Patent ID: 8422179

Claim:
An inrush current control circuit to selectively short-circuit bypass an inrush current limiting resistor (R 1 ) of a power supply that includes a switching transistor (Q 1 ), wherein the switching transistor (Q 1 ) includes a control terminal (gate or base) driven in dependence on a pulse width modulated (PWM) drive signal, a first current path terminal (source or emitter) and a second current path terminal (collector or drain), and wherein inrush current control circuit comprises: a bypass transistor (Q 3 ) including a control terminal (gate or base), a first current path terminal (source or emitter) and a second current path terminal (collector or drain), with a current path between the first and second current path terminals, wherein the current path is connected in parallel with the inrush current limiting resistor (R 1 ); a first resistor (R 3 ) having a first resistor terminal connected to the control terminal (gate or base) of the bypass transistor (Q 3 ), and having a second resistor terminal connected to the first current path terminal (source or emitter) of the bypass transistor (Q 3 ); a capacitor (C 2 ) having a first capacitor terminal connected to the control terminal (gate or base) of the bypass transistor (Q 3 ), and having a second capacitor terminal connected to the first current path terminal (source or emitter) of the bypass transistor (Q 3 ); a second resistor (R 2 ) having a first resistor terminal connected to the control terminal (gate or base) of the bypass transistor (Q 3 ), and having a second resistor terminal; and a diode (D 3 ) having a cathode terminal connected to the second resistor terminal of the second resistor (R 2 ), and having an anode terminal connected to the control terminal (gate or base) of the switching transistor (Q 1 ) of the power supply.