JP2001185380A - Lighting device of discharge lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lighting device of a discharge lamp capable of lighting the other discharge lamps without lowering the brightness in case some discharge lamps have become unloaded out of a plurality of discharge lamps. SOLUTION: The lighting device of a discharge lamp having an inverter circuit IN with a pair of switch element Q1, Q2 is lighted by supplying a high frequency voltage to a plurality of discharge lamps L disposed in parallel from each other through the inverter circuit IN from a direct current electric source by alternately switching on/off a pair of switch element Q1, Q2. When any of the above plural discharge lamps has become unloaded, the frequency of the high frequency voltage of the inverter circuit IN is made to increase, and the duty ratio of the above pair of switch element Q1, Q2 is adjusted to suppress the increase of input voltage to the inverter circuit IN.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge lamp lighting device for lighting a discharge lamp at a high frequency by an output of an inverter circuit.

[0002]

2. Description of the Related Art FIG. 7 shows a conventional discharge lamp lighting device. In FIG. 7, E is a commercial AC power supply, DB is a rectifier circuit constituted by a diode bridge, L1 is an inductance element, the rectifier circuit DB rectifies an AC voltage from the AC power supply E, and the rectifier circuit DB is rectified by the inductance element L1.
Is smoothed. D1 is a diode, and C1 is a smoothing capacitor. IN is an inverter circuit having a pair of switch elements Q1 and Q2.
A pair of switch elements Q1 and Q
2 are alternately turned on and off so that the inverter circuit IN converts the DC voltage VDC from the smoothing capacitor C1 into a high-frequency voltage.

A pair of discharge lamp load circuits B are provided in parallel with each other. Each discharge lamp load circuit B includes a discharge lamp L, a capacitor C2, a choke coil T1, and a capacitor C3.
The discharge lamps L are arranged in parallel with each other. When the pair of switching elements Q1 and Q2 are alternately turned on and off, a plurality of discharge lamps L are supplied from a DC power supply via an inverter circuit IN. To supply a high frequency voltage to the plurality of discharge lamps L. This discharge lamp lighting device is based on a conventional discharge lamp lighting device in which the input ratio is increased and the power supply harmonics are suppressed, and a plurality of discharge lamp load circuits B including a series circuit of a discharge lamp L and a choke coil T1 are connected. When one of the plurality of discharge lamps L has no load, the load is reduced, and the circuit voltage VDC (smoothing which becomes the input voltage to the inverter circuit IN) is performed. Since the voltage across the capacitor C1 rises, the rise of the circuit voltage VDC is detected by a series circuit of the resistor R2 and the resistor R3 to protect the circuit element, and the Zener diode ZD and the switch element Q are detected.
3, one switch element Q of the inverter circuit IN
2, the operation of the inverter circuit IN is stopped.

[0004]

Therefore, in the above-described conventional discharge lamp lighting device, when any one of the plurality of discharge lamps L has no load, the switching elements Q1, In order to protect Q2 and the like, the operation of the inverter circuit IN is stopped or the inverter circuit IN
Since it was necessary to reduce the output by changing the operating frequency of N, the other normal discharge lamps L could not be turned on, or the output lamps became low and the discharge lamps L dimmed significantly. However, there is a problem that the original brightness cannot be maintained.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. Even when one of a plurality of discharge lamps has no load, a high-voltage component can be used without using a high-voltage component. Another discharge lamp can be turned on without reducing its brightness.

[0006]

The technical means of the present invention for solving this technical problem includes a pair of switch elements Q
And a plurality of discharge lamps L provided in parallel from a DC power supply via the inverter circuit IN by alternately turning on and off a pair of switch elements Q1 and Q2. Is supplied to turn on the plurality of discharge lamps L, when any one of the plurality of discharge lamps L has no load, the inverter circuit IN
Is to adjust the duty ratio of the pair of switch elements Q1 and Q2 so as to increase the frequency of the high-frequency voltage output from the inverter circuit IN and to suppress the increase in the input voltage VDC to the inverter circuit IN.

