UC3842 Test Circuit

By on August 27, 2007



uc3842 test circuit

UC3842 IC can be easily found in most of the electronic equipment switching power supply. Normally whenever the power fet shorted, chances are very high that the uc3842 pulse width modulation (PWM) IC may shorted too. Although sometime you can use your meter to measure certain pins of this ic to confirm whether it works or not , i found it to be not accurate. I personally had tested some of the defective UC3842 IC where it tested good with meter but failed when on load (in circuit). In order to fully test this IC you may visit this website that talks about building your own UC3842 IC test circuit.

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36 Comments

  1. Manjunath

    September 14, 2009 at 5:43 pm

    Can you please give me the circuit that generates Triggering Pulses to the power circuit using IC3842.?

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  2. admin

    September 14, 2009 at 7:51 pm

    Hi Manju,

    Sorry i do not have such circuit.

    Jestine

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  3. Thomas

    April 22, 2010 at 7:52 am

    Hi Jestine,
    Do you have any switch mode power supply circuit using UC3843A ?

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  4. admin

    April 22, 2010 at 8:59 am

    HI Thomas,

    Try this link:

    http://electro-tech.narod.ru/schematics/power/comp/atx/sunny_atx230.gif

    Jestine

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  5. syed

    July 23, 2010 at 12:03 pm

    hi yong
    i "syed hussaini" is very glad to know that there is a community of elctronics repairers because i myself being an "ec eng" and would like to be apart of it as i am having more than 25 years of expereiance in this feild and been repairing many types of devices
    so it will be very useful site for me
    thank you

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  6. admin

    July 23, 2010 at 7:52 pm

    HI Syed,

    Welcome to my blog and you can visit http://www.electronicrepairguide.com to become ERG member and it is free.

    Jestine

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  7. manjula

    October 6, 2010 at 3:19 am

    power supply diagram using uc3842 ic

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  8. manjula

    October 6, 2010 at 3:22 am

    please send me online 6kva circuit diagram

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  9. admin

    October 6, 2010 at 7:32 am

    HI Manjula,

    Sorry i do not have such diagram.

    Jestine

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  10. admin

    October 6, 2010 at 7:33 am

    HI Manjula,

    Try here:

    http://www.alldatasheet.com/view.jsp?Searchword=UC3842

    Jestine

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  11. imran

    November 26, 2010 at 11:31 am

    give me induction hiting and furnas curcit camplit

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  12. admin

    November 29, 2010 at 8:43 pm

    Hi Imran,

    Sorry i do not have such circuit.

    Jestine

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  13. rouie

    January 27, 2011 at 3:26 am

    Hi,

    I bought something, its a electric carving pen, at first it was working fine, but after a day, something exploded inside, when I checked it, it was a uc3842 IC that exploded, can there be an explanation why did it exploded, a big chunk of it where the number was printed is the one that popped out.. and where can I buy this IC, and have it replaced..

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  14. admin

    January 27, 2011 at 9:00 am

    HI Rouie,

    There can be many reason why the power ic blown. It can be the design problem or the quality of the ic not good. This ic can be easily found in any electronics shop.

    Jestine

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  15. markos pachoyndakis

    February 11, 2011 at 5:19 am

    very usefull thanks

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  16. laksh

    April 28, 2011 at 1:22 am

    i want the information about uc 3842 and also the circuit of the uc 3842 for the smps input 24vdc to 45vdc ,2amp.

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  17. admin

    April 28, 2011 at 8:07 am

    HI Laksh,

    Sorry i do not have those circuit.

    Jestine

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  18. alireza

    May 4, 2011 at 8:33 am

    hi ,where i can find SMD components data sheets ?
    do you know any website that help me to find SMD datasheets ?
    tanks a lot !

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  19. admin

    May 4, 2011 at 9:50 am

    HI Alireza,

    Try:

    http://www.marsport.org.uk/smd/mainframe.htm

    Jestine

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  20. Alejandro flores gomez

    September 5, 2011 at 10:25 pm

    for 10 year ago idont worked in electronic but now
    is a new opotunity to me to fix a very diferent equipment
    i dont remember mi englihs all the divices are very small

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  21. sebastiao evora

    July 20, 2012 at 2:49 pm

    I want to know whether the more equivalent of this ic

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    • Jestine Yong

      July 21, 2012 at 11:51 pm

      Hi Sebastiao,

      Since this IC is easily get from the market thus you do need need to find the equivalent number. There are IP3842, HA17834, SG3842 and etc.

      Jestine

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  22. Alex Halter

    July 30, 2012 at 7:34 am

    Hi, can 3842 be used as pwm speed controller for motors? And do you have any links on how to implement that? Your response will be highly appreciated. Thank you!

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    • Jestine Yong

      July 30, 2012 at 10:04 pm

      Hi Alex,

      Sorry no info on that. As far as i know they are mainly use in the power section or any circuit that requires a continuous pulse like in boost circuit.

