JP3121306B2 - Inverter circuit for cold cathode discharge tube with dimming function - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter circuit for converting a direct current into an alternating current, and more particularly to an inverter circuit having a dimming function suitable for supplying power to a cold cathode discharge tube.

[0002]

2. Description of the Related Art In order to light a cold cathode discharge tube such as a backlight of a liquid crystal display or an ultraviolet lamp, an inverter circuit for converting a DC power supply such as a battery into a high-voltage AC is required. As such an inverter circuit, conventionally, as shown in FIG. 10, a midpoint tap type resonance circuit 50 in which a lower circuit used in a DC-DC converter is improved is used.
Is used.

This is because a pair of transistors Tr4 and Tr5
The base sides of both transistors are connected to the drive coil 52, respectively.
Reference numeral 52 is connected to a primary coil 56 via a core of a transformer 54. A DC power supply 58 is connected to the middle point of the primary coil 56. One end of the primary coil 56 is connected to the collector of Tr4, and the other end is connected to the collector of Tr5. As a result, the primary coil 56 is divided into a collector coil 56a of Tr4 and a collector coil 56b of Tr5. When power is supplied to the circuit 50, a current flows to the base of either the transistor Tr4 or Tr5, and the circuit 50 is turned on. For example, if Tr4 is turned on,
A collector current flows through Tr4, and a current in a certain direction flows through collector coil 56a. And the transistor Tr4
As the collector current increases, the magnetic flux in the core of the transformer 54 also increases and saturates. When transformer 54 saturates,
The collector current of transistor Tr4 increases sharply to a value limited by the drive voltage provided by drive coil 52. When the voltage reaches the limit value, the voltage across the collector coil 56a drops, so that the transistor Tr4 is turned off. At this moment, an induced voltage is generated in the transformer 54 in a direction opposite to the previous state, and a voltage is also induced in the drive coil 52 in a direction to positively bias the base of the transistor Tr5. As a result, the transistor Tr5 enters the ON state.
Such switching of the transistors Tr4 and Tr5 is performed automatically and continuously, and the direction of the power supply current flowing through the primary coil 56 constantly changes, so that a high-voltage AC output appears on the secondary coil 60 side, and the cold cathode The lighting of the discharge tube 62 is realized.

[0004]

The above-described conventional circuit 50
Has been actively used because of its relatively simple configuration, but basically, it can only control ON / OFF of the cold cathode discharge tube 62, and each transistor Tr4, T4
The switching timing of r5 is fixed in advance. Therefore, the value of the current supplied to the cold cathode discharge tube 18 does not change, and its light output remains constant. If a dimming function for changing the light output of the cold-cathode discharge tube 62 is added to the circuit 50, there is a disadvantage that the circuit configuration becomes complicated, for example, an auxiliary power supply for control is required.

The present invention has been devised to solve the above-mentioned drawbacks of the conventional inverter circuit. It is an object of the present invention to provide a cold cathode discharge using a single power supply while having a simple circuit configuration. An object of the present invention is to realize an inverter circuit capable of controlling the light output of a tube.

[0006]

In order to achieve the above object, an inverter circuit for a cold cathode discharge tube with a dimming function according to the present invention comprises an oscillation controller circuit, a boosting transformer, and an impedance matching circuit. An inverter circuit for a cold-cathode discharge tube interposed between a DC power supply and a cold-cathode discharge tube, wherein the oscillation controller circuit includes a variable resistor and a variable resistor connected at a frequency corresponding to a set value of the variable resistor. An oscillator that generates a pulse signal, a flip-flop that outputs a pair of push-pull signals whose states are alternately inverted by bisecting the pulse signal, and a push-pull signal output from the flip-flop being received at a base. ON /
A pair of transistors that alternately switch OFF, and a middle point of a primary coil of the step-up transformer is connected to the DC power supply, and one end of the primary coil is connected to a collector of the one transistor. The other end of the primary coil is connected to the collector of the other transistor, and the impedance matching circuit is interposed between the boosting transformer and the cold cathode discharge tube, and has one end of a secondary coil of the boosting transformer. And a first capacitor inserted between the other end of the cold cathode discharge tube, a second capacitor inserted between the other end of the secondary coil of the step-up transformer and the other end of the cold cathode discharge tube, A third capacitor inserted between both ends of a secondary coil of the step-up transformer on the step-up transformer side of the first capacitor and the second capacitor; Ri, and configured to perform matching of the impedance of the step-up transformer of the alternating current output from the secondary coil and the cold cathode discharge tube.

