JP3740220B2 - Fluorescent lamp lighting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lighting device for a fluorescent lamp, and in particular, suppresses harmonics contained in an input alternating current, improves a power factor, and reduces lighting and suppresses pulsation of current flowing in the fluorescent lamp. Relates to the device.
[0002]
[Prior art]
The configuration of a conventional harmonic suppression type lighting device is described in, for example, de Groot, JJ and Houkes, H. “Triple-U Electronic Compact Fluorenscent Lamps with Reduced Harmonics” JOURNAL of the Illuminating Enfineering Society, Winter 1994, pp 45-51. ing. The circuit configuration is shown in FIG. This circuit is divided into two parts in terms of function: an active filter circuit 2 for suppressing harmonics and an inverter circuit 3 for lighting a fluorescent lamp. A high-frequency alternating current is supplied to the fluorescent lamp according to the operation of the MOSFETs Q1 and Q2 in the inverter circuit 3, and a current is taken in from the alternating voltage source 1 through the choke coil L1 to charge the power supply capacitors C1 and C2. In a general active filter, an independent switch element is provided, and this element is controlled by PWM (pulse width modulation). In this conventional example, the switch element of the inverter circuit and the active filter circuit is combined, It is only necessary to operate Q1 and Q2 so as to alternately turn on and off at a constant frequency and an equal on-pulse width.
[0003]
[Problems to be solved by the invention]
FIG. 10 shows a current path in the conventional circuit. In FIG. 10, the fluorescent lamp is replaced with an equivalent resistance R1, and in the following other figures, the resistance R1 is equivalent to the fluorescent lamp. Further, the MOSFETs Q1 and Q2 have parasitic diodes for passing a current in the reverse direction. In FIG. 10, these parasitic diodes are indicated as D3 and D4.
[0004]
FIG. 10A shows a current path when the MOSFET Q1 is turned on. A current flows from the AC voltage source 1 through paths C1, Q1, L2, R1, C4, and L1, and this current is represented by iac. At the same time, current flows through the paths of Q1, L2, R1, and C3 due to the voltages of the capacitors C1 and C2, and this current is represented by idc. FIG. 10B shows a current path when Q2 is turned on. Current flows from the AC voltage source 1 through the paths C2, D2, and L1, and the energy stored in the inductor L1 when Q1 is turned on is stored in C2. Further, a current is supplied to the fluorescent lamp R1 through the paths of the capacitors C4, R1, L2, Q2, and D2.
[0005]
When the AC voltage is high, iac> idc, and the fluorescent lamp is mainly supplied with current from the AC power source. On the other hand, since iac is proportional to the instantaneous voltage of the AC voltage source 1, idc> iac when the AC voltage is low. As described above, in the conventional example, the current path differs according to the AC voltage, and the resonance frequency of the circuit also changes accordingly. The resonance frequency of iac is mainly determined by L2 and C4, and the resonance frequency of idc is determined by L2 and C3.
[0006]
Normally, the resonance frequency fr of the circuit and the switching frequency finv of the MOSFETs Q1 and Q2 are set to satisfy fr <finv. In relation to this frequency, for example, when Q1 is turned on, first, a current flows through D3 because of the current continuity of L2, and when this current becomes zero, a current having a reverse polarity is supplied from Q1 to L2. However, in this conventional example, depending on the capacitance values of the capacitors C3 and C4, this condition may collapse and fr> finv. When Q1 is turned on in this frequency relationship, a current flows through D4 at first, and a current of the same polarity is supplied to L2 by turning on Q1. For this reason, when Q1 is turned on, the diode D4 reversely recovers, and carriers such as electrons and holes accumulated inside D4 are forcibly swept out, so that a large reverse recovery current flows. Such an operation is defined as a phase advance mode. In the phase advance mode, switching loss between the diode and the MOSFET becomes a problem.
[0007]
Although there is a method of changing the capacitance values of the capacitors C3 and C4 so as to satisfy the condition of fr <finv, adverse effects such as reduction of harmonic suppression remain. Although there is a method of increasing the switching frequency finv, there are problems such as electromagnetic interference.
[0008]
Further, as shown in FIG. 10 (a), since the current is directly supplied to the fluorescent lamp from the AC power source, this current pulsates due to the influence of the AC power source changing in a sine wave. If this current pulsation exceeds the allowable value of the fluorescent lamp, it may cause flickering.
[0009]
The present invention has been made to solve the above-mentioned problems such as loss, harmonics, electromagnetic interference, and current pulsation. The condition of the resonance frequency fr of the circuit and the switching frequency finv of the MOSFETs Q1 and Q2 is set to fr < An object of the present invention is to obtain a fluorescent lamp lighting device that controls to maintain finv, reduces current pulsation, suppresses harmonics, and reduces electromagnetic interference.
[0010]
[Means for Solving the Problems]
The solution to the above problem is to supply a high-frequency alternating current to the fluorescent lamp from the power supply capacitor using the inverter circuit, and to pass a current from the alternating current power supply to the first choke coil, according to the switching operation of the inverter circuit, A fluorescent lamp lighting device for supplying energy accumulated in the first choke coil to the power supply capacitor via a rectifying means, and at least a power element of the inverter circuit from the AC power supply according to a switching operation of the inverter circuit And a first current through a path passing through the fluorescent lamp, the second choke coil, the first capacitor and the first choke coil, storing energy in the first choke coil, and From a power supply capacitor, at least the power element, the fluorescent lamp, and the second choke coil, A second current is passed through a second capacitor having a smaller capacity than that of the first capacitor, and an instantaneous voltage of the AC power supply or a current or voltage that changes depending on the instantaneous voltage is detected. This can be realized by providing detection means and control means for changing the operating frequency or on-pulse width of the inverter circuit according to the detected value.
[0011]
According to the fluorescent lamp lighting device having the above configuration, harmonic suppression is performed by the operation of the inverter circuit, and a phase advance mode in which harmonic suppression is caused at a certain value or less of the AC voltage is avoided. To avoid the phase advance mode, 1) detect the instantaneous voltage of the AC power supply, 2) detect the polarity of the current flowing through the second choke coil, and 3) detect the polarity of the current flowing through the first choke coil. 4) There is a method of detecting the output voltage of the inverter circuit. 2) and 4) are the inverter circuit, and the current is applied to the diode (or the parasitic) provided in parallel with the power switching element in the opposite direction. Detects the flow and detects the occurrence of the phase advance mode. 3) detects that the current flowing through the first choke coil vibrates in positive and negative polarities in the phase advance mode. When these are detected, the phase advance mode can be prevented by changing the operating frequency of the inverter circuit. Further, the pulsation of the fluorescent lamp current can be achieved by detecting the instantaneous value of the AC power supply and changing the on-pulse width of the inverter circuit.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0013]
FIG. 1 is a circuit diagram showing a first embodiment of the present invention.
[0014]
In the main circuit of FIG. 1, diodes D1 and D2 are connected in series with their forward directions aligned, and the cathode of the diode D1 is connected to one end of the capacitor C1, the other end of the capacitor C1 is connected to one end of the capacitor C2, and the capacitor The other end of C2 is connected to the anode of the diode D2. An AC voltage source 1 is connected between a connection point of the diodes D1 and D2 and a connection point of the capacitors C1 and C2 via an inductor L1 and a filter capacitor C0 for removing harmonics, and a general voltage doubler rectification A circuit is formed. The cathode of the diode D1 is connected to the drain of the N-channel MOSFET Q1, the source of the MOSFET Q1 is connected to the drain of the N-channel MOSFET Q2, and the source of the MOSFET Q2 is connected to the anode of the diode D2. In addition, a capacitor C4 connected in series, a resistor R1 that equivalently represents a fluorescent lamp, and a ballast inductor L2 are connected between a connection point between the diodes D1 and D2 and a connection point between the MOSFETs Q1 and Q2. A capacitor C3 is connected in parallel to the diode D2. As in the conventional example of FIG. 9, 2 is an active filter circuit, and 3 is an inverter circuit. Compared to the conventional example, the connection position of the capacitor C4 is different in this embodiment, but this is intended to simplify the circuit design and further reduce the harmonics by using only the capacitor C3 that contributes to harmonic suppression. ing.
[0015]
Before describing the control circuit of FIG. 1, the operation of the main circuit will be briefly described.
