JPH0311593A - Discharge lamp starting device - Google Patents

Abstract

PURPOSE:To feed an optimum preheating current to a discharge lamp and to carry out a sufficient preheating constantly regardless of the power source voltage, the temperature, and the like, by providing a current control circuit to control the preheating current. CONSTITUTION:A preheating current control unit is composed of a current transformer T1, a diode bridge DB, resisters R1, R4, and R5, a capacitor C3, an operation amplifier OP1, and a standard voltage Vref. When a preheating proceeds, and the standard voltage set value Vref is raised gradually and reaches to a voltage V1 responding to the preheating current i1, the voltage VC at the contact point of the resister R2 and a capacitor C2 is raised gradually, and the oscillation frequency is reduced gradually. In this case, the preheating current flows at the value responding to the standard voltage set value Vref constantly regardless of the power source voltage, the temperature, and the like, and it comes to have a discharge starting frequency f2 at the time when it reaches to the preheating current i2. A discharge lamp 5 starts the discharge, consequently.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a discharge lamp lighting device for lighting a discharge lamp using a high frequency inverter, and particularly relates to a method for starting a discharge lamp.

(b) In the conventional discharge lamp lighting device, for example,
As described in No. 95, there is a system that uses a series resonant circuit of an inductive element and a capacitive element to start a discharge lamp.

As shown in Figure 4, this system includes a DC power supply (1), a high frequency inverter (2), an inductive element (3), a capacitive element (4),
Consists of a discharge lamp (5).

In Fig. 4, the output of a DC power supply (1) is converted into a high frequency voltage by a high frequency inverter (2), and an inductive element (3
) and a capacitive element (4), and the capacitive element (4).
) is connected in parallel to the discharge lamp (5).

Here, the high frequency inverter (2) has a function of changing its output frequency depending on the starting state.

FIG. 2 shows the output characteristics of the series resonant circuit, where the vertical axis represents the current of the capacitive element (4), that is, the preheating current of the electrodes of the discharge lamp (5), and the horizontal axis represents the frequency.

In this method, the starting frequency (f,
) to be higher than the series resonant frequency (fo).9 The oscillation frequency is gradually brought closer to the series resonant frequency (fo) to perform middle molecular heating, generate a high end tube voltage in the discharge lamp (5), and raise the discharge starting frequency (f2). ) to start the discharge and increase the lighting frequency (
Change the frequency until T3).

(c) Problems to be Solved by the Invention" - According to the method described, the frequency (f
Since the temperature is varied from l) to (f,), sufficient preheating may not be performed depending on the power supply voltage, temperature, etc.

In order to solve the above-mentioned problems, the present invention aims to ensure that sufficient preheating is always performed regardless of the power supply voltage, temperature, etc. by providing a current control section that controls the preheating current.

(d) Means for solving the problem A DC power supply, a high frequency inverter that converts the output of the DC power supply into a high frequency voltage, a series resonant circuit consisting of an inductive element and a capacitive element and connected to the inverter, and the inverter. a discharge lamp connected to the discharge lamp, a current detection means for detecting a preheating current of the discharge lamp, a detected value of the current detection means is compared with a reference value that changes as preheating progresses, and the inverter is controlled based on the result. and a preheating current control section for controlling the preheating current.

(E) Operation By the above means, a sufficient preheating current can always be supplied even when the power supply voltage, temperature, etc. change.

(F) Embodiment FIG. 1 shows an embodiment of the present invention. Components common to those in FIG. 4 are indicated by the same numbers.

In FIG. 1, (IcI) is, for example, TI's T L=
This is an oscillation circuit such as 494, whose oscillation frequency is determined by the connected capacitor (C1) and resistor (R1), and the oscillation frequency decreases as the voltage of the resistor (R1) increases. and a drive circuit (6
) has the function of operating the high frequency inverter (2).

(1) is a DC power supply connected to the inverter (2);
(3) and (4) are an inductive element and a capacitive element, which are also connected to the inverter (1) and constitute a series resonant circuit;
) is a discharge lamp connected to the resonant circuit, and one heater wire (51) of the discharge lamp (5) and each of the elements (3) (
4') and the other heater wire (52) are connected in series to the inverter (1). Further, a current transformer (T1) for detecting the current flowing through the discharge lamp (5) is inserted between the other heater wire (52) of the discharge lamp (5) and the inverter (2). has been done.

