JP4103408B2 - Discharge lamp lighting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a discharge lamp lighting device for lighting a discharge lamp at a high frequency by an inverter circuit.
[0002]
[Prior art]
(Conventional example 1)
A first conventional example is shown in FIG. Hereinafter, the circuit configuration will be described. A series circuit of switching elements Q1, Q2 is connected to the DC power source E. The connection point of the switching elements Q1 and Q2 is connected to the power supply side terminal of the filament A of the discharge lamp la via a DC cut capacitor C0 and a resonance (current limiting) inductor L1. The power supply side terminal of the filament B of the discharge lamp la is connected to the low voltage side terminal (circuit ground) of the DC power supply E. The power supply side terminal of the filament A of the discharge lamp la is connected to the high voltage side terminal of the DC power supply E through the resistor R1. A resonance capacitor C1 is connected in parallel between the non-power supply side terminals of both filaments A and B of the discharge lamp la. A series circuit of a resistor R2 and a Zener diode ZD1 is connected between the non-power supply side terminal of the filament A of the discharge lamp la and the low voltage side terminal (circuit ground) of the DC power supply E. A Zener diode ZD1 is connected to a parallel circuit of a capacitor C4 and a resistor R5 via a diode D1. Thus, a DC current loop for charging the capacitor C4 is formed from the DC power source E via the resistor R1, the filament A of the discharge lamp la, the resistor R2, and the diode D1. The potential Vk of the capacitor C4 is input to the control circuit unit S and compared with the reference potential Vref.
[0003]
The circuit operation will be described below. The control circuit unit S determines whether or not the filament A is attached based on the potential Vk of the capacitor C4 before starting the inverter circuit. When the filament A is attached, the capacitor C4 is charged from the DC power source E through the above-described DC current loop. The potential Vk of the capacitor C4 rises to a voltage having a predetermined voltage division ratio with the time constants of the resistors R1, R2, R5 and the capacitor C4, and exceeds the reference potential Vref of the comparator CP provided in the control circuit unit S. Thus, the inverter circuit starts to operate.
[0004]
In the inverter circuit, the switching elements Q1 and Q2 are alternately turned on and off by the drive signal from the control circuit unit S to the switching elements Q1 and Q2, and the resonant load circuit including the inductor L1, the capacitor C1, and the discharge lamp la has a rectangular wave shape. A high frequency voltage is applied to light the discharge lamp la with a sinusoidal high frequency.
[0005]
When the filament A is not attached, since the filament A is open, charging of the capacitor C4 from the DC power source E is interrupted, and the potential Vk of the capacitor C4 does not increase. As a result, the inverter circuit stops when the potential Vk of the capacitor C4 falls below the reference potential Vref of the comparator CP provided in the control circuit section S. In this conventional example, the detection circuit for whether or not the filament B is attached is omitted because it is not directly related to the present invention.
[0006]
When the potential Vk of the capacitor C4 exceeds the reference potential Vref of the comparator CP provided in the control circuit unit S and the inverter circuit starts to operate, the discharge lamp la is turned on and the voltage dividing ratio of the resistors R1, R2, and R5 varies. . Specifically, the impedance is infinite before the discharge lamp la is turned on, but the impedance is greatly reduced by turning on the discharge lamp la. Usually, the resistance values of the resistors R1, R2, and R5 are comprised of several hundreds KΩ to several MΩ in order to suppress the power consumption at the resistors as much as possible and to suppress the circuit current of the inverter circuit. From this, the resistance voltage dividing ratio fluctuates greatly before and after the discharge lamp la is turned on. When the discharge lamp la is lit, although the impedance varies depending on the load rating, it is generally on the order of several hundred Ω to several KΩ, so that almost no DC component of the no-load detection circuit is applied to the resistor R1. The amount of R5 applied is greatly reduced.
[0007]
However, when the discharge lamp la is lit, a sinusoidal high frequency voltage is generated at both ends of the discharge lamp la, and the high frequency voltage of the discharge lamp la is applied to the connection point between the resistor R2 and the diode D1 of the no-load detection circuit. A voltage V1 is generated in which the peak value of the half-wave rectified voltage is clamped by the Zener diode ZD1. This voltage V1 is rectified by the diode D1, and the voltage smoothed by the capacitor C4 and the resistor R5 becomes the potential Vk of the capacitor C4. In other words, after the discharge lamp la is lit, the potential Vk of the capacitor C4 is small, but the resistors R1, R2, and R5 from the DC power supply E, the DC voltage by the divided voltage of the impedance of the discharge lamp la, The above AC voltage is superimposed, and as a result, the potential Vk of the capacitor C4 is ensured to be equal to or higher than the reference potential Vref.
[0008]
This series of operation waveforms is shown in FIG. In the figure, VQ2 (GS) is the gate-source voltage of the switching element Q2, V1 is the voltage at the connection point of the resistor R2 and the Zener diode ZD1, Vla is the voltage across the discharge lamp la, Vk is the potential of the capacitor C4, and Vref is This is the reference potential of the comparator CP.
[0009]
When the discharge lamp load is removed while the discharge lamp la is lit, the filament A is removed, so that the direct current from the DC power supply E is cut off, and the high-frequency voltage across the discharge lamp la is generated by the capacitor C1 being disconnected. Disappear. As a result, the potential Vk of the capacitor C4 decreases, falls below the reference potential Vref, and oscillation of the inverter circuit stops.
With the operation as described above, the presence or absence of a filament is determined based on the presence or absence of a DC current loop at the time of startup, and the presence or absence of a filament is determined based on the presence or absence of a voltage on which a high-frequency voltage and a DC voltage are superimposed.
[0010]
However, when the filament A or B becomes Emires (thermionic emission failure) while the discharge lamp la is lit, the flow of high-frequency current in the discharge lamp la becomes unbalanced, and the discharge lamp la has a half-wave discharge phenomenon. And a voltage in which a DC voltage is superimposed on a high-frequency voltage is generated in the discharge lamp la. The operation waveform at this time is shown in FIG. In the figure, VQ2 (GS) is the gate-source voltage of the switching element Q2, V1 is the voltage at the connection point of the resistor R2 and the Zener diode ZD1, Vla is the voltage across the discharge lamp la, Vk is the potential of the capacitor C4, and Vref is This is the reference potential of the comparator CP.
[0011]
At this time, when a half-wave discharge is generated in a direction in which the filament A has a higher DC potential than the filament B, the DC voltage component of the discharge lamp la is applied to the resistors R2 and R5, and thus the potential Vk of the capacitor C4. Tries to rise. However, because of the Zener diode ZD1, the potential Vk of the capacitor C4 does not rise above the Zener voltage.
[0012]
On the other hand, when a half-wave discharge is generated in such a direction that the filament B has a higher DC potential than the filament A, the DC voltage component of the discharge lamp la is applied to the resistor R2 and the Zener diode ZD1, and the Zener diode ZD1 is in the forward direction. And the voltage V1 at the connection point between the resistor R2 and the diode D1 decreases the voltage in the direction of charging the capacitor C4. At this time, the supply voltage of the charged charge of the capacitor C4 is significantly lowered, and the potential Vk of the capacitor C4 is lowered. Further, the degree of imbalance in half-wave discharge is very unstable, and the potential in the charge charging direction of the capacitor C4 may be lost.
