I am attempting to simplify a schematic by using a zener diode as a regulator for a small radio. At peak, the radio will consume about 50mA @ 3.3V, and in its low power sleep state, virtually nothing (a couple uA). In a previous experiment, where a Zener diode with 1mA Iz and 400mW Pd was used, the voltage would shoot up far above 3.3V. After doing some of the analysis, something is still not quite clicking as to whether or not I would experience voltage fluctuations now while using this particular zener (20mA Iz, 0.5W).
If my voltages at Vz are basically 4.13V and 12V absent the diode on the high and low spectrum of the load draw, respectively, and both would trigger the zener ON, what are some things to keep in mind that might cause this zener to deregulate as mentioned? As far as I know, I'm currently looking at ~200mW dissipation at radio idle, but could come up short of Iz by about 12mA, providing only 8mA of available current when the radio is maxed out.