JPH081834B2 - Discharge lamp lighting device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a discharge lamp lighting device for lighting a discharge lamp such as a high pressure discharge lamp having a large impedance change, and relates to reduction in size and weight.

[Background technology]

Since the discharge lamp has a negative voltage-current characteristic, a stabilizing means is required to maintain lighting. In the conventional general lighting device, the stabilizing means is composed of a choke coil, a transformer or the like alone or in combination thereof, so that both size and weight are large. In order to solve this problem, there has been proposed a discharge lamp lighting device that uses a semiconductor element to perform high-frequency switching to reduce the size and weight.

FIG. 5 shows a circuit diagram of an example of a discharge lamp lighting device of a DC chopper system using a semiconductor that has been conventionally proposed. In FIG. 5, 1 and 2 are DC power supply voltage V
A terminal to which _DC is applied, Q ₆ is a transistor, R _S is a current limiting resistor, 3 is a transistor Q ₆ control circuit, 4 is a current limiting transformer, and 5 and 6 are primary and secondary of the current limiting transformer 4. Winding, D ₃ is a freewheeling diode, C ₂ is a capacitor, LA is a load and is a high pressure discharge lamp. The control circuit 3 operates depending on the current detection result by the current limiting resistor R _S , keeps the transistor Q ₆ off until the current in the secondary winding 6 becomes zero, and the current in the secondary winding 6 becomes Transistor after reaching zero
It operates so as to turn on for a period until the current I _{Q6 of} Q ₆ reaches a predetermined value.

FIG. 6 is a high pressure discharge lamp in the discharge lamp lighting device of FIG.
FIG. 7 is a waveform diagram showing current and voltage waveforms of various portions of LA in a steady state. Hereinafter, the circuit operation of the discharge lamp lighting device of FIG. 5 in the steady state will be described in detail with reference to this figure. At time t ₁ , transistor Q ₆ is forward biased, causing transistor Q ₆ 's collector
The emitter-to-emitter voltage V _CE becomes zero, and a gradually increasing current I _Q6 flows through the transistor Q ₆ . When the voltage across the current limiting resistor R _S reaches a predetermined value at time t ₂ , the base current of the transistor Q ₆ becomes zero. Therefore, transistor Q ₆
Is turned off, and the current _IQ6 becomes zero. When the current I _Q6 becomes zero, an induced voltage is generated in the primary winding 5 of the current limiting transformer 4 and the diode D ₃ conducts and the current I gradually decreases.
_D3 flows. Then, at the time t ₁ when the current I _D3 becomes zero, the transistor Q ₆ is forward-biased again, and the above-described operation is repeated, so that the high-pressure discharge lamp LA receives the current I _LA.
Flows, and the high pressure discharge lamp LA keeps lighting. In this case, the switching frequency f ₁ of transistor Q ₆ is
The period of the I _LA when the T _1, the 1 / T _1.

FIG. 7 is a high pressure discharge lamp in the discharge lamp lighting device of FIG.
It is a wave form diagram which shows the electric current waveform of each part immediately after starting LA. Hereinafter, the circuit operation of the discharge lamp lighting device of FIG. 5 immediately after starting will be described in detail with reference to this drawing. The high-voltage discharge lamp LA has a low lamp voltage V _LA of about 10 to 30 V immediately after starting, and the lamp voltage V _LA increases with time. Immediately after this start becomes a state close to almost short-circuited, the slope of the current becomes steeper, t ₁ -t ₂ between narrows the voltage of the resistor R _S is increased. On the other hand, t ₂ −t ₁
Is the time constant T _LR of the circuit represented by L / R, where L is the inductance of the primary winding 5 and R is the equivalent resistance of the high-pressure discharge lamp LA.
I _D1 is decreasing. At the time of starting, since the equivalent resistance R is small, the time constant T _LR is large, the period T ₂ is large, and the lighting frequency f ₂ (= 1 / T ₂ ) at the time of starting is very low.

 Others are the same as those described in the explanation of the steady state.

FIG. 8 is a diagram showing the relationship between the lamp voltage V _LA and the lighting frequency f. In FIG. 8, f ₂ is the frequency at the time of starting, f ₁
Is the frequency at steady state, f _LC is the resonance frequency of the capacitor C ₂ and the inductance L of the primary winding 5, It is represented by. At startup, the lamp voltage V _LA is small and the time constant T
_{Since TR} is large, the lighting frequency f ₂ at the start is lower than the lighting frequency f ₁ at the steady state. Then, the lighting frequency f rises from the lighting frequency f ₂ at the time of starting to the lighting frequency f ₁ at the steady state with the rise of the lamp voltage V _LA , but in the process, the resonance frequency f _LC may pass through. At this time overcurrent flows through the transistor Q _6, the high frequency component is contained more increased ripple in the lamp current I _LA, arc becomes unstable, the problems will be caused disadvantages that the lamp current I _LA decreases there were.

