JP3585372B2 - Discharge lamp lighting device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a discharge lamp lighting device.
[0002]
[Prior art]
A rectifier of an AC power supply and a chopper and a smoothing capacitor connected in parallel to the output side of the chopper supply a DC power supply to an inverter having a pair of switching elements connected in series for alternately opening and closing, and convert the high frequency output by the inverter. This high-frequency output is connected to a discharge lamp through a series circuit of a first capacitor and a choke coil, and a second capacitor is connected in parallel with the discharge lamp. Set the first capacitor, choke coil, and second capacitor when the discharge lamp is turned off to be lower than the no-load resonance frequency, and set the inverter's dimming lighting oscillation frequency when the discharge lamp dimming lighting is higher than the no-load resonance frequency. The set discharge lamp lighting device is already known.
[0003]
[Problems to be solved by the invention]
However, the output voltage of the chopper during the dimming operation of the discharge lamp is adjusted by changing the output voltage of the chopper during the dimming operation of the discharge lamp to eliminate the problem that the discharge lamp cannot be maintained during the dimming operation of the discharge lamp. The present applicant has already applied for a discharge lamp lighting device capable of maintaining the dimming operation by setting the oscillation frequency at the time of the dimming operation of the inverter to be lower and applying a high voltage to the discharge lamp instead of the discharge lamp. However, when switching the discharge lamp from the dimming lighting state to the all-light lighting state, if the output frequency of the chopper is increased while lowering the oscillation frequency of the inverter, a large-capacity smoothing is generally provided on the output side of the chopper. Due to the presence of the capacitor, the rise of the output voltage is delayed. Then, the discharge lamp extinguishes and becomes in a no-load state, and a fast-phase current flows through the switching element, which may cause heat generation or destruction of the switching element.
Therefore, an object of the present invention is to prevent the discharge lamp from extinguishing when switching the discharge lamp from the dimming lighting state to the all-light lighting state, and to prevent a leading current from flowing through the switching elements constituting the inverter. And
[0004]
[Means for Solving the Problems]
It is as shown in the claims.
[0005]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of the present invention will be described. However, it is an exemplary embodiment adopted based on the present invention, and the present invention should not be interpreted in a limited manner based on matters specific to the embodiment. Instead, the technical scope of the present invention should be determined based on the matters stated in the claims and matters substantially equivalent to the matters.
[0006]
The illustrated embodiment includes a pair of switching elements Q1 and Q2 connected in series to alternately open and close a DC power supply by a rectifier 2 of an AC power supply 1, a chopper 3 and a smoothing capacitor C connected in parallel to the output side of the chopper 3. The high-frequency output is supplied to the inverter 4 and converted into a high-frequency output by the inverter 4. This high-frequency output is connected to the discharge lamp 5 via a series circuit of the first capacitor C <b> 1 and the choke coil L. C2 is connected and the oscillation frequency f1 of the inverter 4 when the discharge lamp 5 is turned on with all light is turned on, and the resonance frequency f0 of the first capacitor C1, the choke coil L, and the second capacitor C2 when the discharge lamp 5 is turned off with no load is set. And the oscillation frequency f2 at the time of dimming of the inverter 4 at the time of dimming lighting of the discharge lamp 5 is set higher than the no-load resonance frequency f0. Lamp 5 dimming lighting time of the chopper 3 of the output voltage (e.g. VDC = 180 V) is a discharge lamp 5 discharge lamp lighting device is set lower than the output voltage of the chopper 3 when the total light illuminated (e.g. VDC = 300 V). When the discharge lamp 5 is switched from the dimming lighting state to the all-light lighting state, means for increasing the output voltage of the chopper 3 and then decreasing the oscillation frequency of the inverter 4 is provided. The output voltage of the chopper 3 can be set relatively freely.
[0007]
When switching the discharge lamp 5 from the all-light lighting state to the dimming lighting state, the output signal of the control means 6 is switched from the L level to the H level at time T1 by an external input signal. This signal is applied as an L level signal to the transistor TR1 via the inversion circuit 7, and the transistor TR1 is turned off. As a result, the resistor R3 is no longer connected in parallel with the resistor R2, and the output voltage of the chopper 3 is reduced by feedback control via the chopper control means 8. The output signal of the control means 6 is also applied to the delay circuit 9, the transistor TR 2 is turned on by the H level signal, the capacitor C 3 is short-circuited, and the output of the comparator CP dims the inverter 4 via the inverter driving means 10. It immediately oscillates at the oscillation frequency f2. In this case, the delay circuit 9 does not perform the delay operation because of the control mode in which the capacitor C3 is short-circuited.
[0008]
At the time of dimming operation of the discharge lamp 5, the inverter 4 oscillates at the oscillation frequency f2 at the time of dimming operation, and the VDC at that time is 180V. When switching the discharge lamp 5 from the dimming lighting state to the all-light lighting state, the output signal of the control means 6 is switched from the H level to the L level at time T2 by an external input signal. This signal is applied as an H level signal to the transistor TR1 via the inversion circuit 7, and the transistor TR1 is turned on. As a result, the resistor R3 is connected in parallel with the resistor R2, and the output voltage of the chopper 3 increases by feedback control via the chopper control means 8. As a result, VDC finally becomes 300V. The output signal of the control means 6 is also applied to the delay circuit 9, and the transistor TR2 is turned off by the L level signal, the capacitor C3 is opened, and the voltage across the capacitor C3 rises relatively slowly. After waiting for VDC to reach 300 V within the delay time (approximately 50 ms) due to this, at time T3, the output of the comparator CP causes the inverter 4 to change the inverter 4 to the oscillation frequency f1 when the all-lights are turned on via the inverter driving means 10. To oscillate. Thus, at VDC = 300 V, the discharge lamp 5 is all-lit at the oscillation frequency f1. With this configuration, when the discharge lamp 5 is switched from the dimming lighting state to the all-light lighting state, the discharge lamp 5 does not go out and the leading current does not flow through the switching elements Q1 and Q2. On the other hand, when the discharge lamp 5 is switched from the dimming lighting state to the all-light lighting state, if the discharge frequency is switched to the oscillating frequency f1 at a stretch, the operation is performed at the white dot in FIG. The leading current flows through the elements Q1 and Q2. Note that the timing of the time T3 may be a time when the VDC rises to some extent without waiting for the VDC to reach 300V. Further, it is obvious to those skilled in the art that circuit means for changing the oscillation frequency of the inverter 4 after detecting a certain rise or completion of the rise of VDC may be used instead of the delay circuit 9.
[0009]
In the above description, an example was described in which the output voltage of the chopper 3 was reduced during dimming lighting of the discharge lamp 5 as compared with all dimming lighting. Means for making the duty ratio for controlling the opening and closing of the switching elements Q1 and Q2 different from approximately 50% / 50% may be employed. As a precautionary measure, such means for making the duty ratio different from approximately 50% / 50%, for example, 20% / 80%, lowers the output voltage VDC of the chopper 3 as in the above example. As a result, | E0 (t) | (the voltage on the output side of the first capacitor C1) shown in FIG. 2 decreases during the dimming operation of the discharge lamp 5, as in the above-described example. In addition, in the case of this example, the same applies to the above-mentioned example, but when the discharge lamp 5 is turned on with all light, the duty ratio for controlling the opening and closing of the pair of switching elements Q1 and Q2 is approximately 50% / 50%. When the discharge lamp 5 is switched from the dimming lighting state to the all-light lighting state, the duty ratio for controlling the opening and closing of the pair of switching elements Q1 and Q2 is switched to approximately 50% / 50%, and then the oscillation frequency of the inverter 4 is changed. It is preferable to provide a means for reducing the pressure. The duty ratio variable control for controlling the opening and closing of the pair of switching elements Q1 and Q2 may be performed by the inverter driving means 10.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an embodiment of the present invention. FIG. 2 is a timing chart for switching the lighting state of the discharge lamp. FIG. 3 is a resonance curve diagram.
REFERENCE SIGNS LIST 1 AC power supply 2 Rectifier 3 Chopper C Smoothing capacitor Q1, Q2 Switching element 4 Inverter C1 First capacitor L Choke coil 5 Discharge lamp C2 Second capacitor f1 All-light-on oscillation frequency f0 No-load resonance frequency f2 Dimming-on oscillation frequency

