Note: Descriptions are shown in the official language in which they were submitted.
CA 02404905 2002-09-25
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METHOD AND DEVICE FOR REMOTE MONITORING OF LED LAMPS.
RELATED APPLICATION
This application is a continuation-in-part of U.S.
application no. 09/543,240 of April 5, 2000, now abandoned.
FIELD OF THE INVENTION
The present invention relates to the electric
supply of light-emitting loads, in particular light-
emitting diode (LED) lamps. More specifically, the present
invention is concerned with electric circuits and methods
required for remote monitoring of LED lamps.
BACKGROUND OF THE INVENTION
Light-emitting diode (LED) lamps are becoming
more and more popular in automotive traffic lights, railway
signal lights and other applications. Their lower power
consumption is an attractive feature, but the main reason
for their popularity is their long life (100 000 hours)
compared to standard incandescent lamps (5 000 hours).
Manifestly, these features allow important reduction in
maintenance costs.
In certain applications, such as railway signal
lights, these lamps may be used, as those skilled in the
art would know, for main line signalling and/or grade
crossing signalling. Grade crossing signals are usually
situated in populated areas such as road intersections.
Remote monitoring of the LED lamps in grade crossing
CA 02404905 2002-09-25
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signals is therefore not necessary. Main line signals, on
the other hand, can be installed in remote areas, which are
not easily accessible. Remote monitoring for checking the
integrity of the lamps signals is therefore common
practice.
For lamps equipped with standard incandescent
bulb; electrical integrity can be easily verified. If the
filament of the incandescent bulb is in normal condition,
current flows through the bulb according to Ohm's law (I -
V/R) . Otherwise, if the filament is open, no current flows
through the bulb and it should be replaced.
For LED lamps, however, LED current is controlled
by a power supply. Current characteristics are therefore
not identical in a LED lamp and in an incandescent lamp. In
a LED lamp, alternative current (ac) line voltage is
rectified and then converted to a suitable level by a dc-do
(direct current) converter, which also regulates LED
current. In case of LED failure, or failure of any other
electrical component in the LED lamp, it is possible for
the power supply to continue drawing current at or near the
nominal current value, even if the LED's are not emitting
any light. Remote monitoring systems could therefore see
the LED lamp as functioning correctly when in reality it is
not. This situation is not acceptable since it can lead to
very hazardous train operations and cause major accidents.
Another problem, related to LED lamps and their
power supplies and controllers, is caused by electric
components which retain residual voltage differentials
after power is removed from the LED lamp. The resulting
characteristic is that a LED lamp will effectively light up
when the power applied to it reaches a first high level
CA 02404905 2002-09-25
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while it will be turned .off only when the power reaches a
second lower level. The resulting problem is that if a
certain power is induced by, for example, other nearby
cables, the LED lamp could remain on while in fact it
should be off. This could also lead to dangerous
situations.
These particularities of LED lamps limit their
widespread use in situations where they need to be remotely
monitored such as in railway main line signalling
applications.
OBJECTS OF THE INVENTION
An object of the present invention is therefore
to allow LED lamps to become compatible with remote
detection systems designed for monitoring of incandescent
lamps.
Another object of the invention is to provide LED
lamp circuitry which will emulate an incandescent lamp's
behaviour upon remote monitoring of the LED lamp.
Yet another object of the invention is to provide
a control circuit for enabling/disabling the power supply
to LED lamps in relation to the level of the line voltage.
SUI~lARY OF THE INVENTION
More specifically, in accordance with the present
invention, there is provided a fuse blow-out circuit for
establishing a short circuit between first and second
voltage and current supply lines to blow out a protection
fuse through which a current supplied to a light-emitting
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load by the first and second lines flows, this fuse blow-
out circuit comprises:
- a timer means responsive to the voltage across the first
and second lines for producing a time-representative signal
after a certain period of time;
- means connected to the timer means for preventing
production of the time-representative signal in response to
the current supplied to the light-emitting load; and
- means for establishing a current path between the first
and second lines in response to the time-representative
signal.
Accordingly, when no current is supplied to the
light-emitting load, the current path is established and
provides the short circuit between the first and second
lines that will blow out the protection fuse and emulate an
open circuit of a defective incandescent lamp.
