Isolation is a means of preventing direct current (DC) and unwanted alternating current (AC) between two parts of a system while still enabling signal and power transfer between those two parts. Isolation is used in a wide variety of applications: to protect human operators and low-voltage circuitry from high voltages, to improve noise immunity, and to handle ground potential differences between communicating subsystems.
Isolators with complementary metal-oxide semiconductor (CMOS) – or transistor-transistor logic (TTL)-level inputs and outputs are called digital isolators. While digital isolators provide signal isolation, complete isolation of the two voltage domains requires power isolation as well.
Traditional approaches to generate isolated power use a DC/DC converter to drive a transformer in flyback, fly-buck or push-pull topologies. Pulsating signals on the secondary side are rectified and filtered to generate an isolated DC supply. Optocoupler-based feedback to the primary side achieves line and load regulation. In certain cases where the DC/DC converter runs in an open-loop configuration, a low-dropout regulator (LDO) is used to post-regulate the converter output. The drawback with this discrete approach is that the complete solution – the transformer and other components – occupies a lot of space on the board. Also, designing a stable and efficient isolated power supply can be challenging.
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