LMS3655: buck negative voltage preregulator

douglas Sudjian

Part Number: LMS3655

Hi,
I need a negative converter design used to function as a preregulator for an negative regulator/LDO in a power supply design.
I am using a LLC converter/transformer with center-tapped secondary to step the voltage down to +/- 24V.
The power supply has Plus/minus outputs.
The positive voltage side is easy.
However for the negative side:
I can simulation a typical buck converter in a feedback loop around the LDO using ground/center tap acting as a floating voltage sense with the negative supply (-24V)
acting as ground. So I am converting to a lower voltage (-3V to -24V) relative to ground.
I know this is very sensitive to the negative power rail @ -24V.

Can someone suggest a better solution?

over 6 years ago

0 Arief Hernadi over 6 years ago

TI__Mastermind 23815 points

Hi,

Do you have a maybe a sketch diagram of what the power block looks like?
Are you trying to convert -24V to -3V?
Are the center tap of the transformer is the ground of the secondary?

Thanks
-Arief

0 douglas Sudjian over 6 years ago in reply to Arief Hernadi

Prodigy 190 points

Hi,

Here is a very simplified schematic

The negative pre-regulator needs to vary from -3 to -17V from a -24V source

0 Arief Hernadi over 5 years ago in reply to douglas Sudjian

TI__Mastermind 23815 points

Hi Doug,
Seems from your block diagram, it makes sense.
Just make sure the amplifier output range and rail are appropriate for the negative pre-regulator.

Thanks
-Arief

0 douglas Sudjian over 5 years ago in reply to Arief Hernadi

Prodigy 190 points

Hi Arief,
I was hoping for another idea or suggestion since I have not seen anyone preregulate a negative power regulator in this manner.
But I don't see a cleaner method, so I guess I can't wish for sometime that may not be available.
Getting a dual secondary center-tapped transformer may be the toughest task.
Doug

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LMS3655: buck negative voltage preregulator