JPH04296495A - Discharge lamp lighting device - Google Patents

Abstract

PURPOSE:To certainly detect a discharge lamp in the life end and reduce the stress of a switch element without sending a simultaneous on current. CONSTITUTION:When a discharge lamp L is in the life end, the on-period of a switch element Q1 is shortened, and the input of an inverter gate G2 is changed from level H to level L while the output Q of D-FFIC2 is in the level L. Then, a pulse is outputted from the output Q of D-FFIC3. Thus, the output Q of R-SFF7 is set to the level H, and a transistor Q3 is laid in on-state. Thus, the collector current of a transistor Q4 is determined depending on the parallel resistance values of resistances R7, R6, and the oscillating period of an astable multivibrator IC1 is shortened. Since the operation frequency of the inverter is thus increased to limit the output, a stress such as overcurrent or heating can be reduced.

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 having a function of detecting the end of the life of a discharge lamp.

0002

[Prior Art] FIG. 7 shows a conventional example. This circuit is a half-bridge inverter, and by alternately turning on and off switch elements Q1 and Q2 connected in series with a power source E, a high frequency signal is applied to a discharge lamp L, which is a load. It supplies electricity and lights up. Note that a transistor is used as the switch element Q1, and an FET is used as the switch element Q2. Switch element Q
1, a diode D1 is connected in parallel in the opposite direction, and when a transistor is used as the switch element Q2, the diode is similarly connected in parallel in the opposite direction.

[0003] Switch elements Q1 and Q2 are the starting circuit 1
The on-period of the switching element Q2 is controlled by the monostable multivibrator 2 and the on-period control section 3. Further, a preheating timer 4 is provided. In addition, a starting circuit 1, a monostable multivibrator 2, an on-period control section 3,
A control unit 5 includes a preheating timer 4 and the like. Among the switching elements Q1 and Q2 connected in series, the low voltage side switching element Q2 is turned on and off by a drive signal from the control unit 5, and the high voltage side switching element Q1 is a current limiting choke L1.
is driven by the secondary winding voltage of

[0004] Due to the H level output of the monostable multivibrator 2 shown in FIG. 8(a), the switching element Q on the low voltage side
2 is turned on, a current flows through the discharge lamp L → capacitor C2 → current limiting choke L1 → switch element Q2, and when switch element Q2 is turned off, the secondary winding shown in FIG. 8(c) is connected to the high voltage side switch element Q1. A base current is supplied by the voltage, and as shown in FIG. 8(d), the switching element Q
1 turns on. When the switch element Q1 is turned on, the charge accumulated in the capacitor C2 is discharged from the discharge lamp L to the switch element Q1 to the current limiting choke L1, and a current flows.

When the switching element Q1 is turned off, the current flows from the damper diode of the switching element Q2 to the current limiting choke L due to the energy stored in the current limiting choke L1.
1 → capacitor C2 → discharge lamp L → power supply E, so when switch element Q1 is off, switch element Q2
The voltage across the power supply E when the switch element Q1 is turned on is
is applied, but the voltage decreases to the forward voltage of the damper diode. This is detected by resistors R1 and R2, divided into voltages, and inputted to the control section 5. The monostable multivibrator 2 of the control unit 5 is
In synchronization with the falling edge of this detection signal, the switch element Q
Outputs an on signal to 2.

That is, after the switch element Q1 is turned off, the switch element Q2 is controlled to be turned on, and the switch elements Q1 and Q2 are alternately turned on and off to continue oscillation. Note that FIG. 8(e) shows the current waveform flowing through the current limiting choke L1, and FIG. 8(f) shows the waveform of the current flowing through the current limiting choke L1.
is the drain-source voltage VDS. The control unit 5 shortens the on period of the switch element Q2 for a certain period from when the power is turned on, lowers the voltage of the capacitor C1 to below the starting voltage of the discharge lamp L, preheats the filament of the discharge lamp L, and causes thermionic emission to occur. Thereafter, by increasing the on-period, the voltage of the capacitor C1 is increased, and the discharge lamp L is turned on.

[0007]

[Problem to be Solved by the Invention] By the way, at the end of a discharge lamp's life, the thermionic emitting material (emitter) coated on the filament scatters and evaporates, so the filament no longer emits thermionic electrons. , changes such as an increase in starting voltage occur due to half-wave discharge and an increase in tube voltage.

When such a discharge lamp at the end of its life is operated using the circuit shown in FIG. 7, the following problems occur. In other words, a discharge lamp at the end of its life has a high tube voltage and a larger equivalent resistance value than a normal lamp, so the resonant frequency f0 of the oscillating circuit consisting of the current limiting choke L1, capacitor C1, and discharge lamp L will be lower than when the normal lamp is lit. Therefore, the switch element Q is set so that the on period is during full lighting.
When Q2 is controlled, the resonant frequency f0 approaches, so that the oscillating current changes to
The current ID of the switch element Q2 has a waveform that returns to zero while it is on.

