JP2000012259A - Cold cathode discharge tube lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a part cost, and to reduce a space by eliminating an electric current detecting element for detecting a discharge current of a power transformer for reducing a commercial power source and a cold cathode discharge tube. SOLUTION: A cold cathode discharge tube lighting device has the step-up transformer part 3, the resonance switching driving circuit part 5 for outputting a pulse for switching and a switching element 6 being electrically continued according to a pulse switched by the resonance switching driving circuit part 5 and supplying voltage to the primary side of the step-up transformed part 3. One end of a cold cathode discharge tube 8 is connected to a secondary side output terminal of the step-up transformer part 3, and the other end of the cold cathode discharge tube 8 is connected to a power input terminal of the resonance switching driving circuit part 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for lighting a cold cathode discharge tube, and more particularly to an inverter type cold cathode discharge tube lighting device using a step-up transformer.

[0002]

2. Description of the Related Art FIG. 3 is a circuit block diagram of a conventional inverter type lighting circuit for a cold cathode discharge tube. In FIG. 3, commercial power is supplied to the primary side of a power transformer TA via a power-on operation switch SW and a filter FL. The power transformer TA steps down the commercial power and supplies the stepped-down AC voltage to the rectifier bridge circuit 2 composed of a diode bridge circuit from the secondary side. Rectifier bridge circuit 2
Rectifies the stepped-down AC voltage. Output plus line 14 and output minus line 1 of the rectifier bridge circuit 2
5 smoothens the rectified voltage to a DC voltage of about 5 V to 20 V.

In the subsequent stage of the smoothing capacitor C1, between the output plus line 14 and the output minus line 15 of the rectifying bridge circuit 2, a resonance switching drive circuit 11, a switching element 6, a step-up transformer 9, a cold cathode discharge Each circuit element of the current detecting element 12 including the tube 8 and the resistor is arranged.

The resonance switching drive circuit 11 is a circuit for outputting a pulse for switching using a DC voltage of 5 V to 20 V as an operation power supply, and for detecting a current flowing through the power supply input terminal U 1 and the cold cathode discharge tube 8. It has four terminals: a current detection terminal U2, an output terminal U3 for outputting a pulse for switching, and a power supply ground terminal U4.

The step-up transformer section 9 comprises a winding L3 and a piezoelectric element type transformer 10. The piezoelectric element type transformer 10 has a primary side connection terminal Q1, a secondary side connection terminal Q2 and a common connection. It has three connection terminals Q3. The winding L3 is connected between the connection terminal Q1 on the primary side of the piezoelectric element type transformer 10 and the common connection terminal Q3.

The piezoelectric element type transformer 10 converts electric energy into vibration energy on the primary side, and
A transformer that converts vibration energy into electric energy again on the secondary side, and that applies a voltage to the primary side to vibrate the piezoelectric element and outputs a voltage corresponding to the vibration of the piezoelectric element from the secondary side It is.

The switching element 6 is composed of a power MOS type field effect transistor, and has a source terminal S,
It has three terminals, a drain terminal D and a gate terminal G.

The power supply input terminal U1 of the resonance switching drive circuit 11 is connected to the output plus side line 14 of the rectifier bridge circuit 2 and has a DC voltage of 5 V as an operating power supply.
２０20 V is supplied to the resonance switching drive circuit 11.

The current detection terminal U2 of the resonance switching drive circuit 11 is connected to a connection point 13 between the cold cathode discharge tube 8 and the current detection element 12, and the output terminal U3 is connected to the switching element 6
The power supply ground terminal U4 is connected to the output minus side line 15 of the rectifier bridge circuit 2.

A connection terminal Q1 on the primary side of the piezoelectric element type transformer 10 in the step-up transformer section 9 is connected to the output plus side line 14 of the rectifier bridge circuit 2, and a connection terminal Q2 on the secondary side of the piezoelectric element type transformer 10. Is connected to one end of the cold cathode discharge tube 8, and the other end of the cold cathode discharge tube 8 is connected to a connection point 13.
Is connected to one end of the current detection element 12, and the other end of the current detection element 12 is connected to the output minus side line 15 of the rectifier bridge circuit 2.