Also in accordance with the present invention,
there is provided a fuse blow-out circuit for establishing
a short circuit between first and second voltage and
current supply lines to blow out a protection fuse through
which a current supplied to a light-emitting load by the
first and second lines flows. This fuse blow-out circuit
comprises:
- a resistor and a capacitor connected in series between
the first and second lines, this resistor having a given
resistance value, and this capacitor having a given
capacitance value and a capacitor charge period dependent
on the given resistance value and the given capacitance
value;
- a trigger circuit connected in parallel with the
capacitor, and comprising a first controllable switch
CA 02404905 2002-09-25
member closed in response to the current supplied to the
light-emitting load to discharge the capacitor; and
- a second controllable switch member defining a current
path between the first and second lines and closed in
response to a given voltage amplitude across the capacitor.
Therefore, in the absence of current supplied to
the light-emitting load for a duration equivalent to the
capacitor charge period, the given voltage amplitude across
the capacitor is reached to thereby close the second switch
member, establish the current path and provide the short
circuit between the first and second lines that will blow
out the protection fuse and emulate an open circuit of a
defective incandescent lamp.
Further in accordance with the present invention,
there is provided a power supply unit responsive to
alternating voltage and current from an ac source for
supplying a do voltage and current to a light-emitting
load, comprising:
- a rectifier unit rectifying the alternating voltage and
current from the ac source and supplying the rectified
voltage and current to first and second voltage and current
supply lines;
- a protection fuse through which the alternating current
from the ac source is supplied to the rectifier unit;
- a converter of the rectified voltage and current into
the do voltage and current supplied to the light-emitting
load;
- a fuse blow-out circuit as described above, for
establishing a short circuit between the first and second
voltage and current supply lines to blow out the protection
fuse; and
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- a controller of the converter in response to the
rectified voltage on the first and second lines.
The present invention also relates to a cold
filament detection circuit connected between first and
second lines through which a voltage and current supply
source supplies voltage and current to a light-emitting
load, the voltage and current supply source having a set up
time during which no current is supplied to the light
emitting load. This cold filament detection circuit
comprises:
- a resistor;
- means for connecting the resistor between the first and
second lines in response to the voltage on the first and
second lines to thereby establish through this resistor a
current path between the first and second lines; and
- means for disconnecting the resistor from between the
first and second lines in response to the current supplied
to the light-emitting load.
Accordingly, during the set up time no current is
supplied to the light-emitting load and the current path is
established through the resistor to emulate the impedance
of an incandescent lamp, and when current is supplied to
the light-emitting load, the resistor is disconnected from
between the first and second lines.
The present invention further relates to a cold
filament detection circuit connected between first and
second lines through which a voltage and current supply
source supplies voltage and current to a light-emitting
load, the voltage and current supply source having a set up
time during which no current is supplied to the light-
CA 02404905 2002-09-25
emitting load. The cold filament detection circuit
comprises:
- a resistor;
- a controllable switch member: connected in series with
the resistor between the first and second lines; responsive
to the voltage on the first and second lines; and having a
current-conductive junction established in response to the
voltage on the first and second lines to thereby establish
through the resistor a current path between the first and
second lines; and
- a switch control unit responsive to the current supplied
to the light-emitting load, connected to the first
controllable switch member, and having a switch-disabling
circuit which prevents the current-conductive junction to
establish as long as current is supplied to the light-
emitting load.
In operation, during the set up time no current
is supplied to the light-emitting load and the current path
is established through the resistor to emulate the
impedance of an incandescent lamp, and when current is
supplied to the light-emitting load, the switch-disabling
circuit prevents the current-conductive junction to
establish whereby the resistor is disconnected from between
the first and second lines.
The present invention still further relates to a
voltage and current supply source responsive to alternating
voltage and current from an ac source for supplying do
voltage and current to a light-emitting load, comprising:
- a rectifier unit rectifying the alternating voltage and
current from the ac source and supplying the rectified
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voltage and current to first and second voltage and current
supply lines;
- a converter of the rectified voltage and current into
the do voltage and current supplied to the light-emitting
load;
- a cold filament detection circuit as defined above,
connected between the first and second lines through which
the voltage and current supply source supplies voltage and
current to the light-emitting load; and
- a controller of the converter in response to the
rectified voltage on the first and second lines.
