UC3845: Power Supply capacitor for the device is going bad after few days of running.

Sendhil Kumar2

Part Number: UC3845

UC3845 is using to generate the output Power of 24V / 5Amps from the Input AC Volts of 88Volts to 265Volts ( with 50Hz to 60Hz).

From the transformer output -diode is connected in series with series termination resistor.and one capacitor connected to gnd near to diode end.

After few days of working the Capacitor is going faulty - when we replace capacitor the power supply system is working fine.

your inputs in this regard is highly appreciable.

Snapshot of the schematics : In which capacitor is becoming faulty. C33 : C1206X225K5RACTU ( CAP,CER,2.2UF,10%,50V,X7R,FLEX,1206,SMT)

Thanks in Advance for your kind support.

Regards,

S.Sendhil kumar.

over 3 years ago

0 Teng Feng over 3 years ago

TI__Genius 13660 points

Hi S.Sendhil,

The attached picture is broken, could you upload it again.

Thank you.
Teng

0 Sendhil Kumar2 over 3 years ago in reply to Teng Feng

Prodigy 50 points

Hi Tang,

I have attached the picture again.

Thanks in Advance for your kind suport.

Regards,

S.Sendhil kumar.

0 Sendhil Kumar2 over 3 years ago in reply to Teng Feng

Prodigy 50 points

0 Teng Feng over 3 years ago in reply to Sendhil Kumar2

TI__Genius 13660 points

Hi S.Sendhil,

I suggest parallel this capacitor C33 with Zener D52, after current limited resister R204, then its voltage can be clamped. But there is already a 220uF capacitor C48 at VCC pin, C33 is not necessary.

Regards,
Teng

0 Sendhil Kumar2 over 3 years ago in reply to Teng Feng

Prodigy 50 points

Hi Teng,

In Texas instruments webench schematic also there are two capacitors ,then may i know the reason for that .

Kindly do the needful.

Thanks and Regards,

S.Sendhil kumar.

0 Teng Feng over 3 years ago in reply to Sendhil Kumar2

TI__Genius 13660 points

Hi S.Sendhil,

Here is the Webench module as your provided specs.

https://webench.ti.com/power-designer/switching-regulator/customize/67?noparams=0

Could you share your Webench module?

If the capacitor is placed before current limiting resister, the capacitor voltage can not be clamped by Zener.

Regards,
Teng

0 Sendhil Kumar2 over 3 years ago in reply to Teng Feng

Prodigy 50 points

Hi Teng,

I hope you are doing good.

I could not able to open the shared link any permission been required.

Kindly share the link which simulation part enable,

Thanks in advance for your kind support.

Regards,

S.Sendhil kumar.

0 Teng Feng over 3 years ago in reply to Sendhil Kumar2

TI__Genius 13660 points

Hi S.Sendhil,

Attached the Webench design report. Could you share your Webench module? Thankyou.6433.WBDesign67.pdf

0 Sathish Rajendran over 3 years ago in reply to Teng Feng

Prodigy 10 points

Hi Teng,

Still the Root Cause of the failure is not concluded, until that we are not privileged to modify the existing design

is there any flaw in the existing design, since the failure observed from the field after several years of operation? what could be the primary cause of Capacitor failure is something related component deraing issues or a Reliability / life failure?

your thoughts are awaited

Thanks and Regards,

Sat

0 Teng Feng over 3 years ago in reply to Sathish Rajendran

TI__Genius 13660 points

Hi Sathish,

My thinking is that this issue is caused by large ripple current on capacitor C33. And this capacitor is not necessary, you can just remove it in the design.

Thank you.

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UC3845: Power Supply capacitor for the device is going bad after few days of running.