JPH0233899A - Lighting device for electric discharge lamp - Google Patents

Abstract

PURPOSE:To make the life of a fluorescent lamp longer by providing a preheating capacitor in series with a filament circuit of the fluorescent lamp and in parallel with the discharge path thereof, and preheating means for operating switching means at a frequency higher than that at the lighting time for a predetermined time period before the lighting. CONSTITUTION:When a DC power supply 1 is turned on, a charging time constant formed by a resistor 18 and a capacitor 19 determines the ON time of a PNP transistor(Tr) 17 and this time constitutes a preheating time period. During the ON period of the Tr 17, an NPN Tr 14 is also in ON state. Accordingly, an oscillation frequency during the preheating is determined by resistors R1, R2 connected in parallel and a capacitor C1, and is higher than the frequency at the lighting time. Therefore, in a series circuit of a current limiting choke 4, an electric discharge lamp 6, and a resonant capacitor CO, the impedance of the choke 4 becomes larger than that of a capacitor 5 and the discharge is prevented. At the same time, a preheating current is supplied to a series circuit including a filament F2 via switching elements 7, 8.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a device for lighting a discharge lamp by switching on and off a DC voltage at a predetermined frequency through a switching means such as a semiconductor switching element, and particularly for preheating a discharge lamp with a simple configuration and long life. Relating to something that has the means.

[Conventional technology]

Most conventional discharge lamp lighting devices of this type operate at a fixed frequency after the power is turned on. However, in this method, discharge starts from a cold state of the discharge lamp, which significantly shortens the life of the discharge tube. Therefore, in order to solve this problem, a mechanical contact or a semiconductor switch, etc. is installed in series with the filament circuit of the discharge lamp and short-circuited the discharge path of the discharge lamp, thereby reducing the voltage across the discharge lamp during the filament preheating period. Methods of heating the filament at a low frequency while suppressing discharge, or methods of providing a separate filament preheating power source have been adopted.

[Problem to be solved by the invention]

However, in both of the above solutions, the lighting device becomes expensive, and in the former solution, problems such as the lifespan of the contacts remain. SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus for lighting a discharge lamp by switching on and off a DC voltage at a predetermined frequency through a switch means and applying it to a DC circuit of a discharge lamp, a reactor, and a capacitor. By providing a discharge lamp lighting device with a function of increasing the frequency higher than the operating frequency during normal operation, the voltage applied to the discharge lamp can be kept lower than the voltage required to start discharge, and the lamp can be sufficiently preheated within the preheating time. The purpose is to solve the above problem.

[Means to solve the problem]

In order to solve the above problems, the device of the present invention provides the following features:
The discharge lamp (
6, etc.), a reactor (current limiting choke 4, etc.), and a capacitor (resonant capacitor CO, etc.). A preheating capacitor (such as 5) connected to the discharge lamp and shunting the discharge path of the discharge lamp, and a preheating capacitor (such as 5) connected to the discharge lamp for a predetermined time (such as the time determined by the timer resistor 18 and the timer capacitor 19) prior to the lighting, which is higher than the frequency (timing resistor 19). R1, R2, timing capacitor 0
Preheating driving means (transistors 14, 17, PWM control ICl 0, pulse transformer 9, etc.) for driving the switching means to open and close at a predetermined frequency (Is, etc.) (determined by Is, etc.).

[For use]

When the preheating timer, which starts when the power is turned on, is in operation, a resistor for determining the preheating frequency is inserted in parallel with the resistor for determining the steady frequency in the CR time constant circuit that determines the oscillation frequency of the discharge lamp via a semiconductor switch. In this manner, by driving the switch element at a predetermined frequency higher than the steady frequency for a predetermined period of time before lighting the discharge lamp, an appropriate preheating current flows through the filament of the discharge lamp.

