Feature: Consumer electronics


Figure 1: Uninterruptible power supply schematic


Figure 2: An ideal diode implementation of the diode OR circuit


one input voltage is higher than the other by more than 600mV, the body diode will conduct. Terefore, if the backup supply voltage is higher than the mains supply, the load’s power will be drawn from the backup supply, which is undesirable. Reversing the PFET stops this problem, but then the body diode conducts if the output voltage is higher than the input voltage by more than 600mV.


22 October 2022 www.electronicsworld.co.uk


Figure 3: A diode OR circuit with bidirectional disconnect A cleaner solution is to add an


additional PFET to each path, as shown in Figure 3. In this circuit, the two body diodes oppose each other so there’s a bidirectional open circuit when the FETs are switched off that isolates each channel, regardless of the input or output voltages. For the 12V circuit, the LTC4416


(DC1059A) evaluation kit was modified


to give a switchover voltage of 11.17V, using a 100kΩ resistor for R3 and a 10kΩ + 2.2kΩ resistor for R1. Tis worked well, but it was found that the Wi-Fi access point needed a precise 12V supply and sometimes rebooted when the mains- generated 12V was switched back on again, due to the voltage step (from 11.17V to 12V) upsetting the router electronics.


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