| 摘要 |
A self-oscillating switch circuit for use in a switching DC-DC converter that is enabled to use amplitude modulation dimming for dimming a load such as a LED is provided. The dimming may be used to provide two or more distinct light output levels, which may be used in automotive combined tail and break lighting, for example. The self-oscillating switch circuit comprises an output terminal (Ton P1), a high-power input terminal (S2) for supplying a first power to the load and a low-power input terminal (S1) for supplying a second power to the load. The second power is lower than the first power The switch circuit further comprises a power switch semi-conductor device (Q1) configured for controlling a load current from at least one of the high-power input terminal (S2) and the low-power input terminal (S1) to the output terminal. A control semi-conductor device (Q2) is coupled to the power switch semi-conductor device (Q1) for supplying a control signal for controlling switching of the power switch semi-conductor device (Q1). A sensing circuit is configured to generate a sensing voltage. The control semi-conductor device (Q2) is configured to control the power switch semi-conductor device (Q1) in response to the sensing voltage. The sensing circuit comprises a first sensing resistor (R1A) and a second sensing resistor (R1B) for generating the sensing voltage such that a load current has a predetermined first peak current level corresponding to the first power, when power is supplied to the high-power input terminal, and the load current has a predetermined second peak current level corresponding to the second power when power is supplied to the low-power input terminal.
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