DRIVE CIRCUIT OF LIGHT EMITTING ELEMENT

摘要

PURPOSE:To suppress a delay of a light emitting output at leading and to improve the waveform distortion by connecting an added circuit comprising series connection of a coil, a resistor and a diode in parallel with a light emitting element so as to flow dividingly a current from a current source to the added circuit and the light emitting element. CONSTITUTION:An electric charge stored in a parasitic capacitance of an LED 2 is discharged through an added circuit comprising series connection of the diode D6, the resistor 5 and the coil 4 when the LED2 is turned off with a transistor (TR) 3 turned off. The D6 acts on the LED2 to keep its terminal voltage over zero V even at turning-off of the 1ED2 and the voltage is offset by the threshold voltage VD of the LED2. In selecting the voltage VD identical to the threshold voltage Vth, since the leading of luminescence of the LED2 when the TR3 is turned on starts from the Vth, the delay in the luminescence at leading is eliminated and distortion of pulse width is suppressed.