PC SMPS schematics with IC 2003 and TL494

What would you do if you have got a couple broken Switch Mode Power Supplies, a screw driver and some curiosity!? Well obviously you would crack it open and try to figure it out. I have to admit, we would probably have opened them before they were even broke. That is exactly what I did.

[sc name="begin_of_toc"]

  • SMPS schematic using IC2003
  • SMPS schematic using IC KA7500
  • SMPS schematic using TL494 and LM339
  • Datasheets
  • Links
  • [sc name="end_of_toc"]

    When I had a couple of them lying around, I cracked them open and after a few days, fixed some of them. It was actually much easier done than said. But one bad thing about SMPS repairs is that there aren’t any good resources out there on the web. (OK may be there are, but I failed to find some). That is why I decided to make a series of posts with my repair notes, schematics and stuff I have learned through opening those bricks. Being the first post, this is the schematic post. You can grab the schematics available on the net here. Please send me a link if you have found a new schematic and I will add it here.

    The Schematics

    There are two circuits commonly available for PC ATX SMPS.

    • Based on IC2003
    • Based on KA7500
    • Based on TL494 and  LM339

    KA7500 and TL494 are pin to pin compatible PWM controllers. There are only minimal differences in their specs. The major difference being for the TI one TL494 DTC offset voltage is 0.1V where as for KA7500 it is 1.2V.

    Thanks goes to : http://electro-tech.narod.ru

    PC SMPS using IC2003

    SMPS schmatic using IC2003. The cheap Chinese SMPS uses a circuit based on IC2003. The EMI filter and output filters are usually left out, and the components heavily underrated. The schematic is hard to find, not drawn by me.

    This schematic along with the low quality parts is normally seen in Mercury branded SMPS. I have 6 of those lying around. All with blown caps and no EMI filter. EMI filters are not much of a concerns usually for ratings below 350W. But a good engineer /designer will always add an EMI filter.

    The manufacturer has omitted this along with output filter coils to cut costs.


    Here is an SMPS based on IC2003 after repairs. I found some inductors to add to the output filter, but couldn't find any for the EMI filter at input.

    SMPS schematic using IC2003

    SMPS schematic using IC KA7500

    ATX-SMPS based on TL494 and LM339

    The TL494 LM39 combination was the most widely used one till recently.

    Click on the images to enlarge. If you know anything about Switching Power supplies, the schematics are quiet obvious. They are simple. Include simple protections and have very few components.


    TI PWM controller datasheet – TL494 | Fairchild PWM controller – KA7500C | National’s Quad Comparator – LM339

    Product page of TI’s TL494 | Product page of KA7500 | Product page of LM339

This entry was posted in Switching and tagged , , . Bookmark the permalink.

39 Responses to PC SMPS schematics with IC 2003 and TL494

  1. sunil shah says:

    They are both of same IC 7500 . you better put what you mention in the category

  2. Pantelis Chatzikonstantinou says:

    Hello there, excellent work… I am trying / repairing PSUs myself too. !!! These schematics are really helpful.

    I would like to ask you, as you seem to be much more experienced than me, what would it take to convert the +3.3v output to a +16v output? I am trying to build something up for a friend and I am stuck.


  3. Murugesh says:


    Very good explanation in this article. I am looking for this IC not able to find out any ware or equivalent the following letter mentioned on that IC. Can you help me regarding this?
    Printed letters are:

    • Ajith says:

      Hi Murugesh,
      Can you please tell me, in what circuit you found it. How many pins does it have? Which is the Vcc and GND etc.. If you can post a picture somewhere, that would be great.

  4. Murugesh says:


    Thanks for your reply This is 16 PIN DIP I will send you picture tell me mail id

  5. Murugesh says:

    Dear Ajith

    Really I am very happy to received mail from you . Thanks a ton for your forum and your effort. I wish to grow your site.

  6. jaiju says:

    Dear Ajith,
    It is very useful information.Especially schematics and explanations are so much useful for people like me.Thank you.
    Can you help me in making a 40V 10A power supply from an ATX SMPS?

    • Ajith says:

      I am not completely sure if I can help you :( I do not have much experience rebuilding a power supply. You can find most of the modification needed to change the voltage of a standard power supply on the net.

      But I think for 40V output, you will need to rewind the transformers or even change the transformer altogether..

  7. diony says:

    Dear Ajith,

    Do you have datasheet for IC 2003? or IC equivalent? I also have this kind of IC on my Atx PSU EGCC 300SFX. I’m suspecting that this causes the trouble on my PSU. Stand-by voltage is OK (4.5V).

    • Ajith says:

      Sorry diony,
      I have searched many a times for the 2003 datasheet, but couldn’t find it anywhere. If I find it, I will post it here :(

  8. Hello! Good work, I have a question regarding the output inductor, anyone knows his number to get it, or preferably buy?.
    I ask this because I would buy the toroidal cores to avoid destroying more sources for PC.

  9. Murugesh says:

    Dear Ajith
    I am looking for SMPS IC (Power Management IC) in bellow spec. Could you please help and tell me your suggestion.
    O/P Voltage is 9.3V DC
    I/P is 85 to 265V AC
    Make: SAMWIN
    IC NO:SW2604

  10. mohan says:

    Hello sir ,
    this is mohan from bangalore i have some smps whitch are not working the problem is if i change smps to my system it does not work after two days and i have to replace the new smps i found the earthing problem and now my system is ok but the smps are still laying only 5vsb is available no other voltages whitch component should be replaced please help me.