[0016]
FIG. 2 shows a current path in the main circuit of FIG. In FIG. 2, when MOSFET Q1 is turned on, current iac flows from AC voltage source 1 through the paths C1, Q1, L2, R1, C4, and L1, and from power supply capacitors C1 and C2, Q1, L1, R1, C4, and C3. The current idc flows through the path returning to C2 via. Similar to the current path of FIG. 10 in the conventional example, when the AC voltage is high, iac> idc, and R1 is mainly supplied with current from the AC power supply. Since iac is proportional to the instantaneous voltage of the AC voltage source 1, when the AC voltage is low, idc> iac. Thus, in the main circuit configuration of FIG. 1, the current path differs depending on the AC voltage, and the resonance frequency of iac is mainly determined by L2 and C4 as in the conventional example. On the other hand, since idc passes through the two capacitors C4 and C3, the resonance frequency of idc is determined by L2 and C34 (the series connection capacitance of C4 and C3). Since C34 has a smaller capacitance value than C4, the resonance frequency of idc is higher than that of iac. As a result, the resonance frequency of idc becomes higher than the switching frequency of the inverter, and when the AC voltage is low, the aforementioned phase advance mode occurs.
[0017]
On the other hand, this embodiment solves this problem as follows.
[0018]
In FIG. 1, reference numeral 4 denotes a full-wave rectifier constituted by a diode bridge, which is provided for detecting the instantaneous voltage of the AC voltage source 1 and its polarity. Reference numeral 5 denotes a reference voltage generator, which is a means for generating a reference voltage when changing the switching frequency of the inverter circuit 3 as will be described later. The switching frequency of the inverter circuit 3 is determined by comparing the instantaneous voltage of the AC power source detected by the full-wave rectifier 4 with the reference voltage of the reference voltage generating circuit 5. An adder 6 subtracts the output voltage Vref of the reference voltage generation circuit 5 from the output voltage Vb of the full-wave rectifier 4 and outputs the deviation.
[0019]
Reference numeral 7 denotes a carrier wave generation circuit which oscillates the switching frequency of the MOSFETs Q1 and Q2 of the inverter circuit 3 in accordance with the output signal of the adder 6. When the output signal of the adder 6 is positive, that is, when the output voltage Vb of the full-wave rectifier 4 is higher than the reference voltage Vref, the switching frequency of Q1 and Q2 is finv1, and the output signal of the adder 6 is negative, that is, the voltage Vb is the reference When the switching frequency when the voltage is lower than the voltage Vref is finv2, the relation of finv1 <finv2 is set. In the PWM control, the switching frequency is a carrier wave signal.
[0020]
A modulation wave generating circuit 8 is a circuit for generating a signal for determining a pulse width for Q1 and Q2. In the present invention, there are two types of control: control for making the pulse width constant for Q1 and Q2 and control for changing the pulse width in accordance with the AC power supply voltage or the load current as described later. Here, PWM control is performed for the latter control, and the output signal 8 has the meaning of a modulated wave. Therefore, hereinafter, even when the pulse wave is made constant, the output of 8 is called a modulation wave and 8 is called a modulation wave generation circuit.
[0021]
A comparator 9 compares the output voltages of the carrier wave generation circuit 7 and the modulation wave generation circuit 8 to generate a pulse width modulation pulse (PWM pulse) for turning on and off Q1 and Q2. Reference numeral 10 denotes a gate drive circuit that gives gate signals to Q1 and Q2 in accordance with the output pulse of the comparator. A dead time is inserted in the gate voltages of Q1 and Q2 to avoid simultaneous ON.
[0022]
FIG. 3 is an operation waveform diagram for explaining the operation of the embodiment of FIG. FIG. 3A shows waveforms of the output voltage Vb of the full-wave rectifier 4 and the reference voltage Vref for frequency conversion. In FIG. 3B, the switching frequency of Q1 and Q2 when the output voltage Vb of the full-wave rectifier 4 is higher than the reference voltage Vref is finv1, and the switching frequency when the output voltage Vb is lower than the reference voltage Vref is finv2. It is set so that finv1 <finv2. As described in the description of the conventional example, there are two resonance frequencies of the circuit from the relationship of the path of the current flowing through the fluorescent lamp. If these are fr1 and fr2 (where fr1 <fr2), fr1 <finv1, fr2 Each switching frequency is determined so as to satisfy the relationship of <finv2. In this way, the aforementioned phase advance mode does not occur.