In the inverter circuit described above, the direction of the power supply current flowing through the primary coil is switched in response to the turning on / off of both transistors, and as a result, an AC output is obtained on the secondary coil side. Can be In addition, if the oscillation frequency of the oscillator is changed by changing the set value of the variable resistor, the ON / O
As the switching speed of the FF changes, the current value of the AC output appearing on the secondary coil side of the step-up transformer also changes,
As a result, the light output of the cold cathode discharge tube also changes.
That is, it is possible to control the light output of the cold cathode discharge tube by simply adjusting the set value of the variable resistor without preparing an auxiliary power supply for dimming separately from the main power supply as in the related art. Become.

A backflow preventing diode is inserted between the collector of the one transistor and one end of the primary coil and between the emitter of the transistor and ground, respectively. It is desirable to insert backflow preventing diodes between the other end of the primary coil and between the emitter of the transistor and the ground.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a cold cathode discharge tube inverter circuit 10 having a dimming function according to the present invention includes an oscillation controller circuit 12, a step-up transformer 14, and an impedance matching circuit 16. ing. Further, an ultraviolet lamp 18 is connected to the impedance matching circuit 16. Further, the oscillation controller circuit 12 includes a DC power supply 20 (9 to 9) for controlling the lighting of the ultraviolet lamp 18 and dimming control.
12 [V] DC), a power switch 22 and a variable resistor 24 are connected.

As shown in FIG. 2, the ultraviolet lamp 18 has a long and thin glass tube curved into a substantially U-shape.
An airtight container 18a having both ends opened in an airtight manner, and a pair of electrodes respectively disposed at both ends of the airtight container 18a.
18b, 18b and the lead wires 18 connected to the respective electrodes 18b, 18b
c, 18c. The airtight container 18a is filled with, for example, an ultraviolet radiation gas obtained by mixing argon and mercury, or an ultraviolet radiation gas mainly containing xenon,
When a voltage is applied to the ultraviolet lamp 18 through the lead wires 18c, 18c, a discharge is generated between the electrodes 18b, 18b, and the electrons collide with the ultraviolet radiation gas to emit ultraviolet rays of various wavelengths. It is. The airtight container 18 is made of, for example, an ultraviolet transmitting glass such as quartz glass or lead glass. still,
Quartz glass can be converted from ultraviolet light with a short wavelength of about 180 nm to about 3 nm.
It is suitable as a constituent material of the hermetic container 18a of the ultraviolet lamp 18 because it can transmit a wide range of ultraviolet light having a long wavelength of 60 nm.

FIG. 3 is a circuit diagram showing a specific example of the configuration of the inverter circuit 10.
IC for switching regulator that constitutes the main part of
26, a small surface-mount step-up transformer 14 having a primary coil 28 and a secondary coil 30, and an impedance matching circuit 16 including capacitors C1, C2 and C3 are shown. One end of the primary coil 28 of the step-up transformer 14 is connected to the IC
The other end is connected to the (11) terminal while being connected to the 26 (8) terminal. The midpoint 28a of the primary coil 28 is connected to the DC power supply 20 (Vcc). As the DC power supply 20, for example, a battery of 9 to 12 [V] is used.

A diode D1 for preventing backflow is inserted between one end of the primary coil 28 and the terminal (8) of the IC 26. Similarly, the other end of the primary coil 28 and (1
1) A diode D2 for backflow prevention is inserted between the terminal and the terminal. The terminals (9) and (10) of the IC 26 are
Both are connected to ground, and are connected to the (8) terminal of IC26.
Diodes D3 and D4 for preventing backflow are inserted between terminals (9) and between terminals (10) and (11), respectively.

