JP2625793B2 - Fluorescent lighting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION INDUSTRIAL APPLICATIONS The present invention relates to office work focusing on copying machines, facsimile machines, etc.
The present invention relates to a fluorescent lamp lighting device used for information equipment.

2. Description of the Related Art A conventional fluorescent lamp lighting device is configured as shown in FIG. That Connect push-pull resonant oscillator X and the preheating circuit Y to the DC power supply B, was lit by applying an AC high frequency voltage generated in the secondary winding Ns of the oscillation transformer T ₁ at both ends of the fluorescent lamp La .

This circuit is a DC power supply B is applied, Low level to the terminal a, i.e. the transistor Q ₆ is OFF, High to the terminal b
Level, i.e., the transistor Q ₅ a base current flows from the DC power supply B transistor Q ₇ is turned ON in the transistor Q ₅ is turned ON. Then the transistor Q ₄ base current flows to the transistor Q ₄ is turned ON through resistor R _5. As a result, from the DC power source B, the resistor R ₈ , the filament F ₁ of the fluorescent lamp La, the secondary winding Ns of the oscillation transformer T ₁ , the filament F ₂ ,
A preheating current for the filaments flows in a loop to the cathode side (earth) of the DC power supply B through the diode D ₃ and the transistor Q ₄ , and both filaments F ₁ and F ₂ are preheated. At this time, the transistor Q ₆ is OFF, the transistor Q ₁ is also OFF, thus oscillating transistor Q _2, base current is not supplied to the Q ₃ push-pull resonant oscillator circuit X fluorescent lamp AC high frequency voltage without oscillation It is not lit because it is not applied to La. This state is called a preheating state, and the time in the preheating state is called a preheating time. The preheating time is usually 2 seconds to 4 seconds. Then terminal a High level, the transistor Q ₆ when the terminal b becomes Low level ON, the transistor Q ₇ is turned OFF. Transistor Q ₅ in the reverse state of the transistor of the preheating circuit Y is a pre-heating state, Q ₄ are both turned OFF, the preheating current is cut off.
On the other hand, in a push-pull resonant oscillator circuit X transistor Q ₁ is turned ON resistance R _3, a base current to the oscillation transistor Q _2, Q ₃ through the diode D ₁ or D ₂ is supplied.
Primary winding N of transistors Q ₂ and Q ₃ and oscillation transistor T ₁
p, feedback winding N transistor Q ₂ and Q ₃ forms a self-oscillating circuit of the push-pull type is causing ON, the repeated self-excited oscillation and OFF alternately. This operation principle is generally known, and a detailed description is omitted. This oscillation circuit has a choke coil L ₁ and the capacitor C ₁ is connected, also, fluorescence as an oscillation transformer T ₁ is generally a primary winding Np and the leakage inductance by reducing the binding of the secondary winding Ns ballast It is configured to create an effect that is inserted in series with the light La. Therefore, this oscillation circuit forms a parallel resonance circuit of the choke coil L ₁ , the excitation inductance of the primary winding Np of the oscillation capacitor T ₁ , the capacitor C ₁ , the leakage inductance and the fluorescent lamp La (in a serial connection state), and the oscillation transformer T 1 ₁ of 1
The voltage and current waveforms of the secondary winding Np, the feedback winding N _B , and the secondary winding Ns are sine waves. Therefore, the sinusoidal AC high-frequency voltage is
Applied to La. At this time, a diode is connected in parallel with the fluorescent lamp La.
D ₃ , transistor Q ₄ , and DC power supply B are connected, but since transistor Q ₄ is OFF, positive high-frequency AC high-frequency current is prevented from flowing into DC power supply B,
Also by the diode D ₃ is the negative direction of the AC high-frequency current from flowing to the DC power supply B is prevented. Therefore, the AC high-frequency voltage is reliably applied to the fluorescent lamp La, and the fluorescent lamp La is turned on.

Since the conventional fluorescent lamp lighting device oscillates in the resonance circuit, it is impossible to control the oscillation circuit to change or stabilize the current flowing through the fluorescent lamp La.

Problems to be Solved by the Invention In OA equipment such as a copying machine and a facsimile, it is necessary to stabilize the light quantity of a light source and to manually adjust the light quantity. This is largely dependent on the tube wall temperature of the amount of light of the fluorescent lamp, and reaches 70% to 80% of the usage range of 0 ° C to 80 ° C with the tube wall temperature of 40 ° C as a peak. Also, an appropriate light amount changes according to the density of the document. At present, as the price of microcomputer chips has fallen, there has been a demand for inexpensively controlling the automatic stabilization of the light amount by an output signal from a microcomputer (hereinafter referred to as a microcomputer).

The present invention has been made in view of the above point, and an object of the present invention is to provide a fluorescent lamp lighting device capable of automatically stabilizing the light amount by adding a simple circuit.

