JP2011146164A - High-voltage discharge lamp lighting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a discharge lamp lighting device capable of downsizing components constituting electronic ballast and a case and reducing cost, and capable of reducing CO2 for measures against global warming through minimization of a circuit loss. <P>SOLUTION: In the on-off control of a switching element Q1 for power adjustment, a voltage Vds is applied to the switching element Q1 during an off-period of the same Q1, and a current flowing in an inductor L1 is gradually decreased. When a current IL of the inductor becomes nearly zero, static energy stored in the switching element Q1 at an-off state, generates damping oscillation between the switching element Q1 and the inductor L1. A control circuit 11 matches a timing for changing over the switching element Q1 from off to on with a timing when the voltage Vds impressed on it becomes minimum by the damping oscillation. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a discharge lamp lighting device for lighting a discharge lamp such as a fluorescent lamp or an HID lamp, and more particularly to improvement of a function of stable lighting by electronic ballast.

  Conventionally, a copper iron type ballast (so-called copper iron ballast) has been used as a lighting device for lighting a discharge lamp such as a fluorescent lamp or an HID lamp. However, copper-iron type ballasts are heavier and larger in size, so in recent years electronic components such as switching elements and diodes have been developed to reduce the weight, size, and functionality of ballasts. A so-called electronic ballast (electronic ballast) is used (for example, see Patent Document 1).

For example, as shown in FIG. 1, the electronic ballast described in Patent Document 1 is connected to an output terminal of a DC power supply circuit 2 and an output terminal of the DC power supply circuit 2 to which an AC output of an AC power supply AC is input and to a discharge lamp La. And a power conversion circuit 3 that adjusts / controls the power supplied.
A step-down chopper circuit is generally used as the power conversion circuit 3. FIG. 2 shows a specific circuit example of an electronic ballast using a step-down chopper circuit. The DC power supply circuit 2 includes a rectifier circuit 5 that rectifies an AC output of an AC power supply AC, and an output of the rectifier circuit 5. A smoothing capacitor C0 connected between the ends and smoothing the output of the rectifier circuit 5 is configured to rectify and smooth the AC voltage of the AC power supply AC into a DC voltage. The power conversion circuit 3 includes a switching element Q1, an inductor L1, a diode D1, a capacitor C1, and a control circuit 11 that controls on / off of the switching element Q1, and a discharge lamp La is connected to both ends of the capacitor C1. Connected. Here, the switching element Q1, the diode D1, and the inductor L1 constitute a step-down chopper circuit. The control circuit 11 detects the voltage across the capacitor C1 as the lamp voltage Vla of the discharge lamp La, and controls the switching frequency or on-duty for turning on and off the switching element Q1 at a high frequency according to the lamp voltage Vla, thereby controlling the discharge lamp La. The power to be supplied is adjusted.

  Here, attention is focused on the current IL flowing through the inductor L1. In the steady lighting state of the discharge lamp La, there are the following three modes as modes of the current IL flowing through the inductor L1 when the control circuit 11 controls the switching element Q1 by the control signal S1 described later. That is, when the control signal S1 as shown in FIGS. 3A, 4A, and 5A is input from the control circuit 11 to the switching element Q1, as shown in FIG. In mode I (hereinafter referred to as discontinuous mode) in which a pause period ta in which the current IL does not flow occurs, as shown in FIG. 4B, the current IL has no pause period and the current IL decreases to zero. At the same time, the mode II in which the control signal S1 changes from the low level to the high level and the current IL flows again (hereinafter referred to as the zero cross switching mode), the current IL has no pause period as shown in FIG. There are three modes, Mode III (hereinafter referred to as a continuous mode) in which the control signal S1 changes from a low level to a high level and the current IL continuously flows before it decreases to zero.

<Generation of switching loss due to current Ids>
By the way, in the above-described continuous mode, when the signal S1 changes from low level to high level and the switching element Q1 changes from off to on, a current having a magnitude of Ic2 (see FIG. 5B) is obtained as the current IL. Since the current flows, the voltage Vds and current Ids of the switching element Q1 change as shown by a solid line and a broken line in FIG. A voltage Vds shown in FIG. 5C indicates a voltage applied between the drain (d) and the source (s) when a field effect transistor (FET) is used as the switching element Q1, and the voltage of the capacitor C0 in the off state. The voltage becomes Vco. A current Ids shown in FIG. 5D indicates a current flowing through the switching element Q1. Here, when the time axis of the portion A where the switching element Q1 is switched from OFF to ON in FIG. 5E is enlarged, the time axis is as shown in FIG. 5F, and the switching element Q1 is indicated by a portion indicated by a two-dot chain line B in FIG. There is a possibility that a switching loss accompanying the current Ids flowing through the switch occurs, the temperature of the switching element Q1 rises, and the switching element Q1 is destroyed. Note that a switching loss occurs in the diode D1 as in the switching element Q1.
On the other hand, in the above-described zero cross switching mode, there is an advantage that the switching loss accompanying the current Ids of the switching element Q1 and the diode D1 can be reduced as compared with the continuous mode.

