PLC810PG 10% problem with LLC VCO frequency
We are using the PLC810PG in a product which is now in its second production cycle, and find 10% exhibit a fault where the voltage at the FBL pin is 1.18V; not the usual 0.8V. Consequently the LLC maximum frequency can not be achieved and no load regulation is problematic. Is there any known fault or failure mechanism that would cause this issue?.
Our design is typical and based on the RDR189, however we have made several innovations to improve performance for our application. These is a cycle by cycle current limit that acts to increase the VCO frequency (simple circuit that works well), and the PFC's Duty cycle is limited to 65%: VCOMP voltage is prevented from falling below 1.2V. The usual PLC810's unlimited Duty cycle can be problematic when operated on a high impedance power supply.
Have attached a pdf of our circuit for consideration.
Comments
Can you send in the defective parts via our RMA process?
I would like to have the parts checked out to determine the root cause of failure.
I have several of the parts here in NZ, the rest (about 50 pieces) are at our China OEM factory. Are these two pieces enough for your investigation or should we get further faulty parts sent from our China OEM?. How do I proceed with the RMA what is the procedure?
Thanks
More than 2 parts would be better.
You can send the bad parts to:
RMA, attn: Tu Giao
Power Integrations
5245 Hellyer Avenue
San Jose, CA USA 95138
phone is (408) 414-9200
Place your contact information in the envelope.
About the frequency foldback circuit..
Have you tested it over temperature? (e.g. 0-50*C)
Will get further defective parts and send for investigation. I haven't specifically tested the frequency fold back circuit at 0 - 50°C. However we have done overload and high temp° testing with no issues. The product has achieved CB compliance, and has TUV safety certificate.
Our China factory has run another production run (500 units). We are having even more faults with the PLC810PG where the FBL control voltage is 1.24V @ 100KHz. (This is normally ~0.8V). We have socketed several Power supplies and changed IC's: 5 out of 10 had the problem which usually casues audible PFC operation and poor LLC regulation during No-Load conditions. It may also result in destroyed LLC MOSFET's, or Burn as the Chinese say.
I have these 5 IC's + another 8 I can send for RMA inspection. All from different IC batches.
Any clues what may cause the IC to fault in this way?
THe schematic and PCB is the same as previously sent - except have now added series LL4148 and 10R resistors to the LLC MOSFET gates to reduce the possibilty of negative voltage spikes on the PLC810PG drivers during the LLC dV/dt's - Didn't solve the issue. I have tried many thiings to try and cause the IC to fail with FBL @ 1.24V. i.e. tried exceeding the GNDL - GND voltage limits, tried overvoltaging the driver and IC circuits, in all cases the IC survived without problem. Over temperature did give a similar failure, however the socketed IC's were never exposed to thermal stress - so this can't be the problem. Do I send the faulty IC's to the address sent previously, is it the same RMA process, or do I need to quote an RMA number.
My last post has gone un-answered for over a week. We need to know what would is casuing the VCO problems on the PLC810PG IC's. We have faulty IC's, that can be sen t to Power Integrations for further investigation, please confirm the RMA process. It seems Power Integrations does not offer technical support via Phone, so am forced to use this sluggish Forum to make contact.
If you send in an RMA, please include a failed and a functioning power supply.
Have sent a package by DHL with the faulty IC's and two power supplies: failed and functional as requested.
The DHL package with faulty PLC810PG IC's & 2 x Power supplies has arrived at Power Integrations (San Jose) on Monday 10th, 11am. Waiting eagerly for your appraisal and advise about what is casuing the IC's to fail, or if there is some power supply design flaw. Thanks.
Please advise if RMA has the package and when they can investigate the IC problem.
Would be good to know something is happening!!
Replacing the PLC810PG has fixed the issue. It seems the IC has been damaged internally - would like to know how so it can be avoided in the future.
All other external voltages appear OK, i.e. Vref = 3.28V. The IC marking (if important)is 0905 PLC810PG M59690AD Thanks