JP2001135493A - Power-source device for lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power-source device for lamps which can realize the extension of life of a discharge lamp and can restrain both of rush current into the discharge lamp and ripple values, without requiring sealing-up of a coil for a filter. SOLUTION: Smoothing capacity 6 and smoothing capacity 14 are connected in parallel, compose a smoothing-capacity group of a chopper circuit 2 and obtain an integrated smoothing-capacity value. A switching element 15 is connected in parallel with the smoothing capacity 14, and by turning on and off it, converts the integrated smoothing-capacity value. A timer 16 controls the switching element 15 so that the integrated smoothing-capacity value may be low during the predetermined time from power-source turning on to the stabilization of lighting of a discharge lamp, and may be high after the lapse of the predetermined time. A coil 13 for a filter is connected between the output side of a coil 5 and a high-voltage pulse generation circuit 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a lamp power supply used for a projector or the like using a discharge lamp as a light source.

[0002]

2. Description of the Related Art Discharge lamps utilizing discharge light emission in metal vapor include metal halide lamps and high-pressure mercury lamps. These discharge lamps require high starting voltages in order to start due to dielectric breakdown. Further, the discharge lamp has a property of being limited by electric power so that the terminal voltage of the lamp decreases as the current flowing therethrough increases. FIG. 4 is a circuit diagram showing a first conventional power supply device for a lamp. In FIG. 4, this power supply device mainly includes a DC power supply 1, a chopper circuit 2, a high-voltage pulse generation circuit 9, and a discharge lamp 12, which will be described below.

The chopper circuit 2 is a non-insulated switching regulator and cannot electrically insulate between input and output. However, the circuit configuration is simpler than that of a converter circuit which is an isolated switching regulator. In addition, the cost can be reduced. Also, considering the actual voltage value of the discharge lamp, the chopper circuit is often more suitable, and the chopper circuit is frequently used in the lamp power supply device. The chopper circuit 2 includes a switching element (first switching element) 3, a commutation diode 4, and a coil.
It comprises a (first coil) 5, a smoothing capacitor (capacitor) 6, a current detecting resistor 7, and a control unit 8, receives a DC input provided by the DC power supply 1, and turns on the switching element 3 by the control unit 8. By performing the OFF control, the electric charge is accumulated / discharged to the coil 5 and the smoothing capacitor 6 and the discharge lamp 1
2 to adjust the power supply.

The control unit 8 detects the output voltage of the chopper circuit 2, that is, the voltage at the point A in the figure as lamp voltage information, and the lamp current flows through the current detection resistor 7, and according to the current value, Since the voltage drop occurs, the voltage at point B in the figure is detected as lamp current information, and the switching element 3 is controlled to control the power of the discharge lamp 12. The high-voltage pulse generation circuit 9 includes a high-voltage transformer 10 and a pulse generation unit 11. The high-voltage transformer 10 boosts a pulse generated by the pulse generation unit 11 to 10 kV to
A high-voltage pulse of about 30 kV is generated, causing dielectric breakdown in the discharge lamp 12 and starting the discharge lamp 12.

Before the discharge lamp is turned on, the load impedance of the chopper circuit 2 is very high, the current is very small, the output voltage of the chopper circuit 2 is high, and the DC power supply 1
The value is close to a DC input (for example, 200 V to 400 V). When the discharge lamp 12 causes dielectric breakdown due to the high-voltage pulse generated by the high-voltage pulse generation circuit 9 and starts and lights, the lamp voltage, that is, the output voltage of the chopper circuit 2 rapidly drops to several tens of volts, and the chopper circuit 2 Since the operation is performed so that the power becomes constant, the current increases rapidly, and the lighting of the discharge lamp 12 is maintained. By the way, in order to stably maintain the lighting of the discharge lamp, in other words, in order to suppress the lamp flicker as much as possible and not to cause the lamp resonance phenomenon, it is necessary to make the ripple value of the current flowing through the discharge lamp as small as possible. Therefore, the larger the capacitance value of the smoothing capacitor 6 of the chopper circuit 2 is, the more preferable.

However, when the discharge lamp 12 is started,
That is, when the output voltage of the chopper circuit 2 rapidly drops from a very high voltage such as 400 V to several tens of volts, the electric charge stored in the smoothing capacitor 6 until immediately before the discharge lamp is started becomes an inrush current to the lamp 12. It flows instantaneously. or,
Before starting the discharge lamp and before stabilizing, the discharge lamp suddenly changes its own impedance, suddenly increases its impedance, and sometimes drops again, and again the lamp voltage changes according to the lamp impedance. Therefore, if the impedance changes rapidly and extremely from a high state to a low state, a similar rush current flows. These inrush currents increase as the electric charge stored in the smoothing capacitor 6 increases, and cause damage to the discharge lamp itself. Therefore, not only the life is affected but also the discharge lamp may be destroyed in some cases.