[Object of the Invention]

An object of the present invention is to provide a discharge lamp lighting device capable of stably shifting a discharge lamp such as a high pressure discharge lamp having a large impedance change from a starting state to a steady state.

[Disclosure of Invention]

The discharge lamp lighting device of the present invention comprises a high pressure discharge lamp having a large impedance change in the period from immediately after lighting to stable lighting, an inductance element connected in series to the high pressure discharge lamp, and a capacitor connected in parallel to the high pressure discharge lamp. And a control circuit that changes the switching frequency of the semiconductor switching element according to the change in the impedance of the high-voltage lamp, and is stable immediately after lighting. The resonance frequency of the inductance element and the capacitor is not included in the change range of the switching frequency of the semiconductor switching element during the period until lighting.

In this way, the high frequency output is applied from the semiconductor switching element to the resonance circuit composed of the discharge lamp, the inductance element and the capacitor to turn on the discharge lamp, and the switching frequency of the semiconductor switching element is changed according to the impedance change of the discharge lamp. In the discharge lamp lighting device as described above, since the resonance frequency of the inductance element and the capacitor is not included within the change range of the switching frequency of the semiconductor switching element, the discharge lamp is changed from the start to the steady state like a period. When the impedance of the discharge lamp changes significantly, the switching frequency changes without passing through the resonance frequency, does not resonate at high frequency output, no overcurrent flows through the semiconductor switching element, and the lamp current Of high frequency ripple The amount of electricity does not increase, the arc can be stabilized, and sudden changes in the lamp current can be prevented, and problems such as extinction can be eliminated, and the discharge lamp can be stabilized from the start to the steady state. Can be transferred.

Embodiment An embodiment of the present invention will be described with reference to FIGS. In this discharge lamp lighting device, as shown in FIG. 1, transistors Q _{1 to} Q ₄ are connected in a bridge shape, and transistors D ₂ and Q ₄ are connected to diodes D ₁ and D ₂ via a current detection resistor R _0. Connected in parallel, and connect a choke coil L between the connection point of transistors Q ₁ and Q _{2 and} the connection point of transistors Q ₃ and Q _4.
1 and high pressure discharge lamp LA series circuit is connected, high pressure discharge lamp L
The capacitor C ₁ is connected to A. 8 is a control unit for controlling on and off of the transistor Q ₁ to Q ₄ based on the voltage drop across the current detection resistor R _0.

FIG. 3A is a timing chart showing the operation of each part of FIG.

The operation of the circuit of FIG. 1 will be described below with reference to this figure.

In this discharge lamp lighting device, the transistors Q ₂ and Q ₄ are alternately turned on and off at a cycle T ₁ (several hundred Hz, for example), and the transistor Q ₄
Transistor Q ₁ is the period T ₂ (for example, when but became ON
It turns on / off (variable duty ratio on / off operation) at about 50 KHz), and when the transistor Q ₂ turns on, the transistor Q ₃ turns on / off similarly (not shown). In this case, the control circuit 8 turns on the transistor Q ₁ again when the current of the diode D ₁ becomes zero based on the voltage drop of the current detection resistor R ₀ , and the current of the diode D ₂ becomes zero. Then turn on transistor Q ₃ again.

In FIG. 3A, the transistor Q ₁ is turned on between t _{1 and} t ₂ , and the circuit of 2-Q ₁ −L ₁ −LA, C ₁ −Q ₄ −1 is formed during this period and the transistor Q ₁ is connected to the transistor Q ₁ . current I _Q1 flows, energy is accumulated in the choke coil L _1. In between following t ₂ -t _3, the transistor Q ₁ is turned off, L ₁ -LA, energy of the choke coil L ₁ in the circuit of C ₁ -Q ₄ -D ₁ is released. I
_D1 is a current flowing through the diode D ₁ at this time, I _L1 is the current flowing through the choke coil L _1, the I _LA is the lamp current.
Then, at time t ₃ when the current I _D1 flowing through the diode D ₁ becomes zero, the transistor Q ₁ is turned on again, and the above-mentioned operation is repeated (a positive half cycle of the lamp current I _LA ).

When such an operation is performed, 2-Q ₁ − at the time of t ₃ −
D surge current does not flow due to circuit ₁ -1.

The same applies when the transistors Q ₂ and Q ₃ are operating (the negative half cycle of the lamp current L _LA ).

FIG. 3B is a diagram showing a current waveform of each part when the transistors Q ₁ and Q ₄ are operating. In the figure, I _C1 is the current of the capacitor C ₁ . Current in choke coil L ₁ I _L1
Shunts into the lamp currents I _LA and I _C1 , but the capacitor C ₁
Has a low impedance at high frequencies, and almost all high frequency components flow to the capacitor C ₁ . The lamp current I _LA has a waveform in which a high frequency is superimposed on a direct current when viewed in a short time.
On the other hand, instantaneously, at time t ₁ , the current I _L1 is zero, the current flowing into the circuit of the high pressure discharge lamp LA and the capacitor C ₁ is zero, and the charge of the capacitor C ₁ is high pressure discharge lamp LA. Will be released to. That is, at time t ₁ , L _L1 = 0
Then, I _C1 = I _LA . Further, at time t ₄ , I _C1 = 0, and I _L1
= I _LA . Time t ₅ is the same as time t ₄ .

By such an operation, each transistor Q ₁ , Q ₃ ,
Switching current can be reduced without surge current flowing through D ₁ and D _2, and a waveform with few high-frequency ripples can be obtained in the lamp current I _LA , causing arc fluctuations in the high-pressure discharge lamp LA due to the acoustic resonance phenomenon. There is a case where the lighting is maintained stably without being caused.

Switching operation of the transistor Q ₁ to Q ₄ are, at the transition from the start to the steady state, the impedance R of the high pressure discharge lamp LA gradually increases, the timing of current I _D1, I _D2 becomes zero Gradually faster, transistor
The operating frequencies of Q ₁ and Q ₃ , that is, the lighting frequency f is lowest at the time of starting and gradually increases toward a steady state. In this case, choke coil L ₁ and capacitor
Resonant frequency of C ₁ Is set to be lower than the lighting frequency f ₁ at the start, as shown in FIG.

As a result of such a configuration, when the high pressure discharge lamp LA shifts from the starting state to the steady state, the lighting frequency f becomes the resonance frequency.
f _LC ′ no longer matches and the load circuit (L ₁ , C ₁ , L
The impedance of A) does not become extremely low, and overcurrent flows through the transistors Q _{1 to} Q ₄ , and the lamp current I _ILA
It is possible to prevent the ripple from increasing due to the high frequency component contained in the arc, and therefore the arc instability and lamp current.
It is possible to prevent the reduction of I _LA , and it is possible to stably shift the high pressure discharge lamp LA from the starting state to the steady state.

Next, the configuration and operation of the control unit 8 will be described with reference to FIG. In FIG. 2, the oscillating circuit 11 oscillates at several hundred Hz, and the flip-flop circuit 10 takes out two signals to obtain the reference drive signals of the positive half cycle and the negative half cycle of the lamp current I _LA . This signal is a base drive circuit 7 for transistors Q ₂ and Q ₄ that turn on and off at several hundred Hz.
Send to. On the other hand, a transistor Q that turns on and off at several tens of KHd
_1, to the base drive circuit 9 of Q _3, timer (IC555: μPC
1555: manufactured by NEC) I ₁ output signal and flip-flop circuit 10
Thus, a signal obtained by synthesizing the output signal of and the AND elements I ₃ and I ₄ is given.

The current detection resistor R ₀ detects the currents I _D1 and I _D2 of the diodes D ₁ and D ₂ , and the comparator I ₂ detects the voltage drop and the reference voltage V _REF.
Is compared with voltage V _R7 divided by resistors R ₆ and R ₇ , and if the voltage across current detection resistor R ₀ is higher than voltage V _R7 , comparator I
The output of ₂ goes "H", turning on transistor Q ₅ . The terminal of the timer I ₁ is a reset terminal, and when the transistor Q ₅ is turned on, the oscillation by the resistors R ₁ , R ₂ and the capacitor C ₂ is stopped. That is, when the current I _D1 or I _D2 is flowing,
The output of the comparator I ₂ turns on the transistor Q ₅ and works resetting.When the current I _D1 or I _D2 becomes almost zero, the transformer Q ₅ turns off and the resistors R ₁ , R ₂ and the capacitor C ₂ When the oscillation starts due to, the output terminal of the timer I ₁ becomes "H" and the voltage of the capacitor C ₂ becomes (2/3) V _CC , the output terminal becomes "L". This time the transistor
It corresponds to the on-time of Q ₁ or Q ₂ . Timer I ₁ is operating as an astable multivibrator, but R ₁ >> R ₂ ,
The “L” time of the output terminal is short because it is approximately determined by the time constant of the C ₂ −R ₂ −− circuit, but once the output terminal becomes “L”, the transistors Q ₁ and Q ₂ of the main circuit are Since the currents I _D1 and I _D2 flow when turned off, the transistor Q ₅ turns on, the timer I ₁ does not oscillate, and the output terminal remains at L. Therefore, the time when the output terminal is "H" is determined by the resistors R ₁ , R ₂ and the capacitor C ₂ , and the time when the output terminal is "L" is the current I _D1 , I _D2.
Is the time until becomes zero.

