Bypass diodes

Sometimes a power source can eliminate the power provided by the other power sources that are connected in series with it. A failing power source might even be damaged by the total voltage of the other power sources that are in series with it, because that voltage will be applied as a reverse voltage to the failing power supply. When those issues are a likely possibility, then it is desirable to give the circuit an alternate path where power can still be provided to a load by diverting current around that weak link power source via parallel diodes.

Bypass diodes in a basic circuit schematic diagram by electronzap
Bypass diodes in a basic circuit schematic diagram by electronzap

Adding a diode that is reverse biased in relationship to a power source that might fail gives the other series power sources an alternative path for their current to flow.

Bypass diodes keep the total voltage (series voltages add up) of the working power sources across the load, while limiting the reverse voltage across the failing power source down to the forward voltage of the diode.

I have Schottky diodes with the part number 15SQ045. They can block up to 45V (the second number of the part number) while reverse biased. They can also pass up to 15A (first number of the part number) of current while forward biased. Their forward voltage is about 0.3V. Which means that you can expect them to only drop about 0.3V from the series power supply(ies) when the 15SQ045 passes current while forward biased.

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