Integrated fan speed control and fault detection circuitry

Aspects for integrating speed control and fault detection in a fan assembly are described. The aspects include a fan, a first circuit is coupled to the fan for regulating speed of the fan, and a second circuit coupled to the fan and to the first circuit for detecting a fault condition in the fan. A ripple regulator is integrated as the first circuit, and a pulse missing detector circuit is integrated as the second circuit.

FIELD OF THE INVENTION

The present invention relates to speed control and fault detection in fan assemblies.

BACKGROUND OF THE INVENTION

A fan is a standard component in most commercial personal computers (PCs). The function of the fan is to provide thermal cooling to the integrated circuits and other components in the PC. A lack of cooling in a PC and other forms of electronic systems can cause premature failure in the circuits and/or components, which is detrimental to proper system operation and results in the need for costly repair/replacement of the system. Thus, it is important to ensure proper fan operation, both by maintaining proper fan speed and detecting fan failures, in order to avoid the detrimental effects of inadequate thermal cooling.

Accordingly, a need exists for an integrated, efficient and straightforward system for controlling fan speed and monitoring for fan failure that can be implemented with existing fan assemblies. The present invention addresses such a need.

SUMMARY OF THE INVENTION

The present invention provides aspects for integrating speed control and fault detection in a fan assembly. The aspects include a fan, a first circuit is coupled to the fan for regulating speed of the fan, and a second circuit coupled to the fan and to the first circuit for detecting a fault condition in the fan. A ripple regulator is integrated as the first circuit, and a pulse missing detector circuit is integrated as the second circuit.

With the present invention, a straightforward and cost effective solution for fan speed control and fan fail indication is achieved. These and other advantages of the aspects of the present invention will be more fully understood in conjunction with the following detailed description and accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to speed control and fault detection in fan assemblies. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Thus, the present invention is not intended to be limited to the embodiment shown, but is to be accorded the widest scope consistent with the principles and features described herein.

FIG. 1 illustrates a typical fan 10 having a three wire signal arrangement. A DC (direct current) input provides a power signal at the appropriate voltage for the fan 10 on a first signal 12 . A tachometer signal transmits a square wave indicative of the RPM (revolutions per minute) of the fan 10 on a second signal wire 14 , and a return signal provides a ground signal for the fan 10 on a third signal wire 16 . As shown, for the fan system of FIG. 1 , there is no integrated control over how fast the fan 10 runs and no integrated fault detection capabilities.

FIG. 2 illustrates a system in accordance with the present invention that is integrated in the fan assembly, or alternatively, embedded on a daughter card that can be attached to a HOT plug-in fan assembly, to regulate fan speed and detect fan failures. The system includes the fan 10 , and integrated first and second circuits, 18 and 19 . The overall fan assembly with the integrated first and second circuits maintains a three signal wire arrangement, as in the prior art, but utilizes the signal wires in a different manner to control speed and detect faults, as presented hereinbelow.

Regulation of the speed of fan 10 occurs with the inclusion of the first circuit 18 that forms a ripple regulator for the fan 10 . The ripple regulator 18 includes a transistor 20 (Q 2 ), a diode 22 (D 1 ), an inductor 24 (L 2 ), a capacitor 26 (C 1 ), a comparator 28 (U 1 ) and resistors 30 (R 1 ), 32 (R 2 ) and 34 (R 3 ). The particular characteristics of the components for the ripple regulator 18 are dependent upon system needs, as is well understood by those skilled in the art. By way of example, L 2 5 H, C 1 47 F, R 1 100 ohm. The fan voltage (V FAN ) is controlled by the equation V FAN V REF (1 R 2 /R 3 ).

The components of the ripple regulator 18 operate in response to variations in a DC speed control signal provided on the second signal wire 14 of the fan system assembly and applied to the non-inverting input of comparator 28 , as is well understood by those skilled in the art. The fan speed is directly proportional to the DC speed control signal, so that if a higher speed for the fan 10 is desired, the speed control DC signal is increased, and conversely, if a lower speed for the fan 10 is desired, the speed control DC signal is decreased. Preferably, the speed control DC signal is provided by a system thermal sense circuit. In this manner, system cooling is managed by varying the speed of the fan which is dependent on system temperature efficiently and effectively within the fan assembly.

In addition, the system includes the second circuit 19 that provides a pulse missing detector circuit. The pulse missing detector 19 is coupled to the ripple regulator 18 at node 42 and isolation from the DC speed control signal is provided by an isolating diode 44 . The pulse missing detector circuit 19 operates using standard techniques to compare the frequency of pulses from the fan (tachometer signal) to a chosen reference frequency generated by a built in timer. If there is a fault in the fan, the pulse missing detector circuit 19 detects a difference between the reference frequency and fan frequency and generates a low output signal if the difference is more than a designed threshold. The low output signal pulls the voltage level at the node 42 to low. Since the level of the DC speed control signal is expected at node 42 , the non-inverting signal measured (<1 volt) in response to the low level from the pulse missing detector circuit 19 indicates a failure of the fan, such as to a service processor in the system normally associated with the fan monitoring. In this manner, fault detection is integrated within the fan assembly.

Thus, a system and method in accordance with the present invention provides aspects for integrating speed control and fault detection in a fan assembly. The aspects include a fan, a first circuit is coupled to the fan for regulating speed of the fan, and a second circuit coupled to the fan and to the first circuit for detecting a fault condition in the fan. A ripple regulator is integrated as the first circuit, and a pulse missing detector circuit is integrated as the second circuit.