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How to get 5 volts from 6.4 volts

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alec_t

Well-Known Member
Most Helpful Member
In that case why not just use a low drop-out 3V regulator?
 

Boncuk

New Member
Boncuk,

I have several rechargeable Nickel-metal hydride batteries. My workplace encourages us to use them as a gesture for the environment. They produce 1.2 volts when fully charged. If you want to allow the end user to use rechargeables, you couldn't use the voltage as an indicator of charge status. Really, the cell is depleted when it produces 0 volts. It is useless when the combined output is less than the requirements of your components (in this case, 1.8 volts total). Assuming the microcontroller and all other components still work acceptably at 1.8 volts, then that's all you need the cells to produce.

Richard


Oops! :(

Completely different story! :confused: :confused:

Please refer to post #1. :mad:
 
Well, look, I guess engineering is all about compromise. Ultimately, you can accept a widely varying input voltage if your components can tolerate it, and you might get identical function from your components or tolerably different behaviour given different input voltages. Or you could try to fix the voltage and accept loss of power as heat. A low drop out regulator limits your margin for error so that you may not be able to use rechargeables at all. One way or another, you're taking the worst of it somewhere.
 

Boncuk

New Member
Well, look, I guess engineering is all about compromise. Ultimately, you can accept a widely varying input voltage if your components can tolerate it, and you might get identical function from your components or tolerably different behaviour given different input voltages. Or you could try to fix the voltage and accept loss of power as heat. A low drop out regulator limits your margin for error so that you may not be able to use rechargeables at all. One way or another, you're taking the worst of it somewhere.

Very niceley said! In other words: Well, look, it's your baby!

Boncuk
 

grizzly1

New Member
Check out an LT1129, I have had good luck with these in many designs. The dropout voltage is pretty low around .3 volts at 300 mA and increases to about .6 at 700 ma which is the max for this. -- You don't mention anything about current (or I missed it) but usually the dropout voltage is a function of the current and most suppliers have a graph in their data sheet. If the microcontroller wil run 1.8 to 5.5 -- use the adjustable regulator and set the microcontroller bias voltage to 4 v then either of your battery choices will do the trick
 

WTP Pepper

Active Member
Why not try and design the circuit properly instead of trying to design a botch regulator to make the oscillator stable for a fixed voltage?

Then we have temperature variations that can and probably negate all the effort.
 
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