CA1040702A - Arrangement provided with a gas and/or vapour discharge lamp - Google Patents

Abstract

ABSTRACT

A circuit arrangement for supplying alternating cur-rent to an electric discharge lamp has a pair of input ter-minals for connection to an alternating voltage source and a series arrangement of a stabilizing inductor and lamp being connected across the input terminals. A circuit consisting of a semiconductor switch is connected in shunt with the lamp and a control circuit is provided for triggering the semi-conductor switch. This control circuit is coupled to a con-trol electrode of the semiconductor switch and includes a branch having an element with a relatively short time con-stant such that the switch is triggered on and off at least several times during every second half cycle of the alternat-ing voltage source. This arrangement operates in the operating condition of the lamp and, together with a stablilizing ballast, generates voltage peaks which ensure rapid reignition of the lamp at each half cycle of the alternating current supply.

Description

~04070Z
The invention relates to an arrangement provided with a gas and/or vapour discharge lamp, which arrangement is intended for supplying said lamp from an alternating voltage source in which two input terminals of the arrangement are connected by a series arrangement of at least a stabilizing inductor and the lamp and in wh1ch the lamp is shunted by a circuit comprising a controlled semi-conductor switch, while in the operating condition - lO of the lamp the semi-conductor switch is rendered conducting through a control circuit at least every `; second half cycle of the alternating voltage source.
~ "Every second half cycle" means: every odd ; - half cycle or every even half cycle.
A known arrangement of the above-mentioned type is described, for example, in United States Patent Specification 3,310,687. A drawback of this ; known arrangement is that the semiconductor switch is a "triac". In triacs likewise as in thyristors, the non-conducting state of this semiconductor switching element can only be achieved when the current flowing therethrough comes below a low hold current value. In circuits for discharge lamps in which a stabilizing inductor is arranged in series with the lamp a voltage peak cannot be generated in a simple `:
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manner with the combination of this inductor and such kinds of triac. To this end more circuit elements are required. This is because the said instant of the switch becoming non-conducting (substantially at zero crossing of the current) is very unsuitable to realize a voltage peak.
An obiect of the invention is to realize voltage peaks across the lamp in an arrangement according to the kind described in the preamble in a simple manner when the semiconductor switching element becomes non-conducting. Such voltage peaks have the advantage that re-ignition of the lamp, during further half cycles of the supply, can easily take place. A further advantage may be that the operating voltage of the lamp may be chosen to be so high that the ratio between the effective value of the mains voltage and said operating voltage may be in the order of 1,5. Another possibility is that if, for example, by switching on some other users in the ambiance, the available supply voltage suddenly becomes lower that when voltage peaks can still be produced across the lamp which maintain a small ionisation current in the lamp. In case of recovery ; of the supply voltage the lamp is then immediately ~ 25 ignited again.

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PHN 69~2 According to the invention an arrangement provided with a gas and/or vapour discharge lamp, which arrangement is intended for supply of said lamp from an alternating voltage source in which two input terminals of the arrangement are connected by a series arrangement of at least a stabilizing inductor and the lamp and in which the lamp is shunted by a circuit comprising a controlled semi-conductor switch and in which in the operating condition of the lamp the semiconductor switch is rendered conducting through a control circuit at least every second half cycle (every odd half cycle or every even half cycle) of the alternating voltage , source is characterized in that the controlled semi-conductor switch can be switched off with the aid of a control voltage on a control electrode of said switch and that the control circuit of said semiconductor switch includes a branch having such a short time constant that the switch becomes at least several times conducting and non-conducting during each of the said half cycles of the alternating voltage source.
An advantage of such an arrangement according to the invention is that every time when the semi-~ conductor switch becomes non-conducting a voltage ;~ 25 peak is generated with the aid of the stabilizing inductor, which peak enhances the achievement of a quick reignition of the lamp.

