JP3327966B2 - Ballast circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ballast circuit for lighting a discharge lamp provided with a DC-AC converter, comprising a pair of AC input terminals for connection to a low-frequency AC voltage source. A rectifier circuit including first and second DC input terminals for connecting to a DC-AC converter, first and second diodes coupling the AC input terminal to the DC input terminal, and the DC input; A load circuit including buffer capacitor means coupled to the terminal, first and second switching transistors connected in series between the first and second DC input terminals, a lamp connection terminal and inductive means; A coupling circuit that couples the load circuit to one of the AC input terminals, and a control electrode that is coupled to each of the first and second switching transistors. 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. 9
2203651.2. The coupling circuit can have components depending on the configuration of the DC-AC converter, but can also be a connection line between the load circuit and the AC input terminal with an impedance substantially equal to zero. It has been found that such a ballast circuit has a relatively large power factor when used to operate a low power fluorescent lamp. However, when operating relatively high power consuming fluorescent lamps with the ballast circuit described above, the power factor is often relatively low or even the national standards for line current distortion are not met.

[0003]

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

[0004]

SUMMARY OF THE INVENTION 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 connection to a low frequency AC voltage source. The first for connecting to the DC-AC converter
A rectifier 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; First and second switching transistors connected in series between first and second DC input terminals, a load circuit including a lamp connection terminal and inductive means, and a coupling for coupling the load circuit to one AC input terminal. A ballast circuit comprising: a circuit; and means coupled to respective control electrodes of the first and second switching transistors for alternately driving the switching transistors in a conducting state and a blocking state at a high frequency. Is constituted by an LC circuit which comprises a discharge lamp, a first interconnection point between the first and second switching transistors, 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 supplied to a part arriving via a rectifier circuit and a part arriving via a switching transistor or a diode means connected in parallel with these switching transistors. Split effectively. By properly selecting the components, the DC-AC converter operates like a high-frequency boost converter that 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, thereby increasing the power factor and reducing high frequency components in the power supply current. The ballast circuit according to the present invention has been found to provide a relatively large power factor even when the fluorescent lamp ignited by the ballast circuit consumes relatively large power.

[0006] Relatively small buffer capacitor means can be used since all of the current to the buffer capacitor means is taken from the DC-to-AC converter rather than all from the AC voltage source.

In order that the fluorescent lamp does not carry 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 is coupled between an interconnection point of the first and second inductors and the one DC input terminal. By doing this,
It has been confirmed that the feedback of the high-frequency current to the buffer capacitor means can be extremely effective.

In a preferred embodiment of the ballast circuit according to the present invention, said buffer capacitor means comprises third and fourth capacitors connected in series between said first and second DC input terminals, And a second diode is connected in series between the first and second DC input terminals; a second interconnection point between the first and second diodes is coupled to a first AC input terminal; A third interconnection point between the third and fourth capacitors is coupled to the second AC input terminal. In this preferred embodiment, the rectifier circuit and the buffer capacitor constitute a voltage doubler circuit. According to this feature, a preferable example is obtained which is very 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 invention, said first and second diodes are connected in series between said first and second DC input terminals, and said first and second DC input terminals are connected. A third and fourth diode are connected in series between the terminals, a second interconnection point between the first and second diodes is coupled to the first AC input terminal, and a third diode between the third and fourth diodes is provided. The interconnection point is coupled to the second AC input terminal. Another preferred embodiment is a relatively simple circuit which has been found to provide a relatively large power factor.

In the latter two preferred embodiments, another boosting effect is obtained by a circuit connected between the second and third interconnection points and having a series circuit of a third inductor and a fifth capacitor. To According to this other boost effect,
Feedback through the rectifier circuit charges the buffer capacitor means to a potential high enough to prevent a peak in power supply current when the amplitude of the low frequency AC power supply voltage is near its maximum. When the coupling circuit is connected to one of the second and third interconnection points, it is possible to very effectively achieve the return of energy from the DC / AC converter to the buffer capacitor means via the rectifier circuit. I checked.

If the means coupled to the control voltage of each of the first and second switching transistors and driving these switching transistors alternately at high frequency into a conducting state and a blocking state does not have a transformer, the first means may be used. And diode means must be connected in parallel to each of the second switching transistors so as to form a path for some of the feedback energy.

By connecting a filter circuit between the AC input terminal and the rectifier circuit, the low frequency AC voltage source can be prevented from being affected by the high frequency current.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, an EMI (electromagnetic interference) filter 5 comprising a first capacitor 9 and a first inductor 6 is shown.
A low frequency AC power supply voltage, for example, 120 volts, 60 Hz is applied to a pair of AC input terminals 1 and 2 coupled to the AC input terminals 1 and 2.
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 8. A first capacitor 9 is coupled between the input terminals 1 and 2, and a second capacitor 10 is connected between the input terminal 1 and an interconnection between the inductors 6 and 7.

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

A pair of series-connected switching transistors 18 and 19 are connected to the DC input terminals 13 and 14, respectively. A third diode 37 and a fourth diode 38 are coupled between both ends of the transistors 18 and 19, respectively, with opposite polarities. One end of a discharge lamp 20, for example a fluorescent lamp, is coupled via a capacitor 21 to the interconnection point 3 of the diodes 11,12. 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 indicated by a dashed line in the figure. However, according to the present invention, instead of one inductor 23, an LC having a first inductor 24 and a second inductor 25 connected in series and having their interconnection point coupled to the DC input terminal 14 via a capacitor 26 is provided. Use a circuit.

