What is the purpose of an isolation diode in an aircraft electrical power system?

• A. To prevent reverse current flow between power sources and allow multiple sources to share loads without backfeeding
• B. To regulate system voltage
• C. To measure current flow
• D. To increase power output

Answer: (A)

A diode acts as a one-way valve for electrical current. In an aircraft electrical power system, isolation diodes between each power source and the common bus prevent reverse current from flowing back into other sources. This lets multiple sources (such as a generator and a battery) connect to the same bus without fighting each other or feeding power into a source that isn’t providing it.

With a diode from each source to the bus, the source with the highest voltage forward-biases its diode and powers the bus, while the other diodes stay reverse-biased and block current. If a source drops out or fails, the remaining sources can continue supplying the bus without current flowing into the failed source. This arrangement also enables load sharing without backfeeding, but it does not regulate voltage, measure current, or increase power output.