The present invention is also concerned with a
voltage control circuit for controlling the amplitude of a
voltage signal on a control terminal of a power controller
unit itself controlling a voltage and current supply source
which supplies a current to a light-emitting load through
first and second voltage and current supply lines. This
voltage control circuit comprises:
- means for producing a first trigger voltage in response
to the voltage across the first and second lines, this
first trigger voltage having an amplitude representative of
the amplitude of the voltage across the first and second
lines;
- first switch means, connected in series with a high
impedance element between the control terminal and one of
the first and second lines, for establishing a high
impedance current path between the control terminal and
said one line when the first trigger voltage reaches a
given amplitude, wherein the first switch means comprises
means for producing a second trigger voltage having a first
amplitude when the high impedance current path is not
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established and a second amplitude when the high impedance
current path is established: and
- second switch means, connected in series with a low
impedance element between the control terminal and said one
line, for establishing a low impedance current path between
the control terminal and said one line when the second
trigger voltage has the first amplitude.
Accordingly, when the first trigger voltage has
an amplitude lower than the given amplitude, the high
impedance current path is not established, a second trigger
voltage of first amplitude is produced, and the low
impedance current path is established to result in a
voltage signal amplitude on the control terminal which
disables the power controller unit and, when the amplitude
of the first trigger voltage reaches the given amplitude,
the high impedance current path is established, a second
trigger voltage of second amplitude is produced, and the
low impedance current path is not established to result in
a voltage signal amplitude on the control terminal which
enables said power controller unit.
The present invention is further concerned with a
voltage control circuit for controlling the amplitude of a
voltage signal on a control terminal of a power controller
unit itself controlling a voltage and current supply source
which supplies a current to a light-emitting load through
first and second voltage and current supply lines. The
voltage control circuit comprises:
- a voltage divider circuit connected between the first
and second lines and comprising resistors which divide the
voltage on the first and second lines to produce a first
trigger voltage signa l
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- a first controllable switch member connected in series
with a high impedance element between the control terminal
and one of the first and second lines to define a high
impedance current path between this control terminal and
said one line, this first controllable switch member being
responsive to the first trigger voltage signal and having a
first current-conductive junction established when the
first trigger voltage reaches a given amplitude, wherein
the high impedance current path produces a second trigger
10 voltage having a first amplitude when the first current-
conductive junction is not established and a second
amplitude when the first current-conductive junction is
established; and
- a second controllable switch member connected in series
with a low impedance element between the control terminal
and said one line to define a low impedance current path
between this control terminal and said one line, this
second controllable switch member being responsive to the
second trigger voltage and having a second current-
conductive junction established when the second trigger
voltage has the first amplitude and non established when
the second trigger voltage signal has the second amplitude.
Therefore, when the first trigger voltage has an
amplitude lower than the given amplitude, the first
current-conductive junction is not established to produce
in the high impedance current path a second trigger voltage
of first amplitude which establishes both the second
current-conductive junction and the low impedance current
path to result in a voltage signal amplitude on the control
terminal which disables the power controller unit and, when
the amplitude of the first trigger voltage reaches the
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given amplitude, both the first current-conductive junction
and the high impedance current path are established to
produce in the high impedance current path a second trigger
voltage of second amplitude whereby both the second
current-conductive junction and the low impedance current
path are not established to result in a voltage signal
amplitude on the control terminal which enables the power
controller unit.
The present invention is still further concerned
with a voltage and current supply source responsive to
alternating voltage and current from an ac source for
supplying do voltage and current to a light-emitting load,
comprising:
- a rectifier unit rectifying the alternating voltage and
current from the ac source and supplying the rectified
voltage and current to first and second voltage and current
supply lines;
- a converter of the rectified voltage and current into
the do voltage and current supplied to the light-emitting
load;
- a power controller unit having a control terminal and
controlling the converter in response to the rectified
voltage on the first and second lines; and
- a voltage control circuit as described above, for
controlling the amplitude of a voltage signal on the
control terminal of the power controller unit.
The embodiments described herein present the
advantage that they permit the use of LED lamps in
applications, such as railway signal light applications,
where there is a need for remote monitoring of the lamps,
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while keeping the advantageous features of lower power
consumption and longer life.