The capacitor C1 of the impedance matching circuit 16 is connected to the secondary coil 30 of the step-up transformer 14.
And one end of the ultraviolet lamp 18. The capacitor C2 is inserted between the other end of the secondary coil 30 of the step-up transformer 14 and the other end of the ultraviolet lamp 18. Further, the capacitor C3 is inserted between both ends of the secondary coil 30 of the step-up transformer 14 on the step-up transformer 14 side with respect to the capacitors C1 and C2.

As in the other impedance matching circuit 16a shown in FIG. 4, a capacitor C1 is inserted between one end of the secondary coil 30 of the step-up transformer 14 and one end of the ultraviolet lamp 18. On the UV lamp 18 side, a capacitor having a capacitor C2 inserted between both ends of the secondary coil 30 of the step-up transformer 14 may be employed.

However, when a material capable of transmitting a wide range of ultraviolet light having a short wavelength to ultraviolet light having a long wavelength, such as quartz glass, is selected as a constituent material of the airtight container 18a of the ultraviolet lamp 18, the impedance of the ultraviolet lamp 18 may be reduced. Becomes very small. In this case, although extremely rare, in the impedance matching circuit 16a of FIG. 4, the output from the secondary coil 30 of the step-up transformer 14 depends on the shape and diameter of the airtight container 18a of the ultraviolet lamp 18 to be used. In some cases, matching between the alternating current and the impedance of the ultraviolet lamp 18 cannot be performed. For this reason,
When the hermetic container 18a of the ultraviolet lamp 18 is made of a material that can transmit a wide range of ultraviolet light having a short wavelength to ultraviolet light having a long wavelength, the secondary coil is formed by using the impedance matching circuit 16 shown in FIG. It is desirable to match the alternating current output from 30 with the impedance of the ultraviolet lamp 18. This will be described with reference to FIG. FIG. 5 shows the values of the capacitors forming the impedance matching circuit and the inverter circuit 10 for the cold-cathode discharge tube (input current) according to the present invention when a certain ultraviolet lamp 18 whose quartz container is made of quartz glass is used. 5 is a graph showing a relationship with a maximum rated input current value of 200 mA. In FIG. 5, A is the impedance matching circuit of FIG.
The value of the capacitors C1 and C2 constituting 16a is set to C1 = 10
3 is a curve showing a change in input current value when 0 pF and C2 = 18 pF, and B is the impedance matching circuit of FIG.
The values of the capacitors C1, C2 and C3 constituting the 16 are represented by C1 =
It is a curve which shows the change of the input current value at the time of 39pF, C2 = 39pF, and C3 = 10pF. Thus, in the impedance matching circuit 16a of FIG. 4, when the input current value is about 2 minutes, the maximum rating exceeds 200 mA and an overflow occurs, causing a circuit failure, and the values of the capacitors C1 and C2 are varied. Even if it was changed, finally, the alternating current output from the secondary coil 30 of the step-up transformer 14 could not be matched with the ultraviolet lamp 18 used in this experiment. On the other hand, in the impedance matching circuit 16 shown in FIG. 3, when the values of the capacitors C1, C2 and C3 are under the above conditions, the input current value is 180 to 190 mA.
Thus, the alternating current output from the secondary coil 30 could be matched with the impedance of the ultraviolet lamp 18 used in this experiment.

One end of a variable resistor 24 is connected to the terminal (6) of the IC 26, and a resistor R1 is inserted between the terminal (6) and the variable resistor 24. The above IC26
(5) A capacitor C4 is inserted between the terminal and the ground. The terminal (4) of the IC 26 is connected to the power supply Vcc. A power switch 22 and a transistor Tr1 are inserted between the terminal (4) and the power supply Vcc. The terminals (2), (15), (13) and (14) of the IC 26 are connected to the terminal (4). further,
The terminals (1), (16) and (7) of the IC 26 are connected to the ground.

FIG. 6 is an equivalent circuit diagram showing the internal structure of the IC 26. The IC 26 includes an oscillator (OSCILATOR) 32 for continuously generating saw-tooth pulses, a D-type flip-flop 34, Switching transistor T
r2, Tr3 and a pair of comparators CMP1, CMP2
And a pair of error amplifiers A1, A2 and the like. Note that (1) to (16) in FIG. 5 correspond to the terminal numbers (1) to (16) of the IC 26 shown in FIG. 3, respectively.