Japanese Patent Laid-Open No. 10-144488

  By the way, in recent years, there is a demand for downsizing, weight reduction, resource saving, and energy saving of an electronic ballast for lighting a high pressure discharge lamp such as a mercury lamp, a metal halide lamp, or a high pressure sodium lamp. In order to satisfy these requirements simultaneously, it is necessary to increase the switching frequency and reduce the circuit loss as much as possible.

<Generation of switching loss with voltage Vds>
The inventor has paid attention to the fact that the switching loss in the switching element Q1 still exists in the above-described zero-cross switching mode (mode II). That is, even in mode II, when the switching element Q1 changes from off to on, the voltage Vds applied to the switching element Q1 cannot be minimized as shown by Vds in FIG. The accompanying switching loss occurs.
4E, the time axis of the portion A where the switching element Q1 switches from OFF to ON is expanded as shown in FIG. 4F, and the voltage Vds of the switching element Q1 is indicated by a portion indicated by a two-dot chain line B. A switching loss has occurred.

In addition to the loss caused by the overlap between the voltage Vds applied to the switching element Q1 and the current Ids, the switching loss includes a heat loss due to an internal short circuit of the FET as shown in FIG. 6A is a diagram schematically showing the output capacity of the switching element Q1 in the circuit of FIG. 2, and FIG. 6B is a diagram for explaining the internal short circuit. When the switching element is constituted by an FET, the charge stored in the output capacitance of the FET is short-circuited inside the FET as shown in FIG. Will occur. For example, when an electronic ballast having a DC voltage Vds input to the step-down chopper circuit of 400 V, a switching frequency f of the switching element Q1 of 120 KHz, an output capacity of 200 pF, and an output of 20 W is used, the heat loss Is 1.92 W from the following equation. This loss is as large as about 9.6% of the output 20 W, and a circuit loss that cannot be ignored occurs.
[Equation 1]
Thermal loss = 1/2 × (FET output capacity) × (Vds) ² × f

  The present invention has been made in view of the above-mentioned reasons, and its purpose is a discharge lamp lighting device capable of reducing the size and cost of parts and cases constituting an electronic ballast, and minimizing circuit loss. By stopping, it is providing the discharge lamp lighting device which can reduce CO2 for global warming countermeasures.

In order to solve the above problem, the inventor controls the switching element in the discontinuous mode (mode I), and further sets the switching timing of the switching element from OFF to ON in the discontinuous mode. It has been found that not only the occurrence of switching loss due to the current flowing through the element can be prevented, but also the occurrence of switching loss due to the voltage applied to the switching element can be reduced.
That is, the discharge lamp lighting device according to the present invention is
A DC power supply circuit for supplying DC power;
A power conversion circuit that is connected to the output terminal of the DC power supply circuit and adjusts the power supplied to the discharge lamp is provided.
And the power conversion circuit comprises:
Includes power conditioning switching elements, inductors, capacitors and diodes,
One end of the power adjustment switching element is connected to one output end of the DC power supply circuit,
The inductor and the capacitor are connected in series between the other output end of the DC power supply circuit and the other end of the power adjustment switching element,
Connecting the discharge lamp in parallel between the terminals of the capacitor;
When the power adjustment switching element is turned on and magnetic energy is accumulated in the inductor by a current from the DC power supply circuit, and the power adjustment switching element is switched from on to off, the inductor due to the release of the magnetic energy Is connected to both ends of the series circuit of the inductor and the capacitor with a diode that flows current only in the direction returning to the inductor so that the current from the capacitor is returned to the inductor again via the discharge lamp.
The power conversion circuit includes a control circuit that controls on / off of the power adjustment switching element.
In the starting process state where the discharge lamp is in a steady lighting state, or the lamp voltage of the discharge lamp is lower than the steady lighting state,
After switching the power adjustment switching element from on to off, the current flowing through the diode to the inductor decreases to substantially zero, and the electrostatic energy stored in the off-state power adjustment switching element is The switching element is switched from OFF to ON in accordance with the timing at which the voltage applied to the switching element becomes a minimum value by moving to the inductor.
The lighting device of the present invention is not limited to the case where the discharge lamp is in a steady lighting state, but can also be applied to a starting process state in which the lamp voltage of the discharge lamp is lower than in the steady lighting state.