[0023]
FIG. 4 is a circuit diagram showing a second embodiment of the present invention. Since the main circuit of FIG. 4 is the same as the main circuit of the first embodiment, description thereof is omitted. The control circuit oscillates the switching frequency for Q1 and Q2 by the switching frequency oscillation circuit 11 based on the voltage detected by the secondary winding that detects the current flowing through the ballast inductor L2.
[0024]
Immediately after Q1 is turned on, a current in the opposite direction to Q1 flows through the diode D3, and a current flows in the ballast inductor L2 in the right direction with respect to FIG. 4. When this state is detected by the secondary winding, the frequency oscillation circuit 11 outputs a signal of frequency finv1 where fr1 <finv1. Conversely, when the secondary winding detects that a current flows through the diode D4 immediately after turning on Q1 and a leftward current flows through L2, it is determined that the phase advance mode is set, and the frequency oscillation circuit 11 Outputs a signal of frequency finv2 where fr2 <finv2. A similar determination is made immediately after Q2 is turned on. That is, immediately after Q2 is turned on, if a current in the opposite direction to Q2 flows through the diode D4 and a current flows in the leftward direction through L2, this state is detected by the secondary winding, and the frequency oscillation circuit 11 Outputs a signal of frequency finv1 where fr1 <finv1. Conversely, when the secondary winding detects that a current flows through D3 immediately after Q2 is turned on and a current in the right direction flows through L2, the frequency oscillation circuit 11 determines that the phase advance mode is in effect. , Fr2 <finv2, and a signal of frequency finv2.
[0025]
Reference numeral 8 denotes a means for generating a modulated wave for determining the pulse width for Q1 and Q2 as in FIG. A comparator 9 compares the output voltages of the switching carrier wave generation circuit 7 and the modulation wave generation circuit 8 to generate a pulse width modulation signal for turning on and off Q1 and Q2. Reference numeral 10 denotes a gate drive circuit that gives gate signals to Q1 and Q2 in accordance with the output pulse of the comparator. The dead voltage is inserted into the gate voltages of Q1 and Q2 to avoid simultaneous ON as in the embodiment of FIG.
[0026]
FIG. 5 shows a third embodiment of the present invention. Since the main circuit of FIG. 5 is also the same as the main circuit of the first embodiment, description thereof is omitted.
[0027]
In the control circuit of FIG. 5, a secondary winding for detecting the current flowing through the inductor L1 is provided. Reference numeral 12 denotes means for oscillating the switching frequency for Q1 and Q2 in accordance with the direction of current flowing through the inductor L1.
[0028]
When the AC voltage is high, the current of the inductor L1 is only in one direction, and the polarity of this current is detected by the secondary winding provided in L1, and the frequency oscillation circuit 12 outputs a signal of frequency finv1 where fr1 <finv1. Output. Next, when the AC voltage is low, the current of the inductor L1 flows so that energy is obtained from the power supply capacitors C1 and C2 and the capacitors L1, the diodes D1 and D2, and the filter capacitor C0 resonate with positive and negative polarities. Therefore, it is determined that there is a high possibility that the phase advance mode occurs when the secondary winding provided in L1 detects that the polarity of the current changes to positive and negative, and the frequency oscillation circuit 12 determines that the frequency finv2 satisfies fr2 <finv2. The signal is output. The other modulation wave generation circuit 8, comparator 9, and gate drive circuit 10 are the same as those in the embodiment of FIGS.
[0029]
FIG. 6 is a circuit diagram showing a fourth embodiment of the present invention. The main circuit of FIG. 6 is also the same as the main circuit of the first embodiment, and thus description thereof is omitted. In the control circuit of FIG. 6, 13 is a means for oscillating the switching frequency for Q1 and Q2 according to the voltage at the connection point between Q1 and Q2.
