Fan control circuit and package

A dual output power module housing a dual output power circuit for providing variable power to two parallel connected fan motors is shown. The power module includes a pad which has disposed thereon two power switching devices, two intelligent power switches, and a power circuit board on which circuits for controlling the intelligent power switches are disposed. The module includes a power shell that surrounds the dual output power circuit, and a resilient, flexible enclosure which encapsulates the power shell and the circuit components within the power shell.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This application relates to power modules and, more specifically, to a fan control power module for automotive use.

2. Description of the Related Art

Radiators in modern automobiles are typically cooled using two independently controllable fans. The motors that run the fans are controlled using fan control circuits. These fan control circuits are large and relatively complex and can be difficult to mount, troubleshoot or replace.

It is, therefore, desirable to provide a simplified fan control circuit and a module type housing that is small, inexpensive, easy to install and remove, and capable of withstanding the harsh environment in an automobile engine to ensure reliable operation.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, a dual output power circuit is packaged in a power module. The dual output power circuit includes two fan control circuits which are used to drive two parallel connected DC brush electrical motors, such as those typically used to run the radiator fans in a car engine. Each control circuit according to the preferred embodiment includes a power switching device such as a MOSFET or an IGBT, an intelligent power switching device (IPS), and an IPS control circuit.

A power module according to the present invention can provide to each electrical motor a profile of current with fixed or variable frequency and variable duty cycle. This allows for more control over the speed of the motors and thus better control over the cooling rate.

A factor that must be considered in the design of a power module is the temperature of the power switching devices during operation. MOSFETs, for example, should remain below 175° C. in order to ensure reliable performance. The temperature of the power switching devices in a module can be controlled by controlling the frequency and the duty cycle. Thus, power dissipation can be varied by manipulating these features. The frequency and the duty cycle can be varied depending on the input. The present preferred embodiment is designed around the following:Frequency=20 HzMax Ambient Temp.=105° C.Steady State Current Across Each Motor=14 Amps at 14VMin. Duty Cycles=30%

These conditions provide a power loss that can be dissipated by the power module without compromising its reliability and functionality. A power module according to the present invention can operate at 50 Hz with few modifications to the control circuit.

The power module, which includes the dual output power circuit, includes a lead frame structure which is supported by a power shell. The lead frame includes a flat copper pattern of a relatively large area. The power switching devices are electronically and thermally connected to the flat copper pattern by, for example, soldering or a conductive epoxy. Respective IPSs for driving the power switching devices may also be connected to the flat copper pattern. Respective circuit components used in the IPS control circuits are disposed on a power circuit board (PCB). The PCB may be glued onto the flat copper pattern as well. Wire bonds may be then used for making the appropriate electrical connections between the various components. The components may then be protected by a potting compound such as a silicone gel.

A power module according to the present invention may also include a feature for detecting the status of the motors. According to the preferred embodiment, the feature for detecting the status of the motors includes a resistor connected to each motor which provide a status output representing the average speed of the electrical motors and warning when one or both are stalled.

A power module according to the present invention includes input and output leads that extend through the power shell to the exterior thereof. The portion of the leads extending outside of the power shell are connected to cables which provide appropriate electrical connections to the components within the power shell. One of the leads according to the present invention extends from an edge of the flat copper pattern through the power shell to the exterior thereof. This extension is electrically and thermally connected to a cable, which cable is connected to a terminal of a power source such as a battery. Thus, electrical power may be transferred from the power source to the power switching devices. Advantageously, the heat generated by the power switching devices may also be dissipated through the cable that is connected to the extension.

A power module according to the present invention also includes a soft, polyamide enclosure which encapsulates the power shell, the leads extending from the power shell, the components contained within the power shell, and at least those portions of wires that are connected to the leads.

In a power module according to the present invention, the flat copper pattern has a wider area than the power switching devices disposed thereon, which results in good heat dissipation due to heat spreading. The heat spreading combined with heat dissipation through the electrical cables allow for effective thermal management.

Moreover, a power module according to the present invention eliminates connector needs, thereby reducing losses incurred due to connections. In addition, because all of the electrical cables going to and coming from the electrical motors are contained within the power module, the module can be installed and removed more easily. Also, the rubbery enclosure makes the module resilient and thus resistant to vibrations, as well as light weight.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIG. 1, a schematic diagram of a dual output power circuit10which may be incorporated in a power module according to the present invention is shown. The dual output power circuit10includes two motor driver circuits12,14, each for driving a respective motor16,18. Each motor driver circuit12,14includes a respective power switching device20,22which is connected between the positive power terminal of a battery +Vbatt and a power terminal of a respective motor16,18. Each power switching device20,22is preferably a MOS-gated device such as a power MOSFET, or IGBT. In a preferred embodiment, vertical conduction MOSFETs (GEN7) which are available from the International Rectifier may be used. Other power switching devices, such as power diodes, can also be used in a power module according to the present invention. Each power switching device20,22is switched by a respective control circuit24,26according to a desired frequency and for a desired duty cycle in order to vary the power delivered to each motor16,18. Each control circuit24,26is connected to a respective input terminal which are electrically connected to respective input leads (28,30, FIG.2). The control circuits24,26receive signals via input terminals according to which the frequency and duty cycle of the current delivered to each motor16,18is controlled.

The fan control circuit10also may include a status terminal32which is connected to respective status resistors34,36. The status resistors34,36are connected to respective motors16,18. The output of each status resistor34,36can be used as an indicator of the performance of each motor16,18, for example through current sensing. The status resistors34,36can also be used to determine whether one or both motors16,18are stalled.

The motors16,18are connected to a circuit common which is connected to the negative terminal of the battery −Vbatt.

Referring now toFIG. 2, a schematic view of a first arrangement of components in a power module38according to the present invention is shown. A power module according to the present invention includes a lead frame comprising a large, flat pad40which has electrically mounted thereon power switching devices20,22. The pad40includes an extension42. The pad40and the extension42are integrally connected so as to form a unitary body. The positive terminal of the battery +Vbatt is connected electrically to the extension42by a wire (not shown). The heat generated by the power switching devices20,22is spread by the pad40and partially dissipated through the body of the power module38. Also, the generated heat from the power switching devices20,22is transferred via the extension42to the cable that connects the extension42to the positive terminal of the battery +Vbatt and is thereby dissipated by the cable. A power circuit board (PCB)44is disposed on the pad40. The PCB44is preferably an ordinary circuit board but may also be a thermally conductive substrate such as an insulated metal substrate (IMS) which has a conductive circuit pattern formed on the top surface thereof. Intelligent power switches (IPSs)46,48for switching respective power switching devices20,22are disposed on the pad40. The IPSs46,48are connected to respective IPS control circuits (not shown) which are disposed on the PCB44. The IPSs46,48and their respective IPS control circuits (not shown) form the control circuits24,26, which are schematically shown in FIG.1. The PCB44includes conductive portions which electrically connect the IPS control circuits (not shown) to respective input terminal leads28,30via wire bonds50,52. A plurality of wire bonds54,56electrically connect the terminals of the power switching devices20,22to respective output terminal leads58,60. The output terminal leads are connected via cables to the motors (16,18, FIG.1).FIG. 2also schematically shows the ground cables60,62which connect the negative terminal −Vbatt of the battery and the motors (16,18, FIG.1).

As shown inFIG. 2, the extension42is disposed between input terminal leads28,30. Also, the input terminal leads28,30and the extension42are disposed along one side of the pad40, while the output terminal leads58,60are disposed along an opposing side of the pad40.

FIG. 3shows the schematic of a second embodiment of power module38. A power module38according to the alternative arrangement includes a status terminal lead66. The status terminal lead66is connected to a conductive portion on the PCB44via a wire bond68. In this embodiment, status resistors (34,36,FIG. 1) are also disposed on PCB44. In normal operation, the voltage at the status terminal lead66should be at the battery voltage. To detect a failing branch, the power switching devices20,22are opened successively. Also, in this embodiment, the extension42is extended from one corner of the pad40rather than being disposed between input terminal leads28,30.

FIG. 4shows the PCB44having disposed thereon the status resistors34,36, and the various components for the IPS control circuits70,72. The status resistors34,36are preferably 0.5 W, 15K ohm resistors. Each IPS control circuit preferably includes a 22 nF capacitor74,76parallel connected with a 40V zener diode78,80. This parallel configuration is series connected with a 60V Schottky diode82,84. Each Schottky diode82,84is series connected with a respective input resistor86,88which are in turn electrically connected to the input terminal leads (28,30, FIG.2and FIG.3).

FIG. 5shows a PCB44according to an alternative embodiment. In this embodiment the 60V Schottky diodes (82,84,FIG. 4) are replaced with 1 W 100 ohm resistors90,92and the input resistors (86,88,FIG. 4) are replaced with jumpers94,96.

The capacitors act as an input filter and for anti-bounce, and the zener diodes act as an active clamps. If desired these components may be included in the IPS control circuits.

A power module according to the present invention is assembled as follows. A blank lead frame98as shown inFIG. 6is first provided. The blank lead frame is substantially flat and is preferably made of a copper plate of approximately 1 mm of thickness. The blank lead frame98includes a pad40having an extension42extending from an edge thereof. The pad has substantially the same thickness as the remainder of the blank lead frame. The terminal leads, namely, the input terminal leads28,30, the status terminal lead68, and the output terminal leads58,60are disposed near an edge of the pad40without making contact with the same.

Next, a power shell100is formed around the lead frame by for example a molding process so as to support the various leads and the power input pad40as shown in FIG.7. The electrical components forming the dual output power circuit are preferably all disposed within the power shell100once it is formed. The power shell100is formed so that the terminal leads (28,30,58,60,68) and the extension42extend through the walls of the power shell100thus providing a means for electrical connection to the components contained therein. Next, the excess portions of the blank lead frame98are trimmed, thus separating the terminal leads (28,30,58,60,68) and the extension42from one another as shown in FIG.8.

Next, as shown inFIG. 9, the power switching devices20,22, the IPSs46,48and the PCB44are placed on the pad40. The PCB44is preferably glued onto the pad40, while the power switching devices20,22and the IPSs46,48are thermally and electrically connected to the pad40by for example a conductive epoxy. Bonding wires are then used to make the appropriate electrical connections to the terminal leads. Potting compound may be then deposited over the circuit arrangement within the power shell100as shown in FIG.10. Alternatively, a COPACK that includes the IPS and the power switching device may be used to protect the power switching devices from environmental damage caused by for example humidity, thus omitting the need to use a potting compound. As a further alternative, dies on a thick (1 mm) copper substrate could also be used. This may, however, increase the cost of wiring and possibly the size of the driver.

As shown inFIG. 10, the power shell100may include two or more wire posts102,104,106. The wire posts may be disposed on the corners of the power shell100. The wire posts102,104,106receive the ground wires61,62and secure the same to the power shell100.

Cables are also connected to the leads28,30,58,60,68and the extension42. The entire arrangement as shown inFIG. 10is then encapsulated in an insulating polyimide compound as schematically shown in FIG.11. This provides for an insulated and flexible enclosure108for the power module. As shown in this figure the cables, which constitute the harness, are partially enclosed by the enclosure108and extend out from the same.

To ensure optimum operability of the power module, full RTHmust be in the range of 20 to 30° C./W, which will also protect the motor and the harness. Also preferably no connectors should be used since it would increase losses and reduce cooling via wires. The harness in a module according to the present invention is integrated with the module which reduces cost (fewer connectors) and improves reliability.

By placing the module in the path of the air flow from the fan further cooling of the module may be accomplished. Depending on the application, however, air flow to cool the module may not be necessary.

If a COPACK is used its structure may include:Co-pack with 2 mils and 20 mils wires.Driver=IPSXXMosfet=GEN7 40V 165 mm by 303 mm Hex 4.5 with current sense;2.5 mOhm 40V in Super 220