JPH0997699A - Discharge lamp lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce stress on an switching element and the like during a process of an electric discharge lamp to move from OFF condition to on condition. SOLUTION: An integrating unit 5 is provided which inputs an output obtained by integrating the detected primary voltage of a transformer T to the negative input terminal of a comparator Comp1 through a diode D41 . When the output of the unit is not zero (0) switching elements Qa, Qb are controlled so that the power to be supplied to an electric lamp La from a DC power supply Vs via switching elements Qa, Qb, transformer T, switching elements Q1 -Q4 and an igniter circuit Ig can be reduced.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a discharge lamp lighting device.

[0002]

2. Description of the Related Art As a first conventional example of the present invention, Japanese Patent Application No. 7-35736 and Japanese Patent Application No. 7-35 filed by the present applicant.
No. 740 is shown in FIG. 9 and FIG.
0 is shown.

The circuit shown in FIG. 9 converts a direct current power source Vs into alternating current power by alternately turning on and off switching elements Qa and Qb via a capacitor C1, and a rectifier consisting of a transformer T, an inductance element L2 and diodes D1 to D4, It is a DC-DC converter that supplies DC power to the load Z by boosting and rectifying it via a capacitor C2. (First Conventional Example) Here, when the load Z is a lamp load, the impedance immediately after lighting of the lamp load becomes low. In order to light the lamp load smoothly, it is necessary to supply a predetermined amount of power even in this low impedance state. However, in the circuit shown in FIG. 9, a certain amount of power is supplied in this low impedance state due to the influence of the inductance element L2. There are characteristics that are difficult to obtain.

In the first conventional example, there is one in which a high pressure discharge lamp such as a metal halide lamp is used as the load Z, and its circuit diagram is shown in FIG. (Second Conventional Example) A point different from the first conventional example shown in FIG. 9 is that a center winding tap is provided on a secondary winding n2 of a transformer T, and a transformer T, a rectifier composed of diodes D1 to D6, and a capacitor C2 are used. The switching element Q supplies the boosted and rectified DC power.
Converted to AC power with an inverter circuit consisting of 1 to Q4,
It is configured to supply power to the igniter Ig and the discharge lamp La, and when the high output is required in the low impedance state, the predetermined power is mainly supplied from the intermediate tap side. The same configurations as those of the conventional example 1 are denoted by the same reference numerals and the description thereof will be omitted. In this circuit, as a method of controlling the power supplied to the discharge lamp La, there is a method of changing the on-duty of the switching elements Qa and Qb as shown in FIG. 11, for example. The diodes D5 and D6
Either one of them may be omitted.

An example of a control circuit for controlling the circuit shown in FIG. 10 is shown in FIG. This circuit includes switching elements Q1 to Q4.
Drive circuit 1a for driving a switching element Q
drive circuit 1b for driving a and Qb, amplifier Amp1 for detecting current flowing into the inverter circuit including switching elements Q1 to Q4, and switching elements Q1 to Q1
An amplifier Amp2 that detects the voltage applied to the inverter circuit including Q4, a multiplier 2 that multiplies the outputs of the amplifiers Amp1 and Amp2, and an error amplifier EA1 that compares and outputs the output of the multiplier 2 and the power command value P1. Amplifier Amp
2 and the error amplifier EA2 for comparing and outputting the voltage maximum limit value V1, the error amplifier EA3 for comparing and outputting the output of the amplifier Amp1 and the current maximum limit value I1, and the error amplifiers EA1 through the diodes D11, D21, D31. E
The control signal is transmitted to the comparator Comp1 which compares and outputs the output of A3 and the output of the high frequency triangular wave generator 4 to the drive circuit 1a via the NOT gate N1 and the switching elements Q1 to Q4 via the drive circuit 1b. And a low frequency oscillator 3.

Next, the operation will be briefly described. In the constant state, the output of the error amplifier EA1 causes the switching element Qa,
The discharge lamp La is stably lit by controlling Qb and controlling the electric power supplied to the discharge lamp La to be substantially constant. In a low impedance state such as immediately after the discharge lamp La is turned on, the error amplifier E
The switching elements Qa and Qb are controlled by the output of A3, and the lamp current is controlled to be below the maximum rating.
When the discharge lamp La is off, the switching elements Qa and Qb are controlled by the output of the error amplifier EA2, and the discharge lamp L is controlled.
The voltage applied to a is higher than that during lighting (for example, 300
V) to start the discharge lamp La.