The semiconductor switch may be, for example, a silicon controlled switch (S.C.S.). It is likewise feasible that the semiconductor switch is another switching element, for example, a transistor.
S It is feasible that in the circuit shunting the lamp two transistors are present which are arranged anti-parallel. One transistor is then used during the odd half cycles of the supply mains (alternating voltage source) and the other transistor is used for the intermediate half cycles. These tran-sistors may then be each equipped with their own control circuit. These control circuits then include, for example, diodes whose pass directions correspond to those of the relevant translstors.
In a preferred embodiment of an arrangement according to the invention in which the semiconductor switch is a transistor the circuit shunting the lamp includes a rectifier bridge in which the main electrodes of the transistor are incorporated in the central branch of this rectifier bridge.
An advantage of this preferred embodiment is that only one controlled semiconductor rectifier, namely one transistor is required. An advantage is that the conducting and non-conducting state during the odd half cycles hardly deviate from those during the even half cycles of the supplying mains voltage.
' ~ ~040702 This would - with the arrangement using two transistors -only be possible if these transistors had been selected for corresponding properties.
In a further preferred embodiment according to the invention the control circuit of the tran-sistor consists of a series arrangement of a first resistor and a capacitor as well as a breakdown element and a second resistor in which the series arrangement of the first resistor and the capacitor shunts the transistor and in which the base of the transistor is connected through the breakdown element to the connection of the first resistor and the capacitor, while the second resistor connects the base and a main electrode of the transistor together.
An advantage of this preferred embodiment is that this leads to a very simple control circuit.
The discharge lamp may be, for example, a low-pressure mercury vapour discharge lamp. By gene-- rating voltage peaks during the operating condition ~, 20 of the lamp the operating voltage of this lamp may be chosen to be so high that the ratio between the effective value of the mai,ns voltage (alternating voltage source) and said operating voltage may be less than 1.7, namely in the order of 1.5. An advantage thereof is that either the wattage of the lamp may be relatively high or a given lamp may also be operated on a mains of relatively low voltage.

It is to ~en40ted7that it is known to choose the operating voltage of a discharge lamp to be re-latively high, that is to say, only slightly lower than the voltage of the supplying mains by using a second supply source having a higher frequency.
To this end see, for example, published Netherlands Patent Application number 6,408,592. A drawback of this known arrangement is, however, that actually a second voltage source is to be present. In an arrangement according to the invention, however, the high-frequency voltage is generated by means of rapidly successive short-lasting short circuits of the lamp.
A second voltage source is then not necessary.
In a further preferred embodiment according to the invention in which the lamp is a low-pressure sodium vapour discharge lamp the stabilizing inductor consists of a choke.
An advantage of this preferred embodiment is that the ballast of this lamp is very simple.
In known low-pressure sodium vapour discharge lamps the ballast is generally formed as a leakage trans-former. This has been done, inter alia, to make available the required relatively high voltage for re-ign~tion of the lamp during each half cycle of the mains. In the said preferred embodiment these re-ignitions are effected with the aid of the voltage peaks realized by the semiconductor switch in combi-` nation with the choke. The ballast is then simple.

~ PH~ 6932 It will be evident from the foregoing that with the aid of the invention the operating voltage of a discharge lamp may be chosen to be higher on the one hand, which means that for the same mains S voltage a discharge tube of higher wattage could be made, while on the other hand the stabilizing ballast might be simpler and hence cheaper.
In a further preferred embodiment according to the invention in which the lamp is a high-pressure discharge lamp the arrangement is also provided with a thyristorstarter for the first ignition of the lamp.
An advantage of this preferred embodiment is that a reliable first ignition of the lamp can be accompanied by a less great sensitivity to sudden ~ mains voltage decreases in the operating condition ;; of the arrangement. When a sudden mains voltage decrease occurs, for example, when switching on several other users the lamp will not completely extinguish but will remain operating at the voltage ~ peaks generated with the aid of the semiconductor ; switch. This has the advantage that after the occurrence of the short-lasting mains voltage decrease it is not necessary to wait until an extinguished lamp has cooled down before its reignition.
The invention will be described in greater . ~
detail with reference to a drawing.
Figure 1 shows an electrical circuit of a ; first arrangement according to the invention.

Figure 2 shows an ele~trical circuit of a second arrangement according to the invention~
In Figure 1, 1 and 2 are connection terminals which are intended to be connected to an alternating voltage mains of, for example, 220 Volt, 50 Hz.
The terminal 1 is connected through an inductor 3 formed as a choke to an electrode 4 of a discharge lamp 5. The lamp 5 is a low-pressure sodium vapour discharge lamp. Details of this lamp such as, for example, an outer envelope encompassing the discharge tube are not shown in the Figure. The input terminal 2 is connected to an electrode 6 of the lamp 5. The elec-trode 4 of the lamp 5 is connected to an input terminal 7 of a diode bridge. Diodes 9 to 12 form part of this bridge. The elèctrode 6 of the lamp 5 is connected to an input terminal 8 of the said diode bridge.
The central branch of the diode bridge 9 to 12 incor-porates a transistor 13. This transistor is of the npn-type. The transistor is provided with a control circuit. This circuit consists of an input circuit constituted by a series arrangement of a resistor 14 and a capacitor 15, which series arrangement shunts the transistor 13. The base of the transistor 13 is connected through a diac 16 to a junction between the resistor 14 and the capacitor 15. In addition the base of the transistor is connected through a -~ resistor 17 to the emitter of the transistor 13.

