JPH03110796A - dimming control circuit - Google Patents

Abstract

PURPOSE:To make a dimming control circuit small and light by regulating the continuity state of a 1st, semiconductor element with a 2nd semiconductor element depending upon the voltage between the both ends of a voltage detecting resistance connected to the same semiconductor element in series. CONSTITUTION:A 1st semiconductor element 12 the continuity state of which is varied corresponding to driving signals from a signal input terminal 6 is inserted between a driving power source 9 and a discharge tube 8, and driving pulses supplied to the discharge tube 8 from the driving power source 9 are pulse-width modulated by the switching of the 1st semiconductor element 12 to dim the discharge lamp 8. In addition, the continuity state of the 1st semiconductor element 12 is regulated with a 2nd semiconductor element 14 depending upon the voltage between the both ends of a voltage detecting resistance 13 connected to the 1st semiconductor element 12 in series, so as that even when voltage variations or the like are generated in the output of the driving power source 9 high voltages cannot be applied to the discharge tube 8. Thereby current limiting elements such as inductors or capacitors or the like for preventing the breakdown of the discharge tube can be needless to miniaturize the dimming control circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a dimming control circuit used for controlling the dimming of a discharge tube.

BACKGROUND OF THE INVENTION In recent years, public image display devices with large screens such as IOX8(m) have been developed. There are various types of such devices, and one that uses self-luminous pixels such as discharge tubes to display clear images even in the daytime has been developed.

In an image display device using discharge tubes, discharge tubes equipped with color filters of three primary colors are arranged in a matrix, and the discharge tubes of each color emit light at a predetermined brightness to provide a full-color display. ing.

Therefore, a dimming control circuit that can be used to control the light emission of such a discharge tube was proposed by the present applicant in Japanese Patent Application Laid-Open No. 59-128800.
It has been proposed as a publication number. Therefore, this device will be described as a conventional example of a dimming control circuit with reference to FIG. This dimming control circuit 1 includes a dimming circuit 5 made up of first and second transistors 2 and 3 and a knot gate 4 connected to a signal input section 6, and a discharge with a filament power source 7 connected to a cathode electrode. A tube 8 is connected in parallel to the second transistor 3 of the dimmer circuit 5. Further, the drive power source 9 is connected to the collector of the first transistor 2 of the dimming circuit 5 via a current limiting element 10 made of an inductor, a capacitor, or the like.

In such a configuration, the dimming control circuit 1 controls the supply of power from the drive power source 9 to the anode electrode of the discharge tube 8 by the first transistor 2 of the dimming circuit 5, which switches according to the drive signal input from the signal input section 6. power is turned on and off. At this time, by switching the second transistor 3, the driving pulse to the discharge tube 8 is pulse width modulated, and the light emission time of the discharge tube 8, which is blinking at high speed, is controlled and dimmed.

Note that in this dimming control circuit 1, the discharge tube 8 and the drive power source 9
By inserting the current limiting element 10 between the discharge tube 8 and the discharge tube 8, electric power flowing into the discharge tube 8 is regulated to prevent destruction.

Problems to be Solved by the Invention The dimming control circuit 1 as described above can cause the discharge tube 8 to emit light at a desired brightness, so it can be used as a drive circuit for a large image display device, etc. . However, the above-mentioned dimming control circuit 1 includes a dimming circuit 5 for controlling the dimming of the discharge tube 8, and a current limiting element lO for regulating the power to prevent the discharge tube 8 from being destroyed. Therefore, the number of parts increases and the productivity of the device decreases. Further, although an inductor, a resistor, or the like is used as the current limiting element 10, these components are generally large and heavy, and have a large current loss, increasing power consumption.

The above-mentioned problems are particularly noticeable in large-sized image display devices in which a huge number of discharge tubes 8 are arranged in series and driven, and there is a demand for the dimming control circuit 1 to be smaller and lighter.

Means for Solving the Problem A first semiconductor element whose conduction state changes according to a drive signal from a signal input section is inserted between a drive power source and a discharge tube,
The second semiconductor element regulates the conduction state of the first semiconductor element in accordance with the voltage across a voltage detection resistor connected in series with the first semiconductor element.

By inserting the first semiconductor element whose conduction state changes according to the drive signal from the action signal input section between the drive power source and the discharge tube, the switching of the first semiconductor element causes the power to be supplied from the drive power source to the discharge tube. The discharge tube can be dimmed by pulse width modulating the driving pulse, and the second semiconductor element changes to the first semiconductor element depending on the voltage across the voltage detection resistor connected in series with the first semiconductor element. By regulating the conduction state of the semiconductor element, even if voltage fluctuations occur in the output of the drive power source, high voltage will not be applied to the discharge tube and destruction will not occur.

