JP3786335B2 - Lamp power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lamp power supply device used in a projector or the like using a discharge lamp as a light source, and more particularly to a lamp power supply device that can prevent the lamp from being destroyed.
[0002]
[Prior art]
There are metal halide lamps, high-pressure mercury lamps, and the like as discharge lamps using discharge luminescence in metal vapor. These discharge lamps require a high starting voltage in order to cause breakdown and start. 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 through the discharge lamp increases.
FIG. 5 is a circuit diagram showing a conventional lamp power supply device. In FIG. 5, this power supply device mainly comprises a DC power supply 1, a chopper circuit 2, a high-voltage pulse generation circuit 9, and a discharge lamp 12, and will be described below.
[0003]
The chopper circuit 2 is a non-isolated switching regulator and cannot electrically insulate between the input and the output. However, the circuit configuration is simpler than the converter circuit that is an isolated switching regulator, and the cost is low. Can also be cheap. Also, considering the actual voltage value of the discharge lamp, the chopper circuit is often more suitable, and the ratio of the chopper circuit used in the lamp power supply device is high.
The chopper circuit 2 includes a switching element 3, a commutation diode 4, a coil 5, a smoothing capacitor (capacitor) 6, a current detection resistor 7, and a control unit 8. The chopper circuit 2 receives a direct current input from the direct current power source 1 and controls it. The unit 8 controls the switching element 3 to be turned on / off, thereby accumulating / releasing charges in the coil 5 and the smoothing capacitor 6 and adjusting the power supplied to the discharge lamp 12.
[0004]
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 a lamp current flows through the current detection resistor 7, and a voltage drop corresponding to the current value. Therefore, 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 the pulse generated by the pulse generation unit 11 to generate a high voltage pulse of about 10 kV to 30 kV. Insulation breakdown occurs, and the discharge lamp 12 is started.
[0005]
Before the discharge lamp is lit, the load impedance of the chopper circuit 2 is very high, and therefore the current is very small. Since the chopper circuit 2 is power-controlled, its output voltage is high and becomes a value close to the output voltage (for example, 200 V to 400 V) of the DC power supply 1. When the discharge lamp 12 breaks down due to the high-pressure pulse generated by the high-pressure pulse generation circuit 9 and starts and lights up, the lamp voltage, that is, the output voltage of the chopper circuit 2 suddenly drops to several tens of volts, and the chopper circuit 2 Operates so that the power becomes constant, the current increases rapidly, and the discharge lamp 12 is kept on.
[0006]
[Problems to be solved by the invention]
As described above, since the chopper circuit 2 is a non-insulated switching regulator, it cannot electrically insulate the input and output. If the switching element 3 is short-circuited for some reason, for example, when the switching element 3 itself is short-circuited or a foreign object is mixed between the electrodes of the switching element 3 while the discharge lamp is lit, the output voltage of the DC power supply 1 is discharged. When applied to the lamp 12, an excessive current (for example, several tens of A to one hundred A or more) flows through the discharge lamp, and the discharge lamp is instantaneously destroyed. Since this lamp breakdown occurs immediately after the short circuit (for example, 100 μs to less than 1 ms), it is difficult to avoid the breakdown after the short circuit state is detected. When the discharge lamp is broken, it is necessary to replace the lamp. However, since the discharge lamp is very expensive and troublesome to replace, the destruction of the discharge lamp is a serious problem.
[0007]
The present invention has been made in order to solve the above-described problem, and when the discharge lamp is turned on, the switching element itself of the chopper circuit is short-circuited or a conductor foreign matter is mixed between the electrodes of the switching element to cause a short circuit. In addition, since the voltage and lamp current between the input and output of the switching element are detected and the output of the chopper circuit is short-circuited to protect the discharge lamp, the discharge lamp can be prevented from being destroyed, and the cost of the expensive discharge lamp can be prevented. An object of the present invention is to provide a lamp power supply device that eliminates the need for payment and exchange.
[0008]
[Means for Solving the Problems]
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 source and a high-pressure pulse generating circuit for generating a high-pressure pulse for starting the discharge lamp are provided. A power supply device for a lamp, wherein the chopper circuit performs a switching element for controlling power of the discharge lamp by performing an on / off operation, a control unit for controlling on / off of the switching element, and an input voltage of the switching element. Input voltage detecting means for detecting; output voltage detecting means for detecting an output voltage of the switching element; voltage comparing means for comparing two output voltages of the input voltage detecting means and the output voltage detecting means; and the discharge lamp. Current detection to detect that the lamp current flowing in the Means, a thyristor that short-circuits the output of the chopper circuit, and the thyristor is turned on when there is no difference between the input voltage and the output voltage of the switching element and the lamp current is larger than a threshold value in the current detection means. And a lamp power supply device characterized by comprising a lamp protection means.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a circuit diagram showing an embodiment of the present invention. In FIG. 1, the same parts as those of the conventional example shown in FIG.
In FIG. 1, the input voltage detection means 13 for detecting the input voltage of the switching element 3 of the chopper circuit 2, the output voltage detection means 14 for detecting the output voltage of the switching element 3, and the output voltages of the two detection means are compared. A voltage comparison means 15 is provided. There are also provided current detection means 16 for detecting the current flowing through the discharge lamp 12 by the current detection resistor 7 and lamp protection means 17 for protecting the discharge lamp 12 from destruction by two outputs of the current detection means 16 and the voltage comparison means 15. ing. Furthermore, a thyristor 18 for short-circuiting the output of the chopper circuit 2 and a fuse 19 between the DC power supply 1 and the chopper circuit 2 are provided by the control from the lamp protection means 17, and the details will be described below. The operation will be described.
[0010]
When the voltage value output from the input voltage detection means 13 and the output voltage detection means 14 is equal to the input voltage of the switching element 3, the voltage output from the output voltage detection means 14 is larger. Set. In other words, the ratio of the output voltage to the observed voltage (input voltage) of the input voltage detection means 13 and the output voltage detection means 14 is changed. For example, if the input voltage detection means 13 is set to 100: 1 and the output voltage detection means 14 is set to 80: 1, if the input voltage of the switching element 3 is assumed to be 400V, the output voltage of the input voltage detection means 13 is 4V. When the output voltage of the switching element 3 is also 400V, the output voltage value of the output voltage detection means 14 is 5V. The output voltage of the switching element 3 at which the output voltage of the output voltage detection means 14 is 4V is 320V.
[0011]
Therefore, if the output of the output voltage detecting means 14 is connected to the non-inverting input terminal of the voltage comparing means 15 and the output of the input voltage detecting means 13 is connected to the inverting input terminal, if the switching element 3 is short-circuited, switching is performed. Since the input voltage and the output voltage of the element 3 become equal and the output voltage value of the output voltage detection means 14 becomes higher, the output of the voltage comparison means 15 becomes a high level. However, even in a normal case, before the discharge lamp is lit, the load impedance of the chopper circuit 2 is high, so that the output voltage of the chopper circuit 2 (switching element 3) is high and close to the input voltage. Of the output of the switching element may be at a high level, and it is not possible to specify a short circuit of the switching element by itself.
[0012]
Therefore, the current detection means 16 is provided so that the output of the current detection means 16 becomes a high level when a current exceeding the threshold flows with the lamp current value flowing through the discharge lamp 12 during normal lighting as a threshold value. Is set. The lamp protection means 17 is composed of an OR circuit (AND circuit) that outputs a high level only when both of the two outputs of the current detection means 16 and the voltage comparison means 15 are at a high level, thereby detecting a short circuit of the switching element 3. enable. That is, in the normal state, when the output voltage of the switching element 3 is high, almost no current flows, and the output of the current detection means 16 is at a low level. The output of the means 16 becomes high level.
[0013]
By the way, in the input voltage detection means 13 and the output voltage detection means 14, if the input voltage is constant, it seems that an absolute voltage value may be detected instead of a voltage difference between input and output. However, when the switching element 3 is actually short-circuited, excessive power is generated, so that depending on the power supply capability of the DC power supply 1, in most cases, the input voltage also drops rapidly, increasing the normal voltage value. Below. Therefore, it is effective to detect a voltage difference between input and output.
[0014]
Further, in the output voltage detection means 14, the detection location is not the output of the chopper circuit 2 but immediately after the switching element 3 in order to speed up the short circuit detection. Since the coil 5 is interposed at the moment when the switching element 3 is short-circuited, the voltage between the input and output of the chopper circuit 2 itself is not near zero, and the discovery of the short circuit is greatly delayed. Therefore, in order to reliably detect a short circuit of the switching element instantaneously, it is necessary to detect a voltage difference immediately before and after the switching element 3.
As described above, when a short circuit of the switching element 3 is detected, the lamp protection means 17 supplies a high level signal to the gate of the thyristor 18. Then, the thyristor 18 becomes conductive, and the output of the chopper circuit 2 is short-circuited. Even if the gate voltage of the thyristor 18 becomes low level, the short-circuit state is maintained and excessive current does not flow to the discharge lamp 12. Operate.
[0015]
However, when the output of the chopper circuit 2 is short-circuited by the thyristor 18, the thyristor 18 is kept in a conductive state, so that as long as the DC power supply 1 continues to supply current, an excessive current flowing to the chopper circuit 2 continues to flow, which is not preferable. .
In the circuit of the present invention, since the fuse 19 is connected between the DC power supply circuit 1 and the chopper circuit 2, even if an excessive current is generated due to the conduction of the thyristor 18, the fuse 19 is immediately turned on (for example, after 1 second). ) Fusing to cut off the excessive current. In addition, this fuse blown also provides double protection from the viewpoint of protection of the discharge lamp 12, thereby further strengthening the protection.
[0016]
If an element having a large surge-on current is used as the thyristor 18, even if the switching element 3 is short-circuited, only the switching element 3 and the fuse 19 need to be replaced. In addition, when a conductor foreign matter enters between the electrodes of the switching element and short-circuits, only the fuse needs to be replaced. In any case, it is much cheaper than the price of the discharge lamp 12 (for example, a cost of about 1/100).
[0017]
FIG. 2 is a circuit diagram showing a specific embodiment of the present invention, which basically performs the same operation as that of FIG. In FIG. 2, the input voltage detecting means 13 is composed of resistors 21 and 22 and a capacitor 23, and the output voltage detecting means 14 is composed of resistors 24 and 25 and a capacitor 26, and the ratio of the output voltage to the observed voltage is divided by resistance division, respectively. It is determined. The capacitance 26 is better when considering the response speed, but the voltage immediately after the switching element 3 is a rectangular pulse in a normal state and needs to be smoothed, and a capacitance value of about 1000 pF is selected. . Since the connection of the voltage comparison means 15 with the input voltage detection means 13 and the output voltage detection means 14 is opposite to that in FIG. 1, the output of the voltage comparison means 15 is also opposite in polarity to that in FIG.
[0018]
The current detection means 16 includes a transistor 29 and resistors 27, 28, 30. A value obtained by dividing the voltage generated by the current detection resistor 7 using the resistors 27, 28 is applied to the base of the transistor 29, and the transistor 29 Is conducted, the output of the current detection means 16 is at a low level. In other words, the current detection threshold value of the current detection means 16 is determined by the resistors 7, 27 and 28. Similarly to the voltage comparison means 15, the output of the current detection means 16 has a polarity opposite to that shown in FIG. It has become.
[0019]
Therefore, when the switching element 3 is short-circuited, that is, when the output voltage of the switching element 3 is high and a current exceeding the threshold value of the lamp current flows, the outputs of the voltage comparison means 15 and the current detection means 16 are Both are low level. Therefore, the lamp protection means 17 in FIG. 2 is a NOR circuit instead of an AND circuit, and is composed of diodes 31 and 32, a transistor 34, and resistors 33 and 35. If either one of the diodes 31 and 32 is turned on, the transistor 34 is also turned on. Therefore, the output of the lamp protection means 17 becomes high level when the two diodes are not turned on, that is, the voltage comparison means 15 is also current. The detection means 16 is also when its output is at a low level.
[0020]
A resistor 36 and a capacitor 37 are connected to the gate of the thyristor 18. The capacitor 37 is an element necessary for actual circuit driving. However, in consideration of the conduction start speed of the thyristor, the one having the smallest capacitance value is possible. Is preferred.
FIG. 3 is a diagram for explaining the place where the fuse is inserted. 1 and 2, the fuse 19 is inserted between the DC power source 1 and the chopper circuit 2. However, the fuse 19 is not limited to this location, and as shown in FIG. Any of 19a to 19e shown in the loop to the thyristor 18 may be used.
[0021]
FIG. 4 is a diagram for explaining a place where a fuse is inserted when connected to a commercial AC power source. Many lamp power supply devices use a commercial AC power supply as a power supply source. In FIG. 4, the lamp power supply device 41 operates by receiving power from the commercial AC power supply 40. Specifically, the power supply from the commercial AC power supply 40 is received by the DC power supply 1. The DC power supply 1 is often composed of a rectifying / smoothing circuit 38 and an active filter 39 for improving the power factor in order to comply with harmonic distortion regulations. In some cases, the rectifying / smoothing circuit 38 is not mounted with the active filter 39 but is increased to a voltage value necessary for lighting the discharge lamp by voltage doubler rectification. In either case, a fuse 19f may be inserted between the commercial AC power supply 40 as shown in FIG. Since the fuse 19f has the function of the fuse 19 in FIGS. 1 and 2, the fuse 19 in FIGS. 1 and 2 is not necessary when the fuse 19f is inserted.
[0022]
【The invention's effect】
The lamp power supply device according to the present invention can also be used for the input / output of the switching element even when the switching element itself of the chopper circuit is short-circuited or a conductor foreign matter enters between the electrodes of the switching element while the discharge lamp is lit. Protects the discharge lamp by short-circuiting the output of the chopper circuit by detecting the voltage and lamp current between them, preventing the discharge lamp from being destroyed, and eliminating the need for expensive discharge lamp payment and replacement There is an extremely excellent effect.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an embodiment of the present invention.
FIG. 2 is a circuit diagram showing a specific embodiment of the present invention.
FIG. 3 is a diagram for explaining a place where a fuse is inserted;
FIG. 4 is a diagram for explaining a place where a fuse is inserted when connected to a commercial AC power supply.
FIG. 5 is a circuit diagram showing a conventional lamp power supply device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 DC power supply 2 Chopper circuit 3 Switching element 4 Commutation diode 5 Coil 6 Smoothing capacity 7 Current detection resistor 8 Control part 9 High voltage pulse generation circuit 10 High voltage transformer 11 Pulse generation part 12 Discharge lamp 13 Input voltage detection means 14 Output voltage detection means 15 Voltage comparison means 16 Current detection means 17 Lamp protection means 18 Thyristor 19 Fuse

Claims (2)

A lamp power supply device comprising: a chopper circuit that controls a DC input voltage from a DC power supply to control the power of a discharge lamp; and a high-pressure pulse generation circuit that generates a high-pressure pulse for starting the discharge lamp,
The chopper circuit is
A switching element for controlling the power of the discharge lamp by performing an on / off operation;
A control unit for controlling on / off of the switching element;
An input voltage detecting means for detecting an input voltage of the switching element;
Output voltage detecting means for detecting the output voltage of the switching element;
Voltage comparison means for comparing two output voltages of the input voltage detection means and the output voltage detection means;
Current detection means for detecting that a lamp current flowing through the discharge lamp is larger than a threshold value which is a lamp current value at normal lighting;
A thyristor for short-circuiting the output of the chopper circuit;
When there is no difference between the input voltage and the output voltage of the switching element, and the lamp current is larger than a threshold value in the current detection means, it comprises lamp protection means for conducting the thyristor. Lamp power supply. The lamp power supply device according to claim 1, comprising a fuse inserted from the DC power supply into a current path of the chopper circuit.

Images