g ; PHN 6932 ~04070i2 The operation of the described circuit is as follows. When the terminals 1 and 2 are connected to the alternating voltage source the capacitor 15 is charged through the circuit 1, 3, 9, 14, 15, 11, 8, 2 and 2, 8, 10, 14, 15, 12, 7, 3, 1 until the breakdown voltage of the diac 16 is reached. If this breakdown voltage is reached the voltage on the base of the transistor 13 becomes so high that the transistor 13 becomes conducting. Subsequently a relatively high current flows through this transistor. The capacitor 15 is then discharged, inter alia, partly across res~stor 17.
As a result the diac 16 shortly thereafter resumes its non-conducting state. The transistor 13-is then also ~;;j cut off. By cutting off the transistor 13 a voltage ` 15 peak is generated with the aid of the inductor 3, ; which peak will be present between the electrodes 4 and 6 of the lamp 5. The control circuit of the tran-, sistor 13 is proportioned in such a manner that such voltage peaks occur a number of times per half cycle of the supply mains. The lamp 5 then ignites. In the operating condition of the lamp the transistor auxiliary arrangement 7 to 17 remains operative and this because - the control circuit 14 to 17 of the transistor also `; remains operative at the operating voltage of the lamp 5. Thus peaks are always generated between the electrodes of the lamp 5. These peaks ensure that the ~ lamp re~gnites early in a half cycle of the mains ,.:
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_ PHN 6932 voltage. In a known arrangement the inductor is formed as a leakage transformer. The choke 3 in the embodiment shown is much cheaper.
In one embodiment of the circuit of Figure 1 the wattage of the lamp 5 was approximately 55 Watts and the operating voltage of this lamp was approximately 107 Volt. The resistors 14 and 17 had values of 18 k.Ohm and 100 Ohm, respectively. The capacitance of capacitor 15 was approximately 4.7 nF. The threshold voltage of the diac 16 was approximately 35 volt. In this case the frequency of the voltage peaks generated with the aid of the transistor 13 was approximately 15 to 20 kHz.
The height of these peaks was approximately 800 Volt during stàrting of the lamp. In the operating condition of the lamp the height of the voltage peak was also determined by the extent to which the contents of the discharge tube of the lamp were ionized at that instant.
This also meant that right after a zero crossing of the lamp current the then occurring voltage peak was relatively high, but generally lower than the said 800 Volt. The lamp then reignited easily at this relatively high voltage peak.
In Figure 2, 21 and 22 are connection terminals which are again intended for connection ; 25 to an alternating voltage source of, for example, 220 Volt, 50 Hz. The terminal 21 is connected to a stabilizing inductor 23. The other side of this ~040702 conductor is connected to a discharge lamp 24.
This is a high-pressure mercury vapour discharge lamp of approximately 400 Watts having an operating voltage of approximately 135 Yolts. The input terminal 22 is connected to another electrode of the lamp 24.
A starter (thyristor-starter) for the lamp 24 is connected to the connection between the inductor 23 and the lamp 24. Another input terminal of this starter is connected to the connection of the lamp 24 and the terminal 22. Furthermore the lamp 24 is shunted by a second auxiliary circuit comprising a diode bridge 25 to 28, inter alia, a transistor 29.
The starter includes a series arrangement of a capacitor 30l, a thyristor 31 and a diode 32 ` lS cbnnected antiparallel thereto, and a resistor 33.
A Zener diode 34 is arranged between the control electrode and the anode of the thyristor 31.
Furthermore the diode 32 is shunted by a series arrangement of a resistor 35 and a capacitor 36.
The combination of the diode 32 and the capacitor 30 is also shunted by a resistor 37.
In the further auxiliary arrangement which is provided with the transistor 29 a control circuit of this transistor is also present. This control circuit consists, inter alia, of a series arrangement of a resistor 40 and a capacitor 41. The series arrangement 40, 41 shunts the transistor 29.
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The base of the transistor 29, which is of the npn type, is connected through a disc 42 to a junction between the resistor 40 and the capacitor 41.
In addition the base of the transistor 29 is connected to the emitter of this transistor through a resistor 43.
This control circuit of the transistor 29 is sub-stantially equal to that of the transistor 13 in Figure 1 also as regards proportioning of the circuit elements. The circuit section constituted by the ; 10 terminals 21 and 22 and the inductor 23 and the lamp 24, as well as the circuit elements 30 to 37, are known from our Canadian Patent 896,070 which issued on March 21, 1972. The novel aspect in the circuit of Figure 2 is the addition of the section constituted by the auxiliary arrangement with the elements 25 to 29 and 40 to 43.
The operation of the described circuit is as follows. Initially the influence of the circuit ; elements 35 to 38 is left out of consideration. When the terminals 21 and 22 are connected to the alternating voltage source, the capacitor 30 will be charged through the resistor 33 and the diode 32, during the next half cycle in which the terminal 22 is positive relative to the terminal 21. During the next half cycle in which ; the terminal 21 is positive relative to the terminal 22 the capacitor 30 will initially not be discharged.
This is effected when the instantaneous value of the mains voltage has become so high that together with the voltage across the capacitor the threshold voltage of - 13 - ~--.~ .