Other objects, advantages and features of the
present invention will become more apparent upon reading of
the following non-restrictive description of preferred
embodiments thereof, given by way of example only with
reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the appended drawings:
Figure 1 is a schematic block diagram showing a
LED lamp assembly including a fuse blow-out circuit, a cold
filament detection circuit, and a turn-off voltage circuit;
Figure 2A is a schematic electrical circuit
diagram of a first embodiment of a fuse blow-out circuit
according to the invention;
Figure 2B is a schematic electrical circuit
diagram of a second embodiment of the fuse blow-out circuit
according to the invention;
Figure 2C is a schematic electrical circuit
diagram of a third embodiment of the fuse blow-out circuit
according to the invention;
Figure 3 is a schematic electrical circuit
diagram of a cold filament detection circuit in accordance
with the present invention; and
Figure 4 is a schematic electrical circuit
diagram of a turn-off voltage circuit according to the
present invention.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to Figure 1, an ac (alternating
current) line voltage is supplied to a LED lamp B by a
voltage and current supply source 10 through a line 11. The
AC line voltage is EMI (Electromagnetic Interference)
filtered and surge suppressed by means of functional block
12 including an EMI filter, a surge suppressor and an input
fuse. Then, the line voltage is rectified through a
rectifier 14 and subsequently converted to a DC voltage
through a DC-DC converter 20. The DC voltage from the
converter 20 is supplied on line 21 to light up a
series/parallel LED (light-emitting diodes) array 22. LEDs
are also more generally referred to in the present
specification as light-emitting loads.
The current flowing through the series/parallel
LED array 22 is sensed by a current sensor 100. This
current sensor 100 produces a LED current sense signal 23
supplied to a power factor controller 28. The function of
the power factor controller 28 is to control the DC-DC
converter 20 through a line 27, which in turn controls the
DC current and voltage on line 21.
In the illustrated example, the series/parallel
LED array 22 is formed of a plurality of subsets 26 of five
(5) serially interconnected light-emitting diodes 24. Each
subset 26 of serially interconnected light-emitting diodes
24 are connected in parallel to form the series/parallel
LED array 22. A particularity is that the anodes of the
first light-emitting diodes of the subsets 26 are
interconnected, the cathodes the first light-emitting
diodes of the subsets 26 and the anodes of the second
light-emitting diodes of the subsets 26 are interconnected,
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the cathodes of the second light-emitting diodes of the
subsets 26 and the anodes of the third light-emitting
diodes of the subsets 26 are interconnected, the cathodes
of the third light-emitting diodes of the subsets 26 and
the anodes of fourth light-emitting diodes of the subsets
26 are interconnected, the cathodes of the fourth light-
emitting diodes of the subsets 26 and the anodes of the
fifth light-emitting diodes of the subsets 26 are
interconnected, and the cathodes of the fifth light-
emitting diodes of the subsets 26 are interconnected. Of
course, other types of arrangements comprising various
numbers of LEDs are possible within the scope of the
present invention.
Various embodiments of EMI filter (block 12),
surge suppressor (block 12), input fuse (block 12),
rectifier 14 and DC-DC converter 20 can be used. These
embodiments are well known to those of ordinary skill in
the art and, accordingly, will not be further described in
the present specification. Also, in a preferred embodiment
of the invention, a Motorola~ MC33262P integrated circuit
(IC) chip is used as power factor controller 28. However,
it is within the scope of the present invention to use
other IC chips commercially available on the market, or
that will become available on the market in the future.
Figure 1 shows a fuse blow-out circuit 16, a cold
filament detection circuit 18 and a turn-off voltage
circuit 30. These circuits will be described in greater
detail hereinafter.
CA 02404905 2002-09-25
FUSE BLOW-OUT CIRCUIT
Referring to Figure 2A, a first embodiment of the
fuse blow-out circuit is shown and generally designated by
the reference 16. The fuse blow-out circuit 16 receives the
rectified voltage from output terminal 15 of the rectifier
14 on an input 48. The fuse blow-out circuit 16 also
comprises a second input 49 to receive the LED current
sense signal 23 from the current sensor 100. As long as no
LED current sense signal 23 appears on the input 49, a FET
10 (Field-Effect Transistor) transistor 42 is turned off.
While transistor 42 is turned off, capacitor 34 is being
charged through resistor 31 and diode 32 from the voltage
supplied on the input 48. Concurrently, capacitor 41 is
being charged through resistor 31, diode 32 and resistor
37. When the voltage across capacitor 41 reaches the
breakdown voltage of Zener diode 40 having its anode
grounded through resistor 47 (while transistor 42 is still
turned off), silicon bilateral switch (or triac) 38 turns
on to supply a current to a trigger electrode 103 of a
thyristor 39 to thereby trigger this thyristor 39.
