LM5030: Diode failiure

Gemini1000

Part Number: LM5030

Hello,

We are using LM5030 for our push pull converter with the following specs :

Input= 24V , output= 70-90VDC, 500W, isolated, EFFICIENCY > 90 %

The converter works well most of the time;however, sometimes we notice that one of our secondary diodes ( full wave bridge with 4 diodes and RC snubber circuit ) get damaged making the converter stop functioning properly! Any idea why that is happening ? We are using a typical voltage fed push pull converter. Highly appreciate your URGENT resposne.

Thanks

over 5 years ago

0 Gemini1000 over 5 years ago

Intellectual 500 points

Also need to add that the spikes( or ringing ) across the diodes were reduced to almost 100V below the maximum voltage rating of secondary diodes after using the snubber circuits.

0 Teng Feng over 5 years ago in reply to Gemini1000

TI__Genius 13660 points

Hi Gemini,

The min rectifier diode voltage is -2*Vin*(Ns/Np)+Vf. I think the diode of 100V rating is too small.

could you capture the voltage on the diode?

Thank you.
Regards

0 Hong Huang over 5 years ago in reply to Gemini1000

TI__Guru 73085 points

Hi,

Can you please provide your schematics for review first?

0 Gemini1000 over 5 years ago in reply to Teng Feng

Intellectual 500 points

The diode rating voltage is 250 V

0 Gemini1000 over 5 years ago in reply to Hong Huang

Intellectual 500 points

Hi Hong,

The schematic is pretty much same as the eval board but with 4 diodes on the secondary. Unfortunately we are not allowed to share the schematic.

0 Hong Huang over 5 years ago in reply to Gemini1000

TI__Guru 73085 points

What is the diode specs, part number, its current rating?

When the diode is damaged, can you measure each diode and let us know what each diode status is, short, open?

Can you provide the voltage waveform of the diode?

0 Gemini1000 over 5 years ago in reply to Hong Huang

Intellectual 500 points

Please see attached the waveform and diode spec.

only one diode gets damaged and the rest of them are good. 8686.waveform.docx

0 Gemini1000 over 5 years ago in reply to Gemini1000

Intellectual 500 points

The max diode voltage is approximately 155V after adding snubber circuits.

0 Hong Huang over 5 years ago in reply to Gemini1000

TI__Guru 73085 points

After adding the snubber, is the diode still damaged? Do you know at what condition the diode damage happened?

0 Hong Huang over 5 years ago in reply to Hong Huang

TI__Guru 73085 points

I see Teng is supporting you. I will let Teng to support you.

0 Gemini1000 over 5 years ago in reply to Hong Huang

Intellectual 500 points

Yes, still gets damaged. Sometimes right after turning off or turning on the converter. It's kind of random.

0 Hong Huang over 5 years ago in reply to Gemini1000

TI__Guru 73085 points

At turn on or off, the spikes may be much higher.

Can you add a temporary voltage clamping to limit the diode voltage below 200 volt to see if the damage still happens? If not, then you need tune up your snubber to make sure the voltage spikes with margin not exceeding the diode voltage rating. If still damage, you may need to verify the diode current rating, including reverse recovery capability.