San Jose, California, U.S.: Standard in low-power applications like mobile phone chargers, primary side regulation (PSR) is now available for high-power applications, as the LinkSwitch-HP off-line switcher ICs from Power Integrations deliver up to 90 W using the technique. PSR relies on control algorithms and the main power transformer and output diode to determine the amount of power to deliver from the primary to the (isolated) secondary side, eliminating the feedback optocoupler.
While reducing cost and complexity, the elimination of the optocoupler also helps designs meet the new Chinese safety standard GB4943.1-2011, which will be mandatory for power supplies manufactured or used in China from December 1, 2012. This standard requires designers to increase the primary-to-secondary clearance by a factor of 1.48 or else add a warning label to the product cautioning against use over 2000 m in altitude.
The LinkSwitch-HP multi-mode control architecture makes it a viable approach for power-supply applications from 9 W to 90 W (see the figure). The devices automatically select their control mode according to prevailing line and load conditions to optimise conversion efficiency and response to transient load demands, while minimising output ripple and audible noise.
Continuous-conduction-mode (CCM) operation results in reduced RMS currents, leading to higher efficiency and less heat dissipation, while 132-kHz, full-load operating frequency enables the use of smaller magnetics and LC post-filter components. LinkSwitch-HP ICs are capable of no-load power consumption of less than 30 mW at 230 V ac and are more than 50% efficient at 0.1-W input power.