing News Corp executive Mark Williams as CEO in a move to get the company back on track. SEC Looks Into UAL Stock Scare; Implications For Online News? (paidContent.org via Yahoo! Finance) A ton of digits have been devoted to this in other spots but the SEC's decision to investigate takes it to another level. The backstory: a six-year-old news story about UAL declaring bankruptcy made it into the Tribune-owned Sun-Sentinel's current news flow, was picked up by a Google News bot and, via a reporter for a newsletter, made it onto Bloomberg News. News Corp says Mark Williams interim Premiere CEO (Reuters via Yahoo! News) News Corp. executive Mark Williams has taken over as chief executive of German pay-TV broadcaster Premiere in an interim capacity, News Corp. said after the move led to renewed takeover speculation. News Corp. says Mark Williams interim Premiere CEO (Reuters via Yahoo! News) Mark Williams, a News Corp. executive named late on Wednesday as chief executive of German pay-TV broadcaster Premiere, has taken over in an interim capacity, a News Corp. spokeswoman said on Thursday. JCDecaux in talks to buy News Corp. billboard unit (AP via Yahoo! Finance) In a deal that would create the world's largest outdoor advertising company, French conglomerate JCDecaux SA said Thursday that it is in talks to buy Russian rival News Outdoor Group from global media company News Corp. Weekly world news quiz (BBC News) At the end of another week, test your knowledge with our world news quiz. UPI NewsTrack Entertainment News (UPI) Kanye arrested in paparazzi scuffle ... Report: Critic smacked Ebert with binder ... Cafe Tacvba nominated for 6 Latin Grammys ... Groban to perform TV songs at Emmys ... News from United Press International. United shares climb after news debacle (UPI) CHICAGO, Sept. 11 (UPI) -- A computer program assigning dates to news stories was partly to blame for a sell-off of United Airlines stock Monday, a Google spokesman said. Site: news - Google News Palm Shares Soar As New Smartphone Wins Wall Street Praise - CNNMoney.com
MORE RESOURCES: Site: Yahoo! News Search Results for hardware IBM offers hardware-based encryption for x servers (SearchSecurity.com) IBM is calling its VAULT hardware-based encryption tool the first of its kind and says the price point should appeal to small and midmarket companies. Everything you want to know about the Zune 3.0 release and new hardware (ZDNet) I posted the news about the new Zune 3.0 software the other day, but if you want to learn all the details of the new Zune hardware, accessories, and Zune 3.0 update coming to you next week then check out Jason Dunn's detailed 6-page writeup on his recent visit to... Uganda: Hardware Guru Now Dares Music (AllAfrica.com) Phiona Natoolo a.k.a Phinato, 29, is one of the biggest businesswomen in Uganda's hardware business, owning several shops at Nakasero and Kansanga [Phinato Hardware]. 9/11/2008 Daily Hardware Reviews -- ATI Radeon HD 4670 Edition (AnandTech) DailyTech's roundup of hardware reviews from around the web for Thursday... Hardware store owner shot, abducted in QC (GMA News) MANNILA, Philippines - Unidentified armed men shot and abducted a 45-year-old hardware store owner in Quezon City Wednesday night, a radio report said early Thursday. US video game sales rise 9 percent in August (AP via Yahoo! News) U.S. sales of video game hardware and software rose 9 percent in August to $994.8 million, boosted by the popularity of the newly released "Madden NFL 09." Snazzy Microsoft mice happy hardware tale (Seattle Times) It's hard to compete with Steve Jobs announcing new iPods, but in a roomful of 100 journalists at Microsoft's computer-hardware launch event Wednesday in Seattle, I saw only a few tracking Jobs while Microsoft entertainment and devices boss Robbie Bach delivered his news Microsoft hardware rumors (IT World) There has been some buzz lately about Microsoft getting into the PC hardware business. There have been no announcements, although the Microsoft muckety-mucks have raised the possibility as part of a theoretical discussion. GotVoice Announces Voicemail Server Support for Service Providers, Voicemail Hardware Vendors and IVR Companies (Marketwire via Yahoo! Finance) GotVoice, Inc., the voice messaging company, today announced voicemail server support for service providers, voicemail hardware vendors and IVR companies. The company is publicizing its ability to retrieve voicemail from carriers and PBX installations without the need for upgrades or changes to existing systems for seamless voicemail-to-text and digital audio file integration. US video game sales rise 9 percent in August (San Francisco Chronicle) U.S. sales of video game hardware and software rose 9 percent in August to $994.8 million, boosted by the popularity of the newly released "Madden NFL 09." Americans bought $384.6 million in video game hardware, up 3 percent from a year ago, lead by sales of... Site: hardware - Google News New Classmate PC all about ?ecosystem? - ZDNet
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