| 摘要 |
PURPOSE:To perform the high speed switching of an LED, by outputting the differential current of an input signal, to a connection point between a light emitting diode (LED) and a constant current source, and making the current charge a stray capacitance. CONSTITUTION:When the voltage VIN of input signal turns to the low level, a transistor 4 turns to an OFF-state, and a differential current ip on the plus side is output from a differentiation circuit 7. As a result, the driving current (i) for an LED 1 and a stray capacitance 6 becomes the sum of a constant current I and the differential current ip. The stray capacitance 6 is charged by this current, and the electric potential VS of a connection point A increases. As a result, the electric potential VS of the connection point A rapidly exceeds the threshold voltage VTH of the LED 1, and reaches a final value. Therefore, all of the constant current I rapidly flows through the LED 1, and its light emitting intensity, too, reaches rapidly the maximum value. |