Further, another technical means of the present invention includes an inverter circuit IN having a pair of switch elements Q1 and Q2, and a DC voltage VDC input to the inverter circuit IN.
A smoothing capacitor C1 is connected in parallel to a series circuit of the pair of switch elements Q1 and Q2 so as to form a step-up chopper circuit that generates a plurality of discharge lamps L by an output of the inverter circuit IN. In order to form a circuit, the pair of switch elements Q1, Q2
A plurality of discharge lamp load circuits B each having a discharge lamp L are connected in parallel to one of the switch elements Q2, and the pair of switch elements Q1 and Q2 are alternately turned on and off, so that the inverter circuit IN is switched from the DC power supply. Supplies a high frequency voltage to the plurality of discharge lamps L via the plurality of discharge lamps L.
In the discharge lamp lighting device, which is turned on, a load detection circuit F for detecting that one of the plurality of discharge lamps L has become unloaded is provided. An over-boost detection circuit G for detecting an over-boost of the input voltage VDC is provided, and when the load detection circuit F detects that no load is applied, the frequency of the high-frequency voltage output from the inverter circuit IN is increased. While driving the pair of switch elements Q1 and Q2,
When the over-boost detection circuit G detects over-boost of the input voltage VDC, control means is provided for adjusting the duty ratio of the pair of switch elements Q1 and Q2 so as to suppress the rise of the input voltage VDC to the inverter circuit IN. It is in that point.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. In FIG. 1, E is a commercial AC power supply, DB is a rectifier circuit constituted by a diode bridge, L1 is an inductance element, and the rectifier circuit DB is an AC power supply from the AC power supply E. A voltage is rectified, and a DC power supply is constituted by an AC power supply E, a rectifier circuit DB, an inductance element L1, a smoothing capacitor C1 described later, and the like.

D1 is a diode, and C1 is a smoothing capacitor. IN is an inverter circuit having a pair of switch elements Q1 and Q2.
Is, for example, an insulated gate field effect transistor (MO
SFET). A is a control circuit that drives a pair of switch elements Q1 and Q2 of the inverter circuit IN. Switching elements Q1 and Q2 connected in series with each other are connected in parallel with the smoothing capacitor C1.
A gate side of a pair of switch elements Q1 and Q2 and a control circuit A
The control circuit A outputs a drive signal to the switching elements Q1 and Q2 as shown in FIGS. 2A and 2B to alternately turn on and off the switching elements Q1 and Q2, and this is repeated. The inverter circuit IN converts the DC voltage VDC from the smoothing capacitor C1 into a high-frequency voltage.

B is a pair of discharge lamp load circuits which are provided in parallel with each other. Each discharge lamp load circuit B includes a discharge lamp L, a capacitor C2, a choke coil T1, and a capacitor C3.
The discharge lamps L are arranged in parallel with each other. When the pair of switching elements Q1 and Q2 are alternately turned on and off, a plurality of discharge lamps L are supplied from a DC power supply via an inverter circuit IN. The discharge lamp L is turned on by supplying a high-frequency voltage to the discharge lamp L. F is a load detection circuit provided for each of the plurality of discharge lamps L. When the corresponding discharge lamp L is not loaded, the voltage across the capacitor 3 becomes substantially 0 V or flows through the capacitor 3. It is configured to detect that the discharge lamp L has become unloaded when the current becomes approximately 0 A, and to output a no-load detection signal to the control circuit A. G is an over-boost detection circuit, which detects when the circuit voltage DVC (the voltage across the smoothing capacitor C1 to be the input voltage to the inverter circuit IN) is over-boosted (predetermined pressure or more) and detects the over-boosted. It is configured to output a signal to the control circuit A.

When the control circuit A inputs a no-load detection signal from the load detection circuit F to the control circuit A, the control circuit A supplies the switching elements Q1 and Q2 with driving signals shown in FIGS. As shown in FIGS. 2 (c) and 2 (d), a drive signal having a short on / off period is output, thereby increasing the frequency of the high frequency voltage output from the inverter circuit IN. When the control circuit A receives an over-boost detection signal from the over-boost detection circuit G, the control circuit A
As shown by dotted lines in FIGS. 2 (c) and 2 (d), a drive signal adjusted so as to shorten the ON period is output to 1, Q2, whereby the control circuit A suppresses an increase in the circuit voltage DVC. Thus, the duty ratio of the switching elements Q1 and Q2 is changed.

