JPH0374090A - Discharge lamp lighting device - Google Patents

Abstract

PURPOSE:To ensure starting of a discharge lamp by quenching an inverter circuit or by controlling the discharge lamp at a frequency higher than that of lighting, when the voltage from a lamp voltage detection circuit is larger than the normal one a certain period after the power source input. CONSTITUTION:From the time t1 on, output of a timer circuit 4 reaches level L, whereby a transistor Q2 is turned ON and a resistance R3 is shortcircuited, and reference voltage Vref is reduced. The time t1 where the output of the timer circuit 4 reaches the L level is the one after a normal lamp La is lighted. When the lamp La is double-emulsion type, it is driven at a frequency f3, and is controlled by an ON period control circuit 2 so as not to approach resonance frequency. Even for a discharge lamp that is not easily started at a low temperature, since high voltage is applied to the discharge lamp for a certain period of time, it can be surely lighted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a discharge lamp lighting device, and more particularly, to protection of a circuit when a discharge lamp at the end of its life is used.

[Prior Art] FIG. 6 shows a conventional example, and shows a -stone inverter circuit. A series circuit of a choke L1 and a switching element Q is connected in parallel to both ends of the DC power supply E, and the switching element Q is controlled to be turned on and off by the control circuit 1. Further, a series circuit of a lamp La and a choke L2 is connected in parallel with the choke L, and a capacitor C2 is connected to the filament on the non-power supply side of the lamp La. Furthermore, a diode D and a capacitor C1 are connected between the collector and emitter of the switching element Ql.

Next, the operation will be briefly explained. When the switching element Ql is turned on, a current flows to the switching element Q as shown in FIG. 7(b) through a series circuit of the choke L, the lamp La, and the choke current. Switching element Q
, turns off, the choke L + , L ! The energy stored in causes a current to flow into capacitor CI. The charge stored in capacitor C3 is then discharged into the series circuit of choke L2 and lamp La. Here, FIG. 7(a) shows the collector-emitter voltage of the switching element Q, FIG. 7(e) shows the current flowing through the choke L, FIG. 7(d) shows the lamp current, and FIG. ) indicate the current flowing through the diode D, respectively.

In this way, an oscillating circuit is formed by the series circuit of the capacitor CI, the choke L2, and the lamp La, and a high frequency current flows through the lamp La.

A capacitor C2 connected to the filament on the non-power supply side of the lamp La is provided to preheat the filament and to apply a high voltage to the lamp La to start it. The resonance curve of choke L2 and capacitor C3 is as shown in FIG. That is, immediately after the power is turned on, the oscillation frequency is increased by narrowing the ON period of the switching element Q1, the voltage across the capacitor C2 is set to a voltage value at which the lamp La does not start discharging, and the filament is preheated at the frequency fo. and promotes thermionic emission from the filament.

Thereafter, the lamp La is started by gradually extending the ON period of the switching element Q and increasing the voltage vc2 across the capacitor C2. 8th r! ! f3 shown in 1
is the starting frequency. When the lamp La is turned on, the resonance curve is shifted as shown in FIG. 8, and the ON period is set so that a predetermined lamp current flows. 8th rf! 1
In, fl is the frequency when all lights are on, and fo is the resonant frequency.

Here, FIG. 9(a) shows the circuit when the lamp La is not lit, FIG. 9(b) shows the circuit when the lamp La is lit, and R indicates the equivalent resistance of the lamp La. There is.

[Problems to be Solved by the Invention] Such an inverter circuit has the following problems when the lamp reaches the end of its life. In other words, at the end of the lamp's life, the emitter (thermionic emission material) that is distributed along the filament scatters, and when one emitter wears out, thermionic emission from one side disappears, causing the lamp to undergo a half-wave discharge. (Hereinafter, this state will be referred to as one-sided emission.) At this time, the choke L1 becomes biased, the choke current of L increases, and heat generation saturation occurs.

Additionally, if the emitter scatters further, the filaments on both sides will not discharge and the lamp will not light up (
(Hereinafter, this state will be referred to as "double emission"). In such a case, the choke L2 and capacitor C2 operate along the resonance curve shown in Figure 8, so the oscillating current increases as it approaches the resonance point, and the switching element may generate heat or exceed the maximum rating and cause damage.

In order to avoid such problems and protect the circuit, the following methods have conventionally been used.

