Discharge Lamp Lighting Apparatus

Abstract

A discharge lamp lighting apparatus adapted to two such lamps, comprising a pair of series circuits of inductance and thyristor and a pair of series circuits of condenser and discharge lamp. The respective series circuit of condenser and discharge lamp are arranged to be in parallel with the respective thyristors which are connected in series with a DC source so that each discharge lamp will be lighted with a sine wave form alternating current of a high frequency through each thyristor, and the respective inductances form series oscillation circuit with the respective condensers so as to provide an oscillatory lamp current to each discharge lamp.

Description

This invention relates to a highly efficient discharge lamp lighting apparatus for two lamps.

It is well known that, when a discharge lamp is lighted with a high frequency alternating current, the luminous efficiency of the discharge lamp will increase by several to about 20 percent and an illumination low in the flickering and high in the quality will be able to be obtained. There have been used such high frequency lighting systems as a system wherein is used such mercury turbine inverter MTI as in FIG. 1 (German Pat. No. 1,237,222), a transistor inverter system wherein one or two transistors are used, a parallel inverter system wherein two silicon controlled rectifying elements (which shall be referred to as SCR hereinafter) or thyristors are used and a series inventer system employing two transistors or SCR elements. However, in the system of German Pat. No. 1,237,222, the high frequency alternating current cannot be obtained so much. In the transistor inverter system, due to such necessity as of shaping wave forms through a transformer, the conversion efficiency is low and, in view of the characteristics of the transistor, it is difficult to handle a load of a large capacity. On the other hand, the SCR parallel inverter system employ generally a type wherein a high frequency current source is formed of an SCR parallel inverter and discharge lamps are connected with it through respective stabilizers so that a plurality of discharge lamps may be lighted and, therefore, not only a wave form converting apparatus of a large capacity is required but also the entire apparatus must be very large and, in the case of lighting a few discharge lamps, disadvantages to the economy will be produced in view of the efficiency. In the series inverter system, the defects of the above mentioned systems are improved and a high frequency lighting is obtained with a small and light device but, in the discharge load, as one discharge lamp is lighted with two switching elements, there is a difficulty in the formation from the economic viewpoint and there has been a defect that the rate of utilization of the current source is not so high. The present invention has been suggested to eliminate the above mentioned defects of the conventional systems.

A main object of the present invention is to provide a highly economical discharge lamp lighting apparatus for two lamps which is small and light.

Another object of the present invention is to provide a discharge lamp lighting apparatus for two lamps high in the efficiency, rate of utilization of the current source and electric characteristics.

A further object of the present invention is to realize a discharge lamp lighting apparatus which is high in the traction of the switching element, small in the interrupting period of the lamp current and high in the moment.

The present invention shall be explained in the following with reference to the drawings, in which:

FIG. 1 is a circuit diagram showing a conventional example.

FIG. 2 shows an embodiment of the present invention.

FIGS. 3A to 3K show wave forms of respective parts in the embodiment of FIG. 2.

FIGS. 4 to 10 show other embodiments of the present invention.

FIG. 11 shows a practical embodiment of the present invention.

FIGS. 12A-12B and 13A-13C show wave forms for explaining the features of the present invention.

In FIG. 2 showing a discharge lamp lighting apparatus according to the present invention, a series circuit of a condenser 2 for charging and discharging, a discharge lamp 3, an SCR 4 in the normal direction to a direct current source 1 and an inductance 5 and a series circuit of an SCR 6 in the normal direction to the direct current source, an inductance 7, a condenser 8 for charging and discharging and a discharge lamp 9 are connected to both ends of the direct current source 1, and are wired so that a series circuit of the condenser 2 and discharge lamp 3 and a series circuit of the SCR 6 and inductance 7 will form a closed circuit and that a series circuit of the condenser 8 and discharge lamp 9 and a series circuit of the SCR 4 and inductance 5 will form another closed circuit and, at the same time, the output ends of a controlling signal device 10 having, for example, a nonstable multivibrator or the like as a main element to emit arc ignition signals alternately at a high frequency are connected to the controlling ends a and b of the respective SCR elements 4 and 6.

Now the operation of the apparatus of the present invention shall be explained with reference to FIGS. 3A to 3K.