The inductance element L1, the switching element Q2, and the switching element (MOSFE)
T) As shown in FIG. 3, the parasitic diode D of Q1 constitutes a step-up chopper circuit that uses the voltage applied to the rectifier circuit DB as the input voltage and the voltage applied by the smoothing capacitor C1 as the output voltage. Also, the smoothing capacitor C
1, a pair of switch elements Q1, Q2, discharge lamp load circuit B
As a result, as shown in FIG. 4, a half-bridge circuit is formed. The switch element Q2 of the step-up chopper circuit and the switch element Q2 of the half-bridge circuit are also used, and the diode D of the step-up chopper circuit and the switch element Q1 of the half-bridge circuit Is also used as the parasitic diode D. Note that such a circuit that also serves as a component is called a shared chopper circuit.

According to the above embodiment, when an AC voltage is applied from the AC power supply E, the AC voltage is converted to the rectifier circuit DB.
Rectifies, the inductance element L1 and the switch element Q
The electric charge which becomes DC energy is accumulated in the smoothing capacitor C1 via the series circuit of one parasitic diode. The control circuit A controls the switching elements Q1, Q of the inverter circuit IN.
2 is turned on and off alternately, the DC voltage VDC from the smoothing capacitor C1 is converted into a high-frequency voltage by the inverter circuit IN, and power based on the voltage is supplied to each discharge lamp load circuit B, and the plurality of discharge lamps L Turn on.

When the switching element Q2 on the ground side of the inverter circuit IN is turned on, the potential at the connection point between the switching element Q1 and the switching element Q2 decreases, and the current flowing from the rectifier circuit DB into the inductance element L1 increases. Energy is stored. On the other hand, the switching element Q2
Is turned off, the potential at the connection point between the switching element Q1 and the switching element Q2 increases, and the switching element (MO
The parasitic diode of the (SFET) Q1 conducts, and the inductance element L1 releases the stored energy, boosts the smoothing capacitor C1, and improves the input ratio. When the smoothing capacitor C1 is over-boosted, an over-boost detection signal is input from the over-boost detection circuit G to the control circuit A that controls the driving of the switching elements Q1 and Q2. Then, the control circuit A
Changes the duty ratio of the switching elements Q1 and Q2 to adjust the voltage VDC of the smoothing capacitor C1.

The circuit voltage VDC of the shared chopper circuit is
It is determined by the balance between the energy generated by the boost chopper circuit and the energy consumed by the load of the half bridge circuit. Therefore, when a plurality of discharge lamps L are turned on by the shared chopper circuit, if any of the plurality of discharge lamps L is unloaded, the energy consumed by the load of the half bridge circuit is reduced. As a result, the generated energy is the same and the consumed energy decreases, so that the circuit voltage VDC increases. As the circuit voltage VDC increases, the current flowing through the discharge lamp L increases.
Therefore, when any one of the plurality of discharge lamps L has no load, the circuit voltage VDC increases due to the above-described factors, and at the same time,
The current flowing through the discharge lamp L will increase.

However, if any one of the plurality of discharge lamps L has no load, for example, if the circuit voltage VDC rises to 60 V and the current flowing through the discharge lamp L rises by 20 mA, any one of the load detection circuits F will cause the discharge lamp L to become unloaded. Upon detecting that no load has occurred, a no-load detection signal is output to the control circuit A. Then, the control circuit A controls the switching elements Q1 and Q2
Instead of the drive signals shown in FIGS. 2A and 2B, FIG.
As shown in (d), a drive signal having a short on / off period is output, and the frequency of the high frequency voltage output from the inverter circuit IN is increased. In this case, for example, if the frequency of the high frequency voltage of the inverter circuit IN is increased by 15%, the circuit voltage VDC is reduced to 30 V, and the current flowing through the discharge lamp L is reduced by 15 mA.