[0007]

However, the following problems occur in the second conventional example.

FIG. 13 shows the on-duty duty (= T) of the switching element Qb when the ON times of the switching elements Qa and Qb are Ta and Tb and one cycle is T.
b / T) and the output power of the circuit shown in FIG.

In the steady lighting of the discharge lamp La, or in the load having an impedance substantially equal to the lamp impedance during the steady lighting, as shown in FIG. 13A, the on-duty duty of the switching element Qb is changed.
The output power increases with increasing. The lamp impedance (or load impedance) is shown in FIG.
When it is slightly lower than that shown in FIG.
As shown in (b), the output power decreases as a whole. When the output is mainly obtained from the intermediate tap provided on the secondary winding n2 of the transformer T in a state where the lamp impedance (or load impedance) is low immediately after the discharge lamp La is turned on, the state shown in FIG. As shown, the output power changes in a substantially parabolic shape as the on-duty duty of the switching element Qb increases. When the on-duty dutyb of the switching element Qb is dm or less, the output power increases as the on-duty duty of the switching element Qb increases. However, when the on-duty dutyb of the switching element Qb exceeds dm, the transformer T
As shown in FIG. 14, the primary current IT1 flowing through the primary winding n1 of the
1, an excessive current flows and is saturated, and as a result, the output power decreases as the on-duty duty of the switching element Qb increases due to the impedance of the circuit. In this way, the output power characteristics greatly differ depending on the value of the lamp impedance (or load impedance).

For example, assuming that the on-duty of the switching element Qb is dutyb = dn, the switching elements Qa, Q
When a state in which the voltage necessary for starting the discharge lamp La (for example, 300 V) is applied to the discharge lamp La to rapidly change from a state in which the lamp impedance is low immediately after the discharge lamp La is turned on to a low lamp impedance, the switching element Qb On-duty du
When the switching elements Qa and Qb are operated with tyb = dn, an excessive primary current IT1 flows through the primary winding n1 of the transformer T and is saturated, which may cause a large stress on the switching elements and the like.

The present invention has been made in view of the above problems, and an object of the present invention is to reduce the stress applied to a switching element or the like in the process of transitioning from the extinguished state to the lit state of a discharge lamp. An object of the present invention is to provide an electric lamp lighting device.

[0012]

In order to solve the above-mentioned problems, according to the invention of claim 1, a pair of bidirectional switching elements connected in series and alternately turned on and off, a direct current power source and one A transformer including a primary winding having a series circuit connected to both ends thereof and a secondary winding having an intermediate tap, a capacitor connected to both ends of the series circuit of both switching elements, and a transformer. In a discharge lamp lighting device comprising a load circuit including at least a discharge lamp, which is connected to both ends of the secondary winding, when the integrated value of the voltage across the primary winding exceeds a predetermined value,
It is characterized in that the power supplied to the discharge lamp is reduced.

According to the second aspect of the present invention, the average value of the voltage across the primary winding is used instead of the integrated value of the voltage across the primary winding.

According to the third aspect of the invention, instead of the integral value of the voltage across the primary winding, the voltage across the primary winding is
It is characterized in that it is a value filtered by a filter circuit having a cutoff frequency lower than the operating frequency of the switching element.

According to a fourth aspect of the present invention, it is characterized in that the decrease in lamp impedance of the discharge lamp is detected and the power supplied to the discharge lamp is reduced.

According to a fifth aspect of the present invention, the instant when the discharge lamp is turned on is detected, and the power supplied to the discharge lamp is once reduced.

According to a sixth aspect of the invention, the capacitor is connected to both ends of a series circuit of a pair of switching elements via a DC power source.

According to the seventh aspect of the invention, the load circuit is an inverter circuit in which a DC voltage obtained by rectifying and smoothing the voltage across the secondary winding of the transformer is converted into an AC voltage and supplied to the discharge lamp. It is characterized in that it is configured to include.

According to an eighth aspect of the invention, the inverter circuit supplies a low-frequency AC voltage to the discharge lamp.

According to the invention of claim 9, the discharge lamp comprises:
It is a high-pressure discharge lamp.

[0021]

[Embodiment]

(Embodiment 1) FIG. 1 shows a circuit diagram of a first embodiment according to the present invention.

