| 摘要 |
PURPOSE:To prolong the life of dry cells, etc., when these cells are used and to raise the output of a light emitting output device when an AC adapter or the like is used by detecting the impression of a source voltage from the outside and switching a power source apply route by a power source switching circuit to apply this voltage to the light emitting output device. CONSTITUTION:This device is so constituted that a signal 101 for the presence or absence of the external input being the output of a circuit 10 for detecting the presence or absence of the external input turns to a high level in the case of the presence of the input from the outside and turns to a low level in the case of use of a power source box 3 built in the liquid crystal display device. This signal is inputted to the power source switching circuit 11. The circuit is turned on to an L side to impress an input voltage to a constant-voltage power source 9 when the signal 101 for the presence or absence of the external input is the low level. The circuit is turned on to the H side to apply the input voltage directly to the light emitting output device 4 without going thru the constant-voltage power source 9 when the above-mentioned signal is the high level. The life of the built-in dry cells or built-in storage batteries are prolonged when these cells or batteries are used as the power source in this way. The output of the light emitting output device is raised to brighten the display when the external input AC adapter or external input car adapter is used as the power source. |
