FLYBACK CONVERTER WITH LIMITED OUTPUT POWER

摘要

A flyback converter (PS) based on a switcher IC (42) with Pulse Width Modulation control (52) of the switching transistor (54). The pulse width is controlled by changing the input current at the control input (CTL). Under normal operating conditions the voltage at the control input (CTL) is maintained at a fixed level, which voltage also serves as supply voltage for the control unit (52). A charge pump (CP) provides extra charge for the smoothing capacitor (50) at the control input (CTL) when the load (B) would cause the voltage across the smoothing capacitor (50) to collapse under the fixed level, thereby preventing the control unit (52) from entering the auto-restart mode of the switcher IC (42). In this way the flyback converter can be used as a constant power source for charging rechargeable batteries with a working voltage lower than the nominal operating output voltage of the converter.