TIDM-PSFB-DCDC: PSFB SCHEMATIC R25 R26 FUNCTION IN VOLTAGE MODE CONTROL

gregg Gonzales

Part Number: TIDM-PSFB-DCDC

Tool/software:

Hi,

In this reference design, Figure 12. HVPSFB Base Board Schematic, page 11, i would like to understand in details the function of R25-26 across C20-21.

We referred to the schematic for our hardware design and our feedback loop control is voltage mode. Generally, these capacitors C20-21 are used as DC blocker to prevent the transformer from saturation. However with R25-26 being there provides a path for DC current to the transformer.

Could ypu please explain the purpose of these resistors? What are the advantage of having them for voltage mode control? If they are taken out, what could possibly happen?

Thanks and Best Regards,

Greggy

3 months ago

0 Shamim Choudhury 3 months ago

TI__Genius 11455 points

This design is

0 Shamim Choudhury 3 months ago in reply to Shamim Choudhury

TI__Genius 11455 points

This design is released as PCMC PSFB DC/DC. So the DC blocking caps are not needed. Resistors there can be removed if you short the jumper J6. Otherwise you can leave those there. Since it runs in PCMC mode , any DC volt caused by switching delay in each half cycle will be corrected by the peak current limit function. The resistors will just carry +ve and -ve current in each half cycle. They will not inject any DC as you wrote.

0 gregg Gonzales 3 months ago in reply to Shamim Choudhury

Prodigy 20 points

Hi,
Thank you for your reply.

I understand that the document is for PCMC control mode. But our design control choice is Voltage Mode which i believe this DC blocking capacitors are needed. Is there any document or design reference that can explain the presence of resistor R25 R26 across C20 C21 capacitors?

Best regards,
Greggy

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TIDM-PSFB-DCDC: PSFB SCHEMATIC R25 R26 FUNCTION IN VOLTAGE MODE CONTROL