JPS58204494A - 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 The present invention relates to an improvement in a discharge lamp starting method in a discharge lamp lighting circuit using a discharge lamp as a load using a step-down chopper circuit.

FIG. 1 shows a discharge lamp lighting circuit using a step-down chopper circuit. The DC power supply 1, the discharge lamp 2, the inductance 3, and the transistor 4 constitute a first closed circuit. The inductance 3, the diode 5, and the discharge lamp 2 constitute a second closed circuit. The capacitor 6 is connected in parallel with the discharge lamp 2, but this is for stabilizing the operation and is not essential. The auxiliary winding 32 wound on the inductance 3, the capacitor 8, and the diode 9 constitute a driving circuit for the transistor 4, and the resistor 7 constitutes a starting circuit for the transistor 4.

The action is the next escape. First, when the transistor 4 becomes conductive, a direct current flows from the power source 1 to the discharge lamp 2 to the inductance 3 to the transistor 4 to the power source 1.

Next, when the transistor 4 is turned off rapidly in the energized state, the current in the inductance 3 generates a back electromotive force in the inductance 3, and the current flows in the order of the inductance 3 -> the diode 5 -> the discharge lamp 2 -> the inductance 3. When this current becomes zero, the multi-transistor 4 becomes conductive again due to the action of the base circuit, and the same operation is repeated thereafter.

When a pressure-resistance type chopper circuit is used in a lighting circuit for a DC discharge tube, the number of circuit elements is small, the transistor cut-off current can be made smaller than that of a normal -stone blocking oscillator, and an inexpensive circuit can be provided as a whole.

A problem when using this circuit as a lighting circuit for a discharge lamp, particularly a discharge lamp having a preheating electrode, is in starting the discharge lamp.

In other words, the starting voltage of the discharge lamp before starting is extremely high unless the electrode 21 is heated. It will not start unless the voltage is extremely high. Therefore, the first closed circuit described above is not formed and oscillation does not occur.

FIG. 2 shows a discharge lamp lighting circuit previously proposed by the present applicant in order to provide good starting characteristics. Power supply 1, diode 11, discharge lamp 2, inductance 3, and transistor 4
constitutes a first closed circuit, and inductance 3, diode 5, and discharge lamp 2 constitute a second closed circuit.

The capacitor 6 is connected to the discharge lamp 2, and the resistor 12 is connected to the diode 11.
The two-terminal thyristor 10 is connected in parallel with the diode 11 and the discharge lamp 2. The breakdown voltage of the thyristor 10 is set to be below the power supply voltage and above the discharge voltage. When the transistor 4 is conductive, the thyristor 10 is also conductive, and the power supply 1 → thyristor 10 → the electrode 21 of the discharge lamp 2 → the inductance 3
→ Transistor 4 → Power supply 1, current flows and heats the electrode. Next, when the transistor 4 in the current-carrying state is cut off, the current in the inductance 3 charges the capacitor 6 via the diode 5. Diode 11 prevents this charging voltage from discharging through thyristor 10. The resistor 12 controls the amount of discharge of the capacitor 6 and sets the base voltage of the capacitor 6 to a desired value. Due to this voltage, the discharge lamp 2
can be started.

After the discharge lamp 2 is started, the thyristor 1o becomes non-conductive and operates in the same manner as described in FIG. At this time, no potential difference is generated at the end of the diode 11, so there is no loss at the resistor 12.

This circuit has the following two drawbacks.

(1) When the transistor 4 is non-conductive, the voltage applied to the transistor 4 is the sum of the power supply voltage and the charging voltage of the capacitor 6. On the other hand, after starting, only the power supply voltage is applied. The charging voltage of the capacitor 6 must be a certain value in order to start the discharge lamp 2, and even if this value is approximately the power supply voltage, the transistor breakdown voltage must be set to twice the power supply voltage.

(2) If the discharge tube whose electrode 21 has reached the end of its life is left connected, most of the input power from the power source 1 will be absorbed by the resistor 1.
2, the resistor 12 generates abnormal heat.

Therefore, an object of the present invention is to provide a discharge lamp lighting device that eliminates the above-mentioned drawbacks.

In order to achieve the above object, the present invention provides a self-breakdown type switch at the end of the radiant lamp, and utilizes the change in oscillation characteristics due to the change in load resistance between starting and lighting to switch the switch. A discharge lamp lighting device is configured to control characteristics, and an inexpensive starting circuit is provided.

Hereinafter, the present invention will be explained in detail using figures.

FIG. 3 shows an embodiment of a discharge lamp lighting device according to the present invention.

