replacing NPN bipolar power transistor in cheap power supply

Thread Starter

bigjoncoop

Joined Feb 1, 2019
113
I have 24 volt 15a power supply that I'm trying to replace the power transistors. they are D13009k(NPN bipolar power transistor) rated 400v 12a.

I found a MJW221196 NPN POWER Tranny rated @ 250v 16a and a MJH6283 rated @ 80v 20a. Can I use these 2 to replace thecD13009k NPN rated at 400v 12a???

i also found some MJH6287 but there PNP . The ones that blew were NPn . Can I i use them instead in my cheap 24v 15a power supply. I'm thinking NO
and if the D13009k that I'm trying to replace are only rated @ 12a, then my power supply is not rated 15a as it's described then huh? so if those npn trannys are rated at 12 amps that's Max current I'm assuming correct? that would explain why I blew it up
 
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Dodgydave

Joined Jun 22, 2012
9,206
You can replace the Npn for the same as long as the current rating is the same or higher, ..
you can't replace it with a Pnp or MOSFET.

Is this a Linear PSU with a transformer?
 

Thread Starter

bigjoncoop

Joined Feb 1, 2019
113
You can replace the Npn for the same as long as the current rating is the same or higher, ..
you can't replace it with a Pnp or MOSFET.

Is this a Linear PSU with a transformer?
I understand. The current ratings are fine but the one of the ones I found is only rated at 80v instead of 400v. And I'm powering it with 120v..

20200518_164946.jpg20200518_164946.jpg
 

AlbertHall

Joined Jun 4, 2014
10,056
This is a switch mode supply and the transistors are on the high voltage side so you need to match the voltage rating as well as the current rating.
 

dendad

Joined Feb 20, 2016
3,566
You will need to test all the parts around the transistors too. Often transistors failing cause other parts to fail. The bridge rectifier too. Did the fuse blow?
I would look for higher voltage transistors that the originals if you can find them.
Often, the electrolytic capacitors loose their value in switch mode supplies, so remove them and measure them to see if they are ok.
When you power the supply up, use no load and run the mains through an incandescent lamp, maybe a 40 or 60W to help limit the smoke output. The lamp will flash then it could have a faint glow when running. If it stays bright, there is still a problem.
And use an isolation transformer if you have one.
 

Dodgydave

Joined Jun 22, 2012
9,206
I have fixed several of these, they use a TL494 chip with a push pull output on the Blue small Transformer , which drives the two large Npn transistors on heatsinks they pulse the Large Blue Transformer across the 350V DC supply, with the Red capacitor as a series DC blocker, so you need to match the same type of transistors ..

By the time you have messed about replacing transistors to no avail, it's cheaper and easier to buy another psu !!
 

MisterBill2

Joined Jan 23, 2018
6,336
Posts #5 and #6 make very good points. Since this is a switching mode power supply the voltage rating is important because the voltages are quite high. In addition, because the operation of a switching supply is a lot more complex, it is likely that other parts may also have failed and been the cause of the problem. So unless this is a personal experimenter's project I suggest replacing the supply with one rated the same or higher current.
Do you know what the actual load current is for the application this supply is for?
 
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