A common connection terminal Q3 of the piezoelectric element type transformer 10 in the step-up transformer section 9 is connected to a drain terminal D of the switching element 6, and a source terminal S of the switching element 6 is connected to the output terminal of the rectifying bridge circuit 2. The negative line 15 is connected.

The operation of the circuit configured as described above will be described. When the power switch SW is closed by being turned on, the commercial power AC 100V is supplied to the power transformer TA through the filter FL, and the AC power is reduced to about 3.6 to 14V AC by the power transformer TA. 2 is rectified and supplied to the DC power supply 5 by being smoothed by the smoothing capacitor C1.
The voltage is set to about 20 V and supplied between the plus side line 14 and the minus side line 15.

When a DC power supply of 5 to 20 V is supplied to the power supply input terminal U1 of the resonance switching drive circuit 11, the resonance switching drive circuit 11 starts a switching operation in response thereto, and outputs a continuous pulse for switching. The signal is sent from the output terminal U3 to the gate terminal G of the switching element 6.

In accordance with the pulse sent from the resonance switching drive circuit 11, the drain terminal D and the source terminal S of the switching element 6 intermittently conduct. That is, when the drain terminal D and the source terminal S of the switching element 6 are in a conductive state, the DC power supplies 5 to 2 are connected between the connection terminal Q1 on the primary side of the step-up transformer 9 and the common connection terminal Q3.
About 0V is applied. By forming a resonance capacitor between the primary side plates facing each other across the piezoelectric element of the piezoelectric element type transformer 10, the resonance capacitor is charged with the applied DC power of about 5 to 20V. When the drain terminal D and the source terminal S of the switching element 6 become non-conductive, a resonance circuit is formed by a closed circuit including the resonance capacitor on the primary side of the piezoelectric element type transformer 10 and the winding L3,
An oscillating current flows through the closed circuit due to the electric energy stored in the resonance capacitor. Accordingly, an alternating current flows through the resonance capacitor on the primary side of the piezoelectric element type transformer 10, and the piezoelectric element vibrates in response thereto, and the vibration of the piezoelectric element is converted into a voltage on the secondary side of the piezoelectric element type transformer 10. As a result, an AC high voltage is generated, a high voltage is applied to both terminals of the cold cathode discharge tube 8, and the cold cathode discharge tube 8 starts discharging.

When the cold cathode discharge tube 8 starts discharging, the connection terminal Q2 on the secondary side of the step-up transformer section 9, the cold cathode discharge tube 8, the connection point 13, the current detecting element 12, the switching element 6, the step-up transformer An alternating current flows through a closed circuit formed by the common connection terminal Q3 of the portion 9 and the connection point 1
3, the current flows to the current detection terminal U2 of the resonance switching drive circuit 11.

At this time, the resonance switching drive circuit 11
Drives the switching element 6 at a frequency that matches the resonance condition of the step-up transformer unit 9, that is, at the resonance frequency.

When the cold cathode discharge tube 8 is abnormal (breakage, outgassing), or when the lead wire of the cold cathode discharge tube 8 is broken,
Since no current flows through the connection point 13, no current is supplied to the current detection terminal U2 of the resonance switching drive circuit 11, and accordingly, the resonance switching drive circuit unit 5 stops the switching operation.

As described above, in the conventional inverter-type lighting circuit for a cold cathode discharge tube, when the step-up transformer or the cold cathode discharge tube is abnormal, for example, the cold cathode discharge tube is damaged or gas is leaked, and the cold cathode discharge tube leads In the event of disconnection of wires or disconnection of windings of the step-up transformer, etc., the current for detecting the discharge current of the cold cathode discharge tube in order to avoid the dangers of circuit breakage, electric shock due to high voltage, and ignition due to abnormal discharge. A detection element is provided to stop the switching operation of the resonance switching drive circuit when the above-described current is not detected.