If the capacitance value of the smoothing capacitor is large with respect to the steep and rapid impedance change of the lamp itself as described above, it takes time to charge and discharge the smoothing capacitor, and cannot respond to the change. In particular, when the impedance suddenly rises, the response is delayed, a necessary voltage or current cannot be secured, and there is a possibility that the discharge lamp may be turned off and then turned off once. As explained above,
The capacitance value of the smoothing capacitor 6 of the chopper circuit 2 is
The smaller the ripple value of the current flowing through the discharge lamp 2 is, the better. The smaller the ripple value is, the better the current is from the rush current to the discharge lamp 12 and the phenomenon of disappearance.

FIG. 5 is a circuit diagram showing a second conventional power supply device for a lamp. This is a circuit of a conventional example which realizes, to some extent, compatibility of two contradictory conditions with respect to the smoothing capacitance 6 of the chopper circuit 2. 5 differs from FIG. 4 in that a filter coil (second coil) 13 is inserted between the chopper circuit 2 and the high-voltage pulse generating circuit 9. The filter coil 13 limits the inrush current to the lamp at the start of discharge lamp lighting, and performs the filter function at the subsequent stable lamp lighting to reduce the ripple value of the lamp current. The capacitance value can be reduced, and both the ripple value and the inrush current of the lamp current can be suppressed. In FIG. 5, the value of the smoothing capacitance 6 actually used is 0.5 μF to 3 μM.
F, the value of the coil 13 is about 100 μH to 1 mH.

[0009]

Some of the discharge lamps include:
In order to achieve a long life and to improve the optical characteristics, there are those in which the inrush current must be extremely suppressed and those in which the change in impedance after lighting is extremely large. In order to cope with these lamps, the capacitance value of the smoothing capacitance 6 needs to be reduced by one digit or more from the above-mentioned value, and the inductance value of the filter coil 13 needs to be increased by the decrease in the capacitance value. . However, the filter coil 13 having an inductance value (for example, 10 mH) which is ten times or more of the above value and capable of securing the reliability for a large lamp current value (for example, 3 A to 10 A) becomes very large. It is heavy, expensive, and unrealistic. Furthermore, if the capacitance value of the smoothing capacitor 6 is reduced to this point, the switching frequency has a limit, so that a large ripple voltage is superimposed on the voltage to be fed back, making it difficult to operate the chopper circuit 2 stably. There are points.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a filter is provided while maintaining the stability of the operation of the chopper circuit by switching the capacitance value of the smoothing capacitance of the chopper circuit at the time of starting the discharge lamp. It is an object of the present invention to provide a lamp power supply device that does not require an increase in the size of a coil for use, and that can suppress both the inrush current to the discharge lamp and the ripple value, thereby extending the life of the discharge lamp.

[0011]

In order to achieve the above object, a chopper circuit for controlling the power of a discharge lamp by controlling a DC input voltage from a DC power supply and a high-voltage pulse for starting the discharge lamp are provided. A power supply device for a lamp, comprising: a high-voltage pulse generating circuit that generates the high-voltage pulse; wherein the chopper circuit performs a power on / off operation of the discharge lamp by performing an on / off operation;
And a first coil connected to the output side of the first switching element, and a plurality of capacitors connected in parallel or in series to form a total smoothing capacitance value. A smoothing capacitor group for smoothing the output voltage of the first coil, and a second capacitor that is connected in parallel or in series with the capacitors in the smoothing capacitor group and switches the total smoothing capacitor value by turning on and off. A switching element, a second coil connected between the output side of the first coil and the high-voltage pulse generating circuit, and a predetermined time from when the power is turned on until the lighting of the discharge lamp is stabilized.
A lamp circuit for controlling the second switching element so that the total smoothing capacitance value is small and the total smoothing capacitance value becomes large after a predetermined time has elapsed. A power supply is provided.

[0012]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention. In FIG. 1, the same portions as those of the conventional example shown in FIGS. 4 and 5 are denoted by the same reference numerals, and description thereof will be omitted. In FIG. 1, the smoothing capacitance of the chopper circuit 2 is configured as a smoothing capacitance group including two serially connected smoothing capacitances 6 and 14 to obtain a total smoothing capacitance value. Switching elements in parallel so that the smoothing capacitor 14 can be short-circuited
A (second switching element) 15 is provided, and further, a timer circuit 16 for controlling ON / OFF of the switching element 15 is provided. The smoothing capacitor 14 to which the switching element 15 is connected in parallel has a very small capacitance (for example, 50
nF), and the other smoothing capacitor 6 is a relatively large capacitor (for example, 1 μF). In FIG. 1, the size of the capacitor is visually indicated by the size of the circuit symbol.

The switching element 15 is a MOS transistor in FIG.
-Although an FET is used, a bipolar transistor and a diode connected in parallel or an electronic power relay may be used. The timer circuit 16 keeps the switching element 15 in an open state for a predetermined time from the time of power-on, which receives a DC input from the DC power supply 1, and controls the switching element 15 to a short-circuit state after a lapse of a predetermined time. And
The predetermined time is set to a time during which the discharge lamp 12 may be turned on to cause a change in impedance, that is, a time until a stable operation is performed.

