JPH01251594A - Lighting device for discharge lamp - Google Patents

Abstract

PURPOSE:To stably light a lamp by connecting a diode in parallel with the capacitor of an LC filter and in the opposite direction to a DC power source. CONSTITUTION:An inductor 31 and a capacitor 32 are connected in a reversed-L shape to form an LC filter 3, a diode 33 is connected in parallel with the capacitor 32 and in the opposite direction to the polarity of a DC power source 1. Since the diode 33 is connected in parallel with the capacitor 32 of the LC filter 3, charges can not be stored on one side of the capacitor 32, thus the electrical vibration by the capacitor 32 and an inductor 55 or the like is suppressed, the generated ringing is reduced, thereby a lamp is stably lighted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a discharge lamp lighting device for lighting a discharge lamp using a DC power source.

[Prior Art] Conventionally, as a device for lighting a discharge lamp (lamp) with a DC power source, current supplied from the DC power source to a load is turned on and off at a high frequency (for example, 20 kHz to 100 kHz) to limit the current. A step-down chopper, an LC filter that smoothes the output of the chipper, and a direct current output from the LC filter that is manually powered through an inductor, which is converted into a rectangular wave alternating current output (for example, 50 Hz) and supplied to the discharge lamp. A device equipped with a bridge inverter is known.

Here, the step-down chopper is used to limit the lamp current of the discharge lamp, which is a negative resistance, during lighting, and the LC filter is used to prevent high-frequency current from flowing through the discharge lamp, making lighting unstable. The purpose of the inductor is to suppress the discharge current of the capacitor of the LC filter when the switching element of the bridge inverter is turned on, thereby reducing the loss of the switching element. Further, the bridge inverter is used to convert DC output into AC output, since normal discharge lamps cannot be lit with DC current.

[Problems to be Solved by the Invention] However, in such a discharge lamp lighting device, there is a problem that ringing occurs in the output current when the output current of the bridge inverter is reversed, and some lamps do not light stably. Ta.

The present invention has been made in view of the above-mentioned problems with the conventional type, and is a discharge lamp lighting device that lights a discharge lamp by converting current limited by a step-down chopper from a DC power source into rectangular wave alternating current using a bridge inverter. The purpose of this invention is to suppress ringing that occurs during switching of a bridge inverter, make the output of this bridge inverter have a current waveform closer to a rectangular wave, and stably light a lamp.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a DC power supply, a step-down chopper that outputs a limited current from the DC power supply,
Discharge lamp lighting comprising: an LC filter that smoothes the output of the chopper; and a bridge inverter that inputs the output of the LC filter via a second inductor and converts it into a rectangular wave AC output to drive the discharge lamp. In the apparatus, the above L
A diode is connected in parallel with the capacitor of the C filter and in the opposite direction to the DC power supply.

[Operation] Ringing during switching of the bridge inverter in the conventional device is caused by the capacitor of the LC filter and other inductance elements, especially the inductor for reducing turn-on loss of the switching element of the bridge inverter. In the present invention, a diode is connected in parallel to the capacitor to prevent charge of opposite polarity from being accumulated in the capacitor, so electrical vibration between the capacitor and the inductance element is limited, and ringing can be reduced.

[Effect] In this way, in the present invention, ringing is suppressed by preventing charge of opposite polarity that is unnecessary for the operation of the device from being accumulated in the capacitor.
Ringing can be reduced without increasing the high frequency ripple of the C filter and the loss of the switching elements of the bridge inverter, and the lamp can be lit stably.

[Example] The present invention will be described in detail below using the drawings.

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

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

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

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

The switching transistor 2I of the step-down chopper 2 is
The base is driven by a pulse generating circuit 22, and the current from the DC power source is turned on and off at high frequency.

The inductor 31 of the LC filter 3 is the transistor 21
When it is turned on, it supplies electromagnetic energy to the bridge inverter 5 while limiting its on-current, and accumulates electromagnetic energy.
When the transistor 21 is off, the accumulated electromagnetic energy causes the inductor 31, the inductor 55 of the bridge inverter 5, and the transistors 51, 52 (or 53.
54) Maintains the current in the circuit consisting of the lamp 6, the diode 23 of the chopper 2, the inductor 31, etc. L
The capacitor 32 of the C filter 3 smoothes the output voltage of the LC filter 3. As a result, a current whose current is limited by the transistor 21 and the inductor 31 and smoothed by the inductor 31, the diode 23, and the capacitor 32 is supplied to the bridge inverter 5.

In the bridge inverter 5, transistors 51, 52 and 53, 54 are alternately driven on and off by a control circuit (not shown), and when the transistors 51 and 52 are turned on, a current flows into the lamp 6 from the left to the right in the diagram. When the transistors 53 and 54 are turned on, a current is supplied to the lamp 6 from the cloth 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 lights up.

By the way, in the conventional lighting device, when the output current (lamp current) is reversed by the switching of the transistors 51, 52, 53, 54 of the bridge inverter 5, the L
Capacitor 32 of C filter 3 and bridge inverter 5
Ringing is generated by the inductor 55 of the lamp 55 and other inductance elements (for example, the inductance of the current transformer 7 in FIG. 2), and the lamp 6 The problem was that the lighting became unstable.

Here, since the diode 33 is connected in parallel with the capacitor 32 of the LC filter, the capacitor 32 cannot store charge on one side, so electrical vibrations caused by the capacitor 32 and the inductor 55, etc. are suppressed and generated. ringing is reduced. As a result, the lamp lights up stably. Furthermore, high frequency ripples do not increase, and loss is also small.

[Modifications] Note that the present invention is not limited to the above-described embodiments, and can be implemented with appropriate modifications. For example, as shown in FIG. 2, by providing a current transformer 7 for lamp current detection and controlling the output of this 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. Furthermore, load abnormalities such as one-way discharge or disconnection of the lamp may be detected based on this lamp current, and the transistor 21 of the chopper 2 may be turned off to perform a so-called safe operation to protect the circuit and the lamp. good.

[Brief explanation of the drawing]

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-nibride inverter, 6: Lamp, 32: Capacitor, 33: Diode, 51.52° 53, 54:
Transistor, 55: Inductor.

Claims (1)

[Claims] 1. A DC power source, and a device that turns on/off the current supplied from the DC power source to a load at a high frequency.
A step-down chopper that turns off and current limits, an LC filter that smoothes the output of the chopper, and a bridge that inputs the output of the LC filter via an inductor and converts it into a square wave AC output to drive the discharge lamp. A discharge lamp lighting device comprising an inverter, characterized in that a diode is connected in parallel with the capacitor of the LC filter and in a direction opposite to the DC power source.