Zener Diode Voltage Regulation

Hi,

I'm putting together a project that incorporates standard opamps at +/- 16v & a few discrete opamps using +/- 24v. I want to use just one bipolar power supply for both types of opamp. I could use a second LM317/LM337 pair of regulators set for +/- 16v in series on the already regulated 24v supply output; or I thought I might incorporate a zener regulation scheme for the lower voltages. I found a zener voltage regulator calculator on the Opamp Labs web site & came up with the resistor value shown in this schematic.

http://www.twin-x.com/groupdiy/displayimage.php?pid=325&fullsize=1

Also, the web site only showed an example illustration for regulating a positive voltage. I adapted that for the -16v regulation schematic - possibly incorrectly. I also added the RC filter after the zener to clean up the output a bit. It was NOT in the original illustration.

Did I adapt that orignal schematic correctly to accomodate the -16v regulation? Since the voltage gain of the standard +/- 16v opamp is small to moderate & the load a fairly high impedance (50k), should I consider using a 1N4745 16 v 15.5 mA DO-41 zener diode instead of the 50mA one as shown in the schematic? Will the zener regulator approach be dirtier or noisier than using a second pair of dedicated regulators like the LM317/LM337 series? I know it's cheaper & has a slightly smaller footprint but I don't want to be challenging the PSRR of the standard opamp.

Ideas, comments or suggestions?

Thanks,
Skip Beach

The resistor between zener and output will compromise regulation. I'd get rid of it.

A good rule of thumb, when selecting the series resistor before the zener, is to allow at least 5mA to flow through the zener at all times. Lower values of zener current may result in less reliable regulation. So take the current draw of your opamp(s) and add 5mA when figuring the series resistor value.

As for power rating of the zener, it should be more than adequate (preferably double or better) to pass the full value of current it would have to draw with no load attached.