UCD3138HSFBEVM-029: When secondary rectifier uses a soft start, there is a problem with the no-load start-up waveform .

wu chenglong

Part Number: UCD3138HSFBEVM-029
Other Parts Discussed in Thread: UCD3138, UCD3138A

The secondary rectifier adopts soft start. The no-load start-up waveform is shown in the figure below. What problem can cause this startup waveform?

over 6 years ago

0 Amiel Hussain over 6 years ago

TI__Expert 4070 points

An engineer will respond to you.

0 wu chenglong over 6 years ago in reply to Amiel Hussain

Prodigy 130 points

No engineer reply me.

0 Yitzhak Bolurian over 6 years ago

TI__Mastermind 18370 points

What is the exact part number you are using? Is it UCD3138 or UCD3138A?

This feature is not enabled as default in the UCD3138HSFBEVM-029

In UCD3138A the hardware increases the SR pulse in the oposite direction, therefore the Sync-FET soft On needs to be handeled by firmware (Firmware implementation does not use the hardware ramp mechanism).

If the device you are using is UCD3138, then you may want to tune the rate of SR soft on and look at the SR pulse growing properly, using an Oscilloscope before you look at the end result.

Hope this makes sense,

Regards,

0 Yitzhak Bolurian over 6 years ago in reply to Yitzhak Bolurian

TI__Mastermind 18370 points

If the reported issue is resolved, please set the status of this post to resolved.
Thanks and regards,

Power management

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UCD3138HSFBEVM-029: When secondary rectifier uses a soft start, there is a problem with the no-load start-up waveform .