PMP8740: Board exploded

Hi Danilo,

First of all the firmware Rev_D can set the converter to work in both modes: simple power supply or battery charger. If you set it into power supply, then you can define Vout. In order to make it working as power supply, it must be set as "Stand Alone" by means of the pushbuttons and menu selection.

Regarding the damaging of the MOSFETs, I have few questions:

Did they use all components according to BOMs?

What main transformer is employed here, the one from Kaschke?

What shim inductor is used? I developed it by myself, by winding it over a PQ20/20/14-1 platform; is it the same?

Most important: did they put all MOSFETs attached to their respective heat sinks (by means of isolator pads)? Even though at light load the converter delivers low power, you have to consider that it works in hard-switching mode (because the switching current is not sufficient to charge and discharge all Coss capacitors of the active components); this leads to several watt lost on each MOSFET. If these components are not cooled, then they can be damaged.

Please let me know if there is any feedback from the customer.

Best regards,

Roberto

Dear Roberto:

We use the PM8740 to build our 2KW power or Charger. Gerber file to make PCB, according to BOM to solder the parts, and we check the soldering parts several times to make sure if it is correct.
Then tested: there were 2 things happened in 2KW P C B A.
1: The output voltage stayed in 27V,and loaded, it gradually goes down with few mA which means the output falls rapidly,even falls to zero voltage. It seems like a UVLO protection is activated. If we loaded with larger current,the Bridge MOSFET and SR MOSFET all are punched through to ground.

2.The ouput voltage change from 27V to 32V or 27V change to 24 V no load condition just 6-8 minutes
the punch through will occur too. To stay at 27 V longer time is safe but must load with no load. Thus, we can't observe bridge waveform, but burst only. We check all transformer polarity are correct.

Best Regards,

Jody

Dear Jody,

Please let me know if the polarity of all transformers are correct. Since you are checking, you may want to send me the datasheets of these transformers, so I can verify it in parallel. 

Other point:

1) Did you use a shim inductor or is it shorted? If you used it, may I have the datasheet, or, at least, the characteristics in terms of inductance and saturation current?

2) Did you apply heatsinks on all MOSFETs (bridge and sync-FETs)?

3) Is also the microcontroller daughterboard inserted on the header of the full bridge board? If it is not, then the converter is not able to deliver power (the resistor R51 connected as pull-up will keep Q4 shorted to ground, therefore the reference voltage of current loop is zero.

Please let me know :-)

Regards,

Roberto

Dear Roberto: 

Good morning ^_^

The attached 2 files are for your reference. The shrim transfomer; I  changed the winding from 330uH to 12.8 uH. Because of  the heating rise very rapidly FOR 330uH.For 12.8uH, the temperature from Heat Sink of bridge is 46 °C.

I want to attach two files here, but I couldn't find the place where I can share my documents here.

Would you please let me know where the pdf file share link is? Or would you please share with me your email address. I think I will try to send two attachments to Danilo first. Maybe he can help us to share the documents to you. 

We answer you the  3 questions:

1.We  use the shim  transformer and its inductance changed to 12.8uH.

2.We applied the heat sink to each of Bridge MOSFET and SR MOSFET.

3. The MSP430F2252 MCU Board is always inserted  on the Full bridge board. May I ask you a question: We bought a 600w power supply  and its PWM chip is UCC28950 .We found out the Pin6;7;8 connected to ground resistor are differnt from the 2KW UCC28950's. Is it one of the shoot-through reason ?

Best Regards,

Jody

Hi Jody,

If you want you can share here your email address and I will contact you directly. Maybe this is the fastest way to do that.

Thanks,

Roberto

Hi Robert,

Good morning ^_^ Thanks for your swiftly reply.

I would like to discuss with you via email.

My email is sales2@asian-electron.com 

I think I would share the two files via email.

I hate to share any documents on E2E website due to some bad experiences before.

I am looking forward to your email soon.

Thank you so much.

Have a nice day

Best Regards,

Jody