Patent ID: 8115536

Claim:
Self-oscillating switch circuit for use in a switching DC-DC converter, the self-oscillating switch circuit comprising: an output terminal (Tout 1 ) for supplying power to a load (LED); a high-power input terminal (S 2 ) for receiving power from a power supply (PS) in order to supply a first power to the load; a low-power input terminal (S 1 ) for receiving power from the power supply in order to supply a second power to the load, the second power being lower than the first power; a power switch semi-conductor device (Q 1 ) having a control terminal, the power switch semi-conductor device being configured for controlling a load current from at least one of the high-power input terminal and the low-power input terminal input terminal to the output terminal; a control semi-conductor device (Q 2 ) coupled to the power switch semi-conductor device for supplying a control signal to the control terminal of the power switch semi-conductor device for controlling switching of the power switch semi-conductor device; a sensing circuit coupled to the control semi-conductor device for generating a sensing voltage, the control semi-conductor device being configured to switch the power switch semi-conductor device non-conductive when the sensing voltage has a predetermined control voltage level; wherein the sensing circuit comprises a first sensing resistor (R 1 A) and a second sensing resistor (R 1 B) for generating the sensing voltage, the sensing circuit being configured such that: the sensing voltage has the predetermined control voltage level, when power is supplied to the high-power input terminal and the load current has a predetermined first peak current level, the first peak current level corresponding to the first power; the sensing voltage has the predetermined control voltage level, when power is supplied to the low-power input terminal and the load current has a predetermined second peak current level, the second peak current level corresponding to the second power.