Note: Descriptions are shown in the official language in which they were submitted.
r 7 ,~ ) ~ , r-.
PIIN 7~9~
]~I
9-1-197~
~D71297
.
"Device for starting and feeding a discharge lamp".
The invention relates to a device for starting
and feeding a gas - and/or vapour discharge lamp which is
provided with two electrodes, the device being provided
with two input terminals which are intended for connection
to an AC voltage source, whose frequency is less than
100Hz, the two input terminals- during starting and feeding
of the lamp- being interconnected by means of a series cir-
cuit of at least a stabilizing inductor, and the lamp,
whilst the two lamp electrodes are interconnected by a
starter comprising a first semiconductor switching element,
whilst parallel to a branch which comprises said semiconduc-
tor switching element a control circuit of the first semi-
conductor switching element is provided, this control cir-
cuit comprising at least a first capacitor~ an auxiliary
transistor of the starter shunting at least the first ca-
~ pacitor, whilst the ~ase of the auxiliary transistor is
connected to a control circuit, namely to a junction of a
first resistor and a second capacitor which aPe connected
in series and which are parallel-to the branch comprising
the first ~emiconductor switching element.
A known device of the said type is for example
shown in Fig. 1 of United States Patent 3.875.459. An ad-
vantage of that k~own device is that, if the lamp refuses
to ignite the auxiliary tranqistor stops, after a given time,
the efforts to start the lamp. However, a ~isadvantage of
that kno~T~ device is that the voltage peaks which are
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generated to start the discharge lamp therewith, show a
relatively large and fairly constant amplitude. This en-
tails, namely, that the first semiconductor switching
element must be able to withstand these voltage peaks in
its non-conducting state.
A further disadvantage of that known device is
that, if the relatively large amplitude of the voltage peaks
is still too small to start the discharge lamp the lamp
will not ignite.
- 10 An object of the invention is to provide the
possibility for a device of the above mentioned type to
rate the first semiconductor switching element for a
relatively low, permissible blocking voltage of a somewhat
longer duration; but, furthermore, if the lamp is difficult
~ 15 to start to generate one or a few brief voltage peak~:s) of
-~ a large amplitude.
A device according to the in~-ention for starting
and feeding a gas - and/or vapour discharge lamp which is
provided with two electrodes, the device being provided
i 20 with two input terminals which are intended for connection
.~ to an AC voltage source whose frequency is less than lOOHz,
the two input terminals~ during s~tarting and feeding of the
~. lamp - being interconnected by means of a series circuitt7 comprising at least a stabilizing inductor and the lamp,the two lamp electrodes being interconnected by means of a
starter comprising a first semiconductor switching element,
whilet a control circuit of the first semiconductor switch-
ing element is provided~ in parallel to a branch which
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P~rN 7892
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~0712g7
comprises said semiconductor switching element, this con-
trol circuit comprising at least a first capacitor~ an
auxiliary transistor of the starter, shunting at least the
first capacitor, whilst the base of the auxiliary transis-
tor is connected to a control circuit, namely to a junction
of a resistor and a second capacitor which are connected in
series and which are in parallel to the branch comprising
the first semiconductor switching element, is characterized
in that the base of the auxiliary transistor is connected
via a voltage-sensitive threshold element to the junction
! of the resistor and the second capacitor and that the lamp
! electrodes are connected by means of a third capacitor and
¦ that a second inductor is included in the connection of
1 the lamp electrodes to the first semiconductor switching
¦ 1~ element.
~¦ An advantage of this device is that, by means
of the voltage-sensitive threshold element incorporated
in the control circuit of the auxiliary transistor, the
instant at which the first semiconductor switching element
~' 20 starts conducting - a short while a~ter the device has
been switched on - can be influenced. This enables in-
fluencing the degree to which the voltage between the lamp
, electrodes can be raised during the starting of the lamp.
c This in~luence is such that the instant at which the first
j 25 semiconductor switching element starts conducting is some-
i what delayed, so that the rise in voltage across the serie
`' circuit of the third capacitor and the second inductor, -
p~ 7892
--~ 9-1-1976
~7~Z97
and consequently the voltage across the lamp which is made
available for starting - is increased.
