Offline power controller for adaptor designs with no heatsink

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By Nick Flaherty

InnoSwitch3 cuts conversion losses by 25% compared to the prior generation, and extends high-efficiency operation over a wider load range.

In common with earlier InnoSwitch chips, the controller is a flyback switcher that uses secondary-side control, with multiple switching modes, and regulates power taken from the incoming mains via PI’s Flux-Link – a magnetic feedback mechanism that employs a single-turn transformer formed in the lead-frame and connection paths within the device package. Output voltage is set by a resistive divider that is referred to an internal source; no optocouplers are used. As with prior families, they integrate the high-voltage MOSFET that performs off-line switching on the primary side; and provide drive for a FET to act as a synchronous rectifier on the secondary side. Designs also allows for diode bridge rectification.

25% reduction in losses comes from an increase in peak efficiency of 92% (previous generation ) to 94%, held over a wide range of line and load conditions. Power supplies and adaptors of up to 65W can be designed without heatsinks, reducing dimensions. A revised package design extends creepage and clearance dimensions to 11 mm, which allows for all relevant regulatory specifications, including operation at 5000m; despite this, package height has been held at 1.5 mm. No-load power is quoted at 15 mW, “including incoming line sensing” – the current path that monitors the line voltage is sampled rather than operating continuously, to reduce the average current. Line and load regulation are held within close limits, and PI says that transient response is also improved over earlier devices.


The InnoSwitch3 IC family is optimized into three application-specific series:

– CE: Current External. Includes accurate CC/CV regulation with external output current sense for optimum design flexibility. Targets compact single-voltage chargers, adapters, IoT and building automation.

– CP: Constant Power. Ideal for USB Power Delivery (PD), rapid charging and other applications where a dynamic output voltage is required.

– EP: Embedded Power. Features the family’s highest-rated MOSFET (725V) and provides full line and load protection with excellent multi-output cross-regulation for demanding industrial applications and appliances.


These flyback switcher ICs employ synchronous rectification, quasi-resonant switching and a precise secondary-side feedback sensing and control circuit. They incorporate multiple protection features, including lossless line overvoltage and under-voltage, output overvoltage, over-power, over-current and over-temperature protection, as well as output rectifier short-circuit protection. Device sub-families are provided with either latching or auto-recovery capability, according to the typical demands of each target application space. All InnoSwitch3 ICs feature on-board high-voltage MOSFETs (rated at 650 V for the CP and CE series and 725 V for the EP series).


InnoSwitch3 ICs target adapters and open-frame power supplies for consumer, computer, communication and industrial applications. InnoSwitch3-CP and InnoSwitch3-CE IC samples are available now, priced at $1.11 (CE) and $1.15 (CP) (10,000). InnoSwitch3-EP parts will be available in November 2017 at $1.18 (also 10,000). An online selection tool, Build Your Own InnoSwitch, is available to help designers customize device features for their particular design specifications. Technical support for InnoSwitch3 ICs, including the PI Expert Online design tool, is available from the Power Integrations website at


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