The voltage across the current-limiting choke L1 has a waveform with a phase lead of 90° relative to the oscillating current, as shown in FIG.
is turned off near its current peak value (Fig. 8(b)), but if it is turned off after reaching near zero as shown in Fig. 9(b), the current limit Chalk L1-2
The next winding voltage has a phase-advanced waveform, and the switching element Q
An attempt is made to turn on the switch element Q1 during the on period of 2, resulting in simultaneous on. Since this simultaneous ON short-circuits the power supply E, a large current flows through the switch element Q1.
, Q2 is destroyed.

The circuit shown in FIG. 10 is a circuit that prevents this simultaneous ON, in which a diode D3 is connected between the base and emitter of the switch element Q1, and the drain of the switch element Q2 is connected to the base of the switch element Q1. While element Q2 is on, the oscillating current is passed through diode D3 →
The voltage flows through the switching element Q2, reverse biasing the base-emitter voltage of the switching element Q1 to the forward voltage of the diode D3, and turning off the switching element Q1. The operating waveform shown in FIG. 9 is the waveform in the circuit shown in FIG. 10, and suppresses simultaneous ON of switch elements Q1 and Q2.

However, even in this circuit, if the waveform causes the current in the switching element Q2 to return to zero, the current in the diode D3 becomes zero, so the current in the switching element Q1 returns to zero.
is not reverse-biased, and the base current is supplied to the switching element Q1 from the secondary winding voltage of the current-limiting choke L1, which may cause simultaneous ON. As a way to prevent this simultaneous on phenomenon that occurs when a discharge lamp at the end of its life is turned on, there is a method to detect a discharge lamp at the end of its life, stop oscillation, raise the oscillation frequency, and reduce the output. The following method has been considered as a method for detecting a discharge lamp at the end of its life.

That is, as shown in FIG. 12, a method for detecting a discharge lamp at the end of its life is to detect an increase in tube voltage. In this method, the lamp voltage detection circuit 6 is used to detect the tube voltage of the discharge lamp L. However, as shown in Figure 11, the tube voltage is temperature dependent, and has the characteristics shown in the figure with respect to changes in tube wall temperature.In order to prevent false detection with a normal lamp, the detection level is set as shown in the figure. Therefore, it is difficult to detect discharge lamps at the end of their lifespan at low temperatures, and it is not possible to prevent the phenomenon of simultaneous turning on at low temperatures.

[0013] A method of detecting by current is also considered, and there is a method of connecting a resistor to the source of the switching element Q2 and detecting by the voltage across the resistor. However, with the current detection method,
There is no big difference between a discharge lamp at the end of its life and a normal discharge lamp.
This was possible by detecting the rush current caused by simultaneous on-currents flowing. This method requires simultaneous on-current to flow at least once for detection, which impairs the reliability of the switching element.

The present invention has been provided in view of the above-mentioned points, and is capable of reliably detecting a discharge lamp at the end of its lifespan.
The present invention provides a discharge lamp lighting device that aims to reduce stress on a switch element without causing simultaneous on-current to flow.

[0015]

[Means for Solving the Problems] The present invention provides a detection means for detecting a change in the on-period of a high-voltage side switching element at the end of the life of a discharge lamp, and an output of the detection means for detecting a change in the on-period of a high-voltage side switching element. A control means for shortening the on-off period is provided.

[0016]

[Function] Therefore, when it is detected from the output of the detection means that the on-period of the high-voltage side switching element changes at the end of the life of the discharge lamp, the on-off period of the low-voltage side switching element is changed by the control means. By making it short, the simultaneous on mode of the switch elements is avoided, and stress on the switch elements such as overcurrent and heat generation is reduced.

[0017]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. The control unit 5 includes an astable multivibrator IC1.
, D-flip-flop IC2, IC3, R-S flip-flop 7, etc. In this circuit, switch elements Q1 and Q2 alternately turn on and off to light the discharge lamp L at high frequency, and the switch element Q1 sends a drive signal synchronized with the voltage generated at the current limiting choke L1 to the secondary winding. The switching element Q2 is a so-called self-excited and other-controlled inverter circuit, which is driven by the control section 5 sending out an ON signal. The circuit consisting of diodes D1 and D2 and capacitors C1 and C2 is a voltage doubler rectifier and smoothing circuit.

