Power switching circuits

The Zero Volt Diode (ZVD) is a circuit useful in a variety of applications including solar chargers of all types. It is a novel circuit in which a power MOSFET acts like a very low voltage drop diode that switches state at 0V and which is used to conduct negative current from drain to source. In D1 type solar engines, a low loss diode can be used
Power switching circuits - schematic

to charge a cap to the open circuit voltage of the solar cell and used in solar battery chargers, the battery is charged at the maximum rate when the source voltage is highest. The diode must be used in series with the solar panel or else the cap or battery would discharge through the solar panel when the panel voltage drops below the stored voltage. The diode or equivalent polarity sensitive switch is therefore essential to solar chargers. Most diodes used in BEAM SEs and solar chargers are Silicon diodes like the 1N4001 which have a voltage drop of 0. 6V to 1V at currents up to 1A. More efficient diodes for currents form >100mA to tens of amps applications are the Schottky type rectifiers with a voltage drop of from 200mV to 1000mV depending on the current level. For <100mA applications a Germanium diode can used with 200mV or less drop. This voltage drop issue is important in competition solar engines since you would like to have the maximum voltage to charge the cap and supply the load (low diode drop) and keep the charge stored on the cap when the lightlevel drops (leakage current cut off) and the SE triggers. Moreover, since the energy in the cap is proportional to the square of the voltage even the small voltage drop of a diode reduces available energy. One obvious simple improvement over the original D1 design is to substitute a Ge 1N34A diode (Radio Shack) instead of the Si 1N4001 diode. An ideal diode would have...

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