JP5576741B2 - Discharge lamp lighting device - Google Patents

Description

  The present invention relates to a discharge lamp lighting device for lighting a discharge lamp such as a fluorescent lamp or an HID lamp, and more particularly to improvement of a lamp voltage detection mechanism thereof.

  Conventionally, as a discharge lamp lighting device, a copper iron type ballast (so-called copper iron ballast) has been used. Ballasts have the role of properly limiting the lamp current, but copper iron ballasts are heavier and larger in size, so in recent years the ballasts have become lighter and smaller. So-called electronic ballasts using electronic components such as switching elements and diodes have been used for the purpose of higher functionality. Furthermore, electronic ballasts that are provided with a control circuit with a built-in microcomputer in the electronic ballasts and are capable of responding to the occurrence of abnormal discharges such as the end of life have come to be used.

  For example, an electronic ballast having a function of appropriately detecting an inability to turn on a discharge lamp, abnormal discharge, or a short circuit and stopping the supply of lighting power is known (see Patent Document 1). According to Patent Document 1, the voltage detection means detects the supply voltage to the discharge lamp, the microcomputer compares the detection voltage with the normal voltage region, and supplies power to the discharge lamp when it deviates from the region. It comes to stop.

  In such an electronic ballast equipped with a microcomputer, an AD converter usually converts the detected value of the lamp voltage from an analog signal to a digital signal and sends the signal to the microcomputer. The microcomputer determines whether or not the supply voltage to the discharge lamp is abnormal based on the AD voltage converted lamp voltage detection value. If the supply voltage is normal, the on-duty of the switching element in the lamp power conversion circuit is calculated, and a command signal for driving the switching element is output to the lamp power conversion circuit to maintain an appropriate power supply. It has become.

JP 2009-289588 A

In an electronic ballast equipped with a conventional switching-type power conversion circuit, the weight and size of the entire ballast can be reduced as the periodic on / off control of the switching element is performed at a higher frequency. If the parts and case that make up the electronic ballast can be reduced in size, the energy loss inside the ballast will be reduced, which will help save resources.
However, when the on / off control is performed at a high frequency, the electromagnetic field generated with a drastic change in the current in the circuit also increases, and the noise density due to the electromagnetic field increases. For this reason, in the microcomputer-mounted electronic ballast described in Patent Document 1, the AD converter provided in the control circuit is strongly influenced by the electromagnetic field generated inside the electronic ballast.
In particular, when detecting a lamp voltage near the ground level, the accuracy of the AD conversion function is limited due to the influence of noise due to the electromagnetic field.

At the time of starting the discharge lamp, the lamp voltage rapidly decreases immediately after the discharge lamp is turned on and approaches the ground level (zero level). For example, when the starting voltage is 240 V, the lamp electrode becomes a short circuit voltage due to lighting and decreases to 10 V or less. A method is adopted in which a sudden drop in voltage is detected to determine lamp lighting, and the control mode is changed from the start control to the start initial control.
In order to further stabilize the starting control of the discharge lamp having the lamp characteristics in which such a severe fluctuation occurs at the time of starting, a more accurate function of detecting the lamp voltage near the ground level is essential. Therefore, the problem that the accuracy of the AD conversion function near the ground level is limited due to the influence of noise due to the generation of the electromagnetic field as described above should be solved immediately.

  The present invention has been made in view of the prior art, and in a discharge lamp lighting device equipped with a microcomputer that performs power conversion control using a lamp voltage detection value converted into a digital voltage signal by an AD converter, The purpose is a discharge lamp with a high-precision AD conversion function that is not easily affected by an electromagnetic field generated by the discharge lamp lighting device itself and has a high-precision AD conversion function for a lamp voltage near the ground level. It is to provide a lighting device. In other words, even if the AD converter is affected by the electromagnetic field and the accuracy of the conversion function near the ground level is limited, it is possible to accurately detect the lamp voltage near the ground level, and the starting stage of the discharge lamp. An object of the present invention is to provide a discharge lamp lighting device capable of performing stable starting control.