[0013]
In such a case, when the potential Vk of the capacitor C4 decreases and falls below the reference potential Vref, it is erroneously detected that the filament has come off even though the discharge lamp la is in the mounted state, and the inverter circuit temporarily stops oscillating, After stopping, the capacitor C4 is charged from the DC power source E and restarted. Then, the inverter circuit oscillates with a load that discharges half-wave, and erroneous detection as described above is performed again. Thus, there has been a problem of repeating a cycle in which the inverter circuit starts and stops. Further, the stop time at the time of repetition is determined by the time constants of the capacitor C4 and the resistor R5. However, since the stop time is short, there is a problem that this flashing cycle is fast and a large stress is applied to the circuit.
[0014]
Therefore, when the half-wave discharge of the discharge lamp la as described above occurs, in order to prevent erroneous detection of the no-load detection circuit, the time constants of the capacitor C4 and the resistor R5 are increased, and the potential Vk of the capacitor C4. Measures have been used to slow down the degree of decline. However, when such a countermeasure is used, it is possible to suppress the erroneous detection at the time of half-wave discharge of the discharge lamp la to some extent. However, when the discharge lamp la is removed during lighting, the connection between the resistor R2 and the diode D1 is possible. Since the voltage V1 at the point disappears at the moment when the discharge lamp la is removed, the potential Vk of the capacitor C4 slowly decreases, so the oscillation of the switching elements Q1 and Q2 continues, and the potential Vk of the capacitor C4 becomes equal to the reference potential Vref. Since the residual oscillation time of the switching elements Q1 and Q2 until it becomes lower becomes longer, the time for performing the resonance operation of the parasitic capacitance component and the stray capacitance component generated between the inductor L1 and other lines becomes longer. There was a problem of applying a large stress to.
[0015]
(Conventional example 2)
A second conventional example is shown in FIG. Hereinafter, the circuit configuration will be described. A series circuit of switching elements Q1, Q2 is connected to the DC power source E. The connection point of the switching elements Q1 and Q2 is connected to the power supply side terminal of the filament A of the discharge lamp la via a DC cut capacitor C0 and a resonance (current limiting) inductor L1. The power supply side terminal of the filament B of the discharge lamp la is connected to the low voltage side terminal (circuit ground) of the DC power supply E. The power supply side terminal of the filament A of the discharge lamp la is connected to the high voltage side terminal of the DC power supply E through the resistor R1. A resonance capacitor C1 is connected in parallel between the non-power supply side terminals of both filaments A and B of the discharge lamp la. Between the non-power supply side terminal of the filament A of the discharge lamp la and the low voltage side terminal (circuit ground) of the DC power supply E, a parallel circuit of a capacitor C2 and a resistor R3 is connected via a resistor R2 and a diode D1. . Thus, a DC current loop for charging the capacitor C2 is formed from the DC power source E via the resistor R1, the filament A of the discharge lamp la, the resistor R2, and the diode D1. The potential Vk of the capacitor C2 is input to the control circuit unit S and compared with the reference potential Vref.
[0016]
The circuit operation will be described below. The control circuit unit S determines whether or not the filament A is attached based on the potential Vk of the capacitor C2 before starting the inverter circuit. When the filament A is attached, the capacitor C2 is charged from the direct current power source E through the direct current loop described above. The potential Vk of the capacitor C2 rises to a voltage having a predetermined voltage division ratio with the time constants of the resistors R1, R2, and R3 and the capacitor C2, and exceeds the reference potential Vref of the comparator CP provided in the control circuit unit S. Thus, the inverter circuit starts to operate.
[0017]
In the inverter circuit, the switching elements Q1 and Q2 are alternately turned on and off by the drive signal from the control circuit unit S to the switching elements Q1 and Q2, and the resonant load circuit including the inductor L1, the capacitor C1, and the discharge lamp la has a rectangular wave shape. A high frequency voltage is applied to light the discharge lamp la with a sinusoidal high frequency.
[0018]
When the filament A is not attached, since the filament A is open, charging of the capacitor C2 from the DC power source E is interrupted, and the potential Vk of the capacitor C2 does not increase. As a result, the inverter circuit stops when the potential Vk of the capacitor C2 falls below the reference potential Vref of the comparator CP provided in the control circuit unit S. In this conventional example, the detection circuit for whether or not the filament B is attached is omitted because it is not directly related to the present invention.
[0019]
When the potential Vk of the capacitor C2 exceeds the reference potential Vref of the comparator CP provided in the control circuit unit S and the inverter circuit starts to operate, the discharge lamp la is turned on and the voltage dividing ratio of the resistors R1, R2, and R3 varies. . Specifically, the impedance is infinite before the discharge lamp la is turned on, but the impedance is greatly reduced by turning on the discharge lamp la. Usually, the resistance values of the resistors R1, R2, and R3 are configured to be several hundreds KΩ to several MΩ in order to suppress the power consumption at the resistors as much as possible and to suppress the circuit current of the inverter circuit. From this, the resistance voltage dividing ratio fluctuates greatly before and after the discharge lamp la is turned on. When the discharge lamp la is lit, although the impedance varies depending on the load rating, it is generally on the order of several hundred Ω to several KΩ, so that almost no DC component of the no-load detection circuit is applied to the resistor R1. The amount of application of decreases significantly.
[0020]
However, when the discharge lamp la is lit, a sinusoidal high frequency voltage is generated at both ends of the discharge lamp la, and the high frequency voltage of the discharge lamp la is half-wave rectified by the diode D1 in the capacitor C2 of the no-load detection circuit. Then, the voltage is divided by the resistors R2 and R3, and the smoothed potential Vk is generated by the capacitor C2. That is, after the discharge lamp la is lit, the potential Vk of the capacitor C2 is small, but the resistors R1, R2, and R3 from the DC power supply E, the DC voltage by the divided voltage of the impedance of the discharge lamp la, The voltage obtained by rectifying and smoothing the above-described AC voltage is superimposed, and as a result, the potential Vk of the capacitor C2 is secured to be equal to or higher than the reference potential Vref.
[0021]
When the discharge lamp load is removed while the discharge lamp la is lit, the filament A is removed, so that the direct current from the DC power supply E is cut off, and the high-frequency voltage across the discharge lamp la is generated by the capacitor C1 being disconnected. Disappear. As a result, the potential Vk of the capacitor C2 decreases and falls below the reference potential Vref, and the oscillation of the inverter circuit stops.
[0022]
With the operation as described above, the presence or absence of a filament is determined based on the presence or absence of a DC current loop at the time of startup, and the presence or absence of a filament is determined based on the presence or absence of a voltage on which a high-frequency voltage and a DC voltage are superimposed.
[0023]
Also in this conventional example, the same problem as in Conventional Example 1 occurs. That is, when the filament A or B becomes Emiles (thermionic emission failure) while the discharge lamp la is lit, the flow of high-frequency current in the discharge lamp la becomes unbalanced, and a half-wave discharge phenomenon occurs in the discharge lamp la. The voltage generated by superimposing the DC voltage on the high-frequency voltage is generated in the discharge lamp la. At this time, when a half-wave discharge is generated in a direction in which the filament A has a higher DC potential than the filament B, the DC voltage component of the discharge lamp la is applied to the resistors R2 and R3. Rises. On the other hand, when a half-wave discharge is generated in such a direction that the filament B has a higher DC potential than the filament A, the DC voltage component of the discharge lamp la is applied to the resistors R2 and R3, and the diode D1 is turned on in the forward direction. The ratio decreases, and the voltage in the direction of charging the capacitor C2 decreases. At this time, the supply voltage of the charge of the capacitor C2 is remarkably lowered, and the potential Vk of the capacitor C2 is lowered. Further, the degree of imbalance of half-wave discharge is very unstable, and the potential in the charge charging direction of the capacitor C2 may be lost.
