For all DC powered devices and systems, polarity guard is needed to prevent accidental reverse polarity DC inputs. At the same time, surge protection is necessary to protect the devices and systems from lighting surges, especially when the devices or systems are installed out-doors, such as out-door camera monitors, wireless routers/switches, remote sensing devices, etc. This paper present a simple and low-cost single transistor control circuit to provide both polarity guard and very high level surge protections up to 6KV at the same time. Therefore, this paper shows a typical example of simple circuit with multiple functions, high performance, and low cost at the same time. A prototype board is built and tested to prove the concept. Measurement results are shown in this paper.
