JPH03230766A - Lighting device for discharge lamp - Google Patents

Abstract

PURPOSE:To operate each comparator and hold circuit by continuing the oscillation in the condition that oscillation currents have decreased when overcurrents have flowed so as to use the voltage by oscillated currents as a power source. CONSTITUTION:When the current larger than the specified current flowing during lighting flows to a transistor 6, a hold circuit 26 operates by the output of a comparator 16A. As a result, by the output of an inverting circuit 27, a transistor 41 becomes on, and the reference voltage of the comparator 16 becomes smaller than ever. For that reason, by the output of the comparator 16, transistors 22 and 23 become on, and the transistor becomes off. When the transistor becomes off, a diode D1 and a transistor 7 are turned on in order, and it becomes the next cycle. Such condition is maintained as it is by a hold circuit 26. Hereby, an oscillating current continues flowing, though feeble, to a reactor 11, so it can continue to supply power to a comparator 16, a comparator 16A, and a hold circuit 26.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a discharge lamp lighting device.

(Prior Art) It is already well known that a half-bridge circuit is used as a high-frequency generating circuit in a configuration in which a high-frequency inverter is used to generate a high-frequency voltage and this is applied to a discharge lamp to perform high-frequency lighting. It is being

Figure 2 shows its configuration, and from the voltage of AC power supply terminal 1,
A DC voltage is obtained by a full-wave rectifier circuit 2 and a capacitor 3, and is supplied to a series circuit of a resistor 4 and a capacitor 5. 6.
7 is a transistor which is turned on and off alternately; 8 is a discharge lamp.

Briefly explaining the operation of this circuit, the voltage of the capacitor 5 charged by the DC voltage is applied to the two-terminal thyristor 9.
It is turned on when the breakover voltage is reached. Then, a base current flows through the transistor 6, turning it on.

When turned on, a current flows through the discharge lamp 8 via the capacitor 10, the inductance 11, the primary winding 13 of the current transformer 12, and the transistor 6 due to the DC voltage.

At this time, as a current flows through the primary winding 13 of the current transformer 12, a voltage whose polarity changes depending on the direction of the oscillating current flowing through the load circuit is induced in the secondary winding 14.15. .

This induced voltage is applied to the base of the transistor 6.7, and at a predetermined period determined by the oscillating current, the transistor 6.7
are switched alternately. As a result, a high frequency current flows through the discharge lamp 8, and the discharge lamp 8 is turned on at a high frequency.

By the way, in this type of lighting device, as a protection measure when an excessive current flows through the transistor 6, the first and second
circuit is available. The first circuit is a circuit that turns off the transistor 6 when an excessive current exceeding the maximum allowable current of the transistor 6 flows.

To explain the operation for this purpose, when an excessive current as described above flows, the emitter potential of the transistor 6 increases,
5 inductance 11 where the comparison input of comparator 16 becomes high
The induced voltage in the secondary winding 17 with the primary winding being
A reference voltage is applied to the comparator 16 from a resistor 20.21 via a resistor 20.21.

Here, as described above, when the comparison input becomes higher than the reference voltage, the output from the comparator 16 turns on the transistor 22. Therefore, transistor 23 is turned on and transistor 6 is turned off. Thereafter, diode D0 and transistor 7 are turned on in sequence, but until transistor 7 is turned on, transistor 23 remains on.

By turning off transistor 6, the previous excessive current is stopped and the comparison input of comparator 16 is reduced, which turns off transistor 22 and allows transistor 6 to turn on again in the next cycle.

The second circuit is a circuit that turns off the transistor 6 when a current between the above-described maximum allowable current and the current flowing during lighting flows. In this case, even if the current decreases thereafter, the off state of the transistor 6 is maintained.

To explain the operation for this purpose, as the emitter potential of transistor 6 becomes higher, the comparison input of comparator 16A increases. A reference voltage is applied here by resistors 24 and 25, and when the comparison input becomes higher than this, the hold circuit 26 is activated by the output from this point.

The hold circuit 26 includes an inverting circuit 27, 28 and a feedback resistor 29.
, a capacitor 3=O, and the output of the inverting circuit 27 is applied to the base of a transistor 31 inserted in a circuit that shorts a part of the secondary winding 14 of the current transformer 12.

When the hold circuit 26 operates, the transistor 31 is turned on, a part of the secondary winding 14 is shorted, and the output of the current transformer 12 is eliminated. As a result, transistor 6
is turned off, and its off state is held as is by the hold circuit 26.

The operating level of the first circuit described above is set higher than the operating level of the second circuit. That is, comparator 16
The reference voltage of the comparator 16 is set higher than A.

This is because before the discharge lamp 8 starts, a high voltage is required across both ends of the discharge lamp, and therefore a large current must flow.

Note that the second circuit is not operated for several seconds when the power is turned on or after the discharge lamp is installed in the socket. The configuration for this purpose is omitted in FIG. However, in FIG. 1, the second circuit is shown as a trigger circuit and a timer circuit 6. However, once the second circuit is activated, it is necessary to keep the transistor 6 off even after the oscillation of the high frequency circuit has stopped.