[0024]
In such a case, when the potential Vk of the capacitor C2 decreases and falls below the reference potential Vref, it is erroneously detected that the filament is detached even though the discharge lamp la is in the mounted state, and the inverter circuit temporarily stops oscillating, After stopping, the capacitor C2 is charged from the DC power source E and restarted. Then, the inverter circuit oscillates with a load that discharges half-wave, and erroneous detection as described above is performed again. Thus, there has been a problem of repeating a cycle in which the inverter circuit starts and stops. Further, the stop time at the time of repetition is determined by the time constants of the capacitor C2 and the resistor R3. However, since the stop time is short, there is a problem that this flashing cycle is fast and a large stress is applied to the circuit.
[0025]
Therefore, when the half-wave discharge of the discharge lamp la as described above occurs, in order to prevent erroneous detection of the no-load detection circuit, the time constants of the capacitor C2 and the resistor R3 are increased, and the potential Vk of the capacitor C2 is lowered. Means have been used to slow the degree. However, when such a countermeasure is used, it is possible to suppress the erroneous detection at the time of half-wave discharge of the discharge lamp la to some extent. However, when the discharge lamp la is removed during lighting, the potential Vk of the capacitor C2 is lowered. Therefore, the oscillation of the switching elements Q1 and Q2 is continued, and the residual oscillation time of the switching elements Q1 and Q2 until the potential Vk of the capacitor C2 falls below the reference potential Vref becomes longer. During this time, the inductor L1 and other lines There is a problem in that a large stress is applied to the circuit because the time for performing the resonance operation with the parasitic capacitance component and the stray capacitance component generated between the terminals becomes long.
[0026]
(Conventional example 3)
A third conventional example is shown in FIG. This conventional example shows a representative example of Japanese Patent Laid-Open No. 1-33955, and its circuit configuration will be described below. A series circuit of switching elements Q1, Q2 is connected to the DC power source E. The connection point of the switching elements Q1 and Q2 is connected to the power supply side terminal of the filament A of the discharge lamp la via a DC cut capacitor C0 and a resonance (current limiting) inductor L1. The power supply side terminal of the filament B of the discharge lamp la is connected to the low voltage side terminal (circuit ground) of the DC power supply E. A resonance capacitor C1 is connected in parallel between the non-power supply side terminals of both filaments A and B of the discharge lamp la. Between the non-power supply side terminal of the filament A of the discharge lamp la and the low voltage side terminal (circuit ground) of the DC power supply E, a series circuit of resistors R2 and R3 is connected. One end of a capacitor C2 is connected to a connection point between the resistors R2 and R3, and the other end of the capacitor C2 is connected to a circuit ground via a diode D1. A parallel circuit of a capacitor C3 and a resistor R4 is connected via a diode D2 between a connection point between the capacitor C2 and the diode D1 and the circuit ground. The potential Vk of the capacitor C3 is input to the control circuit unit S and compared with the reference potential Vref.
[0027]
The Emires detection circuit comprising resistors R2 to R4, diodes D1 and D2, and capacitors C2 and C3 creates a DC voltage Vk obtained by dividing the difference voltage between the positive peak value and the negative peak value of the voltage across the discharge lamp la. . In the negative half cycle in which the filament B of the discharge lamp la has a higher potential than the filament A, the peak value of the voltage obtained by dividing the sinusoidal high-frequency voltage generated in the discharge lamp la by the resistors R2 and R3 passes through the diode D1. The capacitor C2 is charged. Next, in the positive half cycle in which the filament A of the discharge lamp la has a higher potential than the filament B, the peak value of the voltage obtained by dividing the sinusoidal high-frequency voltage generated by the discharge lamp la by the resistors R2 and R3 is the capacitor. The voltage is added to the voltage of C2, and the capacitor C3 is charged via the diode D2.
[0028]
FIG. 19 is an explanatory diagram of the operation of the Emires detection circuit. FIG. 5A shows a voltage V1 obtained by dividing the voltage across the discharge lamp la by resistors R2 and R3, which is a sinusoidal high-frequency voltage. In the figure, e1 means a positive peak value and -e1 means a negative peak value. FIG. 5B shows a voltage Vk ′ for charging the capacitor C3, and a voltage obtained by rectifying the voltage Vk ′ with the diode D2 becomes a potential Vk = e1 − (− e1) = 2 · e1 of the capacitor C3. .
[0029]
As a result, a voltage obtained by dividing the difference voltage between the positive peak value and the negative peak value of the voltage across the discharge lamp la by the resistors R2 and R3 is charged in the capacitor C3. The control circuit section S of the inverter is provided with a comparator CP. If the potential Vk of the capacitor C3 of the Emires detection circuit is higher than the reference potential Vref, the discharge lamp la is determined to be in the Emires state, and is below the reference potential Vref. If there is, it is determined that the discharge lamp la is in a normal state. When it is determined that the discharge lamp la is in the Emileless state, in order to reduce the circuit stress of the inverter, the oscillation is stopped or a sufficient stop section is provided to perform the intermittent oscillation control. In this conventional example, even if half-wave discharge due to Emires occurs, it is possible to extract only a pure AC component generated in the discharge lamp la without being bound by its polarity. Is an effective means.
[0030]
However, even when the discharge lamp la is in the Emires state, the AC component of the voltage across the discharge lamp la does not necessarily increase, and the increase of the AC component is small and only the increase of the DC component may be large. In this case, it is difficult to determine that the discharge lamp la is in the Emiless state at the potential Vk of the capacitor C3. In particular, the higher the temperature of the discharge lamp la or the lower the temperature of the discharge lamp la, the lower the AC voltage during normal lighting (see FIG. 20). Even in the Emires state, it is the same as described above, and the AC component of the voltage across the discharge lamp la decreases at high temperatures and low temperatures. Therefore, at high temperatures and low temperatures, this conventional example makes it difficult to detect Emires. That is, there is a problem that the Emiles detection does not work and a large stress is applied to the circuit.
[0031]
[Problems to be solved by the invention]
The present invention has been made in view of the above-described points, and an object of the present invention is to provide a no-load detection circuit that detects the presence or absence of a filament in a discharge lamp load. An object of the present invention is to provide a configuration that can be detected with an inexpensive circuit configuration.
[0032]
[Means for Solving the Problems]
  In the discharge lamp lighting device according to claim 1, in order to solve the above problem,As shown in FIG. 1, an inverter circuit that converts a DC power source E into a high frequency and supplies high frequency power to the discharge lamp load la via an LC resonance circuit, and a voltage applied to one end of a filament of the discharge lamp load la A no-load detection circuit including a capacitor C4 charged via the first diode D1 and determining the presence or absence of a filament based on the charging voltage Vk of the capacitor C4, and the charging voltage Vk of the capacitor C4 of the no-load detection circuit is a reference voltage Vref And a control unit that starts oscillation of the inverter circuit when the charging voltage Vk of the capacitor C4 exceeds the reference voltage Vref, and the capacitor C4 of the no-load detection circuit includes an inverter circuit. Is supplied from the DC power source E through the filament of the discharge lamp load la before the oscillation starts. When the discharge lamp load la is not half-wave discharged and the filament is connected after charging by the flowing voltage through the first diode D1 until it exceeds the reference voltage Vref and the inverter circuit starts oscillating. The capacitor C4 is charged by the voltage applied to the one end of the filament of the discharge lamp load la through the first diode D1 or from the high frequency voltage generated in the inverter circuit through the second diode D2. When the charging voltage Vk is maintained at the reference voltage Vref or higher and the filament is disconnected after the inverter circuit starts to oscillate, the charging current of the capacitor C4 via the first and second diodes D1 and D2 is The charging voltage Vk of the capacitor C4 is less than the reference voltage Vref by disappearing or decreasing. When the half-wave discharge of the discharge lamp load la is configured and the polarity of the half-wave discharge is such that the charge voltage Vref of the capacitor C4 through the first diode D1 is lowered, By supplying a charging current to the capacitor C4 via the second diode D2 from the high-frequency voltage generated in the inverter circuit when the filament of the discharge lamp load la is connected, the charging voltage Vk of the capacitor C4 becomes the reference voltage. To be maintained above VrefIt is characterized by comprising.
