JPH0414479B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a discharge lamp lighting device that lights a lamp at high frequency by causing so-called LC resonance on the secondary side of an oscillation transformer of an inverter.

Figure 1 shows a general high-frequency lighting circuit. In the figure, 1 is a push-pull self-excited inverter using two transistors Tr ₁ Tr _2. As is well known, this inverter 1 is a transistor that is a switching element. Tr ₁ Tr ₂ alternately turns on and off to obtain a high-frequency output, and this high-frequency output voltage resonates with the leakage inductance of the capacitor C ₂ connected in parallel to the output winding N ₂ of the oscillation transformer OT, and is boosted. 2 is turned on. In the example shown in FIG. 1, two lamps 2 are connected in series, where AC is a commercial power supply, DB is a bridge rectifier constituting a rectifier circuit, and CH is a chiyoke. In this way, the lighting method that boosts the high-frequency voltage by LC vibration on the secondary side of the oscillation transformer OT can reduce the capacity [VA] of the oscillation transformer OT, which is advantageous in terms of loss and miniaturization. be. However, when this method obtains a step-up effect on the fundamental wave of the oscillation frequency, especially in pulsating current lighting, when trying to reduce the loss of the oscillation transformer OT by reducing the gap described later in the oscillation transformer OT, the lamp 2 Re-ignition and lamp 2
It has the disadvantage that abnormal oscillation occurs when the arc is extinguished.

Figure 2 shows the abnormal oscillation waveform. FIG. 2a shows the waveform of the lamp voltage Vla, and FIG. 2b shows the waveform of the lamp current Ila. Figure 3 shows a structural diagram of an oscillation transformer OT, in which a primary winding _N1 and a secondary winding (output winding) _N2 are wound around an E-shaped core 3 and brought together to form a gap G. ing. The reason for the above-mentioned abnormal oscillation is that when the gap G of the oscillation transformer OT is made small, the oscillation frequency in the restriking section decreases, and the core 3 becomes more likely to be saturated. Furthermore, at the time of restriking, the load suddenly becomes heavier and the gap G is reduced, making the primary side of the oscillation transformer OT more susceptible to the influence of the secondary side. It is thought that the balance between the primary and secondary magnetomotive forces is disrupted, causing abnormal oscillation. Therefore, in order to obtain a stable oscillation output, it is necessary to increase the gap G, which also has the disadvantage of increasing the loss of the oscillation transformer OT. The restriking period here refers to the period from when the lamp voltage Vla starts to rise in synchronization with the power supply until the lamp turns on, as shown in FIG.

The present invention has been provided in view of the above-mentioned points, and provides a discharge lamp lighting device aimed at preventing abnormal oscillation and further reducing loss of an oscillation transformer.

Embodiments of the present invention will be described in detail below with reference to the drawings.
Before explaining the present invention, the basic invention of the present invention will be explained. FIG. 4 is a specific circuit diagram, and the structure is the same as the circuit shown in FIG. 1. Here, in the push-pull self-excited inverter 1,
In the step-up lighting method using LC resonance (secondary leakage inductance and capacitor C ₂ ) on the secondary side of the oscillation transformer OT with respect to the fundamental wave of the oscillation frequency, the characteristics with respect to capacitance changes of capacitor C ₂ are as shown in Figure 5. Also, FIG. 6 shows an equivalent circuit of the high frequency converter section viewed from the primary side of the oscillation transformer OT.
In Figure 5, V ₂ is the secondary induced voltage of the oscillation transformer OT, V _c2 is the voltage across the capacitor C ₂ , and f _R is the LC
The oscillation frequency at resonance, f _O is the no-load oscillation frequency. FIG. 6a shows the state when there is no load, FIG. 6b shows the state when resonance occurs, and FIG. 6c shows the state when the device is lit. L ₁
is the inductance of the primary winding N ₁ of the oscillation transformer OT, L ₂₁ is the leakage inductance, B is the load resistance, and the above L ₂₁ , C ₂₁ , and R are the primary converted values. The characteristics shown in Fig. 5 are the characteristics of the equivalent circuit during resonance shown in Fig. 6b, and in the high frequency region on the right side of the boundary line where the frequency regions of the oscillation frequency f _R in Fig. 5 are different, the secondary current I ₂ is the oscillation transformer
The current flows in phase with respect to the secondary induced voltage V ₂ of the OT, and in a region where the oscillation frequency is low on the left side, the current flows in phase with respect to the secondary induced voltage V ₂ . Therefore, for convenience,
Let us call them slow-phase oscillation and fast-phase oscillation, respectively.If capacitor _C2 is determined so that the circuit exhibits fast-phase oscillation, there will be a boosting effect as shown in the characteristic curve of the voltage _Vc2 across capacitor _C2 . , because the oscillation frequency f _R is low, abnormal oscillation occurs in the pulsating current lighting method, as described in the conventional example. Therefore, in order to eliminate such drawbacks that have conventionally occurred, the following configuration is adopted. After turning on the power, when starting the lamp, the secondary current I ₂ of the oscillating transformer OT becomes the secondary induced voltage V ₂
Make it advance in phase with respect to . After starting the lamp, the secondary current I ₂ of the oscillation transformer OT is made to have a phase lag with respect to the secondary induced voltage V ₂ when restarting.
These matters are possible for the following reasons. That is, since lamp 2 has not started after the power is turned on, the impedance of lamp 2 becomes infinite, and as shown in Figure 7, the output winding of oscillation transformer OT
Only capacitor C ₂ is connected to N ₂ ,
Therefore, the secondary current I ₂ can be made to advance in phase with respect to the secondary induced voltage V ₂ . After lamp 2 is turned on, when it is re-ignited, the lamp current Ila is flowing, albeit very small, as shown in Figure 2. Therefore, the entire part surrounded by the dotted line in Figure 8, including lamp 2 and capacitor _C2 , If the capacitance of is C ₂ ′, C ₂ ′＞
It becomes C ₂ . Therefore, from the characteristics shown in FIG. 5, it is possible to make the secondary current I ₂ and the secondary induced voltage V ₂ lag in phase in each restriking section. By taking the above matters into consideration and choosing the capacitance of capacitor C ₂ appropriately, the configuration described above can be achieved.

