Magnetic-feedback PSU ICs applied to auxiliary/standby supplies to 35W

September 21, 2015 // By Graham Prophet
Power Integrations’ 725V InnoSwitch-EP off-line, CV/CC flyback switching ICs are aimed at “embedded” power supplies in the 20W (up to 35W) range, offer high efficiency across the load range, to meet challenging ENERGY STAR and ErP TEC requirements.

PI first used the InnoSwitch configuration in a product released in 2014. It addresses the issue of building small off-line power supplies that are long-term reliable (free from optocoupler degradation), while being accurate (using feedback and secondary-side control), and at the same time economical (without the need for a custom transformer).

The design builds, in a single IC package, the offline switching FET, primary and secondary control ICs, secondary FET drivers – and the feedback path (‘FluxLink’). This is implemented as a magnetic coupling in which the leadframe is used as a single-turn winding, coupled to a further inductive loop that completes the “transformer”. An adjacent anti-phase loop produces common-mode rejection of external magnetic fields and PI claims the overall design has high noise-immunity, seen as essential as the devices are aimed at markets such as white goods and appliances and may be mounted close to motors.

The secondary side of a typical PSU that will use the InnoSwitch EP (‘E’ for ‘embbedded’) uses FETs as synchronous rectifiers to improve efficiency (vs. diodes). The improved accuracy of the magnetic coupling allows the use of synchronous rectification”for free”, a spokesman said.

The main differentiators from the original InnoSwitch are the inclusion of the higher-voltage off-line switching FET; and the provision of multiple outputs that are well regulated individually, and one against another. Poor cross-regulation between multiple outputs is a problem with primary-side regulation, PI asserts.

The new IC family also delivers full line protection and instantaneous transient response with less than 10 mV no load consumption. InnoSwitch-EP ICs are aimed at providing highly-efficient, very accurate and reliable power supply circuits without an optocoupler for auxiliary and standby power in appliances, HVAC, consumer electronics, computing, telecom and data communication applications.

InnoSwitch-EP ICs enable 20 W power supplies to achieve approximately 90% efficiency in a multi-output design, while minimising no-load consumption to less than 30 mW. Line over-voltage regulation is highly accurate at