| 摘要 |
A switch mode power supply or power factor correction unit (PFC) and method for controlling the supply of power from an AC power source 11, 12 to a load, comprising: input terminals for connecting to an AC power source 11,12; at least one output terminal 13 for connecting to a load; an inductor (or inductive transformer L1,L2); a controllable switching device S1 connected to the inductor L1,L2 and controllable to control current flow in the inductor so as to control the supply of power from the connected AC power source, via the inductor, to a connected load; and control means 2 which comprises a drive output terminal 21 to drive a signal to the switching device S1 to control the switching device, the drive signal substantially comprising a square wave signal alternating between a first state and a second state (figure 3). The control means further comprises an input terminal 22 arranged to receive an input signal, derived from the drive signal 21, and responsive to the input signal to switch the drive signal from the first state to the second state in response to the input signal falling below a threshold voltage and to inhibit switching of the drive signal from the first state to the second state if the input signal is above the threshold. An adaptive switching current control circuit 3 (figure 2) provides an inhibit signal to the control means (PFC controller 2) using the drive and control signals as inputs 31,33. An embodiment is based on a flyback converter (figure 1). A method is also disclosed whereby the square wave signal drive is provided as an input to a controller (figure 2) and relies on storage of charge in a capacitor (C11 figure 2) during the one of the two states of the input square waveform. |
