U.S. patent application number 13/943235 was filed with the patent office on 2015-01-22 for method and apparatus for providing supplemental power in a led driver.
The applicant listed for this patent is GE Lighting Solutions, LLC. Invention is credited to Josip BRNADA.
Application Number | 20150022087 13/943235 |
Document ID | / |
Family ID | 51211859 |
Filed Date | 2015-01-22 |
United States Patent
Application |
20150022087 |
Kind Code |
A1 |
BRNADA; Josip |
January 22, 2015 |
METHOD AND APPARATUS FOR PROVIDING SUPPLEMENTAL POWER IN A LED
DRIVER
Abstract
A DC current driver includes a DC current drive circuit
configured to provide a DC supply current and receive a DC return
current. A switch is coupled in series with the DC return current,
and a supplemental power supply is coupled in parallel with the
switch and configured to provide a supplemental voltage. Opening
the switch diverts the DC return current through the supplemental
supply and closing the switch causes the DC return current to
bypass the supplemental supply.
Inventors: |
BRNADA; Josip; (Willoughby,
OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GE Lighting Solutions, LLC |
East Cleveland |
OH |
US |
|
|
Family ID: |
51211859 |
Appl. No.: |
13/943235 |
Filed: |
July 16, 2013 |
Current U.S.
Class: |
315/112 ;
315/291; 323/282 |
Current CPC
Class: |
H05B 45/48 20200101;
H02M 2001/008 20130101; H02M 1/44 20130101; Y02B 70/10 20130101;
H02M 1/4225 20130101; H05B 45/00 20200101; Y02B 70/126 20130101;
H02M 1/12 20130101; H05B 45/37 20200101; H02M 3/156 20130101 |
Class at
Publication: |
315/112 ;
323/282; 315/291 |
International
Class: |
H02M 3/156 20060101
H02M003/156; H05B 33/08 20060101 H05B033/08 |
Claims
1. A DC current driver, comprising: a DC current drive circuit
configured to provide a DC supply current and receive a DC return
current; a switch coupled in series with the DC return current; and
a supplemental power supply coupled parallel with the switch and
configured to provide a supplemental voltage, wherein opening the
switch diverts the DC return current through the supplemental power
supply and closing the switch causes the DC return current to
bypass the supplemental power supply.
2. The driver of claim 1, wherein the supplemental power supply
comprises a control circuit coupled to the supplemental voltage,
the control circuit configured to open and close the switch to
maintain the supplemental voltage at a desired level.
3. The driver of claim 2, wherein the control circuit is configured
to maintain the supplemental voltage at a generally constant
level.
4. The driver of claim 1, wherein the supplemental power supply
comprises a capacitance configured to receive the diverted DC
return current and a voltage of the capacitance is maintained
proportional to the supplemental voltage.
5. The driver of claim 4, wherein the supplemental power supply
comprises a diode connected in series with the capacitance, wherein
the diode is configured to allow the DC return current to charge
the capacitance when the switch is opened and to prevent the
capacitance from discharging through the switch when the switch is
closed.
6. The driver of claim 1, wherein the DC current drive circuit
comprises a boost type switching regulator configured to maintain
the DC supply current at a generally constant level.
7. The driver of claim 1, wherein the DC supply current comprises a
LED supply current, and the DC return current comprises a LED
return current.
8. The driver of claim 1, further comprising a current sensing
circuit coupled in series with the switch and configured to provide
a current sensing voltage related to an amount of the DC return
current.
9. A LED lighting apparatus, comprising: a LED lamp comprising one
or more light emitting diodes; a driver circuit coupled to the LED
lamp and configured to provide a LED supply current to the LED lamp
and to receive a LED return current from the LED lamp; a switch
coupled in series with the LED return current; and a supplemental
power supply configured to receive the LED return current and
produce a supplemental voltage, wherein opening the switch causes
the LED return current to flow through the supplemental power
supply and closing the switch causes the LED return current to
bypass the supplemental power supply.
10. The apparatus of claim 9, wherein the LED lamp comprises one or
more LED elements.
11. The apparatus of claim 9, comprising a cooling device
electrically coupled to the supplemental power supply.
12. The apparatus of claim 11, wherein the cooling device is a
synthetic jet cooling device.
13. The apparatus of claim 9, wherein the supplemental power supply
comprises a control circuit coupled to the supplemental voltage,
the control circuit being configured to open and close the switch
to maintain the supplemental voltage at a desired level.
14. The apparatus of claim 9 wherein the driver circuit comprises a
boost type switching regulator.
15. A method for providing a supplemental voltage in a DC current
driver, the method comprising: producing a DC supply current with
the DC current driver; receiving a DC return current with the DC
current driver; opening a switch that is in series with the DC
return current to divert the DC return current through a
supplemental power supply circuit; closing the switch to have the
DC return current bypass the supplemental power supply circuit; and
using the supply circuit to generate a supplemental voltage from
the DC return current.
16. The method of claim 15, wherein a diode is used to prevent the
supplemental supply voltage from discharging through the
switch.
17. The method of claim 15, further comprising: monitoring the
supplemental voltage and opening and closing the switch to maintain
the supplemental voltage at a generally constant level.
18. The method of claim 15, comprising: providing the DC supply
current to a LED lamp and receiving the DC return current from the
LED lamp.
19. The method of claim 15, wherein producing a DC supply current
comprises using a boost type switching regulator to produce the DC
supply current and receiving the DC return current comprises using
a boost type switching regulator to receive the DC return
current.
20. The method of claim 19, where receiving the DC return current
comprises using a current sensing circuit to monitor the amount of
DC return current and operating the boost type switching regulator
based at least in part on the monitored amount of DC return current
such that the DC supply current is maintained at a generally
constant level.
Description
BACKGROUND
[0001] 1. Field
[0002] The aspects of the present disclosure relate generally to
LED light sources, and in particular DC drive circuits used for LED
lamps.
[0003] 2. Description of Related Art
[0004] A light emitting diode (LED) is an electric light source
constructed from semiconductor materials, often gallium arsenide
and/or gallium nitride. Like other diodes, a light emitting diode
is created by doping the semiconductor material with various
impurities to create a p-n junction. When current is applied to the
LED, charge carriers flow into the p-n junction, where positively
charged holes combine with negatively charged electrons causing the
electrons to fall to lower energy levels thereby releasing energy
as light. As in all diodes, current flows easily from the
positively doped p-side to the negatively doped n-side of the
device, but not in the opposite direction. Therefore, LEDs are
typically driven from a direct current (DC) power source.
[0005] In many applications, such as domestic lighting and street
signaling, DC power may not be readily available, and drive
circuits are used to convert the locally available AC grid power
into regulated DC power to drive the LED lamps. It is important for
these drive circuits to be energy efficient, small in size, and low
cost. Drive circuits used in building lighting and street signaling
applications are also subject to government regulations and must
meet strict requirements, which among other factors, limit
allowable EMI emissions.
[0006] Rising energy costs have created a demand for energy
efficient replacement lighting devices that conform to the same
form factor and electrical requirements as older incandescent light
bulbs, such as those constructed on the ubiquitous Edison screw
base. As LED replacement lamps get higher in wattage, it becomes
necessary to incorporate cooling into the package along with the
drive circuitry and LED lamps. Sub-drivers or supplemental supplies
are often added to the drive circuitry to provide secondary power
for cooling systems or other functionality requiring low level
power. For example, in drive circuits that use a boost type
switching regulator to provide LED drive current, additional
windings are sometimes added to the energy storage inductor to draw
power for the supplemental supplies. However, drive circuits are
typically optimized for the required LED drive current and addition
of supplemental supplies often results in unacceptable performance,
such as EMI emissions in excess of the regulatory limits. Thus, it
becomes challenging to deliver a drive circuit that is cost
effective, has high electrical efficiency, small form factor, and
acceptable EMI performance. This challenge is further complicated
by the need to incorporate supplemental power for secondary loads
such as a cooling system, or other low level circuitry that
provides additional features.