The difference from the second conventional example shown in FIG. 12 is that
The integrator 5 is provided to input the output obtained by detecting and integrating the primary voltage of the transformer T to the negative input terminal of the comparator Comp1 via the diode D41.
The same configurations as those of the conventional example are denoted by the same reference numerals and the description thereof will be omitted.

In the present embodiment, an excessive primary current IT1 as shown in FIG. 14 flows into the primary winding n1 of the transformer T and is saturated. It is applied to the primary winding n1 of the transformer T. 1
It takes advantage of the fact that the integrated value of the next voltage is not zero, and when the output obtained by detecting and integrating the primary voltage of the transformer T by the integrator 5 becomes non-zero, It is determined that the current IT1 is in the direction of saturation, and the control is performed in the direction of reducing the on-duty of the switching element Qb, that is, in the direction of suppressing the output power to the discharge lamp La.

2 to 6 show concrete circuit examples of the integrator 5. In the circuit shown in FIG. 2, the primary voltage of the transformer T is input to the positive and negative input terminals of the error amplifier EA4 via a filter circuit including a resistor Ra and a capacitor Ca, and the error amplifier E
The output of A4 is used as the output of the integrator 5. Here, the time constant composed of the resistor Ra and the capacitor Ca is sufficiently larger than the switching frequency of the switching elements Qa and Qb. During normal operation, the error amplifier E
Both the positive and negative input terminal voltages of A4 become substantially equal values, and the output of the error amplifier EA4 becomes zero. On the other hand, the transformer T 1
When the saturated primary current IT1 flows through the secondary winding n1, the negative input terminal voltage of the error amplifier EA4 becomes lower than the positive input terminal voltage, so the error amplifier EA4 outputs a high level signal, and this signal Thus, it can be determined that the primary current IT1 is approaching saturation. The inputs to the positive and negative input terminals of the error amplifier EA4 are resistors Rb and R, as shown in FIG.
The voltage may be divided by c and the capacitor Cc.

In the circuit shown in FIG. 4, the voltage across the primary winding n1 of the transformer T is divided by two resistors Rd, and the voltage obtained by filtering the midpoint voltage with a capacitor Cd is applied to the negative input of the error amplifier EA4. The DC power supply Vs is input to the positive input terminal. During normal operation, the voltage of the capacitor Cd is substantially equal to the DC power supply Vs, and the output of the error amplifier EA4 is zero. On the other hand, the transformer T 1
When the saturated primary current IT1 flows through the secondary winding n1, the negative input terminal voltage of the error amplifier EA4 becomes lower than the positive input terminal voltage, so the error amplifier EA4 outputs a high level signal, and this signal Thus, it can be determined that the primary current IT1 is approaching saturation. As shown in FIG. 5, the inputs to the negative input terminal of the error amplifier EA4 are resistors Re, Rf, R.
g, the voltage is divided by the capacitor Cg, and the input to the positive input terminal of the error amplifier EA4 is the resistors Rf, Rg,
It may be divided by the condenser Cg.

The circuit shown in FIG. 6 constitutes an integrator circuit with a resistor Rh, a capacitor Ch and an error amplifier EA4.

In the above embodiment, instead of the integrator 5, an average value circuit capable of obtaining the average value of the primary voltage of the transformer T, or the primary voltage of the transformer T is switched to the switching element Qa. , Qb may be filtered using a filter circuit having a cutoff frequency lower than the operating frequency.

(Second Embodiment) FIG. 7 shows a circuit diagram of a second embodiment according to the present invention.

The difference from the second conventional example shown in FIG. 12 is that
A comparator Comp2 for comparing and outputting the output of the amplifier Amp2 and the reference voltage Vx, and an output voltage Vc of the comparator Comp2.
Differentiating circuit 6 for differentiating o2 to obtain voltage V6 and transmitting it to the negative input terminal of the comparator Comp1 via the diode D51. The description is omitted by adding.

In the present embodiment, the comparator Comp2 determines that the output voltage detected by the amplifier Amp2 has become smaller than the reference voltage Vx, thereby determining the moment when the discharge lamp La is lit and the low level. The output voltage Vco2 of the comparator Comp2 that changes from the high level to the high level is input to the differentiating circuit 6. In response to this, the differentiating circuit 6 outputs a pulsed voltage V6 as shown in FIG. 7 and inputs this to the comparator Comp1. As a result, the discharge lamp La
Reduce the power supplied to.

