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LM5161: LM5161 in flybuck topology with 5 secondary outputs not working

Stefano Infante
Expert 2320 points
Part Number: LM5161
Other Parts Discussed in Thread: CSD

Hello,

I have this power circuit on a board:

My problem is that the circuit does not work (output = 0 V).

I have a very similar circuit on another board, which is working perfectly (it only has some different values as it generates 10 V from a 24 V input and has 10 secondary outputs...).

Parameters:

- 48 V input

- about 0.6 A of total output current (primary + secondary outputs)

- the transformer's turns ratio is 1:1:1:1:1:1

What I tried:

- D2 away: no change

- only transformer pins 1&2 connected: V_CSD = 22 V as expected

- only transformer pins 1, 2, 11, 12 connected: no output

- only transformer pins 1, 2, 3, 3 connected: no output and something got burned (well, I cannot see anything burned, but I can smell it...).

Have you got some advice?

Thanks in advance

Regards,

Stefano

  • 0
    TI__Expert 6245 points
    Hello Stefano,

    This will probably take some back and forth. A couple of quick checks to start with:

    Are the diodes (not shown) on the secondary windings able to handle the increased voltage?
    Try a lower input voltage similar to your other design to see if high voltage spikes are interfering with operation.
  • 0 in reply to Robert Blattner
    Expert 2320 points

    Oooookay Robert, I made a BIG mistake: no diodes on the main output. All the SB_x outputs have a diode, but the main one has not.

    Now I am testing it all again. Apart from a new burning smell (I will have to double check later), now I have all voltage outputs.

    Bottom line: NEVER design when you are in a hurry...

    Thanks for your help.

    Stefano