Off-line switchers convert a usually high AC input voltage (e.g. 110-240VAC mains supply) down to a IC-level DC voltage (e.g. 5V). Their design is based on a flyback regulator circuit. The term “off-line switchers” comes from the fact that the DC output voltage is derived straight from the AC input (the DC voltage comes straight “off” the line (AC)).
You can buy everything from just the IC controllers which need a lot of supporting circuitry to entire ready-to-use off-line switcher packages.
Both isolated and non-isolated off-line switchers exist on the market. Isolated versions use a transformer to separate the high voltage AC side from the low-voltage DC side.
And here is an example of a non-isolated version:
The InnoSwitch3-Pro family of off-line converters from Power Integrations features secondary side synchronous rectification (SR), constant voltage (CV) or constant current (CC) control, integrated primary-side switch, integrated 3.6V “
\(uVCC\)” power output to directly powering a microcontroller, cable drop voltage compensation, and an I2C port1.
The I2C port is designed to be connected to a microcontroller powered of the 3.6V, and the microcontroller can configure the main power supply from the converter. You can configure whether it is constant voltage (in 10mV steps), constant current (in 50mA) steps and read back status information. This makes it particularly suitable for USB PD adapters and chargers.
Below is the applications example from it’s datasheet, which shows the circuitry required to build a 40W programmable power supply:
MeanWell PM-15-XX Family
These are ready-to-go PCB-mounted AC/DC converter modules that are designed to be hooked into the AC mains (90-270VAC(rms)) on one side, and output a DC voltage on the other side. The below photos shows the MeanWell
PM-15-12 which outputs 12V at up to 1.25A:
Power Integrations (2022, Nov). InnoSwitch3-Pro Family: Digitally Controllable Off-Line CV/CC QR Flyback Switcher IC with Integrated High-Voltage Switch, Synchronous Rectification and FluxLink Feedback (datasheet). Retrieved 2023-04-24, from https://www.power.com/sites/default/files/documents/innoswitch3-pro_family_datasheet.pdf. ↩︎ ↩︎ ↩︎
This work is licensed under a Creative Commons Attribution 4.0 International License .