When the oscillator 32 continuously outputs a sawtooth pulse signal at a predetermined frequency, the pulse signal is bisected by a flip-flop 34,
From both terminals, a push-pull signal in which the state of “H” and “L” is alternately inverted is continuously output at a constant period, and is input to the bases of the transistors Tr2 and Tr3, respectively.
As a result, the terminals (9) and (10) of the IC 26 are alternately turned on.
/ OFF is repeated, and the direction of the power supply current flowing through the primary coil 28 of the step-up transformer 14 changes.
A high-voltage AC output appears on the secondary coil 30 side of the step-up transformer 14.

As described above, by inserting the diodes D1 to D4 for preventing backflow between the IC 26 and the primary coil 28 and the ground, the direction of the current flowing through the primary coil 28 is output from the flip-flop 34. The switching is accurately performed in accordance with the inversion operation of the push-pull signal, and as a result, a regular current waveform can be generated on the secondary coil side.

The oscillation frequency of the oscillator 32 is determined by the time constant of the capacitance of the capacitor C4 connected to the terminal (5) and the combined resistance of the resistor R1 and the variable resistor 24 connected to the terminal (6). The oscillation frequency of the pulse signal output from the oscillator 32 can be changed in a range of about 20 kHz to 100 kHz by changing the resistance value of the variable resistor 24. That is, as the resistance value of the variable resistor 24 decreases, the frequency of the pulse signal output from the oscillator 32 increases, and the push-pull signal output from the flip-flop 34 is inverted, and the transistors Tr2 and Tr3 are inverted. Since the switching operation speeds up, as a result, the current value of the alternating current output from the secondary coil 30 of the transformer increases.

For example, the resistance value of the variable resistor 24 is set to 24.7 kΩ.
When the oscillation frequency of the oscillator 32 is set to 20 kHz, the off-time of the current supplied to the ultraviolet lamp 18 becomes longer as shown in FIG. 7, and the tube current to the ultraviolet lamp 18 is as low as 2.3 mA. Becomes As a result, the ultraviolet lamp 18
The light output of the device also remains at a low level of about 0.44 mW / cm ² . On the other hand, the resistance value of the variable resistor 24 is set to 4.3 k.
When the oscillation frequency of the oscillator 32 is set to 60 kHz, the waveform of the current supplied to the ultraviolet lamp 18 is as shown in FIG.
As shown in FIG. 7, the off-time decreases, and accordingly, the tube current to the ultraviolet lamp 18 increases to 4.6 mA. As a result,
The light output of the ultraviolet lamp will also rise to 2.3 mW / cm ² . Further, when the resistance value of the variable resistor 24 is set to 0Ω and the oscillation frequency of the oscillator 32 is increased to 104 kHz, the off-time of the waveform of the current supplied to the ultraviolet lamp 18 almost disappears as shown in FIG. And the tube current value is 7.7m
A, and the light output of the UV lamp 18 is the highest, 8mW /
It was marked down for the cm ^2.

The oscillator 32 has a structure in which signal output starts when the terminal (4) of the IC 26 is grounded. Therefore, when the power switch 22 is turned on to turn on the transistor Tr1, signal output from the oscillator 32 is started, and an AC output can be generated on the secondary coil 30 side of the transformer. That is, in the inverter circuit 10, without preparing an auxiliary power supply separately,
The main power source for turning on the ultraviolet lamp 18 can be used as a drive power source for the inverter circuit 10, and the light output from the ultraviolet lamp 18 can be adjusted.

Further, by using a compact IC 26 as the oscillation controller circuit 12, which is a main component of the circuit, and using a small surface-mount type transformer as the step-up transformer 14, the whole inverter circuit can be reduced in size and weight. For example, if the hermetic container 18a of the ultraviolet lamp 18 is made of quartz glass and the ultraviolet lamp 18 emits ultraviolet light having a wavelength of less than 220 nm (particularly 185 nm) having an ozone generating action, it can be turned on by a dry battery. In addition, it is possible to realize a handy ozone generator device whose output can be adjusted according to the purpose of use. On the other hand, if an ultraviolet lamp having a remarkable bactericidal action of 254 nm is generated from an ultraviolet lamp, it can be operated with a dry cell. so,
Moreover, it is possible to realize a handy ultraviolet sterilizer capable of adjusting the output according to the purpose of use. In addition,
The capacitor C constituting the impedance matching circuit 16
It is necessary to determine the capacities of C1, C2 and C3 in consideration of the impedance of the cold cathode discharge tube actually used.

