Application Note AN-72
InnoSwitch3 Family
www.power.com October 2018
Design Guide
Introduction
InnoSwitch™3 devices combine a high-voltage power MOSFET switch,
with both primary-side and secondary-side controllers, an innovative
high-speed magneto-coupling communications technology and a
synchronous rectication driver into one isolated, safety-rated device.
The incorporation of Fluxlink™, which transmits information safely and
reliably across the isolation barrier, eliminates the need for an
optocoupler - used in the feedback loop of conventional power
conversion circuits. This reduces component count and eliminates the
lifetime and reliability limitations inherent in opto-feedback devices.
The InnoSwitch3 integrated circuits feature a variable frequency,
variable peak-current control scheme which together with quasi-
resonant switching and synchronous rectication ensure very high
conversion efciency across the load range. The family can be used to
create power supplies up to 65 W output, including CV/CC chargers
that easily meet average-power-supply-efciency requirements and
offers very low no load input power and outstanding standby
performance. Power Integrations’ EcoSmart™ technology used in
InnoSwitch3 ICs enables designs that consume as little as 15 mW of
no-load power and makes the family ideal for applications that must
meet energy efciency standards such as the United States
Department of Energy DoE 6, California Energy Commission (CEC) and
European Code of Conduct.
The primary-side yback controller in InnoSwitch3 can seamlessly
transition between DCM, QR and CCM switching. The primary
controller consists of start-up circuitry, a frequency jitter oscillator, a
receiver circuit that is magnetically coupled to the secondary side, a
current limit controller, audible noise reduction engine, overvoltage
detection circuitry, lossless input line sensing circuit, over-temperature
protection and a 650 V or 725 V power MOSFET.
The InnoSwitch3 secondary controller consists of a transmitter circuit
that is magnetically coupled to the primary-side, a constant voltage
(CV) and constant current (CC) control circuit, synchronous-rectier-
MOSFET driver, QR mode circuit, and a host of integrated protection
features including output overvoltage, overload, power limit, and
hysteretic thermal overload protection.
At start-up the primary controller is limited to a maximum switching
frequency of 25 kHz and 70% of the maximum programmed current
limit. An auto-restart function limits power dissipation in the switching
MOSFET, transformer, and output SR MOFET during overload,
short-circuit or open-loop fault conditions.
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