LM5185: Schematic and Design Calculator Review for Flyback DC-DC Converter using LM5185.

Vandana D

Part Number: LM5185
Other Parts Discussed in Thread: UCC2897A

Tool/software:

Dear TI Support Team,

I am working on an isolated flyback DC-DC converter design using the LM5185 controller. Based on the design calculations provided by Texas Instruments in the official Excel design tool, I have made the necessary modifications to align the design with our specific application requirements.

Attached are the following documents for your review:

Schematic design of the LM5185-based flyback converter
Design calculator sheet (provided by TI, with updated values based on my requirements)

"Please review the schematic and design calculations at your earliest convenience, focusing on components, transformer specs, snubber, and loop stability, and advise on any required changes."

Best regards,
Vandana DLM5185-DESIGN-CALC_1.xlsx

4 months ago

0 Steven Mappus1 4 months ago

TI__Mastermind 33045 points

Values all seem reasonable. The compensation is targeting 1kHz crossover but the Bode plot shows 10kHz crossover. At 10kHz, although you still have ~30 degrees phase margin the phase is quickly collapsing. How about designing for better stability and reducing the crossover frequency by selecting compensation components closer to the suggested values?

Steve

0 Vandana D 4 months ago in reply to Steven Mappus1

Prodigy 140 points

Thank you for the feedback!

We're still new to this type of design and currently in the learning and exploration phase. To help us better align with the original design target of a 1kHz crossover frequency, could you kindly suggest the exact compensation component values you would recommend?

That guidance would really help us move forward with a more stable design. We appreciate your support!

0 Steven Mappus1 4 months ago in reply to Vandana D

TI__Mastermind 33045 points

try this

LM5185-DESIGN-CALC_E2E.xlsx

0 Vandana D 4 months ago in reply to Steven Mappus1

Prodigy 140 points

Thank you for all the inputs. Regarding the design and calculations shared, could you please confirm if the IC supports a 10A current? Additionally, we would appreciate any suggestions to further improve the efficiency.

0 Vandana D 4 months ago in reply to Vandana D

Prodigy 140 points

"In addition, would a 220 µF capacitor be sufficient for the output stage?"

0 Steven Mappus1 4 months ago in reply to Vandana D

TI__Mastermind 33045 points

150W is too much power for a flyback at VIN=19V. Check the TI reference design library here.

Steve

0 Vandana D 4 months ago in reply to Steven Mappus1

Prodigy 140 points

"As per our design, we are using 48V at VIN. Could you please confirm if a 150W power supply would be sufficient?"

0 Steven Mappus1 4 months ago in reply to Vandana D

TI__Mastermind 33045 points

150W is a lot of power for flyback operating in DCM/CCM. I would recommend a ZVS topology like active clamp forward (UCC2897A). Check the TI reference design library here.

Steve

0 Vandana D 4 months ago in reply to Steven Mappus1

Prodigy 140 points

Thank you for the suggestion — we’ll certainly explore the active clamp forward topology using the UCC2897A.

In the meantime, could you please confirm whether our current flyback DC-DC converter design [LM5185] is achieving approximately 85% efficiency?

0 Steven Mappus1 4 months ago in reply to Vandana D

TI__Mastermind 33045 points

Not sure what you're asking? Have you built a converter and you want to know how to measure the efficiency? The estimated efficiency is provided in the Excel design tool but this is only an estimate.

Steve

0 Vandana D 4 months ago in reply to Steven Mappus1

Prodigy 140 points

150W is too much for flyback in DCM/CCM — agreed. Please share the complete design calculation document for the ZVS topology you suggested (active clamp forward with UCC2897A). Also, are you sure the 82.8% efficiency you mentioned is truly achievable in practice?

0 Vandana D 4 months ago in reply to Vandana D

Prodigy 140 points

"We are specifically looking for automotive-grade ICs, so we hope your recommendations align with that requirement."

Thank you.

0 Steven Mappus1 4 months ago in reply to Vandana D

TI__Mastermind 33045 points

UCC2897A is not AEC rated. Search the ref design link I send you. Also, you can use TI Power Stage Designer to evaluate and compare topology options. I just think 150W is pushing the limits of a single switch flyback topology, operating in DCM/BCM.

Steve

0 Vandana D 4 months ago in reply to Steven Mappus1

Prodigy 140 points

Thanks for the input. Could you please suggest a suitable topology to achieve 150W in an isolated Flyback DC-DC converter [AEC rated].

0 Steven Mappus1 4 months ago in reply to Vandana D

TI__Mastermind 33045 points

forward, push-pull or LLC half-bridge could all handle 150W

Steve

0 Vandana D 4 months ago in reply to Steven Mappus1

Prodigy 140 points

The TI reference design tool suggested earlier seems to have some issues — specifically, the search function isn't working properly. Please do check on it

0 Steven Mappus1 4 months ago in reply to Vandana D

TI__Mastermind 33045 points

What is the error? If you enter so many specific parameters you may not see a result. Start with a broad search with less parameters and you will see a list of reference designs. You then look for something close to what you require. It is likely you may not find an exact match to such specific requirements.

Steve

0 Vandana D 4 months ago in reply to Steven Mappus1

Prodigy 140 points

Got it. As mentioned earlier, could you suggest reference designs using forward, push-pull, or LLC half-bridge topologies that can handle 150W?

0 Steven Mappus1 4 months ago in reply to Vandana D

TI__Mastermind 33045 points

Your original E2E inquiry landed at my inbox because of the part number included in the title. I am supporting TI bias supply products that are low power (typically less than 10W). Please submit a new E2E inquiry for support from the product experts in LLC or Push-Pull, Forward, etc?

Choose a topology
Design the power stage
1. TI Power Stage Designer
Choose a controller
1. TI PWM Controllers

Regards,

Steve

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LM5185: Schematic and Design Calculator Review for Flyback DC-DC Converter using LM5185.