JPS6337480B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a discharge lamp lighting device.

The present inventors have already proposed a method in which a pulse voltage is applied to the discharge lamp in accordance with the thyristor cutoff every half cycle, and the ballast has been made smaller and lighter. A power supply voltage compensation circuit was used to keep the lamp power constant by changing the thyristor's cut-off current value in response to power supply voltage fluctuations over time. The power supply voltage compensation circuit is composed of a resistor 44 and a capacitor 29 shown in the figure. Although the figure shows an embodiment of the present invention to be described later, since the power supply voltage compensation circuit is the same, the explanation will be based on this figure. Now, thyristors 71 and 72 are conductive, transistor 9, diodes 16 and 17, and resistor 3
Assume that a current is flowing through 9. At this time, a charging current flows through the capacitor 29 via the resistor 44. This charging current changes depending on power supply voltage fluctuations, and when the power supply voltage gradient is large and there is an overvoltage, the resistor 39
The voltage across the resistor 44 increases, which corresponds to the difference between the voltage drop caused by this and the charging voltage of the capacitor 29. Therefore, the conduction of the auxiliary thyristor 10 is accelerated, the cutoff current value of the thyristors 71 and 72 is reduced, and the lamp power suppresses an increase in lamp power at the time of overvoltage. Conversely, when the power supply voltage decreases, the power supply voltage gradient becomes smaller, increasing the breaking current values of the thyristors 71 and 72, and serves to suppress a decrease in lamp power at low voltages. The power supply voltage compensation circuit plays the role of suppressing changes in lamp power even when the power supply voltage fluctuates in this manner.

Conventionally, the above-mentioned power supply voltage compensation circuit operates not only when dimming but also when full light is on. Therefore, when the power supply voltage decreases during full light, the thyristors 71 and 72
Increase the breaking current value. However, since there is a limit to the breaking ability of the thyristors 71 and 72, it is necessary to suppress the breaking current value as much as possible. Otherwise, in some cases, due to the presence of a power supply voltage compensation circuit, the breaking capability of the thyristors 71, 72 could be exceeded during full light, resulting in the destruction of the thyristors 71, 72.

When dimming, there is a phenomenon that the lamp goes out, so it is necessary to increase the thyristor's cut-off current value at low voltage to suppress the decrease in lamp power. Furthermore, since the lamp power is originally small during dimming, even if the thyristor's breaking current value is increased at low voltage, there is no need to exceed the breaking capacity limit of the thyristor. However, if a power supply voltage compensation circuit similar to that used in dimming is used during full light, the lamp power is large during full light, so a thyristor interrupting ability greater than that at rated voltage is required at low voltage. Therefore, in order to protect the thyristor from destruction under these conditions, a thyristor is required that has a breaking current capability that can withstand the thyristor breaking current during full light and low voltage. However, increasing the breaking current capability of the thyristor lowers the thyristor manufacturing yield, which in turn leads to an increase in price. By the way, when dimming, there is a phenomenon where the lamp goes out at low voltage, so a power supply voltage guarantee circuit is absolutely necessary.However, at full brightness, the lamp power itself is larger than when dimming, so the lamp will go out even without a power supply voltage compensation circuit. No phenomenon occurs. In view of the above points, the present invention operates the power supply voltage guarantee circuit only during dimming to reduce the required breaking current capability of the thyristor as much as possible.

The illustrated embodiment will be described below. 1 is an AC power supply, 2 is a discharge lamp, and 3 is a choke coil for connecting the discharge lamp 2 to the AC power supply 1. 4 and 5 are capacitors, 6 is a full-wave rectifier circuit, 9 is a transistor, 10 is an auxiliary thyristor, 11 is a preheating thyristor, 12 is an N-gate thyristor, 13 is a constant voltage diode, 14, 15, 16, 17, and 18
and 19, 20, 21 and 22 are diodes, 24, 25, 26, 27, 28 and 29 are capacitors, 3
0 and 31 and 32 and 33 and 34 and 35 and 36 and 37
, 38, 39, 40, 41, 42, 43, 44, 45, and 46 are resistors, 47 is a dimmer switch, 71 and 72 are main thyristors, and 81 and 82 are Zener diodes. First, basic matters regarding the above discharge lamp lighting device will be explained.

A circuit consisting of main thyristors 71 and 72 and connected transistors 9, diodes 16 and 17, and resistor 39 is a circuit that short-circuits discharge lamp 2 via thyristors 71 and 72 and via full-wave rectifier circuit 6. . The reason for using a pair of thyristors 71 and 72 is for pressure resistance reasons. The resistor 39 is a low resistance for current detection that does not impair the short circuit effect. Thyristors 71 and 72 are turned on and off every half cycle of the power supply voltage. During the conduction period from turn-on to turn-off, the discharge lamp 2 is short-circuited and electromagnetic energy is accumulated in the chiyoke coil 3. With the subsequent turn-off, a kick voltage is generated in the choke coil 3, and the discharge lamp 2 is ignited. After ignition, the discharge lamp 2 is supplied with the electromagnetic energy of the chiyoke coil 3 in addition to the input power from the AC power source 1. Immediately after the instantaneous value of the delayed current passing through the choke coil 3 and the discharge lamp 2 becomes zero, the thyristors 71 and 72 are turned on again, and the same operation is repeated in this half cycle. While electromagnetic energy is being accumulated in the chiyoke coil 3, there is a period of no lighting while waiting for ignition, but it should be noted that because the energy is accumulated rapidly during this period, the total lamp power for half a cycle actually increases. It is a point. For this reason, it is possible to suppress lamp power through dimming or increase power supply voltage (increase due to voltage fluctuations).
The lamp power is suppressed by the thyristor 71,
This will be done by advancing the turn-off timing of 72 and shortening the non-lighting period.