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~ PHN 6932 the Zener diode 34 has been reached. Then the thyristor 31 will be rendered conducting. The capacitor 30 will then be discharge and subsequently charged to a negative value. Subsequently the thyrlstor 31 will become non-conducting (because its current becomes zero) and the capacitor 30 will be charged again through the diode 32. This process might be repeated one or more times dùring the same half cycle. This is dependent, inter alia, on the choice of the threshold voltage of the Zener diode 34 and on the value of the other circuit elements such as the resistor 33. The capacitor charges and discharges obtained in the manner described produce high voltage peaks across the series arrangement 33, 31/32, 30, which peaks will be present across the electrodes of the discharge lamp 24. This lamp 24 is then ignited. However, if this lamp might not be immediately ignited, one or more voltage peaks are generated again during a subsequent half cycle.
When the lamp 24 is ignited as a result of the generated voltage peaks, the discharge is maintained by the available mains voltage. After ignition of the lamp 24 the voltage across the bridge 30, 31, 32, 33 decreases to the operating voltage of the lamp.
The Zener diode 34 is proportioned in such a manner that at this operating voltage the control electrode .
of the thyristor 31 no longer receives any control pulses. The impedance 23 then serves for stabilizing ~ PHN 6932 , ~ .
1~40702 ,~ the discharge in the iamp 24. The resistor 33 serves for limiting the current through the thyristor 31 during the ignition process.
The resistor 38 has for-its obiect to prevent the thyristor 31 from becoming conducting as a result of the voltage pulses during the operating condition of the ~amp 24. The series arrangement of the capacltor 36 and the resistor 35 serves to maintain the thyristor 31 non-conducting when quick voltage variations might occur durlng the operating condition of,the lamp 24. The resistor 37 serves to discharge the capacitors 30 and 36 in the case where the starter (30 to 37) is removed from the holders.
During the ignltion process of the lamp 24 the auxiliary arrangement provlded with the transistor 29 also becomes operative. In a corresponding manner as in the circuit of Flgure 1 the transistor 29 then becomes conducting for a short time at a quick rate and is then rendered non-conductlng again. The auxiliary arrangement 25 to 39 and 40 to 43 has. however, hardly any influence,on the ignition process of the lamp 24.
This auxiliary arrangement is mainly important for ,' the sltuation whlch ls obtained after the lamp 24 is ignited. The control circuit 40 to 43 of the translstor 29 is proportloned in such a manner that it also remalns active at the operating voltage of the lamp 24.

