JPH0265100A - Lighting device for discharge lamp - Google Patents

Abstract

PURPOSE:To correctly perform the protective operation with a simple circuit structure without being affected by the ambient temperature by measuring the continuation time of the preheated nonstert state with a timer circuit and switching a circuit to the dimming mode. CONSTITUTION:A saturation detecting circuit DET is removed, and a serial circuit of a mode switch SW and a resistor R14 is instead connected between the connection point of a resistor R2 and a capacitor C2 constituting a time constant circuit and the base of a transistor Q5. The preheated nonstart state is detected by a detecting means Q4, timer means R2 and C2 detect that the preheated nonstart state is continued for a preset time or longer, inverter means Q1 and T1 are set to the dimming mode, thereby a circuit can be correctly protected without being affected by the ambient temperature.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a discharge lamp lighting device, and in particular, the present invention relates to a discharge lamp lighting device, and in particular, the present invention relates to a discharge lamp lighting device. The present invention relates to a lighting device that can accurately prevent the destruction of a circuit device that can be damaged.

[Prior Art] Fig. 3 shows a conventional lighting device that has a function of protecting the device from a preheating non-starting state.
It includes a diode bridge DB for rectifying C, a smoothing capacitor C1, a switching transistor Ql, a ballast transformer T1, choke coils Ll and L2, a resonance capacitor C6, a discharge lamp LP, and the like. Further, a saturation detection circuit DET including a programmable unijunction transistor PUT, and a transistor Q2. Q3, Q
4. It also includes a mode switching circuit composed of Q5 and the like.

In the device shown in FIG. 3, alternating current power AC is rectified and smoothed by diode bridge DB and smoothing capacitor C1 to generate direct current power. This DC power supply causes transistor Ql, ballast transformer TI, choke coil L
The inverter circuit including L, L2, etc. oscillates to generate high frequency power. That is, the signal of the load circuit composed of the capacitor C3 and the choke coil L2 connected to the collector of the transistor Q1 is transmitted to the ballast transformer T1.
It is applied to the secondary coil N1, and feedback is performed from the secondary coil N2 of the transformer T1 to the base of the switching transistor Q1 via the choke coil L1 and capacitor C4.

As a result, the inverter circuit performs automatic oscillation and continues to output high frequency voltage.

The high frequency voltage generated in this way is taken out from the control winding N3 of the ballast transformer T1, rectified and smoothed by the diode D5 and the capacitor C5, and then connected to the detection power line PL.
It is applied to the saturation detection circuit DET etc. via I. For example, assume that the mode switch SW is set to the open state, that is, the all-optical mode. When the inverter circuit oscillates in this state, current is supplied to each electrode of the discharge lamp LP, and preheating is performed. Then, when the output voltage of the inverter circuit increases, a high voltage is applied between the electrodes of the discharge lamp LP, and the discharge lamp is started and lit.

However, while preheating of the discharge lamp LP continues as described above, for example, if the discharge lamp LP is at the end of its life, or for some other reason, the discharge lamp LP is not lit. It is assumed that this continues. In this case, the load impedance of the inverter circuit increases and the loss of the resonant circuit decreases, so the output voltage of the inverter circuit increases until the ballast 1 to the transformer T1 are completely saturated. As the output voltage of the inverter circuit increases, the voltage of the detection power supply line PLI also increases, and when this voltage exceeds a predetermined value, the anode voltage of PUT in the detection circuit DET becomes higher than the gate voltage and the PUT is turned on.

As a result, a base current is supplied to the transistor Q5, and the transistor Q5 is turned on. Accordingly, transistor Q4゜Q2. Q3 will cut off together. Therefore, the base feedback resistance of the switching transistor Q1 is approximately the series connection of the resistors R11 and R12, which shortens the on time of the transistor Q1 and reduces the output voltage of the inverter circuit. As a result, high voltage is not applied to each part of the circuit, and damage to each circuit element is prevented.

[Problems to be Solved by the Invention] In the lighting device shown in FIG. 3, the saturation state of the ballast transformer T1 when the preheating and non-starting state continues is affected by the ambient temperature of the inverter circuit and the like. That is, when the ambient temperature is high, the ballast transformer T1 quickly saturates, and therefore the detection voltage detected from the control winding N3 also rises rapidly, and the detection circuit DET immediately switches to dimming mode to protect the circuit. be done. However, when the ambient temperature is low, the saturation speed of the ballast transformer T1 is slow and it takes a relatively long time for the detection circuit DET to operate. As a result, high voltage is applied to various parts of the circuit for a long period of time, which sometimes causes damage to the circuit components. In addition, in order to prevent the circuit from being damaged even in such a case, it is necessary to use components with higher voltage resistance in the circuit, which is a factor that hinders miniaturization and cost reduction of the lighting device.

An object of the present invention is to provide a simple circuit that can reliably protect the circuit even if the preheating non-starting state continues, and to provide a large and high-voltage circuit component. An object of the present invention is to provide a discharge lamp lighting device that does not require the use of.

[Means for Solving the Problems] A discharge lamp lighting device according to the present invention includes an inverter means that generates a high frequency voltage for lighting the discharge lamp and has a dimming function, and detects a preheating non-starting state of the discharge lamp. a detection means, a timer means for detecting that the preheating non-starting state has continued for a predetermined time or more and generating a control signal, and a mode switching for setting the inverter means to a dimming mode in response to the control signal from the timer means. It is equipped with the means.

[Operation] In the above-mentioned device, the detection means detects the preheating non-starting state, and the timer means detects that the preheating nonstarting state continues for a predetermined time or more, sets the inverter means to the dimming mode, and switches the circuit. protect. Therefore, the circuit is properly protected without being affected by the ambient temperature.

[Example] Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 shows a circuit configuration of a discharge lamp lighting device according to an embodiment of the present invention. The device in the same figure eliminates the saturation detection circuit DET in the device in FIG. 3, and replaces it with a mode switch S.
A series circuit of W and resistor R14 is connected between the connection point of resistor R2 and capacitor C2 constituting a time constant circuit and the base of transistor Q5. The other parts are the same as the circuit of FIG. 3, and the same parts are designated by the same reference numerals. Incidentally, the time constant circuit and other circuit constants can be made different from those shown in FIG. 3 if necessary.

In the circuit shown in FIG. 1, it is assumed that the mode switch SW is off, that is, in the all-optical mode.

In this case, as mentioned above, when the AC power supply AC is turned on, the inverter circuit constituted by the transistor Q1, the ballast transformer T1, and others starts oscillating, and the discharge lamp LP
Supplies preheating current to When the power is first turned on, the voltage across capacitor C2 in the time constant circuit is ■. is sufficiently low that transistor Q4 is turned off, so that transistor Q2 . Q3
Both are turned off, resulting in a dimming state, and in this state, the discharge lamp LP is preheated.

As shown in FIG. 2, as time t passes, capacitor C2 is gradually charged via resistor R2.
For example, at time t1, the voltage across capacitor C2 is
When Q increases to a predetermined value or more, transistor Q4 is turned on. As a result, transistors Q2 and Q3 are also turned on, and both ends of resistor R11 are shorted. Therefore, the base feedback resistor of the transistor Q1 has a resistance value as low as that of the resistor R12, and the inverter circuit operates in the full light state and generates a high secondary voltage. As a result, the discharge lamp LP is normally turned on.

In the above-described operation, consider a case where the discharge lamp LP is at the end of its life and does not light up. In this case, the output voltage of the inverter circuit gradually increases to the voltage V across capacitor C2. As shown in FIG. 2, the temperature continues to rise even after time t2. Then, after a predetermined time in the time constant circuit of resistor R2, capacitor C2, resistors R3, and R4, that is, at time 3, transistor Q5 is turned on, transistor Q4. Q2. Q3 will cut off together. As a result, the circuit enters the dimming mode, and the output voltage of the inverter circuit decreases, thereby protecting each part of the circuit. Incidentally, when the discharge lamp LP is lit as described above, the voltage across the capacitor C2 is ■. does not increase much as shown by the dotted line in FIG. 2, so the transistor Q5 is not turned on and the inverter circuit continues to light the discharge lamp LP at its rated value.

Next, a case will be considered in which the mode switch SW is set to ON, that is, the dimming mode. In this case, the resistor R14 connected in series with the switch SW is connected in parallel with the resistor R3, so that the base voltage of the transistor Q5 rises more rapidly than when the switch SW is open. Therefore, transistor Q5 is turned on and normal dimming operation is performed.

[Effects of the Invention] As described above, according to the present invention, the duration of the preheating non-starting state is measured by the timer circuit and the circuit is switched to the dimming mode. The protection operation can be performed accurately depending on the circuit configuration. Furthermore, it is no longer necessary to use circuit components with higher withstand voltages that have a large margin, and the device can be made smaller and lower in price.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram showing the configuration of a discharge lamp lighting device according to an embodiment of the present invention, FIG. 2 is a graph for explaining the operation of the device in FIG. 1, and FIG. FIG. 2 is an electric circuit diagram showing the configuration of a conventional lighting device. DB: Diode bridge, CI, C2,..., C6
: Capacitor, Ql, Q2. ..., Q5: transistor, T1: ballast transformer, Ll, L2: choke coil, LP: discharge lamp, Di, D2. ...D5=diode, SW: mode selector switch, R1, R2,...
, R14: Resistor, PUT: Programmable unijunction transistor, zD: Zener diode.

Claims (1)

[Scope of Claims] Inverter means that generates a high frequency voltage for lighting a discharge lamp and has a dimming function, a detection means that detects a preheating non-starting state of the discharge lamp, and a preheating nonstarting state that continues for a predetermined time or longer. A discharge lamp lighting device characterized by comprising: timer means for detecting this and generating a control signal; and mode switching means for receiving a control signal from the timer means and setting the inverter means to a dimming mode. .