JP2520280B2 - Discharge lamp lighting device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a discharge lamp lighting device for lighting a discharge lamp with a DC power supply.

[Prior Art] Conventionally, as a device for lighting a discharge lamp (lamp) with a DC power supply, a current supplied from the DC power supply to a load is turned on / off at a high frequency (for example, 20 kHz to 100 kHz) to limit the current. A step-down chopper, an LC filter for smoothing the output of the chopper, and a DC output from the LC filter are input via an inductor, converted into a rectangular wave AC output (for example, 50 Hz) and supplied to a discharge lamp. A device including a bridge inverter is known.

Here, the step-down chopper is for limiting the lamp current of the discharge lamp, which is a negative resistance, at the time of lighting, and the LC filter prevents high-frequency current from flowing to the discharge lamp and makes lighting unstable. The inductor is to prevent the switching element of the bridge inverter from turning on.
This is for suppressing the discharge current of the capacitor of the LC filter and reducing the loss of the switching element. Further, the bridge inverter is for converting a DC output into an AC output because a normal discharge lamp cannot be DC-lit.

[Problems to be Solved by the Invention] By the way, in such a discharge lamp lighting device, there is a disadvantage that ringing occurs in the output current when the output current of the bridge inverter is inverted, and that some lamps do not light stably. It was

The present invention has been made in view of the above-mentioned problems in the conventional type, and a discharge lamp lighting device for lighting a discharge lamp by converting a current limited by a step-down chopper from a DC power source into a rectangular wave AC by a bridge inverter. In order to suppress the ringing generated at the time of switching the bridge inverter, the output of the bridge inverter is made into a current waveform closer to a rectangular wave, and the lamp is stably lit.

[Means for Solving the Problems] In order to achieve the above object, in the present invention, a DC power supply, a step-down chopper that outputs a current limited by the DC power supply, an LC filter that smoothes the output of the chopper, A discharge lamp lighting device, comprising: a bridge inverter for inputting an output of the LC filter through a second inductor and converting the output into a rectangular wave AC output to drive the discharge lamp.
A diode is connected in parallel with the filter capacitor and in the opposite direction to the DC power supply.

[Operation] The ringing at the time of switching the bridge inverter in the conventional device is due to the capacitor for the LC filter and the other inductance element, particularly the inductor for reducing the turn-on loss of the switching element of the bridge inverter. In the present invention, a diode is connected in parallel with the capacitor so that charges of opposite polarity are not stored in the capacitor, so that electrical vibration between the capacitor and the inductance element is limited, and ringing can be reduced.

[Effects] As described above, in the present invention, ringing is suppressed by preventing accumulation of electric charges of opposite polarity, which is unnecessary for the operation of the device, in the capacitor.
The ringing can be reduced without increasing the high frequency ripple of the LC filter and the loss of the switching element of the bridge inverter, and the lamp can be stably lit.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a discharge lamp lighting device according to an embodiment of the present invention. In this device, the input from the DC power supply 1 is limited by the step-down chopper 2, smoothed by the LC filter 3, and the discharge lamp (lamp) 6 is lit by the current converted into the rectangular wave AC by the bridge inverter 5. It is a thing.

The step-down chopper 2 turns on the current from the DC power supply 1.
A switching transistor 21 that is turned off and outputs, a pulse generation circuit 22 that drives this transistor 21, and a diode 23 that cooperates with the LC filter 3 to smooth the output of the chopper 2 are provided. LC filter 3 has an inductor 31
And a capacitor 32 are connected in an inverted L shape, and a diode 33, which is a feature of the present invention, is connected in parallel to the capacitor 32 in the direction opposite to the polarity of the DC power supply 1.

The bridge inverter 5 includes four bridge-connected transistors 51, 52, 53, 54 and an inductor 55 connected in series to the DC input terminal of the bridge circuit.
The lamp 6 is connected to the AC output terminal of the bridge circuit.

 Next, the operation of the apparatus shown in FIG. 1 will be described.

The switching transistor 21 of the step-down chopper 2 is
The base is driven by the pulse generation circuit 22, and the current from the DC power supply is turned on / off at high frequency. The inductor 31 of the LC filter 3 supplies the bridge inverter 5 with limiting its on-current when the transistor 21 is turned on, and also stores electromagnetic energy. When the transistor 21 is turned off, the inductor 31 uses the stored electromagnetic energy to
Inductor 55 and transistor 5 of bridge inverter 5
1, 52 (or 53, 54), the lamp 6, the diode 23 of the chopper 2, the inductor 31, etc. maintain the current of the circuit. The capacitor 32 of the LC filter 3 smoothes the output voltage of the LC filter 3. As a result, the bridge inverter 5 is supplied with a current which is limited by the transistor 21 and the inductor 31 and which is smoothed by the inductor 31, the diode 23 and the capacitor 32.

In the bridge inverter 5, the transistors 51, 52 and 53, 54 are alternately turned on by a control circuit (not shown).
It is turned off and the lamp 6 is turned on when the transistors 51 and 52 are turned on.
Current is supplied from left to right in the figure, and the transistor
When 53, 54 are turned on, the lamp 6 is supplied with a current from the right to the left in the figure. That is, the lamp 6 is driven by the rectangular wave AC output from the bridge inverter 5 and is turned on.

By the way, in the conventional lighting device, when the output current (lamp current) is inverted by switching of the transistors 51, 52, 53, 54 of the bridge inverter 5, the capacitor 32 of the LC filter 3 and the inductor of the bridge inverter 5 are
55, and by another inductance element (not shown) (for example, the inductance component of the current transformer 7 in FIG. 2),
As in the case where ringing occurs and a high frequency ripple is applied to the lamp, there is a drawback that the lighting of the lamp 6 becomes unstable.

Here, since the diode 33 is connected in parallel with the capacitor 32 of the LC filter, the capacitor 32 cannot store the electric charge on the − side, so that the electrical vibration due to the capacitor 32 and the inductor 55, etc. is suppressed, and The ringing is reduced. As a result, the lamp will come on stably. Further, the high frequency ripple does not increase and the loss is small.

[Modifications] The present invention is not limited to the above-described embodiments and can be modified and implemented as appropriate. For example, as shown in FIG. 2, by providing a current transformer 7 for detecting a lamp current, and controlling the output of the current transformer 7, that is, the pulse width output from the pulse generation circuit 22 according to the lamp current. ,
The lamp current may be stabilized. Further, a load abnormality such as one-way discharge or disconnection of the lamp is detected based on the lamp current, and the transistor 21 of the chopper 2 is turned off to perform a so-called safe operation for protecting the circuit and the lamp. Good.

[Brief description of drawings]

FIG. 1 is a schematic circuit diagram of a discharge lamp lighting device according to an embodiment of the present invention, and FIG. 2 is a schematic circuit diagram of a discharge lamp lighting device according to another embodiment of the present invention. 1: DC power supply, 2: Step-down chopper, 3: LC filter, 5: Bridge inverter, 6: Lamp, 32: Capacitor, 33: Diode, 51, 52, 53, 54: Transistor, 55: Inductor.

Claims (1)

(57) [Claims] 1. A DC power supply and a current supplied from the DC power supply to a load are turned on at a high frequency.
A step-down chopper that is turned off to limit the current, an LC filter that smoothes the output of the chopper, and a bridge that drives the discharge lamp by inputting the output of the LC filter through an inductor and converting it to a rectangular wave AC output. A discharge lamp lighting device comprising an inverter, wherein a diode is connected in parallel with the capacitor of the LC filter and in the reverse direction to the DC power supply.