JPH06231888A - Stabilizer circuit - Google Patents

Abstract

PURPOSE: To light a discharge lamp with a large power factor by carrying out a.c. input to a DC/AC transformer through a rectifying circuit and at the same time connecting connection points of a pair of diodes with one end of the discharge lamp through a capacitor, and connecting the other end with a switching transistor through an LC circuit. CONSTITUTION: After passing an EMI filter constituted of an inductane 6 and a capacitor 8 and an EMI filter constituted of an inductance 7 and a capacitor 10, a.c. voltage applied to the a.c. input terminals 1, 2 is rectified by diodes 11, 12. The resultant d.c. voltage is applied to d.c. input terminals 13, 14 of a half bridge DC/AC transformer 15 through a voltage doubler circuit 8. The voltage from the mutual connection points of the diodes 11, 12 is applied to one end electrode 27 of a discharge lamp 20 through a capacitor 21. The other end electrode 28 of the lamp 20 is connected with a mutual connection point 22 of switching transistors 18, 19 through an LC circuit constituted of inductances 24, 25 and the capacitor 26. When either one of Tr 18, 19 is turned on, the control circuit 34 controls as to turn off the other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge lamp lighting ballast circuit provided with a DC / AC converter, and a pair of AC input terminals for connecting to a low frequency AC voltage source, A first and second direct current input terminal for connecting to a direct current-alternating current converter, a rectifying circuit including first and second diodes for coupling the alternating current input terminal to the direct current input terminal, and the direct current input A load circuit including buffer capacitor means coupled to the terminals, first and second switching transistors connected in series between the first and second DC input terminals, a lamp connection terminal and an inductive means; A coupling circuit that couples the load circuit to one of the AC input terminals and a control electrode of each of the first and second switching transistors, and these switching transistors are turned on at a high frequency. It relates ballast circuit and means for driving alternately disengaged state.

[0002]

2. Description of the Related Art The ballast circuit described above is disclosed in European Patent Application No.
No. 2203651.2. The coupling circuit may have components according to the configuration of the DC-AC converter, but it can also be a connection line between the load circuit and the AC input terminal, the impedance of which is substantially equal to zero. It has been determined that such a ballast circuit has a relatively high power factor when used to operate a low power fluorescent lamp. However, when a relatively high power consuming fluorescent lamp is lit with the ballast circuit described above, the power factor is often relatively low or even fails to meet national standards for line current distortion.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a ballast circuit suitable for operating a fluorescent lamp which consumes a relatively large amount of power at a relatively high power factor.

[0004]

The present invention is a ballast circuit for lighting a discharge lamp provided with a DC-AC converter, comprising a pair of AC input terminals for connecting to a low-frequency AC voltage source. First for connecting to said DC-AC converter
And a second DC input terminal, a rectifying circuit including first and second diodes for coupling the AC input terminal to the DC input terminal, buffer capacitor means coupled to the DC input terminal, and A load circuit including first and second switching transistors connected in series between the first and second DC input terminals, a lamp connection terminal and an inductive means, and a coupling for coupling the load circuit to one AC input terminal A ballast circuit comprising a circuit and means for alternately driving the switching transistors into a conducting state and a blocking state at high frequencies, the inductive means being coupled to respective control electrodes of the first and second switching transistors. Is configured with an LC circuit, the LC circuit including a discharge lamp, a first interconnection point between the first and second switching transistors, and It is one coupled to the DC input terminal of one of the first and second DC input terminals and wherein the are.

In the LC circuit according to the present invention, the energy fed back to the buffer capacitor means is delivered to the portion which comes through the rectifier circuit and the portion which comes through the switching transistor or the diode means connected in parallel with these switching transistors. Split effectively. With proper selection of components, the DC-AC converter operates like a high frequency boost converter which raises the voltage of the buffer capacitor means to a value higher than the peak value of the low frequency AC power supply voltage. Therefore, a large capacitor charging current from the AC power supply is avoided, which increases the power factor and lowers the high frequency components in the power supply current. It has been determined that the ballast circuit according to the present invention provides a relatively high power factor even when a fluorescent lamp lit in the ballast circuit consumes relatively high power.