The operation of the control section 5 is as follows. As the astable multivibrator IC1, a general-purpose timer IC "555" is used here. D flip-flop (
Hereinafter, IC2 (hereinafter referred to as D-FF) operates as a T flip-flop whose Q output is inverted every time a C input is input. Further, in the D flip-flop IC3, when the R input is at L level and the C input is input, the state of the D input at that time appears as the Q output. The circuit consisting of NOR gates G8 and G9 is an R-S flip-flop 7, and when an H level is input to the S input, the Q output becomes an H level.

The reset circuit 6 is for reliably setting the Q output of the R-S flip-flop 7 to L level, for example, when the power is turned on. First, a case where the discharge lamp L is lit normally will be described. D-FFI
A drive pulse is sent from C2 to turn on and off switch element Q2, but switch element Q1
An inverter gate G2 and an AND gate G1 are provided so that an on signal does not enter the switch element Q2 when the switch element Q2 is on. That is, the switch element Q
1 is in the on state, the resistors R3 and R4 are connected at both ends.
Since high voltage is applied, inverter gate G2
An H level is input to the input.

Therefore, the inverter gate G2 output is:
Since it becomes L level, the L level signal is surely input to the gate of switch element Q2 via AND gate G1. Here, the relationship between the D-FFIC2 output and the inverter gate G2 output is that when the discharge lamp L is lit normally, the period when the inverter gate G2 input is at H level is longer than the period when the D-FFIC2 output is at L level. is set to be longer.

FIG. 2 shows operating waveforms of each part. Here, as shown in FIG. 2C, the time delay between the rise and fall of the input to the inverter gate G2 is caused by a time constant due to the resistors R3 and R4 and the input capacitance of the inverter gate G2. In addition, inverter gate G3 ~
G6 is inserted to provide a delay time so that the D input is slightly delayed with respect to the C input of the D-FFIC3.

As can be seen by referring to the waveform, D-FFI
When the Q output of C2 falls (FIG. 2(b)), the NOR gate G7 sends out a pulse output as shown in FIG. 2(g) (this is because the Q output of D-FFIC2 goes to L level). (The reason why the input of inverter gate G2 becomes H level is because it follows the above time constant.) However, when the output of NOR gate G7 falls, D-F
The D input of FIC3 has inverter gates G3 to G
Since the L level is included due to the delay time due to the delay time caused by 6, the Q output of the D-FFIC3 remains at the L level as shown in FIG. 2(i).

Therefore, since the Q output of the R-S flip-flop 7 is at the L level, the transistor Q3 is turned off, and the current in the current mirror circuit 8 consisting of the transistors Q4 and Q5 is determined only by the resistor R7, and its value is determined as follows. A charging current flows through the capacitor C5, and the oscillation cycle of the astable multivibrator IC1 is determined. Next, a case will be described in which the discharge lamp L reaches the end of its life. FIG. 3 shows operating waveforms comparing the on and off states of the switching elements Q1 and Q2 during normal lighting and at the end of the lamp life. In other words, when the gate signal of the switch element Q2 changes from H level to L level and the switch element Q2 is turned off, the lamp of FIG. It can be seen that at the end of the life (hereinafter referred to as the EMI-less time), the phase of the current of the current limiting choke L1 advances. Then, current limiting choke L1
The phase of the secondary winding voltage also advances, and therefore the on period of the switch element Q1 becomes shorter.

It should be noted that the H period of the gate signal of the switch element Q2 is longer during the emission period than during normal lighting, but this is because the on period of the switch element Q1 is shortened, and the inverter gate in FIG. The H interval of the input of G2 becomes shorter, and as a result, the Q of D-FFIC2 becomes shorter.
This is because the output H period is directly input to the gate of the switch element Q2 via the AND gate G1.

FIG. 4 shows operational waveforms of each part of the control section 5. That is, the on period of the switch element Q1 becomes shorter, and D-F
While the Q output of FIC2 is at L level (Fig. 4(b)),
As shown in FIG. 4(c), the input of inverter gate G2 changes from H level to L level. Then, Figure 4(d) (
f) As shown in (g) and (h), inverter gate G2
Since the output of inverter gate G1 0 is at H level, the output of inverter gate G1 0 is at L level, and the Q output of D-FFIC2 is at L level, the output of NOR gate G7 is at H level.

[0026]The output of the inverter gate G6 is at H level due to the delay, and therefore, the output of the D-FFIC3 is delayed.
When the C input is input, the D input is at H level, so the D
- A pulse output is sent from the Q output of FFIC3 as shown in FIG. 4(i). Therefore, the Q output of the R-S flip-flop 7 is set to H level, and the transistor Q
3 Turn on. Therefore, since the collector current of transistor Q4 becomes determined by the parallel resistance value of resistors R7 and R6, the charging current of capacitor C5 increases, and therefore the astable multivibrator IC1
The oscillation period becomes shorter. Therefore, the operating frequency of the inverter becomes high and the output is limited, so stress such as overcurrent or heat generation can be reduced.

[0027] Furthermore, resistors R3 and R4, and inverter G2
~G6, G1 0, Noah Gate G7, D-FF
The detection means is composed of IC3, R-S flip-flop 7, etc., and also includes a current mirror circuit 8, astable multivibrator IC1, D-FFIC2, and gate G
1 etc. constitute the control means. (Example 2) Example 2 is shown in FIG. Here, the D-FFIC3 is the same as that in FIG. 1, and the difference from FIG. 1 is that an astable multivibrator IC4 and a D flip-flop IC5 are used instead of the reset circuit and the R-S flip-flop.

The operation is as follows. During normal lighting, as explained in the first embodiment, the Q output of D-FFIC3 is always at L level, so no pulse is applied to the C input of D-FFIC5.
The Q output also remains at L level. On the other hand, when the discharge lamp L enters the emissionless state, a pulse is output from the Q output of the D-FFIC3 as shown in Figure 6(b), so when the output of the astable multivibrator IC4 is at H level (Figure 4(a)
)), D-FFIC5 via AND gate G1 1
At this time, the D input is always connected to the H level (Vcc is the control power supply), so the D-FFIC5
An H level is sent from the Q output of , as shown in FIG. 6(e).

However, astable multivibrator IC
At the same time that the output of 4 becomes L level, the R input is input to D-FFIC5 via inverter gate G1 2 (FIG. 6(d)), so D-FFIC5 is reset and the Q output becomes L level. After that, when the output of astable multivibrator IC4 is at H level, D-FFI
When a pulse is sent from the Q output of C3, Fig. 6(e)
As shown in , the Q output of the D-FFIC 5 is set to H level again.

That is, in this embodiment, the astable multivibrator IC4 periodically issues a reset pulse to periodically cancel the frequency increase operation of the inverter. By doing this, for example, when the lamp is normally lit, even if it is mistakenly determined to be in the EMI-RES state due to noise etc., it can immediately return to normal lighting, so it is possible to provide an EMI-RES detection circuit that is resistant to noise etc. become. Moreover, the effect of stress reduction can be expected on the switching elements as well, as in the first embodiment.

[0031]

Effects of the Invention As described above, the present invention includes a detection means for detecting a change in the on-period of the high-voltage side switching element at the end of the life of a discharge lamp, and a detection means for detecting a change in the on-period of the high-voltage side switching element at the end of the life of the discharge lamp, and detecting a change in the on-period of the low-voltage side switching element using the output of this detection means. Since the control means for shortening the on-off period is provided, the on-period of the high-voltage side switch element changes at the end of the life of the discharge lamp by the detection means, thereby making it possible to reliably detect the discharge lamp at the end of its life. If it is detected from the output of the detection means that the on-period of the high-voltage side switch element changes at the end of the life of the discharge lamp, the control means shortens the on-off period of the low-voltage side switch element to control the switching element. This has the effect of avoiding the simultaneous on mode and reducing stress on the switch elements such as overcurrent and heat generation.

[Brief explanation of drawings]

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

FIG. 2 is an operation waveform diagram during normal lighting.

FIG. 3(a) is an operation waveform diagram during normal lighting. (b) is an operation waveform diagram at the end of the lamp life.

FIG. 4 is an operation waveform diagram at the end of the lamp life.

FIG. 5 is a specific circuit diagram of the main part of the second embodiment.

FIG. 6 is an operational waveform diagram of FIG. 5;

FIG. 7 is a specific circuit diagram of a conventional example.

8 is an operational waveform diagram in the normal state of FIG. 7; FIG.

FIG. 9 is an operation waveform diagram at the end of life.

FIG. 10 is a circuit diagram of another conventional example.

FIG. 11 is an explanatory diagram of a conventional example.

FIG. 12 is a circuit diagram of still another conventional example.

[Explanation of symbols]

5 Control section Q1　　High voltage side switch element Q2　Low pressure side switch element L Discharge lamp C3 Capacitor C4 Capacitor L1 Current limiting choke

Claims (1)

[Claims] Claim 1: A pair of switch elements that are turned on and off alternately to a DC power source are connected in parallel, diodes are connected in parallel to both switch elements in opposite directions, and a discharge lamp, a cup, etc. are connected to both ends of the switch element on the high voltage side. A series circuit of a ring capacitor and a current-limiting choke is connected, a capacitor is connected to both ends of the discharge lamp, and a control section is provided to control the on period of the low-voltage side switching element, and the high-voltage side switching element is connected to the above-mentioned current-limiting choke. In a discharge lamp lighting device that is driven by a secondary winding voltage provided in 1. A discharge lamp lighting device comprising: control means for shortening the on-off period of a low-voltage side switching element.