Linear Power Supply Design

Abbas_BrainAlive

Joined Feb 21, 2018
104
Hello All!

I was wondering what would be the most optimum approach to manage multiple outputs in a linear power supply.

For example, I have a single Li-Ion battery, and I need two different output voltages, say 1V8 and 3V3. I opt for a linear power supply to minimise noise in the system. Now, what would be a better approach to this?
1. Should I extract both the voltages directly from the battery?
2. Or should I extract only 3V3 from the battery, and extract 1V8 from the 3V3 output?
3. Or is there any better approach?

The basis of my question is, in a linear power supply, the greater the difference between the input and the output voltages, the more power is dissipated in the regulator/PMIC itself.

To me, both the approaches (1. and 2.) do not hold any significant difference in terms of power savings.

Any suggestions and/or inputs are appreciated.

Abbas.

Uilnaydar

Joined Jan 30, 2008
118
You need a minimum voltage on the 3V3 regulator to get 3.3V. For example, LD1117 is 4.5V minimum.

Abbas_BrainAlive

Joined Feb 21, 2018
104
You need a minimum voltage on the 3V3 regulator to get 3.3V. For example, LD1117 is 4.5V minimum.
Thanks for the response,

Apart from the minimum input voltage consideration?

My question is mainly focussed on power considerations.

BR-549

Joined Sep 22, 2013
4,938
It will depend on your current demand at those voltages. A linear reg is a heater also.

BobTPH

Joined Jun 5, 2013
2,349
Both methods will waste exactly the same amount of power. The distribution of it between the two regulators will differ. Chaining them will have more power dissipated in the 3V3 regulator and less in the 1V8 one. If the 1V8 has this higher dissipation, that would be a good thing. If not, it would be needlessly increasing dissipation in the 3V3 one.

Figure out how much would be dissipated in each by both methods, and pick the one that makes them more balanced.

Bob