[0033]
  Here, as a configuration for inputting the high frequency voltage generated in the inverter circuit to the no-load detection circuit, the amplitude difference between the positive peak value and the negative peak value of the high frequency AC voltage generated in the discharge lamp load is smoothed and input. Configuration (Claim 3), Configuration of smoothing the peak voltage of one polarity of the AC component of the high-frequency AC voltage generated in the discharge lamp load and inputting it to the no-load detection circuit (Claim 4), generated in the inductor of the resonance circuit A configuration in which the peak voltage of one polarity of the high-frequency AC voltage is smoothed and input to the no-load detection circuit (Claim 5), and the positive peak value and negative value of the AC component of the high-frequency AC voltage generated in the inductor of the resonance circuit Any of a configuration in which the amplitude difference between the peak values is smoothed and input to the no-load detection circuit (Claim 6), and a circuit current of the inverter circuit is converted into a voltage and input to the no-load detection circuit (Claim 7). Adopt It may be.
[0034]
In any of the above cases, the control unit may have a function of temporarily stopping the oscillation of the inverter circuit during half-wave discharge of the discharge lamp load (claim 2). The function to temporarily stop the oscillation of the inverter circuit is to temporarily stop the oscillation of the inverter circuit and intermittently oscillate the inverter circuit at a predetermined period, or after intermittently oscillating a predetermined number of times at a predetermined period, It shall include a function to stop oscillation or a function to maintain oscillation stop.
[0035]
DETAILED DESCRIPTION OF THE INVENTION
(Embodiment 1)
A circuit diagram of the first embodiment is shown in FIG. Hereinafter, the circuit configuration will be described. A series circuit of switching elements Q1, Q2 is connected to the DC power source E. The connection point of the switching elements Q1 and Q2 is connected to the power supply side terminal of the filament A of the discharge lamp la via a DC cut capacitor C0 and a resonance (current limiting) inductor L1. The power supply side terminal of the filament B of the discharge lamp la is connected to the low voltage side terminal (circuit ground) of the DC power supply E. The power supply side terminal of the filament A of the discharge lamp la is connected to the high voltage side terminal of the DC power supply E through the resistor R1. A resonance capacitor C1 is connected in parallel between the non-power supply side terminals of both filaments A and B of the discharge lamp la. A capacitor C2 is connected between the non-power supply side terminal of the filament A of the discharge lamp la and the low voltage side terminal (circuit ground) of the DC power supply E via a resistor R2. A series circuit of resistors R3 and R4 is connected. A parallel circuit of a capacitor C4 and a resistor R5 is connected to the capacitor C2 via a diode D1. Thus, a DC current loop for charging the capacitor C4 is formed from the DC power source E via the resistor R1, the filament A of the discharge lamp la, the resistor R2, and the diode D1. One end of a capacitor C3 is connected to a connection point between the resistors R3 and R4, and the other end of the capacitor C3 is connected to circuit ground via a diode D3. A parallel circuit of a capacitor C4 and a resistor R5 is connected via a diode D2 between a connection point between the capacitor C3 and the diode D3 and the circuit ground. The potential Vk of the capacitor C4 is input to the control circuit unit S and compared with the reference potential Vref.
[0036]
The Emires detection circuit comprising resistors R3 to R5, diodes D2 and D3, and capacitors C3 and C4 creates a DC voltage Vk obtained by dividing the difference voltage between the positive peak value and the negative peak value of the voltage across the discharge lamp la. . In the negative half cycle in which the filament B of the discharge lamp la has a higher potential than the filament A, the peak value of the voltage obtained by dividing the sinusoidal high-frequency voltage generated in the discharge lamp la by the resistors R3 and R4 passes through the diode D3. The capacitor C3 is charged. Next, in the positive half cycle in which the filament A of the discharge lamp la has a higher potential than the filament B, the peak value of the voltage obtained by dividing the sinusoidal high frequency voltage generated by the discharge lamp la by the resistors R3 and R4 is the capacitor. The voltage is added to the voltage of C3, and the capacitor C4 is charged through the diode D2.
[0037]
In this circuit, two systems of no-load detection circuits are configured, and before starting the inverter, the capacitor C2 is charged from the DC power source E through the resistor R1, the filament A, and the resistor R2, and the capacitor C2 is charged. The potential Vk of the capacitor C4 connected in parallel via the diode D1 rises, thereby determining whether or not the filament A is attached. When the filament A is mounted, the potential Vk of the capacitor C4 rises to a voltage having a predetermined voltage dividing ratio with the RC time constant, and this increases the reference potential Vref of the comparator CP provided in the control circuit unit S. By exceeding, the inverter circuit starts to operate.
[0038]
In the inverter circuit, the switching elements Q1 and Q2 are alternately turned on and off by the drive signal from the control circuit unit S to the switching elements Q1 and Q2, and the resonant load circuit including the inductor L1, the capacitor C1, and the discharge lamp la has a rectangular wave shape. A high frequency voltage is applied to light the discharge lamp la with a sinusoidal high frequency.
[0039]
When the filament A is not attached, since the filament A is open, the charging from the DC power source E to the capacitor C2 is cut off. Therefore, the charging to the capacitor C4 is cut off and the potential Vk of the capacitor C4 is cut off. Does not rise. As a result, the inverter circuit stops when the potential Vk of the capacitor C4 falls below the reference potential Vref. In the present embodiment, the detection circuit for whether or not the filament B is mounted is omitted because it is not directly related to the present invention.
[0040]
When the potential Vk of the capacitor C4 exceeds the reference potential Vref and the inverter circuit starts to operate, the discharge lamp la is turned on and the voltage dividing ratio of the resistors R1 and R2 varies. Specifically, the impedance is infinite before the discharge lamp la is lit, but the discharge lamp la is lit. Depending on the load rating, the impedance is several hundred Ω to several KΩ. Greatly decreases.
[0041]
In general, the resistance values of the resistors R1, R2, and R5 are configured to be several hundreds KΩ to several MΩ in order to suppress power consumption at the resistors as much as possible and to suppress a circuit current from flowing around the inverter circuit. From this, the resistance voltage dividing ratio fluctuates greatly before and after the discharge lamp la is turned on. Therefore, most of the direct current component from the direct current power source E is applied to the resistor R1. As a result, the potential V1 of the capacitor C2 of the no-load detection circuit is approximately 0V because the direct current component is substantially 0V and the alternating current component is much smaller than the resistor R2 in the alternating current impedance of the capacitor C2.