【Example】

FIG. 1 is a configuration circuit diagram as an embodiment of the present invention. In the figure, 1 is a DC power supply, 2.3 is a smoothing capacitor that divides this DC power supply 1 to create a new DC power supply, and 7 and 8 are connected between the DC power supply 1 to form a half-bridge circuit. switching element (FET in this example)
), 6 is a discharge lamp, 4 is a current limiting choke as a reactor, and CO is a resonant capacitor. This current limiting choke 4. Discharge lamp 6. The resonant capacitors CO are connected in series with each other, and this series circuit includes the mutual connection point M1 of the smoothing capacitor 2.3, the switching element 7,
8 mutual connection point M2. Reference numeral 10 denotes a PWM (pulse width modulation) control IC which oscillates and outputs a PWM signal with a frequency determined by a time constant to be described later, and alternately drives switching elements 7.8 to open and close via a pulse transformer 9. This causes the current limiting choke 4. Discharge lamp 6. A DC voltage of alternating polarity, that is, an AC voltage, is applied to the series circuit of the resonant capacitor CO via the smoothing capacitor 2.3. During steady operation, the current limiting choke 4 and the resonant capacitor CO are configured to resonate in series. Reference numeral 5 denotes a preheating capacitor constituting a preheating path of the discharge lamp 6, and a filament circuit F at both ends of the discharge lamp 6.
It is connected in series with F2 and so as to shunt the discharge path of the discharge lamp 6. 20 is a bias resistor for producing a low-voltage DC power source from the DC current l; 22 is a smoothing capacitor forming this low-voltage power source; and 21 is a Zener diode for preventing the voltage of this low-voltage power source from becoming excessive. This low voltage power supply includes control ICl0 and pulse transformer 9.
At the same time, it becomes a driving power source for the timer resistor 18. It also serves as a DC power source for a timer circuit, which will be described later, which includes the timer capacitor 19 and the like. The PWM i! The constant oscillation frequency of ICl0 for II is determined by timing capacitor CI and timing resistor R1.
Determined by That is, the oscillation frequency f of this ICl0 itself is expressed as f # 1 /R1·CI, but since the operation of the switching element 7.8 is push-pull, the actual operating frequency r1 of the discharge lamp 6 is "1'. 1/ 2 (R1・C1). Next, the operation at startup, which is the main focus of the present invention, will be described. When the DC power supply 1 is turned on now, the timer capacitor 19 is charged through the timer resistor 18. This resistor 18 and The charging time constant formed by the capacitor 19 determines the ON time of the PNP transistor 17, which becomes the preheating time timer. To be supplied, transistor 1
4 is turned on during the preheating time, and as a result, the timing resistor R2 for determining the preheating frequency is inserted in parallel with the timing resistor R1 for determining the oscillation frequency, and the oscillation frequency (operating frequency) fS during preheating is as follows. This is a predetermined value higher than the normal operating frequency r1 mentioned above. For this reason, current limiting choke 4. Discharge lamp 6. Resonant capacitor C
In the series circuit of O, the impedance of the current limiting choke 4 becomes a large and dominant value, and the impedance of the preheating capacitor 5 decreases. As a result, the voltage across the discharge lamp 6 decreases to prevent its discharge, and the current limiting choke 4. Filament circuit F
l, preheating capacitor5. Filament circuit F2. A suitably limited current for preheating the filament flows through the switching elements 7 and 8 in the series circuit of the resonant capacitor CO.

【Effect of the invention】

A device for lighting the discharge lamp by opening and closing a DC voltage at a predetermined frequency through a switching means and applying it to a series circuit of a discharge lamp, a reactor, and a capacitor, the device being connected in series with the filament circuit of the discharge lamp, and a preheating capacitor that shunts the discharge path of the discharge lamp; and a preheating drive means that drives the switching means to open and close at a predetermined frequency higher than the frequency for a predetermined period of time prior to the lighting. With a simple circuit configuration, not only can a long-life preheating circuit for a discharge lamp be provided at low cost, but also the discharge lamp can have a long life.

[Brief explanation of the drawing]

FIG. 1 is a configuration circuit diagram as an embodiment of the present invention.

Claims (1)

[Scope of Claims] 1) A device for lighting the discharge lamp by switching a DC voltage on and off at a predetermined frequency through a switching means and applying it to a series circuit of a discharge lamp, a reactor, and a capacitor, comprising: a preheating capacitor connected in series with the filament circuit and shunting the discharge path of the discharge lamp; and a preheating drive means for driving the switching means to open and close at a predetermined frequency higher than the frequency for a predetermined period of time prior to the lighting. A discharge lamp lighting device characterized by comprising the following.