| 摘要 |
PURPOSE:To stabilize the brightness by connecting a luminous diode and a constant-current diode in series to form a constant current circuit, and connecting the constant-current circuit and a constant-voltage circuit in parallel each other. CONSTITUTION:When a power supply voltage is applied between terminals (a) and (a), the voltage is applied to both ends of a constant-voltage D4 through a rectifier D1 and a resistance R1 because constantly-opened fixed contacts 1 and 1 are in the opening condition. The voltage at the both ends of the constant-voltage diode D4 is kept constant and the voltage is applied further to a constant-current diode D3 and a luminous diode D2, a current flows through the series circuit, and the luminous diode D2 emits light. In this case, when the constantly-opened fixed contacts 1 and 1 are contacted by the returning of a movable contact 3, the constantly-opened fixed contacts, or an operation display circuit, is short-circuited, and the luminous diode D2 is turned off. In such a way, the operation display circuit can be operated stably even though the power supply voltage is varied in a relatively broad range.
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