Patent ID: 7808460

Claim:
A display LED drive circuit comprising: a first current route and a second current route which are connected to a power circuit in parallel, the first route comprising: a first constant current circuit employing an active element; a first display LED circuit in which a corresponding switching element is serially connected to a first display LED; and a second display LED circuit in which a corresponding switching element is serially connected to a second display LED, connected in series; a first resistor circuit, in which a corresponding switching element is serially connected to a first resistor that generates the same potential difference as the potential difference generated by the first display LED, connected to the first display LED circuit in parallel, and a second resistor circuit, in which a cut-off switching element and a corresponding switching element are serially connected to a second resistor that generates the same potential difference as the potential difference generated by the second display LED, connected to the second display LED circuit in parallel; the second route comprising: a second constant current circuit employing an active element; a third display LED circuit in which a corresponding switching element is serially connected to a third display LED; and a constant voltage diode; a third resistor circuit, in which a corresponding switching element is serially connected to a third resistor that generates the same potential difference as the potential difference generated by the third display LED, connected to the third display LED in parallel, wherein the corresponding switching elements of the respective display LED circuits and the corresponding switching elements of the respective resistor circuits connected in parallel correspondingly with the respective display LED circuits are controlled to be opened and closed in opposite ways, wherein the cut-off switching element is controlled to be opened and closed synchronously with the corresponding switching element of the first display LED circuit disposed on an upstream side, and wherein an output terminal for deriving a voltage is provided between the third display LED circuit and the constant voltage diode.