JPH05226084A - Discharge lamp lighting device - Google Patents

Abstract

PURPOSE:To provide a discharge lamp lighting device, by which bursting of a discharge lamp due to excessive power is prevented, and prevented even when the tube voltage is abnormally reduced as a result of degradation of the discharge lamp, or when a load including the discharge lamp falls in a short-circuited condition. CONSTITUTION:A discharge lamp 4 is lighted by the output of an inverter circuit 2. At the time, a tube current is controlled by a control circuit 7 according to a tube current of the discharge lamp 4. After a predetermined period of time passes after the discharge lamp 4 is lighted, counted by a timer 10, when abnormal current runs due to a power fed to the discharge lamp 4 that is in excess of a set value, the power is gradually transformed into rated power by a protective circuit, and when a short circuit current runs due to a power that is in further excess of the set value, the output of the inverter circuit 2 is immediately stopped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an instantaneous lighting type discharge lamp lighting device which detects a tube voltage of a discharge lamp and sets a tube current.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing a circuit configuration of a conventional discharge lamp lighting device capable of instantaneous lighting, for example, 35 W.
The structure of the lighting circuit of a small metal halide lamp is shown. In the figure, 1 is a direct current power source, 2 is an inverter circuit for converting the direct current into alternating current, and 3 is a starter circuit for starting the discharge lamp 4, which generates a high voltage pulse for starting.

Further, 5 is a tube voltage detecting circuit for detecting the tube voltage of the discharge lamp 4, 6 is a tube current detecting circuit for detecting the tube current of the discharge lamp 4, and 7 is an inverter according to the detected tube voltage and tube current. It is a control circuit that controls the output of the circuit 2 to the discharge lamp 4.

In the lighting device constructed as described above, when the DC power supply 1 is turned on, a high-voltage pulse is generated from the starter circuit 3, and this high-voltage pulse is applied to the discharge lamp 4. As a result, discharge is started in the discharge lamp 4, and further the output current of the inverter circuit 2 advances to arc discharge, and the amount of light emitted from the discharge lamp 4 increases to a stable state (steady state).
Transition to.

Here, in order to speed up the rise of the light emission amount when the discharge lamp 4 is lit, it is necessary to detect the tube voltage of the discharge lamp 4 and control the tube current. That is, as shown in FIG.
When the tube voltage VL is low immediately after the lighting of the discharge lamp 4 (when it is lower than the set voltage VL1), the maximum current IL1 is initially supplied as a warm-up region, and then the tube current IL decreases as the tube voltage VL gradually increases. Therefore, it is necessary to control the output light so as not to be too large or too small. Then, after the tube voltage VL1 in which the output light has increased to some extent, the lamp is turned on with a constant power as the rated range.

[0006]

In the conventional discharge lamp lighting device as described above, since the tube current is controlled by increasing or decreasing from the maximum to the rating according to the detection result of the tube voltage, the life of the discharge lamp is reduced. However, if the tube voltage drops abnormally due to deterioration or the like, there is a problem in that there is a danger that the power will always be overpowered during lighting, and further deterioration will occur and the discharge lamp will burst.

In addition, if the output wiring connected to the discharge lamp, which is a load, is accidentally short-circuited, and if a short-circuit current or an abnormal current exceeding the rating continues to flow when the power is turned on, the inverter circuit or the like lights up due to heat generation. There is a problem that the circuit may be damaged.

The present invention has been made in view of the above problems, and prevents the risk of bursting of the discharge lamp due to overpower even when the tube voltage is abnormally lowered due to the life or deterioration of the discharge lamp. It is an object of the present invention to provide a discharge lamp lighting device that does not damage a lighting circuit such as an inverter circuit due to heat generation or the like even when the output wiring connected to the discharge lamp is accidentally short-circuited.