■ Method of detecting the temperature of the element using a thermal protector This method requires two thermal protectors because the elements that generate heat are different for single-emission lamps and double-emission lamps, and the thermal protector's thermal response is expensive. It's slow and takes a long time to work. Further, when the temperature of the element increases rapidly, the element may be destroyed before the thermal protector operates.

Furthermore, it is sensitive to ambient temperature.

■ Current detection method For both EMIRES lamps, choke L2 and capacitor C
Since it operates near the resonant frequency of the resonant curve of I, the oscillating current increases, and as shown in Figure 6, the current detection block 2
a, 2b generates an oscillating current or a switching element Q,
By detecting the current, it is possible to distinguish between a normal lamp and both Emiles lamps, and the response is good. The difference from the lamp is small, and it is difficult to identify if variations are included, so it is necessary to use it in combination with other single-emission lamp detection methods.

■ Voltage detection method at both ends of the lamp When a half-wave discharge occurs in a single EMIRES lamp, as shown in Figure 10, the half-wave of the voltage across the lamp becomes the lamp voltage, and the half-wave in the opposite direction becomes the applied voltage, so it is normal. The lamp voltage of a single lamp is the voltage across the emiless lamp, which can be identified. However, when starting the lamp, the oscillation frequency is gradually changed from fl to f3, and in the process of increasing the voltage across the lamp, the lamp voltage at lighting becomes the lamp voltage at starting, so detection continues until the lamp lights up. It is necessary to make it inoperable and prevent malfunction.

In both Emires lamps, the lamp does not light up, so during this period of inoperation, the oscillation frequency changes from fl to f,
When the switching element changes to lower than the resonant frequency, the current in the switching element increases at the resonant frequency, and it is also used in phase advance mode below the resonant frequency, resulting in a phenomenon in which the oscillation frequency is disturbed and stress on each component becomes large. . Therefore, during this period of inactivity, current is detected and oscillation is stopped.
This was to prevent this situation from continuing. In addition, since the voltage across the lamp after inoperation decreases in the phase advance mode, it may be difficult to detect a normal lamp depending on the setting of the constant of the series resonant circuit.

Further, such a problem also occurs in a half-bridge circuit as shown in FIG. 5, which uses a series resonant circuit to light a lamp.

The present invention has been provided in view of the above-mentioned points, and detects an abnormality at one location, detects single-emission failure or double-emission failure when a discharge lamp is at the end of its life, and particularly detects both emission failure. The object of the present invention is to provide a discharge lamp lighting device that does not approach the resonant frequency.

[Means for Solving the Problems] The present invention includes a lamp voltage detection circuit that detects the voltage across the discharge lamp, and a voltage from the lamp voltage detection circuit that is necessary for starting the discharge lamp within a certain period after power is turned on. If the lamp voltage reaches a certain level, the control circuit is controlled to fix the oscillation frequency of the inverter circuit, and if the lamp voltage exceeds the normal lamp voltage after a certain period of time, the oscillation of the inverter circuit is stopped or the oscillation frequency is controlled at a higher frequency than the lighting frequency. and control means.

[Function] In response to the output voltage from the lamp voltage detection circuit, the control means causes the voltage from the lamp voltage detection circuit to reach a level necessary for starting the discharge lamp within a certain period of time after power is turned on. If this occurs, the control circuit is controlled to fix the oscillation frequency of the inverter circuit, and if the lamp voltage exceeds the normal lamp voltage after a certain period of time, the inverter circuit oscillates or is controlled at a higher frequency than the lighting frequency. It is.

[Example 1] Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
A specific circuit diagram is shown in the figure.The main circuit is the same as the conventional example, but the switching element Q1 is turned on and off by the on-period control circuit 2, and the voltage across the lamp La is detected by the lamp voltage detection circuit 3. ing. The lamp voltage detection circuit 3 outputs a voltage equivalent to the voltage across the lamp La, and its output is connected to the reference voltage Vref by the comparator CP.
compared to The reference voltage Vref is formed by resistors R and -R3, and the resistor R3 is short-circuited to change the reference voltage Vref by turning on and off the transistor Q2 for ms at the output of the timer circuit 4. The output of the comparator CP is input to AND gates G + and G 2 , respectively, and the frequency of the on-period control circuit 2 is fixed or changed by the outputs of the AND gates G, , G.

