13.8V 15A offline SMPS w/ PFC

[djQUAN]

not actually built from scratch but it's my first time messing with an offline SMPS. luckily, no fireworks and I'm still alive!

started off with a Dell desktop PSU. bought it from a surplus shop for about US$8.00



when I took off the cover and checked what could be done, I realized it isn't the same as most PC PSU's with TL494 and LM339's etc. looked further and saw a chip on the live side, another on the output side, and a small daughter board.

about 2 days of thinking about what to do and learning around the circuit, figured out that the chip on the live side is a TDA16888 which is a PWM controller with PFC. nice! the daughter board supplies 15V to the TDA16888 and continuous 5V 2A for standby and for the watchdog logic (the unknown chip at the output side) and the supply also has temp controller for the fan.

so I proceeded to remove all components related to the watchdog circuit and the outputs that I didn't need. moved a few components, a jumper here and there and there you have it. we have a regulated PSU.

I don't know if I'm allowed to post what mods I did since it is really dangerous to modify these things if you don't know what you're doing.

pictures:

secondary side with most of the components removed, bare essentials are left.




pic of the PWM controller chip and PFC inductor


leftovers


waveform@ trafo 12V secondary, no load



waveform@ trafo 12V secondary, 8A load (don't have any full load tests since I don't have a big enough dummy load)


completed PSU

[star882]

How about use some car headlight bulbs for a full load test?

[djQUAN]

I have a high wattage one here but I'm afraid to use it. it gets really hot really quickly.

might want to try it along with the dummy load to have a burn in test.

[djQUAN]

I just did a 14.6A test at 3min continuous.

I did the finger test and the main switcher heatsink got hot (about 45degC) output rectifier sink got hotter (about 50degC, can keep my finger on it for a few sec) and the output inductor got burnin hot. (didn't give me a burn but it was really hot. can't keep my finger on it for more than a sec.) main primary cap got warm but not hot. same with main trafo.

I suspect output inductor heating is due to I2R losses as it doesn't get warm at idle.

will need to rewind it with thicker wire.

darn. I just realized that the waveform photos in the first post is wrong. the loaded waveform should be this one:

[luka]

Hi

Please do post, what you did, with note that there are HIGH VOLTAGES

Great work, now you can do one that has say 25A at 5v, so you will get supply that will do 25A at your output voltage

[djQUAN]

Originally posted by luka
Hi

Please do post, what you did, with note that there are HIGH VOLTAGES

Great work, now you can do one that has say 25A at 5v, so you will get supply that will do 25A at your output voltage

I have to find the notes where I put everything that I did to this PS. dunno where I left it.

I have a 5V 80A supply over here. but that is too much work. it also has a 12V 65A module in there too. both needs 300VDC and 24VDC input.


I have to figure out a way to put a overcurrent limit to this supply though. I was able to pull around 22A (output drops to only 13.77V!!!) out of it but scared of doing so for more than a few secs as the parts are pushed way above their limits.

[switchmodepower]

Technically you can run the choke up to the rating of the wire (130C wire or 155C wire) if you want so don't get discouraged if you cannot touch it.

[djQUAN]

Originally posted by switchmodepower
Technically you can run the choke up to the rating of the wire (130C wire or 155C wire) if you want so don't get discouraged if you cannot touch it.

I'm more concerned with the core 'cooking' and changing its properties and then BAM!!!

[switchmodepower]

Originally posted by djQUAN



I'm more concerned with the core 'cooking' and changing its properties and then BAM!!!

The curie temp for magnetics is much higher so you can run them super hot. Try to find out what core is used and look at the specs.
It looks like a powered iron core and most likely it is since they are cheaper as compared other materials.

[djQUAN]

it's the long term effects that I know of. I have read here many times that a hot running core loses its capacity to store energy or something like that.

maybe Eva or others could chime in if I'm wrong?