| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a back light control circuit which can maintain constant an electric current flowing to LED for a back light and maintain constant illumination of the back light, regardless of a cell voltage, by operating a transistor in an active region. SOLUTION: The back light control circuit comprises a NTN-type transistor 11, an electric current limiting resistance 12 connected to a base terminal of the transistor 11, a LED 13 for a back light with an anode terminal connected to an emitter terminal of the transistor 11 and a cathode connected to the ground of the transistor 11 and a resistance 15 connected to a collector terminal of the transistor 11 and connected to a battery 14, whereby, an electric current flowing to the LED 13 for the back light is maintained constantly, by limiting a base electric current of the transistor 11, depending to the electric current limiting resistance 12 connected to the transistor 11.</p> |