So the invention i9 in fact based on the idea
to use the auxiliary transistor - when the lamp definitely
refuses to ignite - not only for stopping the attempts to
star$ the lamp by short circuiting the first capacitor, but
also to use that auxiliary transistor during the starting
procedure of the lamp. This i9 effected by rendering that
auxiliary transistor conductive one or more times for a
short period before the end of the starting procedure, so
that charging the first capacitor in the control circuit of
the semiconductor switching element is counteracted. This
implies that it lasts longer before the said first capacitor
has obtained such a voltage that the se~iconductor switching
element can be made conductive therewith. As observed be-
fore, this delay results in a larger rise of the voltage
across the lamp.
I~owever, it takes some time aft0r the device
has been switched on, for the auxiliary transistor to start
conducting. The reason is the presence of the voltage-
sensitive threshold element in the control Tcircuit of the
auxiliary transistor. If, after some time the second capa-
citor is charged to such an extent~hatit causes the auxiliary
transistor to become conductive, the delay in making the
first semiconductor switching element conductive becomes
operative.
As far as the rise in voltage across the discharge
lamp - in the starting procedure - is concerned, it should
l'l~ 78~2
9~1-197~
~6~71Z97
be notod that this is known ~er se from British Patent
Specification 1.208.489. In that case, however, the in-
stant the semiconductor switching element is made conduc-
tive is not variable.
The discharge lamp may, for example, be a lamp
which is not provided with preheatable electrodes, for
example a high pressure metal vapour discharge lamp.
The discharge lamp is preferably a lamp pro-
vided with preheatable electrodes, for example a low-
pressure mercury vapour discharge lamp. The current which
then flows through the semiconductor switching element
during the starting procedure can then also be used to
preheat the lamp electrodes.
The first semiconductor switching element con-
1~ sist~, ~or example of two thyristors which are connected in
anti-parallel. The first semiconduc-tor switching element
may also be~ for example, a "triac" i.e. a semiconductor
switching element having a bidirectional thyristor character-
j istic.
In a preferred embodiment of a device according
to the illvention a diode bridge is included between the lamp
electrodes and the first semiconductor switching element,
-
i this semiconductor switching element being a transistor
which is located in a centre branch of that diode bridge.
2~ An advantage of this preferred embodiment is
that only a simple eemiconductor switc~ing element is re-
quired and that furthermore a n~ber of small voltage peaks
can be produced across the lamp during each hal~ cycle of
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PIIN 78~2
9-1-197
:
11~)7~297
.
the supply voltage.
The voltage-sensitive threshold element in the
control circuit of the auxiliar-y transistor may, for
example, be a neon glow discharge lamp,
.5 In a further preferred embodiment of a device
according to the invention the voltage-sensitive threshold
; element is a first zener diode.
¦ An advantage of this preferred embodiment is
! that, for example, the threshold voltage of the threshold
~ 10 element varies only little in the course of time.
¦ In a following preferred embodiment according to
the invention the control circuit of the auxiliary transis-
~ tor comprises a series connection of 7 in this sequence,
J the resistor, a first diode, a first zener diode and a
i 15 fourth capacitor the pass directions of the first diode
¦ and the zener diode pointing, to one another, the series
. circuit of the first diode the first zener diode and the
fourth capacitor, being shunted by a series circuit of
a second resistor and the second capacitor, whilst the
second capacitor and also the fourth capacitor are each
shunted by a resistor.
An advantage of the last-mentioned preferred
device according to the invention i9 that by means of this
special control circuit for the auxiliary transistor it is
ensured that the auxiliary transistor can be switched to
the conducting and non-conducting state various times dur-
ing each half cycle of the supply voltage. This is caused
inter alia by the fact that now the second capacitor can
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P~IN 7892
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1C17~;~97
fir9t be charged via the first and the second resistor,
whereafter this second capacitor makes the auxiliary transis-
tor conductive via the first diode and the blocl~ing direct-
ion of the first zener diode. Owing to the fact that the
voltage across the branch which comprises the first semi-
conductor switching element shows an oscillation the
voltage across the series circuit of the second resistor and
the second capacitor will fall shortly thereafter to below
the threshold voltage of the first zener diode. As a result
~ 10 the auxiliary transistor becomes non-conductive. As the
¦ frequency o~ the ~orementioned voltage across the branch
which contains the first semiconductor element is as a
rule higher than the frequency of the main supply it is
I pos~ible to repeat the procedure9 outlined above, for
i 15 switching the auxiliary transistor to the conducting and
~ non-conducting state several times each half cycle of the
! main supply.
