JPS5910035B2 - discharge lamp lighting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a discharge lamp lighting device, and its purpose is to enable highly efficient lighting, use low-voltage components in the circuit, and make it small and inexpensive. We have developed a discharge lamp lighting device that improves the current waveform flowing through the discharge lamp to increase the power utilization rate, and also prevents the blackening of the tube end and shortened lamp life that occur due to DC lighting. It is on offer.

Since discharge lamps generally have negative resistance characteristics, it is said that a current limiting element is necessary for stable lighting, but recently, using the dynamic characteristics of discharge lamps, constant voltage sources have been developed. A method for directly lighting a discharge lamp without using a current limiting element has been reported.

The present invention relates to a lighting circuit that does not have a current-limiting element as described above, and generally has a dynamic characteristic of a discharge lamp in which there is a considerable time delay in the rise of current when voltage is applied to the discharge lamp. This is what was used. That is, this dynamic characteristic is expressed as follows: the rate of increase in lamp conductance g due to ions in the tube over time is proportional to the product of lamp current i and lamp voltage , and the rate of decrease is proportional to the product of lamp conductance g due to ions in the tube. It is proportional to g. Expressing this in the formula (2 α
vi-β g・・・・・・・・・・・・1 where g
:: i/ri ・ ・ ・ ・ ・ ・ ・ ・
・ ・ ・2α, β: Constants specific to discharge lamps For example, when the lamp voltage is suddenly increased by 10% in a 40W fluorescent lamp, the time it takes for the lamp current to double its original value is calculated using Equation 12 above. Based on the calculation, it is approximately 1.
6 mSec, and the current continues to increase even after this, and the current finally escapes.

Similarly, if the lamp voltage is lowered by 10%, it will be approximately 1.8 mSe.
Once the lamp current was reduced to 1/2, the current continued to decrease and finally reached zero. Now, when the voltage of the constant voltage source is e ( ) and it is connected to the discharge lamp without a current limiting element, the lamp current 1 (t) is calculated as follows from the above equation 12. However, G. is the equivalent conductance A of the discharge lamp at t=TO, and DC is a constant unique to the discharge lamp.As is known from this, if the period of e(t) is T, then E is outside R.

When e2dt, the current escapes when E>VDC, and E
<VDC, the current disappears, and E here is the effective value of e(t), as is clear from the above definition. Therefore, it is clear that in order to maintain lighting by directly connecting a discharge lamp to a constant voltage source, it is necessary to make the effective value of this constant voltage source equal to VDC and to set the current by some method. becomes.

Focusing on the above-mentioned points, a conventional example of a system that eliminates current-limiting elements that are the main cause of power loss in a discharge lamp lighting device will be described below. FIG. 1 shows a conventional example as a block diagram, FIG. 2a shows the voltage applied to both ends of the discharge lamp 2, and FIG. 2b shows the waveform of the current flowing through the discharge lamp 2. As will be explained below, in this method, instead of applying a voltage higher than the VDC described above, the time is divided into τ, to prevent the current from escaping. Further, the setting of the current is achieved by controlling the switch opening/closing element 4 by the negative feedback circuit 3 and changing the ratio of τ1 and τ2. However, in such a conventional system, the voltage of the power supply 1 is high and the switching frequency of the switch opening/closing element 4 is high, 500 Hz to 40 KHz, so that the switching element forming the switch opening/closing element 4 has a disadvantage that the withstand voltage and loss are large. ing. These drawbacks are largely due to the fact that the voltage stop section is used to set the current, and the presence of the stop section causes the ionization of the vapor in the discharge lamp to rapidly disappear, thus producing ionization again. It was becoming necessary to supply voltage and shorten the switching cycle. In addition, since the power source 1 is opened and closed using the switch opening/closing element 4, the utilization rate of the power source is poor, and furthermore, the light output that can be obtained even if a constant power is supplied to the lamp is low because there is a stop section in the current. It had the disadvantage of being small.

