LP3872: Must the source voltage be pre-regulated?

James VDC

Part Number: LP3872

Hello,

I am hoping to use the LP3872 LDO Regulator in a 5V power supply design. The supply will be used to power (0.08A) and charge (up to 1.0A) a specific device; however, with all such things, someone will likely plug a cell phone into there as well.

I have a dedicated transformer secondary winding, bridge rectifier and generous reservoir capacitor. From here I want to employ the LP3872. If my initial Transformer - Rectifier - Reservoir are appropriately designed, do I need to employ the LP3872?

Thank you

over 1 year ago

0 Nick Butts over 1 year ago

TI__Mastermind 38155 points

Hi James,

I'm not sure I quite understand the question. Are you asking that if the transformer-rectifier-reservoir circuit is appropriately designed whether you will need the LP3872 at all? The title of this post seems to be asking a different question.

Thanks,

Nick

0 James VDC over 1 year ago in reply to Nick Butts

Prodigy 240 points

Nick,

The LP3872 datasheet indicates that "the input supply should be well regulated and free of spurious noise." My question is as to just how "well regulated" the input supply should be? ie: Is a basic power supply topography sufficient or is pre-regulation necessary?

+1 Nick Butts over 1 year ago in reply to James VDC

TI__Mastermind 38155 points

Hi James,

In general the input is not required to be pre-regulated by another device. This device is pretty old and there is no PSRR plot in the datasheet so it's difficult to analyze just how well noise at the input will couple onto the output, but you can expect the device to regulate whether there is noise on the input or not. So to answer your question, a good linear design of the transformer stage will be sufficient for the input of LP3872.

Regards,

Nick

0 James VDC over 1 year ago in reply to Nick Butts

Prodigy 240 points

Thanks Nick!

0 Nick Butts over 1 year ago in reply to James VDC

TI__Mastermind 38155 points

You're very welcome!

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LP3872: Must the source voltage be pre-regulated?