JPS607100A - Device for firing discharge lamp - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a discharge lamp lighting device that controls lighting of a discharge lamp by switching and driving a power transistor with a rectangular wave.

[Technical background of the invention and its problems]

Conventionally, as this type of discharge lamp lighting device, one shown in FIG. 1 is known. In this method, a rectifier circuit 2 is connected to an AC power supply 1, and a choke coil 3 is connected between the output terminals of the rectifier circuit 2.
A discharge lamp 5 is connected through a 74-power transistor 4 of the NPN type in series. A flywheel diode 6 is connected in parallel to the series circuit of the choke coil 3 and the discharge lamp 5 with a polarity opposite to that of the power transistor 4. A rectangular wave voltage is applied to the power transistor 4 by a drive circuit 7. The emitter current of the power transistor 4 is detected by a current detection circuit 8, and a voltage corresponding to the average value of the emitter current is supplied to the drive circuit 7. The current detection circuit 8 includes an emitter resistor 9 and a capacitor 10 connected in parallel with the emitter resistor 9. Furthermore, it is formed by a capacitor 12 connected in parallel via a resistor 1. The drive circuit 7
has a pulse width modulation circuit that variably controls the duty ratio of the rectangular wave voltage according to the output voltage of the current detection circuit 8, and controls the duty ratio to be small when the output voltage is high, and reduces the duty ratio when the output voltage is low. - The average value of the emitter current of the power transistor 4 is kept substantially constant by controlling the T ratio to a large extent.

The rectangular wave output from the power transistor 4 is converted into a direct current by the choke coil 3 and the flywheel diode 6, and then supplied to the discharge lamp 5.

With this circuit, substantially constant power is supplied to the discharge lamp 5 during normal lighting.

However, with this conventional tube manufacturing method, it is not possible to control the duty ratio of the square wave voltage to a sufficiently small value when the lamp impedance is low at the time of starting the discharge lamp, and as a result, a large inrush current flows, leading to blackening of the lamp and shortened lifespan. In extreme cases, there was a risk of rupture. In addition, when the impedance of the discharge lamp decreases during startup or due to a short circuit accident, the output power decreases while the circuit input power remains approximately constant, which increases the collector loss of the tower transistor and generates heat. There was a problem.

[Purpose of the invention]

This invention was made to solve the table problem as described above, and it is possible to suppress the inrush current at the time of starting the discharge lamp, and also to reduce the circuit input power when the impedance is low, thereby preventing lamp blackening and shortening the life of the lamp. It is an object of the present invention to provide a discharge lamp lighting device that can prevent explosion, etc. and also prevent heat generation of a power transistor.

[Summary of the invention]

This invention connects a discharge lamp to the output terminal of a rectifier circuit connected to an AC power source via a noqua transistor, drives the transistor by switching with a rectangular wave voltage from the drive circuit, and converts the emitter current of the transistor into a current. A detection circuit detects and outputs a voltage corresponding to the average value of the emitter current, and a voltage detection circuit detects a rectangular wave voltage applied to the transistor pace and outputs a voltage corresponding to the average value of the rectangular wave voltage. At the same time, a predetermined voltage set in advance is output from the voltage generation means, and the lower one of the predetermined voltage generated from the voltage generation means and the voltage output from the voltage detection circuit is taken out and inputted to the comparator as a reference voltage. In addition, the voltage output from the current detection circuit is input to the comparator, the difference output from the reference voltage is calculated and input to the drive circuit, and the voltage output from the current detection circuit is greater than the reference voltage. The duty ratio of the rectangular wave voltage output from the drive circuit is controlled in the direction of decreasing in accordance with the differential output level at the time.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

A rectifier circuit 22 is connected to an AC power source 21.

A discharge lamp 25 is connected to the rectifier circuit 22 through a choke coil 23 and an NPN type power transistor 24 in series. The negative output terminal of the rectifier circuit 22 is grounded. A flywheel diode 26 is connected in parallel to the series circuit of the choke coil 23 and the discharge lamp 25 with the polarity opposite to that of the power transistor 24. A rectangular wave voltage is applied to the power transistor 24 from a drive circuit 27 . The emitter current of the power transistor 24 is detected by a current detection circuit 28, and a voltage corresponding to the average value of the emitter current is supplied to one input terminal of a comparator 33. The current detection circuit 28 includes an emitter resistor 29 and a capacitor 30 connected in parallel with the emitter resistor 29. Furthermore, it is formed by a capacitor 32 connected in parallel via a resistor 31. A voltage detection circuit 34 detects the rectangular wave voltage applied from the driving circuit 27 to the pace of the transistor 24, and outputs a voltage corresponding to the average value of the rectangular wave voltage. The voltage detection circuit 34 is connected to the transistor 24
A series circuit of a resistor 35 and a capacitor 36 is connected between the pace and ground, a resistor 38 is connected in parallel to the capacitor 36 via a diode 37, and the output voltage across the resistor 380 is amplified by an amplifier 39. It is outputting. Further, a series circuit of resistors 41 and 42 is connected in parallel to the battery 40 whose negative end is grounded to form voltage generating means. Further, the anodes of a pair of diodes 43 and 44 are connected to each other and connected to the other input terminal of the comparator 33, and the cathode of the diode 43 is connected to the output terminal of the amplifier 39 of the voltage detection circuit 34, The cathode of the diode 44 is connected to the connection point of the resistors 4J and 42 [7] to form voltage extraction means. The comparator 33 inputs the voltage output from the voltage extraction means as a reference voltage]7
, the reference voltage and the voltage from the current detection circuit 28 are compared, and the difference output is supplied to the drive circuit 27. The drive circuit 27 controls the duty ratio of the rectangular wave voltage to be outputted in a direction that decreases in accordance with the difference output level when the voltage outputted from the current detection circuit 28 is larger than the reference voltage.