The operating state will be explained below. After turning on the power,
The two transistors Tr ₁ Tr ₂ of the inverter 1 alternately turn on and off to start high frequency oscillation. At this time, due to leakage inductance L ₂₁ and capacitor C ₂ on the secondary side of the oscillation transformer OT, a phase-advanced current flows in the secondary side, and oscillation occurs on the phase-advanced side as shown in Figure 5. Therefore, the lamp 2 oscillates in the lower region of the resonance characteristic and is started by the large voltage V _c2 across capacitor C ₂ . After starting, a small amount of current flows through lamp 2 when restarting, so
Lamp 2 is not completely unloaded, but has a total capacity including the capacitance of capacitor C ₂ in Figure 8.
A slow phase current flows due to C ₂ ′ and secondary leakage inductance L ₂₁ . The oscillation frequency during this period is much higher than the frequency at startup (higher than the oscillation frequency at lighting), as shown in the characteristics of FIG.
Then, in the lighting state after restriking, the lamp impedance becomes very small, the LC vibration collapses, and the secondary leakage inductance L ₂₁ acts as a current limiting element to keep the lamp 2 lit. Figure 9 shows this state, and the frequency of LC resonance changes due to changes in the capacitance of capacitor _C2 , that is, changes in the capacitance _C2 of the capacitor connected in parallel to the secondary side of the oscillation transformer OT. The starting lighting and re-ignition of the lamp 2 are separated by a boundary line dividing into a high range and a low range. In other words, the lamp 2 has a capacity corresponding to the frequency reduction across the boundary line.
The lamp is started and turned on, and the lamp 2 is re-ignited with the corresponding capacity C ₂ so that it oscillates in a high frequency range to prevent abnormal oscillation. Furthermore, lamp 2
Even in the case of a single lamp, the fast-phase oscillation mode is slightly distorted and shifts to the slow-phase mode due to the slight discharge current flowing through the lamp 2 in the restriking section, so it can be applied.

