FWD Pin Resistor Failure
I’ve designed a 9W, 12V power supply using the INN3624 (1250V version). When powered at nominal 240V AC under no-load conditions, the resistor connected to the FWD pin burns out. However, when the input voltage is reduced to around 70V AC, the resistor only heats up and the output voltage appears to regulate correctly. The IC itself is not getting damaged—only the resistor on the FWD pin is affected.
Note:- This design used Diode instead of SRFET and Bias winding is not used as efficiency is not so critical.
What could be causing this issue? What parameters or design aspects should I investigate to resolve it?
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Hi Pavan,
Good day.
I would like to follow up on the requested documents so we can further review your design and check what might be causing the issue.
Thank you and I look forward to your response.
Regards,
Tommy
Hi Tommy.
Thanks for the follow up.
I was trying to download the file from PI expert file but there seems to be glitch as i am using PI core(ungapped) so am unable to select core as there are only option for ferrite core. When i choose custom it doesn't properly taking the value. So will provide the data below.
Lp=671uH ,Np=96 ,Ns=25 , Vin = 240 AC
Not using Bias winding and Using 3A 400V Secondary Rectifier Diode instead of SRFET. Using PI INN3624 Standard Current Limit.
Thank you and I look forward to your response.
Regards,
Pavan
Hello Pavan,
It would be great if you could share the actual schematic diagram, PCB layout (Gerber files), transformer datasheet (with primary inductance and number of turns of each winding information), PI Expert file (exported as PDF), and bill of material of the design so we can take a quick look and check if there's anything unusual with the design that's causing the FWD pin resistor to get burned.
If you can't share the design files here, I would suggest raising a support request through our support page, PowerPros Online Support. Rest assured that we'll get back to you once your request is logged on our system, and you can share the design files by attaching them to the request or through email.
Regards,
Tommy
A forward pin resistor failing repeatedly usually means it’s either underrated for surge/continuous power or there’s unexpected transient stress from the transformer or line conditions. Try increasing wattage, reviewing snubber design, and checking for layout-induced spikes. I’ve seen something similar on a design using an IGBT like RJP30H2A where transient energy wasn’t properly clamped.
Hello Pavan,
Good day and thank you for choosing Power Integrations.
I would appreciate it if you could share your schematic diagram, PCB layout (Gerber files), transformer datasheet (with primary inductance and number of turns of each winding information), PI Expert file, and bill of materials so we can further review your design and check if there's anything unusual that might cause the issue.
Thank you and I'm looking forward to your response.
Best regards,
Tommy