Means for Solving the Problems In order to solve the above problems, the present invention connects a push-pull resonance type oscillation circuit through a chopper regulator in series to the anode side of a DC power supply, and connects the push-pull resonance type oscillation circuit in series with a fluorescent lamp as a load thereof. Is connected to the primary winding of a current transformer, and the rectified and smoothed output of the secondary winding of the current transformer is connected to the input side of the error amplifier in the chopper regulator.

According to the present invention, a feedback signal for stabilizing the amount of light is input to the input side of the error amplifier in the chopper regulator to control the operation of the chopper circuit. Controlled.

Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention. The configuration and operation of the push-pull resonance type oscillation circuit X and the preheating circuit Y are the same as those of the conventional example shown in FIG. Z is a chopper regulator. IC ₁ is a general-purpose IC for chopper regulator control (hereinafter,
The internal configuration is as shown in FIG. 2, and the same numbers in the circles indicating the terminal numbers of the ICs indicate the same terminal numbers in FIGS. 1 and 2. .

The control ICIC ₁ is a switching regulator IC, TL494, manufactured by Texas Instruments. The configuration and operation of the control ICIC ₁ are generally well known, but will be described below with reference to FIG. In the figure, 1 is an oscillator, 2 is a reference voltage generating circuit, 3 is a flip-flop, 4 and 7 are NOR circuits,
And 6 are NPN transistors, 8 is an OR circuit, 9 and 10 are comparators, 11 and 12 are diodes, and 13 and 14 are error amplifiers.
Further, "" is an input terminal of the error amplifier, "" is a reference voltage side terminal of the error amplifier, and "" is a feedback terminal of the error amplifier. Is the dead time control terminal,
Is a ground (GND) terminal. ,, Are IC output terminals, are IC power input terminals, and are reference voltage elements.
Next, the operation of the embodiment shown in FIG. 1 will be described with reference to FIG. Reference voltage side terminal of error amplifier 13 (inverting input terminal)
Is connected to the connection point of the reference resistor R ₉ is connected from the reference voltage terminal of the voltage generating circuit 2 and the multiplexer 19 and the resistor R ₁₉ to R _26, it is set to a reference voltage which is determined by an external signal A. A detection voltage is applied to an input terminal (non-inverting input terminal) of the error amplifier. Now, when the detected voltage becomes higher than the potential of the reference voltage side terminal, the output voltage of the error amplifier becomes higher, and the High period of the output of the comparator 9 determined by comparison with the triangular wave voltage of the oscillation circuit 1 becomes longer. As a result, the high period of the OR circuit becomes longer, and the NOR circuits 4 and 7 become longer.
Of the NPN transistors 5 and 6 becomes longer.
Results F period is eliminated long output acts in the direction to decrease (in the case of this embodiment lowers the current or lamp current flows through the current transformer T _2.). When the detection voltage becomes lower than the potential of the reference voltage side terminal, the operation is completely opposite to the operation described above, and the output increases. As a result, the detected voltage, that is, the lamp current flowing through the current transformer in FIG. 1 is constantly controlled to a value determined by the external signal A. The dead time control terminal is input to the comparator 10 via a built-in power supply of 110 mV, is compared with the triangular wave voltage of the oscillation circuit 1, and its output signal is given to the OR circuit. Therefore, the minimum OFF time of the NPN transistors 5 and 6 is determined regardless of the signal from the error amplifier 13 according to the potential of the dead time control terminal. From the feedback terminal phase correction of the error amplifier 13 is fed back to the reference voltage terminal (inverting input terminal) via a capacitor C ₃ is performed. Is used when externally turned ON / OFF by an external control terminal.

Next, the operation of the chopper regulator will be described.
As described above, the ON and OFF times of the transistors 5 and 6 are controlled so that the input terminal of the error amplifier 13 always has the same potential as the reference voltage terminal.
OFF time as ON of the transistor Q _8, the same as the OFF time, the DC after the power supply voltage from B which is chopped by the transistor Q _8, a choke coil L ₂ and is smoothed by the capacitor C ₅ push-pull resonant oscillator circuit X. The magnitude of this voltage is proportional to the lamp current flowing through the fluorescent lamp La. That is, it is proportional to the amount of light. When the lamp current is detected by the current transformer T ₂ and the rectified and smoothed voltage is fed back to the input terminal of the error amplifier 13, the fluorescent lamp is adjusted so that the voltage of the input terminal matches the reference voltage (terminal voltage) of the error amplifier 13. The lamp current flowing through La is controlled to be constant.

That is, to connect the primary winding Np of the current transformer T ₁ to a fluorescent lamp La series, taken out in the secondary winding Ns, by feedback to the error amplifier 13 as the rectified and smoothed voltage, feeds back the lamp current, The lamp current can be automatically stabilized.

