voltage regulator issue

I am using a digital panel meter to measure the output voltage from a wideband fuel monitor fitted to a car. I need to measure accurately to within 0.2 volts on the panel meter. I am trying to measure a voltage range from 0.7 to 2.0 volts.

I need to ensure the there is a constant 12v power supply to the panel meter in order to ensure an accurate reading.

I am using a 7812 voltage regulator. The voltage on the car's charging circuit varies from 12.7v to 14.1. However the output of the regulator ranges from 11.3-11.7 volts and does not remain constant at 12 volts. I have double checked my wiring and it is correct.

Any ideas/suggestions? Thanks.

The 7812 will not work for you in this application. It needs an input-output differential of about 2 volts to regulate properly. That means for 12v out, the input must be 14v or higher at all times. I don't have a easy solution at hand, but others will jump in with ideas.

Ken

If current isn't an issue you might use an LM2940AZ-12 or LM2931AZ-12. Their max output current is 100mA.

They are LDOs requiring normally 500mV above the stabilized output voltage.

Another solution would be using an LM7809 (output voltage 9V)

Boncuk

trackhound,

Will your digital meter work correctly on a constant 9VDC supply?

Ken

It may be a long way to get there but you could use a 3 pin regulator to ensure the varying voltage from battery won't change it (9V, 5V - whatever), and the use a DC-DC up converter to bump the voltage to the required 12 Volts supply for your meter, keeping an eye of the current consumption of the meter versus the capability of your up-converter IC.

Many panel meters need a power supply which is floating relative to the voltage being measured. Can you provide a link to the datasheet, or provide the part number?

Thanks guys. I bought the panel meter some time ago and no longer have the details or the datasheet. I will try and run off a 9v regulator and see how we go.