Triggering of the thyristor 39 into conduction creates a
short-circuit between output terminal 15 of rectifier 14
(see Figures 1 and 2A) and a ground output terminal 101 of
the same rectifier 14.
This short-circuit will effectively blow out the
input fuse of functional block 12, thereby opening the
circuit. Detection of that open circuit will indicate that
the lamp is defective thereby emulating the open circuit of
a defective incandescent lamp.
It is to be noted that the sequence of events
described above will only take place after a given period
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16
of time (fuse blow-out time) has lapsed during which no
current is sensed by current sensor 100. This given period
of time is constant and is dependent on the values of
resistor 31, resistor 33, resistor 35 and capacitor 34.
If, on the other hand, a LED current sense signal
23 is supplied to the input 49 prior to the end of the
above mentioned given period of time, this LED current
sense signal 23 is applied to the gate electrode 102 of FET
transistor 42 through resistor 43 to turn this transistor
42 on. Capacitor 41 then discharges to the ground 101
through resistor 36 and the source/drain junction of
transistor 42. Accordingly, capacitor 41 will never become
fully charged, the breakdown voltage of Zener diode 40 will
never be reached, and no short circuit will be created
between the terminals 15 and 101 of rectifier 14. Then, the
input fuse of functional block 12 will remain intact.
Referring to Figure 2B, a second embodiment of
the fuse blow-out circuit is shown and still designated by
the reference 16. Again, the fuse blow-out circuit 16
comprises the input 48 to receive the rectified voltage
from terminal 15 of the rectifier 14. The fuse blow-out
circuit 16 also comprises the second input 49 receiving the
LED current sense signal 23 from the current sensor 100
(Figure 1). As long as no LED current sense signal 23
appears on the input 491 FET transistor 42 is turned off.
when transistor 42 is turned off, capacitor 34 is being
charged through resistor 31 and diode 32 from the voltage
supplied on the input 48. when the voltage across the
capacitor 34 reaches the breakdown voltage of the Zener
diode 44, (while transistor 42 is still turned off) Zener
diode 44 starts conducting current. A current is then
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supplied to the base of a PNP transistor 45 through
resistor 31, diode 32 and Zener diode 44 to turn this
transistor 45 on. When turned on, the collector/emitter
junction of the transistor 45 becomes conductive to supply
a current to the gate electrode of a FET transistor 46.
This turns the FET transistor 46 on to establish a short
circuit between output terminals 15 and 101 of the
rectifier 14 through the source/drain junction of the FET
transistor 46. As illustrated, the emitter of the
transistor 45 and ?he gate electrode of the transistor 46
are both connected to the ground through a resistor 47.
Alternatively, as shown in Figure 2C, the Zener
diode 44, transistor 45 and resistor 47 have been removed,
and resistor 36 connected to the base of transistor 46.
This short circuit will effectively blow out the
input fuse of block 12, thereby opening the circuit.
Detection of that open circuit will indicate that the LED
lamp 8 is defective thereby emulating the open circuit of a
defective incandescent lamp.
It should be noted that the sequence of events
described above will only take place after a given period
of time (fuse blow-out time) has lapsed during which no LED
current sense signal 23 appears on the input 49. This given
period of time is constant and depends on the values of
resistor 31, resistor 33, resistor 35 and capacitor 34.
If, on the other hand, the LED current sense
signal 23 appears on the input 49 prior to lapsing of the
above mentioned given period of time, this signal 23 is
supplied to the gate electrode 102 of FET transistor 42 to
thereby turn transistor 42 on. This connects the positive
terminal of capacitor 34 to ground 101 through resistor 36
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to thereby discharge capacitor 34. In this case, the
breakdown voltage of Zener diode 44 will never be reached,
transistor 45 will remain turned off, and no short circuit
will be created between output terminals 15 and 101 of
rectifier 14. The input fuse of block 12 will, in this
case, remain intact.
It should be noted that the "fuse blow-out time"
must be longer than the "LED current set up time". For
example, in an embodiment, the LED current set up time is
approximately 100 msec. Just a word to specify that the
"LED current set up time" is the period of time between
switching the LED lamp on and appearance of the LED current
sense signal 23 at input 49.
COLD FILAMENT DETECTION CIRCUIT
The cold filament detection circuit 18 of Figure
3 is used to simulate an incandescent lamp as seen by a
lamp proving system. Lamp proving is usually performed by
sending a voltage pulse on the voltage supply line 11, and
verifying that current rises to a certain level, within a
certain period of time. This represents the behaviour of an
incandescent lamp, which is equivalent to a simple
resistor.
