zener voltage regulation

I thought zener diodes make fairly good voltage regulators but my simple project failed. I tried to get 3v from 5v source. I connected 100 ohm 1/2W resistor and 3.3v 5W zener diode to ground. I expected 3v at the resistor diode junction but I get only 2.2v with no load. Why?

 

That's the diode I got at Digikey. The "B" should be 5% but that's all the specs I have. So this is no-go. I don't need high current. I was looking to run LCD clock from supercapacitor instead of 3v coin battery and charge the cap from USB charger. Normally I would prefer voltage regulator but the 1.25v drop won't get me 3v from capacitor. At least not long enough for the clock to run a week or two. Besides, I could not find in datasheet what's the minimum voltage input for LM317. Some voltage regulators set the minimum as 4.5v.

 

I have to look up the LDO voltage regulators or something that will work. Then I'll try tiny solar cell in addition to usb charging. Small solar cell rated 5v 30mA should put out 3v and few mA average to charge two 4F 5.5v capacitors. I make some dummy batteries coin and AAA from piece of plastic and 2 wires to see what works and what doesn't work.

 

You are correct. For that reason I would make dummy battery slug and not even opening the powered gizmo and not installing "or" tied diodes. If the capacitor is charged by USB or solar cell it may work when the battery is dead. Pull battery out, put in the dummy and look for replacement battery. Eventually things will run that way. There is energy harvesting research for IoT, so someone will get it done. I see some new car dashcam video recorders use capacitors to save file and shut down when the ignition is turned off.
Maxim makes some LDO voltage regulators with P-channel pass through for minimal quiescent current. It is just hobby right now but helps to learn new things thanks to support like you provide. Thanks.

 

Maxim claims that MAX8882/8883 are improvement over PNP. The P-channel doesn't use bias current. They come in several voltage outputs that may be used to charge single cell battery, 2.7v supercap or 3v coin battery and accept 6.5v input which is just right for USB power source. This may be the part for me to play with. It doesn't require special PCB with copper for exposed pad which is hard to hand solder.