LM5026: Vin 48V to Vout 12V(120W) circuit design.

Mars Wu

Part Number: LM5026
Other Parts Discussed in Thread: PMP22075, , TL431

Tool/software:

Hello,

I modified the circuit design of LM5026 based on PMP22075, but found that Pulse transformer (T6) makes noise when powered on.

The following are the specifications of the circuit design and schematic, could you help to check what happen in this curcuit?

- Vin = 48V
- Vout = 12V
- Pout = 120W

Isolated power design 48V to 12V (120 Watts).pdf

Pulse transformer PA0937NL

T6_PA0937NL.pdf

Best regards,

4 months ago

0 Steven Mappus1 4 months ago

TI__Mastermind 27305 points

If you are hearing audible noise, the frequency is in the range of <20kHz but the transformer is rated for 200kHz<F<500kHz. Measure to determine what signal is the transformer seeing? If the original PMP22075 was rated for 60W and you increased to 120W, make sure you adjusted the CS, compensation and power stage components accordingly. You can use TI Power Stage Designer to help model the power stage and control loop.

Steve

0 Mars Wu 3 months ago in reply to Steven Mappus1

Prodigy 10 points

Hi Steven,

After changing R593 to 20K ohm, the abnormal noise problem of the transformer was solved.

But it still only has 12V/3A output, which cannot reach the 12V/5A output designed as PMP22075.

5732.Isolated power design 48V to 12V (120 Watts).pdf

Are there any key points I'm missing?
Is there an FAE in Taiwan that can help solve this problem?

Thanks a lot!

0 Steven Mappus1 3 months ago in reply to Mars Wu

TI__Mastermind 27305 points

Your compensation and opto/TL431 bias do not look correct. When you are at 3A load, check your COMP and CS voltages. Makes sure the feedback is as you expect, make sure the CS signal is valid and below the max threshold shown in the data sheet.

Steve

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LM5026: Vin 48V to Vout 12V(120W) circuit design.