| 摘要 |
PURPOSE:To enable dispersion of a LED driving current of each chip to be equalized with an operational amplifier, by a method wherein all chips are made equal in external resistance value by establishing the operational amplifier, a transistor monitor, an output transistor for monitor, and an outside fitting external resistance. CONSTITUTION:A transistor for monitor 37 is always in an on state, and a gate potential of an output transistor for monitor 38 becomes equal to a potential of an output of an operational amplifier 36. When a reference voltage Vref is impressed to a non-inversional input terminal 36a of the operational amplifier 36, a current I flowing to an external resistance 51 becomes I-Vref/R. When a control signal of a 'H' level is inputted to a control signal terminal 35, a NMOS 39b in an inverter 39 turns on, and a gate bias voltage of an output transistor 40 becomes equal to the output voltage of the operational amplifier 36. Therefore, when the transistor 37 and 39b, and the transistors 38 and 40 are respectively formed to a same shape, a current flowing from an output terminal 34 to a LED 50 becomes equal to the current I flowing to the external resistor 51. |