      Jestine

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  23. oleg

    October 6, 2012 at 8:43 am

    Excuse me for my bad English!!! I'll try to corrects some mistakes:
    Hi Jestine, I need somebody explains how the following power supply works:  http://electro-tech.narod.ru/schematics/power/comp/atx/sunny_atx230.gif
    I 'm troubleshooting a very similar atx power supply, exactly KY-500ATX model from MaxPower. 5 VSB and 5V ps-on are present, but ps wont start. There is no VCC (zero volt) at pin 7 of UC3842 PWM since 16-17V needed for pwm startup, neither VREF at pin 5. I also has been checked that IC Voltage supervisor  activates a 5V Fault Protection Ouput (FPO) at pin3 and zero Volt PGO at pin 8 of LP-7510.
     
    What can be the problem? Why there is not VCC at UC3842? Why LP-7510 indicates a over/under voltage protection condition? (Shotky rectifiers at secondary seems to be ok and output filters too) How the ps-on circuit works?
     
    Please refers to http://electro-tech.narod.ru/schematics/power/comp/atx/sunny_atx230.gif for better understanding what i am talking about…
     
    Help me please!!
    best regards,
    Oleg. 

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    • Jestine Yong

      October 6, 2012 at 11:25 pm

      Hi Oleg,

      PS ON will cause IC6 PIN 3 to go low thus causing the opto LED to conduct and this in turn will also cause the transistor in IC3 to conduct too. Once IC3 conducts Q2 also will conduct thus allowing supply voltage from D16 to pass through Q2 and turn on the power ic1 through the supply pin 7. This means you have to check all the components from IC6 till pin 7 of IC1. Sometimes if IC1 is shorted or leaky it can also pull down the supply voltage.

      Jestine
      http://www.JestineYong.com

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  24. oleg

    October 9, 2012 at 8:35 am

    Thanks you very much Jestine!!! I really high apreciate your answer because i am a beginner in electronic repairing.
    I took another identical working power supply and swapped a lot of main components one by one. Components extracted from failure power supply worked fine in the other. Also extracted components from the good working power supply were placed in the failure ps with no results, so we can say that the following components were tested and fine:
    IC1 (UC3842), IC2 e IC3 (Optos), IC6 (LP-7510), D16 (FR diode), Q1, Q2, T1, Tl431 and other small bipolar transistors in the secondary.
    After reading your message i will check also D3 and R41.
    I'm thinking that the power supply starts and inmediately stops by protects itself.
    Could be a bad secondary electrolitic capacitors? There are practically the unique components that i not tested yet.
    I will try the D3, R41 and seciondary filters.
    Regards,
    Oleg.

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    • Jestine Yong

      October 11, 2012 at 7:47 am

      Hi Oleg,
      Yes it can be any component includes the electrolytic capacitor. The opto has to get signal from the ic otherwise the primary side ic will not function.

      Jestine

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  25. oleg

    October 13, 2012 at 10:04 am

    Hi Jestine!

    Definetively i need your SMPS repair ebook, but i have no way to buy it, i am a cuban engineer and here there is not way to pay online. Could you help me please with some free materials about atx power supply repair??? The materials i founded on the web are very basic troubleshootings techniques and not going deeper in other problems i founded on atx smps like regulation voltage problems, over or under voltage protection, to high standby voltage, etc, no drive signals on PWMs or supervisor, etc

    Please, help me with something you can.

    I'll really high appreciate it.
    Regards,
    Oleg.

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    • Jestine Yong

      October 15, 2012 at 9:11 pm

      Hi Oleg,

      You can use try use western union or money gram servicesor even bank transfer. As for the atx power supply repair you can try this link:

      http://www.repairfaq.org/sam/smpsfaq.htm

      Jestine

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  26. lee

    October 14, 2012 at 1:43 am

    please..! Can you tell me about Verror of UC3842 ???thank

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    • Jestine Yong

      October 15, 2012 at 1:42 am

      Hi lee,

      Could you elaborate the meaning of verror?

      Jestine

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  27. Lee

    October 15, 2012 at 10:47 am

    Verror-you search datasheet of IC UC 3842 ,it will help you show .!
    Do you have schematic buck-boost use Ic uc3842?
    I have a project : power converter
    in put : 9-19V use buck-boost converter with ic uc 3842
    out put: 12V-4A
    Can you give me schematic buck-boost with ic uc 3842 ?

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    • Jestine Yong

      October 15, 2012 at 10:08 pm

      Hi Lee,

      Sorry i do not have buck boost schematic.

      Jestine

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  28. oleg

    October 20, 2012 at 8:37 am

    Hi Jesting!
    Thanks for the suggested link, but i already readed it. It is very useful link but no covers all the true cases i founded in the real world. Also thanks by suggestions on the ways to buy your ebook, but neither are suitables for me. Keep in mind that i need abut 3 months of working to complete thats money. Also Western Union here is to receive, not to send money. Thanks any way.
    Well, talking about my similar Sunny ATX-230  power supply the problems is that the output voltages are to high. I shorted the FPO 3rd pin of LP7510 to ground an then the PS started. When measured the output voltages were as following: 12V altered to 17V, 3,3V altered to 6,6 and 5V altered to 7V. That's the cause why PS start, then stops.
    Any idea? Any Suggestion?
    Thanks in advance,
    Oleg.
     
     

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    • Jestine Yong

      October 22, 2012 at 10:26 pm

      Hi oleg,

      You can use bank transfer if you need the ebooks. In your case of high voltage check the components surrounding the secondary side of optoisolator IC especially resistor that will turn into high ohm.

      Jestine

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