Power Integrations has introduced a mains power chip that can claim to have zero power dissipation in stand-by mode.
Consumption is cut by allowing the load to almost completely turn off the input circuitry, and turn it on again.
"At 230V input, we measure 4.1mW of leakage caused by leakage by electrolytic capacitors and the small amount of power consumed by the device," said applications engineer Paul Lacey, explaining the 'zero' claim: "IEC standards allow any power below 5mW to be rounded down to zero."
The firm already produced phone charger chips with stand-by in the 10-20mW range, as do CamSemi and iWatt.
In this device, dubbed LinkZero-AX, power-down mode is triggered by a signal accessible to a microcontroller from the secondary side, completely shutting down switch-mode operation and internal switch control circuits.
However, parts of the chip stay alive in power-down mode, allowing the IC to be awakened with a reset pulse or button press.
The by-pass pin on the IC can also, at the expense of increased dissipation, provide up to 500μA of current at 5.85V for use by a system control or sensing circuit - an infra-red remote control receiver for example.
Up to 3W can be delivered to the output by the chip which includes the main mosfet power switch.
Operating frequency is around 100kHz - dropping to 78kHz at high input voltage - modulated by a typically 6% of jitter at 1kHz to reduce EMI.
Application circuits on this video include non-isolated output supplies, and an isolated version including on-off control from an IR receiver.
The devices are available now in an SO-8C package.
Applications are foreseen in TVs and remotely-controlled electronic lighting ballasts.