Further, since the operating voltage of the resonance switching drive circuit is set to about 5 to 20 V DC power supply, when the commercial power supply AC 100 V is used, it is rectified from the AC voltage stepped down by the power transformer TA. Power transformer TA was indispensable.

A fluorescent tube lighting device that generates a fluorescent tube lighting voltage for lighting a fluorescent tube by switching a DC current has been proposed, for example, in Japanese Patent Application Laid-Open No. 2-30996.

This circuit includes an oscillating circuit for generating a switching pulse, a switching circuit for switching a DC current in accordance with a pulse sent from the oscillating circuit, and a fluorescent tube lighting voltage based on the DC current switched by the switching circuit. A step-up transformer that occurs,
A resonance capacitor inserted in a closed circuit formed by the step-up transformer and the fluorescent tube and connected in series with the fluorescent tube;
An oscillation control circuit that stops sending pulses of the oscillation circuit when the voltage applied to the resonance capacitor is no longer detected.

In this device, when the fluorescent tube is removed by cleaning or the like, the current flowing through the resonance capacitor becomes 0, whereby the control output of the oscillation control circuit changes from a high level to a low level. Stops sending pulses for switching, whereby the switching circuit stops the switching operation.

[0023]

SUMMARY OF THE INVENTION It is an object of the present invention to quickly stop the switching operation of the resonance switching drive circuit when a cold cathode discharge tube is damaged, when a lamp lead wire is broken, or when an abnormality occurs in a step-up transformer. In addition, a power supply transformer for stepping down a commercial power supply and a separate power supply circuit for a resonance switching drive circuit, and a current detection element for detecting a discharge current of a cold cathode discharge tube or a current flowing to a switching element can be omitted. An object of the present invention is to provide a cold-cathode discharge tube lighting device capable of realizing a reduction in component cost and space saving.

[0024]

SUMMARY OF THE INVENTION A cold cathode discharge tube lighting device according to the present invention includes a step-up transformer for generating a high AC voltage from a secondary side corresponding to a supply voltage on a primary side, and a switching section for switching. And a switching element that conducts according to the pulse switched by the resonance switching drive circuit section and supplies a voltage to the primary side of the step-up transformer section, One end of a cold cathode discharge tube is connected to an output terminal on the secondary side of the step-up transformer unit, and the other end of the cold cathode discharge tube is connected to a power input terminal of the resonance switching drive circuit unit. It has.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit block diagram showing an electrical configuration of the cold cathode discharge tube lighting device 1 of the present embodiment. The cold-cathode discharge tube lighting device 1 generally includes a rectifier circuit 2 including a diode bridge for rectifying a commercial power supply of AC 100V to generate a DC voltage, a smoothing capacitor C1 for smoothing the DC voltage rectified by the rectifier circuit 2, and a primary side. Step-up transformer section 3 for generating a high-voltage AC voltage from the secondary side corresponding to the supply voltage, start circuit section 4 for supplying operating power for a certain period of time when power is turned on, and resonant switching drive for outputting pulses for switching It has a switching element 6 that conducts according to the pulse switched by the circuit section 5 and the resonance switching drive circuit section 5 and supplies a voltage to the primary side of the boosting transformer section.

In this embodiment, the step-up transformer section 3 comprises a winding type step-up transformer 7 having a primary winding L1 and a secondary winding L2, and a resonance capacitor C2. Has two connection terminals P1 and P2, and has two connection terminals P3 and P4 on the secondary side. The resonance capacitor C2 is connected in parallel to the primary winding L1 connected between the two primary connection terminals P1 and P2.

The resonance switching drive circuit section 5 includes a start power supply input terminal S1 for starting operation, a power supply input terminal S2 for obtaining power after the start of operation, an output terminal S3 for sending out pulses for switching, and a power supply terminal. S
Four.

