JPS6072189A - Circuit for firing discharge lamp - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a discharge lamp lighting circuit for lighting a discharge lamp such as a fluorescent lamp.

2. Description of the Related Art When a device having an optical reading mechanism such as a copying machine or a facsimile machine lights up a discharge lamp for reading, a circuit configuration as shown in FIG. 1 has conventionally been adopted. In FIG. 1, 2 and 2 are terminals for inputting commercial AC power, and 3 is a DC converter for converting AC into DC. 4 is a high frequency power supply circuit. The high frequency power supply circuit 4 includes a transformer 5 having windings 51 and 52, a switching element 6 connected in series to the winding 51 of the transformer 5, an oscillation circuit 7 for driving the switching element 6, and the like. It is configured.

8 is a discharge lamp such as a fluorescent lamp. The filaments 81 and 82 of this discharge lamp 8 are connected to an interfter 9 and a capacitor lO
The series resonant circuits are inserted and connected in series, and then connected to both ends of the winding 52 of the transformer 5. 11 and 12 are power supplies for filaments 81 and 82.

In the above circuit configuration, the AC voltage supplied between the input terminals 1 and 2 is converted into a DC voltage by the DC converter 3, and then the DC voltage is passed through the winding 51 of the transformer 5 to the switching element 6. and switches the switching element 6 at a frequency according to the oscillation frequency of the oscillation circuit 7.Then, the switching output is led from the winding 51 side of the transformer 5 to the winding 52 side, and connects the inductor 9 and capacitor 10. is applied between the filaments 81 and 82 of the discharge lamp 8 through a series resonant circuit.

Before the discharge lamp 8 is lit, the filaments 81 and 82 are in an open state, and in order to light it, a high frequency /(T
A rectangular wave voltage of several hundred V is applied between the filaments 81 and 82 from the f power supply circuit. On the other hand, after lighting the filament) 81
-82 becomes conductive, resulting in a low impedance of around 100Ω, which drops to several tens of volts. The high frequency power supply circuit 4 is a rectangular wave power supply composed of a switching power supply or the like, and if such a rectangular wave voltage is continued to be applied even after the discharge lamp 8 is turned on, a blackening phenomenon will occur in the discharge lamp 8, and the discharge lamp 8's lifespan is shortened. Therefore, a series resonant circuit consisting of an inductor 9 and a capacitor 10 is inserted and connected in series with the power supply circuit from the high frequency power supply circuit 4 to the filaments 81 and 82 of the discharge lamp 8, and this series resonant circuit converts the rectangular wave into a sine wave. By applying the current to the discharge lamp 8, a sine wave current is caused to flow and the blackening phenomenon of the discharge lamp 8 can be prevented.

Disadvantages of the Prior Art However, the conventional discharge lamp lighting circuit has the following drawbacks.

(a) In order to stabilize optical reading in copying machines and facsimile machines, it is necessary to keep the brightness of the discharge lamp 8 constant and stable. The brightness of the discharge lamp 8 changes depending on the input voltage given from the high frequency power supply circuit 4. Conventionally, in order to suppress changes in the brightness of the discharge lamp 8 due to input fluctuations, the direct converter 3 has been configured as a stabilized power source using, for example, a switching power source. As a result, the circuit configuration becomes complicated and large, and the cost increases.

(b) The brightness of the discharge lamp 8 varies greatly depending on the tube current. There are many factors that change the tube current, not just input fluctuations. For example, the oscillation frequency of the oscillation circuit 7, the inductance of the transformer 5, and the values of the inductor 9 and capacitor 10 that constitute the series resonant circuit.

Changes and variations in the impedance value, etc. of the discharge lamp 8 all cause changes in the tube current. However, since the conventional circuit configuration does not have a compensation circuit for these fluctuation factors, it is not possible to suppress variations in the tube current, and it is not possible to stabilize the brightness of the discharge lamp 8. This has caused problems such as adversely affecting optical reading by copiers, facsimile machines, and the like.

OBJECTS OF THE INVENTION Therefore, an object of the present invention is to provide a compact and inexpensive discharge lamp lighting circuit that eliminates the above-mentioned conventional drawbacks, is capable of stabilizing and dimming the brightness of a discharge lamp, and is compact and inexpensive. .

SUMMARY OF THE INVENTION To achieve the object, the present invention provides a discharge lamp comprising a discharge lamp, a resonant circuit connected in series with the filament of the discharge lamp, and a high frequency power supply circuit for driving the discharge lamp through the resonant circuit. The lighting circuit is characterized in that the tube current of the discharge lamp is detected, and the drive frequency of the high frequency power supply circuit is controlled based on the detection signal.

Embodiment FIG. 2 is an electrical circuit connection diagram of a discharge lamp lighting circuit according to the present invention. In the figures, the same reference numerals as in FIGS. 1 and 2 indicate the same components. In this embodiment, the circuit loop through which the tube current of the discharge lamp 8 flows, that is, the circuit loop in which the tube current of the discharge lamp 8 flows,
A tube current detection section 13 is provided in a circuit loop including a resonant circuit of filaments 81 and 82, an inductor 9, and a capacitor 1o in series, and the tube current detection signal detected by the tube current detection section 13 is transmitted to the high frequency power supply circuit 4. The circuit configuration is such that feedback is given to the oscillation circuit 7 constituting the tube, and the oscillation I frequency is controlled in a direction that stabilizes the tube current.