~ ~ PHN 6932 All this leads to the fact that in the normal operating condition of the lamp 24 high voltage peaks are always generated across the lamp 24 by the combination of the`inductor 23 and the transistor 29.
These peaks are particularly important when for some reason or other the voltage between the terminals 21 and 22 would decrease to below the normal value. If that happened, there would be the risk that the lamp extinguishes when this mains voltage decrease would be as far as below the operating voltage of the lamp. The auxiliary arrangement 25 to 29 and 40 to 43 will then, however, remain active for a still longer time, that is to say, also at these large mains voltage decreases, so that voltage peaks are still maintained across the lamp 24 and hence small currents continue to flow through the lamp. As a result a certain ~. .
j ionisation will be maintained in the internal part of the discharge tube of this lamp. If then a short-lasting mains voltage decrease is over, the lamp reignites immediately and exhibits the original ~; lumen value. The addition of the auxiliary arrangement 25 to 29 and 40 to 43 is thus mainly important in the circuit of Figure 2 to obviate detrimental influences of short-lasting mains voltage decreases as much as possible. Furthermore the voltage peaks ~04~)~QZ
generated with the aid of this auxiliary arrangement enhance the quick reignition of the lamp 24 during each half cycle of the supplying alternating voltage in the normal operating condition of the lamp of Figure 2.
In the arrangements of Figure 1 and 2 the total time of a transistor being conductive during a half cycle of the supplying mains was only approximately 1 ~ of the total duration of this half cycle. This meant that the lamps 5 and 24 were short-circuited for approximately 1~ of the duration.
This therefore had hardly any ihfluence on the lumen value of these lamps.
It is, however, feasible that, for example, the resistor 14 in Figure 1 or the resistor 40 in Figure 2 is replaced by a variable resistor so that the ; time of the transistors 13 and 29 being conducting can be made relatively longer. It is then achieved that in these arrangements also dimming of the lamps 5 and 24 becomes possible.
; If desired the resistor 40 may be replaced by a resistor having a negative temperature coefficient (NTC resistor). This may be done, for example, to ; cause the transistor auxiliary arrangement to become active in a delayed manner only after the first ignition of the lamp 24 by the thyristorstarter. The risk of influence on the operation of the thyristorstarter PH~ 6932 ~04070Z
by the transistor auxiliary arrangement can then be further reduced.
The combination of the diode bridge, the transistor and the control circuit of the transistor can be accommodated in a relatively small space which as regards contents and shape may be the same as that of a glow discharge starter for a low-pressure mercury vapour discharge lamp.
Further modifications of the control circuits of the transistors are of course feasible.
It is likewise feasible that with a transistor auxiliary circuit not only one but two or more discharge lamps are operated. This might be done, for example, by incorporating an isolation lS capacitor in a number of the connections between `3 a lamp electrode and the transistor auxiliary circuit.
In a further embodiment (not shown) of an arrangement according to the invention a low-pressure mercury vapour discharge lamp of 40 Watts in series with a choke was used. This series arrangement was connected to an alternating voltage source of lS0 Volt, S0 Hz. The operating voltage of the lamp was approxi-mately 103 Volt. This lamp was furthermore shunted by a transistor auxiliary circuit as denoted by the reference numerals 7 to 17 in Figure 1.
In the embodiment described in the previous paragraph the ratio between the effective mains voltage and the operating voltage of the lamp was 55 = approximately l.S.
The low-pressure mercury vapour discharge lamp of this embodiment operated in a stable manner.

Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A circuit arrangement for supplying alternating current to an operating electric discharge lamp comprising, a pair of input terminals for connecting said lamp to an alternating vol-tage source, means connecting a series arrangement of at least a stabilizing inductor and the lamp across said input terminals, means connecting a circuit comprising a controlled semiconductor switch in shunt with the lamp, a control circuit for triggering the semiconductor switch into conduction at least once every second half cycle of the alternating voltage source in the normal operating condition of the lamp, the control circuit being coupled to a control electrode of the controlled semiconductor switch for applying a switch-off control voltage to the control electrode of said switch, and wherein the control circuit of said semiconductor switch includes a branch having an element with a relatively short time constant such that the switch is triggered on and off at least several times during each of said second half cycles of the alternating voltage source.

2. An arrangement as claimed in Claim 1 in which the semiconductor switch is a transistor, characterized in that the circuit shunting the lamp includes a rectifier bridge, the main electrodes of the transistor being incorporated in a central branch between out-put terminals of said rectifier bridge.

3. An arrangement as claimed in Claim 2, characterized in that the control circuit of the transistor consists of a series arrangement of a first resistor and a capacitor, as well as a breakdown element and a second resistor, the series arrangement of the first resistor and the capacitor shunting the transistor, the base of the transistor being connected through the breakdown element to the connection of the first resistor and the capacitor and the second resistor connecting the base and a main electrode of the transistor together.

4. An arrangement as claimed in Claim 1, 2 or 3, in which the lamp is a low-pressure sodium vapour discharge lamp, characterized in that the stabilizing inductor is a choke.

5. An arrangement as claimed in Claim 1, 2 or 3, in which the lamp is a high-pressure discharge lamp characterized in that the arrangement is also provided with a thyristor-starter for the first ignition of the lamp.

6. An arrangement as claimed in Claim 1, 2 or 3, char-acterized in that the ratio between the operating voltage of the lamp and of the effective value of the voltage of the al-ternating voltage source is more than .

7. An auxiliary arrangement particularly suitable to serve as that part of an arrangement as claimed in Claims 1, 2 or 3, provided with the circuit comprising the controlled semiconductor switch, characterized in that the auxiliary arrangement includes a rectifier bridge and that the semicon-ductor switching element is formed as a transistor, which tran-sistor is present in a central branch between out-put terminals of the rectifier bridge and in which a series connection of a resistor and a capacitor is arranged in parallel with the tran-sistor, a junction of the said resistor and the capacitor being connected to the base of the transistor through a breakdown ele-ment having a breakdown voltage of less than 100 Volt.