In such apparatus as in FIG. 2, when the direct current source 1 is put in and such arc ignition signal T.sub.a as in FIG. 3A is given to the controlling end a of the SCR 4 at the time t.sub.1, the SCR 4 will ignite and conduct, a direct current voltage will be applied to the condenser 2, discharge lamp 3 and inductance 5, the discharge lamp 3 will begin to ignite and a current will flow through the condenser 2, discharge lamp 3, SCR 4 and inductance 5. This current will be made oscillatory by the inductance 5 and condenser 2, showing a sine wave form, and will form such inductance current I.sub.5 as in FIG. 3C, such tube current I.sub.3 as in FIG. 3E and such SCR current I.sub.4 as in FIG. 3G. If this current begins to be turned into a direction reverse to the current source 1 by the completion of the charge of the condenser 2 at a time t.sub.2 a little shorter than the time t.sub.3 at which an ignition signal T.sub.2 to the SCR 6 is generated, the SCR 4 will return to the stopping state and this current will be interrupted. At this time, in the condenser 2, such charged voltage V.sub.2 as in FIG. 3J in the illustrated polarity will appear. Then, at the time t.sub.3, when an ignition signal T.sub.b is given to the SCR 6, th SCR 6 will ignite and conduct, a sine wave form current will flow through the SCR 6, inductance 7, condenser 8 and discharge lamp 9 and a part of an inductance current I.sub.7 and such tube current I.sub.9 as in FIG. 3F will be formed. On the other hand, when the SCR 6 conducts, a discharge circuit of the discharge lamp 3 and inductance 7 will be formed through the SCR 6 in a conducting state at both ends of the condenser 2, the electric charge accumulated in the condenser 2 will be discharged into this circuit, will be added together with the current fed from the current source 1 to the inductance 7, such inductance current I.sub.7 as in FIG. 3D will flow, such tube current I.sub.3 in a direction reverse to that at the time of the conduction of SCR 4 as in FIG. 3E will be fed to the discharge lamp 3 and the current I.sub.6 flowing to the sCR 6 will be represented as a sum of the tube currents I.sub.9 and I.sub.3 as in FIG. 3H. In the oscillation period t.sub.4 of each current circuit, when the charge of the condencer 8 is completed, the discharge of the condenser 2 is completed and the current flowing to the SCR 6 begins to be turned into the reverse direction, the SCR 6 will return to the stopping state. Then, at a time t.sub.5, when an ignition signal T.sub.a to SCR 4 is generated, the SCR 4 will ignite and conduct, the tube current I.sub.3 in the normal direction will be fed to the discharge tube 3 from the electric source 1, the tube current I.sub.9 in the reverse direction by the discharge of the condenser 8 will be fed to the discharge lamp 9, thereafter such operation will be repeated and a since wave form alternating current of a high frequency will be fed to the discharge lamps 3 and 9.

In FIG. 4 showing another embodiment of the present invention, a series circuit of a condenser 2 for charging and discharging, discharge lamp 3 and SCR 4 in a direction normal to a direct current source 1 and a series circuit of an SCR 6 in a direction normal to the direct current source 1, condenser 8 for charging and discharging and discharge lamp 9 are connected to both ends of the direct current source 1 through an inductance 5, and inductance 7 is inserted so that the series circuit of the condenser 2 and discharge lamp 3 and the SCR 6 will form a closed circuit through the inductance 7 and that the series circuit of the condenser 8 and discharge lamp 9 and the SCR 4 will form a closed circuit through the inductance 7 and, at the same time, the output ends of a controlling signal device 10 emitting ignition signals alternately at a high frequency are wired to the gates a and b of the respective SCR elements 4 and 6.

This embodiment in FIG. 4 is substantially the same as the embodiment in FIG. 2 in the operation, but is different in the voltage and current of the choke coil itself due to the difference in the positions of the choke coils. That is to say, in the embodiment in FIG. 4, a charging current for the condenser always flows through one of the choke coils from the current source but, in the other choke coil, a discharging current from the condenser always flows and the current flowing into each choke coil is of a full wave rectified wave form and its peak is the same as the peak of the lamp current. On the other hand, in the embodiment in FIG. 2, sums of charging and discharging currents for a pair of condensers flow alternately to the respective choke coils, therefore, the frequency is one-half that of the embodiment in FIG. 4 and a current twice as large in the peak value flows into each choke coil. This difference is a problem of selection as to which of the embodiments in FIGS. 2 and 4 is more advantageous to the design, dimensions and weight of the choke coil.