A relatively small buffer capacitor means can be used because all of the current to the buffer capacitor means is partially derived from the DC-AC converter, rather than being supplied from the AC voltage source.

To prevent the fluorescent lamp from carrying a direct current during its operation, it is advantageous for the coupling circuit to have a first capacitor.

In a preferred embodiment of the ballast circuit according to the invention said LC circuit comprises first and second inductors connected in series between one end of a discharge lamp and said first interconnection point, A second capacitor coupled between the interconnection point of the first and second inductors and the one DC input terminal. By doing this,
It was confirmed that the feedback of high frequency current to the buffer capacitor means can be made very effective.

In a preferred embodiment of the ballast circuit according to the invention said buffer capacitor means comprises third and fourth capacitors connected in series between said first and second DC input terminals, said first capacitor circuit comprising: And a second diode is connected in series between the first and second DC input terminals, and a second interconnection point between the first and second diodes is coupled to the first AC input terminal, and And a third interconnection point between the third and fourth capacitors of is coupled to the second AC input terminal. In this preferred example, the rectifier circuit and the buffer capacitor means form a voltage doubler circuit. According to this feature, a suitable example is obtained which is extremely suitable for use when the amplitude of the low-frequency AC voltage is relatively lower than the lamp voltage.

In another preferred embodiment of the ballast circuit according to the present invention, the first and second diodes are connected in series between the first and second DC input terminals, and the first and second DC inputs are connected. A third and a fourth diode are connected in series between the terminals, a second interconnection point between the first and the second diode is coupled to a first AC input terminal, and a third between the third and the fourth diode is connected. The interconnection point is coupled to the second AC input terminal. Another preferred example is a relatively simple circuit that has been found to provide a relatively high power factor.

The latter two preferred embodiments further provide another boosting effect by a circuit having a series circuit of a third inductor and a fifth capacitor, which is connected between the second and third interconnection points. To According to this other boosting effect,
Feedback through the rectifier circuit charges the buffer capacitor means to a potential high enough to prevent peaking of the power supply current when the amplitude of the low frequency AC power supply voltage is near its maximum value. If the coupling circuit is connected to either one of the second and third interconnection points, it can be very effectively achieved to return the energy from the DC / AC converter to the buffer capacitor means via the rectifying circuit. I confirmed.

If the means coupled to the respective control voltage of the first and second switching transistors and driving the switching transistors alternately into a conducting state and a blocking state at a high frequency does not have a transformer, the first And a diode means in parallel with each of the second switching transistors to form a path for a portion of the feedback energy.

By coupling a filter circuit between the AC input terminal and the rectifier circuit, it is possible to prevent the low frequency AC voltage source from being affected by the high frequency current.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, an EMI (electromagnetic interference) filter 5 comprising a first capacitor 9 and a first inductor 6.
A low-frequency AC power supply voltage, for example, 120 V, 60 Hz is applied to the pair of AC input terminals 1 and 2 coupled to each other.
The EMI filter 5 is coupled to the input terminals 3 and 4 of the voltage doubler circuit 8 via the second inductor 7 and the second capacitor 10. The first and second inductors 6 and 7 are connected in series between the AC power supply terminal 2 and the input terminal 4 of the voltage doubler circuit 8. The first capacitor 9 is coupled between the input terminals 1 and 2 and the second capacitor 10 is connected between the input terminal 1 and the interconnection point between the inductors 6 and 7.

The voltage doubler circuit 8 is a half bridge high frequency DC-
A pair of diodes 11, 12 connected in series between the DC input terminals 13, 14 of the AC converter 15, and a pair of series-connected buffer (buffer) capacitors 16 connected in parallel with the series-connected diodes 11, 12. 17 and.

A pair of series-connected switching transistors 18 and 19 are coupled to the DC input terminals 13 and 14, respectively. A third diode 37 and a fourth diode 38 are coupled in reverse polarity between the respective ends of the transistors 18 and 19. One end of a discharge lamp 20, for example a fluorescent lamp, is coupled to the interconnection point 3 of the diodes 11, 12 via a capacitor 21. It is known that the other end of the discharge lamp 20 is connected via an inductor 23 to an interconnection point 22 between the switching transistors 18, 19. This known connection is shown in broken lines in the figure. However, according to the present invention, instead of one inductor 23, a first inductor 24 and a second inductor 25 connected in series are provided, and an interconnection point of these is coupled to the DC input terminal 14 via the capacitor 26. Use a circuit.

The electrodes 27 and 28 of the discharge lamp are interconnected via a series connection circuit of a resistor 29 having a positive temperature coefficient (PTC) and a capacitor 30. This PTC resistor 29
Another capacitor 31 is connected in parallel with the series connection circuit of the capacitor 30 and the capacitor 30. The PTC resistor 29 forms a preheat current path that heats the lamp electrodes prior to ignition of the lamp.
This current path is a normal preheating circuit. The interconnection point 22 is connected by a snubber capacitor 32 to another interconnection point 33, which operates to reduce losses in the switching transistor.

The normal control circuit 34 switches the switching transistors 18 and 19 so that when one transistor is on, the other transistor is off and when one transistor is off, the other transistor is on. The transistors are alternately turned on and off. This control circuit may be of the IC driven type, but is preferably part of a load circuit connected between the interconnection points 22 and 33, the primary windings in series with the inductors 24 and 25 and the switching transistor. A transformer having 18 and 19 base and emitter electrodes, respectively, and first and second properly-phased secondary windings, respectively, may be constructed. A resistor may be connected in series with each of the secondary windings in the base circuit of the switching transistor. In this way, a self-oscillation type high frequency DC / AC converter can be formed.
The exact method of driving the switching transistors is not critical to the present invention, and various other driving methods for these transistors may be used, which may also result in satisfactory operation of the circuit.

The lamp 20, the capacitor 31, the inductors 24 and 25, and the capacitor 26 substantially form a resonant circuit that causes the half-bridge DC-AC converter to self-oscillate at high frequencies.

A starting circuit 35 may be provided to start the operation of the high frequency DC / AC converter 15. Since the details of this circuit are ordinary and well known to those skilled in the art, the description thereof will be omitted.

The input current from the AC power supply has a sinusoidal waveform due to the boosting action through the isolation diodes 11 and 12 and the capacitor 21 which form the high frequency passage for returning the resonance energy in the lamp circuit to the electrolytic buffer capacitors 16 and 17. It is very close and therefore the voltage across each of these buffer capacitors is always higher than the line voltage from the AC power supply at terminals 1 and 2. The capacitor 10 and the inductor 7 are part of a booster circuit for the buffer capacitor. The energy returning from the resonant circuit via the capacitor 21 functions to generate a voltage across the inductor 7. This voltage, in addition to the AC line voltage, tries to rise toward a voltage higher than the buffer capacitor voltage, but is clamped to the buffer capacitor voltage by the diode 11 or 12. Therefore, the energy is returned to the buffer capacitor via the diodes 11 and 12. The LC circuit consisting of inductor 25 and capacitor 26 provides an additional boosting action on buffer capacitors 16 and 17. By using an LC circuit instead of one inductor such as the inductor 23, the feedback energy supplied to the capacitors 16 and 17 can be effectively split. That is, a part of this return energy can be taken out from the lamp through the capacitor 21, and the other part can be taken out from the LC circuits 24, 25 and 26. Diodes 37 and 38 form a path for returning energy to the buffer capacitor. Transistor 18
If a transformer is used to drive 19 and 19, diodes 37 and 38 can be omitted. The reason is that the secondary winding and the collector-base junction of the transistor form a low impedance path for returning energy to the buffer capacitor. In this case, the collector-base junction of the transistor acts as a diode.

Another boosting operation is obtained by the inductor 7, which operates as a kind of current source for driving the current to the capacitors 16 and 17 through the separating diodes 11 and 12.

