Patent ID: 7482795

Claim:
A pre-bias protection circuit for a converter circuit including a switching stage having high- and low-side switches connected in series at a switching node and an output stage connected to the switching node having a capacitor having a pre-existing pre-bias voltage at startup of the converter circuit, the pre-bias protection circuit controlling discharge of the pre-bias voltage when the low-side switch is turned ON during a start up of the converter circuit, the pre-bias protection circuit comprising: a first circuit for providing a first output, the first output comprising a first ramp signal, the first circuit receiving a drive signal for the high-side switch and generating said first ramp signal that increases when said drive signal for said high-side switch is received on start-up of the converter circuit; a second circuit providing a second output, the second output comprising a second ramp signal that rises faster than said first ramp signal; and a first comparator circuit for comparing the first output and the second output and producing a third output comprising a pulse width modulated signal for driving the low side switch such that the pulse width modulated signal starts with a first duty cycle and thereafter increases to a larger duty cycle, thereby to prevent the pre-bias voltage from discharging during startup.