Claims (2)

A rectifier of an AC power supply and a chopper and a smoothing capacitor connected in parallel to the output side of the chopper supply a DC power supply to an inverter having a pair of switching elements connected in series to alternately open and close, and convert the high frequency output by the inverter, This high-frequency output is connected to a discharge lamp through a series circuit of a first capacitor and a choke coil, and a second capacitor is connected in parallel with the discharge lamp. Set the first capacitor, choke coil, and second capacitor when the discharge lamp is turned off to be lower than the no-load resonance frequency. Set the output voltage of the chopper when dimming the discharge lamp and lower than the output voltage of the chopper when lighting all light in the discharge lamp. The discharge lamp lighting device, when switching the discharge lamp from dimming lighting state to the total light lighting state, a discharge lamp lighting device provided with means for reducing the oscillation frequency of the inverter from increasing the output voltage of the chopper. A rectifier of an AC power supply and a chopper and a smoothing capacitor connected in parallel to the output side of the chopper supply a DC power supply to an inverter having a pair of switching elements connected in series to alternately open and close, and convert the high frequency output by the inverter, This high-frequency output is connected to a discharge lamp through a series circuit of a first capacitor and a choke coil, and a second capacitor is connected in parallel with the discharge lamp. Set the first capacitor, choke coil, and second capacitor when the discharge lamp is turned off to be lower than the no-load resonance frequency. And the duty ratio for controlling the opening and closing of the pair of switching elements when the discharge lamp is all lit is set to approximately 50% / 50%. A discharge lamp lighting device in which a duty ratio for controlling the opening and closing of the pair of switching elements during discharge lamp dimming lighting is different from approximately 50% / 50%, wherein the discharge lamp is changed from a dimming lighting state to an all-light lighting state. A discharge lamp lighting device provided with means for reducing the oscillation frequency of the inverter after setting the duty ratio for controlling the opening and closing of the pair of switching elements to approximately 50% / 50% when switching.

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