  The inventor has recently developed a higher frequency switching control for power conversion circuits and the like, and the lighting device itself has become a source of a stronger electromagnetic field, so that the detected value of the lamp voltage can be used with a microcomputer. Attention was paid to the fact that the AD converter for converting to a signal is strongly influenced by noise near the ground level, which is an obstacle to making the starting control of the discharge lamp more stable. The inventor has found a detection mechanism capable of AD-converting a lamp voltage signal with high accuracy even in an environment affected by noise at a ground level, unlike a measure for preventing the generation of an electromagnetic field. It came to be completed.

That is, the discharge lamp lighting device according to the present invention to solve the above problems is
A rectifier circuit for full-wave rectification of an AC voltage, and a DC power supply circuit having an electrolytic capacitor connected to both output terminals of the rectifier circuit, and supplying a DC voltage with both ends of the electrolytic capacitor as output terminals;
A power conversion circuit that converts the DC voltage from the DC power supply circuit by on / off control of a switching element; and
A control circuit for controlling on / off of a switching element of the power conversion circuit;
In a discharge lamp lighting device for supplying a predetermined lamp current to a discharge lamp connected to both output ends of the power conversion circuit,
A lamp voltage detection circuit that detects a voltage applied between both terminals of the discharge lamp and sends an analog voltage signal to the control circuit, the lamp voltage detection circuit,
It has a series circuit of two resistors connected between both terminals of the discharge lamp, and one of them is used as a voltage dividing resistor, and the voltage between both terminals of the voltage dividing resistor is divided into the lamp voltage. A voltage dividing section serving as a value;
A constant voltage adding unit that is connected in series to the voltage dividing resistor and adds a constant voltage to the divided voltage value of the lamp voltage, and a series circuit of the voltage dividing resistor and the constant voltage adding unit The voltage between both terminals is output as an analog voltage signal.
Here, the control circuit includes an AD converter that converts an analog voltage signal from the lamp voltage detection circuit into a digital voltage signal, and a microcomputer that performs power conversion control of the power conversion circuit using the digital voltage signal. Have. The constant voltage addition unit raises the divided voltage value of the lamp voltage near the ground level to a level that is not affected by noise near the ground level, and the AD converter converts the raised divided value to be converted. Thus, AD conversion is performed without being affected by noise close to the ground level.

In the discharge lamp lighting device of the present invention,
The lamp voltage detection circuit has a high-frequency ripple removal unit that removes a ripple component from the lamp voltage to be detected,
The high-frequency ripple removing unit consists of a series circuit of a filter resistor and a filter capacitor connected between both terminals of the discharge lamp,
The series circuit of the voltage dividing unit and the constant voltage adding unit is preferably connected between both terminals of the filter capacitor.
Furthermore, it is preferable that the constant voltage adding unit is configured by a parallel circuit of a constant current source and a resistor through which a direct current from the constant current source flows.

  According to the configuration of the present invention, since the lamp voltage detection circuit having the voltage dividing unit and the constant voltage adding unit is used, not only the lamp voltage is divided and detected to an appropriate voltage, but also the detected lamp voltage is detected. It is possible to prevent the signal from being buried in noise near the ground potential. That is, the signal of the conventional AD converter input terminal voltage is replaced with a signal obtained by adding a constant voltage by the voltage adding unit to the divided voltage value of the lamp voltage by the lamp voltage detection circuit of the present invention. As a result, the signal of the AD converter input terminal voltage rises by a certain voltage, so that it is not necessary to be affected by ground level noise during AD conversion.

  When the constant voltage is added by the constant voltage adding unit in this way, the influence of noise does not appear in the voltage value after AD conversion even if the lamp voltage to be detected is at the same level as the conventional one. Since the signal level of the AD converter input terminal voltage can be floated from a noise level close to the ground potential level to a level that is not affected by the noise, the lamp voltage signal is not buried in the noise near the ground potential. That's it.

