| 摘要 |
PROBLEM TO BE SOLVED: To control the luminance of a light emitting device (light emitting diode) without depending on a resistor for limiting a current. SOLUTION: The light control circuit comprises a transformer having a main winding and a sub-winding magnetically coupled with the main one, a main transistor (Q1) for switching with the drain connected to the main winding and the gate and the source connected to the sub-winding of the transformer, a transistor (Q2) for controlling connected between the gate and the source of the main transistor (Q1), and a time constant circuit which is inserted between the base of the transistor (Q2) for controlling and the sub-winding of the transformer and changes the time constant according to a luminance control signal. In order to control the light emitted from the light emitting device which emits light by causing a communication current generated on the main winding side when the main transistor (Q1) is turned off to flow in the light emitting device, the time constant of the time constant circuit is changed to change the current caused to flow in the light emitting device. COPYRIGHT: (C)2005,JPO&NCIPI
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