Cooling fan control strategy for automotive audio system

#The present invention relates in general to controlling a cooling fan in an audio system, and, more specifically, to running the cooling fan in a manner that masks audible noise generated by the cooling fan.

#Amplifiers used in audio systems cannot be designed with 100 percent efficiency and, therefore, always generate heat. Other components of the audio system, including any microcontrollers or other integrated circuits, media player mechanisms (e.g., CD or cassette tape), displays, transistors, or other discrete components, also generate heat during operation. Heat can especially be a problem in automotive audio systems in which all these elements are housed within a single module or box. Heat buildup can lead to improper circuit operation or failure, audio distortion, undesirable surface heating, or heating of the audio media (e.g., a CD ejected from the system may be hot to the touch). Consequently, heat dissipation or removal is an important consideration for any audio system.

#Heat exchange with ambient air is the primary method of removing heat from a typical audio system. In order to increase the heat exchange, a cooling fan may be provided for directing a flow of air through the audio system module so that fresh air is drawn from outside the module, over the heat-generating components, and back outside the module.

#FIG. 1 is a schematic, block diagram showing an audio system of the present invention.

#FIG. 2 is a flowchart showing a preferred fan control strategy of the present invention.

#FIG. 3 is a schematic, block diagram showing a preferred method and apparatus for determining output power being consumed by the audio amplifiers.

#Referring to FIG. 1, an audio system 10 provides amplified audio reproduction signals to output transducers (i.e., loudspeakers) 11, 12, 13, and 14. In a preferred embodiment, audio system 10 is an automotive audio system and speakers 11-14 comprise right-front (RF), left-front (LF), right-rear (RR), and left-rear (LR) channels. Audio system 10 has an enclosure 15 which retains all the main heat-generating components of the audio system other than speakers 11-14. Nevertheless, the present invention is also applicable to enclosures containing only some of the heat-generating components (e.g., a separate power amplifier module).

#Audio system 10 includes at least one audio source 16, such as an AM/FM tuner, a cassette tape mechanism, or a CD mechanism, for providing left and right stereo audio signals. In the preferred embodiment, digital signal processing is employed in audio system 10 for achieving superior performance at low cost and high packaging efficiency. For an analog audio source (e.g., a tuner or cassette tape), analog-to-digital converters 17 and 18 convert analog audio signals into digital audio signals for processing by a digital signal processor (DSP) 20. For a digital audio source, a direct connection may be provided to DSP 20 from audio source 16.

#DSP 20 performs audio processing functions which are known in the art, including volume control, tone control, balance control, fade control, and special effects as determined by commands from a microprocessor 27, which in turn responds to user controls (e.g., input switches or push buttons, not shown). The processed digital audio signals from DSP 20 are coupled to digital-to-analog converters (DAC) 21-24, and the resulting analog signals are provided to power amplifiers 25 and 26 for driving speakers 11-14. Amplifiers 25 and 26 are two-channel (i.e., stereo) amplifiers for handling front and rear channels, respectively, and each may be comprised of a TDA8566 car radio power amplifier sold by Philips Semiconductors, for example.