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.

 
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> Switching power supply device and method of controlling the switching device

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