The electrodes 27 and 28 of the discharge lamp are interconnected via a series connection circuit of a positive temperature coefficient (PTC) resistor 29 and a capacitor 30. This PTC resistor 29
Another capacitor 31 is connected in parallel with the series connection circuit of the capacitor 30. The PTC resistor 29 forms a preheating current path for heating the lamp electrode before the lamp is ignited. This current path is a normal preheating circuit. Interconnection point 2
2 is connected to another interconnection point 33 by a snubber capacitor 32, which operates to reduce losses in the switching transistor.

The normal control circuit 34 controls these switching transistors 18 and 19 such that when one of the switching transistors 18 and 19 is turned on, the other transistor is turned off, and when one transistor is turned off, the other transistor is turned on. The transistors are alternately turned on and off. The control circuit can be IC driven, but is preferably part of a load circuit connected between the interconnection points 22 and 33, a primary winding in series with inductors 24 and 25, and a switching transistor. A transformer having first and second secondary windings coupled to the base and emitter electrodes 18 and 19, respectively, and appropriately phased can be constructed. A resistor can be connected in series with these secondary windings in the base circuit of these switching transistors. 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, and may also cause the circuit to operate satisfactorily.

The lamp 20, the capacitor 31, the inductors 24 and 25, and the capacitor 26 substantially constitute a resonance circuit that causes the half-bridge DC-AC converter (inverter) to self-oscillate at a high frequency.

A starting circuit 35 can be provided to start the operation of the high frequency DC-AC converter 15. The details of this circuit are also ordinary and well known to those skilled in the art, and thus description thereof is omitted.

The input current from the AC power supply has a sinusoidal waveform due to the boosting action via the separation diodes 11 and 12 and the capacitor 21 constituting the high frequency path for returning the resonance energy in the lamp circuit to the electrolytic buffer capacitors 16 and 17. Very similar, so 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. Capacitor 10 and 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 create a voltage across the inductor 7. This voltage, in addition to the AC line voltage, tends to rise toward a voltage higher than the buffer capacitor voltage, but is clamped by the diode 11 or 12 to the buffer capacitor voltage. Thus, energy is returned to the buffer capacitor via diodes 11 and 12. An additional boosting action on buffer capacitors 16 and 17 is provided by an LC circuit consisting of inductor 25 and capacitor 26. 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 divided. That is, a part of this return energy can be extracted from the lamp via the capacitor 21 and another part can be extracted from the LC circuits 24, 25 and 26. Diodes 37 and 38 provide a path for returning energy to the buffer capacitor. Transistor 18
And 19, diodes 37 and 38 can be omitted if a transformer is used to drive them. 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 has a diode function.

Another boosting operation can be obtained by the inductor 7 operating as a kind of current source for driving the current to the capacitors 16 and 17 via the separation 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 on each of buffer capacitors 16 and 17 to a value higher than the peak line voltage. I do. This avoids any large capacitive charging current from the line voltage source, thereby improving the circuit power factor and reducing the high frequency of the line current. Because of the improved power factor, the circuit will draw significantly lower input current.

As described above, capacitors 16 and 17
The input ripple current to the high-frequency half-bridge DC-
Since they are partially removed from the AC converter, small capacitors can be used, and these small capacitors can still keep the ripple voltage low.

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

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one 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 Voltage multiplier 13, 14 DC input terminal 15 Half-bridge DC-AC converter 18, 19 Switching transistor 20 Discharge lamp 34 Control circuit 35 Start circuit

──────────────────────────────────────────────────続 き Continuation of the front page (73) Patent holder 590000248 Groenewoodseweg 1, 5621 BA Eindhoven, The Netherlands (56) References JP-A-57-84597 (JP, A) (58) Fields surveyed (Int. Cl. ⁷ , DB name) H05B 41/02 H05B 41/24 H05B 41/282

Claims (10)

(57) [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; First and second to connect
A DC input terminal; a rectifier 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; First and second switching transistors connected in series between the second DC input terminals, a load circuit including a lamp connection terminal and inductive means, a coupling circuit coupling the load circuit to one AC input terminal, A ballast circuit coupled to respective control electrodes of the first and second switching transistors, and for alternately driving the switching transistors in a conducting state and a blocking state at a high frequency, wherein the inductive means comprises an LC circuit. And this L
A circuit C is coupled to the discharge lamp, a 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 according to claim 1, wherein
A ballast circuit, wherein the coupling circuit has a first capacitor. 3. The ballast circuit according to claim 1, wherein said LC circuit is connected in series between one end of a discharge lamp and said first interconnection point. A second inductor coupled between the inductor and 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 said buffer capacitor means is connected in series between said first and second DC input terminals. A first capacitor and a fourth capacitor, wherein the first and second diodes are connected in series between the first and second DC input terminals, and a second diode between the first and second diodes is provided.
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, a second interconnection point between the first and second diodes is coupled to the first AC input terminal, and a third
And a third interconnect point between the fourth diode and the fourth diode is coupled to the second AC input terminal. 6. The ballast circuit according to claim 4, further comprising a circuit connected between the second and third interconnection points and having a series circuit of a third inductor and a fifth capacitor. And a ballast circuit. 7. The ballast circuit according to claim 4, wherein a terminal of the coupling circuit is the second terminal.
A ballast circuit characterized by being connected to an interconnection point. 8. The ballast circuit according to claim 4, wherein a terminal of the coupling circuit is connected to a third interconnection point. 9. The ballast circuit according to claim 1, wherein diode means is connected in parallel to each of said 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.