¦ The last-mentioned preferred embodiment may
be further improviiSd by adding, to the ~ntrol circuit of
the auxiliary transistor, a non-capacitive voltage divider
which is connected in parallel to the branch which com-
prises the first semiconductor switching element~ whilst
the tap of a voltage divider is connected via a second
diode to the junction of the first diode and the zener
diode~ the pass direction of the second diode pointing to-
wards the last-mentioned junction.
An advantage of this last improvbment is that
if the voltage across the first semiconductor switching
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~l~ 7892
9-1-197~
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element would attain a high value very rapidly, a current
will flow via the non-capacitive voltage divider and the
second diode into the blocking direction of the zener diode
which will rapidly make the auxiliary transistor conductive.
The first capacitor is then practically short-circuited
which prevents the first semiconductor ~witching element
from becoming conductive again. Namely if the first semi-
i conductor switching element, constructed as an auxiliary
transistor, would become conductive at that instant, this
might be disastrous at such a high voltage across its main
electrodes.
In a further preferred embodiment of a device
according to the invention a second voltage-sensitive
threshold element is connected in the branch which con-
tains the first capacitor and which is connected in
parallel to the first semiconductor switching element.
An advantage of this preferred embodiment is
that, quite irrespectiveof the auxiliary transistor and its
control circuit, a delay in the instant the first semicon-
ductor switching element becomes conductive is already ob-
talned by means of the second voltage~sensitive threshold
element, which results in a somewhat higher rise of the
voltage across the lamp. A further advantage of the second
voltage-sensitive threshold element is that this element
is also used to interrupt the starter operation as soon as
the lamp has been started. For that purpose the threshold
voltage must be above the operating voltage o~ the discharge
lamp.
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78~2
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~071297
l`he invention will be further explained with
reference to a drawing in which:
Fig. 1 shows an el0ctrie cireuit of a device
aeeording to the invention together with a diseharge lamp
incorporated in that circuit;
Fig~ 2 shows a graphic representation of the
envelope of the voltage peaks between the electrodes of the
lamp of Fig. 1 as a function of time.
In Fig. 1 references 1 and 2 are terminals for
connection to an AC voltage source of 220V, 50 Hz. An in-
ductive stabilization ballast 3 is connected to terminal
1. If desired a capacitive ballast consisting o~ a series
circuit of a coil and a capacitor, having in total a capa-
citive character may also be used. The other side of ballast
3 is connected to a preheatable electrode ~ o~ a low-pressure
mercury vapour discharge lamp 5. Reference 6 indicates a
, second preheatable electrode of lamp 5. Electrode 6 is
! connected to the input terminal 2. The ends of the electrodes
' -- 4 and 6 nearer to the input terminals 1 and 2 are inter-
¦ 20 connected by means of a capacitor 7. The other ends of the
eleetrodes ~ and 6 are intereonnected by means of a eapacitor
8, In its turn this capacitor 8 is shunted by a series
I eircuit of an induetor 9 and a diode bridge 10 to 13. This
i diode bridge comprises four eentre branches:
The first centre branch comprises a series cir-
cuit of a resistor 20~ a trans~ormer winding 21 and the
main electrodes of an NPN transistor 22. Another winding
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_ rTIN 7~92
107~L297 9.1 -1976
23 of said transformcr is connected between the base and the
emitter of` the transistor 22.
The second centre branch of the diode bridge 10
to 13 comprises a series circuit of a resistor 24~ a ~ener
diode 25 and a capacitor 26. A node between the zener diode
25 and the capacitor 26 is connected to a resistor 27. The
other side of resistor 27 is connected via a bidirectional
breakdown element 28 to the base of the transistor 22. A
resistor 29 is connected between the base and the emitter of
the transistor 22. A load between the resistor 27 and the
breakdown element 28 is connected to the collector of an
NPN-type auxiliary transistor 30. The emitter of this auxilia-
ry transistor 30 is connected to the diodes 12 and 13 of the
diode bridge.