Example An embodiment of the present invention will be described based on FIG.

Note that the same parts as in the conventional example described above are given the same names and numerals, and explanations thereof will be omitted. First, in the dimming control circuit 11 of this embodiment, the emitter of a transistor 12, which is a first semiconductor element whose collector is connected to the drive power supply 9, is connected to the discharge tube 8 via a voltage detection resistor 13. and,
The base of a transistor 14, which is a second semiconductor element whose collector is connected to the base of the first transistor 12 and whose emitter is connected to the discharge tube 8, is connected to the emitter of the first transistor 12 via a resistor 15. It is connected.

Further, in the dimming control circuit 11 of this embodiment, the base of the first transistor 12 is connected to the signal input section 6 via a transistor 18 that forms a loop with a DC power supply 16 and a resistor 17.

In such a configuration, the dimming control circuit 11 of this embodiment
By switching the transistor 18 according to the drive signal input from the signal input section 6, the power applied to the base of the first transistor 12 is turned on and off. Therefore, the first transistor 12 switches and the drive pulse supplied from the drive power source 9 to the anode electrode of the discharge tube 8 is pulse width modulated, thereby controlling the light emitting time of the discharge tube 8 which is blinking at high speed. Dimmed.

Note that in this dimming control circuit 11, power is supplied from the drive power supply 9 to the discharge tube 8 via the first transistor 12 which is turned on by the voltage of the DC power supply 16 as described above. For example, when a voltage fluctuation occurs in the output of the drive power supply 9, the voltage across the voltage detection resistor 13 to which the current passing through the first transistor 12 is applied increases, and this voltage is applied to the second transistor via the resistor 15. It will be applied to the base of transistor 14. Then, the second transistor 14 is turned on, the voltage applied from the DC power supply 16 to the base of the first transistor 12 is reduced, and the first transistor 12 is turned off.

In reality, the above-mentioned operation is stable at a certain level, and the power supplied from this dimming control circuit 11 to the discharge tube 8 is always at a constant voltage, and voltage fluctuations etc. occur in the drive power supply 9. However, the discharge tube 8 will not be destroyed by the application of high voltage.

As mentioned above, this dimming control circuit 11 is formed only with semiconductor elements without using current limiting elements such as inductors or capacitors in order to prevent the discharge tube 8 from being destroyed, so it can be driven with low power loss. It has good followability even when the power is low, and it is easy to downsize the device by mounting circuit components at high density.

Therefore, as illustrated in FIG. 2, the discharge tubes 8 connected to the above-mentioned dimming control circuit 11 and arranged continuously in a matrix are replaced with phosphors that emit light of different colors of green, blue, and red. One pixel is composed of three types of discharge tubes equipped with
Furthermore, by attaching color filters of colors corresponding to the emitted light colors to the display surfaces of the three types of discharge tubes, a large-sized image display device 19 can be formed. In this case, the dimming control circuit 11 of this embodiment is easy to downsize and save power, so it is suitable as a drive circuit for a gigantic image display device 19 that includes a huge number of devices.

Effects of the Invention As described above, the present invention includes inserting the first semiconductor element whose conduction state changes according to the drive signal from the signal input section between the drive power source and the discharge tube, so that the first semiconductor element's conductivity changes. The discharge tube can be dimmed by pulse width modulating the drive pulse supplied from the drive power supply to the discharge tube by switching, and also according to the voltage across the voltage detection resistor connected in series to the first semiconductor element. Since the second semiconductor element regulates the conduction state of the first semiconductor element, even if voltage fluctuations occur in the output of the drive power source, high voltage will not be applied to the discharge tube and damage will occur. Since there is no need to use current-limiting elements such as inductors and capacitors to prevent discharge tube destruction, power loss is small and component mounting can be easily increased in density, allowing for miniaturization and savings in discharge tube lighting devices. This has effects such as being able to contribute to electrification.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram of an image display device, and FIG. 3 is a circuit diagram of a device proposed in the past by the applicant.

Claims (1)

[Claims] A first semiconductor element inserted between the drive power source and the discharge tube and whose conduction state changes according to the drive signal from the signal input section; a voltage detection resistor connected in series with the first semiconductor element; and a second semiconductor element that regulates the conduction state of the first semiconductor element according to the voltage across the voltage detection resistor.