With the above configuration, the present invention detects the voltage across the lamp La or an equivalent voltage, and for a certain period after power-on (a period longer than the period in which the normal lamp L, a is reliably lit), the lamp La When the voltage across the capacitor C! exceeds the voltage required to start the lamp La, the on-period of the switching element Q is controlled and fixed so that it does not rise any further, and the chiller L, capacitor C! control so as not to approach the resonant frequency any further. Also, make sure that the lamp La lights up properly, and the lamp La of both Emires,
It prevents excessive current from flowing through the switching element Q, and after a certain period of time, the normal lamp La and one lamp
The lamps La of both EMIRES are identified, oscillation is stopped, or the ON period of the switching element Q1 is narrowed, and the switching element Q1 is operated at a high frequency to protect the circuit.

After the power is turned on, the timer circuit 4 is activated as shown in Fig. 2 (1).
From then until time tl, an H level signal is output, which is inverted by inverter gate G3 to turn off transistor Q2, and the reference voltage Vref is set high as shown in FIG. Since the fourth output is at the L level, the transistor Q2 is turned on to short-circuit the resistor R3, thereby lowering the reference voltage Vref. The time t when the output of the timer circuit 4 becomes L level is the time after the normal lamp La lights up, as shown in FIG. 2(e). The output of the lamp voltage detection circuit 3 is a normal lamp La (second Qlf(a)), a single-emission lamp L
a (Fig. 2 (d)), the lamp La of both EMIRES (in the case of Fig. 2 (e)), a voltage equivalent to the voltage across both ends of the lamp La is output.The output from this lamp voltage detection circuit 3 The voltage and reference voltage Vref are compared by a comparator CP.

This reference voltage Vref is determined by the values of the resistors R3-R3 at time 1. During the period, the lamp La is at the voltage V when both emitters are applied.
, is a detectable value, and is set to be between the voltage (2) outputted when the lamp La is normal and the voltage vl outputted when the lamp La is in a single emission state. In other words,
Until time t, the case where the lamp La is both emissive is detected, and after time t1, the case where the lamp La is normal, one side and four emissive, or both emissive is detected is detected.

As shown in FIG. 2 (6), when the lamp La is normal, the lamp voltage detection circuit is activated during the process of changing the frequency of the lamp La from preheating to lighting, and even after lighting. Since the voltage VI outputted from the timer circuit 3 is lower than the reference voltage V ref regardless of the output of the timer circuit 4, no abnormality is detected and the output of the comparator CP is not inverted, and the on-period control circuit 2 switches the switching element Q1 to the normal state. When the power is turned on, it is driven at a high frequency and changes to a low frequency,
The lamp La is controlled to be turned on.

When the lamp La is single-emission, it is started and turned on in the same way as in the normal case, but after the lamp is turned on, the time 1 after the timer period ends. Hereafter, the voltage V from the lamp voltage detection circuit 3
, is higher than the reference voltage Vref, so the comparator C
P is inverted, and the on-period control circuit 2 is driven by the H level signal from the AND gate G2, and the switching element Q1 is controlled to be driven at a higher frequency than the frequency when oscillation is stopped or turned on.

In the case of both Emiles, the lamp La is shown in Figure 2 (Fig. 2) during preheating.
As shown in e), the frequency f is controlled by the on-period control circuit 2.
, when the voltage vl output from the lamp voltage detection circuit 3 exceeds the reference voltage Vref during the process of preheating and changing the frequency from fl to ft, the AND gate G
2 outputs a frequency fixed signal, and is driven at frequency fl, and is controlled by the on-period control circuit 2 so as not to approach the resonance frequency f shown in FIG. Emires is detected by CP and AND gate G2, and the oscillation is stopped or the ON period control circuit 2 is turned on at a high frequency as in the case of single emileres.
to drive the switching element Q1.

Note that a control means is constituted by the timer circuit 4, each gate G to G5, comparator CP, transistor Q2, etc.

[Example 2] Example 2 is shown in FIG. 3. In the previous example, the reference voltage Vr
The level of ef was changed in the previous example, but in this embodiment, the output from the lamp voltage detection circuit 3 is changed. The reference voltage Vref of the comparator CP is the resistance R
, and R2, and in the lamp voltage detection circuit 3, a series circuit of resistors R3 to R5 is connected in parallel to the diode D, and a transistor Q! is connected in parallel to the resistor R%. are connected.