A LED lamp uses a power supply which has a
current set up time. Therefore, when sending a pulse on
line 11, the current will not rise immediately, but only
after the power factor controller 28 is turned on (for
example after about 100 msec in an embodiment). The cold
filament detection circuit 18 of Figure 3 solves this
problem.
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As soon as power is supplied on line 11, the
voltage drop across resistor 51, connected between the
output terminal 15 (input 56 of the cold filament detection
circuit 18) and a gate electrode 104 of a FET transistor,
will turn on this transistor 53. This will connect resistor
52 between the output terminals 15 and 101 of the rectifier
14.
When power is applied on line 11 for a period of
time which is longer than the LED current set up time, the
LED current sense signal 23 will be supplied on an input 57
of the cold filament detection circuit 18. This signal 23
is applied to the base 105 of a PNP transistor 54 to turn
on this transistor 54 thereby turning transistor 53 off by
forcing its gate electrode 104 to the ground 101. The cold
filament detection circuit 18 is thereby disabled to enable
the LED lamp 8 to operate normally. Biasing resistor 50 and
Zener diode 55 are connected in series between the input 56
and the base electrode 105. Biasing resistor 50 is also
used for overvoltage protection.
The cold filament detection circuit 18 also
serves as a back up for the fuse blow-out circuit 16. If
fuse blow-out circuit 16 was to fail (that is, it does not
cause a short circuit to blow out the input fuse of block
12 when in fact it should), transistor 53 would remain
turned on since no LED current sense signal 23 would appear
on input 57. The current draw through resistor 52 is
sufficiently high to blow out the input fuse of block 12
after a certain period of time. For example, in an
embodiment of the invention, this time period is of a few
minutes.
CA 02404905 2002-09-25
TURN-OFF VOLTAGE CIRCUIT
The turn-off voltage circuit 30 of Figure 4
simply inhibits the power factor controller 28 (see Figure
1) when the input voltage on line 11 of the circuit 30 is
below a first predetermined trigger voltage.
The turn-off voltage circuit 30 comprises an
input 70 supplied with the voltage on the output terminal
15 of the rectifier 14. The first predetermined trigger
voltage 72 is determined by a voltage divider comprising
10 resistors 60 and 69 serially connected between the input 70
of the turn-off voltage circuit 30 and the ground 101. The
first predetermined trigger voltage is established after a
capacitor 68 has been charged through the resistor 60 and
the diode 61, i.e. after a given period of time following
application of the voltage on the input 70. This period of
time is determined by the values of the resistors 60, 69
and 107 and of the capacitor 68.
The first predetermined trigger voltage 72 is
applied to a gate electrode 106 of a FET transistor 65
20 through the diode 61. when the first trigger voltage 72
reaches the breakdown voltage of the gate electrode 106 of
the FET transistor 65, transistor 65 is turned on.
The turn-off voltage circuit 30 comprises a
terminal 71 connected to a control terminal 29 of the power
factor controller 28. Before the transistor 65 is turned
on, the power factor controller 28 produces a voltage drop
across high impedance resistor 62, to thereby produce a
second trigger voltage 73, which in turn turns on a FET
transistor 63. This in turn creates a low impedance path
comprising resistor 67 between terminal 29 of the power
factor controller 2 and the ground 101. As long as
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transistor 63 is turned on, the voltage on terminal 29 of
power factor controller 28 will be lower than the voltage
level required to turn on the power factor controller 28.
When transistor 65 is turned on, this will modify
the second trigger voltage 73 thereby turning off
transistor 63. The voltage on terminal 29 will then reach
the level required to turn on the power factor controller
28, due to the high impedance value of the resistor 62.
Note that the LED lamp 8 will not be turned on
until the first trigger voltage 72 is reached and once the
lamp 8 is lit, it will stay on until the voltage on input
70 produces a first trigger voltage 72 which is below the
transistor 65 trigger voltage (breakdown voltage of the
gate electrode 106).
Although the present disclosure describes
particular types of transistors in the different circuits
of Figures 2A, 2B, 3 and 3, it should be kept in mind that
these different types of transistors can be substituted or
replaced by other available types of transistors.
Although the present invention has been described
hereinabove by way of preferred embodiments thereof, it can
be modified, without departing from the spirit and nature
of the subject invention as defined in the appended claims.