As described above, according to the present invention, the lamp voltage near the ground level can be AD-converted with high accuracy against noise caused by the electromagnetic field generated by the discharge lamp lighting device itself. That is, even if the AD converter is affected by the electromagnetic field near the ground level, the lamp voltage can be accurately detected, and more stable starting control can be performed at the starting stage of the discharge lamp.
In addition, by providing the lamp voltage detection circuit with a high-frequency ripple removing unit, the high-frequency component (noise component) included in the lamp voltage can be removed smoothly by an RC integration circuit comprising a filter resistor and a filter capacitor. It is possible to prevent high-frequency noise from being mixed in the ramp voltage signal sent to the subsequent voltage divider. As a result, the signal of the AD converter input terminal voltage does not contain a high-frequency noise component, so that the SN ratio of the AD converter input terminal voltage can be maintained at the level of the SN ratio of the ramp voltage signal.

It is a schematic circuit block diagram of the discharge lamp lighting device concerning this invention. It is a circuit block diagram of the discharge lamp lighting device concerning 1st Embodiment. (A) shows the relationship between the lamp voltage and the AD converter input terminal voltage in the conventional discharge lamp lighting device, and (B) shows the relationship between the lamp voltage and the numerical data of the voltage recognized by the microcomputer after AD conversion. It is a graph to show. FIG. 3 is a circuit diagram of a lamp voltage detection circuit in the circuit of FIG. 2. It is a graph which shows together the relationship between the lamp voltage and AD converter input terminal voltage in the discharge lamp lighting device of the present invention, and the relationship between the lamp voltage and the numerical data of the voltage recognized by the microcomputer after AD conversion. It is a graph which shows the relationship between the lamp voltage in the discharge lamp lighting device of this invention, and the data which correct | amended the numerical data of the voltage which the microcomputer recognized. It is a circuit diagram of the lamp voltage detection circuit of the discharge lamp lighting device concerning 2nd Embodiment. (A) is a figure which shows the signal waveform of the lamp voltage of the zero level vicinity detected by the lamp voltage detection circuit and correct | amended by the microcomputer as an Example, (B) is the comparative example.

(First embodiment)
Preferred embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows an outline of a circuit configuration of a discharge lamp lighting device according to the present embodiment. The discharge lamp lighting device rectifies an alternating current into a direct current, controls the direct current voltage to a predetermined magnitude, and supplies it to the discharge lamp. For example, a high pressure discharge lamp such as a mercury lamp, a metal halide lamp, and a high pressure sodium lamp Used to control lighting of La. The discharge lamp lighting device is roughly divided into a DC power supply circuit 2, a power conversion circuit 3, a control circuit 1, and a lamp voltage detection circuit 6.

As shown in FIG. 1, the DC power supply circuit 2 generates stable DC power from the AC power from the AC power supply AC and supplies the DC power to the power conversion circuit 3 connected to the subsequent stage.
The power conversion circuit 3 converts DC power into appropriate power according to the lamp voltage of the high-pressure discharge lamp La and supplies it to the high-pressure discharge lamp La.
The high-pressure discharge lamp La is connected between both output ends 1 a and 1 b of the power conversion circuit 3.

The lamp voltage detection circuit 6 detects a lamp voltage V ₁ applied between both output terminals 1 a and 1 b of the power conversion circuit 3 and outputs the detected value to the control circuit 1 as an analog voltage signal.
The control circuit 1 is a circuit for controlling on / off driving of the switching element Q <b> 1 built in the power conversion circuit 3, and includes an AD converter 5 and a microcomputer 4. The control circuit 1 has a pair of terminals 2 a and 2 b for inputting an analog voltage signal from the lamp voltage detection circuit 6.