Further, in the present invention, the control circuit further reduces a quarter of the damped oscillation of the electrostatic energy generated between the switching element in the off state and the inductor after the current flowing through the inductor is reduced to substantially zero. It is preferable to switch the switching element from OFF to ON in accordance with the timing after one cycle.
Furthermore, in the present invention, a polarity reversing circuit is provided between the power conversion circuit and the discharge lamp to convert the current flowing through the discharge lamp into an alternating current having a frequency lower than the switching frequency of the switching element. preferable.

  In the present invention, the polarity inversion circuit includes a first series circuit of the second and third switching elements and a second series circuit of the fourth and fifth switching elements between the output terminals of the power conversion circuit. Are connected in parallel, and the discharge lamp is connected between a connection point between the second and third switching elements and a connection point between the fourth and fifth switching elements. preferable.

In the present invention, it is preferable that the power conversion circuit and the polarity inversion circuit are configured by a full bridge circuit.
Furthermore, in the present invention, it is preferable that the power conversion circuit and the polarity inversion circuit are configured by a half bridge circuit.

2 and 7 and 8, the voltage applied to the switching element Q1 after the inductor current IL decreases and becomes substantially zero when the switching element Q1 is off. This will be described because there is a point where Vds becomes a minimum value.
For example, when the timing of switching the switching element Q1 from OFF to ON is controlled so that the current IL flowing through the inductor becomes a discontinuous current with a pause period ta as shown in FIG. While IL decreases, the drain-source voltage Vds of the switching element Q1 indicates the output terminal voltage Vco of the DC power supply circuit 2 as shown in FIG. Here, the drain-source region of the switching element Q1 in the off state can be regarded as a capacitor. When the inductor current IL becomes substantially zero in the off state and the rest period ta starts, the electrostatic energy accumulated in the drain-source capacitance due to the voltage Vds of the switching element Q1 is released. That is, the switching element Q1 and the inductor L1 start exchanging energy in two states of electrostatic energy and magnetic energy. During the rest period ta, this energy exchange oscillates while being attenuated, and the voltage Vds of the switching element draws a waveform of damped oscillation as shown in FIG.

In the conventional discontinuous mode, as shown in FIGS. 3C and 7C, the timing of switching from OFF to ON during the rest period ta is controlled regardless of the waveform of the voltage Vds. In a state that is not the bottom of the damped vibration (minimum value), the switch was turned on, and the switching loss due to the voltage Vds was still increased.
On the other hand, in the present invention, focusing on the fact that the voltage Vds oscillates in a section where no current flows through the inductor L, when the current IL of the inductor decreases to substantially zero, FIGS. As described above, the switching element is controlled from OFF to ON in accordance with the timing when the voltage Vds of the switching element is minimized by the series resonance by the output capacitance of the switching element Q1 and the inductor L1. If the switching element Q1 is turned on in this way, as shown in FIGS. 8D to 8F, it is based on the loss accompanying the output capacity of the switching element Q1, that is, the voltage Vds applied to the switching element Q1. Switching loss can be minimized. 8E, the time axis of the portion A where the switching element Q1 switches from OFF to ON is expanded as shown in FIG. 8F, and the voltage Vds of the switching element Q1 is indicated by the portion indicated by a two-dot chain line B. The switching loss associated with is reduced as compared with FIG. 4F in the zero cross switching mode.

By appropriately controlling the switching timing in this way, zero current switching, which is a discontinuous mode related to the current flowing through the inductor, and minimal voltage switching in which the voltage applied to the switching element is minimized are simultaneously realized. The circuit loss of the electronic ballast can be reduced, and the entire device can be reduced in size and cost. In other words, the energy stored in the output capacity of the switching element is not wasted as a heat generation of the switching element, but is beneficially recovered as a lamp current.
In the present invention, a polarity reversing circuit is provided between the power conversion circuit and the discharge lamp to convert the current flowing through the discharge lamp into an alternating current, or the power conversion circuit and the polarity reversing circuit are connected to the full bridge circuit. Further, by constituting with a half bridge circuit, the discharge lamp is turned on by alternating current, and stress can be prevented from being biased to the electrode on one side of the lamp as compared with the case of direct current lighting.