The switching element 6 is composed of a power MOS type field effect transistor, and has a source terminal S,
It has three terminals, a drain terminal D and a gate terminal G.

In FIG. 1, a rectifier circuit 2 composed of a diode bridge is connected to a commercial power supply of AC 100 V via a power switch SW which is manually closed. A smoothing capacitor C2 is connected between the plus side line 14 and the minus side line 15 of the output of the rectifier circuit 2, and the commercial power supply AC100V becomes a rectified and smoothed DC through the rectifier circuit 2 and the smoothing capacitor C1. 14 and the minus side line 15.

In the positive line 14 of the output of the rectifier circuit 2, the input terminal of the start circuit section 4 and the primary connection terminal P1 of the step-up transformer section 3 are connected downstream of the smoothing capacitor C1. The primary-side connection terminal P2 of the step-up transformer unit 3 is connected to the drain terminal D of the switching element 6, and the source terminal S of the switching element 6 is connected to the negative line 15 of the output of the rectifier circuit 2 at the subsequent stage of the smoothing capacitor C1. It is connected to the.

The output terminal of the start circuit section 4 is connected to the start power supply input terminal S1 of the resonance switching drive circuit section 5.
And the output terminal S3 of the resonance switching drive circuit unit 5 is connected to the gate terminal G of the switching element 6.

The power supply terminal S4 of the resonance switching drive circuit section 5 is connected to the minus line 15 of the output of the rectifier circuit 2 at the subsequent stage of the smoothing capacitor C1.
Further, the power input terminal S of the resonance switching drive circuit unit 5
2 is connected to one terminal of the cold cathode discharge tube 8, and the other terminal of the cold cathode discharge tube 8 is connected to a connection terminal P 3 on the secondary side of the step-up transformer section 3. The connection terminal P4 on the side is connected to the minus line 15 of the output of the rectifier circuit 2 at the subsequent stage of the smoothing capacitor C1. That is, the cold cathode discharge tubes 8 are connected in series to the power input terminal S2 of the switching drive circuit unit 5.

The operation of the circuit configured as described above will be described. When the power switch SW is closed by being turned on, the commercial power supply AC100V is supplied to the rectifier circuit 2 and rectified, and further smoothed by the smoothing capacitor C1 to make the DC power supply about 140V, and the plus side line 14 and the minus side are connected. It is supplied between lines 15.

The start circuit section 4 operates for a fixed time when the power is turned on by turning on the power switch SW, and supplies a current to the power input terminal S1 of the resonance switching drive circuit section 5 to supply operating power at the start. . In response, the resonance switching drive circuit unit 5 starts the switching operation, and outputs a continuous pulse for switching from the output terminal S3 to the gate terminal G of the switching element 6.
To send to.

The drain terminal D and the source terminal S of the switching element 6 intermittently conduct according to the pulse sent from the resonance switching drive circuit section 5. That is, when the drain terminal D and the source terminal S of the switching element 6 are conducting, the DC power supply 14 is connected between the primary connection terminal P1 and the primary connection terminal P2 of the step-up transformer unit 3.
When about 0 V is applied, the resonance capacitor C2
Is charged. When the drain terminal D and the source terminal S of the switching element 6 become non-conductive, the resonance capacitor C2
A resonance circuit is formed by the closed circuit including the coil L1 and the winding L1, and a current flows in accordance with the resonance circuit. Therefore, the step-up transformer unit 3
And a high voltage is applied to both terminals of the cold cathode discharge tube 8, and the cold cathode discharge tube 8 starts discharging.

When the cold cathode discharge tube 8 starts discharging, the secondary connection terminal P3 of the step-up transformer unit 3, the cold cathode discharge tube 8, the power supply input terminal S2 of the resonance switching drive circuit unit 5, the resonance switching drive Power supply terminal S of circuit section 5
4. An alternating current flows through a closed circuit composed of the secondary side connection terminal P4 of the step-up transformer section 3, and an operating power is supplied to the resonance switching drive circuit 5.

