[moved] Voltage Sources RQD - low load

[Docara]

Hi all,

I need to supply two voltage for sensing purposes via a DP relay, for a third party device.

I know nothing about the load (current) characteristics or input impedance of this device, but the input voltage is approx 11Vdc to 15.2Vdc

Now (assuming the correctly chosen resistor values) could I use two Zeners connected in the usual way but introduce a load (LED & resistor say) and still have the Zener voltages available to be monitored?

Alternatively, would a low drop out regulator be better.

Thanks
Doc

 

[BradtheRad]

Does the led/resistor need a regulated voltage? Why not drive it from the input voltage? That will take a burden off your regulating device.

A zener is the simplest method of voltage regulation. You must select the series resistor so it allows some current to go through the zener, and some current through your load. If you don't know how much the load will draw, then you must set a maximum rated amount. Test your device to ensure it will drive a load at that rating, without anything getting broken.

If you find a zener is not sufficiently robust, then you must consider putting a transistor or IC in your project.

 

[Docara]

Thanks for the reply

No, the LED doesn't need a regulated supply. Before I posted here I did a quick net search and found info saying that the Zener need a minimum load (over and above the normal series current limiting resistor) in order to operate so the LED / resistor combo which just there to load the Zener.

Just a bit of background - I'm using a DPDT relay in which one set of contacts for normal switching of a supply and thinking of using the second set of contacts to monitor the operation of the relay, so it doesn't need to be anything special. All I'm doing is having two voltages which arn't 0v or 12-14.4Vdc


Doc