JPH03285296A - Discharge lamp lighting device - Google Patents

Abstract

PURPOSE:To prevent excessive loads from being exerted on a filter condensor by providing a thermal switch in contact with the resistance of a smoothing circuit connected in parallel to a discharge lamp, and varying the duty ratio of a current regulator circuit by means of the thermal switch. CONSTITUTION:When the temperature of the ferrite core of a filter choke 120 is abnormalily rises and a ripple current is increased due to lowering of saturated magnetic flux density, heat of a ripple current limiting resistor 130 connected in series with a filter condensor 126 is also increased and the contact of a thermal switch 132 provided in contact with or in proximity to the ripple current limiting resistor 130 is opened by the heat. As a result, the power or signal of a chopper frequency oscillator 112 connected to the thermal switch 132 is blocked and thereby oscillation of an inverter is stopped or oscillation frequency of the inverter is varied so as to adjust the output of the inverter and prevent more than a fixed rate of current from being supplied to the filter condensor 126.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a discharge lamp lighting device, and particularly to improvements in its current adjustment mechanism.

[Prior Art] In recent years, a discharge lamp lighting device has been developed that lights a discharge lamp such as a fluorescent lamp using a direct current obtained by rectifying an alternating current from an alternating current power source, and it is possible to obtain flicker-free light output.

However, in such a discharge lamp lighting device,
Heat generated from semiconductors, choke coils, etc. raises the temperature inside the power supply, and this heat can lower the saturation magnetic flux density of the ferrite core of the filter choke. As a result, the current saturates and the ripple current increases, which cannot be limited by the filter choke, and the ripple current supplied to the filter capacitor also increases, increasing the load on the filter capacitor and shortening the life of the filter capacitor. There were times when I was forced to do something.

Therefore, a discharge lamp lighting device equipped with an inverter circuit as shown in FIG. 6 has been developed as a discharge lamp lighting device that solves such problems.

The discharge lamp lighting device shown in the figure is for lighting a discharge lamp 14 by converting a DC current from a DC power supply 10 into a pulse current using a chopper frequency oscillator 12 and stepping down the voltage.

That is, the inverter circuit 16 in the discharge lamp device
consists of a chopper frequency oscillator 12 and a step-down chopper transistor 18 that is turned on and off by the chopper frequency oscillator 12.

Further, the step-down chopper transistor 18 is connected to one electrode 14a of the discharge lamp 14, which is a load, through a filter choke 20, and the other electrode 14b is connected to a power source through a lamp current detection resistor 22, so that the lamp current Based on the lamp current detected by the detection resistor 22, the oscillation frequency of the chopper frequency oscillator is changed.

The series circuit of the filter choke 24 and the filter capacitor 26 has one end connected between the filter choke 20 and the discharge lamp electrode 14a, and the other end connected between the discharge lamp electrode 14b and the lamp current detection resistor 22.

Furthermore, the freewheel diode 28 has one end connected between the step-down chopper transistor 18 and the filter choke 20, and the other end connected between the negative side of the DC power supply 10 and the lamp current resistor 2.
It is connected between 2.

The discharge lamp lighting device according to the illustrated example is roughly configured as described above, and its operation will be explained next.

First, when the DC power supply 1o is turned on, a lighting current is supplied to the lamp 14 via the step-down chopper transistor 18.

The DC current from the step-down chopper transistor 18 is converted into a pulse current by the chopper frequency oscillator 12, smoothed by the filter choke 20, filter choke 24, and filter capacitor 26, and then supplied to the discharge lamp 14.

Further, the current from the discharge lamp 14 flows through the lamp current detection resistor 22, the frequency of the chopper frequency oscillator 12 is adjusted according to the detected lamp current value, and the current is controlled by the step-down chopper transistor 18.

Therefore, even when the power supply voltage changes, the lamp current can be controlled to be constant in a feedback manner.

