Power Integrations' InnoSwitch cuts optocouplers from switching supply circuit

November 14, 2014 // By Graham Prophet
Power Integrations has introduced several generations of off-line switching power supply Ics;the latest, InnoSwitch, returns to deriving feedback information to control output regulation direct from the output, but feeds that data back to the primary switch controller via an air-core magnetic coupler.

Calling it FluxLink, PI says that its safety-isolated communication technology combines primary- and secondary-switcher circuitry to reduce component count, eliminate slow and unreliable optocouplers, outperform primary-side controllers and reduce manufacturing costs

A single package with all necessary creepage and clearance spacings includes primary switching controller with integrated power FET on one die, secondary synchronous rectifier and associated circuitry on a second die, and the secondary-to-primary feedback path. This is implemented using the copper leadframe of the part. Part of the leadframe and chip bond wires form the 'primary' of a single-turn, air-core transformer (the 'primary' of the transformer is on the secondary or output side of the power supply layout, as it is passing output voltage level information back to the input switching controller). This loop couples to a further loop in the leadframe, connected to the controller IC; the physical layout is configured to cancel stray magnetic field effects. Clearances between the transformer loops are sufficient to give safety and regulatory isolation levels. On the PCB, the single package spans the gap between input and output sections.

The InnoSwitch family of highly integrated switcher ICs, PI says, combines primary, secondary and feedback circuits into a single, worldwide safety-rated, surface-mount package that exceeds all global regulatory standards for efficiency and no-load consumption, while minimising component count and providing highly accurate constant voltage and constant current, up to 25W. The InnoSwitch family is suitable for smart mobile device chargers and adapters for a wide range of applications such as set-top boxes, networking equipment and computer peripherals.

Inside the new device, highly accurate secondary-side direct voltage and current measurements are communicated across the safety isolation barrier using the high-speed digital FluxLink technology. This proprietary new feedback technique permits precise control without the need for a bulky optocoupler, while avoiding the performance compromises inherent in primary-side regulation (PSR), such as limited accuracy and efficiency and poor transient response versus no-load consumption. Unlike primary-side