JP4069650B2 - Discharge lamp lighting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a discharge lamp lighting device having a function of detecting a phenomenon at the end of the life of a discharge lamp and protecting a circuit.
[0002]
[Prior art]
FIG. 6 shows a circuit diagram of a conventional discharge lamp lighting device. This discharge lamp lighting device includes an inverter circuit 1 including a pair of switching elements Q1 and Q2 connected in series between both ends of a DC power supply E, a coupling capacitor C0, and a switching element Q2 via the capacitor C0. And a load circuit 2 connected to both ends. The load circuit 2 includes a resonance choke coil L connected in series with the capacitor C0 and a pair of filaments, and a discharge lamp La connected to both ends of the switching element Q2 via the capacitor C0 and the choke coil L. And a capacitor C2 for energizing the resonance and filament preheating current connected to the non-power supply side of both filaments of the discharge lamp La. C1 is a capacitor connected in parallel with the switching element Q1 or Q2 for the purpose of reducing switching loss and noise of the switching elements Q1 and Q2, and is connected in parallel with the switching element Q1 here. A control circuit 6 for alternately turning on / off the switching elements Q1, Q2 is provided. According to the discharge lamp lighting device configured as described above, the power of the DC power source E is converted into high-frequency power and supplied to the discharge lamp La by the on / off and resonance of the switching elements Q1 and Q2, and the discharge lamp La After the two filaments are preheated, the discharge lamp La is started and turned on.
[0003]
By the way, in the discharge lamp lighting device having the above-described configuration, a fluorescent lamp is used as the discharge lamp La. In general, in the case of a fluorescent lamp, the filament's electron-emitting substance (referred to as an emitter) is consumed at the end of its life. The phenomenon of half-wave discharge may occur due to so-called single-sided Emires, where only the electron-emitting material is consumed, and the tube voltage increases due to so-called double-sided Emires, where the electron-emitting material on both sides of the filament is consumed. A phenomenon may occur. Alternatively, a so-called no-load state may occur due to filament breakage of the discharge lamp.
[0004]
For this reason, in the discharge lamp lighting device, a resistor R1 is connected in series with the switching element Q2, and a current flowing through the switching element Q2 is detected by the resistor R1, and is configured by a diode D1, resistors R2, R3, and a capacitor C5. The peak voltage is held by the circuit unit that is input to the abnormality detection means 5, and when the voltage exceeds the predetermined voltage, an abnormality detection signal is output from the abnormality detection means 5 to the control circuit 6, and the output of the inverter circuit 1 is reduced or stopped. This protects the discharge lamp lighting device.
[0005]
Hereinafter, the operation of the switching current detector 3 in the end-of-life state and the no-load state will be described. FIG. 7 shows a resonance curve (the voltage of the capacitor C2) when the impedance of the lamp La changes. The resonance curve changes from a → b → c as the impedance of the lamp La increases, and the operating point changes. Changes from the slow phase toward the same phase. In the figure, fs is an operating frequency of the inverter circuit 1 and d is a resonance curve at no load.
[0006]
FIG. 8 shows waveforms of the voltage V _DS across the switching element Q2 and the switching current _ID flowing through the switching element Q2. During the period Tf in which the switching current _ID flows in the negative direction, the flywheel current due to the resonance circuit flows through the parasitic diode (anti-parallel diode) of the switching element Q2 made of MOSFET. (A), (b), and (c) of FIG. 8 correspond to the resonance curves a, b, and c of FIG. 7, respectively, and the switching current _ID is a flywheel current as the impedance of the lamp La increases. _{Decreases and} the peak value of the switching current _ID increases.
[0007]
Here, as shown in FIGS. 8B and 8C, the steep current generated when the switching current _ID starts to flow in the positive direction is the charging current of the capacitor C1 in FIG. When the switching element Q1 changes from on to off, the charging current of the capacitor C1 flows as part of the resonance current, and the falling slope of V _DS is smoothed. When the switching element Q2 changes from on to off The discharge current of the capacitor C1 as a part of the resonance current flows to smooth the rising slope of V _DS . This charging / discharging current flows as a steep charging / discharging current via the switching element Q2 when the switching element Q2 is turned on unless charging / discharging is completed in the period Tf in which the flywheel current flows. That is, as the flywheel current decreases, the amount that can be charged in the capacitor C1 decreases, and the remaining amount is fully charged by the forward current to the switching element Q2, so that the current flows to the switching element Q2 as the flywheel current decreases. A steep current has a large peak and a wider width.