[0009]

DISCLOSURE OF THE INVENTION A discharge lamp lighting device according to the present invention includes a tube voltage detection circuit for detecting a tube voltage of a discharge lamp, a control circuit for controlling a tube current according to the detected voltage, and a discharge lamp. When the electric power supplied to the discharge lamp exceeds the first set value after a predetermined time has passed from the lighting, it is shifted to the rated power, and when it exceeds the second set value larger than the first set value, it is released. And a protection circuit for stopping the output to the electric lamp.

Further, the above-mentioned protection circuit discriminates whether the output current to the discharge lamp is a short-circuit current or an abnormal current smaller than this and larger than the rating, a timer for setting the timing of the discrimination, and a short-circuit current. When it does, the output to the discharge lamp is immediately stopped, and when an abnormal current is discriminated, the sequencer gradually shifts to a steady current.

[0011]

In the discharge lamp lighting device of the present invention, the discharge lamp becomes rated power when an abnormal current flows beyond a certain set value supplied to the discharge lamp a predetermined time after the discharge lamp is lit. The output to the discharge lamp is controlled when it is controlled and becomes a value higher than the set value.

[0012]

1 is a block diagram showing a circuit configuration of a discharge lamp lighting device according to an embodiment of the present invention, and the same reference numerals as those in FIG. 3 denote the same components. In the figure, 1 is a direct current power source such as a vehicle battery, 2 is an inverter circuit for converting the direct current into alternating current, 3 is a starter circuit for starting the discharge lamp 4, and 5 is a tube voltage for detecting the tube voltage of the discharge lamp 4. A detection circuit, 6 is a tube current detection circuit for detecting the tube current of the discharge lamp 4,
A control circuit 7 controls the output of the inverter circuit 2, and controls the tube current according to the detected tube voltage of the discharge lamp 4.

Reference numeral 8 is a protection circuit for protecting the discharge lamp 4 from overpower, and after a lapse of a predetermined time after the discharge lamp 4 is lit, the power supplied to the discharge lamp 4 exceeds a first set value and is larger than the rated current. If current flows, switch to rated power and
When the short-circuit current flows beyond the second set value larger than the set value of, the output to the discharge lamp 4 is stopped. That is,
The protection circuit 8 discriminates whether the output current to the discharge lamp 4 is a short circuit current or an abnormal current smaller than the short circuit current and larger than the rating, a timer 10 for setting the timing of the discrimination, and a short circuit current. When it does, the output to the discharge lamp 4 is immediately stopped, and when an abnormal current is discriminated, the sequencer 11 gradually shifts to a steady current.

Next, the operation will be described. When the power source from the DC power source 1 is input to the inverter circuit 2, the discharge lamp 4 starts discharging due to the high-voltage pulse from the starting unit circuit 3,
After that, the discharge lamp 4 continues to light in a steady state by the output of the inverter circuit 2. At that time, the control circuit 7 controls the tube current according to the tube voltage of the discharge lamp 4 detected by the tube voltage detection circuit 5, and the discharge lamp 4 is instantly turned on and becomes stable.

FIG. 2 shows the circuit operation immediately after the discharge lamp 4 is started. Inverter circuit 2 including discharge lamp 4
When the load is normal, the normal warm-up current flows through the discharge lamp 4, as shown in FIG. That is, the maximum current IL1 is supplied until the tube voltage rises to some extent after the discharge lamp 4 is activated, and thereafter, the tube current IL is decreased as the tube voltage rises. Then, in a steady state, the tube current IL is reduced to a current so that the rated power is obtained, and the discharge lamp 4 is stabilized.

FIG. 2B is a diagram showing an operation when a load abnormality occurs such as when the output side of the inverter circuit 2 is in a short-circuited state or when the discharge lamp 4 is deteriorated. At this time, when the output is short-circuited, the tube voltage is detected as 0 V, and the output of the inverter circuit 2 is the maximum current (short-circuit current) I as indicated by A.
L1 always flows. Further, when the discharge lamp 4 is deteriorated, the tube voltage is abnormally lowered, and the tube voltage is detected to be low even when stable, so it is determined that warm-up is in progress, and an abnormal current such as B that causes an overpower larger than the rated value. (Tube current) IL2 will always flow.

