| 摘要 |
<p>PURPOSE:To obtain a light signal with a constant light quantity and to prolong the life of a device by providing a driving means which drives a light emitting element with a constant current. CONSTITUTION:The potential difference generated across a resistance R1 with a driving current is supplied to the base of a transistor (TR) Q2 for negative feedback through a variable resistor VR and the impedance of the TR Q3 is adjusted. Consequently, the voltage obtained by dividing the voltage of a driving power source V through resistances R2 and R3 and the TR Q3 for negative feedback is applied to the base of a TR Q2 for control and the impedance of the control TR Q2 is adjusted. When a driving current flowing to one light emitting diode selected among L1-Ln is larger than a specific value, such a negative feedback circuit that the impedance of the control TR Q2 is larger is formed and the driving current becomes constant. Therefore, even if lead wires for flowing driving currents to the light emitting diodes L1-Ln and the pattern of a printed wiring board differ in resistance value, the light emitting diodes L1-Ln are driven with the constant currents and a light signal with a constant light quantity is outputted.</p> |