At the same time, the over-boost detection circuit G detects an increase in the circuit voltage DVC, and an over-boost detection signal is input from the over-boost detection circuit G to the control circuit A.
Outputs a drive signal to the switching elements Q1 and Q2 so that the ON period is shortened as shown by the dotted lines in FIGS. 2 (c) and 2 (d), whereby the control circuit A outputs the circuit voltage DVC The switching element Q
The duty ratio of Q1 and Q2 is changed. For example, when the duty ratio is reduced from 50% to 40%, the circuit voltage V
DC drops by 30 V, and the current flowing through the discharge lamp L decreases by 5 mA.

In the case of adjusting only the frequency, for example, if the frequency of the high frequency voltage of the inverter circuit IN can be increased by 30%, the circuit voltage VDC decreases by 60 V, the current flowing through the discharge lamp L decreases by 30 mA, and the circuit voltage VDC decreases. Although the rise can be suppressed, the current flowing through the discharge lamp L is reduced by 10 mA from the original current, and the brightness of the other normal discharge lamps L cannot be maintained. When only the duty ratio of the switching elements Q1 and Q2 is adjusted, for example, if the duty ratio is reduced from 50% to 30%, the circuit voltage VDC decreases by 60V,
The current flowing through the discharge lamp L decreases by 10 mA, and the circuit voltage V
Although the rise of DC can be suppressed, the current flowing through the discharge lamp L is
The current becomes 10 mA higher than the original current, so that an increase in the current flowing through the discharge lamp L cannot be prevented.

Therefore, the frequency and the switching elements Q1, Q2
When the duty ratio is adjusted simultaneously, for example, if the frequency of the high-frequency voltage of the inverter circuit IN is increased by 15% and the duty ratio is reduced from 50% to 40%, the circuit voltage VDC is reduced by 60 V and flows to the discharge lamp L. The current is reduced by 20 mA to suppress an increase in the circuit voltage VDC, prevent an increase in the current flowing through the discharge lamp L, and at the same time light another normal discharge lamp L without reducing its brightness. it can. Therefore, even if any one of the plurality of discharge lamps L has no load, an increase in the circuit voltage VDC can be suppressed, and an increase in current flowing through the discharge lamps L can be prevented. Can be continued with a predetermined power, and it is not necessary to use a high breakdown voltage component.

FIG. 5 shows another embodiment, in which a load detection circuit F is connected in parallel with each of a plurality of discharge lamps L, and the corresponding discharge lamps L are loaded without load by this load detection circuit F. Then, when the voltage between the connecting portions of the discharge lamp L rises to a predetermined pressure or more, it is detected that the discharge lamp L has no load, and a no-load detection signal is output to the control circuit A. It is what was constituted. The other points are the same as those in the above embodiment. FIG. 6 shows another embodiment, in which a secondary winding n2 is provided in each of the choke coils T1 of the plurality of discharge lamp load circuits B, and a load detection circuit F is connected to each of the secondary windings n2. The load detection circuit F takes out the difference between the voltages generated at both ends of each secondary winding n2,
When any one of the plurality of discharge lamps L has no load, the difference between the voltages generated in the respective secondary windings is equal to or higher than a predetermined voltage. It is configured to detect that a load has occurred and output a no-load detection signal to the control circuit A. The other points are the same as those in the above embodiment.

According to the embodiment, the load detection circuit F for detecting that one of the plurality of discharge lamps L has become unloaded is provided, and the load detection circuit F is connected to the inverter circuit IN. An over-boost detection circuit G for detecting over-boost of the input voltage VDC is provided, and when the load detection circuit F detects that the load is no longer loaded, the frequency of the high-frequency voltage output from the inverter circuit IN is increased. When the over-boost detection circuit G detects over-boost of the input voltage VDC, the pair of switch elements Q1 and Q2 are driven so as to suppress the rise of the input voltage VDC to the inverter circuit IN. , Q2 are adjusted, but instead, the over-boost detection circuit G is omitted, and when the load detection circuit F detects that no load is applied, Only the inverter circuit IN is to raise the frequency of the high frequency voltage output, it may be omitted adjustment of the duty ratio of the pair of switching elements Q1, Q2. Further, the over-boost detection circuit G is omitted,
When the load detection circuit F detects that no load has been applied,
The frequency of the high frequency voltage output from the inverter circuit IN is increased, and the input voltage VD to the inverter circuit IN is increased.
C, the pair of switch elements Q1,
The duty ratio of Q2 may be adjusted.

