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LM5123-Q1: Not switching, output same as input

Kryštof Vydra

Prodigy 10 points

Part Number: LM5123-Q1

Tool/software:

Hi Texas,

I have a boost regulator circuit designed by WEBENCH POWER DESIGNER for LM5123-Q1. It should boost from 6-8V on input to 12V on output. However in my case it seems like it is not switching at all. The output is similar to input with roughly 0.5V voltage drop (without load). By increasing load, the voltage drops more. The schematic is attached bellow. The C23 Soft-Start capacitor is replaced with 220nF capacitor.

What could cause or help to identify the issue?

Best Regards

Krystof Vydra

0 Moritz 5 months ago

TI__Genius 16085 points

Hi Krystof,

Thanks for reaching out.

Can you please share your webench design?

Best regards

Moritz

0 Kryštof Vydra 5 months ago in reply to Moritz

Prodigy 10 points

Hello Moritz,

here is the shared webench design:
https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=02428D895C9A6441

Best regards

Krystof

0 Moritz 5 months ago in reply to Kryštof Vydra

TI__Genius 16085 points

Hi Krystof,

Thanks for the design. I thought you mean that the design is not switching in the simulation, but you already built the circuit, right?

Sorry for the misunderstanding.

In this case i would like to see some measurements. Can you please attach scopeshots of Bias, Vout, TRK and COMP?

Thanks and best regards

Moritz