It is a schematic block diagram which shows the conventional high pressure discharge lamp lighting device. It is a circuit block diagram of the high pressure discharge lamp lighting device shown in FIG. It is a wave form diagram of the conventional discontinuous mode. It is a wave form diagram of the conventional zero cross switching mode. It is a wave form diagram of the conventional continuous mode. It is a figure which shows typically the output capacity | capacitance of the switching element in the circuit of FIG. 2, and its internal short circuit. It is a figure for demonstrating the waveform of the discontinuous mode of this invention. It is a wave form diagram of discontinuous mode of the present invention. It is a circuit block diagram of the high pressure discharge lamp lighting device which concerns on 1st Embodiment. It is a circuit block diagram which shows 2nd Embodiment. It is operation | movement explanatory drawing of the circuit of FIG. It is a circuit block diagram which shows 3rd Embodiment. It is operation | movement explanatory drawing of the circuit of FIG. It is a circuit block diagram which shows 4th Embodiment. It is operation | movement explanatory drawing of the circuit of FIG.

Preferred embodiments of the present invention will be described below with reference to the drawings.
(First embodiment)
In FIG. 9, the circuit block diagram of the high pressure discharge lamp lighting device of this invention is shown. In the figure, the high pressure discharge lamp lighting device adjusts the power supplied to the discharge lamp La connected to the output terminal of the DC power supply circuit 2 and the DC power supply circuit 2 that supplies the DC power supply based on the AC power supply of the AC power supply AC. A step-down chopper type power conversion circuit 3.
The DC power supply circuit 2 includes a rectifier circuit 5 that rectifies the AC output of the AC power supply AC, and a smoothing capacitor C0 that is connected between the output terminals of the rectifier circuit 5 and smoothes the output of the rectifier circuit 5. Rectify and smooth AC voltage to DC voltage.

The power conversion circuit 3 is configured by connecting each element as follows. First, one end of the power adjustment switching element Q1 is connected to the positive output side of the smoothing capacitor C0, and the inductor L1 and the capacitor are connected between the negative output side of the smoothing capacitor C0 and the other end of the power adjustment switching element Q1. A series circuit of C1 is connected, and a discharge lamp La is connected in parallel between terminals of the capacitor C1. The power adjustment switching element Q1 is turned on and off at a high frequency of several tens of kHz.
During the period in which the power adjustment switching element Q1 is in the ON state, magnetic energy is accumulated in the inductor L1 by the DC current of the DC power supply circuit 2 flowing through the switching element Q1. Then, when the power adjustment switching element Q1 is switched from on to off, the current tends to continuously flow through the inductor L1 due to the release of the magnetic energy of the inductor L1. The power conversion circuit 3 is formed with a closed loop current path in which the current from the inductor L1 returns to the inductor L1 again via the discharge lamp La after the switching element Q1 is switched off. That is, both ends of the series circuit of the inductor L1 and the capacitor C1 are connected by the diode D1 that allows current to flow only in the direction returning to the inductor L1.
In this way, in the power conversion circuit 3, when the switching element Q1 that switches at a high frequency is turned on, the direct current from the positive terminal of the smoothing capacitor C0 is applied to the smoothing capacitor C0 in the order of the switching element Q1 → the inductor L1 → the discharge lamp La. Flowing to the negative terminal, magnetic energy is stored in the inductor L1. When the switching element Q1 is turned off, the supply of direct current is cut off, and the voltage at the connection point between the switching element Q1 and the inductor L1 becomes substantially zero. The magnetic energy of the inductor L1 is released as a current, and returns to the inductor L1 in the order of the discharge lamp La → the diode D1.

  Further, the power conversion circuit 3 includes a control circuit 11 that controls on / off of the power adjustment switching element Q1. The control circuit 11 is constituted by a micro computer and has an algorithm for determining a switching frequency based on the DC voltage Vco at both ends of the smoothing capacitor C0 and the lamp voltage Vla of the discharge lamp La at both ends of the capacitor C1. In addition, the lamp voltage Vla and the lamp current Ila are multiplied to calculate the input power to the discharge lamp La, and control is performed to determine the on-duty so that the target power value is obtained. In the present embodiment, the voltage across the capacitor C1 is detected as the lamp voltage Vla, and the current IL flowing through the inductor L1 is detected as the lamp current Ila.

