LM5021: About PMP10215 circuit question

aggil liang

Part Number: LM5021
Other Parts Discussed in Thread: PMP10215

Hi Team,

We want to use PMP10215 for our product, and we find a question about this circuit, pls. help to explain the function of the below circuit red highlight.

tidrlm1a.pdf

over 5 years ago

0 aggil liang over 5 years ago

Expert 2660 points

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0 John Griffin1 over 5 years ago in reply to aggil liang

TI__Mastermind 34465 points

Hello aggil,

This is an auxiliary buck switcher configured with discrete parts and its input is from the main 36V 200W output.

I will contact the circuit designer and find out why this is a feature of the PMP10215

Regards

John

0 John Griffin1 over 5 years ago in reply to John Griffin1

TI__Mastermind 34465 points

Hello aggil,

I received this reply from the designer:

The circuit in the red line is actually a Buck converter.

When the voltage on C12 is higher than V(D25)+V(D28), which means we have a spike on anode of D31, we have a current through R69. If this current is sufficient to drive the Schmidt trigger input (pin 2 of SN74LVC….), then we have a Ton over Q13. During this small Ton (which is synchronous with switching waveform of the main converter, but has duty cycle dependent on the amount of energy is contained in the spike), the Buck converter, defined by Q13, L10 and D27, will inject the energy during Ton into Vout (36V).

This way the energy in the spike is recovered cycle-by-cycle and not wasted in a snubber resistor. It’s actually an “active snubber”.

Regards

John

0 aggil liang over 5 years ago in reply to John Griffin1

Expert 2660 points

Hi John
thank you very much.

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LM5021: About PMP10215 circuit question