After the initial operation, even if the current from the start circuit section 4 is interrupted, the resonance switching drive circuit section 5
Keeps stable and steady switching operation.

At this time, the resonance switching drive circuit 5
Is the resonance capacitor C2 and the winding L on the primary side of the step-up transformer.
1, a connection terminal P3 on the secondary side of the step-up transformer section 3, a cold cathode discharge tube 8, a power input terminal S2 of the resonance switching drive circuit section 5, a power supply terminal S4 of the resonance switching drive circuit section 5, The switching element 6 is driven at a frequency suitable for a resonance condition with a closed circuit including the secondary-side connection terminal P4 of the step-up transformer unit 3, that is, a resonance frequency.

In the initial operation in which a current flows through the start circuit section 4, when the cold cathode discharge tube 8 is abnormal (breakage, outgassing), and when the lead wire of the cold cathode discharge tube 8 is broken, The connection terminal P3 on the secondary side of the step-up transformer unit 3, the cold cathode discharge tube 8, the power supply input terminal S2 of the resonance switching drive circuit unit 5, and the power supply terminal of the resonance switching drive circuit unit 5 at the time of abnormality (winding disconnection). S4: If there is an abnormality in the closed circuit composed of the secondary side connection terminal P4 of the step-up transformer section 3, no current flows through the closed circuit, so that the power input terminal S2 of the resonance switching drive circuit section 5 -No power is supplied between the power supply terminals S4, and the resonance switching drive circuit unit 5 does not continue the switching operation.

Also, during the normal switching operation following the initial operation, even when the cold cathode discharge tube 8 is damaged or the lead wire is broken, power is supplied to the resonance switching drive circuit unit 5 for the same reason. Is stopped, and the resonance switching drive circuit unit 5 stops the switching operation.

It should be noted that the present invention is not limited to the above-described embodiment, and a circuit using a piezoelectric element type step-up transformer 9 as shown in FIG. It is.

In FIG. 2, the primary connection terminal Q 1 of the piezoelectric element type transformer 10 in the step-up transformer section 9 is connected to the output plus side line 14 of the rectifying bridge circuit 2, and the secondary side of the piezoelectric element type transformer 10 Is connected to one end of the cold-cathode discharge tube 8, and the other end of the cold-cathode discharge tube 8 is connected to the power input terminal S of the resonance switching drive circuit unit 5.
2, the common connection terminal Q3 of the piezoelectric element type transformer 10 in the step-up transformer section 9 is connected to the drain terminal D of the switching element 6. Other circuit elements and connections are the same as those of the circuit of FIG.

The start circuit section 4 operates for a fixed time when the power is turned on by turning on the power switch SW, and supplies a current to the power input terminal S1 of the resonance switching drive circuit section 5 to supply operating power at the start. . In response, the resonance switching drive circuit unit 5 starts the switching operation, and outputs a continuous pulse for switching from the output terminal S3 to the gate terminal G of the switching element 6.
To send to.

The drain terminal D and the source terminal S of the switching element 6 intermittently conduct according to the pulse sent from the resonance switching drive circuit section 5. When the drain terminal D and the source terminal S of the switching element 6 are conductive, the connection terminal Q on the primary side of the step-up transformer 9
A DC power supply of about 140 V is applied between the power supply 1 and the common connection terminal Q3. By forming a capacitance between the primary-side plates facing each other across the piezoelectric element of the piezoelectric element type transformer 10, the transformer is charged with a DC power supply of about 140 V to which the capacitance is applied. At this time, almost no current flows through the winding L3. When the drain terminal D and the source terminal S of the switching element 6 become non-conductive, the piezoelectric element type transformer 10
A resonance circuit is formed by a closed circuit including the primary-side capacitance and the winding L3, and an oscillating current flows through the closed circuit by electric energy stored in the capacitance. Therefore, an alternating current flows through the capacitance on the primary side of the piezoelectric element type transformer 10, and the piezoelectric element vibrates in response thereto, and the vibration of the piezoelectric element is converted into a voltage on the secondary side of the piezoelectric element type transformer 10. As a result, an AC high voltage is generated, a high voltage is applied to both terminals of the cold cathode discharge tube 8, and the cold cathode discharge tube 8 starts discharging.