Further, when any one of the plurality of discharge lamps L has no load, a pair of switch elements Q1 and Q2 are provided so as to suppress an increase in input voltage VDC to inverter circuit IN. By merely adjusting the duty ratio, the increase in the frequency of the high-frequency voltage output from the inverter circuit IN may be omitted.

[0023]

According to the present invention, even when one of the discharge lamps becomes unloaded, the other normal discharge lamps are turned on without reducing the brightness without using high-voltage parts. Will be able to do it.

[Brief description of the drawings]

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

FIG. 2 is a waveform diagram showing a drive signal of a switch element.

FIG. 3 is a circuit diagram of a boost chopper circuit unit.

FIG. 4 is a circuit diagram of a half bridge circuit unit.

FIG. 5 is a circuit diagram showing another embodiment.

FIG. 6 is a circuit diagram showing another embodiment.

FIG. 7 is a circuit diagram showing a conventional example.

[Explanation of symbols]

 IN Inverter circuit IN Q1 Switch element Q2 Switch element L Discharge lamp F Load detection circuit G Over-boost detection circuit A Control circuit (control means)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shunichi Hongo 404-1 Nishinobumatsu, Himeji-shi, Hyogo F-term in Ikeda Electric Co., Ltd. (reference) 3K072 AA01 AB01 BB01 CA07 CA16 CB07 DA06 EA02 GB03 HA10

Claims (2)

[Claims] An inverter circuit (IN) having a pair of switch elements (Q1, Q2) is provided, and the pair of switch elements (Q1, Q2) are turned on and off alternately.
In a discharge lamp lighting device, a high frequency voltage is supplied to a plurality of discharge lamps (L) provided in parallel from a DC power supply via an inverter circuit (IN) to light the plurality of discharge lamps (L). When one of the plurality of discharge lamps (L) has no load, the inverter circuit (I)
N) increases the frequency of the high-frequency voltage output from the pair of switch elements (Q1, Q2) so as to suppress an increase in the input voltage VDC to the inverter circuit (IN).
2) A discharge lamp lighting device, wherein the duty ratio is adjusted. 2. An inverter circuit (IN) having a pair of switch elements (Q1, Q2), said booster chopper circuit generating a DC voltage VDC input to said inverter circuit (IN). A smoothing capacitor (C1) is connected in parallel to a series circuit of the switch elements (Q1, Q2) to form a half-bridge circuit for lighting a plurality of discharge lamps (L) with the output of the inverter circuit (IN). , The pair of switch elements (Q1, Q
2) A plurality of discharge lamp load circuits (B) each having a discharge lamp (L) are connected in parallel to one of the switch elements (Q2), and the pair of switch elements (Q1, Q2) are alternately turned on and off. In the discharge lamp lighting device, a high frequency voltage is supplied to the plurality of discharge lamps (L) from a DC power supply via an inverter circuit (IN) to light the plurality of discharge lamps (L). A load detection circuit (F) for detecting that one of the plurality of discharge lamps (L) has no load is provided, and a load detection circuit (F) for detecting an input voltage VDC to the inverter circuit (IN) is provided. An over-boost detection circuit (G) for detecting over-boost is provided, and when the load detection circuit (F) detects that there is no load, the frequency of the high-frequency voltage output from the inverter circuit (IN) is increased. Said one to let When the over-boost detection circuit (G) detects over-boosting of the input voltage VDC, the pair of switching elements (Q1, Q2) is driven. The pair of switch elements (Q1, Q
2) A discharge lamp lighting device comprising a control means for adjusting the duty ratio of 2).