[0042]
On the other hand, when an AC voltage is generated in the discharge lamp la, an AC voltage is also generated in the resistors R3 and R4. Then, the AC voltage V2 divided by the resistors R3 and R4 is generated at the connection point of the resistors R3 and R4. In the negative half cycle in which the filament B of the discharge lamp la has a higher potential than the filament A, the negative peak value of the AC voltage V2 is charged to the capacitor C3 via the diode D3. Next, in the positive half cycle in which the filament A of the discharge lamp la is at a higher potential than the filament B, the positive peak value of the AC voltage V2 is added to the voltage of the capacitor C3, and is added to the capacitor C4 via the diode D2. Charged. As a result, the capacitor C4 is charged with the DC voltage Vk obtained by dividing the voltage difference between the positive peak value and the negative peak value of the voltage across the discharge lamp la.
[0043]
If the filament A is disconnected while the discharge lamp la is lit, the DC voltage from the DC power source E is cut off, and the high-frequency voltage across the discharge lamp la disappears due to the removal of the capacitor C1 and does not occur. As a result, the high-frequency voltage V2 generated at the connection point of the resistors R3 and R4 is also eliminated, so that the potential Vk of the capacitor C4 decreases and falls below the reference potential Vref of the comparator CP provided in the control circuit unit S. Stops oscillation.
[0044]
In other words, before starting the inverter circuit, whether or not the filament A is installed is determined based on the presence or absence of a DC current loop from the DC power source E to the capacitor C4, and the discharge lamp la is turned on by determining that the filament A is installed. The capacitor C4 is charged not by the DC current loop through the resistor R2, but by the high-frequency AC voltage generated in the discharge lamp la to ensure the detection voltage Vk through the resistor R3. When the discharge lamp la is disconnected during lighting, it is determined that the discharge lamp la has been disconnected due to the absence of the high frequency voltage.
[0045]
On the other hand, when the discharge lamp la is in an Emileless state, half-wave discharge is generated, and a DC component voltage is generated with a reverse polarity with respect to the DC voltage application direction of the no-load detection circuit composed of a series circuit of the resistor R2 and the capacitor C2. The DC voltage component of the half wave discharge is applied to the capacitor C2 in the negative direction, and as a result, the voltage V1 charged in the negative direction as shown in FIG. 3 is applied to the capacitor C2. Similarly, a voltage V2 in which a negative direct current component is superimposed on a high-frequency alternating current is applied to the voltage V2 generated at the connection point of the resistors R3 and R4 as shown in FIG. However, the peak-to-peak voltage of the AC component obtained by removing the DC component of the voltage V2 is applied to the potential Vk of the capacitor C4. Therefore, since the potential Vk of the capacitor C4 is stable without being affected by the generation of the direct current component of the half-wave discharge of the discharge lamp la, the discharge is performed despite the fact that the filament as shown in the conventional example is connected. There is no false detection that the lamp load la is off.
[0046]
Because of the above characteristics, the degree of freedom in the design width of the time constant of the capacitor C4 and the resistor R5 is increased, so that the discharge lamp load la is disconnected during lighting, and the potential Vk of the capacitor C4 becomes the reference potential. It becomes easy to design to shorten the time until it falls below Vref compared to the conventional example. That is, since the responsiveness of detecting the load detachment is good, the residual oscillation time until the inverter circuit completely stops oscillating is shortened, so that the circuit stress can be suppressed.
As described above, according to the present embodiment, no-load detection can be realized with high accuracy without being affected by the discharge state of the discharge lamp load la. In addition, it is easy to design with good detection sensitivity.
[0047]
(Embodiment 2)
A circuit diagram of the second embodiment is shown in FIG. Hereinafter, the circuit configuration will be described. A series circuit of switching elements Q1, Q2 is connected to the DC power source E. The connection point of the switching elements Q1 and Q2 is connected to the power supply side terminal of the filament A of the discharge lamp la via a DC cut capacitor C0 and a resonance (current limiting) inductor L1. The power supply side terminal of the filament B of the discharge lamp la is connected to the low voltage side terminal (circuit ground) of the DC power supply E. The power supply side terminal of the filament A of the discharge lamp la is connected to the high voltage side terminal of the DC power supply E through the resistor R1. A resonance capacitor C1 is connected in parallel between the non-power supply side terminals of both filaments A and B of the discharge lamp la. A capacitor C2 is connected between the non-power supply side terminal of the filament A of the discharge lamp la and the low voltage side terminal (circuit ground) of the DC power supply E via resistors R2 and R3. A parallel circuit of a capacitor C4 and a resistor R5 is connected to the capacitor C2 via a diode D1. Thus, a DC current loop for charging the capacitor C4 is formed from the DC power source E through the resistor R1, the filament A of the discharge lamp la, the resistors R2 and R3, and the diode D1. One end of a capacitor C3 is connected to a connection point between the resistors R2 and R3, and the other end of the capacitor C3 is connected to a circuit ground via a diode D3. A parallel circuit of a capacitor C4 and a resistor R5 is connected via a diode D2 between a connection point between the capacitor C3 and the diode D3 and the circuit ground. The potential Vk of the capacitor C4 is input to the control circuit unit S and compared with the reference potential Vref.
[0048]
This embodiment is an example in which the DC component voltage detection path and a part of the AC component voltage detection path are configured by one series impedance (resistors R2, R3) from the circuit diagram of the first embodiment. The DC component voltage is detected by the DC power source E, the filament A, the resistors R2 and R3, and the capacitor C2. The AC component voltage is detected by the resistors R2 and R3 in the series circuit of the resistors R2 and R3 and the capacitor C2. And the capacitor C4 is charged from the capacitor C3 and the diodes D2 and D3. The operation of the no-load detection circuit is the same as in the first embodiment.
In the present embodiment, as in the first embodiment, no-load detection can be realized with high accuracy without being affected by the discharge state of the discharge lamp load la. In addition, it is easy to design with good detection sensitivity.
[0049]
(Embodiment 3)
A circuit diagram of the third embodiment is shown in FIG. Hereinafter, the circuit configuration will be described. A series circuit of switching elements Q1, Q2 is connected to the DC power source E. The connection point of the switching elements Q1, Q2 is connected to the power supply side terminal of the filament A of the discharge lamp la through a resonance (current limiting) inductor L1. The power supply side terminal of the filament B of the discharge lamp la is connected to the low voltage side terminal (circuit ground) of the DC power supply E through the DC cut capacitor C0. The non-power supply side terminal of the filament A of the discharge lamp la is connected to the high voltage side terminal of the DC power supply E via the resistor R1. A resistor R6 is connected in parallel between the power supply side terminals of both filaments A and B of the discharge lamp la, and a resonance capacitor C1 is connected in parallel between the non-power supply side terminals. A capacitor C2 is connected between the non-power supply side terminal of the filament B of the discharge lamp la and the low voltage side terminal (circuit ground) of the DC power supply E via a resistor R2. A parallel circuit of a capacitor C4 and a resistor R5 is connected to the capacitor C2 via a diode D1. Thus, a DC current loop for charging the capacitor C4 is formed from the DC power source E through the resistor R1, the filament A of the discharge lamp la, the resistor R6, the filament B, the resistor R2, and the diode D1.
[0050]
A capacitor C3 is connected from the circuit ground via a diode D3 between the non-power supply side terminal of the filament A of the discharge lamp la and the low voltage side terminal (circuit ground) of the DC power supply E. A parallel circuit of a capacitor C4 and a resistor R5 is connected via a diode D2 between a connection point between the capacitor C3 and the diode D3 and the circuit ground. The potential Vk of the capacitor C4 is input to the control circuit unit S and compared with the reference potential Vref.