Power supply 1, transistor 4, inductance 3 and discharge lamp 2
constitutes a first closed circuit, and the inductance 3, discharge lamp 2, and diode 5 constitute a second closed circuit. A capacitor 6 is connected in parallel with the discharge lamp 2, and a switch element 10 is connected to the discharge lamp 2.
are also connected in parallel. The discharge lamp 2 can be started with an applied voltage lower than the power supply voltage when the electrodes are sufficiently heated, and the breakdown voltage of the switch element 10 is set to be lower than the power supply voltage and higher than the discharge voltage of the discharge lamp 2. When using an SCR as shown in the figure as the switch element 10, the self-breakdown voltage can be arbitrarily set using the resistors 11 and 12.

The operating characteristics of the pace circuit and the value of the capacitor 6 are also important in obtaining the effects of the present invention. The pace circuit applies the induced voltage of the auxiliary winding 32 wound around the inductance 3 to the pace emitter of the transistor 4 via the capacitor 8, thereby making the transistor 4 conductive. First, when the transistor 4 becomes conductive, a voltage of [power supply voltage - load voltage] is applied to the inductance 3. This voltage is converted into a voltage approximately determined by the turns ratio between the main winding 31 and the auxiliary winding 32 and appears on the auxiliary winding 32. This voltage causes a current to flow between the base and emitter of the transistor 4 via the capacitor 8, thereby ensuring that the transistor 4 is conductive. When capacitor 8 finishes charging, no current flows between the base and emitter of transistor 4, so transistor 4 quickly becomes non-conductive. Then, a back electromotive force is generated in the inductance 3, and a current flows from the inductance 3 to the load consisting of the discharge tube 2, the switching element 1o, the resistors 1i and tz, and then to the diode 5. During this time, the voltage appearing across the inductance 3 is of opposite polarity to that when the transistor 4 is conducting. Auxiliary winding 32
The sum of the induced reverse voltage and the charging voltage of the capacitor 8 causes a reverse current to flow through the diode 9. For this reason,'·
A reverse voltage is applied to the emitter-base of transistor 4, ensuring that transistor 4 is non-conducting. Now, if the voltage induced in the auxiliary winding 32, that is, the voltage obtained by stepping down the load voltage by the turns ratio of the main winding 31 and the auxiliary winding 32, does not exceed the forward voltage of the diode 9, then The photoelectric voltage of the capacitor 8 is then applied to the transistor 4
Do not charge if the polarity is conductive.

In addition, the inductance 3 and the capacitor 6 cause vibrations, but otherwise they do not vibrate and are attenuated. Here, R is the load resistance, L is the inductance of the inductance 3, and C is the capacitance of the capacitor 6. When the closed circuit is damping, the period during which the current in the diode 5 becomes zero, and therefore the non-conducting period of the transistor 4, becomes significantly longer than when the closed circuit is oscillatory.

Next, the operation at the time of starting the discharge lamp 2 will be explained. Now, when the transistor 4 becomes conductive and almost the power supply voltage is applied to the thyristor 1o, and the thyristor 1o also becomes conductive, a current flows from the power supply 1 to the transistor 4 to the inductance 3 to the thyristor 10 to the electrode 21 to the power supply 1. Next, transistor 4
When is cut off, inductance 3-→thyristor 1o→
A current flows from the electrode 21 to the diode 5. This is it,
Electrode 21 is heated. If the thyristor 10 does not start non-conducting during the non-conducting period of the transistor 4, the transistor 4 becomes conductive again and repeats the same operation. In this state, although the electrode 21 is heated, since the end of the discharge lamp 2 is always short-circuited by the thyristor 1o, no voltage is applied and the discharge lamp 2 cannot be started.

However, it should be noted that the load in the above state is only the resistance of the electrode 21, and the load resistance is significantly smaller than when the discharge lamp 4 is lit. Therefore, the closed circuit constituted by the inductance 3, the capacitor 6, and the electrode resistance 21 is attenuated, and the non-conducting period of the transistor 4 increases significantly. In addition, since the load resistance becomes significantly smaller, the voltage appearing across the inductance 3 also becomes significantly smaller.If the ratio between the main winding 31 and the auxiliary winding 32 is selected appropriately, the capacitor 8 The voltage can be set so as not to charge to a polarity that would cause the transistor 4 to conduct. Therefore, the following operation occurs.

First, if the vibration of the load circuit is damped, the transistor 4
As the non-conducting period increases, the current flowing through the thyristor 10 decreases, so when the current t becomes almost zero (below the holding current of the thyristor 10), the thyristor 10 easily becomes non-conducting. can be recovered. Even if the thyristor 4 becomes non-conductive, the capacitor 8 is not charged with the polarity that makes the transistor 4 conductive, so the transistor 4 does not become conductive immediately. The transistor 4 becomes conductive again until the current flowing through the starting resistor 7 charges the capacitor 8 and reaches a voltage equivalent to the base-emitter voltage of the transistor 4. Therefore, if the time constant of the starting resistor 7 and the capacitor 8 is made long enough,
The circuit becomes temporarily unstoppable. During this time, thyristor 1
0 will definitely restore non-conduction. Next, transistor 4
When restarted, since the capacitor 6 is discharged while the thyristor IO is conducting, a closed circuit of the transistor 4 → inductance 3 → capacitor 6 → power supply 1 is formed.