Next, the operation of the apparatus according to the embodiment of the present invention constructed as described above will be described. Also, the resistor 29 in the current detection circuit 28
The voltage across it is V. , the output voltage in the same circuit 28 is V
&p The voltage across the capacitor 36 in the voltage detection circuit 34 is 7, the voltage across the resistor 380 in the same circuit 28 is V^', the output voltage in the same circuit 28 is VB, and the resistor 4 is
Let vR be the voltage between both ends of 2, and VOO be the reference voltage.

The rectangular wave voltage from the drive circuit 27 causes the transistor 2 to
4 is switched, and the discharge lamp 25 is controlled to be lit. When the transistor 24 is turned on, an emitter current flows through the emitter resistor 29. As a result, a voltage VE is generated across the emitter resistor 29, and the voltage V= is smoothed by capacitors 30 and 32, averaged, and output as a voltage V/. On the other hand, the rectangular wave voltage input from the drive circuit 27 to the pace of the transistor 24 is averaged by the capacitor 36 and becomes a voltage vA.
The diode 37 lowers the voltage level by about 65 volts to the voltage A', and that voltage A' is then applied to the amplifier 3.
9, the signal is amplified approximately five times, for example, and output as a voltage VB. Furthermore, the voltage vR across the resistor 42 is 41.42
For example, 2? is set to default. The voltages VA, VA, and VB change as the duty ratio of the rectangular wave voltage changes. That is, the duty ratio of the rectangular wave voltage and each voltage V, , vA.

If the relationship between VB and Vn is shown in a graph, it will be as shown in FIG. And the reference voltage VO input to the comparator 33
Since O is determined by preferentially extracting the lower voltage VB and vR, Vn is selected in the range where the duty ratio is less than about 25 to 30 inches, and VB=2V in the range above. This reference voltage VOO is applied to the current detection circuit 28 by the comparator 33.
In the region of Voo < Vg, the duty ratio of the rectangular wave voltage output from the drive circuit 27 decreases rapidly as shown in FIG.
The amount of emitter current is suppressed by shortening the on-operation period of the emitter.

Therefore, when the load becomes low impedance, such as when starting and lighting the discharge lamp 25, the duty ratio of the rectangular wave voltage supplied to the transistor 24 decreases, and as a result, each voltage VA, vA', vB decreases. do. When the data ratio is in the range of 25 to 30 inches, the voltage VB becomes VR
The duty ratio, which decreases to the reference voltage VOO, is controlled to be even smaller, and the amount of emitter current of the transistor 24 is suppressed. In this way, when the discharge lamp 25 has a low impedance, the output voltage V of the current detection circuit 28 can be kept lower than during normal lighting, and the emitter current can be reduced. Therefore, it is possible to prevent a large inrush current from flowing when the discharge lamp 25 is started and turned on, and it is possible to prevent the rung from becoming black and shortening its life due to the inrush current. Figure 5 shows the load characteristics. When the load impedance reaches a point where it decreases, the reference voltage VOO to the ratio V converter 33 decreases, and the output current changes as shown by the solid line in the figure, as shown by the dotted line in the figure. The output does not increase as in the conventional case, but remains almost constant, and the output decreases.

In addition, when the impedance is low, such as when starting a discharge lamp or when a short circuit occurs, the on-operation period of the transistor 240 is minimized to reduce the circuit input power, thereby preventing an increase in the collector loss of the transistor 24 and preventing the transistor 24 from generating heat. can be prevented.

〔Effect of the invention〕

As described in detail above, according to the present invention, it is possible to suppress the inrush current at the time of starting the discharge lamp to a small level, thereby preventing lamp blackening, shortening the lamp life, and even preventing lamp explosion. Accordingly, it is possible to provide a discharge lamp lighting device that can prevent this.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional example, Fig. 2 is a circuit diagram showing an embodiment of the present invention, Fig. 3 is a graph showing voltages at various parts with respect to the duty ratio of the drive circuit output in the same embodiment, and Fig. 4 5 is a graph showing the duty ratio change of the drive circuit output with respect to the current detection circuit output in the same embodiment, and FIG. 5 is a graph showing the load characteristics in the same embodiment. 21... AC' power supply, 22... Rectifier circuit, 24...
・Power transistor, 25...Discharge lamp, 27...
Drive circuit, 28... Current detection circuit, 33... Comparator, 34... Voltage detection circuit, 40... Battery, 41.4
2...Resistor, 43.44...Diode.

Claims (1)

[Claims] An AC power source, a rectifier circuit connected to this AC power source, a discharge lamp connected to the output terminal of this rectifier circuit via a power transistor, and the emitter current of the transistor are detected, and the average value of the emitter current is calculated. a current detection circuit that outputs a corresponding voltage; a drive circuit that applies a rectangular wave voltage to the pace of the transistor to drive the transistor for switching; and a drive circuit that detects the rectangular wave voltage applied to the pace of the transistor and detects the a voltage detection circuit that outputs a voltage corresponding to the average value of the wave voltage; a voltage generation means that generates a predetermined voltage; a predetermined voltage generated from the voltage generation means; and a voltage output from the voltage detection circuit. The voltage extracted by the voltage extraction means and the voltage extracted by this voltage extraction means is inputted as a reference voltage, the reference voltage is compared with the voltage output from the current detection circuit, and the difference output is used as the voltage output for the drive. In addition to a comparator supplied to the circuit, the drive circuit outputs a difference when the voltage output from the current detection circuit is larger than the reference voltage. A discharge lamp lighting device characterized by controlling in a direction of decreasing size.