[0007] Accordingly, it would be desirable to provide an LED drive
circuit that addresses at least some of the problems identified
above.
BRIEF DESCRIPTION OF THE DISCLOSED EMBODIMENTS
[0008] As described herein, the exemplary embodiments overcome one
or more of the above or other disadvantages known in the art.
[0009] One aspect of the exemplary embodiments relates to a DC
current driver. In one embodiment, the DC current driver includes a
DC current drive circuit configured to provide a DC supply current
and receive a DC return current, a switch coupled in series with
the DC return current, and a supplemental power supply coupled in
parallel with the switch and configured to provide a supplemental
voltage. Opening the switch diverts the DC return current through
the supplemental supply and closing the switch causes the DC return
current to bypass the supplemental supply.
[0010] Another aspect of the exemplary embodiments relates to a LED
lighting apparatus. In one embodiment, the LED lighting apparatus
includes a LED lamp that has one or more light emitting diodes, a
driver circuit coupled to the LED lamp and configured to provide a
LED supply current to the LED lamp and to receive a LED return
current from the LED lamp, a switch coupled in series with the LED
return current, and a supplemental supply configured to receive the
LED return current and produce a supplemental voltage. Opening the
switch causes the LED return current to flow through the
supplemental power circuit and closing the switch causes the LED
return current to bypass the supplemental power circuit.
[0011] Another aspect of the exemplary embodiments relates to a
method for providing a supplemental voltage in a DC current driver.
In one embodiment, the method includes producing a DC supply
current with the DC current driver, receiving a DC return current
with the DC current driver, placing a switch in series with the DC
return current, opening the switch to divert the DC return current
through a supplemental supply circuit, closing the switch to have
the DC return current bypass the supplemental supply circuit, and
using the supply circuit to generate a supplemental voltage from
the DC return current.
[0012] These and other aspects and advantages of the exemplary
embodiments will become apparent from the following detailed
description considered in conjunction with the accompanying
drawings. It is to be understood, however, that the drawings are
designed solely for purposes of illustration and not as a
definition of the limits of the invention, for which reference
should be made to the appended claims. Additional aspects and
advantages of the invention will be set forth in the description
that follows, and in part will be obvious from the description, or
may be learned by practice of the invention. Moreover, the aspects
and advantages of the invention may be realized and obtained by
means of the instrumentalities and combinations particularly
pointed out in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] In the drawings:
[0014] FIG. 1 illustrates a schematic diagram of one embodiment of
a LED drive circuit configured to provide supplemental power using
a secondary winding on the energy storage inductor.
[0015] FIG. 2 illustrates a block diagram of one embodiment of a
LED drive circuit incorporating aspects of the present
disclosure.
[0016] FIG. 3 illustrates a schematic diagram of one embodiment of
a supplemental power supply incorporating aspects of the present
disclosure.
[0017] FIG. 4 illustrates a graph of EMI performance of one
embodiment of a LED drive circuit incorporating aspects of the
present disclosure.
[0018] FIG. 5 illustrates a flowchart of one embodiment of a method
for using LED drive current for supplemental power incorporating
aspects of the present disclosure.
DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS
[0019] FIG. 1 illustrates a schematic diagram of an exemplary LED
drive circuit or driver, generally indicated by reference 100, as
may be used to provide DC power to a LED type lamp. The LED drive
circuit 100 is configured to receive AC input power, Vin, across
input terminals J1 and J2 where the input power Vin may be any
suitable AC power such as for example, the locally available grid
power, 120 volt (V) 60 Hertz (Hz) power generally available in
North America or the 230V 50 Hz power available in many European
countries, or other suitable AC power sources. The AC input power
Vin is converted to DC power, illustrated as V.sub.DC.sup.+,
V.sub.DC.sup.-, by a diode bridge BR1 where one bridge input 130 is
connected to the AC input terminal J1 through a series connected
fuse F1 and the other bridge input 132 is connected to the other AC
input terminal J2 through a series connected inductance L1. Fuse F1
protects the LED drive circuit 100 from excessive current. A metal
oxide varistor (MOV) RV1 coupled across the bridge inputs 130 and
132 protects circuitry such as the diode bridge BR1 from surges in
the input power which could otherwise damage the LED drive circuit
100. Inductor L1 is used to reduce EMI emissions. Further EMI
reduction can be provided by a filter capacitor C1 connected across
the DC power V.sub.DC.sup.+, V.sub.DC.sup.- through an inrush
current protection or limiting circuit 104. The inrush current
protection circuit 104 connects one side of the filter capacitor C1
to V.sub.DC.sup.- and includes a metal oxide semiconductor field
effect transistor (MOSFET) M1B coupled in series with resistor R1
to limit inrush current to a safe amount. The gate voltage of
MOSFET M1B is controlled by a circuit including resistor R18,
bipolar junction transistor (BJT) Q4, and resistor R10 where the
gate of MOSFET M1B is connected to the collector of BJT Q4 and to a
control voltage Vcc through resistor R10. The base of BJT Q4 is
connected to the source of MOSFET M1B and connected to
V.sub.DC.sup.-.
[0020] LED drive current is regulated by a boost type switching
regulator comprised of an energy storage inductor T1A coupled in
series with a freewheeling diode D1 and a boost switch MOSFET M1A
coupling the inductor T1A to circuit common 134. The LED drive
circuit 100 provides DC power across terminals J3 and J4 and the
drive power is stabilized by a filter capacitor C3 coupled in
parallel across the terminals J3 and J4. When a load is connected
across the terminals J3 and J4 thereby completing the circuit, a DC
current will flow out of terminal J3, through the load, and back
into terminal J4. Using standard current polarity convention, where
positive current is defined as flowing in the opposite direction of
electron flow, as used herein the current flowing out of terminal
J3 is the DC supply current I.sub.S and the current flowing into
terminal J4 is the DC return current I.sub.R. In certain
embodiments the load connected across DC power terminals J3 and J4
includes a suitable LED lamp assembly (not shown). When the load
includes an LED lamp, the DC supply current I.sub.S is referred to
herein as a LED supply current, and the DC return current is
referred to as a LED return current. Alternatively, other types of
loads requiring a regulated DC power may also be advantageously
connected across terminals J3 and J4. The DC return current I.sub.R
flowing into terminal J4 flows through circuit common 134 to a
current sensing circuit 108 before returning to the diode bridge
BR1. DC return current I.sub.R is converted to a proportional
voltage in the current sensing circuit 108 by a pair of resistors
R2 and R2A, referred to as sensing resistors, which are connected
in parallel with each other. A diode VR1 is coupled in parallel
with sensing resistors R2 and R2a to provide voltage protection for
the sensing resistors R2, R2A. In certain embodiments where it is
desirable to use a lower wattage LED lamp assembly, only one
sensing resistor R2 can be used and the other sensing resistor R2A
can be removed.
[0021] A self-oscillating switching control circuit 106 supplies a
switch drive signal 110 to the gate of the boost switch M1A. The
switch drive signal 110 is generated by a buffer circuit including
a pair of complementary bipolar junction transistors Q3A and Q3B.
The n-p-n transistor Q3A is shown connected between the control
voltage Vcc and the switching control signal 110 and p-n-p
transistor Q3B is shown connected between the switching control
signal 110 and circuit common 134. Control current is applied to
the base of both transistor Q3A and transistor Q3B through a
resistor R11. A set point 112 is generated by a resistor divider
network including resistors R6 and R15 and a complementary
transistor Q18 coupled in series between the control voltage Vcc
and the negative dc voltage at V.sub.DC.sup.-. The complementary
transistor Q18 is coupled in series with the resistor divider R6,
R15 to offset the diode drop across transistor Q1A.
[0022] Input voltage at V.sub.DC.sup.+ is included in the setpoint
112 through resistor R16 to improve total harmonic distortion of
the LED driver circuit 100. A summing circuit including BJT Q1A,
resistor R13, and resistor R7 combines the setpoint 112 with the
sense resistor voltage 118, on circuit node 118, to create a
switching control signal at circuit node 116. The sense resistor
voltage 118 is created by the LED return current I.sub.R flowing
through the sensing circuit 108. A latching circuit formed by a
pair of transistors Q2A and Q2B, which each receive their collector
voltage from the control voltage VCC through resistors R9 and R10
respectively is used to latch the switching control signal 116. The
latched switching signal at circuit node 114 is then provided to
the buffer transistors Q3A and Q3B through resistor R11. Combining
setpoint 112 with the control signal 110 through resistor R17
sustains self-oscillatory behavior of the switching control circuit
106. Overvoltage protection is provided by coupling the switching
control signal 116 to the driver output at terminal J3 through a
pair of zener diodes Z1 and Z2 in series with resistor R8.
[0023] Control voltage Vcc is generated during normal operation by
a charge pump circuit 120 including two pumping capacitors C4 and
C2, a pair of series connected diodes D3 and 4 and resistor R5. The
charge pump circuit 120 receives power from a secondary winding T1B
magnetically coupled to the boost inductor T1A. A zener diode Z3
maintains the control voltage Vcc at a steady level. When the LED
driver circuit 100 starts, there is a time period before the charge
pump circuit 120 begins to supply the control voltage Vcc. A
start-up circuit 122 is included to provide control voltage Vcc
during this start-up phase until the charge pump circuit 120 takes
over. A MOSFET M2 receives a gate voltage through series connected
resistor R4 and R4A and allows DC drive power at terminal J3 to
flow through resistor R3 to the control voltage Vcc. Once the
control voltage Vcc achieves its desired level, FET M2 turns off
and control voltage Vcc is provided by the charge pump circuit
120.
[0024] In many LED applications or other DC driver applications it
is desirable to have the driver provide supplemental power for
additional features such as a cooling device which may be used to
control the temperature of a LED lamp. In the exemplary LED drive
circuit 100 illustrated in FIG. 1, a transformer winding T1A is
used as boost energy storage element and a secondary winding T1B is
used to provide power to the switching control circuit 106. In this
configuration the transformer winding T1A, which in this example is
referred to as a boost inductor, also acts as an EMI filter.
Supplemental power is obtained by adding a third winding T1C
magnetically coupled to the boost inductor T1A. However adding a
third winding T1C, shown across terminals J5, J6, to power a
cooling system or other load, can alter the characteristics of the
boost inductor T1A causing the EMI filter band to change, which can
adversely impact the EMI filtering characteristics of the boost
inductor T1A.
[0025] Referring now to FIG. 2, the pictorial diagram illustrates
one embodiment for providing supplemental power in a LED driver
using a boost type regulator, such as the exemplary LED driver
circuit 100 shown in FIG. 1 and described above. In this example,
the LED supply current I.sub.S flows through freewheeling diode D1
and terminal J3 to an LED lamp assembly 204. The LED return current
I.sub.R flows from the LED lamp assembly 204 through terminal J4
back into the LED driver circuit (not shown) through the current
sensing circuit 108. A switch 214 is placed in series with the LED
return current I.sub.R such that when the switch 214 is opened the
LED return current I.sub.R is diverted through a supplemental power
supply or circuit 222 and when the switch 214 is closed the LED
return current I.sub.R bypasses the supplemental power circuit 222
and flows directly back to the LED driver circuit. Referring to
FIG. 1, the LED return current I.sub.R passes through current
sensing circuit 108.
[0026] Switch 214 may be any appropriate type of semiconductor or
mechanical switch capable of efficiently switching the LED return
current I.sub.R as required to regulate power delivered to the
supplemental power circuit 222. A supplemental power control
circuit 220 monitors the supplemental power circuit 222 through a
voltage sensing signal 208 and provides a switching control signal
218 that opens and closes the switch 214. The switching control
signal 218 is alternately opened and closed such that the
supplemental supply voltage 228 is maintained at a generally
constant level. Alternatively, the switch control signal 218 may be
adapted to maintain the supplemental supply voltage 228 at any
desired level including varying levels. The control voltage Vcc,
which in one embodiment can be a low level control voltage, is
received by the supplemental power control circuit 220 and is
returned to the current sensing circuit 108. FIG. 2 illustrates how
the disclosed supplemental power generation method and apparatus
may be applied to a boost type LED driver circuit; however those
skilled in the art will readily recognize that the disclosed method
and circuits may be applied in any type of LED driver circuit or
other DC driver circuit without straying from the spirit and scope
of the disclosed embodiments.
[0027] FIG. 3 illustrates a schematic diagram of one embodiment of
a circuit, generally indicated by numeral 300, fir providing
supplemental power in a LED driver circuit, such as LED driver
circuit 100 of FIG. 1, or other type of DC current driver
incorporating aspects of the present disclosure. In this example, a
supplemental power switch Q100 is placed in series with the return
current I.sub.R which is received at circuit node 312, such that
when the supplemental power switch Q100 is turned on the return
current I.sub.R passes through the supplemental power switch Q100
and exits at circuit node 302 where it returns to a DC driver
circuit (not shown), such as the exemplary LED driver circuit 100
shown in FIG. 1. In the exemplary circuit illustrated in FIG. 3 the
supplemental power switch Q100 is illustrated as an n-channel
MOSFET, however any suitable type of semiconductor or mechanical
switch that is capable of switching the return current I.sub.R at
the desired frequencies may be advantageously used. A supplemental
power control circuit 306 provides a switching signal 310 to
control the supplemental power switch Q100 such that the DC return
current I.sub.R is selectively diverted into a supplemental power
circuit 304 or allowed to bypass the supplemental power circuit
304. When the supplemental power switch Q100 is opened, LED return
current I.sub.R is diverted into the supplemental power circuit 304
which is connected in parallel with the supplemental switch Q100,
where a pair of high capacity electrolytic capacitors C101 and C102
are connected in parallel with the supplemental supply voltage Vs
such that they act to maintain and stabilize the supplemental
voltage Vs. A lower value filter capacitor C103 is also connected
in parallel with the supplemental voltage Vs and provides filtering
of high frequency voltage fluctuations. A diode D101 has its anode
connected to the drain of the supplemental power switch Q100 and
its cathode connected to the positive side of the supplemental
voltage Vs, thus preventing the supplemental voltage from
discharging through the switch Q100 when the switch Q100 is opened.
In this fashion opening the switch Q100 causes the return current
to bypass the supplemental power circuit 304 or supply without
discharging the supplemental supply voltage. In one embodiment, the
second diode D102 has its anode connected to the negative side of
the supplemental voltage Vs and its cathode connected to the
positive side of the supplemental voltage Vs thereby protecting the
supplemental supply capacitors C101 and C102 from negative
voltages. The output voltage Vs may be regulated by selectively
closing and opening the supplemental power switch Q100 such that
the DC return current I.sub.R is diverted to charge the capacitors
C101 and C102 or allowed to bypass the supplemental power circuit
304 respectively.
[0028] The supplemental power control circuit 306 monitors the
supplemental voltage Vs produced across the capacitors C101, C102
of the supplemental power circuit 304 and creates a switching
control signal 310 to regulate the supplemental voltage Vs at a
generally constant level. A control voltage Vcc is received by the
control circuit 306 from any suitable source, such as for example,
the control voltage Vcc produced by the exemplary DC driver circuit
100 illustrated in FIG. 1 and described above. Series connected
resistors R101 and R105 are coupled between control voltage Vcc and
circuit common 316 with the central node 310 connected to the gate
of MOSFET Q100 to provide a current path for the switching signal
310. A Schmitt trigger is constructed from operational amplifier
(op-amp) U1A and feedback resistor R106 and the op-amp U1A receives
its operating power from control voltage Vcc. A reference voltage
is created at the central node 314 of a series connected resistor
R101 and capacitor C104 coupled between the control voltage Vcc and
circuit common 316 and is applied to the inverting input of op-amp
U1A. A diode D103 is coupled in parallel with capacitor C104.
Supplemental voltage Vs is sensed by a resistor divider network
including resistors R103 and R104 coupled between the supplemental
voltage Vs and circuit common 316 such that a feedback voltage is
created at circuit node 308. By applying the feedback voltage at
circuit ode 308 to the non-inverting input of op-amp U1A, the
switching signal 310 will be turned on and off when the
supplemental voltage Vs falls below or rises above, respectively, a
desired value as determined by the reference voltage 314.
[0029] Use of a secondary winding, such as winding T1C as
illustrated in FIG. 1, on the DC driver's boost inductor, which is
magnetically coupled to the energy storage inductor T1A, may
increase EMI emissions above levels allowed by government
regulatory agencies. A supplemental power source coupled to a DC
driver, such as LED driver circuit 100 of FIG. 1, by placing a
supplemental power switch Q100 in series with the DC return current
I.sub.R such that the LED return current I.sub.R can be selectively
diverted into a supplemental power circuit 222, 306 as is
illustrated in FIGS. 2 and 3 and described above, can provide
supplemental power without increasing EMI emissions above
regulatory limits.
[0030] FIG. 4 illustrates a graph of EMI emissions create by the
supplemental power supply 300 illustrated in FIG. 3 when coupled to
an exemplary DC driver such as the LED drive circuit 100 of FIG. 1.
The graph 400 plots EMI emissions 404 in decibel-microvolts versus
frequency in Hertz against one government standard 402, known as
Part 15 Class B, published by the Federal Communications Commission
(FCC) which is an independent agency of the United States Federal
Government. As can be seen in the graph 400, the EMI emissions 404
produced by the exemplary supplemental power supply 300 remain
below the limit set by the FCC throughout the entire spectrum from
1150 kilohertz to 30 megahertz.
[0031] In addition to meeting regulatory limits, the disclosed
exemplary supplemental power supply 300 results in a DC LED driver
with desirable performance characteristics. Table 1 provides some
operating values for an exemplary boost type LED driver including a
supplemental supply 300 coupled to the LED return current I.sub.R
as shown in FIG. 3. The supplemental supply in the example driver
of Table 1 is used to drive a synthetic jet cooling device which is
used to cool the LED lamp. The LED driver receives 23.96 watts of
AC power (Power In) at 119.98 volts (Vin) root mean square (rms)
and 0.203 amps (Iin) rms. The LED driver provides a high power
factor (PF In) of 0.985 with a low total harmonic distortion (THD)
of 15.9%. The LED driver produces 21.98 watts of DC power (Power
Out) at 191.04 volts (Vdc Out) and 114.52 mill-amps (Idc Out)
yielding an efficiency of 91.70%. The advantages of using a
synthetic jet cooling device to cool an LED lamp can be seen in
Table 2. The first row provides measurements made on a standard LED
lamp five minutes after starting the lamp and the second row shows
measurements made on the same lamp ten minutes after starting the
lamp. Current used by the lamp increased by 30 milliamps resulting
in a slight increase in power usage from 23.8 watts to 23.9 watts
while the light output remains stable as shown by the measurements
of Lumens, Xcolor, Ycolor and CCT.
TABLE-US-00001 TABLE 1 Pow- Pow- Vin Iin er PF Vdc Idc er Effic-
(rms) (rms) In In Out Out Out iency THD 119.98 0.203 23.96 0.985
191.04 114.52 21.98 91.70% 15.9%
TABLE-US-00002 TABLE 2 Volts Amps Watts Lumens Xcolor Ycolor CCT
After 119.99 0.2016 23.8 1594.9 .4378 .3996 2949 5 min After 119.99
0.2019 23.9 1581.3 .4377 .3994 2949 10 min
[0032] FIG. 5 illustrates one embodiment of an exemplary method of
generating a supplemental voltage in a DC current driver
incorporating aspects of the present disclosure. The exemplary
method may be used with a variety of DC current driver circuits
such as for example the exemplary LED drive circuit illustrated in
FIG. 1. The method includes using the LED drive circuit 100 of FIG.
1 to generate 502a DC supply current I.sub.S and DC return current
I.sub.R. The DC supply current I.sub.S may be used to drive a LED
lamp assembly or other load requiring a generally constant DC
current and the current flowing from the load back to the DC drive
circuit is referred to herein as the DC return current I.sub.R. A
switch, such as switch 214 of FIG. 2, is placed 504 in series with
the DC return current I.sub.R and may be advantageously placed
between the load and the DC current driver such that the DC return
current I.sub.R flows through the switch 214. A supplemental power
supply, such as power supply 222 of FIG. 2, is coupled 506 in
parallel with the switch 214 such that opening 508 the switch 214
causes the DC return current I.sub.R to be diverted through the
supplemental power supply 222 before it returns to the DC current
driver. Closing 510 the switch 214 causes the DC return current
I.sub.R to bypass the supplemental power supply 222 and return
directly to the DC driver. The DC return current I.sub.R that is
diverted through the supplemental power supply 222 when the switch
214 is opened 508 can then be used to provide 512 a supplemental
supply voltage for use by other circuits or devices. For example
when the exemplary method 500 is used in a LED driver circuit 100,
such as that shown in FIG. 1, the supplemental supply voltage may
be used to power a synthetic jet cooling device adapted to lower
the temperature of the LED lamp. In certain embodiments is
desirable to use a diode to prevent the provided supplemental
supply voltage from discharging when the switch 214 is closed 510.
In one embodiment, this can be achieved by placing a diode, such as
diode D1 of FIG. 2, between the positive side of the switch 214,
which in certain embodiments would be the drain of an n-channel.
MOSFET, and the positive side of the provided supplemental supply
voltage. In some applications it is desirable to use the DC supply
current I.sub.S and DC return current I.sub.R to power a LED lamp.
In these embodiments the DC supply current I.sub.S is provided to a
LED lamp assembly and the current returning from the LED tamp
assembly is the LED return current I.sub.R.
[0033] Thus, while there have been shown, described and pointed
out, fundamental novel features of the invention as applied to the
exemplary embodiments thereof, it will be understood that various
omissions and substitutions and changes in the form and details of
devices and methods illustrated, and in their operation, may be
made by those skilled in the an without departing from the spirit
and scope of the invention. Moreover, it is expressly intended that
all combinations of those elements, which perform substantially the
same function in substantially the same way to achieve the same
results, are within the scope of the invention. Moreover, it should
be recognized that structures and/or elements shown and/or
described in connection with any disclosed form or embodiment of
the invention may be incorporated in any other disclosed or
described or suggested form or embodiment as a general matter of
design choice. It is the intention, therefore, to be limited only
as indicated by the scope of the claims appended hereto.
* * * * *