JPS6126198B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a discharge lamp lighting circuit.

Recently, the lighting method for discharge lamps is to oscillate an oscillating transistor such as an inverter and emit light using a high-frequency voltage because it is more efficient and smaller and lighter than the conventional iron and copper ballast that uses commercial power frequency voltage. Various methods for lighting electric lights have been proposed. As an example, as shown in Fig. 1, the + side of a DC power supply 1 is connected to the intermediate tap 5 of the primary coil 4 of a transformer 3 via the coil 2, and one side constitutes a push-pull inverter. The two oscillation transistors 6 and 7 are connected to their respective ends of the primary coil 4 through their emitters and collectors, and the bases of the oscillation transistors 6 and 7 each have a base resistor 8 connected to the + side of the DC power supply 1. , 9 are connected, and a feedback coil 10 is also connected. And the secondary coil 1 of transformer 3
A discharge lamp 12 is connected to the lamp, and an oscillation lighting circuit 13 is constructed by these. As a result, the oscillation transistors 6 and 7 are turned on and off alternately by the direct current flowing through the feedback coil 10 while receiving the DC power supply 1, and the transformer is activated by the high frequency voltage of the oscillation transistors 6 and 7 due to the symmetrical sine wave. 3, the discharge lamp 12 is turned on. However, although this kind of operation does not pose a problem when the discharge lamp 12 is lit normally, when the discharge lamp reaches the end of its life, the discharge lamp 12
The filaments at both ends of the lamp become unbalanced with each other, resulting in unbalanced positive and negative direct current lighting, or the discharge sustaining voltage increases, making lighting unstable, resulting in abnormal oscillation. That is,
When looking at the discharge lamp 12, a filament coated with an active substance is provided at both ends, and the discharge lamp 12 lights up by alternately discharging between the filaments, but at the end of its life, one of the filaments is coated with an active substance. If the active substance on the filament is completely peeled off and discharge occurs in only one direction, resulting in so-called "DC lighting," or if only a small amount of active substance remains on one filament, the imbalance between the left and right sides of that filament causes direct current. This may result in abnormal lighting, which is slightly different from normal lighting. When the filament becomes unbalanced in this way, a large current 3 to 4 times the normal flow flows through the oscillation transistors 6 and 7, resulting in DC loss, which places a burden on the oscillation transistors 6 and 7 and the transformer 3, and increases the temperature. Abnormal rise in oscillation transistors 6 and 7
This results in an abnormal state of destruction. Therefore, the transformer 3, the oscillation transistor 6,
The oscillation transistor 6,
A large heat dissipation plate is provided for the 7 series to improve heat dissipation. However, with such a pair, the entire lighting device becomes large and expensive, which ultimately goes against the initial purpose and becomes a major obstacle to practical application. Lighting is performed using a commercial frequency voltage using a ballast.

The present invention has been made in view of the above points, and it is possible to perform lighting using a practical high-frequency voltage by eliminating problems such as abnormal oscillation of the oscillation transistor due to the imbalance phenomenon at the end of the life of the discharge lamp. The purpose is to obtain a discharge lamp lighting circuit.

The present invention includes an oscillation lighting circuit that lights a discharge lamp via a transformer by oscillation of an oscillation transistor, and a positive/negative unbalance detection circuit for detecting a DC component of a difference in positive/negative unbalance at the end of the life of the discharge lamp in the transformer. The detection signal is fed back to the oscillation lighting circuit to adjust the base voltage of the oscillation transistor so as to limit the output of the oscillation transistor or stop the oscillation according to the level of the detection signal of the positive/negative imbalance detection circuit. It is characterized by the fact that Therefore, by providing a positive/negative imbalance detection circuit for the oscillation lighting circuit, when the discharge lamp reaches the end of its life and a positive/negative imbalance occurs, the detection signal of the positive/negative imbalance detection circuit is used to detect the oscillation transistor. It is possible to limit the output and stop oscillation, thereby preventing abnormalities such as destruction of the oscillation transistor, and is designed to be put into practical use without increasing the size or cost. be.

