Positive Voltage Reference

John A. Zoidberg

Hello there,

I'm making a little digital room thermometer here - with the classic LM35DZ, with a small microcontroller.

I'm using a 2.56V voltage reference which connects to the +Vref pin.

However, an issue - the 2.56V must be maintained, so I think a(nother) regulator is needed too.

Is it possible that I can put a TL431 alongside with the voltage dividers?

Opinions welcome.

Mike Green

A TL431 would work fine. As shown in the datasheet, you'll need 3 resistors to set the output voltage to 2.56V, one to drop the supply voltage to 2.56V and the other two to make a voltage divider to provide the reference voltage to the TL431.

erco

If you already have a fixed regulator such as 5V, you can adjust a 10-turn 10K trimpot voltage divider to get a nice steady 2.56 volts.

Adding another regulator (LM317T) is also possible, but it's redundant.

kwinn

John A. Zoidberg wrote: »

Hello there,

I'm making a little digital room thermometer here - with the classic LM35DZ, with a small microcontroller.

I'm using a 2.56V voltage reference which connects to the +Vref pin.

However, an issue - the 2.56V must be maintained, so I think a(nother) regulator is needed too.

Is it possible that I can put a TL431 alongside with the voltage dividers?

Opinions welcome.

I must be missing something here. You already have a microcontroller (presumably with a built in ADC), a 2.56V reference, and a regulated power supply or battery for the circuit. The LM35 operates over a 4-20V range so It can run off the micro's supply. What do you need another 2.56V supply for?

John A. Zoidberg

Sorry for the inconvenience - I got up and felt still a bit groggy when I was working on the little thermometer. I totally forgotten about the regulated supply.

I'll just use a normal volt. divider (with a potentiometer, of course) to go with it.