In addition, in such a conventional example, since voltage is always applied in the same direction to the discharge lamp 2, blackening occurs only at one tube end of the discharge lamp, resulting in a reduction in lamp life. There were also drawbacks. In view of the above, the present invention does not particularly provide a voltage stop section, and connects the discharge lamp to the discharge lamp without using a current limiting element by raising and lowering the discharge lamp rated voltage VDC by using a power supply voltage whose polarity is alternately reversed. An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 3a shows a block diagram of one embodiment of the present invention. In this embodiment, a filter 4 has an extremely high impedance to the rectangular wave power source 1b and has virtually no impedance to the DC power source 1a;
A constant voltage source 1 is configured by adding power sources 1a and 1b in parallel using a filter 5 that has extremely high impedance to the DC power source 1a and has substantially zero impedance to the rectangular wave power source 1b. This is what we are doing.
In this example, the voltage of the rectangular discharge source 1b is set higher than the voltage of the DC power source 1b, so the composite voltage waveform is instantaneously generated by superimposing the AC component on the DC component, as shown in Figure b. It passes through zero voltage. In this embodiment, the constant voltage source 1 is configured in this manner, and the negative feedback circuit 3 detects the load condition of the discharge lamp 2 and feeds it back to the constant voltage source 1, setting the current to a specified value. are doing.
FIG. 3b shows an example of the voltage waveform applied to the discharge lamp 2 at this time. With this configuration, stable operation of the discharge lamp 2 can be continued as in the conventional system described in FIGS. 1 and 2. However, as shown in the calculation results earlier, if a voltage lower than the discharge lamp rated voltage VDC is applied, the current continues to decrease and eventually reaches extinguishment, but the applied voltage does not reach the discharge lamp rated voltage VDC. In the case where the arc is near, a considerable amount of time is allowed until the arc is extinguished, and this time period is used for generating electric power, which is a big difference from the conventional example. As a result, unlike the conventional method, there is no stopping section in the voltage applied to the discharge lamp 2, so the method has the following advantages compared to the conventional method. That is, in the above embodiment, since there is no voltage stop and therefore no current stop, residual ions that mainly occur in the current stop section are less likely to disappear due to diffusion and recombination, and the discharge lamp 2 can be lit with high efficiency. Therefore, a particularly high voltage is not required, and as shown in Figure 3b, it is only necessary to apply a voltage that is slightly above or below the discharge lamp rated voltage VDC, and the lamp condenser Since the change in resistance is gradual, there is no need to use a particularly high frequency for the rectangular wave power source 1b.
In addition, since the current is not forcibly cut off, the power utilization rate is increased, and by improving the current waveform, lamp input can be efficiently converted to optical output, and transient high voltages are not generated in the circuit. The circuit can be constructed at low cost by using low-voltage components. Furthermore, instead of the rectangular wave AC power source 1b, a sine wave AC power source or the like can also be used. In this way, the present invention uses a constant voltage source 1 that fluctuates around the discharge lamp rated voltage VDC and does not have a voltage rest area, to obtain the above effects. FIG. 4 shows another specific embodiment of the present invention, in which three DC power supplies 1a, 1
The constant voltage source 1 as described above is obtained by combining the switches c and 1d with the switch 6. Although not mentioned above, the discharge lamp 2 can be started by applying a high voltage pulse voltage only at the time of starting, and the effective value of the voltage of the constant voltage source is equal to the discharge lamp rated voltage VDC. It is not necessary that the values match exactly in each cycle, but it is sufficient that they match as a whole within a certain period of time.

As described above, the present invention superimposes an AC voltage component with a period of several tens of cycles per second or more on a DC voltage component, and generates a voltage whose effective value is slightly higher than the discharge lamp rated voltage, and a voltage whose polarity is opposite to this voltage. Since a constant voltage source is provided whose effective value is alternately switched to a voltage slightly lower than the rated voltage of the discharge lamp, there is no period during which the voltage stops or the current stops, and residual ions do not disappear. It has the effect of being able to perform highly efficient lighting and does not require high voltage for restriking.
There is no need to forcibly interrupt the current flowing through the circuit,
The power utilization rate is improved, and the circuit does not generate excessive high voltage, allowing the use of low-voltage components.Furthermore, it does not require current-limiting elements, making the circuit smaller, lighter, and less expensive. It has the effect of

In addition, in the present invention, since voltages of different polarities are alternately applied between both ends of the discharge lamp, only one end of the discharge lamp does not become black, and the lamp life is reduced. It has the effect of being able to prevent the decline of O.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the conventional example, FIG. 2 is an explanatory diagram of the same operation as above, FIGS. 3A and 3B are block diagrams and voltage waveform diagrams of one embodiment of the present invention, respectively, and FIG. This is an example block diagram, where 1 is a constant voltage source, 2 is a discharge lamp, and 3 is a negative feedback circuit.

Claims (1)

[Claims] 1. A constant voltage source consisting of a DC power source and a power source that generates an AC voltage component with a period of several tens to hundreds of cycles per second to be superimposed on the DC voltage of the DC power source; It is equipped with a negative feedback circuit that detects the load condition of the discharge lamp connected without using any elements and controls the voltage applied to the discharge lamp from the constant voltage source, and the AC/DC superimposed voltage of the constant voltage source is such that the effective value is The voltage is alternately switched between a voltage slightly higher than the lamp rated voltage and a voltage whose polarity is opposite to this voltage and whose effective value is slightly lower than the discharge lamp rated voltage, and there is no section where the voltage value is zero. A discharge lamp lighting device characterized by being set as follows.