Regulated 5v from unregulated 5v!

[Joao]

Hello,
I have one device that can be powered from one poorly regulated supply of 4v to 5.5v.

From it I must power digital electronics devices including one microcontroller. The logic is 5v.

I am having really trouble to find one chip that accepts 5v and regulates to 5v (low noise)!

It should be capable of delivering at least 700mA.

Any help will be mostly welcomed

Thanks

 

[Koeppel]

Even the best LDO regulators cannot produce a regulated 5VDC from something less than 5V in. You must first amplify the voltage to something like >5.3V and then regulate it to 5.0VDC.

 

[jbartos]

One way to increase the voltage is over a transformer. However, 4V if dc, has to be chopped first, then stepped up to 5.5V (or higher) and then regulated to 5.5V (and rectified back to dc, if applicable).