Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F21—LIGHTING
  • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
  • F21V29/00—Protecting lighting devices from thermal damage; Cooling or heating arrangements specially adapted for lighting devices or systems
  • F21V29/50—Cooling arrangements
  • F21V29/60—Cooling arrangements characterised by the use of a forced flow of gas, e.g. air
  • F21V29/61—Cooling arrangements characterised by the use of a forced flow of gas, e.g. air characterised by control arrangements
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F21—LIGHTING
  • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
  • F21V29/00—Protecting lighting devices from thermal damage; Cooling or heating arrangements specially adapted for lighting devices or systems
  • F21V29/50—Cooling arrangements
  • F21V29/70—Cooling arrangements characterised by passive heat-dissipating elements, e.g. heat-sinks
  • F21V29/80—Cooling arrangements characterised by passive heat-dissipating elements, e.g. heat-sinks with pins or wires
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
  • G05D23/00—Control of temperature
  • G05D23/19—Control of temperature characterised by the use of electric means
  • G05D23/20—Control of temperature characterised by the use of electric means with sensing elements having variation of electric or magnetic properties with change of temperature
  • G05D23/24—Control of temperature characterised by the use of electric means with sensing elements having variation of electric or magnetic properties with change of temperature the sensing element having a resistance varying with temperature, e.g. a thermistor
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
  • H05B45/30—Driver circuits
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F21—LIGHTING
  • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
  • F21V29/00—Protecting lighting devices from thermal damage; Cooling or heating arrangements specially adapted for lighting devices or systems
  • F21V29/50—Cooling arrangements
  • F21V29/60—Cooling arrangements characterised by the use of a forced flow of gas, e.g. air
  • F21V29/67—Cooling arrangements characterised by the use of a forced flow of gas, e.g. air characterised by the arrangement of fans
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F21—LIGHTING
  • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
  • F21V29/00—Protecting lighting devices from thermal damage; Cooling or heating arrangements specially adapted for lighting devices or systems
  • F21V29/50—Cooling arrangements
  • F21V29/70—Cooling arrangements characterised by passive heat-dissipating elements, e.g. heat-sinks
  • F21V29/74—Cooling arrangements characterised by passive heat-dissipating elements, e.g. heat-sinks with fins or blades
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F21—LIGHTING
  • F21Y—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES F21K, F21L, F21S and F21V, RELATING TO THE FORM OR THE KIND OF THE LIGHT SOURCES OR OF THE COLOUR OF THE LIGHT EMITTED
  • F21Y2105/00—Planar light sources
  • F21Y2105/10—Planar light sources comprising a two-dimensional array of point-like light-generating elements
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F21—LIGHTING
  • F21Y—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES F21K, F21L, F21S and F21V, RELATING TO THE FORM OR THE KIND OF THE LIGHT SOURCES OR OF THE COLOUR OF THE LIGHT EMITTED
  • F21Y2115/00—Light-generating elements of semiconductor light sources
  • F21Y2115/10—Light-emitting diodes [LED]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/0001—Technical content checked by a classifier
  • H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

Definitions

• the present invention relates to light-emitting diodes and, in particular, to a thermal control system for a light-emitting diode fixture.
• Light-emitting diodes like any semiconductor, emit heat during their operation. This is because not all of the electrical energy provided to a light-emitting diode is converted to luminous energy. A significant portion of the electrical energy is converted to thermal energy which results in an increase in the temperature of the light-emitting diode.
• resistor driven circuits as the temperature of the light-emitting diode increases, the forward voltage drops and the current passing through the PN junction of the light-emitting diode increases. The increased current causes additional heating of the PN junction and may thermally stress the light-emitting diode.
• Thermally stressed light-emitting diodes lose efficiency and their output is diminished. In certain situations, optical wavelengths may even shift causing white light to appear with a blue tinge. Thermally stressed light-emitting diodes may also impose an increased load on related driver components causing their temperature to increase as well. This may result in broken wire bonds, delaminating, internal solder j oint detachment, damage to die-bond epoxy, and lens yellowing. If nothing is done to control the increasing temperature of the light emitting diode, the PN junction may fail, possibly resulting in thermal runaway and catastrophic failure.
• Thermal control of light-emitting diodes involves the transfer of thermal energy from the light-emitting diode. Accordingly, one aspect of light-emitting diode fixture design involves efficiently transferring as much thermal energy as possible away from the PN junction of the light-emitting diode. This can generally be accomplished, at least in part, through the use of a heat sink. However, for more powerful light-emitting diode fixtures in the 20 to 60 watt range or in applications where numerous light-emitting diodes are disposed within a confined space, an additional cooling means may be required to maintain performance. This is because the thermal energy generated by the light-emitting diodes may at times exceed the thermal energy absorbed and dissipated by the heat sink. In these situations a cooling fan is typically used in combination with the heat sink.
• a heat sink and a cooling fan are thermally coupled to a light source comprised of a plurality of light-emitting diodes.
• a thermal sensor senses the temperature of the light source and signals a controller to operate a variable speed cooling fan, based on the temperature of the light source, to maintain the fixture within a desired temperature range.
• a controller typically in the form of microprocessor, increases the number of components in the thermal control system and thereby increases manufacturing costs.
• a thermal control system for a light-emitting diode fixture which has a reduced number of component parts.
• a thermal control system for a light-emitting diode comprising a thermistor thermally coupled to a heat sink.
• the thermistor is disposed within a thermally conductive member.
• a power supply is electrically connected to the thermistor.
• a cooling device is electrically connected in series with the power supply and the thermistor with the thermistor being disposed between the power supply and the cooling device.
• a rheostat may further be electrically connected, in series, between the thermistor and the power supply.
• a light-emitting diode fixture having a thermal control system.
• the fixture comprises a heat sink thermally coupled to a light-emitting diode.
• a thermistor is thermally coupled to the heat sink.
• the thermistor is disposed within a thermally conductive member.
• a power supply is electrically connected in parallel to the light-emitting diode and the thermistor.
• a cooling device is electrically connected in series with the power supply and the thermistor with the thermistor being disposed between the power supply and the cooling device.
• a rheostat may further be electrically connected, in series, between the thermistor and the power supply.
• Figure l is a simplified block diagram of an improved thermal control system for a light- emitting diode fixture according to an embodiment of the present invention
• Figure 2 is a circuit diagram of the thermal control system of Figure 1;
• Figure 3 is a perspective view, partly in section, of a light-emitting diode fixture provided with the thermal control system of Figure 1; and
• Figure 4 is a graph showing various temperatures of a light-emitting diode fixture provided with the thermal control system of Figure 1.
• FIG. 1 shows a simplified block diagram of an improved thermal control system cooling system 10 for a light-emitting diode fixture 11 which is shown in Figure 3.
• a DC power supply 12 is connected to a light- emitting diode 14 mounted on a printed circuit board 18.
• the light-emitting diode 14 and printed circuit board 18 are thermally coupled to heat sink 16 by a thermal conductive member, in this example, a metal plate 19.
• a thermal conductive member in this example, a metal plate 19.
• the metal plate 19 preferably formed of copper or aluminum, is disposed between the printed circuit board 18 and the heat sink 16.
• the power supply 12 is also connected to a cooling device which, in this example, is cooling fan 20.
• a thermistor 22, thermally coupled to the heat sink 16, is connected in series between the DC power supply 12 and the cooling fan 20.
• the thermistor 22 is disposed within, or nested in, the metal plate 19.
• a resistor, in the form of a rheostat 24, is further connected in series between the thermistor 22 and the cooling fan 20.
• the cooling fan 20, thermistor 22, and rheostat 24 define a control circuit.
• FIG. 2 shows a circuit diagram of the thermal control system 10.
• a plurality of light-emitting diodes 14a, 14b, 14c, and 14d form an LED array 15.
• the light-emitting diodes may be connected in both series and in parallel.
• TheLED arrayl5 is thermally coupled to the heat sink 16.
• the DC power supply 12 provides current to the individual light-emitting diodes 14a, 14b, 14c, and 14d.
• the LED array 15 converts electrical energy from the current provided by the DC power supply 12 into both luminous energy and thermal energy. The luminous energy is emitted as light and the thermal energy is absorbed and subsequently dissipated by the heat sink 16.
• the DC power supply 12 also provides current to a DC motor 26 of the cooling fan 20.
• the thermistor array 28 is thermally coupled to the heat sink 16 and is sensitive to the temperature of the heat sink
• the resistance of the thermistor array 28 decreases. As the temperature of the heat sink 16 decreases, the resistance of the thermistor array 28 increases. Accordingly, the flow of current to the motor 26 of the cooling fan 20 is a function of the temperature of the heat sink 16.
• Other embodiments of the thermal control system may not include a rheostat connected in series between the thermistor array and the cooling fan. In such embodiments the cooling fan simply operates in an operational/non-operational manner dependent on the flow of current to the motor of the cooling fan which, as a result of the thermistor array, is a function of the temperature of the heat sink.
• other wiring diagrams for the light-emitting diodes and thermistors may be used to form the LED array and the thermistor array.
• FIG. 3 shows the thermal control system 10 disposed within a housing 30 of the light-emitting diode fixture 11.
• the heat sink 16 is connected to the housing 30 and a rear of the housing 30 incorporates the heat sink 16.
• the heat sink 16 is formed of copper or aluminum in this example and has a plurality of fins 32a and 32b which increase the surface area of the heat sink 16.
• Thermal energy generated by the light-emitting diodes 14a, 14b, 14c, and 14d in the LED array 15 is transferred to the heat sink 16 by conduction.
• the cooling fan 20 is also disposed within the housing 30 and faces the heat sink 16. The cooling fan 20 provides cooling air to the heat sink 16 to assist in transfer of thermal energy from heat sink 16 by convection. The addition of the cooling air increases the efficiency of the heat sink 16 by 20%-30%.
• Ps The approximate total power consumption (Ps) of the LED array is determined using the following equation:
• PD is the nominal value power of the individual light-emitting diodes; and N is the total number of light-emitting diodes in the LED array.
• Vs the required voltage
• Vf is the forward voltage drop of the light-emitting diodes
• n is the number of light-emitting diodes which are connected in series in the LED array. and the required current (Is) is determined using the following equation:
• If is the forward current of the light-emitting diodes; and m is the number of strings or legs connected in parallel in the LED array.
• Si is the value of the minimum dissipative surface area of the heat sink required to maintain the desired temperature (TPCB) of the LED array and to compensate for thermal energy from 1 W of the total power consumption (Ps) of the LED array.
• Si values can be obtained by statistical analysis of experimental data from trials on different heat sinks and LED arrays.
• the base area (SB), or footprint, of the heat sink and the height (HHS) of the heat sink are determined using known geometric principles.
• the type, quantity, and connection diagram for the cooling fan or fans used in the thermal control system is determined to satisfy the following conditions:
• the total power (PFT) applied to the fans must not be more than:
• the voltage drop (VFS) of the fan or series-connected fans and the voltage drop of the control circuit (Vc), ie. forward voltage drop of the series connection of the resistance of the thermistor array and the rheostat, must not be more than:
• VFS + VC VS (Equation 6) Taking into account that:
• Equation 5 Equation 8
• Equation 9 the appropriate type of fans can be selected.
• the overall dimensions of the selected fans must be matched with the calculated overall dimensions of the heat sink.
• Equation 8 Equation 11, and Equation 13 the value (RT) of the thermistor is determined using the following equation:
• Equation 12 Equation 12 and Equation 13 the value RR is determined using the following equation:
• Equation 16 and Equation 18 provide the ability to select the basic components of the thermal control system 10, i.e. the thermistors 22a, 22b, 22c, and 22d, the rheostat 24, and the cooling fan 20 using one basic value, namely, the resistance (Rs) of the LED array 15.
• the temperature of the fixture 11 exceeds the temperature of the ambient environment, or room temperature, as best shown in Figure 4. This is because electrical energy supplied to the light-emitting diodes 14a, 14b, 14c, and 14d by the DC power supply 12, is converted to both luminous and thermal energy.
• the thermal energy is, in part, absorbed and dissipated by the heat sink 16 allowing the light- emitting diodes 14a, 14b, 14c, and 14d to remain near a predetermined set temperature point to prevent thermal runaway.
• the resistance of the thermistor array 28 decreases. This causes an increased current flow from the DC power source 12, through the thermistor array 28 and the rheostat 24, to the cooling fan 20.
• the increased current flow to the cooling fan 20 results in an increase in the output of the cooling fan 20.
• the cooling fan 20 blows cooling air over and/or through the heat sink 16 to increase the heat transfer coefficient, i.e. the rate at which the heat sink 16 transfers the thermal energy to the ambient environment, thereby increasing the efficiency of the heat sink 16 and preventing the fixture 11 from overheating.
• the resistance of the thermistor array increases. This causes a decrease in the current flow from the DC power source 12, through the thermistor array 28 and the rheostat 24, to the cooling fan 20.
• the decreased current flow to the cooling fan 20 results in a decrease in the output of the cooling fan 20 thereby conserving energy and minimizing noise.
• the cooling fan 20 in non-operational. Accordingly, in conditions where the heat sink 16 alone is able to effectively dissipate the thermal energy generated by the light-emitting diodes 14a, 14b, 14c, and 14d the cooling fan 20 is non-operational.
• the cooling fan 20 When the temperature of the heat sink again increases and exceeds the threshold value the cooling fan 20 is again operational. [0022] As shown in Figure 4, by operating in a cyclic, variable speed operational/non- operational manner, as described above, the cooling fan 20 is able to maintain the heat sink 16, and by extension the LED array 15, within a desired temperature range when the fixture 11 is ON. It will be understood that when the fan is operational it may operate consistently at full speed or at variable speeds dependent on the circuitry of the thermal control system

Landscapes

• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Automation & Control Theory (AREA)
• Led Device Packages (AREA)
• Cooling Or The Like Of Semiconductors Or Solid State Devices (AREA)
• Non-Portable Lighting Devices Or Systems Thereof (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

Family

ID=41608172

Family Applications (1)

Country Status (5)

Cited By (3)

Families Citing this family (47)

Citations (2)

Family Cites Families (31)

• 2008
  • 2008-07-30 US US12/182,972 patent/US8070324B2/en not_active Expired - Fee Related
• 2009
  • 2009-07-30 JP JP2011520291A patent/JP2011529627A/ja active Pending
  • 2009-07-30 CA CA2770394A patent/CA2770394C/en active Active
  • 2009-07-30 DE DE112009001839T patent/DE112009001839T5/de not_active Withdrawn
  • 2009-07-30 WO PCT/CA2009/001050 patent/WO2010012084A1/en not_active Ceased

Patent Citations (2)

Also Published As

Similar Documents

Legal Events