| 摘要 |
<p>PROBLEM TO BE SOLVED: To permit the setting of desired const. current with housing a forward voltage required for a light emitting element at a low power voltage, by feeding a drive voltage to an input circuit according to the comparison result of a potential at a connection of first current input and output of a differential output circuit with a reference voltage. SOLUTION: The emitters of npn type transistors Q221, Q222 in a differential output circuit 22 are mutually connected at a common connection point grounded through a resistance element R221. A comparator circuit 24 is composed of an operational amplifier OP241 for comparing the voltage VD on the emitter connection N221 of the differential output circuit 22 with a reference voltage VE generated, by a reference voltage generator circuit 23 to output a signal S24 of a level according to this comparison result to a variable voltage feed circuit 25, which feeds a voltage according to the input level of the output signal S24 of the comparator circuit 24 as a drive voltage of an input circuit 21.</p> |