When the cold cathode discharge tube 8 starts discharging, the secondary connection terminal Q2 of the step-up transformer section 9, the cold cathode discharge tube 8, the power supply input terminal S2 of the resonance switching drive circuit 5, the resonance switching drive Power supply terminal S of circuit section 5
4. An alternating current flows through a closed circuit including the common connection terminal Q3 of the step-up transformer section 9 and the resonance switching drive circuit 5
Is supplied with operating power.

After the initial operation, even if the current from the start circuit section 4 is interrupted, the resonance switching drive circuit section 5
Keeps stable and steady switching operation.

When there is an abnormality in the above closed circuit such as breakage of the cold cathode discharge tube 8 and breakage of the lead wire, no current flows through the closed circuit. No power is supplied between the input terminal S2 and the power supply terminal S4, and the resonance switching drive circuit unit 5 does not continue the switching operation.

Also, during a normal switching operation following the initial operation, even when the cold cathode discharge tube 8 is damaged or the lead wire is disconnected, power is supplied to the resonance switching drive circuit unit 5 for the same reason. Is stopped, and the resonance switching drive circuit unit 5 stops the switching operation.

Also, in the embodiment shown in FIGS. 1 and 2, a configuration is shown in which a commercial power supply is converted to a direct current as a power supply source.
The present invention is also applicable to a device configured to be supplied by a portable battery or the like.

[0050]

According to the cold-cathode discharge tube lighting device of the present invention, the cold-cathode discharge tube is lit by the AC current boosted by the boosting transformer section, and is connected in series to the cold-cathode discharge tube to provide a resonant switching drive circuit. When using commercial power, the power transformer for stepping down the commercial power and a separate power circuit for the resonant switching drive circuit can be omitted, and at the same time, the breakage of the cold cathode discharge tube and When the lamp lead wire is broken or the step-up transformer is abnormal, the power supply of the resonance switching drive circuit is cut off.
Since the switching operation of the resonant switching drive circuit stops and the boosting operation stops immediately, the occurrence of abnormal voltage of the step-up transformer can be prevented, ignition and electric shock due to the abnormal voltage can be prevented, and the discharge of the cold cathode discharge tube can be prevented. It is possible to omit a current detecting element for detecting a current, thereby realizing a reduction in component cost and a space saving.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing an electrical configuration of a cold cathode discharge tube lighting device according to an embodiment.

FIG. 2 is a circuit block diagram showing an electric configuration of a cold cathode discharge tube lighting device in which a piezoelectric element type transformer is applied to the boosting transformer section of FIG.

FIG. 3 is a circuit block diagram showing an electrical configuration of a conventional cold cathode discharge tube lighting device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 cold-cathode discharge tube lighting device 2 rectifier circuit 3 step-up transformer section 4 start circuit section 5 resonance switching drive circuit section 6 switching element 7 wire-wound step-up transformer 8 cold-cathode discharge tube 9 step-up transformer section 10 piezoelectric element type transformer 11 resonance switching drive Circuit 12 Current detection element 13 Connection point 14 Positive side line 15 Minus side line C1 Smoothing capacitor C2 Resonant capacitor L1 winding L2 winding L3 winding SW power switch FL filter TA power transformer

Claims (1)

[Claims] A step-up transformer for generating a high-voltage AC voltage from a secondary side in accordance with a supply voltage on a primary side; a resonance switching drive circuit for outputting a pulse for switching; A switching element that conducts in response to a pulse switched by the drive circuit unit and supplies a voltage to a primary side of the step-up transformer unit. A cold-cathode discharge tube lighting device, wherein one end of the tube is connected, and the other end of the cold-cathode discharge tube is connected to a power input terminal of the resonance switching drive circuit section.