Winding supply circuit with current and thermal protective elements

A winding circuit for use in a fan includes first and second integrated circuits that each include a transistor for powering first and second fan windings in the fan, and at least one of a thermal shutdown element that switches the winding circuit "off" if the integrated circuit reaches a predetermined temperature, and a current regulating circuit. The fan includes a rotor having a magnet, and a stator having a magnet sensor to alternatively transmit current to the first and second windings, which also are located in the stator. The integrated circuits may be autoprotected MOSFETs and the magnet sensor may be a Hall effect sensor.

FIELD OF THE INVENTION 
This invention generally relates to fans and, more particularly, to winding 
supply circuits for fans. 
BACKGROUND OF THE INVENTION 
Fans commonly are utilized in many applications such as, for example, for 
cooling electronic elements within a computer system. One such fan is 
shown in U.S. Pat. No. 4,656,553 (Brown), the disclosure of which is 
incorporated herein, in its entirety, by reference. The fan shown in Brown 
("Brown fan") has been distributed under the trade name "THERMAPRO-V.TM.", 
distributed by Comair Rotron, Inc. of San Ysidro, Calif. 
The Brown fan includes a rotor having a rotor magnet, and a stator having a 
pair of windings that magnetically interact with the rotor magnet. During 
operation, the windings are controlled by a winding supply circuit to 
rotate the rotor. Among other elements, the supply circuit includes a pair 
of power transistors that each power one of the two windings, a magnetic 
sensor for selectively energizing the power transistors, an adjustable 
voltage regulator for protecting the fan motor and controlling fan 
performance, and an external programmable element that cooperates with the 
regulator for externally controlling (i.e., programming) the speed of the 
fan. 
The power transistors, programmable element, and regulator each are voltage 
drops in the winding circuit that reduce the effective voltage across the 
windings. Consequently, these three elements utilize a significant amount 
of the input voltage that is introduced to the circuit at the voltage 
input In addition to powering the three noted elements, however, the input 
voltage also energizes the windings. Accordingly, the input voltage must 
be sufficiently high to effectively energize the windings, in addition to 
the power transistors, programmable element, and regulator. 
The regulator, which is disclosed as a conventional integrated circuit, may 
be internally adjusted by an adjust terminal to control the voltage at an 
output terminal of the regulator. This adjusting feature internally sets 
the speed of the fan so that one fan may be used for different 
applications. The voltage regulator also includes a thermal shutdown 
element and current regulator that together prevent the motor windings and 
the winding supply circuit from overheating due to receipt of too much 
current. Specifically, the current regulator limits the current to a 
maximum value and the thermal shutdown element shuts down the circuit for 
a predetermined time period if the voltage regulator reaches a preselected 
temperature. A number of discrete elements, such as Zener diodes and 
resistors, also are required to ensure that the voltage regulator operates 
as specified. Reference is made to Brown for a more detailed description 
of the voltage regulator and other features of the winding supply circuit. 
SUMMARY OF THE INVENTION 
In accordance with one aspect of the invention, a winding circuit for use 
in a fan includes first and second integrated circuits that each include a 
transistor for powering first and second fan windings in the fan, and a 
thermal shutdown element that switches the winding circuit "off" (i.e., 
preventing current transmission through the circuit) if the integrated 
circuit reaches a predetermined temperature. The fan includes a rotor 
having a magnet, and a stator having a magnet sensor to alternatively 
transmit current to the first and second windings, which also are located 
in the stator. The integrated circuits also may include a current 
regulating element that limits current to a predetermined maximum value. 
The integrated circuits may include metal oxide semiconductor field effect 
transistors (a/k/a "MOSFETs") and the magnet sensor may be a Hall effect 
sensor. 
In accordance with another aspect of the invention, a winding circuit for 
use in a fan includes first and second integrated circuits that each 
include a transistor for powering first and second fan windings in the 
fan, and a current regulating element that limits current to a 
predetermined maximum value. The fan includes a rotor having a magnet, and 
a stator having a magnet sensor to alternatively transmit current to the 
first and second windings, which also are located in the stator. The 
integrated circuits also may include a thermal shutdown element that 
switches the winding circuit off if the integrated circuit reaches a 
predetermined temperature. The integrated circuits may include MOSFETs and 
the magnet sensor may be a Hall effect sensor. 
Some embodiments of the invention advantageously control the flow of 
current to the fan windings, consequently dissipating less power than the 
prior art Brown '553 fan and providing more of the input voltage to the 
windings. Moreover, embodiments of the fan may be manufactured at lower 
cost than the Brown '553 fan.

DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT 
FIG. 1 shows a brushless DC fan 10 that may incorporate a preferred 
embodiment of the inventive winding circuit (discussed in detail below 
with reference to FIG. 3). The description of the fan 10 is for exemplary 
purposes only, however, since the inventive winding circuit may be 
utilized in other types of fans known in the art. 
The fan 10 includes a housing 11 with a front surface 12, a rear surface 
13, and a venturi 14 extending between the front and rear surfaces 12 and 
13. A motor, shown generally at 15, is centrally located in the housing 
11. The motor 15 may be any conventional motor used within fans such as, 
for example, a single-phase or poly-phase motor. The winding circuit 
(discussed below) and a stator are supported in fixed relation to the 
housing 11 in a central housing portion 16 that is connected to the 
venturi 14 by struts 17 of a spider structure. Leads 19 and 20 are brought 
out from the motor electronics along one strut 17'. Strut 17' is specially 
formed for this purpose with a longitudinal channel leading to a narrow 
groove 23 at the outer periphery of the housing 11. The groove 23 retains 
the leads 19 and 20 in the channel while directing them toward the 
generally cylindrical exterior 25 of the housing 11 as shown. 
FIGS. 2a and 2b respectively show the rotational and stationary parts of 
the fan 10 of FIG. 1. FIG. 2b shows the housing 11, a stator 28, and 
circuitry 29 (including the winding circuit) of the fan 10 inverted from 
their position in FIG. 1. FIG. 2a illustrates an impeller 30 of the fan 10 
as shown in FIG. 1. The impeller 30 includes fan blades 31 supported on a 
hub 32 (e.g., manufactured from plastic), which in turn is secured to a 
rotor 35 of the fan motor 15. The rotor 35 has an annular permanent magnet 
37 in a steel cup 38. The central shaft 39, which is secured to the end 
face of the cup 38, is received in bearings 41 in the stator assembly of 
FIG. 2b when the fan 10 is assembled. 
As shown in FIG. 2b, the fan circuitry 29 is mounted on a circular printed 
circuit board 43. For the purpose of communication, a magnetic sensor 45 
(e.g., a conventional Hall effect sensor) is supported on the printed 
circuit board 43 inside the magnet 37 to sense the changing magnetic 
field. More particularly, the magnetic sensor 45 is positioned just 
opposite a communication portion of the magnet 37 and is used to control 
switching of current to windings 47 on the stator 28 as described, for 
example, in the applicant's earlier U.S. Pat. No. 4,494,028, the 
disclosure of which is incorporated herein, in its entirety, by reference. 
A field magnet portion of the magnet 37 interacts with the poles 49 of the 
stator 28 to effect rotation of the impeller 30 upon communication of the 
energizing current to the windings 47 of the stator 28. Leads 19 and 20 
supply the electrical power that activates the circuit 29 and energizes 
the windings 47. 
FIG. 3 shows a preferred embodiment of a winding circuit 60 (i.e., a part 
of the circuitry 29) that may be implemented on the printed circuit board 
43 within the fan housing 11. The circuit 60 receives an input voltage 
across leads 19 and 20. The lead 19 preferably is the high side or 
positive supply voltage, and the lead 20 preferably is ground. The circuit 
60 includes a first portion, which includes a current limiting fuse 62, 
noise limiting first and second capacitors 64 and 66, and a first diode 
68. The first portion limits the effect of transients that may be 
transmitted through the leads 19 and 20. Moreover, the diode 68 of the 
first portion provides reverse polarity protection if the intended 
polarity of the leads 19 and 20 is accidentally reversed. The first 
portion connects the high input lead 19 to a center tap of fan windings 
(discussed below). 
The winding circuit 60 further includes the magnetic sensor 45, a first 
powering integrated circuit 72 connected between the magnetic sensor 45 
and a first of the windings 47, a second powering integrated circuit 74 
connected between the magnetic sensor 45 and a second of the windings 47, 
and a Zener regulation circuit to regulate input voltage into the magnetic 
sensor 45. The Zener regulation circuit includes a resistor 76 and a Zener 
diode 78 to clamp the voltage across the magnetic sensor 45 to a 
preselected maximum voltage. In the preferred embodiment, a fan operating 
at about twelve volts has the following element values: 
fuse 62: about a seven ampere maximum current limit; 
first diode 68: a Schottky diode with about a 0.25 voltage drop; 
second diode 80: a "dump" diode with a 200 peak inverse voltage at one 
ampere (e.g., Motorola diode number 1N4003); 
first capacitor 64: about 0.01 microfarads; 
second capacitor 66: about twenty-two microfarads; 
resistor 76: about 100 ohms; and 
Zener diode 78: a reverse breakdown voltage of about twelve volts. 
Each of the two powering integrated circuits 72 and 74 preferably comprise 
autoprotected power metal oxide semiconductor field effect transistors 
("autoprotected MOSFETs"), such as those distributed under the trade name 
OMNIFET.TM. by SGS-Thompson Microelectronics Incorporated of Carlton, Tex. 
Reference is made to "Feature II: OMNIFETs-Fully Autoprotected Power 
MOSFETS", published in SGS-Thompson Microelectronics Marketing News, Issue 
15, dated May of 1996, the disclosure of which is incorporated herein by 
reference. During normal operation, the powering integrated circuits 72 
and 74 alternatively power their respective windings 47. Each integrated 
circuit 72 and 74 includes either or both a thermal shutdown element (see 
FIG. 4) and a current regulator element (see FIG. 4). In accordance with a 
preferred embodiment of the invention, each integrated circuit 72 and 74 
includes both such elements that together protect the circuit 60 and 
windings 47 from overheating due to receipt of too much current. 
Specifically, the thermal shutdown element enables the integrated circuit 
being utilized to shut down the winding circuit 60 (i.e., turn the circuit 
60 "off" to prevent current flow through the circuit 60) if the 
temperature of such integrated circuit becomes too high. Accordingly, the 
circuit 60 should turn off for a time period that enables the temperature 
of the integrated circuit 72 or 74 to cool to a temperature that is below 
a preselected temperature. In some embodiments, the circuit 60 remains off 
for about 0.1 seconds, which should enable the integrated circuit 72 or 74 
to fall below about 150 degrees Centigrade. 
Similarly, the current regulator element of the integrated circuits 72 and 
74 ensures that no more than a maximum current (e.g., five to seven 
amperes) may be drawn from the source through the winding circuit 60. Such 
maximum currents typically are drawn by the motor during start-up. 
Accordingly, the current through the circuit 60 is clamped at the 
predetermined maximum current when large currents are drawn. 
The integrated circuits 72 and 74 each have three terminals. Specifically, 
the integrated circuits 72 and 74 each include a drain terminal connected 
to the respective winding, a source terminal connected to both the ground 
lead 20 and a second diode 80 (which is connected to a center tap 82 of 
the windings 47), and an input terminal for receiving an input signal from 
the magnetic sensor 45. 
FIG. 4 schematically shows the internal configuration of an autoprotected 
MOSFET chip 400 that may be utilized in the integrated circuits 72 and 74 
in a preferred embodiment of the invention. The autoprotected MOSFET chip 
400 includes a current regulator element 402 to limit current to the 
predetermined maximum current, a MOSFET 404 to power the windings, and a 
thermal shutdown element to turn the circuit off if the temperature in the 
chip 400 becomes too high (as discussed above). The thermal shutdown 
element includes a gate control element to receive an input power signal 
that powers the chip 400, a status element 410 that determines if the 
temperature of the chip 400 is at the predetermined maximum, and an 
over-temperature element 408 (i.e., thermal shutdown element, noted above) 
having circuitry to negate the input power signal (i.e., turning the chip 
400 off) in response to input from the status element 410. Circuitry in 
the status element 410 both senses the temperature and controls the 
over-temperature element 408 to negate the gate control signal if the 
temperature is at the predetermined maximum. In addition to the above 
noted elements, the chip 400 also includes an over-voltage clamp 402 for 
protecting against voltage transients. 
In use, the integrated circuits 72 and 74 operate similar to conventional 
power MOSFETS by alternatively providing a circuit to ground for their 
respective windings 47. Unlike conventional power MOSFETS, however, the 
integrated circuits 72 and 74 each continually monitor their respective 
temperatures and shut off if the temperature reaches the predetermined 
maximum value. Similarly, the integrated circuits 72 and 74 each provide 
the current regulation to protect the circuit from overheating due to 
receipt of too much current. 
The circuit 60 preferably does not include externally programmable elements 
(e.g., the external programmable element in the Brown '553 patent) or 
voltage adjusting elements (e.g., the adjust terminal in the Brown '553 
patent), thus simplifying the design and eliminating the need for 
additional discrete elements associated with their functions. Accordingly, 
the ultimate manufacturing cost of the fan is decreased since fewer 
elements are required. Moreover, the integrated circuits 72 and 74 each 
represent one voltage drop (instead of three) between the circuit input 
and the windings 47, thus supplying more of the input voltage to the 
windings 47. This consequently improves the power efficiency of the 
winding circuit 60, thereby decreasing the operating cost of the fan 10. 
Although various exemplary embodiments of the invention have been 
disclosed, it should be apparent to those skilled in the art that various 
changes and modifications can be made which will achieve some of the 
advantages of the invention without departing from the true scope of the 
invention. These and other obvious modifications are intended to be 
covered by the appended claims.