JPH03110792A - Lighting device for discharge lamp - Google Patents

Abstract

PURPOSE:To light a discharge lamp stably with no beats or flickers by controlling switching of a DC-AC inverter with pulse signals of a multiplied frequency of a commercial power source frequency. CONSTITUTION:A pulse generating circuit PG is provided to generate voltage pulses of a frequency multiplied 2<n> times of a commercial power source frequency. And the switching of a DC-AC inverter IV is controlled with pulse signals synchronized to the commercial AC frequency to generate an AC voltage of a frequency synchronized to the commercial power source frequency and supply to a discharge lamp La. Thus the driving AC power supplied to the discharge lamp has a frequency synchronized to the commercial power source frequency, different from a power using CR oscillator or the like as the driving signal source of DC-AC inverters, to stabilize the frequency of the power. Thereby the discharge lamp can be lighted stably with no beats or flickers.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is mainly applicable to a light source for video equipment such as a projection device using a liquid crystal or a liquid crystal television receiver, or a light source or lighting equipment for OA equipment such as a copying machine. The present invention relates to a lighting device for an AC-driven discharge lamp.

<Prior art> Conventionally, in order to stably start and light AC-driven discharge lamps used for this type of application, a general ballast that uses back electromotive force from a choke coil has been used to connect a commercial AC power source and a discharge lamp. There was an intervening connection between the two. However, this choke coil ballast is relatively heavy, making it unsuitable for, for example, portable video equipment.
Also, since the general commercial power frequency of 6011z is used, flickering occurs due to the commercial frequency when used as a light source for video equipment, and there is a drawback that visual fatigue is significant in video equipment.

Therefore, in recent years, a lighting device using a ballast having an electronic configuration as shown in FIG. 3 has been adopted. In this lighting device, 100 cm of commercial AC power input from a power plug P is full-wave rectified by a full-wave rectifier OB consisting of a diode bridge, smoothed by an electrolytic capacitor C1, and converted into 140 cm of direct current. Ru. Subsequently, this DC power is converted into pulses by a chopper regulator in the next stage and controlled to a desired set voltage. This chopper regulator divides the output voltage of an MO3 type field effect transistor Q1 for the chopper by two resistors RIR2 and inputs it to the operational amplifier OP. Outputs a signal such that the difference is zero when compared with the set reference voltage of
This signal controls switching of the transistor Q1 via the inverter driver IDI, and as a result, the output voltage of the transistor Q1 is controlled to a constant voltage set to the signal source S. The pulse voltage output from this chopper regulator is smoothed again by capacitor C2.

This smoothed set DC power is the DC-AC inverter I
V is supplied. This D C-A C inverter TV consists of four bridge-connected MO3 type field effect transistors Q2 to Q5 and two transistors Q2 . Q5 and Q3. A pair of inverter drivers ID2 for driving Q4 alternately. ID
3 and a pair of drivers DVI and DV2.

This DC-AC inverter IV is switched and driven by a predetermined frequency signal from the signal generator O8C. The signal generator OSC includes resistors R3 to R5, inverter driver ID4. ID5 and capacitor C3 constitute a well-known CR oscillator, and its oscillation frequency signal causes a pair of inverter drivers ID2. A pair of transistors Q2. through ID3. Q5. , and a pair of transistors Q3Q through a pair of drivers DVI, DV2.
4 are alternately switched and controlled, and AC power having a frequency corresponding to the output frequency of the signal generator OSC is supplied to the discharge lamp La.

Here, in the igniter circuit IN, the capacitor C4 is charged through the resistor R6, and when the terminal voltage of the capacitor C4 reaches a predetermined voltage, current flows through the trigger element TD to the primary winding of the step-up transformer T1, and the secondary winding The voltage induced in the line causes capacitor C5 to pass through diode D.
is charged, and when the terminal voltage of this capacitor C5 reaches a predetermined voltage, discharge occurs in the spark gap SG and several kilograms
A pulsed high voltage of V is generated, and this pulsed high voltage is applied through the transformer T2, so that the discharge lamp La immediately shifts to the lighting state, and then the DC-AC inverter I
(2) AC power is supplied to maintain a stable lighting condition.

<Problems to be Solved by the Invention> However, in the lighting device, the CR oscillator generally used as the signal generator O8C for controlling the switching of the separately excited DC-AC inverter IV is
The oscillation frequency tends to become unstable due to variations in the resistors R3 to R5, temperature drift, etc., and since stable AC power cannot always be supplied, flickering and beats occur, making it impossible to stably light the discharge lamp La. There is.

The present invention has been made in view of these conventional problems, and provides a discharge lamp lighting device that can constantly supply stable AC power and stably light a discharge lamp without beats or flickering. The technical challenge is to do so.