[Problems to be Solved by the Invention] However, in the conventional improved discharge lamp lighting device as described above, the filter choke 24 connected in series to the filter capacitor 26 has a low resistance component, so that ripple current is generated. Even if the temperature increases, the heat generation is small,
There is a problem in that the increase in ripple current as described above may not be detected due to the heat generation of the filter choke 24.

The present invention was made in view of the problems of the prior art, and its purpose is to easily detect an increase in ripple current, safely adjust the output of the inverter, or stop oscillation, and
An object of the present invention is to provide a discharge lamp lighting device that does not impose an excessive load on a filter capacitor.

[Means for Solving the Problems] In order to achieve the above object, a discharge lamp lighting device according to the present invention has a resistor connected in series to a filter capacitor for smoothing a pulse current, and a resistor in contact with the resistor, Alternatively, the inverter is characterized in that a thermal switch is provided nearby, and when the ripple current increases, the thermal switch is activated by the heat generated by the resistor to adjust the output of the inverter or stop oscillation.

[Function] Since the discharge lamp lighting device according to the present invention has the above-described means, when the ripple current increases due to magnetic saturation that occurs when the temperature of the ferrite core of the filter choke rises abnormally, the heat generation of the resistor also increases. This heat generation indirectly detects an increase in ripple current and activates a thermal switch, thereby making it possible to adjust the output of the inverter or stop oscillation.

[Embodiments] Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

FIG. 1 shows a discharge lamp lighting device according to an embodiment of the present invention, and parts corresponding to those in FIG. 6 are denoted by 100.
will be added and the explanation will be omitted.

A feature of the present invention is that it includes a circuit that detects an increase in ripple current by heat generation of a resistor and adjusts the output of the inverter or stops oscillation by operating a thermal switch. For this reason, in this embodiment, the ripple current limiting resistor 130. A thermal switch 132 is provided.

Here, the ripple current limiting resistor 130 is connected in series to the filter capacitor 126, and a thermal switch 132 is provided in contact with or in the vicinity of the ripple current limiting resistor 130, and the thermal switch 132 is connected to the chopper frequency oscillator 112. has been done.

The discharge lamp lighting device according to this embodiment is roughly constructed as described above, and its operation will be explained next.

First, the alternating current supplied from the alternating current power source 134 is passed through the rectifier circuit 13 consisting of a rectifier 136 and a smoothing capacitor 138.
9, it is converted into a direct current.

Then, the DC current is transmitted to a chopper frequency oscillator 112.
is converted into a pulse current by That is, a current as shown in FIG. 2(a) flows through the step-down chopper transistor 118, and a current as shown in FIG. 2(b) flows through the freewheel diode 128.
A current as shown in FIG. 2 flows through the filter choke 120, and the current shown in FIG.
) flows as shown below.

However, the current shown in FIG. 2 as described above flows only when the filter choke 120 is at a normal temperature.
When the temperature of the ferrite core of the filter choke 120 rises abnormally due to heat generation from within the power supply, the current flow changes.

This is because the saturation magnetic flux density of the ferrite core of the filter choke 120 changes depending on the temperature, and as shown in FIG.
It is understood that as the temperature of the ferrite core of No. 20 increases, the saturation magnetic flux density decreases.

Therefore, when the temperature of the ferrite core of the filter choke 120 abnormally increases, the currents shown in FIGS. (a), (b), (corresponding to
The current changes as shown in C).

Therefore, when the temperature of the ferrite core of the filter choke 120 is normal, the ripple current flowing through the ripple current limiting resistor 130 is as shown in FIG. The saturation current changes to an increased current as shown in Figure (b).

Therefore, as described above, when the temperature of the ferrite core of the filter choke 120 rises abnormally and the ripple current increases due to a decrease in saturation magnetic flux density, the ripple current limiting resistor 1 connected in series with the filter capacitor 126
30 also increases, and due to this heat generation, the contact point of the thermal switch 132 provided in contact with or in the vicinity of the ripple current limiting resistor 130 is turned off.

As a result, the power supply or signal of the chopper frequency oscillator 112 connected to the thermal switch 132 is cut off, and the oscillation of the inverter is stopped, or the oscillation frequency is changed to adjust the output, and the filter capacitor 126 receives a current exceeding a certain value. is not supplied.

Furthermore, by using the ripple current limiting resistor 130 to limit the current to the filter capacitor 126, there is no need to provide multiple expensive coils, so the cost is lower than that of the conventional discharge lamp lighting device shown in FIG. can do.

However, in the conventional discharge lamp device shown in FIG. 6, when the filter choke 20 and the filter choke 24 are connected closely, a mutual induction effect occurs, and the flow from the filter choke 20 to the filter choke 24 occurs. This makes it difficult for the ripple current to be absorbed, and the effect of limiting the ripple current supplied to the filter capacitor 26 by the filter choke 24 is reduced.

However, in the discharge lamp lighting device according to this embodiment, since the filter choke 24 is replaced with the ripple current limiting resistor 130, the mutual induction effect does not occur as described above.
The effect of limiting the ripple current supplied to the filter capacitor 126 by the ripple current limiting resistor 130 also does not deteriorate.

Note that when a full-bridge transistor circuit is installed on the output side of the filter capacitor to perform square wave lighting, the discharge current from the filter capacitor is limited by the ripple current limiting resistor 130. can also be prevented from being destroyed.

[Effects of the Invention] As explained above, according to the discharge lamp lighting device according to the present invention, the increase in ripple current due to the decrease in the saturation state magnetic flux density that occurs when the temperature of the ferrite core of the filter choke rises abnormally can be resisted. The thermal switch is activated to adjust the inverter's output or stop oscillation, so it is possible to extend the life of the capacitor by not placing more than a certain amount of load on the capacitor. .

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram of a discharge lamp lighting device according to an embodiment of the present invention, and FIG. 2 shows waveforms of various parts of the embodiment device shown in FIG. 1 during normal operation. ) is the current waveform of the step-down chopper transistor 118, (b) is the current waveform of the freewheel diode 128, and (C) is the current waveform of the filter choke 120.
3 is an explanatory diagram of the temperature characteristics of the saturation magnetic flux density of the ferrite core used in the filter choke. FIG. 4 is the current waveform of the filter choke 120 in the embodiment shown in FIG. 1 when it is saturated. The waveform is shown in the same figure (a).
is the current waveform of the step-down chopper transistor 118, (b)
5 shows the current waveform of the freewheel diode 128, (C) shows the current waveform of the filter choke 120, and FIG. 5 shows the current waveform of the ripple current limiting resistor 130 in the embodiment shown in FIG. (a) is a current waveform during normal operation, (b) is a current waveform when filter choke 120 is saturated, and FIG. 6 is a circuit configuration diagram of a conventional discharge lamp lighting device. 26, 126 ・・・・・・ 130 ・・・・・・・・・・・・132 ・
・・・・・・・・・・・・134 ・・・・・・・・・
・・・・・・139 ・・・・・・・・・Filter capacitor ripple current limiting resistor thermal switch AC power rectifier circuit

Claims (1)

[Claims] (1) A discharge lamp lighting device that supplies a DC lighting current to a discharge lamp via a filter choke, comprising: a current adjustment circuit that conducts or cuts off the DC current at a predetermined duty ratio based on the oscillation frequency of an oscillator; a smoothing circuit formed by connecting a resistor and a capacitor in series, connected in parallel with the smoothing circuit, and having a thermal switch in contact with or in close proximity to the resistor of the smoothing circuit, the thermal switch being connected to the resistor of the resistor. By turning on/off due to heat generation,
A discharge lamp lighting device characterized in that the duty ratio of the current adjustment circuit is changed.