This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM5161-Q1: LM5161-Q1 Fly-Buck spec review

Part Number: LM5161-Q1
Other Parts Discussed in Thread: UCC28C45-Q1, UCC28C45

Dear Sir,

My customer consider as below spec using LM5161-Q1.

Could  you please check it possible or not.

1. if possible, could you provide reference schematic and let me know transformer spec about below spec.

2. if impossible, could you provide maximum spec such as min, max vin rage and max output range(Vout, Iout)

topology : Fly-Buck (dual output)

vin: 9V~95V

Vout: 12V 1A

Voutiso: 12V 1A

  • Dexter,

    The LM5161-Q1 will not be able to achieve this.

    1. VIN must always be greater than VOUT. You cannot convert 9V to 12V with a buck (or the primary of a flybuck)
    2. Current limit - The part is rated for 1A. That means 12V at 1A on the primary leaves no current for the secondary.
    3. Flybucks have duty cycle limitations due to the leakage inductance of the transformer. The regulation of the secondary starts to become bad at high duty cycles (>50% for high Lleak). This wide input range requires a large duty cycle variation from VIN_MIN to VIN_MAX

    For the specifications listed you may need a dual-stage solution. If the specs are flexible, which specs are flexible?


  • Dear Sam,

    Thank you for your reply.

    Can you recommend the solution one of below specs.

    1. Vin 9V~95V, Vout1-12V 2A (isolation), Vout2- 12V 1A(isolation), Vout3- 6V 1A(Isolation)

    2. Vin 9V~95V, Vout1- 12V 2A (non-isolation), Vout2- 12V 1A (isolation)


  • Dexter,

    For these specs I'd recommend a flyback. I will notify the flyback group to help you with your part selection. They should respond in a day or two.

    Thank you,


  • Dexter

    One of our single ended current mode PWM controller like UCC28C45 configured as a flyback would work best here.  If you need AEC Q100 grade the automotive version of this device UCC28C45-Q1 will work.

    Unfortunately we don't have a reference design that is close to their design requirements.  This is a fixed frequency flyback controller, so the following collateral will help with a design with this device

    Best Regards,