In another variant of the circuit according to the invention, a capacitor 36 can be connected between the interconnection point 33 and the input terminal 14. With proper selection of capacitors 21 and 36, the half-bridge DC-AC converter acts like a high frequency boost converter that raises the voltage of each of buffer capacitors 16 and 17 to a value higher than the peak line voltage. To do. This avoids any large capacitive charging current from the line voltage source, thereby improving the circuit power factor and reducing the high frequency line current. The improved power factor results in the circuit carrying significantly lower input currents.

As mentioned above, capacitors 16 and 17
The input ripple current to the high frequency half-bridge DC- is not completely drawn from the low frequency (60Hz) AC power supply.
Because they are partially taken from the AC converter, small capacitors can be used, and these small capacitors can still keep the ripple voltage low.

2 is a voltage doubler circuit (11,
12, 16, 17) are diode bridges (11, 1)
2, 41, 42) and the capacitor 16 for connecting the DC terminals 13 and 14 to each other, which is a difference from the circuit of FIG. Since the circuit of FIG. 2 operates in the same manner as the circuit of FIG. 1, its detailed description is omitted.

[0026]

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a ballast circuit according to the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the present invention.

[Explanation of symbols]

 1, 2 AC input terminal 5 EMI filter 8 times voltage circuit 13, 14 DC input terminal 15 Half bridge DC-AC converter 18, 19 Switching transistor 20 Discharge lamp 34 Control circuit 35 Starting circuit

Claims (10)

[Claims] 1. A ballast circuit for lighting a discharge lamp provided with a DC-AC converter, comprising a pair of AC input terminals for connecting to a low-frequency AC voltage source, and the DC-AC converter. First and second for connecting
A direct current input terminal; a rectifier circuit including first and second diodes for coupling the alternating current input terminal to the direct current input terminal; buffer capacitor means coupled to the direct current input terminal; A first and a second switching transistor connected in series between the second DC input terminals, a load circuit including a lamp connection terminal and an inductive means, and a coupling circuit for coupling the load circuit to one AC input terminal, A ballast circuit coupled to the respective control electrodes of the first and second switching transistors, the means for alternately driving the switching transistors into a conducting state and a blocking state at a high frequency, wherein the inductive means is an LC circuit. This L
A C circuit is coupled to the discharge lamp, the first interconnection point between the first and second switching transistors, and one of the first and second DC input terminals. And ballast circuit. 2. The ballast circuit of claim 1, wherein:
A ballast circuit, wherein the coupling circuit comprises a first capacitor. 3. The ballast circuit of claim 1 or 2, wherein the LC circuit is connected in series between one end of a discharge lamp and the first interconnection point. An inductor and a second inductor coupled between the interconnection point of the first and second inductors and the one DC input terminal.
A ballast circuit comprising a capacitor. 4. The ballast circuit according to claim 1, wherein the buffer capacitor means is connected in series between the first and second DC input terminals. A four-capacitor, the first and second diodes are connected in series between the first and second DC input terminals, and the second diode between the first and second diodes is connected.
A ballast circuit, wherein an interconnection point is coupled to a first AC input terminal and a third interconnection point between the third and fourth capacitors is coupled to a second AC input terminal. 5. The ballast circuit according to claim 1, wherein the first and second diodes are connected in series between the first and second DC input terminals. Third and fourth diodes are connected in series between the first and second DC input terminals, and a second interconnection point between the first and second diodes is coupled to the first AC input terminal.
And a third interconnection point between the fourth diode and the fourth diode is coupled to the second AC input terminal. 6. The ballast circuit of claim 4 or 5, wherein a circuit having a series circuit of a third inductor and a fifth capacitor connected between the second and third interconnection points is provided. A ballast circuit characterized by: 7. The ballast circuit according to claim 4, wherein a terminal of the coupling circuit is the second circuit.
A ballast circuit characterized in that it is connected to an interconnection point. 8. A ballast circuit as claimed in any one of claims 4 to 6, characterized in that the terminals of the coupling circuit are connected to a third interconnection point. 9. A ballast circuit as claimed in claim 1, characterized in that diode means are coupled in parallel with each of the first and second switching transistors. Circuit. 10. The ballast circuit according to claim 1, wherein a filter circuit is coupled between the AC input terminal and the rectifier circuit. Circuit.