As a result, the total smoothing capacitance value of the chopper circuit 2 is small when the lamp is started or when the impedance changes (the smoothing capacitance 14 is much smaller than the smoothing capacitance 6;
The overall smoothing capacity value is substantially equal to the capacity value of the smoothing capacity 14), and the filter coil (second coil) 13 is also assisted, so that the rush current to the discharge lamp 12 can be suppressed to a very small value. When the lamp is stably operated, only the smoothing capacity 6 is provided. Therefore, the total smoothing capacity value is larger than that at the time of starting the lamp, and the ripple value of the current flowing to the discharge lamp 12 can be suppressed with the help of the filter coil 13.

When the switching element 15 is open and the total smoothing capacitance value of the chopper circuit 2 is extremely small, the voltage across the smoothing capacitance is dominated by the ripple voltage and can no longer be called a DC voltage. It is difficult to control this chopper circuit 2 (switching element 3) by feeding back this voltage as lamp voltage information. Therefore, in FIG. 1, the control unit 8 controls on / off of the switching element 3 using the output voltage after the filter coil 13 as lamp voltage information. The output voltage after the filter coil 13 is close to the DC voltage even when the switching element 15 is open, so that the switching element 3 can be controlled stably.

FIG. 2 is a specific circuit diagram of FIG. 2, the timer circuit 16 includes resistors 18, 21, 23, 23
25, a capacitor 19, a Zener diode 20, and NPN transistors 22 and 24. The capacitor 19 is charged by the voltage of the DC power supply 17 via the resistor 18, and when this charged voltage reaches the Zener voltage of the Zener diode 20, The diode 20 conducts, causing the base current of the transistor 22 to flow, causing the transistor 22 to conduct. As a result, the transistor 24 is opened and the DC power supply 1
7 is supplied to the switching element 15 via the resistor 25.

Accordingly, if the DC power supply 17 and the DC power supply 1 start operating at the same time, that is, if two of a plurality of outputs of the same switching power supply circuit are used, the resistor 18, the capacitor 19, and the zener diode 20 If the determined predetermined time is set to be approximately equal to the stabilization time of the discharge lamp, the switching element 15 may be used until the lamp reaches a stable state before starting.
In an open state, and thereafter the switching element 15 can be controlled to a conductive state.

FIG. 3 is a circuit diagram showing a second embodiment of the present invention. 3, the difference from FIG. 1 is that the connection of the smoothing capacitor group of the chopper circuit 2 is parallel, and the switching element 15 is provided in series with the smoothing capacitor 6 having a large capacitance value. The operation is the same as that of FIG. 1, and the switching element 15 is opened from before the lamp is started until the lamp reaches a stable state, and thereafter, the switching element 15 is turned on. As explained in detail above,
The lamp power supply device of the present invention shown in FIGS. 1 to 3 suppresses the inrush current to the discharge lamp, extends the life of the discharge lamp, and prevents the breakdown of the discharge lamp, while maintaining the operation stability of the chopper circuit. In addition, the response speed of the chopper circuit is increased to eliminate the phenomenon of the discharge lamp going out.

[0019]

According to the lamp power supply device of the present invention, the filter coil is enlarged while the operation of the chopper circuit is maintained stable by switching the capacitance value of the smoothing capacity of the chopper circuit when the discharge lamp is started. There is no need, and there is an extremely excellent effect that both the inrush current to the discharge lamp and the ripple value can be suppressed and the life of the discharge lamp can be extended.

[Brief description of the drawings]

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

FIG. 2 is a specific circuit diagram of FIG.

FIG. 3 is a circuit diagram showing a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing a first conventional power supply device for a lamp.

FIG. 5 is a circuit diagram showing a second conventional lamp power supply device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC power supply 2 Chopper circuit 3 Switching element (1st switching element) 4 Commutation diode 5 Coil (1st coil) 6,14 Smoothing capacity 7 Current detection resistance 8 Control part 9 High voltage pulse generation circuit 10 High voltage transformer 11 Pulse Generator 12 Discharge lamp 13 Filter coil (second coil) 15 Switching element (second switching element) 16 Timer circuit

Claims (2)

[Claims] A power supply for a lamp, comprising: a chopper circuit for controlling the power of a discharge lamp by controlling a DC input voltage from a DC power supply; and a high-voltage pulse generating circuit for generating a high-voltage pulse for starting the discharge lamp. An apparatus, wherein the chopper circuit includes a first switching element that controls power of the discharge lamp by performing an on / off operation; a control unit that controls on / off of the first switching element; The first connected to the output side of the device
And a plurality of capacitors connected in parallel or in series, having a total smoothing capacitance value, and a smoothing capacitance group for smoothing the output voltage of the first coil; A second switching element connected in parallel or series with the capacitor and switching the total smoothing capacitance value by turning on and off; and a second switching element connected between the output side of the first coil and the high-voltage pulse generating circuit. The coil and the second smoothing capacity value so that the total smoothing capacity value is small during a predetermined time from when the power is turned on until the lighting of the discharge lamp is stabilized, and the second smoothing capacity value is large after the predetermined time has elapsed. A lamp power supply device comprising: a timer circuit for controlling a switching element. 2. The control unit according to claim 1, wherein a voltage on an output side of said second coil is detected as a voltage of said discharge lamp, and on / off of said first switching element is controlled. A power supply device for a lamp according to claim 1.