[0030]
As described in the description of the embodiment of FIG. 4, immediately after Q1 is turned on, a current in the opposite direction to Q1 flows through the diode D3. In this state, the voltage at the connection point is the charging voltage of the power supply capacitors C1 and C2. High voltage equal to the sum of The frequency oscillation circuit 13 detects that the node voltage immediately after turning on Q1 is a high voltage, and outputs a signal of frequency finv1 where fr1 <finv1. On the other hand, when a current flows through the diode D4 immediately after turning on of Q1, the connection point voltage is a low voltage equal to the forward voltage (about several V) of D4. Therefore, when this state is detected by the connection point voltage, it is determined that the phase advance mode is set, and the frequency oscillation circuit 13 outputs a signal of the frequency finv2 where fr2 <finv2. The same is determined immediately after Q2 is turned on. That is, immediately after Q2 is turned on, if a current flows through D4 and the voltage at the connection point is low, the frequency oscillation circuit 13 outputs a signal of frequency finv1 where fr1 <finv1. On the other hand, if a current flows through D3 and the voltage at the connection point is high, the frequency oscillation circuit 13 determines that the phase advance mode is in effect and outputs a signal of frequency finv2 where fr2 <finv2. The other modulation wave generation circuit 8, comparator 9, and gate drive circuit 10 are the same as those in the embodiment of FIGS.
[0031]
FIG. 7 shows a fifth embodiment of the present invention. This embodiment relates to control means for suppressing current pulsation. The main circuit of FIG. 7 is the same as the main circuit of the first embodiment, and the currents iac and idc shown in FIG. 2 flow through the equivalent resistance R1 of the fluorescent lamp. Here, if the on-pulse width (hereinafter referred to as on-duty) in the switching period of Q1 and Q2 is constant, iac increases as the instantaneous value of the AC voltage increases, so the combined current flowing through R1 is the AC voltage. It pulsates according to the period. The pulsation of the current may cause the magnetism of the choke coil L2 of the lighting circuit, and if the pulsation is large, the fluorescent lamp flickers. In order to reduce the current pulsation, it is desirable to change the on-duty according to the time change of the AC voltage. That is, when the instantaneous value of the AC voltage is high and iac increases, the on-duty is reduced to reduce iac. This control can be achieved by the PWM control method. The PWM control method will be described below with reference to FIG. 7 and the next FIG.
[0032]
FIG. 8 is a diagram showing the function of the control means shown in FIG. First, the full-wave rectifier 4 performs full-wave rectification of the AC power supply voltage with a diode bridge, adjusts the amplitude of the voltage Vb, and has an amplitude equal to this amplitude and the same phase as the AC power supply voltage. A signal V2 having the same amplitude as the signal V1 but having a phase difference of 180 degrees is generated. Next, the adder 6 adds the V1 and V2 signals to the reference voltage Vref produced by the reference voltage generating circuit 5, and sets the added signals as V1 'and V2', respectively. The carrier wave generation circuit 7 generates a high-frequency triangular wave, and the frequency is changed in accordance with the AC voltage in order to avoid the above-described phase advance mode, but here it is assumed to be a constant frequency in order to simplify the explanation. The comparator 9 uses V1 'and V2' as modulated waves, and compares these with triangular waves. However, when the triangular wave is larger than V1 ′ for the FET Q1, the on pulse is used when the triangular wave is smaller than V2 ′ for the FET Q2. By controlling in this way, in the period when the instantaneous value of the AC power supply voltage is high, the on-pulse width is short for both Q1 and Q2, and iac can be reduced.
[0033]
【The invention's effect】
According to the present invention, an increase in loss due to the phase advance mode is prevented and current pulsation is reduced by changing the switching frequency according to the instantaneous value of the AC power supply voltage and by pulse width modulation.
[Brief description of the drawings]
FIG. 1 is a configuration diagram illustrating a first embodiment of a harmonic suppression type lighting device.
FIG. 2 is a diagram illustrating a current path related to the main circuit of the embodiment of FIG. 1;
FIG. 3 is a diagram for explaining the operation of the control circuit in the embodiment of FIG. 1;
FIG. 4 is a configuration diagram illustrating a second embodiment of the harmonic suppression type lighting device.
FIG. 5 is a configuration diagram illustrating a third embodiment of the harmonic suppression type lighting device.