The characteristic feature of the present invention is that the switching timing of the switching element Q1 is appropriately set in order to minimize the switching loss based on the voltage Vds applied to the switching element Q1, as shown in FIG. There is to control. That is, after the control circuit 11 switches the power adjustment switching element Q1 from on to off, the current IL flowing through the diode D1 to the inductor L1 decreases to substantially zero. Thereafter, the electrostatic energy stored in the off-state power adjustment switching element Q1 by the applied voltage Vds moves to the inductor L1, thereby causing a damped oscillation. The control circuit 11 switches the switching element Q1 from OFF to ON in accordance with the timing at which the applied voltage Vds of the switching element Q1 becomes a minimum value due to this damped oscillation.
The control circuit 11 is configured to switch the switching element Q1 from OFF to ON regardless of whether the discharge lamp La is in a steady lighting state or a starting process state in which the lamp voltage of the discharge lamp La is lower than that in the steady lighting state. Are similarly controlled.

  Further, the characteristic of the present invention is that when the period of the damped oscillation of the voltage Vds of the power adjustment switching element Q1 is T, the control circuit 11 has a current IL flowing through the inductor substantially as shown in FIG. After decreasing to zero, the power is adjusted to the timing after a quarter period (T / 4) of the damped oscillation of electrostatic energy generated between the power adjustment switching element Q1 in the off state and the inductor L1. The switching element Q1 for adjustment is switched from OFF to ON.

The control circuit 11 calculates the time from when the switching element Q1 is switched off until the inductor current IL becomes substantially zero based on the detected value of the lamp voltage Vla. Alternatively, the time until the current IL becomes substantially zero may be calculated based on both detected values of the lamp voltage Vla and the voltage Vco of the smoothing capacitor C0. This time is substantially determined from the detected value of the lamp voltage Vla, but is also affected by the voltage Vco of the smoothing capacitor C0.
The time from when the inductor current IL becomes substantially zero to when the damped oscillation of the voltage Vds of the switching element Q1 reaches a minimum value is calculated based on the drain-source capacitance of the switching element Q1 and the inductance of the inductor L1. Use the set value. The control circuit 11 is provided with an on-switching time determining means for determining the timing for switching switching from off to on in this way. The control circuit 11 may be provided with a storage means in which the ON switching timing corresponding to the detected value of the lamp voltage Vla is stored in advance as a correspondence table.

In the present embodiment, in this way, series resonance is generated by the output capacitance of the switching element Q1 and the inductor L1, and control is performed to switch the switching element Q1 from OFF to ON in accordance with the timing when the voltage Vds of the switching element becomes minimum. . Therefore, as shown in FIGS. 8E and 8F, the loss accompanying the output capacity of the switching element Q1, that is, the switching loss based on the voltage Vds applied to the switching element Q1 can be minimized. By appropriately controlling the switching timing, zero current switching and extremely low voltage switching can be realized simultaneously, circuit loss of the electronic ballast can be reduced, and the entire device can be reduced in size and cost. Become.
For example, when a 20 W lamp is used, the loss of the entire circuit including the switching loss can be improved from 5 W (25% of 20 W) to 4 W (20% of the same).
In the present embodiment, the circuit configuration is not limited to that of FIG. 9. For example, one end of a series circuit of an inductor L1 and a capacitor C1 is connected to the positive output terminal of the smoothing capacitor C0. A power adjustment switching element Q1 may be provided between the output terminal on the negative electrode side of C0. That is, the position of the power adjustment switching element Q1 may be provided not on the position in FIG. 9 but on the wiring connecting the negative electrode side of the smoothing capacitor C0 and the negative electrode side of the diode D1.
In the circuit configuration of FIG. 9, the positive electrode and the negative electrode of the smoothing capacitor C0 may be reversed. In this case, the diode D1 is connected so that the direction in which the current of the diode D1 flows is also opposite.

(Second Embodiment)
In the high pressure discharge lamp lighting device of the first embodiment, since the discharge lamp La is dc-lit, stress is biased to the electrode on one side of the lamp. This embodiment improves this point, and in the high pressure discharge lamp lighting device of the first embodiment, as shown in FIG. 10, the discharge lamp La is connected between the power conversion circuit 3 and the discharge lamp La. A polarity inversion circuit 22 for lighting is added. The polarity inversion circuit 22 includes a first series circuit of switching elements Q2 and Q3 and a second series circuit of switching elements Q4 and Q5 connected in parallel to the capacitor C0 of the power conversion circuit 3, and the switching elements Q2, A discharge lamp La is connected between a connection point between Q3 and a connection point between the switching elements Q4 and Q5.