However, as a matter of fact, in the embodiment in FIG. 2, a pair of choke coils can be coupled and the traction of the thyristor or SCR can be elevated to be higher. Further, it can be used also for a lighting apparatus by inserting a discharge lamp into the part of a bridge and is therefore adapted to practical uses.

In FIG. 5 showing another embodiment of the present invention, a series circuit of a diode 13 in a direction reverse to a current source 1 is formed by winding coupling coils 11 and 12 respectively on the inductances 5 and 7 in FIG. 1 and is connected to both ends of the current source 1.

A feature of this coil is that, if the discharge lamps 3 and 9 which are loads of the circuit are high pressure mercury lamps or the like and the impedance is low at the time of starting them, an excess current will flow through the circuit, therefore the terminal voltage of the condenser for charging and discharging and SCR will be likely to become very high, therefore, in case the voltage of the coils 11 and 12 tends to become a voltage higher than the current source voltage due to the excess current, a feedback current will be made to flow through the diode 13 so that the voltage of the coils 11 and 12 will be controlled to be below the current source voltage and the terminal voltage of SCR and condenser will be of a proper value.

In FIG. 6 showing another embodiment of the present invention, a resistance 16 is made common to the respective series circuits of a charging and discharging condenser and discharge lamp and a series circuit of the resistance 16 and a diode 14 and a series circuit of the resistance 16 and a diode 15 are provided in parallel. It is to form a bypass circuit for the current by the reverse charging voltage of the condenser so that the terminal voltage of the condenser and SCR will be prevented from becoming excess.

In FIG. 7 showing another embodiment of the present invention, the inductances 5 and 7 in the circuit in FIG. 2 are wound on the same iron core and are coupled. When two SCR elements 4 and 6 are simultaneously ignited to conduct by a misoperation, the circuit will be shortened so as to be very dangerous. In order to prevent it, when one SCR is conducting and a current is flowing also through the inductance in series with the conducting SCR, a reverse voltage will be impressed on the other SCR by the voltage induced in the inductance in series with the other SCR so that the other SCR will be prevented from being ignited.

In FIG. 8 showing another embodiment of the present invention, heated filament type discharge lamps are used for the discharge lamps 3 and 9 in FIG. 2 both filaments are connected respectively with condensers 14 and 15 so that the starting of the discharge lamps will be easy.

In FIG. 9 showing an embodiment of the present invention, both poles in the discharge lamps 3 and 9 in FIG. 4 are connected respectively with condensers 14 and 15 so that the starting of the discharge lamps will be easy.

In FIG. 10 showing another embodiment of the present invention which is effective in the cases that it is desired to obtain a load voltage of a voltage higher than a low current source voltage, to well match the source voltage and lamp voltage with each other, and to insulate the load, discharge lamps 3 and 9 are connected to the respective secondary sides of transformers 16 and 17 directly or through such reactances 18 and 19 as proper choke coils.

In FIG. 11 showing the most practical embodiment of the present invention, 22 is a discharge lamp lighting part, 21 is a rectifying part which rectifying an alternating current voltage of an alternating current source so as to be a direct current voltage and 20 is a pulse signal generating circuit applying pulse signals synchronized with the alternating current source alternately to the respective SCR elements 4 and 6. Now, the superiority of the traction of the SCR which is one of the greatest features of the present invention shall be described in the following with reference to FIG. 12.

That is, in the discharge lamp lighting apparatus for two lamps of the present invention (FIG. 12A), as the choke coil is inserted always in series with the SCR, the rise of the SCR voltage at the moment when the SCR on one side is in a conducting state, that is, at the time t.sub.2 or t.sub.6 in FIG. 12A, will be so slowly oscillatory that the SCR on the other side will not ingnite and conduct with steep dV/dt, further a negative voltage will be applied to the SCR during the illustrated time t, therefore a sufficient turn-off spare time will be given and the SCR will be turned off positively. On the other hand, if the choke coil is not inserted in series with SCR (FIG. 12B), the moment the SCR on one side is in a conducting state, a current source voltage E will be applied to the SCR on the other side, therefore, the dV/dt of t.sub.2 and t.sub.6 will be theoretically .infin., the SCR or any other switching element will be very likely to be ignited or broken by mistake, further there will be no spare time at all for a negative voltage to be applied to the SCR and, therefore, a time band (between t.sub.1 and t.sub.2 or between t.sub.5 and t.sub.6) in which both SCR elements are in a nonconducting state will be required.