Resonant circuit 9 through the transformer 5 from the high frequency power supply circuit 4 side.
The relationship between the drive frequency f supplied to the 10 side and the corresponding tube current is determined by the resonance characteristics of the resonance circuit 9.10.
The characteristics are as shown in FIG. That is, the tube current reaches its maximum at the point where the driving frequency matches the resonant frequency fo of the resonant circuit 9.10. In the present invention, we focus on this characteristic,
The tube current is detected by the detection unit i3, and the detection signal is fed back to the oscillation circuit 7 to change the oscillation frequency, thereby changing the switching frequency of the switching element 6, and transmitting the signal from the high frequency power supply circuit 4 side to the resonance circuit 9. The drive frequency supplied to the 10 side is controlled in a direction that stabilizes the tube current. For example, change the driving frequency to the resonant frequency f
When set to a frequency range higher than O (A),
When the tube current decreases below the set value 11 (Fig. 3),
The drive frequency is controlled in a direction that decreases, that is, the oscillation frequency of the oscillation circuit 7 is controlled in a direction that is decreased, and conversely, when the current saving increases beyond the set value ■l, the oscillation frequency of the oscillation circuit 7 is controlled in a direction that becomes high. control. If the drive frequency is set to a frequency range (b) lower than the resonance frequency fo,
The control direction of the oscillation circuit 7 is the opposite direction.

The above-mentioned control action prevents changes and variations in the oscillation frequency of the oscillation circuit 7, the inductance of the transformer 5, the ratio of the inductor 9 and capacitor 10 forming the series resonant circuit, the impedance value of the radiator light 8, etc. Regardless, the tube current is kept constant and the brightness of the discharge lamp 8 is stabilized.

Moreover, this control action can also compensate for changes in tube current due to fluctuations in input voltage, so there is no need for the DC converter 3 to have a voltage stabilization function, unlike in the past. By simply providing a simple rectifier circuit such as a di-rectifier circuit, it becomes possible to drive directly from a commercial AC power source, simplifying and downsizing the entire circuit configuration and reducing costs. An example is shown in FIG.
It has a simple circuit configuration that only includes a smoothing capacitor 15 and a smoothing capacitor 15. Further, in this embodiment, the tube current detection section 13 is constituted by a current transformer, and the primary side and the secondary side are insulated. 16 is a diode, and 17 is a capacitor. Note that it is also possible to use a photocoupler or the like instead of the current transformer.

FIG. 5 is a diagram showing a circuit configuration for controlling the oscillation frequency of the oscillation circuit 7. As shown in FIG. The oscillation circuit 7 is constructed of an IC for use in a normal switching regulator. The oscillation frequency of this type of oscillation circuit 7 is determined by the time constant of an externally attached capacitor 18 and resistor 19. Therefore, in this embodiment, the transistor 2 is connected to the resistor 19.
By connecting transistors 2o in parallel and controlling this transistor 2o with a tube current detection signal, the composite epeetance seen across the resistor 19 is varied and the oscillation frequency of the oscillation circuit 7 is controlled. Further, in this embodiment, a variable resistor 21 is inserted and connected in series to the circuit from the current transformer constituting the tube current detection section 13 to the heath of the transistor 2o, and by variably adjusting this variable resistor 21, the tube current The brightness of the discharge lamp 8 can be adjusted by variably adjusting the set value. Note that 22 to 24 are resistors.

Effects of the Present Invention As described above, the present invention provides a discharge lamp, a resonant circuit connected in series to the filament of the discharge lamp, and a high-frequency circuit for driving the discharge lamp through the resonant circuit. In the lamp lighting circuit, detecting the tube current of the discharge lamp,
To provide a discharge lamp lighting circuit which is characterized in that the drive frequency of the high frequency power supply circuit is controlled by the detection signal, and is capable of stabilizing and dimming the brightness of a discharge lamp, and which is compact and inexpensive. I can do it. −

[Brief explanation of drawings]

Figure 1 is an electric circuit connection diagram of a conventional discharge lamp lighting circuit, Figure 2
The figure is an electric circuit connection diagram of the discharge lamp lighting circuit according to the present invention, FIG. 3 is a characteristic diagram showing the relationship between driving frequency and tube current, and FIG.
The figure is an electric circuit connection diagram of another embodiment of the discharge lamp lighting circuit according to the present invention, and FIG. 5 is an electric circuit connection diagram of the main part of the discharge lamp lighting circuit according to the present invention. 4...High frequency power supply circuit 5...Transformer 6 and...switching element 7...Oscillation circuit 8, writing, hkMl lamp
8t, 82...Filament 9, fist, inductor 1
oφ・Capacitor 13・War・Tube current detection part

Claims (1)

[Claims] (1) In a discharge lamp lighting circuit comprising a discharge lamp, a resonant circuit connected in series to a filament of the discharge lamp, and a high frequency power supply circuit that drives the discharge lamp through the resonant circuit, the tube current of the discharge lamp is detected. A discharge lamp lighting circuit, characterized in that the drive frequency of the high frequency power supply circuit is controlled by the detection signal.