LM5180EVM-DUAL: Flyback diode issue of BSR052A BOM

Jeffrey Chung1

Part Number: LM5180EVM-DUAL
Other Parts Discussed in Thread: LM5180

Hi TI Team,

I'd like to ask you on flyback diode of BSR052A BOM(snvr472.zip). My customer made their board like LM5180EVM-DUAL, they found that the output voltage was 18V with flyback diode US1DFA(ONSEMI), but it was 15V normally when changed US1DFA to S1J(Vishay). According to the design file(snvr472.zip), the flyback diode of BSR052A BOM is US1DFA(ONSEMI). Please let me know the reason why this issue happens.

Regards,

over 3 years ago

0 Daniel Li14 over 3 years ago

TI__Mastermind 27470 points

are all the components same as our evm board or have some changes?

for 18V and 15V output voltage with different diode, do you know what is the load condition?

Thanks

0 Timothy Hegarty over 3 years ago in reply to Daniel Li14

TI__Guru 72702 points

Hi Jeffrey,

18V occurs at no load based on the output clamp zener. Just load the output with 10mA or more and check that it regulates at 15V as expected.

Note that the Vishay S1J is a 600V diode, and S1D is the 200V equivalent. You may even be able to use a 100V diode, depending on Vin-max, etc.

Regards,

Tim

0 Jeffrey Chung1 over 3 years ago in reply to Timothy Hegarty

Genius 3260 points

Hi Timothy,

Let me check it with my customer and let you know the verification result.

Regards,

0 Denislav Petkov over 3 years ago in reply to Jeffrey Chung1

TI__Mastermind 19891 points

Hi Jeffrey,

Let us know when you have verification results.

Cheers,
Denislav

0 Jeffrey Chung1 over 3 years ago in reply to Timothy Hegarty

Genius 3260 points

Hi Timothy,

As I checked with my customer, the output voltage is 18V even though the load current of output is 200mA. So I attached their schematic below. Please check it and let me know the points that have to be changed.

Schematic_LM5180.pdf

Regards,

0 Timothy Hegarty over 3 years ago in reply to Jeffrey Chung1

TI__Guru 72702 points

Hi Jeffrey,

I recommend checking your schematic with the LM5180 quickstart calculator. It looks okay, just check to ensure the transformer mag inductance is correct and the sat current is 2A or higher. There must be some issue with the Vishay diode if it causes te converter to run the output at the zener clamp level of 18V, which is very dissipative. We have not tested this Vishay diode or its characteristics near zero current when output voltage sensing/detection occurs for regulation.

Regards,

Tim

0 Jeffrey Chung1 over 3 years ago in reply to Timothy Hegarty

Genius 3260 points

Hi Timothy,

Let me check the transformer's specifications. In case of Vishay diode(S1J), the output voltage is 15V@400mA(load current). So there is more thermal than Onsemi diode(US1DFA) on the transformer due to the increase of load current.

Regards,

0 Timothy Hegarty over 3 years ago in reply to Jeffrey Chung1

TI__Guru 72702 points

ok, thanks Jeffrey.

0 Jeffrey Chung1 over 3 years ago in reply to Timothy Hegarty

Genius 3260 points

Hi Timothy,

I checked the transformer's specification(ZB1114-AL of Coilcraft) and attached it that is same as YA8916-BL. Please check it.

ZB1114-AL_Coilcraft.pdf

Regards,

0 Timothy Hegarty over 3 years ago in reply to Jeffrey Chung1

TI__Guru 72702 points

Hi Jeffrey,

The transformer spec looks great with 30uH mag inductance and 2A sat current. Thanks for sending. You can also check it using the LM5180 quickstart calculator.

Regards,

Tim

0 Jeffrey Chung1 over 3 years ago in reply to Timothy Hegarty

Genius 3260 points

Hi Timothy,

As you told me, I checked it using LM5180 quickstart design tool, it looks okay. Are there any other check points?

Regards,

0 Timothy Hegarty over 3 years ago in reply to Jeffrey Chung1

TI__Guru 72702 points

Looks good, Jeffrey, thanks. This seems very similar to the LM5180 dual-output EVM.

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LM5180EVM-DUAL: Flyback diode issue of BSR052A BOM