JPS5919435B2 - Power supply for xenon lamp - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power supply for a xenon lamp using a transistor switching system, and is intended to improve the lighting of the xenon lamp and reduce the loss of the drooping resistor.

Conventional power supplies for xenon lamps have the output characteristics shown in Figure 1, but because the high no-load voltage Vo is dropped using an AC reactor or a leaky transformer, the transformer is large and Also, since it does not have perfect constant current characteristics,
Due to load fluctuations such as fluctuations in the input power supply voltage and variations in the spacing between the lamp electrodes of the xenon lamp, the lamp current does not become constant, and therefore the arc does not stabilize.

Therefore, in recent years, as shown in Figure 2a, the no-load voltage has increased.

A power supply for a xenon lamp is constructed by combining a power supply having a characteristic of drooping at a small current with a power supply having a characteristic of low voltage and large current as shown in FIG. Note that in FIGS. 1 and 2, point V indicates the lighting voltage of the xenon lamp, that is, the rated voltage VY. However, this type of power supply has a high no-load voltage Vo to ensure good lighting of the xenon lamp, but by connecting a resistor etc., the no-load voltage can be increased.

Since the wires are hanging down, the resistance loss is large, which is an obstacle to downsizing devices. This invention has been made with the above points in mind, and will now be described in detail with reference to FIG. 3 showing one embodiment thereof.

In the figure, T is a transformer in which one end of the primary winding Ni is connected to the positive terminal 1 of the DC power source E4, and a secondary winding N2 and an additional winding N3 are provided on the secondary side, and Q is a transformer T. A transistor whose collector is connected to the other end of the primary winding N2 and whose emitter is connected to the negative terminal 2 of the DC power supply E, D4 is one end of each of the secondary winding N2 and the additional winding N3 of the transformer T. D2 is another diode whose one end is connected to the other end of the additional winding N3 of the transformer T, R has one end connected to the other end of the diode D2, and the other end to the diode D4. A drooping resistor connected to the other end, F
is a smoothing section consisting of a reactor L and a capacitor C connected between the other end of the drooping resistor R, the other end of the secondary winding N, and the output terminals 3 and 4, and CT is a converter that detects the output of the smoothing section F. The current transformer, CO, is a control section including an oscillation section that receives the detection signal of the current transformer CT and drives the transistor Q at a high frequency of about 20 KHz.

Then, a DC power source E is applied to terminals 1 and 2, and the transistor Q is connected to the control section C.

When driven by a high frequency of about 20 KHz from
is applied, and a rectangular voltage is generated in the secondary winding N2 and the additional winding of the transformer T, respectively. By the way, the voltage generated in the secondary winding N of the transformer T is appropriately determined by the xenon lamp connected to the output terminals 3 and 4, but it is desirable that the voltage be about twice the rated voltage VY of the xenon lamp, and The voltage generated in the additional winding N3 of the transformer T, in addition to the voltage generated in the secondary winding N, will supply a no-load voltage VO that is about four times the rated voltage v of the xenon lamp. The degree of drooping is determined by the magnitude of the drooping resistance R.

Then, until just before the xenon lamp is lit, the no-load voltage 01 required to light the xenon lamp, that is, the high voltage generated by both windings N, N3, is applied to the series circuit of the diode D and the drooping resistor R, and the smoothing part Y. Furthermore, when the xenon lamp is lit, the current flowing through the xenon lamp increases, so the no-load voltage V.

Power is supplied to the xenon lamp through the diode D1 and the smoothing section F, and the control section C
. The output current is detected and the frequency of the transistor Q is controlled so that the output voltage E becomes the rated voltage VY. Therefore, due to the switching of the transistor Q, a rectangular wave voltage is applied to the drooping resistor R, which is smaller on average than the no-load voltage that was applied just before the xenon lamp was turned on. Therefore, the loss of the drooping resistor R is small, and the equipment can be made smaller. Also, since the no-load voltage can be sufficiently increased during lighting, the xenon lamp can be lit well. Note that the same effect as described above can be obtained even if the other end of the drooping resistor R is directly connected to the output terminal 3, as shown by the broken line in FIG. As described above, according to the power supply for a xenon lamp of the present invention, DC power is intermittently applied to the primary side by switching the transistor, and the secondary winding for the rated voltage of the xenon lamp is connected to the secondary winding on the secondary side. a transformer installed in series with the additional winding for load voltage; a diode that rectifies the rectangular wave output of the secondary winding and supplies it to the xenon lamp; another diode that is supplied to the xenon lamp via a drooping resistor for forming characteristics; a detection means that detects the current flowing through the xenon lamp; and a detection signal that drives the transistor at a high frequency and receives a detection signal from the detection means. ) A control unit that controls the frequency of switching of the transistor, and controls the no-load voltage required to light the xenon lamp until just before the xenon lamp is lit, and the rated voltage required to continue lighting the xenon lamp after the xenon lamp is lit. By applying the voltage to the xenon lamp, it is possible to improve the lighting of the xenon lamp, reduce the loss of the hanging resistor, and make it possible to downsize the device.

[Brief explanation of drawings]

1 and 2 are output characteristic diagrams of a power source for a xenon lamp, and FIG. 3 is a circuit diagram of an embodiment of the power source for a xenon lamp according to the present invention. T...transistor, Q...transistor, Dl, D2
...Diode, R...Resistance for drooping.

Claims (1)

[Claims] 1. A transformer in which DC power is intermittently applied to the primary side by switching a transistor, and a secondary winding for the rated voltage of the xenon lamp and an additional winding wire for the no-load voltage are provided in series on the secondary side; a diode that rectifies the rectangular wave output of the secondary winding and supplies it to the xenon lamp; and a diode that rectifies the rectangular wave output of both of the windings and supplies it to the xenon lamp via a drooping resistor for forming a drooping characteristic. another diode, a detection means for detecting a current flowing through the xenon lamp, and a control section that drives the transistor at a high frequency and controls the frequency of switching of the transistor using a detection signal from the detection means, A power supply for a xenon lamp, characterized in that a no-load voltage required to light the xenon lamp is applied to the xenon lamp immediately before the xenon lamp is lit, and a rated voltage required for continued lighting is applied to the xenon lamp after the xenon lamp is lit.