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.

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  • 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.

    68 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:

    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).

    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 😀

      • 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

      • Ajith says:

        Hi Maarten,

        since this is an ATX PSU, it can be started by connecting the Green (PS_ON) pin on the 20/24 pin ATX connector to any Black (GND) wire. Please note that you must provide some load, 12V lamp, to the 12V and the 5V rails.

    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!

    27. Ahmed Soliman El Sayed says:

      Hey , Very nice blog :) I need a high current DC-DC converter , I have a punch of used ATX power supplies , Can I convert one of those to step down 48 Vdc instead of the 220 Vac ?

      • Ajith says:

        Hi Ahmed,

        it is not very practical to @convert@ on of the 220V SMPS to accept 48V. You can however salvage the parts like inductors, transformers and caps and build your own circuit based on guide from TI. Please find the links for the same, at the end of the post.

    28. vinayakamurugan says:

      Great help from your side for doing my project on SMPS

    29. mario dumais says:

      Hi, any clue where I can find the datasheet for that IC2003 or a replacement/equivalent?
      I know that the question was addressed before but I can’t find any answer.
      I also searched for hours and hours without any success


    30. Gijs Meirmans says:

      Hi Ajith,
      I need a powersupply 9v 7A and I also have some pc powerupply’s laying around
      I wonder if it’s possible to reduce the output voltage of the power supply
      As I look to the schematics it can be done by changing a reference resistor but I am not shure wich one I also think I will also reduce the other voltage’s like the 5v if i change the 12V Please direct me into the right way
      I have search the web for answers but could not find

      Gijs Meirmans
      The netherlands

      • Ajith says:

        Hi Gijs,

        due to the circuit used in cheap power supplies, if you change the 12V rail using reference resistors, the other lines will also drop correspondingly.

    31. Dileep says:

      I need to talk with u Mr.Ajith……..send me ur mail. ID

    32. Sebin Jacob says:

      Is the Ic 2003 and ULN 2003 same.Where can i get the Ic 2003.

    33. Dhruba Paul says:

      Dear Sir ….. I want ic KA7500 for Philips home theater HTS 5520/94 but could not get it in my local elctronics wholesale market please help me with your suggestion, how and from where to get it.

      Dhruba J Paul

      • Ajith says:

        Hi Dhruba,
        I was not able to find the IC online, or in local shops. You can get this IC from China via ebay.com Please be sure to choose the ones with free shipping though. Another way is by opening up scraped SMPS, but this is a long shot.

    34. I do not even know how I stopped up here, however I thought this post used to be good. I don’t know who you might be however definitely you’re going to a well-known blogger if you happen to aren’t already. Cheers!

    35. diode says:

      Dear Ajith,

      My TL494 is outputting a sine wave of 50Hz both on the C1 as well as the C2 output. The sine wave seems to have a ‘bend’ around the zero crossing point. This is measured with a scope. Although the power supply seems to work (outputting the correct voltages) I’m not able to measure the PWM or display it on my scope. I did apply a band pass filter on the scope between 40 and 200kHz. The calculated value of the PWM should be around 60kHz. My load is 18W @12V.

      Do I maybe load the power supply not enough? Or do I measure the outputs incorrectly? The pin of my probe on CH1 is connected to C1 while the pin of my second probe on CH2 is connected to C2.

      Thank you for any help.

    36. usefule and helpful this schematic.

    37. Raj says:

      Hello Mr. Ajith,

      I have a Mercury ATX switching power supply – 450w based on WelTrend WT7520 IC and its not powering on. Upon checking I found that Fuse has blown up and also a Zener diode is gone.. The portion of the board under that zener diode was in burnt condition by doing cold check itself. So, I want to replace that Zener Diode, but I don’t know what value diode we should replace with. While googling for this SMPS, came across this site. Please help me. I don’t find any circuit diagrams of this particular SMPS anywhere. The Diode reference code on the circuit is “D36” . Please help.

      Regards, Raj

    38. F Saxena says:

      Hi Ajith and thanks for all the info.
      I trying to repair a Antec EA 750 W PSU, all outputs are dead There are no visible signs of damage and so far I have checked the caps,resistors,fuse which all seem to work right.It has a complex circuit with SMDs and Modular design so it is little bit difficult to check it normally. Please give some suggestions to make it working.

    39. Somnath says:

      Hi Ajith,
      My psu suddenly death. I check the psu, only PS-on and +5vsb volt ok. After shorting the GREEN wire with Ground (black) smps not stats. no voltage output such as pg-good, +5, +12v etc. no physcical damaged parts founds. Psu make with KA7500 and LM339. I replace LM 339 but status same. pls help me to trouble shoot the smps.

      • Ajith says:

        Hi Somnath,

        as I mentioned the most common reason for SMPS failure is electrolytic caps failing. You can check them to see if they are damaged using a multimeter.

    40. miguel Felix says:

      Bom dia amigos , preciso de uma ajuda estou com um regulador pifado e estou com dificuldades para achar o Ci ou equivalente – se alguem por ai tiver uma diga agradeço Ci com problema SDC 7500 =


    41. biju says:

      Sir, if any replacement of ic2003 in atx smps

    42. vipin says:

      can any one enplane the topology used
      just the input section
      primary of T1 and T2 combined

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