low voltage power source

Thread Starter

sotinam

Joined Apr 20, 2016
10
Hi all,

I have a circuit which needs an adjustable voltage source of ~1.5 V (It should be able to be adjusted on any number between 1 V and 1.8 V). One option might be using a voltage regulator based circuit (https://www.sparkfun.com/products/526) that provides a fixed 3.3V output and then using a voltage divider (with one potentiometer and one fixed resistor) to reduce the output to desired voltage. I was wondering if somebody knows a better/simpler (with less needed input power) way to do it?

Any advice is appreciated,
S
 

EM Fields

Joined Jun 8, 2016
583
Hi all,

I have a circuit which needs an adjustable voltage source of ~1.5 V (It should be able to be adjusted on any number between 1 V and 1.8 V). One option might be using a voltage regulator based circuit (https://www.sparkfun.com/products/526) that provides a fixed 3.3V output and then using a voltage divider (with one potentiometer and one fixed resistor) to reduce the output to desired voltage. I was wondering if somebody knows a better/simpler (with less needed input power) way to do it?

Any advice is appreciated,
S

How much current will the adjustable source be required to deliver, and will the load presented to the adjustable source vary once the voltage is set?
 

wayneh

Joined Sep 9, 2010
17,496
I think the LM317 is a viable option if you don't want to use the op-amp above (which is a good solution). Shift the bottom voltage up with a diode, so that the LM317 controls down to 1.2-0.7 =0.5V. Do the calculations to choose a pot giving full scale adjustment over the the required range. Use a dummy load to ensure the regulator is always loaded to at least ~10mA. (Check the data sheet for the minimum required load.)

The diode voltage drop is not fixed or entirely predictable, so if you need great precision, this wouldn't be so hot. If ±0.1V is OK, then it's fine.
 

hp1729

Joined Nov 23, 2015
2,304
I think the LM317 is a viable option if you don't want to use the op-amp above (which is a good solution). Shift the bottom voltage up with a diode, so that the LM317 controls down to 1.2-0.7 =0.5V. Do the calculations to choose a pot giving full scale adjustment over the the required range. Use a dummy load to ensure the regulator is always loaded to at least ~10mA. (Check the data sheet for the minimum required load.)

The diode voltage drop is not fixed or entirely predictable, so if you need great precision, this wouldn't be so hot. If ±0.1V is OK, then it's fine.
LM317LZ (TO-92 package for that low a current) is a good choice. If you take the reference circuit down to -1.2 V instead of ground you can get the LM317 to go down to zero volts. It takes a little creativity because it throws things off.
The diode idea is predictable if you know how much voltage that diode will drop at what current.
 

hp1729

Joined Nov 23, 2015
2,304
Design 495 LM317 down to zero 7660.PNG [QU
OTE="hp1729, post: 1012327, member: 298400"]LM317LZ (TO-92 package for that low a current) is a good choice. If you take the reference circuit down to -1.2 V instead of ground you can get the LM317 to go down to zero volts. It takes a little creativity because it throws things off.
The diode idea is predictable if you know how much voltage that diode will drop at what current.[/QUOTE]

LM317 taken down to zero.

It is made for 0 to +12 V or so. You may have to make adjustments for a lower voltage only.
 
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