The AD converter 5 is a circuit element that performs analog-digital conversion. The analog voltage signal from the ramp voltage detection circuit 6 is input to the AD converter 5 via the input terminals 2a and 2b. The voltage applied to the input terminal of the AD converter 5 is referred to as AD converter input terminal voltage V _2. That, AD converter 5 is to convert the AD converter input terminal voltage V ₂ is an analog voltage signal into a digital voltage signal V _2d.
The microcomputer 4 performs power conversion control of the power conversion circuit 3 using the digital voltage signal V _2d from the AD converter 5.

FIG. 2 shows specific circuit configurations of the DC power supply circuit 2 and the power conversion circuit 3 in the discharge lamp lighting device according to the first embodiment.
The DC power supply circuit 2 includes a full-wave rectifier circuit 21 configured by a diode bridge and the like, and an electrolytic capacitor C ₀ connected to both output terminals of the full-wave rectifier circuit 21. The full-wave rectification circuit 21 performs full-wave rectification on the alternating current and converts it to direct current. The electrolytic capacitor C ₀ is charged by a rectified direct current, and supplies direct-current power to the power conversion circuit 3 while the switching element Q ₁ built in the power conversion circuit 3 is on. That is, the DC voltage is supplied to both ends of the electrolytic capacitor C ₀ as the output end.

Power conversion circuit 3 is connected to the subsequent stage of the DC power source circuit 2, to the power converting DC power from the DC power source circuit 2 by on-off driving of the switching element Q _1. The power conversion circuit 3, a typical step-down chopper circuit is used and the switching elements Q _1, inductor L _1, is constituted by a diode D ₁ and a smoothing capacitor C _2, release pressure to both terminals of the smoothing capacitor C ₂ An electric lamp La is connected.
The power conversion circuit 3 is configured by connecting each element as follows. First, _one end of the switching element Q ₁ is connected to the positive output side of the electrolytic capacitor C ₀ , and the inductor L ₁ and the smoothing capacitor are connected between the negative output side of the smoothing capacitor C ₀ and the other end of the switching element Q _1. a series circuit of a C _2, to connect the discharge lamp La in parallel between the smoothing capacitor C ₂ terminal. The switching element Q ₁ is adapted to OFF at a high frequency of several tens kHz.

The switching element Q ₁ is the period in the ON state, the power supply charge stored in the electrolytic capacitor V _C0, a switching element Q ₁ DC current flows, the energy of the magnetic field is stored in the inductor L _1. When the switching element Q ₁ is switched to OFF state from ON, the current flows in the inductor L ₁ by the release of energy in the inductor L ₁ is continuous. The power conversion circuit 3, the switching element Q ₁ is then switched off, the current from the inductor L ₁ is, the closed loop of the current path back to the inductor L ₁ again via the discharge lamp La is formed . That is, across the series circuit of an inductor L ₁ and the smoothing capacitor C ₂ are connected by the diode D ₁ to flow only in the current direction back to the inductor L _1.

In this way the power conversion circuit 3, the switching element Q ₁ is switched at a high frequency is turned on, the DC current from the terminal of the positive electrode of the electrolytic capacitor C ₀ is in the order of the switching elements Q ₁ → inductor L ₁ → discharge lamp La Flowing to the negative terminal of the electrolytic capacitor C ₀ , magnetic field energy is stored in the inductor L ₁ . The switching element Q ₁ is becomes clear, is cut off the supply of direct current, the voltage at the connection point of the switching elements Q _1, inductor L ₁ becomes substantially zero. Then, the energy of the inductor L ₁ is released as current, and is reset to the inductor L ₁ in the order of the discharge lamp La → the diode D _1.
Therefore, the power conversion circuit 3 converts the output DC voltage V _C0 of the DC power supply circuit 2 into a lamp voltage V ₁ that can be lit at a power value determined by the rating of the high-pressure discharge lamp La, and the lamp current corresponding to this is converted to a high voltage. It can be supplied to the discharge lamp La.