Therefore, as shown in FIG. 2C, the output Vt of the timer 10 in the protection circuit 8 is detected from the lighting after the start of the discharge lamp 4 and after a lapse of time t1 from L (low level) to H (high level). Level). This time t1 is set to be a time sufficient for ending the warm-up after the normal discharge lamp 4 is started and shifting to the steady state. The protection circuit 8 protects the inverter circuit 2 and the discharge lamp 4 from overpower.

That is, FIG. 2D shows the operation of the protection circuit 8 when the load is abnormal. When the output short circuit of the inverter circuit 2 occurs, the time t1 set by the timer 10 is set.
After that, the discrimination circuit 9 detects the short-circuit current of A and inputs the detection signal to the sequencer 11. Then, the output of the sequencer 11 causes the control circuit 7 to stop the inverter operation of the inverter circuit 2 and stop the output.

When the discharge lamp 4 deteriorates and the tube voltage drops abnormally, the discrimination circuit 9 similarly detects an abnormal current of B after time t1 and inputs the detection signal to the sequencer 11. At this time, the control circuit 7 controls the inverter circuit 2 in accordance with the signal from the sequencer 11 so as to smoothly reduce the tube current from the state of being overpowered to the discharge lamp 4 to the rated power.

As described above, when the electric power supplied to the discharge lamp 4 exceeds a certain set value and an abnormal current flows after a lapse of a predetermined time after the discharge lamp 4 is lit, the discharge lamp 4 is controlled to have a rated power. Therefore, rapid deterioration is suppressed even in the discharge lamp 4 in which the tube voltage has abnormally decreased due to life, deterioration, etc., and the risk of explosion due to overpower is prevented. Further, when the power supplied to the discharge lamp 4 becomes higher than the set value and a short-circuit current flows, the output of the inverter circuit 2 to the discharge lamp 4 is stopped, so that the discharge lamp 4 is connected. Even if the connected wiring is accidentally short-circuited, it is possible to prevent the lighting circuit such as the inverter circuit 2 from being damaged by heat generation.

[0021]

As described above, according to the present invention, when the electric power supplied to the discharge lamp exceeds a certain set value after a predetermined time has passed since the discharge lamp was lit, the electric power is controlled to be the rated electric power,
When the value is higher than the set value, the output to the discharge lamp is stopped, so even if the tube voltage drops abnormally due to the life or deterioration of the discharge lamp, the discharge lamp may not burst due to overpower. There is an effect that danger can be prevented, and even if the output wiring connected to the discharge lamp is accidentally short-circuited, the lighting circuit such as the inverter circuit can be prevented from being damaged by heat generation.

[Brief description of drawings]

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

FIG. 2 is a waveform diagram showing the operation of the circuit of FIG.

FIG. 3 is a block diagram showing a configuration of a conventional example.

FIG. 4 is a characteristic diagram showing the relationship between the tube voltage and the tube current when the discharge lamp is started.

[Explanation of symbols]

 1 DC power supply 2 Inverter circuit 4 Discharge lamp 5 Tube voltage detection circuit 6 Tube current detection circuit 7 Control circuit 8 Protection circuit 9 Discrimination circuit 10 Timer 11 Sequencer

Claims (2)

[Claims] 1. A tube voltage detection circuit for detecting a tube voltage of a discharge lamp, a control circuit for controlling a tube current according to the detected voltage, and a supply to the discharge lamp after a predetermined time has passed since the discharge lamp was lit. A protective circuit is provided which, when the power exceeds the first set value, shifts to the rated power and stops the output to the discharge lamp when the second set value larger than the first set value is exceeded. A discharge lamp lighting device characterized by the above. 2. The protection circuit discriminates whether the output current to the discharge lamp is a short-circuit current or an abnormal current smaller than this and larger than the rating, a timer for setting the timing of the discrimination, and a short-circuit current. 2. The discharge lamp lighting device according to claim 1, further comprising: a sequencer that immediately stops the output to the discharge lamp when it does, and gradually shifts to a steady current when an abnormal current is discriminated.