<Means for Solving the Problems> In the present invention, as a technical means for achieving the above-mentioned problems, a lighting device for a discharge lamp is configured as follows. That is, in a device that supplies direct current obtained by rectifying and smoothing commercial alternating current to a DC-AC inverter, and supplies alternating current power converted to a predetermined frequency by the inverter to an AC-driven discharge lamp to light the discharge lamp, the commercial alternating current is A pulse generation circuit is provided which differentiates the signal, converts it into a Hals waveform, and outputs a pulse signal with a frequency twice as high as the commercial power supply frequency, and the DC-AC inverter is driven for switching by the output pulse of this pulse generation circuit. It is structured as a feature.

<Operation> In the pulse generation circuit, a pulse voltage with a frequency multiplied by 2'' is generated based on the commercial power supply frequency, and a pulse signal synchronized with this commercial AC frequency is used to generate a DC voltage.
- The switching of the AC inverter is controlled, and an alternating current voltage having a frequency synchronized with the commercial power frequency is generated and supplied to the discharge lamp.

Therefore, the driving AC power supplied to the discharge lamp has a frequency that is synchronized with the commercial power supply frequency, and unlike when a CR oscillator is used as a signal source for driving a DC-AC inverter, the frequency is stable, so there is no beat or flicker. It is possible to stably light the discharge lamp without causing this.

<Example> Hereinafter, a preferred example of the present invention will be described in detail with reference to the drawings.

In FIG. 1 showing an embodiment of the present invention, the same or equivalent parts as in FIG. 3 are given the same reference numerals, and the explanation thereof will be omitted. The difference from Figure 3 is that DC-A
As a signal source for driving the CC inverter La, a pulse generation circuit 1) G consisting of a differentiation circuit DC and a waveform shaping circuit CP in place of the signal generator OSC, and a pulse width modulation circuit PW are used.
The pulse generator circuit PG and the pulse width modulation circuit PWM generate a pulse voltage with a frequency that is 2" times the commercial power supply frequency, and the pulse voltage generates a DC-A
This is only a configuration in which switching control is performed on C inverter IV. Commercial AC power is divided by two resistors R7 and R8 and input to the differentiator DC. The waveform shaping circuit CP is composed of a comparator.

Next, the operation of the above embodiment will be explained with reference to FIG. 2. Figure 2 (al to (fl) respectively show the waveform diagram of the operating voltage at points A-F in Figure 1. is applied to the differentiating circuit DC, which generates a detection signal of the changing part of the commercial AC waveform as shown in FIG. 2(b), and rectifies this detection signal with two diodes to generate a A signal with a frequency twice the commercial AC frequency as shown in Figure 2 (C) is output.This frequency signal is converted into a pulse by the waveform shaping circuit CP as shown in Figure 2 (dl).This pulse signal is , pulse width modulation circuit PW
M modulates the pulse width so that the low level period and high level period are the same as shown in FIG. 2(e), and this modulated pulse voltage drives the DC-AC inverter IV for switching. According to Fig. 2 (
As shown in f), the DC power from the chopper regulator is converted into an AC voltage with a frequency that is twice the commercial power supply frequency, and is supplied to the discharge lamp La. In this way, since the discharge lamp La is driven with AC power having a frequency synchronized with the commercial power supply frequency, the discharge lamp La can be stably lit without beat or flickering.

Note that the present invention is not limited by the contents of the above description and drawings, and may include various modifications without departing from the scope of the claims. For example, in the above embodiment, a case has been described in which AC power is generated at a frequency that is twice the commercial power supply frequency.
It is also possible to generate AC power with a frequency that is doubled.

<Effects of the Invention> As described above, according to the discharge lamp lighting device of the present invention, the DC-
Since the AC inverter is configured to perform switching control, the discharge lamp is lit by supplying AC power with a frequency synchronized with the commercial power supply frequency, so the discharge lamp can be lit in a stable state without beats or flickering. can.

[Brief explanation of drawings]

Figure 1 is an electrical circuit diagram of one embodiment of the present invention, and Figure 2 is the electrical circuit diagram of one embodiment of the present invention.
FIG. 3 is a waveform diagram showing the operating voltage of each part in the figure, and FIG. 3 is an electric circuit diagram of the conventional device. OB--Full-wave rectifier C1-Smoothing capacitor I v-D C-A C Inverter La-Discharge lamp PG--Pulse generating circuit DC--Differentiating circuit CP-Waveform shaping circuit

Claims (1)

[Claims] (1) In a device for supplying direct current obtained by rectifying and smoothing commercial alternating current to a DC-AC inverter, and supplying alternating current power converted to a predetermined frequency by the inverter to an AC-driven discharge lamp to light the discharge lamp, A pulse generation circuit is provided that differentiates alternating current, shapes it into a pulse waveform, and outputs a pulse signal with a frequency 2^n times the commercial power supply frequency, and the output pulses of this pulse generation circuit drive the DC-AC inverter for switching. A lighting device for a discharge lamp, characterized in that: