Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K7/00—Constructional details common to different types of electric apparatus
  • H05K7/20—Modifications to facilitate cooling, ventilating, or heating
  • H05K7/2089—Modifications to facilitate cooling, ventilating, or heating for power electronics, e.g. for inverters for controlling motor
  • H05K7/209—Heat transfer by conduction from internal heat source to heat radiating structure
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H9/00—Details of switching devices, not covered by groups H01H1/00 - H01H7/00
  • H01H9/52—Cooling of switch parts
• • 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 generally relates to electrically isolated control modules. More particularly, the invention relates to an electrically isolated control module having dual insulation layers between an internal line voltage and an external heat sink.
• the typical power tool has a voltage system providing the line voltage for the tool (based on a commercial AC source) and a tool housing enclosing the system.
• Control modules such as a speed controller
• the speed controller may control the rotational speed of the saw blade based on the line voltage and one or more switching signals.
• a controller is typically embedded into an internal enclosure and positioned far enough away from the tool housing to provide the desired amount of electrical isolation between the tool housing and the line voltage.
• the above and other objectives are provided by a power tool in accordance with the principles of the present invention.
• the tool has a voltage system providing a line voltage for the tool and a user-graspable tool housing enclosing the voltage system.
• a double insulated (Dl) control module is connected to the line voltage and mechanically coupled to an interior tool housing surface such that the metal tool housing itself functions as a heat sink for the control module.
• an electronic module includes a power device and a thermal pad.
• the power device is connected to a line voltage, where the power device provides a first layer of electrical insulation between the line voltage and an external tab of the power device.
• the thermal pad is disposed between the external tab and a heat sink.
• the thermal pad provides a second layer of electrical insulation between the external tab and the heat sink.
• a method for isolating a line voltage from a heat sink includes the steps of electrically connecting a power device to the line voltage, and providing a first layer of electrical insulation between the line voltage and an external tab of the power device. The method further provides for positioning a thermal pad between the heat sink and tool housing such that the thermal pad provides a second layer of electrical insulation between the heat sink and tool housing. Isolation is therefore provided by the combination of the first and second layers.
• Figure 1 is a perspective view of a power tool with a user-accessible tool housing in accordance with the principles of the present invention
• FIG. 2 is a perspective view of a power tool housing showing a representative control module location in accordance with the principles of the present invention
• FIG. 3 is a perspective view of a power tool housing cavity showing a control module in accordance with the principles of the present invention
• FIG. 4 is a perspective view of an electronic control module in accordance with the principles of the present invention.
• Figure 5 is a plan view of the electronic control module shown in Figure 4.
• Figure 6A is a section view of the control module taken along lines 6A- 6A shown in Figure 5;
• Figure 6B is a section view of the control module taken along lines 6B-
• Figure 6C is a section view of the control module taken along lines 6C- 6C shown in Figure 5;
• Figure 6D is a section view of the control module taken along lines 6D- 6D shown in Figure 5; and Figure 7 is a perspective view of an alternative embodiment of a control module mounted to an exterior of a power tool housing showing an external thermal pad.
• FIG. 1 a perspective view of an exemplary power tool 10 is shown.
• the present invention will be primarily described with respect to power tools and appliances, the invention is not so limited. In fact, the principles described herein can improve the functionality of any electronic device in which electrical isolation is desired.
• the control module described below is only one type of electronic module that can benefit from the present invention. Thus, sensing modules, power supply modules, display modules and other electronic modules can be improved using the principles described herein. Notwithstanding, the following discussion will demonstrate that power tool control modules have a number of aspects for which the present invention is uniquely suited.
• the power tool 10 has a power cord 12 for providing AC power to the tool 10, and a tool housing 14 that is accessible by a user 16.
• Tool housing 14 encloses a portion of the power cord 12 while the location of a control module 18 of the present invention is shown in phantom. It will be appreciated that the module 18 could be supported within the tool 10 at different locations within the tool.
• the illustration of the control module 18 as being within the handle portion therefore represents one suitable internal area of the tool 10 where the control module 18 could be located.
• the housing 18 may be entirely of a metallic material or some portions thereof may be made from other materials such as plastic.
• control module 18 connects to the power cord 12 and mechanically couples to an interior surface 20 of the tool housing 14 such that the tool housing 14 functions as a heat sink for the electronic control module 18. While the discussion herein will primarily refer to the specific use of the heat sink as a tool housing 14, it will be appreciated that the heat sink is not limited to such an application. Nevertheless, by coupling the control module 18 directly to the tool housing 14, significant space savings and flexibility in mounting the control module 18 are realized.
• the power tool 10 being operated by a user 16 has various external surfaces that are accessible or touchable by the user 16 or which otherwise make user 16 contact.
• the tool housing 14 are often made of a material that is electrically conductive, such as a metal alloy.
• an insulating material such as plastic comprises the tool housing 14 or the exterior surface of the tool housing 14.
• the control module 18 has a housing 22 forming a container with a heat sink cover 24 secured to the module housing 22 by screws 26 and 28.
• the control module 18 is secured to a mounting surface, such as interior surface 20 of tool housing 14 as shown in Figure 3, by fastening members which extend through holes 30 and 32.
• the control module 18 may be secured to a mounting surface by an adhesive.
• the heat sink cover 24 and module housing 22 provide a gap 34 for a wiring harness 36 to pass and be operatively coupled to the power cord 12.
• the module housing 22 encloses a circuit board, power device and thermal pad (to be described below).
• the control module 18 includes a power device 38 and a thermal pad 40.
• the power device 38 is preferably an isolated-tab thyristor and is electrically connected to an AC voltage source.
• an external tab 42 of the power device 38 is electrically isolated from the AC voltage source. Isolated-tab thyristors are commercially available and commonly provide a minimum breakdown voltage of 2700 volts.
• the power device 38 provides a first layer of electrical insulation between the line voltage and the external tab 42.
• the thermal pad 40 is disposed between the external tab 42 and the heat sink cover 24.
• the thermal pad 40 provides a second layer of electrical insulation between the external tab 42 and the heat sink cover 24.
• the power device 38 and thermal pad 40 combine to provide a predetermined amount of electrical insulation between the AC source and the tool housing 14 ( Figure 1 ).
• This double layer of insulation enables a user 16 to contact all external surfaces of the tool housing 14 without fear or risk of electrical shock. Additionally, this double layer of insulation meets TUV and UL requirements with respect to insulation and control module 18 spacing requirements from a user contact surface.
• connection mechanism 44 is coupled to the module housing 22.
• the connection mechanism is formed by screws 26 and 28 and a support component 49.
• the support component 49 is formed by a first post 50, a second post 52 and a bridge 54 extending between the posts 50 and 52.
• the connection mechanism 44 functions to compress the thermal pad 40 to a controlled minimum thickness of about 1.0 mm.
• One such thermal pad 40 for example, is available from Fuji Polymer Industries of Japan under the trade name Sarcon®. This material provides a minimum of approximately 2000 volts of electrical insulation and is compressed to a thickness of approximately 1.1 mm. This 1.1 mm thickness meets the mechanical UL requirement for isolation. Considerations in selecting the thermal pad 40 include strength of the material, softness, thermal conductivity, and electrical conductivity.
• a wiring harness 36 couples the AC line voltage from the power cord 12 to the control module 18.
• the circuit board 46 is coupled to the power device 38 and to the wiring harness 36.
• the circuit board 46 contains conductors for coupling the AC line voltage to the power device 38.
• the control module 18 includes a module housing 22 coupled to the tool housing 14, where the module housing 22 encloses the circuit board 46, the power device 38 and the thermal pad 40.
• a potting compound 48 is disposed within the module housing 22 to provide required further isolation, structural support, and environmental protection. Acceptable potting compounds are commercially available from a number of well known sources.
• the preferred connection mechanism 44 includes the support member 49 having the first post 50, contacting a first edge of the circuit board 46, and the first screw 26, coupled to the first post 50.
• the second post 52 contacts a second edge of the circuit board 46, while the second screw 28 couples to the second post 52.
• the bridge 54 includes wall portion 56 and portion 58 which cooperatively form a receptacle for nesting the power device 38 therein.
• the bridge 54 is also responsible for maintaining the required thickness of the thermal pad 40 between the external tab 42 and the heat sink cover 24, enhancing the mechanical support provided to the power device 38, and maintaining isolation between screws 26 and 28 and the AC line voltage.
• the support member 49 is preferably made of plastic, and preferably formed as a single integral formed component.
• Assembling the control module 18 of the present invention entails soldering the power device 38 to the circuit board 46 including bending an electrical lead of the power device 38 into a generally "L" shaped configuration 38a that extends into and through the circuit board 46 and into the potting compound 48 as shown in Figure 6D.
• the bridge 54 is disposed between the power device 38 and the circuit board 46.
• the thermal pad 40 is then applied to the heat sink cover 24, and the thermal pad 40 and heat sink cover 24 assembly is coupled to the circuit board 46 and associated bridge 54, via the connection mechanism 44 shown in Figures 6A and 6B.
• the circuit board 46, connection mechanism 44, and thermal pad 40 assembly is disposed within the module housing 22 and then potted with the potting compound 48.
• the control module 60 includes a thermal pad 62 interposed between a module heat sink cover 64 and a tool housing 66.
• the thermal pad 62 is preferably approximately 1.2 mm thick and provides the additional insulation necessary to surpass current Dl standards for Europe and the United States.
• a wiring harness 68 extends through an aperture 70 defined by a housing surface 72 of a module housing 74. Screws 76 and 78 extend through holes 80 and 82, respectively, for attachment of the module housing 74 to the tool housing 66. Also, a creepage and clearance distance/path between the tool housing 66 and the heat sink cover 64, in accordance with arrow 65, needs to be provided of about 4 mm.
• the tool housing 66 is usable as a heat sink for the control module 60 without risk of electrical shock if user contact is made with tool housing 66.
• the control module 60 of the Figure 7 embodiment does not possess a thermal pad 40 enclosed within the control module 18, as shown in Figures 6A-6D.
• control module 60 exemplifies an external thermal pad 62 approach to a dual insulation layer concept.
• wiring harness 68 must meet applicable UL insulation requirements.
• An electronic control module 18 is therefore provided that offers a dual insulation arrangement between the power cord 12 and the tool housing 14 that also serves as a heat sink thereby allowing versatility in mounting the electronic control module 18 to the interior surface 20 and also eliminating the risk of electrical shock to a user 16 making contact with the tool housing 14. Additionally, the double insulated control module 18 provided meets or exceeds TUV and UL standards for its application within a tool housing 14.

Landscapes

• Engineering & Computer Science (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Cooling Or The Like Of Electrical Apparatus (AREA)
• Cooling Or The Like Of Semiconductors Or Solid State Devices (AREA)
• Registering, Tensioning, Guiding Webs, And Rollers Therefor (AREA)
• Conductive Materials (AREA)
• Control And Other Processes For Unpacking Of Materials (AREA)
• Internal Circuitry In Semiconductor Integrated Circuit Devices (AREA)
• Control Of Electric Motors In General (AREA)

Priority Applications (9)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

Country Status (11)

Cited By (2)

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Citations (2)

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• 2002
  • 2002-08-09 DE DE60239942T patent/DE60239942D1/de not_active Expired - Lifetime
  • 2002-08-09 NZ NZ531008A patent/NZ531008A/en not_active IP Right Cessation
  • 2002-08-09 JP JP2003521074A patent/JP4130628B2/ja not_active Expired - Fee Related
  • 2002-08-09 CN CN02820232.5A patent/CN1593075B/zh not_active Expired - Fee Related
  • 2002-08-09 WO PCT/US2002/025547 patent/WO2003017742A1/en not_active Ceased
  • 2002-08-09 CA CA002457438A patent/CA2457438A1/en not_active Abandoned
  • 2002-08-09 EP EP02780260A patent/EP1421837B1/en not_active Expired - Lifetime
  • 2002-08-09 AU AU2002343325A patent/AU2002343325B2/en not_active Ceased
  • 2002-08-09 AT AT02780260T patent/ATE508621T1/de not_active IP Right Cessation
  • 2002-08-09 TW TW091118014A patent/TW579322B/zh not_active IP Right Cessation
  • 2002-08-09 BR BR0211840-8A patent/BR0211840A/pt not_active IP Right Cessation

Patent Citations (2)

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