The intention of the DC distribution network is to save electric power: One central power supply unit provides an intermediate DC voltage (here about 20 Volts). Some local high-efficiency DC/DC converters provide individual power to all the devices (5V, 12V). The total efficiency (from 230V AC line to DC input of the devices) is somewhat better than using their wall warts.
This provides a few (about 3 ... 5) watts power saving, assumed the system is running off the AC line. Additionally my system achieves a huge amount of power saving by providing power off a solar panel. As long as there is enough sunshine, the solar panel fully supplies the devices, and no AC power is required.
If there isn't full sunshine, the solar panel provides part of the required power.
Both sources (solar panel and AC powered supply) and an additional battery must be combined. Until now I've used some shottky diodes to do that. The drawback of these diodes is their forward voltage drop (about 0.3 ... 0.5V). So the diodes dissipate total about 1W, just for beeing there and beeing necessary to decouple the power sources.
Using P-Channel MOSFETs and some active circuitry, I've made a triple "ideal diode". This circuit is able to
combine the power sources while maintaining about 30mV...40mV voltage drop, resulting in 0.1W dissipation.
Using the components as shown in the schematic, this diode should be able to operate with input voltages from 12V to 25V, and output current up to 5A.
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