A third centre branch of' the diode bridge
comprises a series circuit of a resistor 31, a first diode
32, a zener diode 33 and a capacitor 34. The capacitor 34
is shunted by a resistor 35. Furthermore~ the series
- circuit 32, 33, 35 is shunted by a series circuit of a
resistor 36 'in series with a parallel circuit of a capaci-
tor 37 and a resistor 3~.
A fourth centre branch of the diode bridge 10
to 13 shows a resistor voltage divider comprising a series
circuit of a resistor 39 and a resistor 40. A node between
the reslstors 39 and 40 is connected to a diode 41. The
other side this diode is connected to a 3unction point be-
! tween the diode 32 and the zener diode 33. The pass di-
rections of the three diodes 32, 33 and 41 all point to
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~712g7
their junction point.
Finally a node between the inductor 9 and diode
10 and a node between the diode 13 and the electrode 6 are
interconnected by means of a spike suppressor which is in-
dicated by reference 42.
- The circuit described Dperates as follows. When
the terminals 1 and 2 are connécted to an AC voltage source
of 220~ 50Hz a current will flow when there is a sufficient
instantaneous voltage between 1 and 2, depending on the po-
larity of the AC voltage source~ in the circuits 1, 3~ 9, 10~
24, 25, 26, 13 to terminal 2 or ~n the circuit~ 2, 6, 11, 24,
- 25~ 26~ 12, 9, 3 to terminal 1, ~l0n-as a result the capaci-
tor 26 has obtained such a voltage that the breakdown value
of the breakdown- or threshold element 28 is exceeded the
lg transistor 22 will become fully conductive by means of the
transformer 21, 23. Consequently a current will start flowing
in the first centre branch of the diode bridge, namely in
; the branch 20~ 21, 22. By means of this current the electrodes
4 and 6 of the lamp 5 are preheated. I~hen this current has
reached a constant value the drive of the transistor 22 is
stopped. Owing to the known delay caused by the draining of
charge carriers from the transistar,this transistor becomes
non-conductive again a little later. While the transistor
22 is conducting, the capacitor 26 is partly discharged via
the resistor 27, the threshold element 28 and the resistor
29. Owing to the fact that the transistor 22 becomes non-
conductive the voltage across the capacitors 7 and 8 and
co~.~.sequently the voltage across the lamp 5 is raised. This
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P]IN 7~92
9-1-1976
1071Z97
is a rise in the voltage which is effected in about the
same way as specified in the mentioned British Patent
Specification 1. 208.489.
However, in the meantime the capacitor 37 is
slightly charged via the resistors 31 and 36. When the
voltage across capacitor 37 - perhaps after some half cycles
of` the supply voltage between the terminals 1 and 2- has
attained a certain, relatively largel value a eurrent will
thereafter periodically flow, from resistor-31 via diode 32
into the blocking direction of diode 33, which eauses the
auxiliary transistor 30 to start eonducting, causing the
series circuit of resistor 27 and capacitor 26 to be short-
eircuited. This will of course lead to a partial discharge
of the capacitor 26. So this actually opposes the eha~ging
of this capacitor 26 v~a resistor 24. Owing to this delay
in the charging of the eapacitor 26, the instants at which
the transistor 22 is made conductive are delayed, so that
on the one hand the eircuit of the eapacitor 7 and 8 and~
on the other hand~ the inductor 9 is closed somewh* later
by that transistor 22~ This results in a greater rise of the
voltage across those two capacitors 7 and 8 and consequent-
ly to a corrosponding voltage rise aeross lamp 5.
If the.voltage between the lamp electrodes 4 and
6 would suddenly become very high,current will immediately
flow via the voltage divider 39~ 40 and the diode 41 into
the blocking direction of the zener diode 33, which switches
the transistor 15 very rapidly to the conducting state,
thus preventing that the transistor 22 becomes further
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^~ PlIN 7892
9-1-197~
1071Z97
.
conducting. This is favourable because such a transistor
should not be more conductive at such a high voltage at
its main electrodes as this might have disastrous conse-
~uences ~or the transistor. The spike suppressor 42 is a
further, additional protection for the starter.