[0008]
The end-of-life state is a phenomenon in which the equivalent impedance of the lamp La increases, so that as shown in FIGS. 8B and 8C, the peak value of the resonance current increases and the steepness from the capacitor C1 increases. The current also has a large peak and a wider width. In the no-load state, as shown in FIG. 9, since the current (resonant current) to the load disappears, all the charging current to the capacitor C1 flows through the switching element Q2, and the peak is the largest and the width Wide charging current flows. Thus, the switching current detection unit 3 in FIG. 6 detects that the current flowing through the switching element Q2 increases when the end of life state or no load state is reached.
[0009]
[Problems to be solved by the invention]
However, the impedance of the discharge lamp changes depending on the ambient temperature or the like, and there may occur a case where the difference in impedance from the normal state does not become large even at the end of life. That is, there is a problem that the difference between the currents flowing through the switching element Q2 is small between the normal state and the end of life state, and the configuration of the switching current detection unit 3 in FIG. 6 cannot accurately detect the end of life state.
[0010]
The present invention has been made in view of these points, and an object of the present invention is to provide a discharge lamp lighting device that reliably detects a phenomenon at the end of the life of a discharge lamp with a simple configuration and protects the circuit. .
[0011]
[Means for Solving the Problems]
According to the first aspect of the present invention, in order to solve the above-mentioned problem, as shown in FIG. 1, a pair of switching elements Q1, Q2 connected in series between both ends of the DC power supply E and the DC power supply E as shown in FIG. An inverter circuit 1 comprising: a load circuit 2 connected in parallel with one of the pair of switching elements Q1 and Q2, and a first capacitor C1 connected in parallel with at least one of the pair of switching elements Q1 and Q2. The first resistor R1 inserted in series between the switching element Q2 on the low potential side of the pair of switching elements Q1 and Q2 and the ground of the DC power supply E, and the output of the inverter circuit 1 is reduced or stopped. And an abnormality detection means 5 for outputting an abnormality detection signal for causing the load circuit 2 to be arranged in parallel with the inductor L, the second capacitor C2, and the second capacitor C2. Ri Do from the resonant circuit of the discharge lamp La to be connected, the first connected to the resistor R1 in parallel differentiating circuit 4, abnormality detection from the abnormal detection unit 5 and the output of the differentiating circuit 4 becomes equal to or larger than a predetermined value A discharge lamp lighting device that outputs a signal , wherein the abnormality detection means 5 outputs an abnormality detection signal with an input of a predetermined value or less, and as shown in FIG. 4, the abnormality detection means 5 has an input of a predetermined value or less. An abnormality detection signal is output, a smoothing voltage charged in the third capacitor C3 is input to the abnormality detection means 5, and an output of the differentiation circuit 4 is input to a control electrode of the third switching element Q3. When the output of the differentiating circuit 4 exceeds a predetermined value, the smoothing voltage charged in the third capacitor C3 is discharged by the third switching element Q3, and the input of the abnormality detecting means 5 is set to a predetermined value or less. Features It is intended to.
[0012]
According to the invention of claim 2 , as shown in FIG. 5, a second resistor R6 is inserted between the third switching element Q3 and the third capacitor C3, and the third capacitor C3 and the third capacitor C3 It has a time constant circuit composed of a second resistor R6.
According to the invention of claim 3 , as shown in FIG. 5 , when the output of the differentiation circuit 4 is intermittent for a predetermined period and becomes a predetermined value or more, an abnormality detection signal is output from the abnormality detection means 5. To do.
In the following first and second embodiments, a configuration which is a premise of the present invention will be described. The third embodiment will explain the invention of claim 1, and the fourth embodiment will explain the invention of claims 2 and 3.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
(Embodiment 1)
FIG. 1 shows a first embodiment. The circuit of FIG. 1 differs from the circuit of FIG. 6 only in the configuration of the switching current detector 3, and the other configurations are the same as those in FIG. As shown in FIG. 1, this embodiment is characterized in that a differentiating circuit 4 including a capacitor C4 and a resistor R4 is connected in parallel with a resistor R1 that detects a current flowing through the switching element Q2. That is, the current flowing through the switching element Q2 is focused on the fact that a steep charge / discharge current of the capacitor C1 flows at the end of the lifetime, etc., so that the abnormality can be reliably detected by using the differentiation circuit 4. .
[0014]
FIG. 2 shows the output of the differentiation circuit 4, that is, the voltage waveform at the connection point of the capacitor C4 and the resistor R4. FIGS. 2 (a) and 2 (b) are shown in FIGS. 7 (a) and 8 (b). Each is a corresponding waveform. The output of the differentiation circuit 4 is exactly the waveform obtained by differentiating the waveform of the current _ID of the switching element Q2, and the voltage value in the case of (a) in which the normal resonance current flows is low, but it is like the charge / discharge current of the capacitor C1. The voltage value in the case of (b) where a steep current flows is high.