  As shown in FIGS. 11A to 11D, the polarity inverting circuit 22 includes switching elements Q2 and Q5 being on and switching elements Q3 and Q4 being off, and switching elements Q2 and Q5 being off and switching element Q3 being off. , Q4 is turned on alternately at low frequencies (for example, several tens Hz to several hundreds Hz). Therefore, a substantially rectangular wave lamp current Ila that alternates at a frequency lower than that of the power adjustment switching element Q1 as shown in FIG. 11E flows through the discharge lamp La. In the present embodiment, since the lamp current Ila flowing through the discharge lamp La is changed to an alternating current, it is possible to solve the problem that stress is biased to the electrode on one side of the lamp in direct current lighting as in the reference example and the first embodiment. .

In the present embodiment, the lamp current Ila flowing through the discharge lamp La is a rectangular wave. However, the present invention is not limited to a rectangular wave. For example, the on / off control of the switching elements Q2 to Q5 is different from the above-described control. Of course, the lamp current Ila may have a substantially sinusoidal shape.
According to the present embodiment, similarly to the above-described embodiment, the voltage Vds of the switching element Q1 is set by matching the timing of switching the power adjustment switching element Q1 from OFF to ON with the timing at which the voltage Vds of the switching element is minimized. The switching loss based on can be minimized.

(Third embodiment)
In this embodiment, a circuit having both functions of the power conversion circuit 3 and the polarity inversion circuit 22 in the second embodiment is a full bridge circuit in which four switching elements Q6 to Q9 are bridge-connected as shown in FIG. 27.
Hereinafter, lighting control of the discharge lamp La using the full bridge circuit 27 of the present embodiment will be described.
In general, the light output (light quantity) of an LED is proportional to the current, not the input power. On the other hand, since the light output of the discharge lamp La such as an HID lamp is proportional to the input power, power control is adopted for lighting control of the discharge lamp La. Further, in the case of a discharge lamp, particularly an HID lamp, the electrical resistance of the discharge lamp itself is not a constant and always varies. Specifically, the electrical resistance of the discharge lamp is expected to be a function of temperature, current, time, etc., and is considered an unstable constant voltage element, but has not yet been clarified. For example, if the voltage applied to the discharge lamp La is increased only slightly, the current increases, thereby reducing the equivalent electrical resistance of the discharge lamp. Even if it returns to the original voltage, it does not return to the original current value. In order to return to the original current value, it is necessary to make it lower than the original voltage. If the state in which the voltage applied to the discharge lamp La is slightly increased is continued, the lamp current increases, resulting in a decrease in the equivalent electrical resistance of the discharge lamp La, further increasing the current indefinitely, and the discharge lamp La It will continue until the damage of the circuit or the circuit. Thus, since the lamp current value for the same lamp voltage is not fixed, it is not possible to control the power of the discharge lamp based on the lamp voltage value.

In the present embodiment, almost all of the electric power (Vco × I) input to the full bridge circuit 27 shown in FIG. 12 is supplied to the discharge lamp La that is a load. This is because the full bridge circuit 27 is composed of reactance components (coils, capacitors) except for the switching elements Q6 to Q9, so that no circuit loss theoretically occurs. Therefore, by controlling the input power (Vco × I) to the bridge circuit, it is possible to perform power control, that is, lighting control of the discharge lamp La.
In order to know the power supplied to the discharge lamp La, the current IL flowing through the inductor L1 may be detected. However, in this embodiment, since the input power to the full bridge circuit 27 is detected as described above, it is used for current detection. The current I flowing through the resistor 28 is detected. Further, in the present embodiment, this current I is detected as a voltage drop voltage generated in the current detection resistor 28, and the control circuit 11 performs on / off control of the switching elements Q6 to Q9 based on this voltage. The bridge circuit 27 of FIG. 12 is provided with a small-capacitance capacitor C2 for bypassing high-frequency components in order to prevent high-frequency current from flowing through the resistor 28. The capacitor C2 is provided so as to connect both ends of the series circuit of the switching elements Q6 and Q7.
The reason why the control circuit 11 performs the on / off control based on the current I of the resistor 28 and the voltage drop voltage at the resistor 28 is that the current detecting resistor 28 is in a state where it can be considered that there is almost no lamp voltage variation during lighting. This is because the generated voltage drop voltage is proportional to the current Ila flowing through the discharge lamp. For example, when Vco is 400 V, Vc1 is 100 V, and the current flowing through the current detection resistor 28 is 0.25 A, the current flowing through the discharge lamp La is 1.0 A.