If the capacitance of the capacitor 6 is made appropriately large, the charging voltage of the capacitor 6 will still be sufficiently low when the transistor 4 is cut off. Next, current flows through the inductance 3 → capacitor 6 → diode 5, and the capacitor 6 is further charged. Thereafter, the same operation is repeated, and the charging voltage of the capacitor 6 gradually increases. When this reaches the self-breakdown voltage of the thyristor 10 set by the resistors 11 and 12, the thyristor 10 rapidly conducts, and the capacitor The charging energy of 6 heats the electrode 21 via the thyristor 10.

FIG. 4 shows the discharge lamp terminal voltage waveform and the collector current waveform of the transistor 4 at this time.

In this way, the self-breakdown voltage of the thyristor 10 can be applied to the end of the discharge lamp, and the electrodes can be heated, so that if the starting voltage of the discharge lamp 2 when heating the electrodes is equal to or lower than the self-breakdown voltage of the thyristor 10, The discharge lamp 2 can be started easily. The condition that the starting voltage of the discharge lamp 2 is lower than the power supply voltage is not so important. For example, it is well known that by providing the discharge lamp 2 with a nearby conductor, it is possible to significantly reduce the starting voltage if the electrodes are heated.

In this configuration, it is electrode 2 that consumes power during startup.
1, even if a lamp whose electrodes have reached the end of their lifespan is connected, the circuit components will not generate heat. In addition, the step-down chopper type circuit has a characteristic that the input power decreases significantly when the load voltage decreases, but by providing the thyristor 10 with a non-conducting period, the apparent average value of the load voltage can be increased. It also has the advantage of being able to consume a large amount of electric power and significantly shortening the time required to start up. Additionally, if a lamp is connected whose electrodes have reached the end of their service life,
The thyristor 10 may operate continuously and generate heat, but then the holding current decreases and continuous conduction can be achieved. In this case, the apparent load voltage decreases, so the input power decreases, which is useful from a safety point of view. In addition, if the power supply voltage is too high, the restart time of the transistor 4 will be shortened and the thyristor 4 will become continuously conductive, which will actually reduce the input power, which is advantageous for safety. be.

After the discharge lamp 2 is started, the load voltage increases compared to when it is started, and therefore the oscillation frequency of the transistor 4 becomes determined only by the base circuit, and the load circuit also becomes oscillatory, resulting in normal oscillation.

In the above explanation, a thyristor was used as the switching element, but it is clear that a self-breakdown type two-terminal thyristor can also perform the same operation. In addition, in FIG. 3, the resistor 12 of the thyristor 10 is connected to the gate end via the electrode 21.
This is to increase the holding current by lowering the potential at the gate end from the cathode end of 0. If the holding current is more than necessary, a resistor 12 may be connected between the gate and the cand.

-Also, if the positions of the capacitor 6 and the thyristor 1o are exchanged, the charging current of the capacitor 6 can also be changed to [[i.

21 heating current can be used.

By configuring the circuit as explained above, the withstand voltage of each element (transistor 4, diode 5) can be made up to the power supply voltage even during startup as well as during lighting.
Not only can the price be reduced, but the number of parts that make up the starting circuit can also be reduced. In addition, even if a discharge lamp with a long-life electrode is used, there are no parts in the circuit that generate abnormal heat, so the overall reliability is high.

The price can be reduced, and the practical effects are extremely high.

[Brief explanation of drawings]

Figure 1 is a conventional basic configuration diagram when a step-down chopper circuit is used as a discharge lamp lighting circuit, Figure 2 is a configuration diagram of a conventional starting circuit when a step-down chopper circuit is used as a discharge lamp lighting circuit, and FIG. 3 is a circuit configuration diagram of an embodiment of the discharge lamp lighting device according to the present invention, and FIG. 4 is a voltage/current waveform diagram at the time of starting the circuit shown in FIG. 3. ! 1 Dialogue? U7 no 1θ TJ diagram? 1 Figure 4

Claims (1)

[Claims] 1. In a discharge lamp lighting device in which a first switch element, an inductance, a discharge lamp, and a power source constitute a closed circuit of $J1, and a second closed circuit is constituted by the inductance, the discharge lamp, and a diode. , a second switch element is connected in parallel with the discharge lamp, and when the discharge lamp is started, the non-conducting period of the first switch element is longer than the breakdown voltage recovery time of the second switch element. 1. A discharge lamp lighting device characterized in that the discharge lamp lighting device is configured such that the length of the discharge lamp becomes longer.