Therefore, as shown in the figure, the output voltage of the full-wave rectifier circuit 2 is taken as the power supply voltage, and the voltage divided by the voltage dividing resistor 32 is made into a constant smoothed voltage by the constant voltage element 33 and the smoothing capacitor 34. The obtained DC voltage is used as the power supply voltage for the comparator 16A and the hold circuit 26.

(Problems to be Solved by the Invention) According to such a configuration, the voltage dividing resistor 32 is required to obtain the current necessary to turn on the transistor 31 from the inverting circuit 27, and therefore, the voltage dividing resistor 32 is required. 32 has a large amount of power and generates a large amount of heat.

For example, when the voltage of the AC power supply terminal 1 is 200V, the resistance value of the voltage dividing resistor 32 is required to be 12.6 KΩ.

The electric power at this time is 1.61, and therefore, it is necessary to use a resistor with a rating of about 18 V, for example, in consideration of the thermal influence on the surroundings.

This invention does not rely on a high-voltage power source, and therefore uses a high-power field voltage dividing resistor as a power source for a circuit that turns off a high-frequency oscillation transistor when an excessive current flows through the transistor. The purpose is to ensure operation due to the transistor being turned off.

(Means for Solving the Problems) This invention provides a method for reducing the oscillation current and continuing oscillation when an excessive current exceeding a specified current flowing during lighting flows through the oscillation transistor. The present invention is characterized in that the power supply voltage for the hold circuit is obtained from the voltage obtained from the oscillation circuit at that time.

(Function) When the excessive current flows, oscillation is continued with the oscillation current reduced. Therefore, a voltage is obtained from the oscillation circuit due to the oscillation current. This voltage is used as a power source to operate each comparator and hold circuit. This eliminates the need to use voltage from an AC power source as a power source, and also eliminates the need for voltage dividing resistors.

(Example) An embodiment of the invention will be described with reference to FIG.

Note that parts given the same reference numerals as in FIG. 2 indicate the same or corresponding parts.

According to the invention, a transistor 41 is connected in parallel to the resistor 21 for obtaining the reference voltage of the comparator 16. The base current of this transistor 41 is supplied by the output of the inverting circuit 27 of the hold circuit 26.

The voltage from the secondary winding 17 of the reactor 11 is used as the power supply voltage for the comparator 16A and the hold circuit 26.

In the above configuration, if a current larger than the specified current flows through the transistor 6 during lighting, the comparator 1
The hold circuit is activated by the 6A output.

As a result, the output of the inverting circuit 27 causes the transistor 41 to
is turned on, and the reference voltage of the comparator 16 becomes smaller than before. Therefore, the output from comparator 16 turns on transistors 22 and 23 and turns off transistor 6.

When transistor 6 is turned off, diode D1. Transistors 7 are turned on one after another, starting the next cycle. Such a state is maintained as it is by the hold circuit 26.

In the conventional device shown in FIG. 2, oscillation is stopped by the second circuit described above, whereas in the case of FIG. 1, oscillation is not stopped.

As a result, the oscillation current continues to flow through the reactor 11, although it is weak, so that the power supply voltage continues to be supplied to the comparator 16, the comparator 16A, and the hold circuit 26. Therefore, in order to obtain these power supply voltages, the voltage dividing resistor 32 as shown in FIG. 2 is no longer necessary.

Note that when the power is turned on, a hold signal must not be given to the hold circuit 26 for several seconds after the discharge lamp is attached, so a trigger circuit 42 and a timer circuit 43 are provided for this purpose. When the power is turned on and when the discharge lamp is attached, the trigger circuit 42 operates and provides a signal to the timer circuit 43.

The timer circuit 43 receives this signal for several seconds (for example, 1
output for only 1 second). By this output, the inverting circuit 2
7 outputs an L output to forcibly turn off the transistor 41.

(Effects of the Invention) As detailed above, according to the present invention, in order to obtain power for the comparator and hold circuit necessary for suppressing excessive current, AC voltage is not divided as in the conventional method. So,
This eliminates the need for a voltage dividing resistor and also eliminates the heat generated by it.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional device. 1... AC power supply terminal, 6, 7... Transistor for oscillation, 8... Discharge lamp, 11 - Inductance, 16
゜16A... Comparator, 22, 23.41... Transistor, 26... Hold circuit. Light 7 figure

Claims (1)

[Claims] A discharge lamp lighting device that includes a pair of transistors and is lit by a high-frequency voltage generated by alternately turning on and off the transistors, wherein a current exceeding a specified current during lighting of the discharge lamp is a detection means for detecting that a current flows through the transistor; an off means for turning off the transistor when a current exceeding a maximum operating current flows through the transistor; a holding means for holding the detection result of the detection means; When the holding means holds the detection result,
and means for lowering the maximum operating current of the off means.