JPH0366199U

JPH0366199U -

Info

Publication number: JPH0366199U
Application number: JP12729389U
Authority: JP
Priority date: 1989-10-31
Filing date: 1989-10-31
Publication date: 1991-06-27
Anticipated expiration: 2004-10-31
Also published as: JPH0711438Y2

Description

[Brief explanation of drawings]

第１図は本考案のバツクライト調光回路の具体
的実施例を示すブロツク回路図、第２図は第１図
の説明に供するタイムチヤート、第３図は従来の
技術の説明に供する図、第４図は第３図の動作の
説明に供するタイムチヤートである。１……増光スイツチ、２……減光スイツチ、３
，３０……制御回路、５，５０……アツプダウン
カウンタ、６，６０……ＤＡＣ、７……バツクラ
イト駆動回路、８……バツクライト（蛍光管）、
９……パルス幅変調器、１０……ゲート回路、１
１……抵抗回路、４０……ＶＣＯ（電圧制御発振
器）、７０……インバータ。 FIG. 1 is a block circuit diagram showing a specific embodiment of the backlight dimming circuit of the present invention, FIG. 2 is a time chart for explaining FIG. 1, and FIG. 3 is a diagram for explaining the conventional technology. FIG. 4 is a time chart for explaining the operation of FIG. 3. 1...Brightness switch, 2...Dimension switch, 3
, 30... Control circuit, 5, 50... Up-down counter, 6, 60... DAC, 7... Backlight drive circuit, 8... Backlight (fluorescent tube),
9...Pulse width modulator, 10...Gate circuit, 1
1... Resistance circuit, 40... VCO (voltage controlled oscillator), 70... Inverter.

Claims

[Scope of utility model registration request]

It has a control circuit to which a signal of a brightness increase switch or a dimming switch is guided, and an up-down counter to which a signal of the control circuit is guided, and when the brightness increase switch is operated, the count value of the up-down counter is increased through the control circuit. In the backlight dimming circuit that reduces the count value and dims the backlight brightness when the dimmer switch is operated, the control circuit sends a brightness increase signal or a dimmer signal while the brightness increase switch or the dimmer switch is operated. is synchronized with a clock pulse from a voltage controlled oscillator and outputted to a gate circuit disposed between the control circuit and the up-down counter, and when the brightening switch and dimming switch are operated simultaneously, the brightening signal and the dimming signal are output. The gate circuit outputs a count-up signal to the up-down counter when the brightening signal is present, and outputs a count-down signal to the up-down counter when the dimming signal is present. The up/down counter is configured to increase the count value when the count up signal is present and decrease the count value when the count down signal is present. A digital-to-analog conversion circuit inputs a counter value, converts it into an analog current, and outputs an analog output voltage proportional to the count value, and compares the output of the digital-to-analog conversion circuit with the output of a triangular wave oscillator to convert the digital-to-analog conversion circuit into an analog current. a pulse width modulator that outputs a pulse width modulated signal with a duty ratio proportional to the output; an inverter that oscillates based on the signal of the pulse width modulator and applies a high voltage to the backlight to turn it on; The output of the digital-to-analog conversion circuit is input, and this input is output to the voltage controlled oscillator via a resistor, and the voltage obtained by the variable resistor is added to the voltage output obtained via the resistor. It comprises a resistance circuit configured to output to a voltage controlled oscillator, and when the output of the digital-to-analog conversion circuit is 0 [V], the voltage controlled oscillator oscillates only by the voltage applied from the variable resistor; The backlight control is characterized in that when the output of the digital-to-analog conversion circuit rises and starts flowing through the resistor, this value is added to the voltage from the variable resistor and input to the voltage controlled oscillator. optical circuit.