  FIG. 2 shows an example of a discharge lamp lighting device according to the present invention. The configuration of the DC power supply circuit 2 may be a configuration including the above-described full-wave rectifier circuit and a boost chopper type power factor correction circuit. Alternatively, a lamp voltage polarity inversion circuit may be added to the subsequent stage of the power conversion circuit 3 to apply a lamp voltage alternating at a predetermined cycle to the high-pressure discharge lamp La.

In the discharge lamp lighting apparatus of Figure 2, the lamp voltage detection circuit 6 detects the voltage across the smoothing capacitor C ₂ as the lamp voltage V ₁ of the high pressure discharge lamp La, the control circuit 1 based on the detected value of the lamp voltages V ₁ the switching element Q ₁ switching frequency to off at a high frequency, or to determine the on-duty, and outputs a command signal for controlling the switching element Q _1. In this way, the control circuit 1 adjusts the power supplied to the high-pressure discharge lamp La.

Here, the problem of the conventional discharge lamp lighting device will be described in detail based on the graph. FIG. 3A shows the relationship between the ramp voltage V ₁ and the AD converter input terminal voltage V ₂ when the ramp voltage detection circuit is configured by only the normal voltage dividing circuit 7. Further, in FIG. (B), in the case of using the same lamp voltage detection circuit, the lamp voltage V ₁ and the microcomputer 4 after AD conversion showing the relationship recognizing the voltage value V _1d. In the conventional discharge lamp lighting device, the lower limit value of the lamp voltage that can be detected by the lamp voltage detection circuit is about 0.2 V, for example, as shown in FIG. In addition, the lower limit value of the voltage value that can be recognized by the microcomputer 4 increases (deteriorates) to about 0.5 V, for example.

  This is because the AD converter 5 is affected by noise when detecting a ground level potential. It has been found that this noise is caused by an electromagnetic field generated in the power conversion circuit 3 controlled by high frequency switching. When noise countermeasures for the AD converter 5 are not taken, the lamp voltage value near the ground level is buried by noise due to electromagnetic waves from the discharge lamp lighting device itself. As a result, it has been difficult to AD convert the detected value of the lamp voltage near the ground level with higher accuracy.

What is characteristic of the present invention is that the ramp voltage detection circuit 6 is divided into a voltage dividing circuit (corresponding to a voltage dividing unit) 7 shown in FIG. 4 so that the AD converter 5 can execute AD conversion with higher accuracy. And a constant voltage source (corresponding to a constant voltage adding unit) 8.
The voltage dividing circuit 7 has a series circuit of two resistors R ₂ and R ₃ connected between both terminals (1a, 1b) of the high-pressure discharge lamp La. The smaller one of the two resistors R ₂ and R ₃ is used as the voltage dividing resistor R ₂ . Then, the voltage between the two terminals of the dividing resistors R ₂ is a divided value of the lamp voltage V _1.

Constant voltage source 8 is connected in series to the voltage dividing resistor R _2, the partial pressure value of the voltage dividing resistors R ₂ lamp voltages V ₁ by, for adding a constant voltage (offset voltage). That is, the lamp voltage detection circuit 6, a voltage between both terminals of the series circuit of the voltage dividing resistors R ₂ and constant voltage source 8 outputs an analog voltage signal. The output voltage becomes the AD converter input terminal voltage V _2.

A specific circuit configuration of the constant voltage source 8 will be described.
The constant voltage source 8 includes a parallel circuit of a constant current source 9 and a resistor R1 as shown in FIG. Constant current source 9, a series circuit of resistors R ₅ and stabilizing the DC power source E _1. That is, the resistor R ₁ , the resistor R _2, and the resistor R ₃ are connected in series between the high potential side terminal 1 a and the ground line side terminal 1 b of the high pressure discharge lamp La, and the resistor R _The constant current source 9 is connected in parallel between the two terminals. Direct current from the stabilized direct current power source E ₁ is a resistor to flow R ₅ → the order of the resistor R ₁ → stabilized DC power source E _1, the offset voltage is generated across the resistor R _1.