Next, (DB) is a diode bridge connected to the secondary output side of the current transformer (T,) to rectify the output of the transformer (T1), and (R,) (R1) is a diode bridge of this bridge (DB). It is a voltage dividing resistor connected between the output terminals,
The voltage dividing point (D) is connected to an operational amplifier (OPI) that controls the high frequency inverter (2) according to the current flowing through the discharge lamp (5).
), and one end of the resistor (R1) is grounded.

Further, a capacitor (C1) is connected to the resistor (R5) in parallel with the ground level, and both are grounded. The + side terminal of the operational amplifier (OPI) is connected to a reference voltage (V, , ), which changes according to the progress of preheating.
For example, a capacitor charging voltage is applied. or,
The output terminal of the operational amplifier (OPI) is a resistor (R3)
A feedback connection is made to that example terminal via.

(R,)(C2) is a resistor and a capacitor connected in parallel to the ground level with the resistor (R1) connected to the oscillation circuit (Ic1.), and the resistor and capacitor ((R,) The connection point (VC) of (C2) is connected to the output terminal of the comparator (OPI) via the diode (Dl).
T, ), diode bridge (DB), resistor (R,) (
R, ) (R5), capacitor (C1), operational amplifier (O
A preheating current control section is configured by the reference voltage (V, , f).

Figure 3 shows the reference voltage setting value (V, .) connected to the + side terminal of the operational amplifier (OPI), the resistor (R7), and (C2
) shows the change in voltage (Vc) at the connection point at startup.

After the power is turned on, the oscillation circuit (ICI) is connected to the resistor (R,) (R
, ) At this time, the output current of the high frequency inverter (2) is detected by the current transformer (T, ), diode bridge (DB) resistor (Rj) (R1), and capacitor (C3), and is connected to the negative terminal of the operational amplifier (OPI). A voltage is applied to.

The reference voltage setting value (V
, e+) are initially at zero level, and the resistance (R2) and (C
The voltage (VC) at the connection point 2) is also at zero level.

As the preheating progresses, the reference voltage setting value (V,
-+) gradually rises and reaches the voltage (■1) corresponding to the preheating current (11) in Fig. 2, the resistance (R2) and (C3
) gradually increases by 1, and the oscillation frequency gradually decreases.

At this time, the preheating current always flows according to the reference voltage setting value (Vz+) regardless of the power supply voltage or temperature, and when it reaches (12) in Figure 2, it becomes the discharge start frequency (f, ). The discharge lamp (5) starts discharging.

After that, the reference voltage setting value (V, , +) further increases, but after the start of discharge, the operation of the high frequency inverter (2) becomes stable and the output current decreases, so the output of the operational amplifier (OPI) is saturated. It is locked by a diode (Dl). Also, the voltage at the connection point between resistors (R2) and (C7) (
VC) further increases by 1 and reaches the maximum value (VM), and the oscillation frequency of the high frequency inverter (2) increases to the lighting frequency (T3
) to keep the discharge lamp (5) lit.

(G) Effects of the Invention According to the present invention, by providing a current control circuit that controls the preheating current, an optimal preheating current can be supplied to the discharge lamp, and sufficient preheating is always achieved regardless of the power supply voltage, temperature, etc. will be held.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a discharge lamp lighting device according to the present invention, FIG. 2 is a diagram showing output characteristics of a series resonant circuit,
Figure 3 shows the reference voltage setting value (V,...) connected to the + side terminal of the operational amplifier (OPl,) in Figure 1 and the resistor (R3).
) and the voltage (■, ) at the connection point of the capacitor (C, ) during startup. FIG. 4 is a conventional circuit diagram corresponding to FIG. 1. (1) DC power supply, (2) High frequency inverter, (3)
Inductive element, (4) Capacitive element, (T1) current transformer, (OPI) operational amplifier.

Claims (1)

[Claims] (1) A DC power supply, a high-frequency inverter that converts the output of the DC power supply into a high-frequency voltage, a series resonant circuit made up of an inductive element and a capacitive element and connected to the inverter, and a discharge lamp connected to the inverter. , a current detection means for detecting a preheating current of the discharge lamp, and a preheating current control section that compares a detected value of the current detection means with a reference value that changes as preheating progresses, and controls the inverter based on the result. , a discharge lamp lighting device consisting of.