FIG. 6 is a configuration diagram illustrating a fourth embodiment of the harmonic suppression type lighting device.
FIG. 7 is a configuration diagram illustrating a fifth embodiment of the harmonic suppression type lighting device.
FIG. 8 is a diagram for explaining the operation of the control circuit in the embodiment of FIG. 7;
FIG. 9 is a configuration diagram illustrating a conventional harmonic suppression type lighting device.
10 is a current path in the conventional example of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... AC voltage source, 2 ... Active filter and power supply circuit, 3 ... Inverter circuit, 4 ... Full wave rectifier, 5 ... Reference voltage generation circuit, 6 ... Adder, 7 ... Carrier wave generation circuit, 8, 14 ... Modulation wave generation Circuit, 9: Comparator, 10: Gate drive circuit, 11, 12, 13 ... Frequency oscillation circuit, C ... Preheating capacitor, C0 ... Filter capacitor, C1-C4 ... Capacitor, D1-D4 ... Diode, L1 ... Inductor, L2 ... ballast inductor, Q1, Q2 ... MOSFET, R1 ... resistor or fluorescent lamp.

Claims (5)

One end of a rectifier having a diode connected in series, one end of a power capacitor connected in series, and the other end of the power capacitor connected in series to the other end of the rectifier,
One end of an AC voltage source is connected to a connection point of the diode of the rectifying means via a first choke coil, and the other end of the AC voltage source is connected to a connection point of the power supply capacitor connected in series.
One end and the other end of the rectifying means are connected to one end and the other end of a series connection body in which power switching elements having diodes connected in antiparallel are connected in series,
A fluorescent lamp is connected via a second choke coil and a first capacitor between a connection point of the series connection body of the power switching elements and a connection point of the diode of the rectifying means,
A fluorescent lamp lighting device having a second capacitor having both ends connected between a connection point of a diode of the rectifying means and the other end of the rectifying means ,
In accordance with a switching operation of the power switching element, through said power switching element from said AC voltage source, and the fluorescent lamp, and the second choke coil, said first capacitor, said first choke coil Passing a first current through the path, storing energy in the first choke coil,
From the power source capacitor connected to said series, and said power switching element, the fluorescent lamp and the second choke coil, said first capacitor and Tsuryu the second current path through the second capacitor And
Instantaneous voltage of the AC voltage source, or depending on the instantaneous voltage detected current or voltage changes, by changing the switching frequency of the power switching element in response to the detection value, or a switching frequency of the power switching element by changing the pulse width,
The power and the resonant frequency fr of the switching frequency f in the circuit of the switching elements, fr <fluorescent lamp lighting apparatus, characterized in that it comprises a control means for controlling so as to maintain the f in. In the fluorescent lamp lighting device according to claim 1 ,
Said control means, said instantaneous voltage and the reference voltage of the detected AC voltage source as compared with the switching frequency of the power switching elements when the instantaneous voltage of the AC voltage source is higher than the reference voltage, the instantaneous voltage of the AC voltage source A fluorescent lamp lighting device comprising frequency setting means for lowering the switching frequency of the power switching element when the voltage is lower than a reference voltage . In the fluorescent lamp lighting device according to claim 1,
Said control means, said second detecting a current flowing through the choke coil, on the basis of the position of the power switching elements is conductive and the direction in which the detected current flows, varies the switching frequency of the power switching element A fluorescent lamp lighting device comprising frequency setting means for causing the fluorescent lamp to turn on. In the fluorescent lamp lighting device according to claim 1,
Fluorescence which said control means detects a current flowing through the first choke coil, on the basis of a direction in which the detected current flows, characterized in that it comprises a frequency setting means for varying the switching frequency of the power switching element Lamp lighting device. In the fluorescent lamp lighting device according to claim 1,
The control means detects the voltage at the connection point of the series connection body of the power switching elements instead of the instantaneous voltage of the AC voltage source, or a current or voltage that changes depending on the instantaneous voltage ,
Based on the position of the power switching element is electrically connected to the magnitude of the detected voltage, fluorescent lamp lighting apparatus comprising: a frequency setting means for varying the switching frequency of the power switching elements.

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