By using the lamp voltage detection circuit 6 having such a configuration, not only the lamp voltages V ₁ can be detected divide the voltage of the appropriate size, the detected lamp voltage signal is buried in the ground potential close to the noise Can be prevented. That is, the signal of the conventional AD converter input terminal voltage V ₂ shown in FIG. 3A is converted by the ramp voltage detection circuit 6 of the present invention to the offset voltage of the constant voltage source 8 to the divided voltage value of the ramp voltage V _1. Replaced by the added signal. As a result, the lower limit value of the AD converter input terminal voltage V ₂ of the signal rises by the offset voltage level component as shown in FIG. 5, so need not influenced by the ground level noise during AD conversion .

When performing addition of the offset voltage by the constant voltage source 8, to also match in the vicinity of ground level and the AD converter input terminal voltage V ₂ and the microcomputer 4 after AD conversion recognizes the voltage value V _2d as shown in FIG. 5 become. Therefore, even if the lamp voltage V _{1 to} be detected is the same level, the influence of noise does not appear in the voltage value after AD conversion by using the lamp voltage detection circuit 6. In this way, the signal level of the AD converter input terminal voltage V ₂ can be floated from a noise level close to the ground potential level to a level that is not affected by noise, so that the ramp voltage signal is close to the ground potential. You don't have to be buried in the noise. The AD converter 5 can be the same as the conventional one.

The microcomputer 4 can easily correct the recognized digital signal. Here, a method for correcting the digital signal after AD conversion recognized by the microcomputer 4 to the original ramp voltage will be described.
The AD converter 5 performs AD conversion of the signal of the AD converter input terminal voltage V ₂ floated from the noise level close to the ground potential level. Then, the microcomputer 4, than numeric data after the AD conversion, to calculate the original lamp voltages V ₁ using the following equation.
(Equation 1)
_{V 1 = K 1 × (V} 2 - K 2)
However,
K ₁ = 1 / (1.0 − ((R ₁ + R ₅ ) · R ₃ / X))
K ₂ = E ₁ · R ₁ · R ₃ / X
X = (R ₁ + R ₅ ) (R ₃ + R ₂ + R ₁ ) −R ₁ · R ₁
Each coefficient used in the above equation corresponds to the specification of each element of the lamp voltage detection circuit 6 shown in FIG. FIG. 6 shows the lamp voltage value corrected by the microcomputer 4.

(Second Embodiment)
In the present embodiment, the lamp voltage detection circuit 6 in the first embodiment is replaced with a ramp voltage detection circuit 106 having a ripple removal circuit 10 as shown in FIG. Since the DC power supply circuit 2, the power conversion circuit 3, and the control circuit 1 in the first embodiment are common to the present embodiment, description thereof is omitted.
The ramp voltage detection circuit 106 includes a voltage dividing circuit 7 and a constant voltage source 8 as in the first embodiment, and further, a high frequency ripple removal circuit (in the ripple removal unit) that removes a ripple component from the detected ramp voltage V1. (Corresponding) 10.

Frequency ripple removal portion 10 is composed of a series circuit of the two terminals (1a, 1b) filter resistor R ₄ and the filter capacitor C ₁ connected between the high-pressure discharge lamp La. A series circuit of the two resistors R ₂ and R ₃ of the voltage dividing circuit 7 and the constant voltage source 8 is connected between both terminals of the filter capacitor C ₁ .

If divided by the R ₂ of the lower resistance value R ₃ of high resistance value without passing through the integration circuit consisting of filter resistor R4 and the filtering capacitor C _1, a high frequency component contained in the lamp voltage signal noise component including the will pass through the parasitic capacitance components of the resistor R _3, incorporated into the voltage between both terminals of the voltage dividing resistor R _2. As a result, high-frequency noise component together with the signal of the AD converter input terminal voltage V _2, will be AD converted, high-frequency noise components is generated. SN ratio at the input terminal voltage V ₂ of the AD converter 5 (the ratio of the signal and noise components) are deteriorated than the SN ratio of the lamp voltage signal.

However, according to the present embodiment, the high-frequency component (noise component) included in the lamp voltage V ₁ is smoothed by the RC integrating circuit including the filter resistor R ₄ and the filter capacitor C ₁ as shown in FIG. Since it is removed, it is possible to prevent high-frequency noise from being mixed in the ramp voltage signal sent to the subsequent voltage dividing circuit 7. As a result, since the signal of the AD converter input terminal voltage V ₂ does not contain a high frequency noise component, the SN ratio of the AD converter input terminal voltage V ₂ can be maintained at the level of the SN ratio of the ramp voltage signal. .

The microcomputer 4 can calculate the original lamp voltage V1 from the numerical data after AD conversion using the following equation.
(Equation 2)
_{V 1 = K 1 × (V} 2 - K 2)
However,
K ₁ = 1 / (1.0 − ((R ₁ + R ₅ ) (R ₃ + R ₄ ) / X))
K ₂ = E ₁ · R ₁ · (R ₃ + R ₄ ) / X
_{X = (R 1 + R 5} ) (R 4 + R 3 + R 2 + R 1) -R 1 · R 1
Each coefficient used in the above equation corresponds to the specification of each element of the lamp voltage detection circuit 6 shown in FIG.

The correction formula when each element in the circuit configuration of FIG. 7 is set as follows will be exemplified.
The voltage dividing circuit 7 is configured by setting the resistor R ₃ to 510 KΩ and the voltage dividing resistor R ₂ to 5.1 KΩ. Further, the constant current source 9 is configured by setting the stabilized DC power supply E ₁ to 5.0 V and the resistor R ₅ to 10 KΩ. Then, the resistor R ₁ is set to 1.5 KΩ, and the resistor R ₁ and the constant current source 9 constitute the constant voltage source 8. In addition, the filter resistor R ₄ of the ripple removing circuit 10 is set to 5.1 KΩ, and the filter capacitor C ₁ is set to 2200 pF.

Advance, by flowing stabilized direct current from the constant current source 9 to the resistor R _1, allowed to generate an offset voltage.
First, a high-frequency component contained in the lamp voltage V ₁ applied between both terminals 1 a and 1 b of the high-pressure discharge lamp La is removed by the ripple removal circuit 10. Further, the voltage divided by the voltage dividing circuit 7, the voltage between the words of the dividing resistors R ₂ terminals, a material obtained by adding an offset voltage generated in the resistor R ₁ and AD converter input terminal voltage V _2.

If the AD converter input terminal voltage V ₂ is AD converted to V _2d , the above-described correction formula (2) is as follows.
(Equation 3)
V _1d = 81.0 × (V _2d −0.64)
V _1d in the formula (3) indicates a numerical value obtained by AD conversion of the lamp voltage V ₁ without background noise. With this correction formula, it is possible to calculate the AD converted voltage value V _1d without background noise.

FIG. 8 shows an example and a comparative example according to the present invention. FIG. 2A shows a lamp voltage signal waveform detected by a lamp voltage detection circuit and A / D converted and corrected by a microcomputer as an embodiment. FIG. 5B shows a signal waveform of a lamp voltage recognized by a microcomputer after being detected and AD converted by a conventional lamp voltage detection circuit having only a voltage dividing circuit, as a comparative example. In all cases, a voltage near zero level is detected, and the configuration other than the lamp voltage detection circuit (for example, an AD converter) is the same. The signal waveform of the lamp voltage output from the microcomputer by the DA converter was detected using a normal probe and visualized with an oscilloscope (FIG. 8). Therefore, each signal waveform of the example and the comparative example obtained by the oscilloscope contains the same amount of noise accompanying detection by the probe. In a normal probe, a loop-shaped cross-section composed of wiring for meter reading and ground connection functions as a kind of loop antenna, and the noise component picked up by the loop antenna overlaps the measured waveform, and the original waveform is noisy. There is a problem that the ingredients become thicker.
Under such a premise, when comparing the example and the comparative example, it can be seen that the noise level included in the signal waveform recognized by the microcomputer becomes smaller when the voltage detection circuit of the present invention is used. That is, even when the lamp voltage is near zero level, the voltage detection circuit of the present invention adds a constant voltage to the lamp voltage, so that it is not affected by noise near the ground level during AD conversion. Further, since the microcomputer can easily correct the digital signal after AD conversion to the level of the ramp voltage before the addition of the constant voltage, as shown in FIG. A highly accurate waveform signal can be obtained.

