The 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 are dominating. All transferred energy is used to slowly activate or deactivate the switching transistors. This can cause violations of the reverse bias safe operating area (RBSOA). As the switching transistors are operated without protection functions, unexpected operating conditions can lead to detrimental overcurrent or over-temperature situations that can even damage solid-state relays. This paper proposes a concept of a solid-state isolator with ultra-low power to protect the power switches. It is implemented based on a larger energy transmission. The protection scheme provides a fast overcurrent protection with a reaction time of several hundred nanoseconds for protecting against low-impedance overloads. Furthermore, an over-temperature protection that is able to measure the chip temperature of the switching transistors is proposed. It covers overloads above nominal current but below the overcurrent protection level. Both protections are verified by measurements.
