14V@ 20 Amps PSU: Smoked PCB after successful testing

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#21
Razor-Edge said:


Hello Eva,

Attached is the corrected gate drive. Please comment. Also, i have been using EE25 for gate driving, how about EE16 or may be EE13.5.

You also suggested CD4000 series for implementing dead time how about a diode resistor network (for each outut of SG3524), similar to the ones used at the mosfet gate? 🙄
Click to expand...

It's still wrong, there is nothing to pull down the bases of the buffer transistors. Concerning the transformer, you can use a smaller one if you can live with the increased leakage inductance and the chore of winding a tiny former with tiny wires while keeping good isolation.
 
#22
luka said:
Hi

Do you want for supply to shutdown or limit output current as in charger?

I have lost my protection in proces of redoing it:xeye:
Click to expand...


Hi Luka,

You have a very valid question. It should be current limiting but after the smoke i have seen, i would rather first go for complete shut down the DIY way and may be then start working on CC, CV circuit.

Thanks for your concerns.. 🙂

Eva said:


It's still wrong, there is nothing to pull down the bases of the buffer transistors. Concerning the transformer, you can use a smaller one if you can live with the increased leakage inductance and the chore of winding a tiny former with tiny wires while keeping good isolation.
Click to expand...


Hi Eva,

Thanks for your to the point reply.

I will check this and post results (probably by monday).

After reading your answers, i wonder how much time i will it take me to reach even 10% of your abilities in analog electronics.

Thanks for your valuable comments once again.
 
#23
Hi Luka,

If you notice the schematics i had posted of this PSU i had posted. I made a terrible blunder. I have not used 2 bulk caps for each half but only one 470uF/400V on HVDC rail.

In the last iteration, it worked because i had 2 220uF/400V caps for each half. and one big 680uF/400V cap on HVDC.

Worst part is, i didnt realised it while assembly as well.


Now a smoked charred PCB with almost everything roasted... :bawling:

now one this is sure, i am working on it till it starts working... :smash:

Thats the DIY way right?? 😀
 
#25
Strange problem

Hello Luka,

Based on your and EVA's suggestions, 2 weeks back i rigged correctly working gate drive. I am now facing a strange problem. One of the Mosfets is not switching ON.

In this half bridge, one of the mosfets turn ON for a short while and the primary side pulses vanish is 2~3 seconds...!

Both the gate drives look perfectly fine but... 🙁

Also, i had not been using coupling capacitor for power transformer. I think this is a reason for what is looks like power transfomer saturation...?

If i change the gate drive connections the other mosfet starts working and the pulses die out in the other direction.

Do you thing for all this, coupling capacitor to the power transform is a problem?

EVA could you throw some light as well?
 
#27
coupling capacitor

Hello Eva,

Thank you for your reply.

Very strange though this PSU started working without coupling capacitor to the power transformer!!

This happened as soon as i removed circuit on the secondary side of new gate drive (diode and turn off transistor). Now their is only a 330 ohms resistor across gate to source of the Mosfet.

I could not understand this whole thing.

Have you ever encountered such an issue?

This PSU started working but, the turn off times are very bad (FET warm at Just 1Amp load).

Secondary side of the gate drive are excatly same for both LOW and HIGH sides.

Should i change polarity of one of the diode D2 or D4?

Have a done something wrong?

Please help.
 

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#29
The coupling capacitor should be placed in the primary side. No capacitor is required in the secondary side. Leave the diodes as they are. Note that different gate drive circuits may make the circuit more or less prone to transformer saturation, but the SG3525A (or any other IC) will always suffer from some degree of asymmetry thus requiring a coupling capacitor.
 
#32
Fry,

How did you find an ATX psu to match the schemo shown? What I mean is, since there are literally hundreds of AT & ATX psu manufacturers, how did you find the matching original ATX schematic to your unit before modification? Or was it just dumb luck?

Steve
 
#33
N-Channel said:
Fry,

How did you find an ATX psu to match the schemo shown? What I mean is, since there are literally hundreds of AT & ATX psu manufacturers, how did you find the matching original ATX schematic to your unit before modification? Or was it just dumb luck?

Steve
Click to expand...


Just dumb luck :smash: and finding a bunch of old PC's at the local dump😀

I was able to get 14.4V@ ~30A for a short period, as previously stated, I still need to upgrade a few things to make it 100% duty cycle.
 
#34
Cool! 😎 I have an old AT Board I'm converting, but to a +/-18V out. It will require some major surgery on the secondary side. The ild +5V bus is now the +18V bus, and the old +12V bus is now the -18V bus. Very tricky making sure the (+) & (-) Vouts track each other. Control IC is the usual TL494, and the switching transistors are going from MJE13007s (400V 8A) to MJE13009s (400V 12A). Not sure I really need them, but as long as I have them, what the he11? The output rectifiers are MUR1620CT and MUR1620CTR. - When I ever finish it. :bawling:
 
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