A pre-charge apparatus and method for controlling startup transients in a
capacitively-coupled switching power stage provide lower cost and
improved startup transient performance in Class D amplifiers, as well as
in other AC power converter applications. A charging source is activated
at startup to control the charging of an external capacitor from a single
power supply rail to an operating point voltage equal to the average DC
output of the switching circuit, while a control circuit disables the
output power stage of the switching converter. The current source may be
a constant-current source and/or may be controlled via feedback from the
voltage or current at the output terminal of the converter to taper the
current level to more accurately control the charging. A discharge
circuit can also be provided to discharge the output terminal to an
opposite power supply rail before commencing the controlled charging.