In the above embodiment, the resonance frequency f _LC ′ is set lower than the lighting frequency f ₂ at the start, and the storefront frequency f due to the impedance increase of the high pressure discharge lamp LA when the high pressure discharge lamp LA shifts from the start to the steady state. However, the same effect can be obtained by skipping the resonance frequency f _LC ′ and changing the frequency when the lighting frequency f shifts from f ₂ to f ₁ .

Further, the present invention can be applied to both a DC chopper type and an AC chopper type discharge lamp lighting device.

〔The invention's effect〕

In the discharge lamp lighting device of the present invention, a high frequency output is applied from a semiconductor switching element to a resonance circuit composed of the discharge lamp, an inductance element and a capacitor to turn on the discharge lamp, and the semiconductor switching element of the semiconductor switching element is changed according to the impedance change of the discharge lamp. In the discharge lamp lighting device that changes the switching frequency, since the resonance frequency of the inductance element and the capacitor is not included in the change range of the switching frequency of the semiconductor switching element, the discharge lamp changes from the start to the steady state. In the case where the impedance of the discharge lamp largely changes as in the period of, the switching frequency does not pass through the resonance frequency, does not resonate at high frequency output, and the overcurrent does not flow in the semiconductor switching element. , Again during lamp current The high-frequency ripple content does not increase, the arc can be stabilized, and sudden changes in the lamp current can be prevented, so that problems such as extinction can be eliminated, and the discharge lamp can be stabilized from the start to the steady state. Can be moved to.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is a detailed circuit diagram of a main portion thereof, and FIGS. 3A and 3B are respectively a first circuit diagram.
FIG. 4 is a waveform diagram of each part of the figure, FIG. 4 is a diagram showing the relationship between the lamp voltage and the lighting frequency in the circuit of FIG. 1, FIG. 5 is a circuit diagram of a conventional discharge lamp lighting device, and FIG. FIG. 7 is a waveform diagram of each part during steady lighting of the circuit, FIG. 7 is a waveform diagram of each part immediately after the circuit of FIG. 5 is started, and FIG. 8 is a diagram showing the relationship between the lamp voltage and the lighting frequency in the circuit of FIG. is there. LA ...... high pressure discharge lamp, Q _1, Q ₃ ...... transistor (semiconductor switching devices), L ₁ ...... choke coil (inductance element), C ₁ ...... capacitor, D _1, D ₂ ...... diode

Claims (4)

[Claims] 1. A resonance circuit comprising a high-pressure discharge lamp having a large impedance change during a period from immediately after lighting to stable lighting, an inductance element connected in series to the high-pressure discharge lamp, and a capacitor connected in parallel to the high-pressure discharge lamp. A semiconductor switching element that gives a high-frequency output to the resonance circuit, and a control circuit that changes the switching frequency of the semiconductor switching element in accordance with a change in impedance of the high-pressure discharge lamp, from immediately after lighting until stable lighting A discharge lamp lighting device in which a resonance frequency of the inductance element and the capacitor is not included in a change range of a switching frequency of the semiconductor switching element in a period. 2. A semiconductor switching element comprises four semiconductor switching elements, first to fourth, and a series circuit of first and second semiconductor switching elements and a third and fourth semiconductor switching element between both ends of a DC power supply. A series circuit of semiconductor switching elements is connected in parallel in this arrangement, and resonance occurs between a connection point of the first and second semiconductor switching elements and a connection point of the series circuits of the third and fourth semiconductor switching elements. The discharge lamp lighting device according to claim (1), wherein a circuit is connected. 3. A first and a second diode are respectively connected in anti-parallel to a second and a fourth semiconductor switching element, and the second and the fourth semiconductor switching element are alternately driven at a low frequency to drive the fourth semiconductor switching element. The first semiconductor switching element is driven at a high frequency during the ON period of the semiconductor switching element, and the third semiconductor switching element is driven at a high frequency during the ON period of the second semiconductor switching element. The discharge lamp lighting device according to the item. 4. The control circuit, when a predetermined time elapses after operating the first semiconductor switching element, shuts off the first semiconductor switching element and the induced current flowing through the first diode becomes substantially zero. The first semiconductor switching element is re-conducted, and the third semiconductor switching element is shut off after a lapse of a certain time after the third semiconductor switching element is operated, so that the induced current flowing through the second diode becomes substantially zero. When it comes to the third
The discharge lamp lighting device according to claim (3), wherein the semiconductor switching element is re-energized.