This transistor Q2 is driven by the output of the timer circuit 4 via an inverter gate G3. As shown in FIG. 4, the output voltage V from the lamp voltage detection circuit 3 is sequentially higher when the lamp La is in a single emission mode or both emission modes, compared to when the lamp La is normal. In i, Emires is detected and control is performed in the same manner as in the previous embodiment.In addition, in the case of both Emires, preliminary preheating is performed and fl
In the process of changing the frequency from f2 to f2, the lamp voltage detection circuit 3
As shown in FIG. 4(d), when the output voltage V, exceeds the reference voltage Vref, the frequency is fixed at 3 and the lamp La is prevented from entering the phase advance mode, as in the previous embodiment. It is prevented. In addition, the capacitor C5 inserted in the main circuit is
This functions to increase the voltage across the lamp Lm in the one-emissionless lamp and the double-emissionless lamp Lm, so that the lamp La can be easily distinguished from a normal lamp La.

Furthermore, the half-bridge inverter circuit shown in FIG. 5 also produces similar effects.

[Effects of the Invention] As described above, the present invention includes a lamp voltage detection circuit that detects the voltage across the discharge lamp, and a voltage from the lamp voltage detection circuit that is necessary for starting the discharge lamp within a certain period of time after power is turned on. If the lamp voltage reaches a certain level, the control circuit is controlled to fix the oscillation frequency of the inverter circuit, and if the lamp voltage exceeds the normal lamp voltage after a certain period of time, the oscillation of the inverter circuit is stopped or the oscillation frequency is controlled at a higher frequency than the lighting frequency. In response to the output voltage from the lamp voltage detection circuit, the control means controls the voltage from the lamp voltage detection circuit to the level necessary for starting the discharge lamp within a certain period of time after the power is turned on. If the lamp voltage reaches this level, the control circuit is controlled to fix the oscillation frequency of the inverter circuit, and if the lamp voltage exceeds the normal lamp voltage after a certain period of time, the oscillation of the inverter circuit is stopped or the oscillation frequency of the inverter circuit is controlled at a higher frequency than the lighting frequency. This makes it possible to reliably detect lamps with one or both emisions, and even if a discharge lamp with both emisions is used, it can be controlled so that it does not approach the phase advance mode or the resonant frequency. The stress is small, and by fixing the double-Emires discharge lamp in slow phase mode, it is easy to distinguish it from a normal discharge lamp. It is possible to distinguish between both EMIRES discharge lamps using a single lamp voltage detection circuit, and the oscillation frequency is fixed during the starting process.

For example, even if a discharge lamp is difficult to start in a low-temperature atmosphere, high voltage is applied to the discharge lamp for a certain period of time, so that the discharge lamp can be started reliably.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is an operating waveform diagram of the same as above, FIG. 3 is a circuit diagram of another embodiment of the same, FIG. 4 is an operating waveform diagram of the same as above, and FIG. is the same circuit diagram as above, FIG. 6 is a circuit diagram of the conventional example, FIG. 7 is an operation waveform diagram of same as above, FIG. 8 is an explanatory diagram of same as above, and FIGS. 9(a) and (b) are equivalent circuits of same as above. FIGS. 10(a) and 10(b) are explanatory diagrams of the same as above, respectively. 2 is an on-period control circuit, 3 is a lamp voltage detection circuit, La
is a lamp. Figure 5

Claims (1)

[Claims] (1) An inverter circuit that converts DC voltage into high-frequency voltage, a discharge lamp connected to the inverter circuit via a current limiting inductance, a preheating capacitor connected to the non-power supply side of the filament of the discharge lamp, and an inverter circuit. In a discharge lamp lighting device equipped with a control circuit that controls the oscillation frequency of the lamp, drives at a high frequency when the power is turned on, and then changes the frequency to a lower frequency to start and light the discharge lamp, the voltage across the discharge lamp is detected. If the voltage from the lamp voltage detection circuit reaches the level required to start the discharge lamp within a certain period of time after the power is turned on, the control circuit is controlled to adjust the oscillation frequency of the inverter circuit. Along with fixing
1. A discharge lamp lighting device comprising: control means for stopping oscillation of an inverter circuit or controlling the lighting frequency at a higher frequency if the lamp voltage exceeds a normal lamp voltage after a certain period of time.