Variable power supplies for efficient amplification, using charge pumps

摘要

The power supply 80 for an audio amplifier output stage 40 provides voltages which vary in dependence on a volume control signal S2 which controls the gain of amplifier stage 20. The power supply comprises a flying capacitor charge pump circuit (figures 5b, 16b) which provides opposite polarity supplies from a single polarity input. The charge pump may be fed through a controllable DC-DC buck converter (1010, figure 26), which can be bypassed when the battery voltage is low. The supply voltages may be regulated (figure 15). The charge pump may have dual modes (figures 10,16b) wherein it can be controlled to provide outputs which are either equal to the input voltage or a fraction of the input voltage. The variable power supply technique may be applied to line drivers for data transmission (figure 31).