In a preferred embodiment, there is provided a
switched mode power supply operable in start-up mode,
normal mode and standby mode. The power supply may comprise a
transformer having a primary winding on a primary side and a secondary winding on a
secondary side, the primary winding being coupleable to a DC input
voltage, and circuitry on the
secondary side being arranged to provide a DC output
voltage; and a
power controller. The
power controller may comprise a regulation controller for regulating a DC supply
voltage on a supply line during standby mode, and a
high voltage device coupled to the DC input voltage and the supply line. The current through the
high voltage device to the supply line, during standby mode, may be controlled by the regulation controller. During standby mode, when the supply voltage is greater than or equal to a reference voltage, the current through the
high voltage device to the supply line is substantially zero. When the supply voltage is less than the reference voltage, the greater the difference between the supply voltage and the reference voltage, the greater the current through the high voltage device to the supply line. In other preferred embodiments, there is also provided the
power controller itself and a method for regulating a supply voltage during standby mode.