With such a configuration, the discharge lamp La
At the moment when is turned on, it is forcibly operated in the direction in which the power supplied to the discharge lamp La is reduced, that is, in the direction in which the on-duty of the switching element Qb is reduced, and the saturation of the primary current IT1 is prevented. The output power at this time decreases to such an extent that the discharge lamp La does not go out.

In all of the above-mentioned embodiments, the switching element Q uses the FET, but other switching elements such as a transistor may be used. Further, the inverter circuit connected to the primary side of the transformer T and configured to include the switching elements Qa and Qb may have a configuration as shown in FIG. 8, for example, and this configuration has the switching elements Qa and Qb. Capacitor C1 is connected in parallel at both ends of the series connection of Vs and the primary winding n1 of the transformer T.
Is connected in series to both ends of the switching element Qb.

[0033]

According to the present invention, it is possible to provide a discharge lamp lighting device capable of reducing stress applied to a switching element or the like in the process of transitioning the discharge lamp from the extinguished state to the lit state.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment according to the present invention.

FIG. 2 is a circuit diagram showing an example of a specific circuit of an integrator.

FIG. 3 is a circuit diagram showing an example of a specific circuit of an integrator.

FIG. 4 is a circuit diagram showing an example of a specific circuit of an integrator.

FIG. 5 is a circuit diagram showing an example of a specific circuit of an integrator.

FIG. 6 is a circuit diagram showing an example of a specific circuit of an integrator.

FIG. 7 is a circuit diagram showing a second embodiment according to the present invention.

FIG. 8 is a circuit diagram showing another circuit example according to all the embodiments.

FIG. 9 is a circuit diagram showing a first conventional example according to the present invention.

FIG. 10 is a circuit diagram showing a second conventional example according to the present invention.

FIG. 11 is a diagram showing a relationship between on-duty and outputs of switching elements Qa and Qb.

FIG. 12 is a circuit diagram with a control circuit showing a second conventional example according to the present invention.

FIG. 13 is a characteristic diagram showing the relationship between the on-duty of the switching element Qb and the output power.

FIG. 14 is a waveform diagram showing the state of saturation of the primary current flowing through the primary winding of the transformer.

[Explanation of symbols]

 C capacitor La discharge lamp n winding Q switching element T transformer Vs DC power supply

Claims (9)

[Claims] 1. A pair of bidirectional switching elements that are connected in series with each other and are alternately turned on and off, a primary winding having a series circuit composed of a DC power source and one of the switching elements connected to both ends, and an intermediate tap. A transformer including a secondary winding; a capacitor connected to both ends of a series circuit of the switching elements;
In a discharge lamp lighting device provided with a load circuit including at least a discharge lamp, which is connected to both ends of a secondary winding, when an integrated value of the voltage across the primary winding exceeds a predetermined value,
A discharge lamp lighting device, characterized in that power supplied to the discharge lamp is reduced. 2. The discharge lamp lighting device according to claim 1, wherein the average value of the voltage across the primary winding is used instead of the integrated value of the voltage across the primary winding. 3. A value obtained by filtering the voltage across the primary winding with a filter circuit having a cutoff frequency lower than the operating frequency of the switching element, instead of the integrated value of the voltage across the primary winding. The discharge lamp lighting device according to claim 1, wherein: 4. The discharge lamp according to claim 1, wherein a decrease in the lamp impedance of the discharge lamp is detected to reduce the power supplied to the discharge lamp. Lighting device. 5. The moment when the discharge lamp is lit is detected,
The discharge lamp lighting device according to claim 1, wherein the electric power supplied to the discharge lamp is once reduced. 6. The discharge lamp lighting according to claim 1, wherein the capacitor is connected to both ends of a series circuit of a pair of the switching elements via the DC power source. apparatus. 7. The load circuit includes an inverter circuit that converts a DC voltage obtained by rectifying and smoothing a voltage across a secondary winding of the transformer into an AC voltage and supplies the AC voltage to the discharge lamp. The discharge lamp lighting device according to any one of claims 1 to 6, characterized in that. 8. The discharge lamp lighting device according to claim 1, wherein the inverter circuit supplies a low-frequency AC voltage to the discharge lamp. 9. The discharge lamp lighting device according to claim 1, wherein the discharge lamp is a high pressure discharge lamp.