JPH02123697A - Discharge lamp lighting apparatus - Google Patents

Abstract

PURPOSE:To simplify circuit consumption by making a safety circuit and a soft start circuit having a part in common between them and using a detecting coil in common between both circuits. CONSTITUTION:In lighting apparatus having two discharge lamps 20a, 20b, detecting coils 28a, 28b are rolled on inductors 19a, 19b for ballasts, a soft start circuit 31 and a safety circuit 43, which are connected to the inductors, are so formed to have a structural part in common between them, and the detecting coils are used in common between both circuits. Diodes 29a, 29b, and a capacitor 30 are connected to connection terminals (a), (b), (c), (d) of each detecting coils 28a, 28b to form the soft start circuit 31 and using of a part of it in common, a safety circuit 43 is composed of resistors 44, 46, a capacitor 40, a transistor 47, and a Zener diode 48.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a discharge lamp lighting device that lights a discharge lamp at high frequency using an inverter circuit.

Conventional technology Generally, a pair of power switching transistors (main transistors) are used as a lighting device for discharge lamps such as fluorescent lamps.
A half-bridge type series inverter circuit is known.

Also known is a self-excited type in which the output current of such a series inverter circuit is detected by a transformer and fed back to the base from the secondary winding of the transformer to alternately turn on and off the L transistor. There is. In such a lighting device, a discharge lamp as a load is connected to an output terminal of an inverter circuit via a current-limiting inductance, and a discharge lamp starting capacitor is connected in parallel with the discharge lamp.

When such an inverter circuit is operated under conditions of high load impedance such as due to a filament abnormality, a large current flows through the switching transistor of the inverter circuit due to series resonance between the current limiting inductor and the starting capacitor, and the operating conditions become rated. As a result, there was a danger that the power transistor would go into thermal runaway. There was also a risk that the discharge lamp would be damaged.

On the other hand, what about discharge lamps such as fluorescent lamps? If a so-called cold start is performed, in which discharge is started before the 5 filaments are heated by the middle molecules when the source is turned on, phenomena such as early blackening of the discharge lamp will occur, which will significantly shorten the life of the discharge lamp. There is a problem.

Therefore, in the conventional discharge lamp lighting device,
As described in Publication No. 3-59774, when a large current flows due to series resonance between the current limiting inductor and the starting capacitor, this condition is detected and the oscillation of the inverter circuit is stopped or the oscillation is stopped intermittently. A safety circuit that operates normally, and software that performs a so-called soft start, which reduces the voltage applied to the discharge lamp from the time the power is turned on until the filament is sufficiently preheated to prevent the aforementioned cold start. It is common practice to provide a start circuit.

Problems to be Solved by the Invention In the case where a safety circuit and a soft start circuit are provided as described above, the soft start circuit is connected to one side of a pair of transistor drive circuits that constitute a self-excited series inverter, and the soft start circuit is connected to the other side. Since the safety circuit is configured to be connected, the safety circuit and the soft start circuit must be configured completely separately. Therefore, there is a problem that the respective circuit configurations become complicated.

Means for Solving the Problem An inverter circuit that is connected to a DC power supply and a starting circuit and performs high frequency output through the switching operation of a pair of switching transistors, and a pair of primary windings that are connected to the output terminal of this inverter circuit. a discharge lamp connected via an inductance element and a feedback transformer comprising a secondary winding of the feedback transformer, and a pair of drives for positively feeding back voltage induced in each secondary winding of the feedback transformer to the switching transistor. 1 due to the circuit, the detection winding wound around the inductance element, and the voltage generated in this detection winding.
) a soft start circuit that operates for a predetermined period of time after power is applied to the drive circuit i to reduce the high frequency output supplied to the discharge lamp; The soft start circuit is configured with a safety circuit that shares a part of the soft start circuit that reduces the driving of the switching transistor and reduces the high frequency output supplied to the radiator lamp.

A part of the operation safety circuit and the soft start circuit are shared to control the operation of the drive circuit, and the detection winding that detects the preheating state and abnormality of the discharge lamp is used for both. Therefore, the functions of soft-starting the discharge lamp and ensuring safety in the event of an abnormality of the discharge lamp can be obtained with a simple circuit configuration.

Example An embodiment of the present invention will be described based on the drawings.

First, a rectifier circuit 5 as DC'its consisting of a diode bridge circuit 3 and a smoothing capacitor 4 (C,) is connected from a commercial power source 1 via a filter circuit 2 for surge absorption and noise prevention.

The second rectifier circuit 5 is connected to an inverter circuit 8 including a pair of switching transistors 6.7 (Q, ,Q,) connected in a 5EPP manner. This inverter circuit 8
is a so-called saturable current transformer type self-excited series inverter, and the feedback transformer 9 (T,) is a saturable type current transformer, with one primary winding W l l and two secondary windings oppositely wound. It has windings W, la, W, and b. The primary winding W l is inserted in series with the output terminal of the inverter circuit 8, detects the load current flowing therein, and applies secondary voltages corresponding to the load current with opposite phases to each secondary winding W, It is caused in a, W, and b. Next, the secondary winding il W, a has a resistance of 10 (
It is connected to the base of the switching transistor 6 via R, a). Furthermore, the base of the switching transistor 6 is connected to a transistor 11 (Q,) and a diode 12 (D,), which are part of a drive circuit. The transistor 11 and the diode 12 are connected to a resistor 13 (Rb,) connected to the base of the transistor 11 and an emitter resistor 14 (RE) connected to the transistor 11, which is necessary for lighting the discharge lamp. It is a feedback circuit that sets the lamp secondary voltage. Furthermore, the other secondary winding faWob is also connected to the base of the switching transistor 7 via a resistor 10 (R, b), similarly to the secondary windings W1, a. Furthermore, a transistor 15 (Q,), which is a part of the drive circuit, is connected to the base of the switching transistor.
and diode l6(D,) are connected. Further, the transistor 15 and the diode 16 are connected to a resistor 17 (R
b, ) and the emitter resistor 18 (RE, ) connected to the transistor 15 form a feedback circuit that sets the lamp secondary voltage necessary when lighting the discharge lamp.

Next, the output terminal of the inverter circuit 8 is connected to the primary @, taw, of the current transformer 9, and a ballast inductor 19a recognized as an inductance element.
A pair of discharge lamps 20a are connected to the negative side DC output terminal of the rectifier circuit 5 via (L, , ), 19 b (L4.'),
20b are connected in parallel.

Here, capacitors 21 and 22 (C4, , C, .) are dividing capacitors, and capacitor 23 (C.

, ), (C,,') are for starting the discharge lamps 20a and 20b.

Further, a series circuit that connects the positive side DC input terminal to the output terminal of the inverter circuit 8 and connects to the negative side DC terminal via a resistor 24 (R,) and a capacitor 25 (C,) in order; The starting circuit 27 of the inverter circuit 8 is activated by a relaxation oscillation circuit composed of a bidirectional thyristor 26 (SS) connected in series from the contact point of the resistor 24 and the capacitor 25 to the base of one of the switching transistors 7. It is formed.

Next, detection windings 28a (r-44) and 2sb (+=, *') are wound around the ballast inductor 19. These detection windings 28a(L,,),
28 b (L, 4°) has connection terminals a, b and c, d, respectively.

Next, as shown in FIG. 2, the detection winding 28a (L
A diode 29 a (D**) is connected to the a terminal of 44), and the detection winding 1328 b (L,, ")
A diode 29b (D.,) is connected to the C terminal of. These diodes 29 a (Dll, ), 29
A capacitor 30 (C, ,) is connected to b (D, ,), and a soft I.
Start time + JPT3L is connected. That is,
This soft start circuit 31 includes two photocouplers 32 a (PQ, ) and 32 b (PQ, ) connected in series.
The light emitting parts 33a and 33b, the resistor 34, and the transistor 35
(Q.) and the transistor 35 (Q.).
A resistor 36 (R, , ) is connected to the base of the transistor 36 (R, , ), and a transistor 38 (
Q,), a resistor 39 (R,.) forming a time constant circuit connected to the base of this transistor 38 (Q,), and a capacitor 40 connected in parallel to this resistor 39 (R,,).
It consists of (C,,). Then, the photocoupler 32
a(PQ,), , 32b(PQ,) light receiving section 41a,
41b is connected together with diodes 42a, 42b between the secondary winding W2 al w,b of the transformer T1 and the transistor 11.15.

Next, a safety circuit 43 is formed by sharing a part of the soft start circuit 31. That is, the diodes 29 (D, , ), (D, ,
) through a resistor 44 (R, , ) to a capacitor 45 (C,
, ) and a resistor 46 are connected. Further, the resistor 39 (R, ) constituting the time constant circuit and this resistor 39 (
The collector-emitter of a transistor 47 (Q,) is connected in parallel to the capacitor 40 (C, , ), which is connected in parallel to R, , ). And the transistor 4
At the base of 7(Q,), there is a Zener diode 48(Z
D. ) are connected to the capacitors 47 (C, , ).

In such a configuration, when the commercial 'It source 1 is turned on, this AC output is rectified by the rectifier circuit 5, the DC current is supplied to the inverter circuit 8, and electric charge is accumulated in the capacitor 25 via the resistor 24. . As a result, the potential at the connection point between the resistor 24 and the capacitor 25 rises, and when this exceeds the breakdown voltage of the bidirectional thyristor 26, the thyristor 26 becomes conductive and supplies base current to the switching transistor 7 on one side. The transistor 7 becomes conductive. The current flowing through the transistor 7 flows through the primary winding W11 of the transformer 9, the ballast inductor 19, the filament of the discharge lamp 20, and the starting capacitor 23, and then flows through the base of the transistor 7 through the secondary winding W2b. will be given positive feedback.

While this transistor 7 is in a conductive state, the primary winding iW,
, increases with time, and the saturable transformer 9 eventually becomes saturated as the magnetic flux density within its core increases. Then, the induced voltage in the secondary winding W2b becomes zero, and the transistor 7 is turned off. Therefore, when the current flowing through the primary winding W l 1, that is, the magnetomotive force applied to the core of the transformer 9, decreases and becomes smaller than the level that saturates the core, a positive voltage is induced in the secondary winding MAW, a. and transistor 6 is turned on. This on state continues until the transformer 9 is saturated due to positive feedback via the primary winding W1° and the secondary windings W1, a. Thereafter, similarly, transistors 6 and 7 are alternately turned on, and inverter circuit 8 continues to oscillate. .

Next, the operation of the inverter circuit 8 when starting the discharge lamp will be explained. First, when the power is turned on, as can be seen from the above-mentioned explanation of the operation of the inverter circuit 8, the on/off operation of the switching transistor 6.7 causes the current limiting inductors 19a, 19b and the starting capacitor 23a,
23b resonates in series, and a resonant current flows. Then, the detection winding 28a.

A voltage is induced in 28b, the capacitor 3o is charged with electric charge, and a current flows in the resistor 36, and the transistor 35
is turned on, current flows through the light emitting parts 33a and 33b of the phototransistors 32a and 32b, the light receiving parts 41a and 41b connected to the drive circuit are turned on, and the transistors 11 and 15 are turned on.
turns on. As a result, the switching transistor 6
．． As a result, the series resonance current between the current limiting inductors 19a, 19b and the starting capacitors 23a, 23b decreases, and the starting capacitors 23a, 2
The voltage between terminals 3b becomes lower than the voltage that starts the discharge lamp. Note that even in this case, the discharge lamps 20a, 20b
Sufficient current is supplied to the filament due to the aforementioned series resonance to preheat the filament.