Most of the components on the right side of the illustrated full-wave rectifier circuit 6 are control components for turning on or turning off the thyristors 71 and 72. The thyristors 71, 72 which are in a conductive state are turned off when the current flowing through them reaches the cut-off current value of the thyristors 71, 72. Thyristor 71,7
When the cut-off current value of No. 2 decreases and the turn-off timing advances, the lamp power is suppressed, and when the cut-off current value increases, and when the turn-off timing is delayed, the lamp power increases. The breaking current values of the thyristors 71 and 72 can be controlled.
When the potential of the anode with respect to the gate of 2 becomes high, the cutoff current value decreases, and when it becomes low, it increases. If the interrupting current value is large and a corresponding current is actually interrupted, the switching loss associated with the interruption will be large and the load on the thyristors 71 and 72 will increase.

The power supply voltage compensation circuit, which mainly includes the resistor 44 and the capacitor 29, has been described above, but a little additional explanation will be given here. When the value increases due to fluctuations in the power supply voltage, the voltage across the resistor 44 increases and the auxiliary thyristor 10 becomes conductive. Therefore, the base current of the transistor 9 decreases and the operating resistance value of the transistor 9 increases, so that the potential of the anode with respect to the gates of the thyristors 71 and 72 increases, and the cut-off current value thereof decreases. This suppresses the lamp power and cancels out fluctuations in the power supply voltage.

Dimming switching is performed using a dimming switch 47, and when the switch 47 is closed, the resistor 36 and capacitor 25
The charging circuit operates, and after a certain period of time has elapsed after the switch 47 is closed, the gate potential of the N-gate thyristor 12 increases and becomes non-conductive. As a result, the resistance that mainly determines the breaking current value of the thyristors 71 and 72 becomes smaller than the parallel resistance 38 and 39 of the single resistance 3.
9 and its resistance value increases. This reduces the breaking current of the thyristors 71 and 72 and dims the light. On the other hand, in the full light state, the gate control circuit of the N gate thyristor 12 consisting of the capacitor 25 and the resistors 35 and 37 makes the N gate thyristor 12 conductive at all times, and the parallel resistors 38 and 39 increase the cutoff current of the thyristors 71 and 72. It is said that

As mentioned above, the power supply voltage compensation circuit is composed of the resistor 44 and the capacitor 29, but in this specific example, the diode 22 is connected between the anode of the N-gate thyristor 12 at the upper end of the capacitor 29 shown in the figure. When the N-gate thyristor 12 is conductive, that is, in the full light state, the diode 22 and the N-gate thyristor 12 short-circuit the capacitor 29. This results in eliminating the effect of the power supply voltage compensation circuit consisting of the resistor 44 and capacitor 29, and in full light, the thyristor cut-off current value determined by the parallel resistors 38 and 39 remains constant even if the power supply voltage fluctuates. be able to achieve the objectives of the term. As is clear from the above description, the circuit including the switch 44, resistor 36, diode 21, N-gate thyristor 12, etc. functions as a dimming circuit, and the circuit including the diode 22 and N-gate thyristor 12 controls the operation of the power supply voltage compensation circuit. It functions as a compensation stop circuit.

As described above, the present invention is to stop the function of the power supply voltage compensation circuit during dimming. According to this, it is possible to use a thyristor with a low breaking current capability even though there is a power supply voltage compensation circuit.

[Brief explanation of the drawing]

The figure is a circuit diagram showing a specific example of the present invention. 1 is an AC power supply, 2 is a discharge lamp, 3 is a chiyoke coil, 9 is a transistor, 12 is an N-gate thyristor, 22 is a diode, 25 and 29 are capacitors, 36, 38, 39 and 44 are resistors, 47 is a dimming switch , 71 and 72 are the main thyristors.

Claims (1)

[Claims] 1 A circuit that short-circuits the discharge lamp via a thyristor is connected to both ends of the discharge lamp, which is connected to an AC power supply via a chiyoke coil, and the thyristor is turned on every half cycle of the power supply voltage, and the current flowing accordingly. A discharge lamp lighting device that turns off a thyristor when the thyristor reaches its cut-off current value, and a dimming circuit that reduces the cut-off current value of the thyristor during dimming, and a dimming circuit that reduces the power supply voltage in response to the power supply voltage. A discharge lamp lighting device characterized by comprising a power supply voltage compensation circuit that increases the breaking current value of the thyristor, and further comprising a compensation stop circuit that stops the operation of the power supply voltage compensation circuit during full light.