JPH0645079A - Discharge lamp lighting device - Google Patents

Abstract

PURPOSE:To prevent the early blacking and life deterioration of by cold start of a discharge lamp by suppressing the frequency to a switching frequency in which filament preheating can be performed but discharge lamp start can not be performed for a determined period from power source input. CONSTITUTION:A switch 42 is ON by a filament preheating means 4 until a determined time is elapsed after power source input. Thus, the synthetic capacity of capacitors 16, 41 is relatively small, and the resonance frequency of a series resonance circuit is raised. Therefore, the ON-time of base current is controlled shorter, the oscillating frequency of an inverter 1 is increased, and the output voltage is reduced. At this time, the induced voltage of the secondary winding 11s of an output transformer 11 given between both electrodes of a discharge lamp 2 is set lower than the start voltage of the discharge lamp 2, whereby the discharge lamp 2 can perform the soft start for heating a filament without discharging the discharge lamp 2 by the high frequency output from the inverter 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge lamp lighting device using a transistor inverter.

[0002]

2. Description of the Related Art Conventionally, as an inverter, for example, Japanese Unexamined Patent Publication
The one disclosed in Japanese Patent No. 58-54874 is proposed. This one is
An output transformer having a primary winding and a feedback winding, and a transistor for controlling the power supplied to the primary winding, and a base supplied from the feedback winding through an LC series resonance circuit.
The high-frequency voltage is generated by driving the transistor with a discharge current. Further, the output transformer is provided with a resonance capacitor that forms a parallel resonance circuit with the inductance component of the output transformer.

The inverter disclosed in Japanese Patent Laid-Open No. 58-54874 is designed to light a discharge lamp as a load.

When the discharge lamp of the above-mentioned Japanese Patent Laid-Open No. 58-54874 is to be lit, a high voltage is generated at the same time when the DC power source is turned on, so that the filament of the discharge lamp is not preheated sufficiently to start. This causes a so-called cold start, which causes problems such as early blackening and a short life of the discharge lamp.

On the other hand, JP-A-57-110084 has been proposed. This one reduces the output voltage of the inverter at the time of starting the discharge lamp by reducing the base current of the switching transistor of the transistor inverter from that at the time of normal lighting until the filament is sufficiently heated. A so-called soft start is performed to make the voltage lower than the starting voltage of the lamp.

However, in the method disclosed in Japanese Patent Laid-Open No. 57-110084, since the base current of the switching transistor is reduced from that in the normal state, the switching transistor is likely to operate in class A and the power loss in the switching transistor is large. However, there is a problem in that the switching transistor is easily loaded.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and it is possible to achieve early blackening and a short life of the discharge lamp without increasing the power loss in the switching transistor. It is an object of the present invention to provide a small-sized discharge lamp lighting device which can eliminate or reduce the problem causing it and which has a relatively simple structure.

[0008]

The present invention comprises a switching transistor for switching a DC power supply voltage and a resonance circuit supplied with the switching output of the switching transistor, and converts the DC power supply voltage into a high frequency voltage. A transistor inverter whose output is variable according to the switching frequency of the switching transistor, and a discharge lamp whose filament is preheated while being lit by the high-frequency output of the transistor inverter are provided, and the switching frequency of the switching transistor is set. Filament preheating means for preheating the filament sufficiently from the time of turning on the DC power supply and suppressing the frequency to such a degree that the discharge lamp cannot be started, and switching to a frequency sufficient to start the discharge lamp after the predetermined time has elapsed. Set up Those were.

In the present invention, the transistor inverter outputs a part of the output voltage to the main transistor.
This is a one-stone transistor inverter that positively feeds back between the base and the emitter, and the filament preheating means is a switch for changing the capacity of the capacitor provided between the base and the emitter of the main transistor, and a timer for operating this switch. It may be composed of a circuit, and the switch may be composed of a diode and a thyristor.

[0010]

According to the present invention, when the discharge lamp is started by the filament preheating means, the switching frequency of the switching transistor is suppressed to a frequency at which the filament can be preheated sufficiently and the discharge lamp cannot be started. Therefore, the discharge lamp only preheats the filament for a predetermined period at the time of starting.

The filament preheating means switches to a frequency sufficient to start the discharge lamp after the predetermined period. Therefore, the discharge lamp whose filament has been preheated does not undergo so-called cold start and is prevented from having a reduced life.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. For example, the one-stone blocking oscillation known between the output terminals a and b of a DC power source (not shown) composed of an AC power source and a smoothing or non-smoothing rectifying circuit or a battery is well known and disclosed in, for example, Japanese Patent Laid-Open No. 58-54874. The transistor inverter 1 of the shape is connected. This inverter 1
The discharge lamp 2 as a load is connected to the secondary winding 11s of the output transformer 11.

The inverter 1 mainly includes an output transformer 11 and a switching transistor 12. Hereinafter, the inverter 1 will be described in detail.
The primary winding 11p of the output transformer 11 is connected between the positive side output terminal a of the DC power source and the collector of the transistor 12, and the resonance capacitor 13 is connected in parallel with the primary winding 11p. The emitter of the transistor 12 is connected via a diode 14 to the negative output terminal (common terminal) b of the DC power supply. In this embodiment, the base period winding 11f of the output transformer 11, which is the feedback power supply, has one end connected to the negative output terminal b of the DC power supply, and the other end which is an LC series resonance including an inductor element 15 and a capacitor 16. It is connected to the base of the transistor 12 via a circuit. The emitter and collector of the transistor 31 of the reset circuit 3 are connected to both ends of the capacitor 16, and the base of the transistor 31 is connected to the base feedback winding 11f of the output transformer 11 via the diode 32 and the like. It is connected to the terminal wound up on the other end side.

The filament preheating means 4 is a condenser 1
6, an auxiliary capacitor 41 provided in parallel, and a unidirectional switch 4 connected in series with the auxiliary capacitor 41.
2, a diode 43 connected in reverse parallel to the unidirectional switch 42, and a control device 44 for controlling conduction of the unidirectional switch 42, for example, a timer circuit. Such filament preheating means 4
Is a control device 44, such as a timer circuit, for disconnecting the auxiliary capacitor 41 for a predetermined period when the discharge lamp 2 is started. As a result, the synthetic capacitance is reduced and the resonance frequency of the LC series resonance circuit for supplying the base current of the transistor 12 is increased, thereby shortening the ON period of the transistor 12, that is, increasing the oscillation frequency. The voltage applied to the discharge lamp 2 can be lowered by increasing the oscillation frequency of the inverter 1 or by reducing the power stored in the output transformer 11.

The diode 14 is a transistor 12
To protect the base from the reverse voltage between the base and the emitter, and to supply the base extraction current without excess or deficiency.
Further, the reset circuit 3 has a capacitor 16 when the transistor 12 is turned off and the base feedback winding voltage becomes negative.
To discharge and reset the capacitor 1
By connecting a discharging resistor in parallel with 6, the Q reduction of the LC resonance circuit and the deterioration of the switching characteristic of the transistor 12 are prevented.

Next, the operation will be described. When the DC power source is turned on and applied to the inverter 1, the inverter is turned on.
In the case of transistor 1, the transistor 12
A base current is applied to the transistor 12 to turn on the transistor 12. When the transistor 12 is turned on, the transformer 11 becomes 1
A voltage is generated in the next winding 11p and the feedback winding 11f, and in this embodiment, the voltage of the base feedback winding 11f is the base feedback winding 11f-the capacitor 16-the inductor 15-the base of the transistor 12. It joins the positive feedback loop consisting of an emitter and forward biases the transistor 12.

On the other hand, in the filament preheating means 4, the switch 42 is operated until a predetermined time elapses after the power is turned on.
Is off. Therefore, the combined capacitance of the capacitors 16 and 41 is relatively small, and the resonance frequency of the series resonant circuit is high. Therefore, the on time of the base current is controlled to be shorter, and the oscillating frequency of the inverter 1 becomes higher and the output voltage becomes lower.

When the transistor 12 is turned off, the inductance component of the transformer 11 and the resonance capacitor 13
Resonate with each other, and when this resonance voltage is about to be inverted, the transistor 12 is forward biased again and turned on. Thereafter, by repeating such an operation, a high frequency voltage is generated in each winding 11p, 11s, 11f of the transformer 11.

As described above, in order to shorten the on-time and lower the output voltage, the induced voltage of the secondary winding 11s of the output transformer 11 applied between both electrodes of the discharge lamp 2 at this time starts the discharge lamp 2. By setting the voltage lower than the voltage, the discharge lamp 2 can perform a soft start for heating the filament without discharging the discharge lamp 2 by the high frequency output from the inverter 1.

In this embodiment, the filament preheating means 4 operates with the output voltage of the feedback winding 11f. Then, when the filament of the discharge lamp 2 is sufficiently preheated after the power is turned on and the filament preheating means 4 turns on the switch 42, the combined capacitance of the capacitors 16 and 41 becomes relatively large, and the series resonant circuit of the series resonance circuit. The resonance frequency is low. Therefore, the ON period of the transistor 12 becomes relatively long, and the output voltage value of the inverter 1 becomes relatively large. As a result, the sufficiently preheated discharge lamp 2 is applied with a high-frequency voltage that is sufficiently higher than the ignition voltage between both electrodes and starts lighting.

The present invention is not limited to the above-mentioned embodiments, but can be carried out by appropriately modifying it without departing from the concept of the present invention. For example, as an inverter, a part of the output is rectified and stored in a capacitor, and the output of a rectifier circuit that performs non-smooth rectification of the AC power supply is low while the output is low.
It may be applied to a so-called auxiliary power source type inverter which is supplied as auxiliary power to the inverter.

[0022]

As described above, according to the present invention, the filament preheating means is provided so that the filament can be preheated sufficiently until the predetermined period elapses after the power is turned on, but the switching frequency of the discharge lamp cannot be started. ,
It is possible to prevent early blackening and life deterioration due to the cold start of the discharge lamp. Moreover, since it controls the switching frequency of the switching transistor, it does not increase the power loss as in the case of operating the switching transistor in class A, and the structure is relatively simple, and the discharge lamp is small and inexpensive. A lighting device can be provided.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a discharge lamp lighting device according to an embodiment of the present invention.

[Explanation of symbols]

1 ... Inverter, 11 ... Output transformer, 12 ... Switching transistor, 13 ... Resonance capacitor, 2 ...
Discharge lamp, 4 ... Filament preheating means.

Claims (1)

[Claims] 1. A transistor inverter having a switching transistor for switching a DC power supply voltage and a resonance circuit supplied with a switching output of the switching transistor, the transistor inverter having an output variable according to the switching frequency of the switching transistor; A discharge lamp which is lit by the high frequency output of the inverter and preheats the filament; the filament is sufficiently preheated until the switching frequency of the switching transistor is turned on for a predetermined period of time and the discharge lamp is A discharge lamp lighting device comprising: a filament preheating unit that suppresses the frequency to a level at which the discharge lamp cannot be started and switches the frequency to a frequency sufficient to start the discharge lamp after a predetermined period of time.