An embodiment of the present invention will be described based on FIGS. 2 and 3. Components that are the same as those shown in FIG. 1 are designated by the same reference numerals, and description thereof will be omitted. In this embodiment, a detection coil 14 is provided for the transformer 3, and a diode 16 and a capacitor 17 are connected between an intermediate tap 15 of the detection coil 14 and one end, and a diode 16 and a capacitor 17 are connected between the intermediate tap 15 of the detection coil 14 and the other end. A positive/negative imbalance detection circuit 20 is provided in between, which is formed by connecting a diode 18 and a capacitor 19. Here, the intermediate tap 15 is connected to the DC power source 1.
connected to one side of the In addition, the detection coil 14
The detection voltage at one end is V ₁₁ , the detection voltage at the other end is V ₂₁ , and the capacitors 17 and 19
The voltages are V ₁ and V ₂ , respectively. An amplifier 21 for differentially amplifying the difference between voltages V ₁ and V ₂ , that is, a signal of V ₂ -V ₁ , is provided for this positive/negative imbalance detection circuit 20.
are connected to resistors 22 and 23 that divide the output. Further, a resistor 24 and a capacitor 25 are connected between this resistor 23 and one side of the DC power supply 1, and a transistor 26 whose base resistance is this resistor 24 has its emitter connected to one side of the DC power supply 1. On the collector side of this transistor 26, there is a collector-base resistor 27 connected to the + side of the DC power supply 1 together with this collector.
A transistor 28 is provided having a base connected to the base thereof. The emitter of this transistor 28 is connected to the midpoint of the base resistors 8 and 9 via a Zener diode 29, and an unbalanced amplification control circuit 30 is configured.

In such a configuration, when the discharge lamp 12 has not reached the end of its life and is lit normally, the detection voltages V ₁₁ and V ₂₁ generated in the detection coil 14, and therefore the voltages V 1 and V ¹ of the capacitors 17 and 19, Since V ₂ has a positive and negative balance and does not produce an output below the amplifier 21, the positive and negative imbalance detection circuit 2
0 and the unbalanced amplification control circuit 30 do not limit the oscillation lighting circuit 13 and the oscillation lighting circuit 1
3 operates as in the conventional manner, and the discharge lamp 12 continues to be lit with a high frequency voltage generated by a sine wave based on the oscillation of the oscillation transistors 6 and 7.

However, when the discharge lamp 12 reaches the end of its life, some active material remains in one filament and a small amount remains in the other filament, and the current flowing through the discharge lamp 12 becomes unbalanced between positive and negative. This positive/negative imbalance is detected by the detection coil 14, and the detected voltages V ₁₁ and V ₂₁ become asymmetric between positive and negative, as shown in FIG. 3(a), for example. The detection voltages V ₁₁ and V ₂₁ are connected to the diodes 16,
The capacitor 17 is divided into positive and negative by 18,
19 and the voltages V ₁ and V ₂ are respectively shown in Figure 3.
The detection signal is converted to DC as shown in (b) and (c). These two detection signals V ₁ and V ₂ are differentially amplified by an amplifier 21, with the difference V ₂ −V ₁ being amplified. The output from this amplifier 21 becomes an unbalanced DC component signal, which is divided by resistors 22 and 23 and then divided by resistors 24 and 24.
to the base of transistor 26 through. Here, since the collector of this transistor 26 is connected to the base of the transistor 28, the bias of this transistor 28 changes depending on the output amount of the amplifier 21, that is, the level of the unbalanced signal, and the base of the oscillation transistors 6 and 7 changes. The voltage will be adjusted. Therefore, V ₂
- If the unbalanced signal of V ₁ is large, both oscillation transistors 6 and 7 turn off and stop oscillation, and if V ₂ -V ₁ is below a certain level, the base voltage of oscillation transistors 6 and 7 is suppressed and the This limits the output. As a result, the oscillation transistors 6 and 7 are protected from abnormal states caused by unbalance phenomena, and the oscillation transistors 6 and 7 can be made compact, lightweight, and highly efficient without having to increase their capacity or provide large heat sinks. It is possible to put it into practical use while maintaining the initial advantages.

Although this embodiment describes a push-pull inverter system, other systems may be used as long as the oscillation lighting circuit 13 has an oscillation transistor and power is supplied to its base. It is applicable.

In the present invention, as described above, a positive/negative imbalance detection circuit is provided for the oscillation lighting circuit, so when the discharge lamp reaches the end of its life and a positive/negative imbalance occurs, the detection signal of the positive/negative imbalance detection circuit is used. It is possible to protect the oscillation transistor by limiting its output or stopping oscillation.This allows the oscillation transistor to be made smaller and lighter without having to increase its capacity or provide a large heat sink. This has the advantage of being able to be put to practical use as a high frequency voltage system.

[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, and FIG. 3 is a waveform diagram thereof. 6-7...Oscillation transistor, 12...Discharge lamp, 1
3...Oscillation lighting circuit, 20...Positive/negative imbalance detection circuit.

Claims (1)

[Claims] 1. An oscillation lighting circuit is provided for lighting a discharge lamp via a transformer by oscillation of an oscillation transistor, and the transformer is provided with a positive/negative imbalance detection circuit for detecting a DC component of a difference in positive/negative imbalance at the end of the life of the discharge lamp. The detection signal is fed back to the oscillation lighting circuit to adjust the base voltage of the oscillation transistor so as to limit the output of the oscillation transistor or stop the oscillation according to the level of the detection signal of the positive/negative imbalance detection circuit. A discharge lamp lighting circuit featuring: