U.S. patent application number 10/371027 was filed with the patent office on 2003-07-17 for supply assembly for a led lighting module.
This patent application is currently assigned to U.S. Philips Corporation. Invention is credited to Hontele, Bertrand Johan Edward, Jacobs, Ronny Andreas Antonius Maria, Marinus, Antonius Adrianus Maria.
Application Number | 20030132721 10/371027 |
Document ID | / |
Family ID | 8170974 |
Filed Date | 2003-07-17 |
United States Patent
Application |
20030132721 |
Kind Code |
A1 |
Jacobs, Ronny Andreas Antonius
Maria ; et al. |
July 17, 2003 |
Supply assembly for a LED lighting module
Abstract
A supply assembly for a LED lighting module, comprising a supply
unit to which the LED lighting module can be connected and a burst
control unit which is capable of switching the power supply unit on
and off with a burst frequency (fburst) so as to control the mean
light output. Preferably, the burst control unit is provided with a
pulse duration modulator for controlling the pulse length (T pulse)
during which the supply unit is operative.
Inventors: |
Jacobs, Ronny Andreas Antonius
Maria; (Eindhoven, NL) ; Hontele, Bertrand Johan
Edward; (Eindhoven, NL) ; Marinus, Antonius Adrianus
Maria; (Eindhoven, NL) |
Correspondence
Address: |
PHILIPS ELECTRONICS NORTH AMERICAN CORP
580 WHITE PLAINS RD
TARRYTOWN
NY
10591
US
|
Assignee: |
U.S. Philips Corporation
|
Family ID: |
8170974 |
Appl. No.: |
10/371027 |
Filed: |
February 20, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10371027 |
Feb 20, 2003 |
|
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09773159 |
Jan 31, 2001 |
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Current U.S.
Class: |
315/291 |
Current CPC
Class: |
Y02B 20/30 20130101;
H05B 45/18 20200101; H05B 45/375 20200101; H05B 45/3725 20200101;
H05B 45/345 20200101; H05B 45/10 20200101; H05B 45/385 20200101;
H05B 45/327 20200101; H05B 45/12 20200101 |
Class at
Publication: |
315/291 |
International
Class: |
G05F 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 3, 2000 |
EP |
00200370.5 |
Claims
1. A supply assembly for a LED lighting module, comprising a supply
unit to which the LED lighting module can be connected and a burst
control unit which is capable of switching the power supply to the
LED lighting module on and off with a burst frequency (fburst) so
as to control the mean light output of the LED lighting module,
characterized in that the burst control unit is capable of
switching the supply unit on and off with the burst frequency
(fburst).
2. A supply assembly as claimed in claim 1, characterized in that
the burst control unit comprises a pulse-duration modulator which
is capable of controlling the length (Tpulse) of the pulses during
which the supply unit is in the on-state.
3. A supply assembly as claimed in claim 1 or 2, characterized in
that the supply unit is a controlled constant-current source.
4. A supply assembly as claimed in claim 1, 2 or 3, characterized
in that the supply unit is a high-frequency switch mode power
supply which supplies a ripple DC current or a ripple DC
voltage.
5. A supply assembly as claimed in claim 4, characterized in that
the pulse duration modulator can switch the converter on and off
with the burst frequency (fburst).
6. A supply assembly as claimed in claim 4 or 5, characterized in
that the ripple frequency of the converter is an integer multiple
of the burst frequency (fburst), and the ripple DC voltage or
ripple DC current can be synchronized with the burst control
signal.
7. A supply assembly as claimed in any one of the preceding claims,
characterized in that the burst frequency (fburst) is an integer
multiple of the frequency of the mains voltage to which the supply
assembly can be connected, and the burst control signal can be
synchronized with the mains voltage signal.
8. A supply assembly as claimed in any one of the preceding claims,
characterized in that the burst frequency (fburst) lies in the
range between 50 and 200 Hz or above 20 kHz.
9. A supply assembly as claimed in any one of the preceding claims,
characterized in that the burst frequency (fburst) is 100 or 120
Hz.
10. A supply assembly as claimed in any one of the preceding
claims, characterized in that the current (ILED) supplied by the
supply unit in the on-state to the LED lighting module is a
constant current which has been chosen as a nominal current, and
which results in an optimum light output of the LED lighting
module.
Description
[0001] The invention relates to a supply assembly for a LED
lighting module, comprising a supply unit to which the LED lighting
module can be connected and a burst control unit which is capable
of switching the power supply (the voltage or the current) to the
LED lighting module on and off with a burst frequency so as to
control the mean light output of the LED lighting module.
[0002] LED lighting modules are being used more and more to
illuminate objects. They are also used as signal lighting, for
example in traffic lights. The light output of a LED lighting
module can be controlled in various well-known ways. One of said
ways consists in controlling (dimming) the current intensity
through the module. This has the drawback that at a current
intensity below approximately 20% of the nominal current intensity,
the relation between the current intensity and the light output
becomes largely non-linear, and the efficiency of the module
becomes far from optimal. Therefore, solutions have been sought
which enable the light intensity to be controlled while the nominal
current intensity through the module is maintained. U.S. Pat. No.
5,661,645 describes a supply unit for a LED lighting module as
described in the opening paragraph. In said document, the burst
control unit is arranged between an output of a voltage source and
the LED lighting module, so that the power supply to the module
with a certain burst frequency can be switched on and off. The
voltage source is continuously in the on-state, also when the power
supply to the LED lighting module is cut off, which results in an
unnecessary loss of energy.
[0003] It is an object of the invention to provide an efficient,
reliable, inexpensive and simple supply assembly for a LED lighting
module with an improved efficacy.
[0004] This is achieved in accordance with the invention in that
the burst control unit is capable of switching the power supply
unit on and off with the burst frequency. In this case, the supply
unit is in the on-state only when current is actually being
supplied, so that the generation of heat and energy losses are
minimized, resulting in an improved efficacy of the system.
[0005] Preferably, the burst control unit comprises a
pulse-duration modulator which is capable of controlling the length
of the pulses during which the supply unit is in the on-state. This
enables the mean light output to be controlled.
[0006] Preferably, the supply unit is a controlled constant-current
source. This has the advantage that further measures in the LED
module, such as the provision of additional resistors, are not
necessary to control the electric current through the LEDs.
[0007] Preferably, the supply unit is a high-frequency switch mode
power supply (smps) which supplies a ripple DC current or a ripple
DC voltage, said supply unit preferably comprising a half-bridge
converter, a buck converter or a flyback converter. The pulse
duration modulator can preferably switch the converter on and off
with the burst frequency. In this way, the desired effect can be
achieved very efficiently. In addition, preferably the ripple
frequency of the converter is an integer multiple of the burst
frequency, and the ripple DC voltage or ripple DC current can be
synchronized with the burst control signal, resulting in a
reduction of any stability problems and loss of energy in the
system.
[0008] For the same reason, the burst frequency preferably is an
integer multiple of the frequency (customarily 50 Hz or 60 Hz) of
the voltage source, for example the mains voltage to which the
supply assembly can be connected, and the burst control signal is
synchronized with the mains voltage signal.
[0009] Preferably, the burst frequency lies in the range between 50
and 200 Hz or above 20 kHz; more preferably the burst frequency is
100 Hz (if the mains frequency is 50 Hz) or 120 Hz (if the mains
frequency is 60 Hz). When use is made of a half-bridge converter,
it is best if the burst frequency is chosen as low as possible in
connection with switching losses. However, the frequency should
preferably exceed the frequency that can be observed by the human
eye (approximately 70 Hz), because at a lower frequency the flicker
produced by the LEDs is noticeable, which is annoying. In addition,
the frequency should preferably be outside the human range of
hearing of 200 Hz to 20 kHz to preclude disturbing sound
effects.
[0010] Preferably, the current supplied by the supply unit in the
on-state to the LED lighting module is a constant current which has
been chosen as a nominal current, and which results in an optimum
light output of the LED lighting module, so that the supply unit
can be optimized for the nominal current intensity, which has a
favorable effect on the efficacy.
[0011] In a preferred embodiment, the burst control unit is coupled
to a sensor which is capable of measuring the temperature and/or
the light output of the LED lighting module, said burst control
unit being capable of controlling the length of the pulses during
which the supply unit is in the on-state in dependence upon the
value measured by the sensor. By virtue thereof, the light output
of the module can be stabilized under varying conditions. In a
further preferred embodiment, the duration of the pulses can be
adjusted by a user. By virtue thereof, the light output of the
module can be dimmed in accordance with the user's needs.
[0012] The supply assembly as herein disclosed is also suitable to
operate a LED lighting module which forms part of a display unit,
for instance a liquid crystal display (LCD).
[0013] These and other aspects of the invention will be apparent
from and elucidated with reference to the embodiments described
hereinafter.
[0014] In the drawings:
[0015] FIG. 1A diagrammatically shows a supply assembly to which a
LED lighting module is connected.
[0016] FIG. 2 shows a graph wherein the current through the LED
lighting module is shown as a function of time.
[0017] FIG. 3 shows a first detailed example of the system shown in
FIG. 1.
[0018] FIG. 4 shows a second detailed example of the system shown
in FIG. 1.
[0019] As shown in FIG. 1, a supply assembly I comprises a supply
unit, preferably a controlled constant-current source 1, which
supplies current to a LED lighting module 2. The LED lighting
module 2, for instance as backlight for a LCD comprises a number of
lightemitting diodes (LEDs) 3, which may be parallel-connected or
series-connected. The figure diagrammatically shows that a burst
control unit 4 is capable of switching the controlled
constant-current source 1 on and off. For this purpose, the burst
control unit 4 emits a burst control signal 5 which is composed of
pulses having a duration Tpulse which switch on the controlled
constant-current source 1 with a burst frequency fburst, as shown
in FIG. 2. The burst frequency fburst should exceed the frequency
that can be observed by the human eye (approximately 70 Hz) because
at a lower frequency the flicker produced by the LED lighting
module would be very disturbing (cf the monitor of a display tube).
However, the burst frequency fburst should not exceed a certain
value because this would lead to an unnecessary amount of switching
losses and, in addition, might cause undesirable, audible
background noises.
[0020] In this example, the controlled constant-current source 1 is
a high-frequency switch mode power supply (smps) comprising a
half-bridge converter, which half-bridge converter can be switched
on and off by the burst control unit. Other high-frequency
converters, such as a buck converter, a flyback converter and other
types of converters can also suitably be used as a controlled
constant-current source. Such a known controlled constant-current
source delivers direct current, the current intensity and/or the
voltage of which can be controlled. The distinctive feature of such
a controlled constant-current source is that the direct current is
a ripple direct current, which means that the current intensity
varies with a high ripple frequency between a minimum value 6 and a
maximum value 7. The mean of this minimum value 6 and maximum value
7 is the mean direct-current intensity 8 of the controlled
constant-current source 1. This current intensity 8 is preferably
equal to the current chosen as the nominal current for the LED
lighting module 2. The ripple signal of the controlled
constant-current source 1 is preferably synchronized with the burst
control signal in order to preclude additional switching
losses.
[0021] FIG. 2 shows the situation wherein the mean size of the
current 9 through the LED lighting module 2 is set at 50% of the
mean current 8 of the controlled constant-current source. This is
achieved by setting the pulse duration Tpulse at 50% of the cycle
length (fburst). By varying the pulse duration Tpulse, the mean
size of the current 9 through the LED lighting module 2 can obtain
any desired value between 0% and 100% of the nominal current
delivered by the controlled constant-current source 1. To this end
the burst control unit 4 is provided with a pulse duration
modulator.
[0022] FIGS. 3 and 4 show preferred embodiments of a supply
assembly I, the supply assembly I as shown in FIG. 3 being
connectable to an AC voltage source, such as the mains, and the
supply assembly I as shown in FIG. 4 being connectable to a DC
voltage source, such as a battery. In common with FIG. 1, the
high-frequency switch mode power supply shown in FIGS. 3 and 4
comprises a controlled constant-current source (Switch mode current
source) 1, the LED lighting module (LED MODULE) 2 and the burst
control unit (Burst control) 4.
[0023] The burst control unit 4 may be connected to a dimming
device (Dim interface) 14 which can be set by a user via a bus
(Bus). The dimming device is capable of controlling the pulse
duration (also referred to as pulse width) Tpulse of the burst
control unit 4 by means of a voltage signal (Vdim).
[0024] As the light output of LEDs is temperature-dependent, the
LED lighting unit 2 may be provided with sensors which observe the
temperature (TEMP_OUT) and/or the light output (OPT_OUT) of the LED
lighting unit 2. The sensors can send a voltage signal (VTF and
VOF, respectively) to the burst control unit 4, said voltage
signals also being capable of controlling the pulse duration
Tpulse. By means of this feedback the light output of the LED
lighting module 2 can be efficiently stabilized.
[0025] In accordance with FIG. 3, the controlled constant-current
source 1 is fed, in a manner which is known per se, by a
filter/rectifier (Filter/rect.) 10 and a preconditioning device
(Preconditioner) 11, which are connected to, for example, a
grounded electric mains (110V/60 Hz or 230V/50 Hz) with terminals
L, N and PE. In the case of low-power systems (<25W), the
preconditioning device can be replaced by a simple energy buffer.
To preclude any problems regarding the stability of the
preconditioning device, it is important to synchronize the burst
control signal with the mains voltage signal by means of a
synchronization signal (Sync). Auxiliary supply (Aux. supply) 15
provides the different parts of the system with the necessary
low-voltage supply.
[0026] In accordance with FIG. 4, the controlled constant-current
source 1 is fed by a DC filter (Filter) 12, and optionally a DC/DC
converter (DC-DC converter) 13, which are connected to a storage
cell or a battery having terminals L and N.
* * * * *