JP3051753B2 - Discharge lamp lighting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a device for lighting a discharge lamp such as a fluorescent lamp at a high frequency.

<Prior Art> It is well known that lighting a discharge lamp such as a fluorescent lamp at a high frequency makes it possible to reduce the size and weight of a lighting device and improve luminous efficiency.

As a lighting device of this type, there is one using a so-called one-stone self-excited inverter circuit as shown in FIG. 8, for example. This connects the rectifier smoothing capacitor C ₁₁ to the RF ₂ which is connected to a commercial AC power source 11, a DC power supply circuit 12 to output the rectified and smoothed DC voltage, between which the output terminals, resonance 1 of the capacitor C ₁₂ and the oscillation transformer T ₂
A parallel circuit of primary winding T _2a is connected via the collector-emitter of the switching transistor Q _2, the primary winding T
Preheating capacitor C between a pair of electrodes Fa and Fb between terminals _2a
Discharge lamp FL ₂ with ₁₃ inserted, one choke coil
_11, the other is connected via a capacitor C ₁₄ for AC coupling, the resistance of the one end of the base winding T _2b of the oscillation transformer T ₂ R
Switching transistor Q via ₁₂ and capacitor C ₁₅
Connected to _second base, the other end of the base winding T _2b connected to the negative side output terminal of the DC power supply circuit 12, the switching transistor a positive side output terminal via the starting resistor R ₁₁ of the DC power supply circuit 12 and a lighting circuit 13 which is connected to the base of Q _2.

When the commercial AC power source 11 is supplied to the DC power supply circuit 12 by turning on the power switch (not shown), the DC power supply circuit 12, a rectifier RF ₂ and smoothing capacitor C _11, an AC input full-wave rectified, this Is output as a smoothed DC voltage. This DC voltage, base current flows to the switching transistor Q ₂ through a starting resistor R _11, the switching transistor Q ₂ is turned on. At this time, the collector current of the transistor Q ₂ is, through a path of _{C 11 → T 2a → Q 2} → C 11. The base winding T _2b of the oscillation transformer T _2, the voltage in a direction to turn on the transistor Q ₂ is induced, the transistor Q ₂ is kept on.

At this time, the capacitor C ₁₅ through the resistor R ₁₂ by the induced voltage generated in the base winding T _2b is charged to the polarity shown in the CR time constant, the charging current decreases becomes accompanied with the progress of the charging, which decreases also the base current of the transistor Q ₂ as the result the direction of turning off, which the collector current is also directed to the reduced saturation as, so the direction in which the induced voltage off base winding T _2b, the capacitor C ₁₅ is the charge C ₁₅ → T
Discharging the path of the emitter-base → C ₁₅ of _2b → Q _2, transistor Q ₂ is rapidly turned off. When turned off, the output again by the base current flows through the transistor Q ₂ through a starting resistor R ₁₁ of the DC power supply circuit 12, the transistor Q ₂ is repeated the same operation thereafter, performs high-frequency oscillation.

Then, the transistor when Q ₂ is turned off, the oscillation during the ON period of the transistor Q ₂ transformer T ₂ and energy resonance capacitor accumulated in the choke coil L ₁₁
C ₁₂ , Preheating capacitor C ₁₃ , AC coupling capacitor C ₁₄
One resonates in parallel and the other resonates in series. As a result, the high frequency of the resonance voltage is generated in the primary winding T _2a of the oscillation transformer T _2, electrodes Fa of the resonance voltage discharge lamp FL _2, is applied between Fb, the discharge lamp FL ₂ is turned. When the discharge lamp FL ₂ is lit, the electrodes Fa of the discharge lamp FL _2, the impedance between Fb decreases, because this impedance is sufficiently smaller than the impedance of the preheating capacitor C _13, the current flowing through the choke coil L ₁₁ is approximately It flows to the discharge lamp FL _2.

<Problems to be Solved by the Invention> However, in the above-described configuration, since the resonance elements are two, that is, parallel resonance and series resonance,
There is a problem that the resonance waveform is likely to be distorted, the peak value of the resonance voltage is lowered and the lamp is not lit, or the resonance frequency is lowered to enter an audible band and generate abnormal noise such as electromagnetic noise. Have.

The present invention has been made in view of the above points, and an object of the present invention is to provide a lighting device which can solve the above-mentioned problems with a simplified configuration and can be manufactured economically.

<Means for Solving the Problems> In order to achieve the above object, the present invention provides that a preheating capacitor is inserted between electrodes at an output end of a DC power supply circuit, and an AC coupling capacitor is connected to one of the electrodes. A connected discharge lamp, one of the first and second windings magnetically coupled, and a collector connected in series to a switching transistor having a collector connected to the one winding are connected in series. Between the electrodes of the lamp, a diode, the anode of which is connected to the output terminal of the DC power supply circuit, a forward diode connected to the electrode of the discharge lamp, and the AC coupling capacitor, through the first and the second. The other of the two windings is connected, and when the switching transistor is turned off, the energy accumulated in one of the windings is inverted and discharged through the other winding. I do.

<Operation> By the output of the DC power supply circuit, when the switching transistor is turned on, a current flows through one of the windings via the discharge lamp electrode, the preheating capacitor, and the AC coupling capacitor, and the energy stored in the one winding. When the switching transistor is turned off, the discharge lamp is turned on by the resonance voltage generated by the series resonance by inverting and discharging the current to the other winding via the forward diode.

<Embodiment> First, generation of AC high voltage in the present invention is described in the second.
This will be described with reference to FIGS. In FIG. 2,
When switch S is closed, DC power supply E switches to + E → Ca → Cb →
Current starts to flow through the path of La → S → −E. At this time,
Since a voltage e _Lb having a polarity for reversely biasing the diode Da whose anode is connected to the positive electrode of the DC power supply E is induced in the winding Lb, FIG. 2 is equivalent to FIG. 3, and LC is a series circuit. And the current i _ON when the switch S is on is And the current i _ON flows in a sinusoidal waveform. Capacitor Ca,
Assuming that the charging voltage of Cb is e _cab and the voltage drop of the winding La is e _La , , And both e _cab and e _La are sinusoidal.

Now, assuming that the windings La and Lb are the same, the induced voltage e _Lb of the winding _Lb becomes the same as the voltage drop e _La of the winding La, while the voltage across the capacitors Ca and Cb connected in series is obtained. Since e _cab is expressed as in the above equation (2), a voltage having a polarity for reversely biasing the diode Da is applied, and its value is determined by the voltage e _cab across the capacitors Ca and Cb and the voltage of the winding La. Descent e _La
(E _cab −e _La ), and becomes the maximum immediately after the switch S is turned on, then decreases in a sinusoidal manner with time, and eventually crosses zero to forward bias the diode Da.

The time when the diode Da is forward-biased is
The point is that when the number of turns of La and Lb is the same, the above-mentioned voltages e _cab and e _La are 1/2 of the DC power supply E. Winding ratio of winding La and Lb (Lb / L
When a) is n, the induced voltage e _Lb of the winding _Lb is equal to the voltage e of the winding La.
Becomes n times _La, under this condition, since the voltage e _Lb and e _cab diode when the same value Da is forward biased, the voltage e _cab is of the direct current power supply E At this point, the diode Da is forward-biased, and a current starts to flow through the winding Lb. That is, the winding of the winding La, Lb is Na,
Assuming Nb, the turns ratio n is And the on (forward bias) of diode Da is When the switch S is opened at the time when the voltages e _Lb and e _cab have the same value, an action of maintaining the current in the windings La and Lb and trying to flow the current occurs, and the windings La and Lb Although a voltage is induced, no current flows from the winding La because the switch S is open, and as a result, the current i _OFF changes from Lb → Cb → Ca → Da
→ It flows on the route of Lb, and FIG. 2 is equivalent to FIG.

When the number of windings of the windings La and Lb is the same (Na = Nb), Lb → Cb → Ca →
A regenerative current flows through the path of Da → Lb. At this time, the capacitor Ca / Cb charged when the switch S was closed
Is discharged, and the capacitors Ca and Cb are charged to the polarity shown in FIG.

When the switch S is closed, the winding La and the capacitor
All of the energy stored in Ca and Cb is released in reverse via winding Lb when switch S is open,
Ca, if that charge the Cb in opposite polarity accumulated energy P _L and the capacitor Ca of the winding La, energy P _C of Cb is Therefore, the total energy of the winding La and the capacitors Ca and Cb after inversion emission is the sum of W _La and W _cab .

In the LC circuit discharge, the charge q and the current i at an arbitrary time are represented by q = Acosωt + Bsinωt (14) i = ω (Bcosωt−Asinωt) (15), which is the same as FIG. Since the capacitors Ca and Cb in series are denoted by C, the initial condition t = 0, q =
Q, i = -ionp the above (14), (15) from equation Q = Acos 0 + Bsin 0 Therefore _{A = Q -i onp = ω (} Bcos 0-Asin 0) Therefore, from the expressions (14) and (15), the electric charge q of C and the current i _OFF flowing in the LC circuit are expressed as follows. From the above equations (6) and (7), That is, the voltage and the current when the switch S is open are all sinusoidal functions.

Therefore, when the switch S is opened and closed, the capacitors Ca, C
The current and voltage waveforms flowing through the circuit b are AC waveforms as shown in FIG. 5, and the current i is a waveform symmetrical between positive and negative.

Hereinafter, an embodiment of the present invention will be described with reference to FIG. In the figure, 1 is a commercial AC power supply, 2 is a DC power supply circuit,
Between the output terminals of the commercial AC power source 1 to the rectifier coupled RF _1, by inserting the smoothing capacitor C _1, and outputs a DC voltage obtained by rectifying and smoothing the inter-terminal capacitor C _1. 3 is a connection terminal P,
This is a lighting circuit connected via N. This is the connection terminal P connected to one end of one electrode F _a of the discharge lamp FL ₁ having a pair of electrodes F _a · F _b, the other end and the other electrode F _b of the electrode F _a
Preheating capacitor between one end (ie, for mutual electrode use)
Insert the C _2, via an AC coupling capacitor C ₃ to the other end of the other electrode F _b, first, second winding magnetically coupled
T _1a, T _1b and base - connecting one end of the scan winding T _1c and the third formed by winding a winding T _1d oscillation transformer T ₁ of the above first winding T _1a, the first the other end of the between the other end and the connection terminal N of the winding T _1a, the switching transistor inserted between the collector and the emitter of Q _1, the electrodes Fa of the discharge lamp FL ₁ to the base of the switching transistor Q ₁ with connecting connected with starting resistor R _1, the other end of the base winding T _1c of the transistor to Q ₁ oscillation transformer T ₁ having one end connected to the emitter via a resistor R ₂ and capacitor C ₄ Connect the above discharge lamp
Between the other ends of the electrode F _b of the electrode F _a of FL _1, via a diode D ₁ and the AC coupling capacitor C ₃ having an anode connected to the other end of the electrode Fa, the second insert the winding T _1b, connection terminals P, when a DC voltage is applied to the N, transistor Q ₁ through a starting resistor R ₁ base - turned on by the scan current flows, thereby 2 → F _a → C ₂ → F _b → C ₃ → T _1a
→ A current flows through the path of Q ₁ → 2, and an induced voltage in the direction of turning on the transistor Q ₁ is generated in the base winding T _1c , and the base voltage is applied to the transistor Q ₁ via the resistor R ₂ and the capacitor C _4. by flowing a scan current, maintains the on-state transistor Q _1, the charging current by the capacitor C ₄ is charged with C ₄ R ₂ time constant decreases, which as the base current of the transistor Q ₁ is also reduced also it reduces the collector current accordingly, the transistor Q ₁ is turned off, the capacitor C ₄ is the charge C ₄ → R ₂ → T _1c
→ Q ₁ of the emitter-base - to discharge the path of the scan → C _4, rapidly turning off the transistor Q _1, than off of transistor Q _1,
The energy stored in the winding T _1a is converted into T _1b → C ₃ → F _b → C ₂ → D ₁
→ Invert and discharge to the path of T _1b and capacitors C ₃ and C
_Second charge also is simultaneously discharged by the path, so as to light the discharge lamp FL ₁ by the resonance voltage generated by the series resonance. The diode D ₂ whose anode is connected to the connection terminal N is the protection of the switching transistor Q _1. Also, between the connection terminals PN, the _first of the oscillation transformer T1,
Second winding T _1a, T _1b and a third winding T _1d which magnetically coupled
The cathode is connected via a diode D ₃ connected to the connection terminal P, when the voltage in order to release the energy stored in the first winding T _1a occurs, proportional to the voltage and the number of turns The first voltage is formed to induce the applied voltage.
The voltage generated in the winding T _1a is, when an attempt to exceed the collector maximum voltage of the transistor Q _1, diode - by applying a current to the DC power supply side to conduct de D _3, an overvoltage breakdown of the transistor Q ₁ To prevent it.

Next, the operation will be described. When a power switch (not shown) is turned on, the DC power supply circuit 2 receiving the commercial AC power supply 1 outputs full-wave rectified and smoothed DC voltage. Transistor Q ₁ This was received through the electrode F _a and the start-up resistor R ₁ of the discharge lamp FL ₁ Baie - to scan current flows to turn on, 2 → F to the winding T _1a of the oscillation transformer T ₁ by the ON operation _a
→ C ₂ → F _b → C ₃ → T _1a → Current flows through the collector / emitter path of Q ₁ → 2, and the electrodes _Fa and F _{b of the} discharge lamp FL ₁ are preheated and the base winding T _1c induced voltage in a direction that turns on the transistor Q ₁ is _{generated, T 1C → R 2 → C} 4 → for Q ₁ base - scan emitter → a current flows through a path of T _1C, the on-state transistor Q ₁ to maintain, but because the capacitor C ₄ is charged in the shown polarity having a C ₄ R ₂ time constant, the transistor Q ₁ base as charge - scan current decreases, the collector current is also decreased with this , the transistor Q ₁ is turned off, the capacitor C ₄ is the charge _{C 4 → R 2 → T 1C} → Q 1 emitter Baie - discharging the path of the scan → C ₄ rapidly off the transistor Q ₁ and.

The off of the transistor Q _1, the energy stored in the winding T _1a - with the inverted release the path of _{T 1b → C 3 → F b} → C 2 → D 1 → T 1b, capacitor C _2, C ₃ to discharge also the charge at the same time, the capacitor C _2, C ₃ is charged to the illustrated polarity opposite the discharge lamp FL ₁ is the electrode F _a, the resonance voltage by the series resonance between F _b is applied.

When the transistor Q ₁ is turned off, through a starting resistor R _1, again base transistor Q ₁ - scan current is turned on to flow, by repeated the above similar operation, the discharge lamp
In the FL ₁ , the preheating and the application of the resonance voltage are repeatedly performed on the electrode, the electrodes F _a and F _b are discharged, and the discharge lamp FL ₁ is turned on.
After lighting the electrode F _a, Inpi between F _b - dance capacitor C ₂
Of Inpi - since sufficiently smaller than dance, the current flowing substantially electrode F _a, flows between F _b, maintaining the lighting.

At this time, the current flowing between the electrodes F _a and F _b has a positive-negative symmetric waveform, so that blackening of the electrodes is prevented and lighting is maintained for a long time. The switching frequency of the transistor Q ₁ is will be determined by C ₄ R ₂ time constant of the capacitor C ₄ and the resistor R _2, and the resonance element is only the series resonance, the discharge lamp without causing a reduction in the frequency The high-frequency lighting operation is performed. Then, the winding T _1d, at the time of the on transistors Q _1, in proportion to the winding T _1a and turns diode - the direction of the voltage of the de D ₃ reverse bias is induced at the time of the off-transistor Q _1, the energy stored in the winding T _1a - in proportion to the voltage generated in order to release the diode - direction of the voltage of the de D ₃ to forward bias is induced. Therefore, when a voltage exceeding the collector maximum voltage at the time of the off transistor Q ₁ is attempted to generate the winding T _1a is diode by a voltage induced in the winding T _1d - de D ₃
Through, by applying a current to the DC power source circuit 2, it will be called clamping the output voltage of the DC power source circuit 2, to prevent destruction of the transistor Q _1. In other words protecting transistor Q ₁ from the overvoltage.

Then, when removing the discharge lamp FL ₁ before lighting, the lighting circuit 3 even if a DC voltage is outputted from the DC power source circuit 2 is not responding.

Further, the energy stored in the winding T _1a when disconnecting the discharge lamp FL ₁ after lighting - when the voltage trying releasing occurs a voltage that is about to exceed the collector maximum voltage of the transistor Q ₁ is, performing the above same overvoltage protection operation voltage proportional thereto is induced in the winding T _1d.

FIGS. 6 and 7 show another embodiment of the lighting circuit 3 and operate in the same manner as described above.

The present invention is not limited to the above embodiment, and it goes without saying that various changes can be made without changing the gist.

[Effects of the Invention] According to the present invention, a preheating capacitor is inserted between electrodes at the output end of a DC power supply circuit, and a discharge lamp having an AC coupling capacitor connected to one of the electrodes is magnetically coupled. One of the first and second windings and the collector are connected in series with a switching transistor connected to the one winding, and a diode is provided between the electrodes of the discharge lamp, and the anode is the anode. The other one of the first and second windings is connected via a forward diode connected to an electrode of the discharge lamp connected to the output terminal of the DC power supply circuit and the AC coupling capacitor. Then, when the switching transistor is turned on, the energy stored in the one winding is reversely discharged to the other winding via both capacitors for preheating and AC coupling, so that the discharge lamp is turned on. Ah Therefore, the resonance element can be formed only by series resonance, and a stable resonance voltage can be generated without lowering the frequency, and the discharge lamp can be turned on. In addition, since the capacitor for LC series resonance can be used as both the capacitor for preheating the discharge lamp and the capacitor for AC coupling, the number of components is reduced, and the circuit is simplified and reduced in size and weight. can do. Also, since the energy stored in one of the first and second windings is reversely discharged to the other winding via both the capacitor for preheating and the capacitor for AC coupling, The current flowing in the circuit can have a symmetrical positive and negative waveform, and blackening of the discharge lamp can be prevented, and stable lighting can be performed for a long time. Moreover,
The switching transistor is turned on to either one of the first and second windings via the electrodes of the discharge lamp to allow current to flow, so even if the discharge lamp is removed during lighting, the load There is no need to control the output of the inverter due to the fluctuations, and the control can maintain a stable high-frequency band without increasing the frequency.

Further, a third winding magnetically coupled to the first and second windings between input terminals of the lighting circuit is connected to an output terminal having a cathode connected to an electrode of the discharge lamp by a diode. In this case, a voltage proportional to the voltage generated due to the release of energy stored in one of the first and second windings is induced. Therefore, feedback can be made to the DC power supply side, and overvoltage damage of the switching transistor can be prevented to protect the inverter.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIGS. 2 to 5 illustrate the principle of generation of an AC voltage according to the present invention. FIGS. 2 to 4 are circuit diagrams thereof and FIG. The figure shows the voltage and current waveforms. 6 and 7 are circuit diagrams showing another embodiment of the lighting circuit of FIG. 1, and FIG. 8 is a block diagram showing a conventional example. 2: DC power supply circuit, 3: lighting circuit FL _1: discharge lamp, Fa, Fb: electrodes T _1: the oscillation transformer, T _1a: first winding T _1b: second winding, T _1C: base - scan Winding T _1d : Third winding D ₁ , D ₂ , D ₃ : Diode Q ₁ : Switching transistor C ₂ : Preheating capacitor C ₃ : AC coupling capacitor

Claims (2)

(57) [Claims] 1. A discharge lamp in which a preheating capacitor is inserted between electrodes at an output terminal of a DC power supply circuit and an AC coupling capacitor is connected to one of the electrodes, and first and second magnetically coupled discharge lamps.
One of the windings, and a collector connected in series with a switching transistor having a collector connected to the one winding, and a diode between the electrodes of the discharge lamp, the anode of which is the DC power supply circuit. The other one of the first and second windings is connected via a diode connected to an electrode of the discharge lamp connected to the output terminal of the discharge lamp and the AC coupling capacitor, and the switching transistor Wherein the energy stored in one of the windings is inverted via the other winding when the device is turned off. 2. The method according to claim 1, further comprising the step of:
1, wherein a third winding magnetically coupled to the second winding is connected to a diode via a diode whose cathode is connected to an output terminal connected to the electrode of the discharge lamp. The discharge lamp lighting device according to claim 1.