my 12V external power supply broke and it looks like I need to replace transistor. On my board is installed transistor UTC 5N60l. I've searched for a while and found a schematic for my power supply board. But from a schematic, there should be IRFS730 transistor (Q1 in the scheme). I'm a newbie, so could you please tell me what's different between these two transistors and what should I use next time? Adding schematic.

My power supplyThanks

  • \$\begingroup\$ Compare both their datasheets. \$\endgroup\$
    – user16324
    Nov 15, 2016 at 16:25
  • \$\begingroup\$ Do you have any database with transistors or something? Unfortunately, I don't have any :/ \$\endgroup\$
    – Bukk94
    Nov 15, 2016 at 16:26
  • \$\begingroup\$ You can find many transistors with online sellers like Mouser and Farnell. But if you cannot distinguish your Vce from your beta then I suggest you go seek a professional repair service to do this for you. Especially since this circuit is to be directly connected to the mains voltage. There might be a reason why the transistor broke. This is not newbie territory. \$\endgroup\$ Nov 15, 2016 at 16:32
  • \$\begingroup\$ Sorry to be a smartass, but there's this thing called the internet that has all of the datasheets you could ever possibly need. Search for UTC5N601 and datasheet. Do the same for IRFS730. \$\endgroup\$
    – JRE
    Nov 15, 2016 at 16:33
  • \$\begingroup\$ @FakeMoustache I know how to handle soldering iron and soldering. I just don't know a lot about transistors. I know how they works and how they should be connected. That's why I'm asking here hoping for help from someone who's more experienced with this. \$\endgroup\$
    – Bukk94
    Nov 15, 2016 at 16:45

2 Answers 2


Failure of the switching transistor in this type of power supply is not uncommon. Similar problems can be found in monitor and TV supplies.

The most common cause is that the peak voltages for some components are rather low. They are just enough but one or two spikes and they are gone.

The IFRS730 has only a Vds limit of 400 V (See datasheet) where in this kind of application a Vds of 600V is to be preferred. Therefore the FDPF8N60ZUT proposed by Seth is a better alternative.

It would go to far to explain the complete working of the powersupply but on top of the N channel mosfet replace also C1 by a 630V type and replace furthermore D1 -D4. If F1 is a soldered in type of fuse make sure to replace it with the same value.


You are working on the mains side of the power supply. Disconnect the supply from the mains when working on it and wait a couple of minutes before you touch the circuits. (C1 must be discharged).

Take time in desoldering the mosfet and the capacitor and keep everything clean. Make sure that you maintain insulation between the mosfet and the chassis of the powersupply.

Look at the warnings in the comments and answer. When testing the unit after replacing the mosfet, capacitor and diodes "Keep your fingers away" and do not to kill yourself.

If you are carefull and able to work clean the job can be simple. However if the parts blow after the first attempt then leave it alone and look for professional assistance.

  • \$\begingroup\$ Thanks for the useful and honest answer! I've measured almost all components on the board and it looks like the transistor or the transformer is broken. Before it blew up the fuse, it was really hot. Even with aluminum coolant radiator. It was running over 5 hours straight so I guess it wasn't designed to run this long. I'll try the FDPF8N60ZUT, thanks also to you @Seth \$\endgroup\$
    – Bukk94
    Nov 15, 2016 at 21:09
  • \$\begingroup\$ It should be already done. But maybe you can't see my upvote because of my low rep. \$\endgroup\$
    – Bukk94
    Nov 15, 2016 at 22:03

If your transistor is the only thing that broke, then Fairchild's FDPF8N60ZUT is a viable replacement. But as FakeMoustache mentions, this might just be the symptom and not the cause, so replacing the transistor, especially if not done cleanly, will be dangerous!


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