[0024]

In the inverter circuit for a cold-cathode discharge tube having a dimming function according to the present invention, the setting value of the variable resistor is adjusted without providing an auxiliary power supply dedicated to dimming, and the controller circuit for oscillation is used. By changing the oscillation frequency, the current value of the alternating current supplied to the cold cathode discharge tube can be controlled, and as a result, the light output of the cold cathode discharge tube can be controlled.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration of a cold cathode discharge tube inverter circuit with a dimming function according to the present invention.

FIG. 2 is a sectional view showing an ultraviolet lamp.

FIG. 3 is a circuit diagram showing a specific configuration of the inverter circuit for a cold cathode discharge tube with a dimming function.

FIG. 4 is a circuit diagram showing another impedance matching circuit.

FIG. 5 is a graph showing a relationship between a value of a capacitor constituting an impedance matching circuit and a value of an input current of an inverter circuit for a cold cathode discharge tube.

FIG. 6 is an equivalent circuit diagram showing the inside of an IC constituting an oscillation controller circuit of the inverter circuit for a cold cathode discharge tube with a dimming function.

FIG. 7 is a waveform diagram showing an example of an alternating current input to a cold cathode discharge tube.

FIG. 8 is a waveform diagram showing another example of an alternating current input to a cold cathode discharge tube.

FIG. 9 is a waveform diagram showing another example of the alternating current input to the cold cathode discharge tube.

FIG. 10 is a circuit diagram showing a conventional inverter circuit for a cold cathode discharge tube.

[Explanation of symbols]

 10 Inverter circuit for cold cathode discharge tube with dimming function 12 Controller circuit for oscillation 14 Boost transformer 16 Impedance matching circuit 18 Ultraviolet lamp 20 DC power supply 24 Variable resistor 28 Primary coil 30 Secondary coil 32 Oscillator 34 Flip-flop Tr2, Tr3 transistor C1 , C2, C3 Capacitor D1, D2, D3, D4 Diode

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H05B 41/392

Claims (2)

(57) [Claims] An inverter circuit for a cold-cathode discharge tube, comprising a controller circuit for oscillation, a step-up transformer, and an impedance matching circuit, interposed between a DC power supply and the cold-cathode discharge tube. The controller circuit includes a variable resistor, an oscillator that continuously generates a pulse signal at a frequency corresponding to the set value of the variable resistor, and a pair of push-pull signals that divide the pulse signal into two and alternately invert the state. On the basis of the push-pull signal output from the flip-flop
And a pair of transistors that alternately switch between ON and OFF. The middle point of the primary coil of the step-up transformer is connected to the DC power supply, and one end of the primary coil is connected to the collector of the one transistor. And
The other end of the primary coil is connected to the collector of the other transistor, and the impedance matching circuit is interposed between the boosting transformer and the cold cathode discharge tube,
A first capacitor inserted between one end of the secondary coil of the step-up transformer and one end of the cold cathode discharge tube, and a first capacitor inserted between the other end of the secondary coil of the step-up transformer and the other end of the cold cathode discharge tube And a third capacitor inserted between both ends of a secondary coil of the step-up transformer on the side of the step-up transformer with respect to the first capacitor and the second capacitor. An inverter circuit for a cold-cathode discharge tube with a dimming function, which performs matching between an alternating current output from a secondary coil of a transformer and impedance of the cold-cathode discharge tube. 2. A diode for preventing backflow is inserted between the collector of the one transistor and one end of the primary coil and between the emitter of the transistor and ground, and the collector of the other transistor is inserted. 2. A cold cathode with a dimming function according to claim 1, wherein a diode for preventing backflow is inserted between the transistor and the other end of the primary coil and between the emitter of the transistor and the ground. Inverter circuit for discharge tube.