  In the above embodiment, the electronic ballast of the high-intensity high-pressure discharge lamp (so-called HID lamp) has been described. However, the electronic ballast of the present invention is also applied to a discharge lamp such as a fluorescent lamp. Applicable.

DESCRIPTION OF SYMBOLS 1 Control circuit 2 DC power supply circuit 3 Power conversion circuit 4 Microcomputer 5 AD converter 6, 106 Lamp voltage detection circuit 7 Voltage dividing circuit (voltage dividing part)
8 Constant voltage source (Constant voltage addition unit)
9 Constant current source 10 Ripple removal circuit (ripple removal unit)
AC AC power source C ₀ Electrolytic capacitor C ₁ Filter capacitor E ₁ Stabilized DC power source La High pressure discharge lamp R ₁ Resistor R ₂ Divider resistor R ₃ Resistor R ₄ Filter resistor R ₅ Resistor V ₁ Lamp voltage V ₂ AD converter input terminal voltage

Claims (3)

A rectifier circuit for full-wave rectification of an AC voltage, and a DC power supply circuit having an electrolytic capacitor connected to both output terminals of the rectifier circuit, and supplying a DC voltage with both ends of the electrolytic capacitor as output terminals;
A power conversion circuit that converts the DC voltage from the DC power supply circuit by on / off control of a switching element; and
A control circuit for controlling on / off of a switching element of the power conversion circuit;
In a discharge lamp lighting device for supplying a predetermined lamp current to a discharge lamp connected to both output ends of the power conversion circuit,
A lamp voltage detection circuit that detects a voltage applied between both terminals of the discharge lamp and sends an analog voltage signal to the control circuit, the lamp voltage detection circuit,
It has a series circuit of two resistors connected between both terminals of the discharge lamp, and one of them is used as a voltage dividing resistor, and the voltage between both terminals of the voltage dividing resistor is divided into the lamp voltage. A voltage dividing section serving as a value;
A constant voltage adding unit that is connected in series to the voltage dividing resistor and adds a constant voltage to the divided voltage value of the lamp voltage, and a series circuit of the voltage dividing resistor and the constant voltage adding unit The voltage between both terminals in is output as an analog voltage signal,
Wherein the control circuit, possess an AD converter for converting an analog voltage signal from the lamp voltage detection circuit into a digital voltage signal, and a microcomputer that performs power conversion control of the power conversion circuit using the digital voltage signal ,
The constant voltage adding unit increases the divided voltage value of the lamp voltage near the ground level to a level not affected by noise near the ground level,
The A / D converter performs the A / D conversion without being affected by noise close to the ground level, with the increased partial pressure value as a conversion target . In the discharge lamp lighting device according to claim 1,
The lamp voltage detection circuit has a high-frequency ripple removal unit that removes a ripple component from the lamp voltage to be detected,
The high-frequency ripple removing unit consists of a series circuit of a filter resistor and a filter capacitor connected between both terminals of the discharge lamp,
The discharge lamp lighting device, wherein a series circuit of the voltage dividing unit and the constant voltage adding unit is connected between both terminals of the filter capacitor. 3. The discharge lamp lighting device according to claim 1, wherein the constant voltage addition unit is configured by a parallel circuit of a constant current source and a resistor through which a direct current from the constant current source flows. Discharge lamp lighting device.

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