[0015]
That is, by providing the differentiation circuit 4 in the switching current detection unit 3, it is possible to reliably detect the charge / discharge current of the capacitor C1, and the output of the differentiation circuit 4 is input to the abnormality detection means 5 so that it exceeds the predetermined voltage. If this is the case, an abnormality detection signal can be output from the abnormality detection means 5 to the control circuit 6, and the discharge lamp lighting device can be protected by reliably reducing or stopping the output of the inverter circuit 1 at the end of life or in an abnormal state of no load. is there.
[0016]
The control circuit 6 oscillates the switching frequency, the drive circuit 8 that alternately turns on and off the switching elements Q1 and Q2 by the output of the oscillator 7, and the output of the oscillator 7 when the abnormality detection signal is input. Alternatively, the output control unit 9 is configured to control the switching frequency to be higher. However, the present invention is not limited to this. For example, in the self-excited inverter circuit, one of the switching elements receives an abnormality detection signal. The output may be stopped by always turning off the power.
[0017]
(Embodiment 2)
FIG. 3 shows a second embodiment. This embodiment is an example in which the abnormality detection means 5 is provided with a timer function in the embodiment of FIG. Since the differentiation circuit 4 is very sensitive to voltage changes, it is important to consider external noise and the like. Therefore, in the present embodiment, an abnormality detection signal is output when a detection signal continuous in synchronization with the oscillation cycle of the inverter circuit 1 is input to the abnormality detection means 5.
[0018]
Details will be described below. The output of the differentiation circuit 4 is input to the comparator 51, and if the voltage is equal to or higher than the predetermined voltage Vref, the output of the comparator 51 becomes High, and the High signal is input to the input of the D-flip flop 52. On the other hand, the rising edge of the signal obtained by delaying the output of the drive circuit 8 to the switching element Q2 by the delay circuit 53 becomes the clock signal CLK of the D-flip flop 52. The delay time by the delay circuit 53 is about 300 nsec. That is, the clock signal is given at the timing when the charging current of the capacitor C1 flows. Therefore, when the charging current of the capacitor C1 flows through the switching element Q2 at the end of the lifetime, the output of the D-flip flop 52 becomes High output, and the stop signal of the counter 55 becomes Low by the inverting circuit 54. Since the clock signal to the counter 55 is the same as the clock signal to the D-flip flop 52, if the High output of the D-flip flop 52 continues for a predetermined period determined by the counter 55, the output of the abnormality detection means 5 is output. The High signal is output to the control circuit 6 as follows. That is, when the output of the differentiating circuit 4 is intermittently and exceeds a predetermined voltage for a predetermined period determined by the counter 55, a High signal is output as an output of the abnormality detecting means 5.
[0019]
As described above, in this embodiment, since the abnormality detection means 5 has a timer function, there is no malfunction due to external noise or the like, and the output of the inverter circuit 1 is reliably reduced in an abnormal state such as the end of life or no load. Or it can be stopped to protect the discharge lamp lighting device.
[0020]
(Embodiment 3)
FIG. 4 shows a third embodiment. The present embodiment is an example in which an abnormality detection signal is output to the control circuit 6 when the input of the abnormality detection means 5 becomes a predetermined voltage or less. The control electrode (base) of the switching element Q3 receives the output of the differentiation circuit composed of the capacitor C4 and the resistor R4. When the output of the differentiation circuit becomes equal to or higher than the ON voltage of the switching element Q3, the switching element Q3 is turned on. To do. On the other hand, the smoothing voltage charged in the capacitor C3 is input from the voltage source E ′ through the resistor R5 to the input of the abnormality detecting means 5. When the output of the differentiating circuit becomes equal to or higher than the ON voltage of the switching element Q3, the switching element Q3 is turned ON to discharge the electric charge of the capacitor C3, and the input of the abnormality detecting means 5 becomes equal to or lower than a predetermined value, so Is output. The voltage source E ′ may use, for example, the control power supply voltage Vcc of the control circuit 5 or the drive circuit output to the switching element Q2, and any voltage generator that generates a voltage higher than a predetermined voltage as an average value can be used.
[0021]
(Embodiment 4)
FIG. 5 shows a fourth embodiment. In this embodiment, a resistor R6 is added between the capacitor C3 and the switching element Q3 of the third embodiment, and a discharge time constant circuit is configured by the capacitor C3 and the resistor R6. That is, this is an example in which the switching current detector 3 is provided with a timer function so that it is less susceptible to malfunctions caused by external noise or the like. When the output of the differential circuit composed of the capacitor C4 and the resistor R4 becomes equal to or higher than the on-voltage of the switching element Q3, the switching element Q3 is turned on and the capacitor C3 is discharged. At this time, the voltage of the capacitor C3 does not immediately become lower than the predetermined value due to the time constant of the resistor R6 and the capacitor C3 to the extent that the switching element Q3 is turned on once due to external noise or the like.
[0022]
On the other hand, when the switching element Q3 is repeatedly turned on / off continuously at the end of its life, etc., if the amount of discharge through the resistor R6 is increased relative to the amount of charge from the resistor R5, the voltage of the capacitor C3 decreases. Thus, it can be set to a predetermined value or less.
[0023]
As described above, since the switching current detector 3 has a timer function, there is no malfunction due to external noise or the like, and the output of the inverter circuit 1 is reliably reduced or stopped in an abnormal state such as the end of life or no load. The discharge lamp lighting device can be protected. Similarly to the second embodiment, if the abnormality detection means 5 is also provided with a timer function, a discharge lamp lighting device having further excellent noise resistance can be provided.
[0024]
【The invention's effect】
According to the invention of claim 1, one switching element in the half-bridge inverter circuit is provided with a parallel capacitor, and this parallel capacitor is charged and discharged by a current flowing through a load circuit including an LC resonance circuit and a discharge lamp. In a discharge lamp lighting device that reduces switching loss and noise by mitigating steep changes in voltage, a phenomenon in which the charging current of the parallel capacitor flows through the switching element when the lamp impedance becomes large at the end of the lifetime, etc. Is detected by a differentiating circuit, and the output of the inverter circuit is reduced or stopped. Therefore, there is an effect that the discharge lamp lighting device can be protected by reliably detecting an abnormal state with a simple circuit configuration. According to the first to third aspects of the present invention, the abnormality detection signal is obtained by accumulating the output of the differentiating circuit, so that it is possible to prevent malfunction due to a single external noise.
[Brief description of the drawings]
FIG. 1 is a circuit diagram according to a first embodiment of the present invention.
FIG. 2 is an operation waveform diagram according to the first embodiment of the present invention.
FIG. 3 is a circuit diagram of a main part of a second embodiment of the present invention.
FIG. 4 is a main part circuit diagram of Embodiment 3 of the present invention.
FIG. 5 is a main part circuit diagram of Embodiment 4 of the present invention.
FIG. 6 is a circuit diagram of a conventional discharge lamp lighting device.
FIG. 7 is a characteristic diagram showing a relationship between a switching frequency and an output in a conventional example.
FIG. 8 is a waveform diagram showing voltage and current of a conventional switching element.
FIG. 9 is a waveform diagram showing the voltage and current of the switching element when no load is applied in the conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Inverter circuit 2 Load circuit 3 Switching current detection part 4 Differentiation circuit 5 Abnormality detection means 6 Control circuit

Claims (3)

A DC power supply, an inverter circuit comprising a pair of switching elements connected in series between both ends of the DC power supply, a load circuit connected in parallel with any one of the pair of switching elements, and at least one of the pair of switching elements A first capacitor connected in parallel with the other, a first resistor inserted in series between the switching element on the low potential side of the pair of switching elements and the ground of the DC power supply, and the output of the inverter circuit It includes reducing or an abnormality detection means for outputting an abnormality detection signal for stopping the load circuit Ri Do from the resonance circuit with the discharge lamp connected in parallel to the inductor and a second capacitor and a second capacitor, the second When a differential circuit is connected in parallel with the resistor 1 and the output of the differential circuit exceeds a predetermined value, the abnormality detection means sends an abnormality detection signal. The discharge lamp lighting device for outputting the abnormality detection means outputs an abnormality detection signal in the following input predetermined value, said abnormality detection means smoothed voltage charged in the third capacitor is input, the The output of the differentiating circuit is input to the control electrode of the third switching element. When the output of the differentiating circuit exceeds a predetermined value, the smoothing voltage charged in the third capacitor is discharged by the third switching element. A discharge lamp lighting device characterized in that an input of the abnormality detection means is set to a predetermined value or less . 2. A time constant circuit comprising a second resistor inserted between the third switching element and the third capacitor and configured by the third capacitor and the second resistor. 1 a discharge lamp lighting device according. 3. The discharge lamp lighting device according to claim 1, wherein when the output of the differentiating circuit is intermittent for a predetermined period and becomes equal to or greater than a predetermined value, an abnormality detection signal is output from the abnormality detection means.

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