    • Ajith says:

      Hi Mohan,
      I do not know what part would be broken but I can point you in the right direction I guess. Start by checking the two small blue(most of the time) capacitors connected across Line, Neutral and GND. Then if its OK try all the electrolytic. There is a good chance that the electrolytics are faulty. After that check for the primary side transistors and then the secondary side rectifiers.

  11. Mazyar says:

    Thank You Dear Friend …

  12. Santhosh says:

    I have a 400W mercury ATX SMPS using the IC2003 ! I was searching for the schematic and pinout ot the IC atlast I found it on your website! Thank you!

  13. Santhosh says:

    Is there any replacement IC for IC2003 ??

  14. Santhosh says:

    If you have the schematic diagram of 400wmercury ATX SMPS using the IC2003 similar to the one you have posted on this site ,please E-mail me!
    Thanks in advance!

    • Ajith says:

      I have a Mercury 44W ATX SMPS and the schematic shown here and the circuit of that SMPS are actually the same. The only difference is that the output filter coils are not present and the input EMI filter are also absent.

  15. Kirk says:

    Hi Ajith and thanks for all the info.
    I trying to repair a PW Tecnoware FAL550FS , all outputs are dead except 5VDC which is working ok.There are no visible signs of damage and so far I have checked the caps,resistors,fuse which all seem to work right.
    It uses a LM339N & a 7500b.
    Any ideas ?

    Greetings from Greece :D

    • Ajith says:

      Hi Kirk,
      I assume you tested the caps by checking them with your multimeter in resistance mode and you are shorting the GREEN wire with Ground (black). These are the steps I follow to check electrolytics.

      You are getting 5V because it comes from an LM7805 – Q15 (you can see this in the circuit right below the four diodes at primary side.)

      1. Check the voltage across the cap and discharge it by using a resistor or simply shorting it (if the voltage is really low).
      2. Place the multimeter on around 200K or 400K range and touch + and – of cap.
      3. The resistance should momentarily be zero (very low) and start to climb up and after sometime the meter shows ‘over load’.

      If the meter gets stuck at a fixed resistance or even after shorting the cap, the meter shows infinite resistance, then the cap is probably faulty. Most of the time you won’t have to desolder the caps as the secondary circuit mostly do not affect the caps.

      Also I usually replace all the electrolytics even if only a few are faulty.

      If you have done this and made sure all resistors are OK, then try the rectifiers, both primary side and secondary side and then the switcher transistors.

      Do let me know of how you repaired it :)


  16. Sashimoto says:

    Hello Ajith,
    Thanks for all of the info published here. I’d like to ask you is there any replacement of IC2003 found yet? The failure in my SMPS is in 2003 I suppose. I’m afraid that this IC is not available in my area.
    Thank you!

  17. jessy says:

    can i know what type of transistors and diodes use in the TL 494 combination with LM339

  18. S.N.BANERJEE says:

    I am trying to make circuit for domestic induction cooker. I understand nobody in India is making it and all are being imported cheap material with 1 year warranty from China.Problem I faced in getting required components which are all supplied by MNCs and everybody ask for the required quantity. If they are in thousands, then only they will supply. No way for experimentation. Can anybody help in designing simple circuit may not be fully auto-controlled.

  19. amrutamundra says:

    Sir, it would be helpful if you can send me the complete component list along with its specification of any one of the circuit shown above i wish to try the project on my own for my final year engineering

  20. diysmps says:

    Welcome to the SMPS forums


    Thanks for all

  21. dave says:

    I have an Octogen atx psu 300w, that uses a 2005 chip. Is this the same pin out as the 2003??

  22. hecky11 says:

    thanks alot.. i got schematic of my atx psu (y-b200atx) here..it is going to be really helpful.. thanks alot !!!!!

  23. Divyanshu says:

    I’m a student and I wanted to know that wheather a SMPS has a 12V outport. So, that I can connect some LEDs in my gaming PC I have a iBALL 650W SMPS.

  24. Roland says:


    I have been searching in vain for a datasheet of the 2003 PWM controller chip, about 2 years now but zero found. Does ANYONE have it? I am trying to modify a PSU for a higher output voltage, this to be followed by conventional analogue regulators for a bench supply. It works but regulation is poor because it’s monitoring the +5V and +12V outputs and I can’t figure out how it make it sense the higher voltage without a datasheet. I’m trying to get + and -30VDC.

    Thanks, Roland.

  25. Maarten Boer says:

    Dear Ajith,

    am looking at a PC40n250EV from an XP Shuttle PC; it has no power switch so expect you start it by giving a pulse to some of the leads, or connecting a small voltage to zero; do you have any tips? right now I cannot measure anything!
    greetings, Maarten
    Where can I

  26. ziz says:

    Do you think its possible to modify the +3,3V voltage line to 3,65V on a psu based on the 2003 chip?
    thanks a lot!

Leave a Reply

Your email address will not be published. Required fields are marked *


You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>