In FIGS. 13A and 13B which are wave form diagrams in case the time band between t.sub.1 and t.sub.2 (t.sub.5 and t.sub.6) is eliminated, if the choke coil is not inserted in series with the SCR (FIG. 13B), the moment the SCR on one side is off, a normal voltage will be applied, therefore, the SCR will be on immediately, after all both SCR elements will be on and the circuit will be shortened. On the other hand, in the present invention, (FIGS. 13A), a reverse voltage will be applied during t and, therefore, the SCR will be positively turned off. Further, even if the period is contracted so that, while the SCR on one side is on, the SCR on the other side will be forcibly on, if the reverse voltage impressing time t (or t') is larger than the turn-off time of the element, the SCR will be able to be safely turned off.

The discharge lamp lighting apparatus according to the present invention is formed as mentioned above so that two discharge lamps will be lighted with a sine wave form alternating current of a high frequency by using two SCR elements. As one discharge lamp is lighted with one SCR element, it is much more economical in the formation than any conventional system wherein one discharge lamp is lighted by using two SCR elements by utilizing a series inverter. Further, as a choke coil is always inserted in series in each SCR element, if the period giving ignition signals to two SCR elements 4 and 6 and the period of the traction determined by the oscillation period of two oscillatory closed circuits formed by the ignition and conduction of the SCR elements 4 and 6 are well adjusted so that the traction period will be selected to be the same as or a little shorter than the ignition signal generating period, the input moment will be able to be made very high without producing a stopping section of the lamp current and the wiring capacity and the like will be improved and, further, when the frequency is taken to be high or, for example, higher than several hundred H.sub.z, the advantages of the high frequency lighting will be able to be obtained as they are, the wave form will be obtained as a sine wave form highly symmetrical above and below of an alternating current, there will be substantially no other part comsuming the electric power than the discharge lamps in the circuit and the luminous efficiency will be increased by the high frequency lighting. Thus a highly efficient discharge lamp lighting apparatus can be provided.

Claims

What I claim is:

1. A discharge lamp lighting device comprising the combination of

a. a first condensor and a first discharge lamp connected to each other to form a first series circuit,

b. a second condensor and a second discharge lamp connected to each other to form a second series circuit,

c. first electronic switching means having a control electrode and connected in series with said first series circuit,

d. second electronic switching means having a control electrode and connected in series with said second series circuit,

e. said first series circuit and said second switching means being connected to form a first closed loop,

f. said second series circuit and said first switching means being connected to form a second closed loop,

g. a power source connected in parallel with the series arrangement of subparagraph (c) and with the series arrangement of subparagraph (d),

h. a pair of inductors connected in series with each other and in parallel with said power source,

i. and a control signal source connected to the control electrodes of said first and second switching means for applying input signals alternately to said control electrodes to alternately render said first and second switching means conductive and thereby alternately charge said first and second condensors from said source and through said first and second discharge lamps, the accumulated charges in said condensors being alternately discharged through said discharge lamps to light the same whenever the switching means connected in series with one of said discharge lamps is not conductive.

2. A discharge lamp lighting apparatus according to claim 1 wherein each of said inductors is provided with a coupling coil, said coupling coil being connected in series with said power source through a diode which has a direction reverse to that of said power source.

3. A discharge lamp lighting apparatus according to claim 1 wherein said first and second series circuits are connected in parallel through a common resistor to a diode which has a direction reverse to that of said power source.

4. A discharge lamp lighting apparatus according to claim 1 wherein said inductors are provided on a common core.

5. A discharge lamp lighting device as set forth in claim 1 wherein said first series circuit forms a closed loop with a series circuit comprising said second switching means and one of said inductors, and said second series circuit forms a closed loop with a series circuit comprising said first switching means and the other of said inductors.

6. A discharge lamp lighting device as set forth in claim 1 wherein one of said inductors is connected between said power source and said series arrangements connected in parallel with said power source, and the other of said inductors is connected between the connection of said first series circuit with said first switching means and the connection of said second series circuit with said second switching means.

7. A discharge lamp lighting apparatus according to claim 1 wherein each of said first and second discharge lamps is provided with a condenser connected between the respective filaments of said discharge lamp.