[0051]
In this embodiment, a DC cut capacitor C0 of the inverter circuit is connected to the ground side, and no-load detection based on a DC voltage at startup is inserted in both filaments A and B. The AC component is detected by a capacitor C3 and diodes D3 and D2. Even if the filament A or B is disconnected during lighting, the AC voltage of the discharge lamp la is also reduced by disconnecting the capacitor C1 from the resonant load circuit, so that no-load detection is possible.
The effect of the present embodiment is the same as that of the first and second embodiments, and there is no potential drop of the no-load detection voltage due to the voltage of the direct current component generated by the half-wave discharge of the discharge lamp la. I can do it. In addition, it is easy to design with good detection sensitivity.
[0052]
(Embodiment 4)
A circuit diagram of the fourth embodiment is shown in FIG. Hereinafter, the circuit configuration will be described. A series circuit of switching elements Q1, Q2 is connected to the DC power source E. The connection point of the switching elements Q1, Q2 is connected to one end of the primary winding of the leakage transformer LT1 via a DC cut capacitor C0. The other end of the primary winding of the leakage transformer LT1 is connected to the low voltage side terminal (circuit ground) of the DC power supply E. One end of the secondary winding of the leakage transformer LT1 is connected to the power supply side terminal of the filament A of the discharge lamp la through a parallel circuit of a DC cut capacitor C0 'and a resistor R4. The power supply side terminal of the filament B of the discharge lamp la is connected to the other end of the secondary winding of the leakage transformer LT1. The non-power supply side terminal of the filament A of the discharge lamp la is connected to the high voltage side terminal of the DC power supply E via the resistor R1. A resonance capacitor C1 is connected in parallel between the non-power supply side terminals of both filaments A and B of the discharge lamp la. A capacitor C2 is connected between the non-power supply side terminal of the filament B of the discharge lamp la and the low voltage side terminal (circuit ground) of the DC power supply E via resistors R2 and R3. A parallel circuit of a capacitor C4 and a resistor R5 is connected to the capacitor C2 via a diode D1. Thus, the DC power supply E charges the capacitor C4 via the resistor R1, the filament A of the discharge lamp la, the resistor R4, the secondary winding of the leakage transformer LT1, the filament B, the resistors R2 and R3, and the diode D1. A current loop is formed.
[0053]
Further, one end of a capacitor C3 is connected to the connection point of the resistors R2 and R3, and the other end of the capacitor C3 is connected to circuit ground via a diode D3. A parallel circuit of a capacitor C4 and a resistor R5 is connected via a diode D2 between the connection point of the capacitor C3 and the diode D3 and the circuit ground. The potential Vk of the capacitor C4 is input to the control circuit unit S and compared with the reference potential Vref.
[0054]
The present embodiment is an example in which a resonant load circuit of an inverter circuit is configured by a discharge lamp la, a resonant capacitor C1, and a leakage transformer LT1. The capacitor C0 'is a DC component cutting capacitor, like the capacitor C0. The resistor R4 connected in parallel to the capacitor C0 ′ is a high resistance that allows a direct current to flow to detect the presence or absence of the filaments A and B when the inverter circuit is started. This is like the resistor R6 in FIG. You may connect in parallel between the power supply side terminals of the filaments A and B.
[0055]
In this embodiment, before starting the oscillation of the inverter circuit, it is detected whether or not a direct current flows through the path of the resistor R1, the filament A, the resistor R4, the filament B, the resistors R2 and R3, the diode D1, and the resistor R5. Then, whether or not the filaments A and B are attached is detected, and after the oscillation of the inverter circuit is started, no-load detection by the AC voltage is performed from the connection point of the resistors R2 and R3, the capacitor C3, the diodes D2 and D3, and the resistor R5. The voltage Vk rectified and smoothed by the capacitor C4 is realized.
[0056]
The potential at the connection point of the resistors R2 and R3 when the discharge lamp la is lit is the combined voltage of the AC voltage generated by the discharge lamp la and the voltages generated by the resistors R1, R2 and R3, and the capacitor C2. Since a voltage is generated so as to be, an AC voltage is generated. Even if the filament A or B is disconnected during lighting, the AC voltage of the discharge lamp la is also reduced by disconnecting the capacitor C1 from the resonant load circuit, so that no-load detection is possible.
The effect of this embodiment is the same as that of the first and second embodiments, and the no-load detection voltage is not lowered due to the voltage of the direct current component generated by the half-wave discharge of the discharge lamp la. I can do it. In addition, it is easy to design with good detection sensitivity.
[0057]
(Embodiment 5)
A circuit diagram of the fifth embodiment is shown in FIG. This embodiment is an example in which a circuit is configured with a series of two discharge lamp loads from the first embodiment, and filaments B and C on the common side of two discharge lamps connected in series are connected to two inductors L1. Preheating is performed from the next winding through a DC cut capacitor C5. Since the operation of the no-load detection circuit is the same as that of the first embodiment, description thereof is omitted.
The effect of the present embodiment is the same as that of the first embodiment, and since there is no potential drop of the no-load detection voltage due to the voltage of the DC component generated by the half-wave discharge of the discharge lamp la, the no-load detection can be realized with high accuracy. I can do it. In addition, it is easy to design with good detection sensitivity.
[0058]
(Embodiment 6)
A circuit diagram of the sixth embodiment is shown in FIG. Hereinafter, the circuit configuration will be described. In this embodiment, a series circuit of resistors R3 and R4 is connected to the secondary winding outputs a and b of the inductor L1 in the first embodiment (FIG. 1). Also in the present embodiment, when the filament A is disconnected during lighting, the capacitor C1 is disconnected from the resonant load circuit, so that the AC voltage of the discharge lamp la is also reduced, so that the secondary winding output of the inductor L1 is reduced. Load detection is possible. Even if half-wave discharge occurs in the discharge lamp la, the potential Vk of the capacitor C4 is charged with the peak-to-peak voltage of the AC voltage applied from the secondary winding voltage of the inductor L1, so that the filament is Despite being connected, there is no false detection that the discharge lamp load la is disconnected.
The effect of the present embodiment is the same as that of the first embodiment, and since there is no potential drop of the no-load detection voltage due to the voltage of the DC component generated by the half-wave discharge of the discharge lamp la, the no-load detection can be realized with high accuracy. I can do it. In addition, it is easy to design with good detection sensitivity.
[0059]
(Embodiment 7)
A circuit diagram of the seventh embodiment is shown in FIG. Hereinafter, the circuit configuration will be described. A series circuit of switching elements Q1, Q2 and a resistor Rs is connected to the DC power source E. The resistor Rs is connected between the switching element Q2 and the circuit ground so that the current flowing through the switching element Q2 can be detected as a voltage generated between the terminals a and b. Between the terminals a and b, a diode D3 is connected in parallel in the same direction as the antiparallel diode of the switching element Q2. Therefore, a voltage corresponding to the switching current flowing in the forward direction through the switching element Q2 is detected between the terminals a and b. The voltage between the terminals a and b is applied to the parallel circuit of the capacitor C4 and the resistor R5 via the resistor R3 and the diode D2, and the capacitor C4 generates a voltage Vk corresponding to the switching current.
[0060]
The connection point of the switching elements Q1 and Q2 is connected to the power supply side terminal of the filament A of the discharge lamp la via a DC cut capacitor C0 and a resonance (current limiting) inductor L1. The power supply side terminal of the filament B of the discharge lamp la is connected to the low voltage side terminal (circuit ground) of the DC power supply E. The power supply side terminal of the filament A of the discharge lamp la is connected to the high voltage side terminal of the DC power supply E through the resistor R1. A resonance capacitor C1 is connected in parallel between the non-power supply side terminals of both filaments A and B of the discharge lamp la. A capacitor C2 is connected between the non-power supply side terminal of the filament A of the discharge lamp la and the low voltage side terminal (circuit ground) of the DC power supply E via a resistor R2. A parallel circuit of a capacitor C4 and a resistor R5 is connected to the capacitor C2 via a diode D1. Thus, a DC current loop for charging the capacitor C4 is formed from the DC power source E via the resistor R1, the filament A of the discharge lamp la, the resistor R2, and the diode D1. The potential Vk of the capacitor C4 is input to the control circuit unit S and compared with the reference potential Vref.
[0061]
The present embodiment is an example in which the detection of the AC component voltage of the no-load detection circuit is detected by the voltage generated in the resistor Rs inserted between the switching element Q2 and the circuit ground. Also in the present embodiment, when the filament A is detached, the resonance capacitor C1 is detached, and the current flowing through the resistor Rs is greatly reduced, so that no-load detection can be realized with high accuracy.
[0062]
(Embodiment 8)
A circuit diagram of the eighth embodiment is shown in FIG. Hereinafter, the circuit configuration will be described. A series circuit of switching elements Q1, Q2 is connected to the DC power source E. The connection point of the switching elements Q1 and Q2 is connected to the power supply side terminal of the filament A of the discharge lamp la via a DC cut capacitor C0 and a resonance (current limiting) inductor L1. The power supply side terminal of the filament B of the discharge lamp la is connected to the low voltage side terminal (circuit ground) of the DC power supply E. The power supply side terminal of the filament A of the discharge lamp la is connected to the high voltage side terminal of the DC power supply E through the resistor R1. A resonance capacitor C1 is connected in parallel between the non-power supply side terminals of both filaments A and B of the discharge lamp la. A capacitor C2 is connected between the non-power supply side terminal of the filament A of the discharge lamp la and the low voltage side terminal (circuit ground) of the DC power supply E via a resistor R2. A parallel circuit of a capacitor C4 and a resistor R5 is connected to the capacitor C2 via a diode D1. Thus, a DC current loop for charging the capacitor C4 is formed from the DC power source E via the resistor R1, the filament A of the discharge lamp la, the resistor R2, and the diode D1. A series circuit of resistors R3 and R4 is connected to the secondary winding of the inductor L1 through a diode D3. One end b of the secondary winding of the inductor L1 is connected to the circuit ground. A parallel circuit of a capacitor C4 and a resistor R5 is connected via a diode D2 between the connection point of the resistors R3 and R4 and the circuit ground. The potential Vk of the capacitor C4 is input to the control circuit unit S and compared with the reference potential Vref. This embodiment is an example in which the secondary winding voltage of the ballast choke L1 is half-wave rectified by the diode D3 to obtain the voltage Vk of the capacitor C4 in the sixth embodiment (FIG. 8). The same effect as the form can be obtained.
[0063]
(Embodiment 9)
A circuit diagram of the ninth embodiment is shown in FIG. Hereinafter, the circuit configuration will be described. A series circuit of switching elements Q1, Q2 is connected to the DC power source E. The connection point of the switching elements Q1 and Q2 is connected to the power supply side terminal of the filament A of the discharge lamp la via a DC cut capacitor C0 and a resonance (current limiting) inductor L1. The power supply side terminal of the filament B of the discharge lamp la is connected to the low voltage side terminal (circuit ground) of the DC power supply E. The power supply side terminal of the filament A of the discharge lamp la is connected to the high voltage side terminal of the DC power supply E through the resistor R1. A resonance capacitor C1 is connected in parallel between the non-power supply side terminals of both filaments A and B of the discharge lamp la. A capacitor C2 is connected between the non-power supply side terminal of the filament A of the discharge lamp la and the low voltage side terminal (circuit ground) of the DC power supply E via a resistor R2. A series circuit of resistors R3 and R4 is connected via a capacitor C3. A parallel circuit of a capacitor C4 and a resistor R5 is connected to the capacitor C2 via a diode D1. Thus, a DC current loop for charging the capacitor C4 is formed from the DC power source E via the resistor R1, the filament A of the discharge lamp la, the resistor R2, and the diode D1. On the other hand, a parallel circuit of a capacitor C4 and a resistor R5 is connected to the resistor R4 via a diode D2. The potential Vk of the capacitor C4 is input to the control circuit unit S and compared with the reference potential Vref.
[0064]
In the present embodiment, the AC voltage generated by the discharge lamp la is applied to the series circuit of the resistors R3 and R4 via the DC cut capacitor C3, and the AC voltage divided by the resistors R3 and R4 is halved by the diode D2. In this example, the detection voltage Vk is obtained by wave rectification and smoothing by the capacitor C4. In the present embodiment, since all the DC voltage components generated by the half-wave discharge of the discharge lamp la are applied to the DC-cut capacitor C3, the half-wave discharge is generated with any polarity as in the first embodiment. Even if it occurs, the potential of the resistor R4 does not decrease, and the detection voltage Vk becomes stable. When the filament is removed, the resonance capacitor C1 is removed, so that the voltage of the discharge lamp la is lowered, the detection voltage Vk is lowered, and no-load detection can be performed.
The effect of the present embodiment is the same as that of the first embodiment, and no-load detection can be realized with high accuracy without being affected by the discharge state of the discharge lamp load. In addition, it is easy to design with good detection sensitivity.
[0065]
(Embodiment 10)
A circuit diagram of the tenth embodiment is shown in FIG. In the present embodiment, in the circuit of the first embodiment shown in FIG. 1, a Zener diode ZD1 that bypasses a DC bias in the reverse direction is connected in parallel to the capacitor C2, and a protective Zener is provided at the location where the detection voltage Vk is generated. This is an example in which the diode ZD2 is connected in parallel. The difference from the first embodiment is that even if a half wave discharge of the discharge lamp la in the negative direction of the capacitor C2 occurs, the potential of the capacitor C2 is bypassed by the Zener diode ZD1, and therefore the negative charge potential is changed to the capacitor C2. It is not going to enter. Other effects are the same as those of the first embodiment.
[0066]
(Embodiment 11)
A circuit diagram of the eleventh embodiment is shown in FIG. In the present embodiment, a secondary winding is provided in the inductor L1 in the tenth embodiment of FIG. Is provided with an Emires detection circuit that inputs to the second comparator CP1 provided in the control circuit section S as the detection voltage Vk1. When the discharge lamp la enters the Emileless state and the second detection voltage Vk1 exceeds the second reference voltage Vref1, it has a function of stopping the oscillation of the inverter circuit. Further, when the detection voltage Vk is lower than the reference voltage Vref and exceeds the reference voltage Vref again, the oscillation stop maintenance is released and the inverter circuit is restarted. That is, even if the inverter circuit stops oscillating due to Emires detection, there is a reset function that cancels the oscillation stop by the no-load detection voltage Vk, and restarts when the load is replaced. In particular, in the inverter circuit having such a function, the no-load detection voltage Vk needs to be stable in any state other than the filament detachment regardless of the state of the discharge lamp la. This is because if the discharge lamp la goes into an Emires state and discharges half-wave, and the detection voltage Vk drops momentarily, the Emires detection circuit does not work and repeats starting and stopping, resulting in unexpected large stress. This is because it will join the circuit. However, as described in the tenth embodiment, in this embodiment, the detection voltage Vk when the filament is mounted can be stabilized without being affected by the state of the discharge lamp load.
[0067]
According to this embodiment, no-load detection can be realized with high accuracy without being affected by the discharge state of the discharge lamp load la. In addition, it is easy to design with good detection sensitivity. It goes without saying that the same effect can be obtained even if the Emires detection circuit is of another control method, for example, a control method such as intermittent oscillation or stop maintenance after intermittent oscillation.
Needless to say, the same effect can be obtained even if the Zener diodes ZD1 and ZD2 inserted in FIG. 12 or 13 are inserted in the circuits of the first to ninth embodiments.
[0068]
【The invention's effect】
  According to the present invention,straightAn inverter circuit that converts high-frequency power into high-frequency power and supplies high-frequency power to the discharge lamp load via the LC resonance circuit, and the filament of the discharge lamp loadA capacitor charged through a first diode by a voltage applied to one end is provided, and the presence or absence of a filament is determined by the charging voltage of the capacitor.The no-load detection circuit and the no-load detection circuitWhen the capacitor charging voltage falls below the reference voltageWhile stopping the oscillation of the inverter circuitWhen the charging voltage of the capacitor exceeds the reference voltageA control unit for starting oscillation of the inverter circuit,The capacitor of the no-load detection circuit is before the inverter circuit starts oscillating until it exceeds the reference voltage via the first diode by the DC voltage supplied from the DC power source via the filament of the discharge lamp load. After the charging and the inverter circuit starts oscillating, when the discharge lamp load is not half-wave discharge and the filament is connected, the first voltage is applied to the one end of the filament of the discharge lamp load. The charging voltage of the capacitor is maintained to be equal to or higher than the reference voltage by being charged through the diode or from the high-frequency voltage generated in the inverter circuit through the second diode. After the inverter circuit starts oscillating, the filament Is removed, the charging current of the capacitor through the first and second diodes disappears or decreases. Thus, the charging voltage of the capacitor is configured to be lower than the reference voltage, and the charging voltage of the capacitor is the half-wave discharging polarity of the discharge lamp load when the polarity of the half-wave discharging is via the first diode. When the polarity is such that the filament of the discharge lamp load is connected, a charging current is supplied to the capacitor through the second diode from the high-frequency voltage generated in the inverter circuit. To maintain the charging voltage above the reference voltageSince configured, no-load detection can be realized with high accuracy without being affected by the discharge state of the discharge lamp load. In addition, there is an effect that a design with good detection sensitivity responsiveness is facilitated.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a first embodiment of the present invention.
FIG. 2 is an operation waveform diagram at the time of start-up according to the first embodiment of the present invention.
FIG. 3 is an operation waveform diagram at the time of Emires in the first embodiment of the present invention.
FIG. 4 is a circuit diagram of a second embodiment of the present invention.
FIG. 5 is a circuit diagram of a third embodiment of the present invention.
FIG. 6 is a circuit diagram of a fourth embodiment of the present invention.
FIG. 7 is a circuit diagram of a fifth embodiment of the present invention.
FIG. 8 is a circuit diagram of a sixth embodiment of the present invention.
FIG. 9 is a circuit diagram of a seventh embodiment of the present invention.
FIG. 10 is a circuit diagram of an eighth embodiment of the present invention.
FIG. 11 is a circuit diagram of a ninth embodiment of the present invention.
FIG. 12 is a circuit diagram of a tenth embodiment of the present invention.
FIG. 13 is a circuit diagram of an eleventh embodiment of the present invention.
FIG. 14 is a circuit diagram of a first conventional example.
FIG. 15 is an operation waveform diagram at the time of activation of the first conventional example.
FIG. 16 is an operation waveform diagram at the time of Emires in the first conventional example.
FIG. 17 is a circuit diagram of a second conventional example.
FIG. 18 is a circuit diagram of a third conventional example.
FIG. 19 is an operation waveform diagram at the time of Emires in the third conventional example.
FIG. 20 is a characteristic diagram showing a temperature characteristic of a lamp voltage of a discharge lamp.
[Explanation of symbols]
Q1 switching element
Q2 switching element
la Discharge lamp
C1 capacitor
L1 inductor
S control circuit
CP comparator

Claims (7)

Converts the dc power supply to a high frequency, an inverter circuit for supplying high frequency power to the discharge lamp load via an LC resonant circuit, via the first diode is charged by a voltage applied to one end of the filament of the lamp load A no-load detection circuit for determining the presence or absence of a filament based on a charging voltage of the capacitor, and when the charging voltage of the capacitor of the no-load detection circuit falls below a reference voltage, the inverter circuit stops oscillating and the charging voltage of the capacitor And a control unit that starts oscillation of the inverter circuit when the voltage exceeds the reference voltage ,
The no-load detection circuit capacitor is:
Before the inverter circuit starts to oscillate, it is charged by the DC voltage supplied from the DC power source via the filament of the discharge lamp load until it exceeds the reference voltage via the first diode,
After the inverter circuit starts oscillating, when the discharge lamp load is not half-wave discharge and the filament is connected, the voltage applied to the one end of the filament of the discharge lamp load is passed through the first diode. Or the charging voltage of the capacitor is maintained above the reference voltage by being charged through the second diode from the high frequency voltage generated in the inverter circuit,
When the filament is disconnected after the inverter circuit starts oscillating, the charging current of the capacitor via the first and second diodes is eliminated or decreased so that the charging voltage of the capacitor falls below the reference voltage. Configured,
When the discharge lamp load is half-wave discharge, and the polarity of the half-wave discharge is such that the charging voltage of the capacitor through the first diode is lowered, the filament of the discharge lamp load is connected. The charging voltage of the capacitor is maintained at a reference voltage or higher by supplying a charging current to the capacitor through a second diode from a high-frequency voltage generated in the inverter circuit when Discharge lamp lighting device.     2. The discharge lamp lighting device according to claim 1, which has a function of temporarily stopping oscillation of the inverter circuit during half-wave discharge of the discharge lamp load.     The high frequency voltage generated in the inverter circuit according to claim 1 is input to the no-load detection circuit by smoothing an amplitude difference between a positive peak value and a negative peak value of the high frequency AC voltage generated in the discharge lamp load. A discharge lamp lighting device characterized by that.     The high-frequency voltage generated in the inverter circuit according to claim 1 or 2 is characterized in that the peak voltage of one polarity of the AC component of the high-frequency AC voltage generated in the discharge lamp load is smoothed and input to the no-load detection circuit. A discharge lamp lighting device.     The high-frequency voltage generated in the inverter circuit according to claim 1 or 2 is characterized in that a peak voltage of one polarity of the high-frequency AC voltage generated in the inductor of the resonance circuit is smoothed and input to the no-load detection circuit. Discharge lamp lighting device.     The high-frequency voltage generated in the inverter circuit according to claim 1 or 2 smoothes the amplitude difference between the positive peak value and the negative peak value of the AC component of the high-frequency AC voltage generated in the inductor of the resonance circuit, and becomes a no-load detection circuit. A discharge lamp lighting device characterized by inputting. The discharge lamp lighting device according to claim 1, wherein the high-frequency voltage generated in the inverter circuit according to claim 1 is converted into a voltage from the circuit current of the inverter circuit and input to the no-load detection circuit .

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