LNK623 failure in AC-DC power supply

Hi Sakjain92, 

Good day! 

Thanks for using Power Integration products. 

We would like to below data so that we can help you on your query.

 - Vin min 

 - Vin max  

 - MOV1 complete manufacturing part number 

 - R11 complete manufacturing part number

 - What is the function of Q7?  

 - What is the Transformer Primary and Secondary turns? If you can provide the TRF construction the better. 

 - Are there other component damage aside from LNK623? 

Thanks 

Regards 

PI-CHLOE

Hi,



The nominal input voltage is 230V. Min/Max can be taken as 100-300VAC.

MOV: S14K510 (From EPCOS: Datasheet: https://www.tdk-electronics.tdk.com/inf/70/db/var/SIOV_Leaded_StandarD.pdf)

We don't have a fixed make for R11 (it varies during production as per supply). It's a wire-wound resistor of 100E/2W.

The purpose of Q7 along with TVS is to clamp the input voltage (bus line) to ~3*207V (to clamp surges on the input line)

The specs of the transformer (101 Turns on primary, 18 Turns on S1, 13 Turns on S2, and 13 turns on S3. See the pin numbers mentioned in the schematic with the pin number mentioned in pic attached)

No other components apart from LNK623 were damaged.

Hi Sakjain92 

LNK623 Vds have an absolute max of 725V. 

Now the MOV used was S14K510.

According to the datasheet: 

 - SK14K510 will NOT ACTIVATE / CLAMP when input voltage is below 520Vrms (735Vp) 

 - It will start to clamp with 1mA current when voltage across it is 820V. Clamping of the MOV will start at 820V which is above the absolute max of the IC. 

MOV protection or clamping action is beyond the IC absolute max. IC will be damage because it will see a very high input voltage during any surge event. 

Since max Vin is 300Vac, suggest to use S14K320 or S14K350.  

Thanks 

Regards 

PI-CHLOE

Hi Cloe,



This is why we are using Q7. The Q7, along with D14,D15,D17 clamps the bus clamp after Q7 to 3*Vclamp of TVS (Datasheet of P6KE150A says that Vclamp will be between 150V-207V) So after Q7, the bus line voltage will be between 450V-621V. (Essentially we have both MOV & the clamping circuit for dealing with surges)

We have also tried modifying the circuit to remove D17 so that Q7 clamps the bus line voltage to between 300V-414V but still the LNK623 got damaged.

Hi Sakjain92 

Changing MOV from S14K510 to S14K320 or S14K350 is needed because the present S14K510 will not help.

This can also remove the Q7 circuit. 

I think you can replicate the issue. Do you have any data in which the power supply fails?

Meaning do you have Vin and loading condition information on the time of failure? or any other condition during the point of failure.

Better to add probe on the Vds and Ids so that we can understand the concern fully. 

I have other question. 

 - There is only one output which is 12V with 0.2A Load. why the TRF have two winding to support the 12V (winding 6-7 and 9-10). 

 - Is winding 6-7 generates another output voltage? 

 - If there is only 12V output, you just need to have one winding and one power diode. Meaning D6, C3, R6 can be remove. 

 - Have you run PIExpert to for the TRF design? If yes, can you provide me the PIExpert. 

 - What is the inductance of the Primary winding? 

Thanks 

Regards 

PI-CHLOE