10 to 12 show embodiments of the present invention, and FIG. 10 shows a specific circuit diagram. 10th
_The circuit shown in the figure differs from _the circuit shown _in FIG _. SW is connected. This switch SW connects capacitor C ₂ ,
A changeover switch is configured to change the combined capacity of C ₂₀ at the time of starting the lamp 2 and at the time of re-ignition after starting the lamp. Figure 11 is an equivalent circuit of the high frequency conversion section on the secondary side of the oscillation transformer OT.
1 shows the state when there is no load, b shows the resonance when the switch SW is turned off, c shows the resonance when the switch SW is turned on, and d shows the state when the light is on.
L21 is the secondary leakage inductance of the oscillation transformer OT, _C21 is the capacitance of capacitor _C2 , _C20 ' is the capacitance of capacitor _C20 , _B21 is the load resistance, and _L21 ,
C ₂₁ , C ₂₀ ′, and R ₂₁ are all linear conversion values. Now, when starting, turn off the switch SW, and set it so that it turns on after the light turns on. Time-advanced phase resonance where the capacitor capacity on the secondary side is C ₂ × C ₂₀ / C ₂ + C ₂₀ ,
In addition, _the capacitor C ₂ ,
If a capacity of C ₂₀ is selected, phase-advanced resonance occurs at startup, and the secondary current I ₂ becomes phase-advanced relative to the secondary induced voltage V ₂ . After lighting, at the time of re-ignition, slow phase resonance occurs,
The secondary current I ₂ has a phase lag with respect to the secondary induced voltage V ₂ . That is, as shown in Fig. 12, when the lamp 2 is started, phase-advanced resonance is performed by turning off the switch SW.
After lighting, the switch SW is turned on to perform slow phase resonance when the lamp 2 is lit again. In this way, after lighting, re-ignition and lighting are repeated in the slow phase mode, so stable oscillation is performed without the frequency shifting between phase-advancing and slow-phase modes. The oscillation frequency during arcing becomes a considerably high frequency (higher than when the lamp is lit), which prevents saturation of the oscillation transformer OT due to rapid fluctuations in lamp impedance, and prevents the abnormal oscillation that previously occurred. Therefore, even if the gap G of the oscillation transformer OT is narrowed, abnormal oscillation will not occur, and the loss of the oscillation transformer OT can be greatly reduced.

As described above, the present invention reduces the combined capacitance of a plurality of capacitors so that the secondary current of the oscillation transformer becomes phase advanced with respect to the secondary induced voltage when the lamp is started after the power is turned on, and after the lamp is started. A changeover switch is installed to increase the secondary current of the oscillation transformer with a lag in phase with respect to the secondary induced voltage at the time of restriking, so the changeover switch must be turned on when starting the lamp after power is turned on. Operate and
The secondary current of the oscillating transformer is decreased so that it is in phase advance with respect to the secondary induced voltage, and when the lamp is restarted after starting, the changeover switch is operated again to reduce the secondary current of the oscillating transformer to the secondary induced voltage. By increasing the phase so that it is delayed with respect to the induced voltage, the oscillation frequency at the time of restriking becomes higher than the oscillation frequency at the time of lighting, which causes abnormal oscillation even if the gap of the oscillation transformer is made small as in the past. This has the effect that the loss of the oscillation transformer can be significantly reduced.

[Brief explanation of drawings]

Figure 1 is a transistor inverter type lighting circuit diagram, Figures 2a and b are operating waveform diagrams of the same as above, Figure 3 is a structural diagram of the oscillation transformer of the same as above, and Figure 4 is a specific example of the invention that is the basis of the present invention. Circuit diagram, Fig. 5 is a resonant frequency characteristic diagram for capacitance changes of the secondary capacitor of the oscillation transformer shown above, Fig. 6 a, b, and c are equivalent circuit diagrams of the above, and Fig. 7 is equivalent when starting the lamp of the same. Circuit diagram, Figure 8 is an equivalent circuit diagram at the time of re-ignition after lighting the same lamp, Figure 9 is a characteristic diagram of the same as above,
FIG. 10 is a specific circuit diagram of an embodiment of the present invention, and FIG.
Figures a to d are equivalent circuit diagrams of the same as above, and Fig. 12 is a characteristic diagram of the same. 1 is the inverter, 2 is the lamp, _N2 is the output winding,
OT is an oscillation transformer, I ₂ is a secondary current, V ₂ is a secondary induced voltage, and C ₂ is a capacitor.

Claims (1)

[Claims] 1. An AC power supply, a rectifier circuit that full-wave rectifies the AC voltage of the AC power supply and outputs a pulsating voltage, an inverter that generates a high-frequency voltage in the output winding of an oscillation transformer through the oscillation operation of a switching element, and In a discharge lamp lighting device consisting of an output winding and a lamp that is lit using a high-frequency resonant voltage obtained by resonating with a plurality of capacitors connected in parallel to the output winding, the combined capacitance of the plurality of capacitors is , when the lamp is started after the power is turned on, the secondary current of the oscillation transformer is decreased so as to lead the secondary induced voltage, and when the lamp is restarted after the lamp is started, the secondary current of the oscillating transformer is reduced to the secondary induced voltage. 1. A discharge lamp lighting device comprising a changeover switch for increasing the voltage with a delay in phase with respect to the voltage.