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Defect INN2604 units

Posted by: BAMA_AK on Thu, 09/30/2021

Dear sir or madam,

we are utilising the INN2604 in one of our power supply designs. This power supply is in production for 4+ years already without notable difficulties.

 

This summer we recieved a customer complaint, where multiple units (>30) fail to deliver power after circa one year in the field. Our product is used in a IT / data center application. Input power is universal 100V-240Vac. Our customer states the whole installation is sourced by a online uninterruptable power supply (UPS).

The load itself appears to be fine. Supplied with an external lab bench power supply the current draw is fine and there is no short circuit. But there are defect components on the secondary side (e.g. rectifier diode - parallel to the SR MOSFET)

 

I have five units with me. I check the drain-source voltage Vds of the INN2604 internal MOSFET. The MOSFET is turned off and the measurement shows the rectified and filtered 325Vdc, as to be expected with 230Vac RMS line voltage.

There is no "sign of life". The converter will not start switching.

I check the Input Voltage Monitor pin. It is about 12V, which is too high. Counter-check with a "healthy" unit there are about 4V, which is fine.

I disable the Input Voltage Monitor (V) pin and tie it to the Primary Bypass (BPP) pin. This net now measures 0V (BPP vs. Source/Primary GND).

 

I tried to supply 5.95V via an external power supply directly  to the primary BPP pin. The lab bench power supply enters current limitation (> 100mA), the pin appears to be shorted to ground.

 

I checked the RCD snubber circuit. All the parts, which I previously desoldered from the board, are intact and have their nominal values.

 

Furthermore, I tried to change the IC itself. On the backside a hole in the enclosure revealed itself. It is located in proximity to the drain and source pin. Please find pictures attached to this post. The desoldering itself is not the issue, because I have another unit where the INN2604 is still on the board and you can see the same bit of molten enclosure.

 

What conclusions can be drawn?  What might have caused the damage of the INN2604 converter IC?

Is there any possiblity to investigate this further?

Best regards

Alexander

Comments

Submitted by BAMA_AK on Thu, 09/30/2021

Edited

Submitted by PI-PIke on Tue, 10/12/2021

Hi BAMA_AK,

 

Could you please upload your schematic and layout?

 

Also when did the IC blew up? Is it on normal operation or at startup?

 

Regards,
PI-Pike

Submitted by PI-Lupin the Third on Tue, 10/12/2021

Hello, 

I already reached out to one of our engineers to help you in your concern. Meanwhile, you may also contact directly our local FAE in your area. Here's the link where you can find them. Sales Offices | Power Integrations, Inc.

Thank you and regards,

PI-Lupin the Third

Submitted by BAMA_AK on Tue, 10/12/2021

Hello PI-Pike, hello PI-Lupin,

thank you for your reply. Please find attached screenshots of the schematic and the layout. I attached the datasheet of the transformer as well. (There is another part to this circuit, another DC-DC converter, but this was not assembled. The components are not populated in this assembly variant.)

It is more likely the IC blew up in normal operation. The customer had the product installed and it was functioning. The product has a LAN interface. Later down the line, the customer could not reach the product (due to the missing internal voltage supply).

I exchanged the defect IC with a new one and now the power supply is working again (Changed D3, Q1 and U1 - Q1 was OK though). The continious load is 110 mA. Thermal is looking OK so far. I attached a IR image about 1 hour in after taking it into operation again. Hot spots are the Drain / Source area of the IC and on the other side the rectifier diode D4 of the auxiliary pin. I had it running for 4-5 hours that day and the voltage regulation was fine.

I will check the MOV with internal thermal fuse R38 next. If the thermal fuse operated or the MOV is damaged, this might suggest a problem with overvoltage in the grid. But after that, I am running out of options...

Best regards

Alexander

Submitted by BAMA_AK on Thu, 10/14/2021

Hello, 

the varistor R38 is fine. The integrated fuse did not activate and the voltage across the varistor (450VDC) at 1mA current through the component is within the valid range stated in the datasheet (387 to 473 VDC).

Best regards

Alexander

Submitted by PI-Martok on Mon, 10/18/2021

Hi Alexander,

     Did you observed a vent  on the input bulk capacitor C3? Another possible root cause could be high voltage surge or EFT. Common mode surge could damaged the SRFET and the output rectifier.

Regards

Mark

 

Submitted by BAMA_AK on Fri, 10/22/2021

Hi Mark,

there are no vents in the input bulk capacitor C3 recognizable. 

Regards

Alexander

Submitted by PI-Martok on Fri, 10/22/2021

Hi Alexander,

   Thanks for your Input.  I was wondering why the secondary SRFET and diode were also got damage. Kindly please check the following?

1. What is the voltage rating of the SRFET and Diode. I was thinking these components were damage first before the primary MOSFET got damage. The voltage across the primary will fly high if the output rectifiers are open.

2. Check the secondary snubber if still ok. Measure the capacitor value or check for micro crack

3. Check sign of output overvoltage.  Zener diode might be shorted or vent output capacitors

4.  I was also thinking these could be SRFET batch issue. Need to perform proper FA on those failed components even the IC. Please contact our local sales for IC FA

 

Submitted by BAMA_AK on Wed, 10/27/2021

Hello,

regarding your bulletpoints:
 

  1. The voltage rating on the SRFET (Vishay Si7456DP) and the diode (Diodes Inc. B1100-13-F) is 100V. Please find the datasheets attached. I was wondering of those components were pre-damaged or went bad over time, too. Out of curiousity I started an experiment: I put a switch in parallel to the SRFET and Diode, to manually add a short-circuit as if those components failed. I expected to damage the power supply.
    The power supply was running. 24V output was OK. I introduced the short-circuit: No voltage output, obviously. Removing the short-circuit, the power supply delivered 24V output again. No immediate damage or anything. I repeated this a few times. No harm.
    (Unfortunately I don't remember the load current. It might have been no-load condition. But I can repeat the test.)
  2. Secondary Snubber seems to be ok. I have to check at the laboratory under the microscope. At the moment I work from home.
  3. No obvious damage can be detected. I am going to double check the diode at the lab. No vents on the output capacitors.
  4. Yes, I will contact the local sales representative.

Alexander

Submitted by BAMA_AK on Fri, 11/05/2021

Hello Mark,

as a follow-up:

1. Datasheets attached - new try.
2. No micro crack at the secondary side snubber components.
3. Zener Diodes are OK on all units. No vents at output capacitors.

4. I tried to contact the local sales. Regarding my request via the Power.com homepage I only received a notice of arrival. I tried to call the sales office in Munich. Unfortunately the landline phone numbers  +4989552739100 and +498955273920 are not valid or assigned anymore.
Can you please give a hint: Who can I contact?

Best regards

Alexander

Attachment Size
Datasheet Diode 440.06 KB
Datasheet SR MOSFET 291.89 KB
Submitted by PI-Lupin the Third on Fri, 11/05/2021

Hi Alexander,

You may contact directly RMA@power.com for your concern. Please let me know if you have any concern.

Thank you and regards,

PI-Lupin the Third