  As shown in FIGS. 13A to 13D, the switching elements Q6 to Q9 are switched on by the control signal from the control circuit 11, and the switching element Q6 is turned on, the high frequency switching of Q9 is performed and the switching elements Q7 and Q8 are turned off. The state and the state in which the switching elements Q6 and Q9 are off, the switching element Q7 is on, and the Q8 is high-frequency switched are alternately repeated at a low frequency (several tens to several hundreds of Hz). That is, the switching elements Q1 and Q2 to Q5 in FIG. 10 are substituted by the elements Q6 to Q9.

  In the period when the switching element Q6 is on and Q9 is switching at high frequency, when the switching element Q9 is off, the energy accumulated in the inductor L1 is released, and the inductor L1 → the diode D8 → the switching element Q6 → the discharge lamp La. → Current flows through the path of the inductor L1. On the other hand, during a period in which switching element Q7 is on and Q8 is switching at high frequency, when switching element Q8 is off, energy stored in inductor L1 is released, and inductor L1 → discharge lamp La → switching element Q7 → A current flows through the path from the diode D9 to the inductor L1. For this reason, the diode D1 in FIG. 10 can be substituted by the diodes D8 to D9.

  In the present embodiment, since the current I flowing through the current detection resistor 28 has a correlation with the current IL flowing through the inductor L1, the second embodiment is achieved by controlling the switching elements Q6 to Q9 based on the current I. Similarly, an alternating current can be supplied to the discharge lamp La, and the discharge lamp La can be turned on with an adjusted power.

  According to the present embodiment, similarly to the above-described embodiment, the switching elements Q8, Q9 that are switched at a high frequency are switched from OFF to ON by matching the timing at which the voltage Vds of the switching element is minimized, Switching loss based on the voltage Vds of Q9 can be minimized.

  Further, if, for example, FETs (MOSFETs) are employed as the switching elements Q6 to Q9, the FETs have parasitic diodes, so that the diodes D8 to D9 can also be used by the parasitic diodes of the FETs, and the second FET is the second FET. Since the six elements of the switching element Q1, the diode D1, and the switching elements Q2 to Q5 in the embodiment can be substituted, the number of parts can be reduced, and the cost and size of the entire apparatus can be reduced.

(Fourth embodiment)
In this embodiment, a circuit having both functions of the power conversion circuit 3 and the polarity inversion circuit 22 in the second embodiment shown in FIG. 10 is replaced with a series circuit of a pair of switching elements Q10 and Q11 as shown in FIG. This is constituted by a half bridge circuit 37 having Here, between the connection point of both capacitors C0 and C0 ′ of the DC power supply circuit 2 and the connection point of both switching elements Q10 and Q11 of the half bridge circuit 37, the discharge lamp La and the capacitor C1 are connected via an inductor L1. Are connected in parallel. In the present embodiment, both switching elements Q10 and Q11 are alternately turned on and off by the control circuit 11, thereby supplying an alternating current to the discharge lamp La. Hereinafter, the operation of the present embodiment will be described with reference to FIG.

  The switching elements Q10 and Q11 repeat high-frequency switching alternately as shown in FIGS. 15A and 15B, respectively, similarly to the relationship of the switching elements Q8 and Q9 of the third embodiment. That is, the switching elements Q10 and Q11 substitute for the switching elements Q1 and switching elements Q2 to Q5 in FIG. In the present embodiment, during the period when the switching element Q11 is performing high-frequency switching, when the switching element Q11 is off, the energy accumulated in the inductor L1 is released, and the inductor L1 → the diode D10 → the smoothing capacitor C0 → the discharge lamp La. → Current flows through the path of the inductor L1 (that is, the energy of the inductor L1 is fed back to the smoothing capacitor C0 via the diode D10). Further, during the period when the switching element Q10 is switching at high frequency, when the switching element Q10 is turned off, the energy accumulated in the inductor L1 is released, and the inductor L1 → the discharge lamp La → the smoothing capacitor C0 ′ → the diode D11 → the inductor. A current flows through the path L1 (that is, the energy of the inductor L1 is fed back to the capacitor C0 ′ via the diode D11). Therefore, the diode D1 in FIG. 10 can be substituted by the diodes D10 and D11, and it is not necessary to connect a diode separately, and the number of parts can be reduced and the size can be reduced.

