Big SMPS Help!

[mgm2000ro]

Hello everyone !
I'm looking for some help with a problem that has been bugging me for a while.

I've built a half-bridge SMPS based on the sg3525 (which works at 35kHz) + tx4424 + GDT + IGBT. The end result should be a 14.4v and 200A DC power supply

When testing it failed after a matter of seconds. During the testing, the conduction time T-ON peaked at 47% out of a 50% maximum.
I suspected the dead-time was too little and reduced T-ON to 45%. Could a too low dead-time have caused the failure ? Or is there another cause ?

Here are some waveforms to help finding the cause of the failure

Scematic:


Video IGBT Blow at 14.4V /200A+
IGBTs blow - YouTube

Idle IGBT gate waveform


Idle primary waveform


Loud 14.4V / 50A igbt waveform


Loud 14.4V / 50A primary waveform


Please let me know what you think about the waveforms and what else I could do to improve them.

[savu]

For the purpose of lov voltage and big current output the best topology is:
Phase Shifted Syncronous Rectified smps. This has the advantage of running in ZVS mode. So more sw frequency at lower sw losses.
With SG3525 you run it in forced switching mode witch is lossy and stresses the sw elements.
Take a look at LTC1922 or UUC38950.
Regards,
Savu

[mgm2000ro]

What you suggest me is to change the topology and all I make!
You think you helped me with something (on topic)

[dtproff]

I ill be honest, at those power levels I would have been running MOSFET's. It would appear that the driver circuit you are using is for a MosFet so the change should be easy. For some reason I seem to remember that IGBT's need a current pulse to turn off completely. Maybe they have fixed things since I used them or maybe I am just mis-remembering.

Second item, can you show the primary side current waveform into the transformer? Also, the primary side transformer construction, Lp, turns ratio, and gap in the transformer would all be helpful. There is a possibility that the core may not be saturating.

Tony

[mgm2000ro]

Transformer ration 12: 2+2
Toroidal core R63 material K2006, Ae=300mm^2
datesheet: http://www.kaschke.de/ferrite/pdf/da...ge2/R63-25.pdf
After I broke igbt's a test temp of ferrite core and it was cold.
I have an industrial smsp 14.4V 100A half bridge (tl494+totempole+GDT+ 47A-MOSFET) and i test it and this is rezult:

Idle (no loud) primary waveform


Loud 14.4V 50A primary waveform


I compared the results with my smps and I think are similar.

Ps I change my values of resistors(5R) and caps(1nF) on snubber whit 75R+1nF on my smps and this is result:


I wait your opinions!
Best regards,

[johansen]

can you get a better shot of the voltage at the gate? during turn on specifically, it would appear your circuit is sufficient for turn off. however it appears it is oscillating at turn on. you may need to wind a stiffer gate transformer/

also, unless you cancel out the igbt diode with a schottky diode in series with the drain, that external diode is not going to do much to stop any failure mode related to the internal igbt diode.

[luka]

Do you have any gate waveforms when under load?
Or any primary current waveforms?

transistor is colsed if current is 0, I know Eva said she had to apply negative voltage to transistor, to really speed things up, if not, current didn't drop to 0 any time fast

[DjLeco]

Man, try to use anything against trafo driver, with trafo driver you cannot adjust deadtime, and pulses are very distorted.

You can try this one, just mention to use ultrafast diode and good capacitor for bootstrapped supply (D4 and C4 in demo schematic on pdf), C4 use 22uF/25Vdc low esr, parralel with 0,1uF ceramic capacitor, as closest to pin 8 and 6, and 8,2-10 ohms gate resistor, without diode parralel.

The switch On-Off, will be fast enough.

http://www.onsemi.com/pub_link/Collateral/NCP5181-D.PDF

Good luck, trafo driver is rudimentary...

[eem2am]

There is something wrong with your gate drive.

There is no path for the base current of the PNP's.

Also, you have 2KW....you cannot do this with a half-bridge unless you also have fans to cool the semiconductors.

Also, maybe you switch in the capacitive region in which case you get big switching losses.

Is it supposed to be an Asymetric resonant half-bridge?

[eem2am]

we have no hesitation in directing mgm2000r0 to the full bridge........but then.......full bridge is a waste of time isnt it?...because the phase shifted full bridge costs just the same but has lower switching losses...

so we will see the basic full bridge go extinct ?