JPS5928038B2 - discharge lamp lighting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a discharge lamp lighting device that lights a discharge lamp at high frequency using a high-frequency inverter. The light can be dimmed.

In order to make lighting devices more compact, more efficient, and eliminate flicker, high-frequency inverters using semiconductor devices are used to light discharge lamps at high frequencies. However, it is difficult to control light by the phase control method used temporarily in commercial frequency lighting.

That is, since the oscillation frequency of the inverter is set to around 20KH2 in order to reduce noise and make the inverter transformer compact, a control element with a short turn-off time is required, but such an element is difficult to obtain and expensive. be. In addition, normally, the output of the inverter transformer for the discharge lamp load is
A ballast capacitor or choke coil is connected,
This circuit forms a type of resonant circuit that includes the equivalent resistance of the discharge lamp, so if you try to change the output by controlling the on (off) period etc. of the semiconductor elements of the inverter, matching with the resonant circuit will be difficult. It was not working properly and the power loss was increasing. Therefore, the easiest way to change the output of the inverter is to change the power supply voltage of the inverter.

In other words, when the power supply voltage is changed, the output voltage of the inverter simply changes, and the tube current of the discharge lamp changes accordingly, and the resonant frequency is not affected, so there is no reduction in discharge. In this case, if you put a resistor etc. in series with the power supply to change the input voltage of the inverter and change the resistance value, you can dim the light, but the disadvantage is that the power loss of the resistor is extremely large. There is. Also, if a semiconductor switch is inserted between the power supply and the inverter, and this semiconductor switch is turned on and off, the average value of the input voltage of the inverter is determined by the ratio of the on period to the off period, and this ratio can be varied. For example, the input voltage of the inverter can be varied without power loss, and as a result, the tube current of the discharge lamp can be varied and dimmed, but since the load in this case is a discharge lamp, During the off-period of the semiconductor switch, no tube current flows, and during this period, the imitation lamp is in a state where it is difficult to discharge.When the semiconductor switch is turned on again, the discharge starting voltage of the discharge lamp becomes high, and the discharge start voltage of the semiconductor switch increases. After turning on, the tube current does not rise immediately, but there is a time delay, and the power loss of the inverter increases during this time.

In other words, the inverter operates when the discharge lamp is fully lit (
Since the efficiency is set to be maximum in the arc discharge state), the efficiency is poor when the tube voltage is high and the discharge lamp is not fully lit. In view of these problems, the present invention aims to control the input voltage of an inverter with less power loss without causing any malfunction in the operation of the inverter, and to efficiently dim and light a discharge lamp. The purpose of this device is to provide a discharge lamp lighting device in which a high frequency inverter is interposed between the power source and the discharge lamp, and the inverter lights the discharge lamp at high frequency. A semiconductor switch is connected to the input side of the inverter, and a semiconductor switch that is periodically turned on and off at a frequency lower than the oscillation frequency of the inverter is interposed between one end of the power supply and the chiyoke coil, and the semiconductor switch and the chiyoke coil are connected. A diode is connected between the point and the other end of the power source in such a direction that the semiconductor switch is turned off when it is turned on, and a control circuit is provided to vary the conduction period of the semiconductor switch.

Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.
In the figure, 1 is a power source, 2 is a discharge lamp, and 3 is a high-frequency inverter, which includes a pair of transistors, an inverter transformer, etc., and its oscillation frequency is approximately 20 to 30 KHz.
is set to .

Reference numeral 4 denotes a choke coil inserted on the power input side of the inverter 3 to reduce switching loss of the inverter 3.

5 is a ballast capacitor.

Reference numeral 6 denotes a semiconductor switch interposed between the power supply 1 and the chiyoke coil 4, which is composed of a transistor, etc., and is turned on and off at a frequency of about 1 to 5 KHz by a control circuit 7VC such as an oscillation circuit.
Controlled off.

The control circuit 7 has a variable resistor 8, and by adjusting the resistance value of the variable resistor 8, the ratio between the on period and the off period of the semiconductor switch 6 can be varied. A diode 9 is connected between the connection point of the semiconductor switch 6 and the choke coil 4 and one end of the power supply 1 on the side opposite to the semiconductor switch 6, so that the diode is turned off when the semiconductor switch 6 is on. There is.

In the above configuration, the control circuit 7 controls the semiconductor switch 6
When the semiconductor switch 6 is turned on and off as shown in the waveform shown in FIG. ! A current 11 is supplied to t- from the power supply 1 via the semiconductor switch 6.

On the other hand, during the off period T2 of the semiconductor switch 6, the current from the power supply 1 is not supplied to the inverter 3, but the diode 9 is conductive, so the diode 9 and the switch coil 4
A closed circuit is formed between the inverter 3 and the inverter 3, and a current 12 is supplied to the inverter 3 via the diode 9 by the energy stored in the choke coil 4. Therefore, the input current waveform of the inverter 3 becomes as shown in FIG. 2B. In other words, when the semiconductor switch 6 is off, the energy stored in the switch coil 4 is used as the input power source for the inverter 3 via the diode 9. is applied, the discharge lamp 2 is not extinguished, and the restriking voltage does not increase as in the conventional case, so the inverter 3 is always driven in an efficient state.
Therefore, by changing the conduction period of the semiconductor switch 6, it is possible to control and light the discharge lamp 2 very smoothly. As described above, in the present invention, since voltage can be constantly applied to the inverter, the input voltage of the inverter can be changed to
It can be varied without causing power loss, and the inverter can be driven efficiently. Therefore, the discharge lamp can be dimmed and lit efficiently over a wide range.

[Brief explanation of the drawing]

The drawings illustrate one embodiment of the present invention, with FIG. 1 being a circuit diagram and FIG. 2 being a waveform diagram thereof. 1...Power supply, 2...Discharge lamp, 3...
...High frequency inverter, 4...Chiyoke coil, 6...Semiconductor switch, 7...Control circuit, 9...Diode.

Claims (1)

[Claims] 1 A high frequency inverter is interposed between the power source and the discharge lamp,
In a discharge lamp lighting device that uses the inverter to light a discharge lamp at a high frequency, a choke coil is connected to the input side of the inverter, and a choke coil is connected between one end of the power supply and the choke coil at a frequency lower than the oscillation frequency of the inverter. A semiconductor switch that is turned on and off periodically is interposed, and a diode is connected between the connection point of the semiconductor switch and the choke coil and the other end of the power source in a direction that turns off when the semiconductor switch is on. A discharge lamp lighting device comprising: a control circuit connected to the semiconductor switch to vary the conduction period of the semiconductor switch.