In the present embodiment, as in the second embodiment and the third embodiment, an alternating current can be supplied to the discharge lamp La, and the discharge lamp La can be turned on with adjusted power.
Similarly to the above-described embodiment, the switching elements Q10 and Q11 that are switched at a high frequency are switched to the timing at which the voltage Vds of the switching element is minimized to match the voltage Vds of the switching elements Q10 and Q11. Based on the switching loss can be minimized.
Also in this embodiment, if an element having a parasitic diode such as an FET is used as the switching elements Q10 and Q11, the diodes D10 and D11 can also be used as a parasitic diode of the FET. Since the six elements of switching element Q1, diode D1, and switching elements Q2 to Q5 can be substituted, the cost and size can be reduced.

The present invention can be applied to lighting devices for high-pressure discharge lamps including xenon lamps in addition to HID lamps such as mercury lamps, metal halide lamps, and high-pressure sodium lamps.
In addition, although each said embodiment demonstrated only about the case where a high pressure discharge lamp was used as a load, since there are various load states, such as at the time of preheating and dimming, in a fluorescent lamp, the same control method and each embodiment and A lighting device can be applied.

2 DC power supply circuit 3 Power conversion circuit 11 Control circuit C1 Capacitor D1 Diode L1 Inductor La Discharge lamp Q1 Power adjustment switching element

Claims (6)

A DC power supply circuit for supplying DC power;
A power conversion circuit for adjusting the power supplied to the discharge lamp connected to the output terminal of the DC power supply circuit;
With
The power conversion circuit includes:
Includes power conditioning switching elements, inductors, capacitors and diodes,
One end of the power adjustment switching element is connected to one output end of the DC power supply circuit,
The inductor and the capacitor are connected in series between the other output end of the DC power supply circuit and the other end of the power adjustment switching element,
Connecting the discharge lamp in parallel between the terminals of the capacitor;
When the power adjustment switching element is turned on and magnetic energy is accumulated in the inductor by a current from the DC power supply circuit, and the power adjustment switching element is switched from on to off, the inductor due to the release of the magnetic energy In order to return the current from the inductor to the inductor again via the discharge lamp, both ends of the series circuit of the inductor and the capacitor are connected by a diode that conducts current only in the direction returning to the inductor,
A control circuit for controlling on / off of the power adjustment switching element;
The control circuit includes:
In the starting process state where the discharge lamp is in a steady lighting state, or the lamp voltage of the discharge lamp is lower than the steady lighting state,
After switching the power adjustment switching element from on to off, the current flowing through the diode to the inductor decreases to substantially zero, and the electrostatic energy stored in the off-state power adjustment switching element is A discharge lamp lighting device, wherein the switching element is switched from OFF to ON in accordance with a timing at which the voltage applied to the switching element becomes a minimum value by moving to the inductor. In the discharge lamp lighting device according to claim 1,
After the current flowing through the inductor is reduced to substantially zero, the control circuit further performs a quarter cycle of the damped oscillation of the electrostatic energy generated between the off-state power adjustment switching element and the inductor. A discharge lamp lighting device characterized in that the power adjustment switching element is switched from OFF to ON in accordance with a later timing. In the discharge lamp lighting device according to claim 1 or 2,
A polarity inversion circuit is provided between the power conversion circuit and the discharge lamp to convert the current flowing through the discharge lamp to an alternating current having a frequency lower than the switching frequency of the power adjustment switching element. Discharge lamp lighting device. In the discharge lamp lighting device according to claim 3,
The polarity inversion circuit connects a first series circuit of second and third switching elements and a second series circuit of fourth and fifth switching elements in parallel between the output ends of the power conversion circuit. A discharge lamp lighting comprising: connecting the discharge lamp between a connection point between the second and third switching elements and a connection point between the fourth and fifth switching elements. apparatus. In the discharge lamp lighting device according to claim 3,
A discharge lamp lighting device, wherein the power conversion circuit and the polarity inversion circuit are configured by a full bridge circuit. In the discharge lamp lighting device according to claim 3,
A discharge lamp lighting device, wherein the power conversion circuit and the polarity inversion circuit are configured by a half bridge circuit.

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