Innovative Solid-State Isolators With Overcurrent And Over-temperature Protection For Solid-State Relays

Energy transfer from the control side to the output side in today’s integrated solid-state relays and integrated solid-state isolators is extremely low. Energy transmission by LEDs and photo diodes is dominant. All transferred energy is used to slowly activate or deactivate the switching transistors. This can violate the reverse bias safe operating area (RBSOA). As the switching transistors are operated without protection functions, unexpected operating conditions can easily lead to detrimental overcurrent or over-temperature situations that can even damage solid-state relays. This paper proposes a concept of ultra-low power protection circuits for the power switches that is implemented based on a larger energy transmission. The protection scheme provides a fast overcurrent and over-temperature protection with a reaction time of several hundred nanoseconds (ns) to protect against low-impedance overloads.