precision voltage regulator adjustable

[Rajinder]

Hi all,
I am looking to build a precision adjustable voltage regulator. I need to be able to control a voltage in the range of 5 to 10mV with great accuracy using a microcontroller. The other issue is that from the microcontroller I have a length of 2 core screened wire (around 500mm in length) going to the unit under test. So I might get some loss or fluctuations in my reading.
Any ideas? I was thinking of PWM and low pass filter. Not sure though.
Best regards,
Raj

 

[Alec_t]

What % tolerance is acceptable?
What resolution is required within the 5-10mV range?
What load will the mV source have to drive?

 

[Rajinder]

The acceptable resolution is 0.25mV. with a tolerance of 5 percent.
This is used to simulate a change of 5mV within a certain time to detect heat.
The rare of change can then alert if heat has risen quickly indicating a fire.

 

[Alec_t]

In that case the PWM approach, with a precision potential divider, looks feasible; providing whatever the divider drives doesn't load it down beyond the tolerance.

 

[Rajinder]

Thanks for your help. So when you say potential divider I presume you mean a RC low pass filter?

 

[Alec_t]

No, I mean two resistors in series, with output from the junction. Your PWM will be putting out 5V (or 3.3V, depending on your micro's supply) pulses, so you will need to reduce that in order to get mV levels without resorting to absurdly small duty cycles. The low-pass filter could go before or after the divider. The division ratio needed would be around 1000:1 for a 5V micro supply.

 

[Rajinder]

Thanks

 

[TedA]

Raj,

To really address your problem we need to know more.

What sort of load must this voltage source drive?

How much output current must it provide?

Is the load resistive in nature? Or at least predictable?

What do you have in the way of DAC or PWM outputs at your microcontroller?
( How many bits, voltage swing, Vref sources, etc.)

Is there a Vref source in your system?

Ted