On the other hand, A is an external signal, and a light amount sensor (not shown)
When the information from the switch and the information from the manual switching adjustment are mixed and input to the multiplexer 19 from the output port 16 of the microcomputer 15 shown in FIG. and one analog switch is conductive, ICIC control the voltage of the reference voltage terminal IC ₁ 'resistor R ₉ and the resistor R ₁₉ ~ ₂₆ (connection resistance of the resistor by conduction the switch R ₁₉ ~ ₂₆ is determined) by divide ₁ terminal, that is, the reference voltage side terminal of the error amplifier. As a result, the lamp current flowing through the fluorescent lamp is constantly controlled by a signal from the microcomputer.

Since the signal from the microcomputer 15 mixes the information from the light amount sensor and the information from manual adjustment based on the density of the original, the optimal light intensity is always controlled according to the density of the original even if the tube wall temperature of the fluorescent lamp changes. For control
Components around ICIC ₁ and the current transformer, that is, resistors R _{9 to} R ₁₆ , capacitors C _{2 to} C ₆ , choke coil L ₂ ,
The transistor Q ₈ and the diode D ₆ are in the lamp current control range,
It is appropriately selected according to the oscillation frequency of the chopper regulator.

In addition, as an example of the multiplexer 19, a 3-bit input 8
There is MC14051BP made by Motorola of level output switching,
For the second source, Fujitsu MB84051B, NEC μPD4
051BC etc.

As described above, according to the present invention, the primary winding of the current transformer is connected in series to the fluorescent lamp, the rectifying and smoothing circuit is connected to the secondary winding of the current transformer, and the error amplifier in the chopper regulator is provided. By connecting the output side of the rectifying / smoothing circuit to the input side of the above, the light quantity can be automatically stabilized with a simple circuit configuration.

In the configuration in which the reference voltage of the error amplifier in the chopper regulator is changed by an external signal, manual adjustment based on the density of the original can be easily performed. Further, a plurality of resistors and a level converter, A configuration including a multiplexer including a decoder and an analog switch, wherein the multiplexer selects one of the connection points of the plurality of resistors according to an external signal and connects the selected one to the reference voltage side of the error amplifier in the chopper regulator. In this case, manual adjustment can be performed very easily by a microcomputer signal.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a fluorescent lamp lighting device according to an embodiment of the present invention, FIG. 2 is a circuit diagram of a chopper regulator IC which is a principal part thereof, and FIG. 3 is a multiplexer and a periphery thereof which are the principal part thereof. FIG. 4 is a circuit diagram showing a conventional fluorescent lamp lighting device. X: Push-pull resonance type oscillation circuit, Q ₂ , Q _3: Oscillation transistor, C _1: Capacitor, T _1: Oscillation transformer,
Np: Primary winding of oscillation transformer, Ns: 2 of oscillation transformer
Next winding, L ₁ …… Choke coil, La …… Fluorescent lamp, Z, Z ′
... Chopper regulator, 1 ... Input terminal of error amplifier in chopper regulator, 2 ... Reference voltage terminal of error amplifier in chopper regulator, 14 ... Reference voltage terminal of control IC in chopper regulator, T ₂ ... Current Transformer, N ₁ … Current transformer primary winding, N ₂ … Current transformer secondary winding, D ₆ , C ₆ , R ₁₄ , R ₁₅ … Rectifying and smoothing circuit, A… External signal, B… DC power supply, R _17, R ₁₈ ...... resistors, 17 ...... external signal input terminal, 18 ...... level converter decoder, 19 ...... multiplexer, 20 ...... analog switches, R _9, R ₁₉ to R ₂₆ ...... resistance .

Claims (3)

(57) [Claims] 1. A push-pull resonant oscillation circuit in which a choke coil is connected in series to a parallel circuit of at least two transistors, a capacitor, and a primary winding of a transformer via a chopper regulator in series on the anode side of a DC power supply. In a fluorescent lamp lighting device for connecting and connecting a fluorescent lamp as a load of a secondary winding of the transformer, a primary winding of a current transformer is connected in series with the fluorescent lamp, and a rectifying and smoothing circuit is connected to a secondary winding of the current transformer. Wherein the output side of the rectifying and smoothing circuit is connected to the input side of the error amplifier in the chopper regulator. 2. The method according to claim 1, wherein the reference voltage of the error amplifier in the chopper regulator is changed by an external signal.
Item 3. The fluorescent lamp lighting device according to Item 1. 3. A multiplexer comprising a plurality of resistors and a level converter, a decoder and an analog switch, wherein the multiplexer selects one of the connection points of the plurality of resistors by an external signal. 3. The fluorescent lamp lighting device according to claim 2, wherein the fluorescent lamp lighting device is connected to a reference voltage side of an error amplifier in a chopper regulator.