In a practical embodiment, the value of the
inductor 3 is approximately 1,2Henry. The lamp 5 is a
low-pDessure mercury vapour discharge lamp of approximate-
ly 40 Wa~ts. The capacitance value of the capacitor 7 is
, 10 approximately 22 nFarad and that of capacitor 8 approxima
¦ tely 2,5 n Farad. The self-inductance of the inductor 9 is
approximately 0,2 m Henry. The resistance of the resistor
20 is about 27 Ohm, that of resistor 24 about 18 kOhm, that
of resistor 27 about 10 Ohm, that of resistor 29 about
100 Ohm, that of resistor 31 about 390 kOhm, that of resis-
tor 35 about 10 kOhm, that of resistor 36 about 6,8 kOhm
and that of resistor 38 about 150 kOhm. The resistor 39
has a resistance of about 100 kOhm and resistor 40 of about
3~9 kOhm. The CapacitQrS 26, 34 and 37 have a capacitance
of ~espectively 5,6 n Farad; 3~3 n Farad and 6,8/u Farad.
The zener voltage of zener diode 33 is ab~ut 22 volts and
that of zéner diode 25 is about 150 volt. The breakdown
voltage of the threshold element 28 is about 28 volts, the
spike suppressor 42 responds at a voltage of about 680 V at
1 m Ampère.
The arrangement with the two capacitors 7 and 8
is also useful to protect the starter if an electrod~ of
the lamp 5 ~ails during the starting procedure.
.
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~IIN 7S92
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1071Z97
Witll the device described the lamp 5 was started
without any flickcring. A reliable ignition was obtained
in the temperature range between -20C and ~70~.
If for some reason or another the lamp 5 refuses
to igniteJ,the auxiliary transistor 30 blocksJafter some
time, the further operation of the starter, owing to the
fact that then the voltage across the series circuit of
the resistor 36 and the (second capacitor 35) remains per-
manently above the zener voltage of the zener diode 33.
A great advantage of this device according to
the invention is that this auxiliary transistor 30 also has
a second function, namely it opposes, as described above,
the charging of the capacitor 26, which enables the higher
voltages between the lamp electrodes 4 and 6 during the
6 tarting procedure to be used.
i By way of a further explanation the envelope
of the instantaneous voltage e between the electrode 4
and 6 of the lamp 5 of Fig. 1 is plotted as a function of
the time ~ in Fig. 7. Three cases will now be considered~
namely:
a) a lamp 5 which is easy to start;
b) a lamp 5 which is difficult to start;
c) a lamp 5 which refuses to start.
Let us assume that the terminals 1 and 2 of
Fig. 1 are connected to the supply source at an instant
to. Until the instant t1 only that part of the starter
designated by 7 to 29~ in Fig. 1 is in operation. This
means that the auxiliary transistor 30, with its control
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p~ 7S92
9-1-1976
1~71297
circuit, has as yet no influence on the starting operation.
The time from to to t1 is about 1,2 seconds. The peak
voltage between the lamp electrodes is then about 500 V.
From the instant t1 to t2 the auxiliary transis-
tor 30 is periodically switched to the conducting and the
non-conducting state which results in an increased voltage
between the lamp electrodes 4 and 6 as specified in the
description of Fig. 1. The time from t1 to t2 is about
0,1 sec. The peak voltage between the lamp electrodes is
; 10 then about 800 Volt.
After the instant t2 the auxiliary transistor
30 blocks the operation of the starter. Then the mains
voltage is found between the lamp electrodes.
When the lamp 5 ignites~ the outlined starter
procedure will be immediately interr~pted and the voltage
between the lamp electrodes 4 and 6 will immediably become
equal to the operating voltage of the lamp. The starter is
then not actuated by the action of the zener diode ~ whose
threshold voltage (150V) is higher than the operating volt-
age (100V) o~ the lamp 5.
In the above mentioned case a of the lamp~ which
; easy to ignite, the starting procedure is already interrupt-
ed between the instants to and t1~ That means that the
voltage between the lamp elec~rodes ~ and 6 will already
be equal to the operating voltage B of the lamp (about
100V) at an instant between to and t1~
In the case b of the lamp which is difficult to
ignite the start~ng procedure is interrupted between the
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A
P]IN 7892
9-1-1976
1071Z97
instants tl and t2.
; In the case c of the lamp which refuses to
igni~Z the voltage between the lamp electrodes follows the
mains voltage (220 Volt) after the instant t2. The auxiliary
transistor 30 (see Fig. 1) is then permanentl~ conductive
~o that no ~urther =tarting effort~ are madc.
'i
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