Microwave Energy Harvesting Voltage Regulation

I am trying to develop a super low power, batteryless device that needs to power a microcontroller. The power comes from 2.4 GHz wireless signal that is received by an antenna and inputted into a Dickson charge pump to produce the DC voltage needed to power the microcontroller. This voltage is variable based on the input power to the charge pump (which changes as it gets closer or farther from the wireless transmitter). What is the most efficient way to regulate this voltage to 1.8 or 3.3 V? Voltage regulators tend to be inefficient.

Any thoughts are welcome. Thanks.

A zener diode would be an obvious answer. If it has a high enough watt rating then you don't need to install a resistor inline.

Or try the equivalent of a 1A zener, made from 5 diodes in series, each with a 1A rating.

If the total drop is too far short of 3.3 V, then add a sixth diode.

If necessary you can 'bend' the regulated V by

(a) adding a series resistor if you are using 5 diodes, or

(b) putting a resistor across the 6th diode.

Brad,

Thanks for the response. I imagine it is something as shown here. http://www.reuk.co.uk/Zener-Diode-Voltage-Regulator.htm

Do you know if this is dramatically more efficient than a voltage reg? I am looking for a low cost and low power solution so this would probably work.

Thanks again.

If the incoming amperage is low, then you may need only to put a zener in parallel with the supply pins of your microcontroller. The internal impedance of the supply is (in effect) the safety resistor.

The hard part will be to adjust the regulated voltage so it will drive your micro-c. in all conditions.

A zener rated 3.3 V, for instance...

may yield a range of 3 (if incoming mA is very low)...

to 3.4 (if incoming mA is high).