Further, at this time, the terminal voltage of the capacitor 45 is set lower than the Zener voltage of the Zener diode 48, and the transistor 47 does not become conductive.

Next, the detection operation when an abnormality occurs in the discharge lamps 20a and 20b will be explained. First, when the discharge lamps 20a and 20b become abnormal,
The voltage level of the detection windings 28 a, 28 b wound around the current limiting inductors l 9 a, 19 b increased compared to the normal voltage of the discharge lamps 20 a, 20 b, and was charged via the resistor 44. The terminal voltage of capacitor 45 increases. Then, the terminal voltage is the Zener diode 4
At the point where the Zener voltage of 8 is exceeded, the transistor 47 is turned on. As a result, transistor 38 is turned off and transistor 35 is turned on. Then, the photocabra 32a.

The light emitting parts 33a and 33b of 32b emit light, the light receiving parts 41a and 41b connected to the drive circuit as described above turn on, the transistor 11.15 turns on, and the base current of the switching transistor 6.7 decreases. As a result, the series resonance current between the current limiting inductors 19a, 19b and the starting capacitors 23a, 23b decreases, and this state is maintained.

Effects of the Invention As described above, the present invention includes an inverter circuit that is connected to a DC power source and a starting circuit and performs high-frequency output through the switching operation of a pair of switching transistors, and one primary circuit that is connected to the output terminal of this inverter circuit. A discharge lamp is connected to a feedback transformer including a winding and a pair of secondary windings through an inductance element, and the voltage induced in each secondary winding of the feedback transformer is positively fed back to the switching transistor. a pair of drive circuits, a detection winding wound around the inductance element, and a voltage generated in the detection winding that acts on the drive circuit for a predetermined time after power is turned on to generate a high-frequency output that is supplied to the discharge lamp. and a soft start circuit that detects an abnormality in the discharge lamp using a voltage generated in the detection winding to reduce driving of the switching transistor and reduce high frequency output supplied to the discharge lamp. A part of the safety circuit and a soft start circuit are shared to control the operation of the drive circuit, and a part of the safety circuit and the soft start circuit are shared to control the operation of the drive circuit. Since the detection winding is used for both, it is possible to obtain the functions of soft-starting the discharge lamp and ensuring safety in the event of an abnormality of the discharge lamp with a simple circuit configuration.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the present invention, and is a circuit diagram of a connection state between an inverter circuit and a discharge lamp, and FIG. 2 is a circuit diagram of a soft start circuit and a safety circuit. 5... DC power supply, 6, 7... Switching transistor, 8... Inverter circuit, 9... Feedback transformer, 11.15... Drive circuit, l 9 a, 19
b...Inductance element, 20a, 20b-...Discharge lamp, 28a. 28b...Detection winding, 31...Soft start circuit, 43-...Safety circuit, W,... Primary winding, W, a
, W, b/Secondary winding Applicant: Tokyo Electric Co., Ltd.

Claims (1)

[Claims] An inverter circuit that is connected to a DC power supply and a starting circuit and performs high-frequency output through the switching operation of a pair of switching transistors, and one primary winding and a pair of secondary windings that are connected to the output terminal of this inverter circuit. a discharge lamp connected through a feedback transformer and an inductance element; a pair of drive circuits that positively feed back voltage induced in each secondary winding of the feedback transformer to the switching transistor; a wound detection winding; a soft start circuit that acts on the drive circuit for a predetermined period of time after power is turned on using a voltage generated in the detection winding to reduce the high frequency output supplied to the discharge lamp; and the detection winding. A safety circuit that shares a part of the soft start circuit detects an abnormality in the discharge lamp based on the voltage generated in the line, reduces the driving of the switching transistor, and reduces the high frequency output supplied to the discharge lamp. A discharge lamp lighting device characterized by: