Audio power circuit and method

An apparatus and method for controlling an audio power circuit. The audio power circuit includes an audio amplifier having a power input and a speaker connected to the audio amplifier. The audio power circuit also includes a control circuit configured to be connected to a battery and the power input and to control a supply of power to the power input. The audio power circuit further includes a thermal protection circuit connected between the audio amplifier and the speaker, the thermal protection circuit configured to generate a thermal protection signal and provide the same to the control circuit, wherein the control circuit is further configured to control the supply of power based on the thermal protection signal.

BACKGROUND OF THE INVENTION

Portable communications devices, for example, two-way radios, smart telephones, and the like may become heated. Heating of a portable communications device may occur due to exposure to external heat sources, for example, sun light, a radiator, etc. Heating may also occur as a result of heat generated by internal components.

DETAILED DESCRIPTION OF THE INVENTION

While reducing or mitigating heating due to external sources may be addressed by simply moving a communication device away from an external source of heat, addressing heating due to internal sources often requires a more sophisticated approach. In many instances, regulating the amount of heat generated by internal components is important to maintain proper operation of the portable communications devices and to maintain the surface of the portable communications device below a temperature that causes physical discomfort to a user.

The speakers used by portable communications devices may temporarily malfunction due to short circuit, where one terminal of the speaker is grounded. In a short-circuit condition, current flow through the speaker may generate heat, which may affect other internal components and radiate to an external surface of the portable communications device. Among, other things, embodiments of the invention help control heating of a portable communications device.

One embodiment provides an audio power circuit including an audio amplifier having a power input and a speaker connected to the audio amplifier. The audio power circuit also includes a control circuit configured to be connected to a battery and the power input and to control a supply of power to the power input. The audio power circuit further includes a thermal protection circuit connected between the audio amplifier and the speaker. The thermal protection circuit is configured to generate a thermal protection signal and provide the same to the control circuit. The control circuit is further configured to control the supply of power based on the thermal protection signal.

Another embodiment provides a method for controlling an audio power circuit including providing, with a battery, a supply of power to an audio amplifier connected to a speaker. The method also includes outputting, with a thermal protection circuit connected between the audio amplifier and the speaker, a thermal protection signal. The method further includes controlling, with a control circuit connected between the battery and the audio amplifier. The supply of power to the audio amplifier is based on the thermal protection signal.

Another embodiment provides a portable communications device including a transceiver, an electronic processor coupled to the transceiver, and an audio processor coupled to the electronic processor. The audio processor is configured to receive audio signals from an internal microphone and provide audio output to an internal speaker. The portable communications device also includes an audio amplifier connected between the audio processor and the internal speaker. The audio amplifier has a power input. The portable communications device further includes a control circuit configured to be connected to a battery and the power input and to control a supply of power to the power input. The portable communications device further includes a thermal protection circuit connected between the audio amplifier and the internal speaker. The thermal protection circuit is configured to generate a thermal protection signal and provide the same to the control circuit. The control circuit is further configured to control the supply of power based on the thermal protection signal.

FIG. 1is a diagram of one embodiment of a portable communications device100. The portable communications device100may be, for example, a two-way radio, a mobile device, a table computer, a personal computer, and the like. In the example illustrated, the portable communications device100includes an electronic processor110, a memory120, a transceiver130, an input/output interface140, and an audio processor150. The electronic processor110, the memory120, the transceiver130, the input/output interface140, and the audio processor150communicate over one or more control and/or data buses (for example, a communication bus160).FIG. 1illustrates only one exemplary embodiment of a portable communications device100. The portable communications device100may include more or fewer components and may perform functions other than those explicitly described herein.

In some embodiments, the electronic processor110is implemented as a microprocessor with separate memory, such as the memory120. In other embodiments, the electronic processor110may be implemented as a microcontroller (with memory120on the same chip). In other embodiments, the electronic processor110may be implemented using multiple processors. In addition, the electronic processor110may be implemented partially or entirely as, for example, a field-programmable gate array (FPGA), and application specific integrated circuit (ASIC), and the like and the memory120may not be needed or be modified accordingly. In the example illustrated, the memory120includes non-transitory, computer-readable memory that stores instructions that are received and executed by the electronic processor110to carry out functionality of the portable communications device100described herein. The memory120may include, for example, a program storage area and a data storage area. The program storage area and the data storage area may include combinations of different types of memory, such as read-only memory and random-access memory.

The transceiver130enables wireless communication from the portable communications device100to, for example, other portable communications devices100, a call controller, or other electronic devices. In other embodiments, rather than the transceiver130, the portable communications device100may include separate transmitting and receiving components, for example, a transmitter, and a receiver. In yet other embodiments, the portable communications device100may not include a transceiver130and may communicate with other electronic devices via a network interface and a wired connection to a communication network.

As noted above, the portable communications device100may include the input/output interface140. The input/output interface140may include one or more input mechanisms (for example, a touch screen, a keypad, a button, a knob, and the like), one or more output mechanisms (for example, a display, a printer, and the like), or a combination thereof. The input/output interface140receives input from input devices actuated by a user, and provides output to output devices with which a user interacts.

The audio processor150is electrically connected to a microphone170. The audio processor150is also electrically connected to a speaker190through an audio power circuit180. The audio processor150receives audio input from the microphone170and converts the analog audio signals to digital signals that may be processed by the electronic processor110and transmitted via the transceiver130. The audio processor150may also convert digital signals that are received from, for example, the transceiver130or the electronic processor110to analog signals that may be output using the speaker190. In some embodiments, the audio processor150, the microphone170, the audio power circuit180, and the speaker190form part of the input/output interface140.

FIG. 2is a block diagram of one embodiment of the audio power circuit180. The audio power circuit180prevents excess current flowing to the speaker190. The audio power circuit180also prevents the speaker190and the portable communications device100from generating excess heat. In the example illustrated, the audio power circuit180includes an audio amplifier210, first current limiting control circuit220, a second current limiting control circuit230, a first thermal protection circuit240, and a second thermal protection circuit250.FIG. 2illustrates only one exemplary embodiment of an audio power circuit180. The audio power circuit180may include more or fewer components than illustrated and may perform additional functions other than those described herein.

The audio amplifier210includes a power input215. The power input215is connected to a battery260of the portable communications device100through a first load switch225and a second load switch235. The audio amplifier210receives audio signals from the audio processor150. The audio amplifier210amplifies the audio signals from the audio processor150and provides the amplified audio signals to the speaker190.

The first current limiting control circuit220is connected to the battery260and controls a supply of power to the power input215through the first load switch225. The first current limiting control circuit220monitors a current flow between the battery260and the power input215. More specifically, the first current limiting control circuit220monitors a current at node262. The first current limiting control circuit220provides a control signal to the first load switch225. When the first current limiting control circuit220determines that the current flowing between the battery260and the power input215exceeds a threshold, the first current limiting control circuit220opens the first load switch225to limit the current flow.

The second current limiting control circuit230is connected in series with the first current limiting control circuit220to the battery260and controls a supply of power to the power input215through the second load switch235. The second current limiting control circuit230monitors a current flow between the battery260and the speaker190. More specifically, the second current limiting control circuit230monitors a current at node264. In some embodiments, rather than monitoring current at node264, the second current limiting control circuit230may monitor a current at node262. The second current limiting control circuit230provides a control signal to the second load switch235. The second current limiting control circuit230operates similar to the first current limiting control circuit220to control the second load switch235.

The first thermal protection circuit240is connected between the audio amplifier210and the speaker190. The first thermal protection circuit240monitors a voltage between a positive terminal292and a negative terminal294of the speaker190(for example, a speaker voltage). As described in more detail below, the first thermal protection circuit240includes a reference voltage input to receive a reference voltage. The first thermal protection circuit240generates a first thermal protection signal and provides the same through a first thermal protection input245to the first load switch225. When the first thermal protection circuit240determines that the voltage between the positive terminal292and the negative terminal294of the speaker190exceeds a reference voltage, the first thermal protection circuit240opens the first load switch225.

The second thermal protection circuit250is connected in parallel to the first thermal protection circuit240and between the audio amplifier210and the speaker190. The second thermal protection circuit250monitors a voltage between the positive terminal292and the negative terminal294of the speaker190. As described in more detail below, the second thermal protection circuit250includes a second reference voltage input to receive a reference voltage. The second thermal protection circuit250generates a second thermal protection signal and provides the same through a second thermal protection input255to the second load switch235. The second thermal protection circuit250operates similar to the first thermal protection circuit240to control the second load switch235.

In some embodiments, the first current limiting control circuit220, the first load switch225, the second current limiting control circuit230, and the second load switch235together form a control circuit270. The control circuit270controls a supply of power to the power input215. In other embodiments, the control circuit270may include different component circuits instead of the first current limiting control circuit220, the first load switch225, the second current limiting control circuit230, and the second load switch235to control the supply of power to the power input215. In some embodiments, rather than cutting off the supply of power to the audio amplifier210, the control circuit270may limit the amount of current to the audio amplifier210. For example, the control circuit270may limit the current to four hundred thirty (430) milliamperes during a fault condition. Controlling the supply of power may include controlling the voltage provided to the audio amplifier210and/or the current provided to the audio amplifier210. In one embodiment, controlling the supply of power includes controlling a current provided to the audio amplifier210. In some embodiments, a fuse265is connected between the battery260and the audio power circuit180to protect the components of the audio power circuit180. The fuse265prevents the need for high-power components in the control circuit270to meet HAZLOC standards.

In some embodiments, the first current limiting control circuit220and the first load switch225may together form a first current limiting circuit272and the second current limiting control circuit230and the second load switch235may together form the second current limiting circuit274. In these embodiments, the first thermal protection signal is provided to the first current limiting circuit272and the second thermal protection signal is provided to the second current limiting circuit274.

In some embodiments, the audio power circuit180may include only one thermal protection circuit, for example, only the first thermal protection circuit240. In these embodiments, the first thermal protection circuit240provides the first thermal protection signal to the control circuit270and the control circuit270controls the supply of power based on the first thermal protection signal. A person skilled in the art would appreciate that the second current limiting control circuit230, the second load switch235, and the second thermal protection circuit250are redundant and provided in case of failure to the first current limiting control circuit220, the first load switch225, or the first thermal protection circuit240. Other combinations of the current limiting control circuits, the load switches, and the thermal protection circuits may be used to achieve the functionality described herein. For example, the control circuit270may include only the first current limiting circuit272and the first thermal protection signal and the second thermal protection signal may both be provided to the first current limiting circuit272to control the first load switch225.

FIG. 3is a schematic diagram of one embodiment of a thermal protection circuit300. The first thermal protection circuit240and the second thermal protection circuit250may be implemented similar to the thermal protection circuit300. In the example illustrated, the thermal protection circuit300includes a peak suppressor310(for example, a first peak suppressor and a second peak suppressor), a filter320(for example, a first filter and a second filter), a rectifier330(for example a first rectifier and a second rectifier), and a comparator340(for example, a first comparator and a second comparator). The peak suppressor310is connected to the positive terminal292and the negative terminal294of the speaker190. The peak suppressor310receives the amplified alternating current (AC) signals from the audio amplifier210. The peak suppressor310includes voltage regulator double diodes315which act as limiter diodes to prevent audio AC peaks from triggering the thermal protection circuit300. The output of the peak suppressor310is connected to the filter320.

In the example illustrated, the filter320includes a combination of resistors322and capacitors324to form a low-pass filter and prevent audio frequency signals from triggering the thermal protection circuit300. The output of the filter320is connected to the rectifier330. In the example illustrated, the rectifier330includes diodes335, for example, Schottky diodes, to convert AC voltage to direct current (DC) voltage. The rectifier330converts the AC voltage across the speaker190to DC voltage for use by the comparator340. The output of the rectifier330is connected to the comparator340through, for example, a voltage divider345.

In the example illustrated, the positive supply V+ of the comparator340is connected to the battery260. In some embodiments, the positive supply V+ may also be connected to a voltage regulator (not shown) in order to provide improved functioning of the comparator340. The negative supply V− is connected to ground. The inverting input IN− of the comparator340receives the reference voltage. The reference voltage may be provided to the comparator340by a step down regulator (not shown). The step down regulator may receive a power supply from the battery260and step-down the battery voltage to an optimum value set in accordance with surface temperature standards of the portable communications device100to operate in certain environments. In one example, the reference voltage may be three (3) Volts to meet certain technical or regulatory standards such as a maximum 90° Celsius surface temperature rating to operate in hazardous locations (sometimes referred to herein as “HAZLOC”). The non-inverting input IN+ receives the converted DC signals from the rectifier330. The comparator340compares the voltages at the non-inverting input IN+ and inverting input IN−. The output VOUT of the comparator340is provided to a thermal protection input to control the first load switch225. For example, the thermal protection input may be the first thermal protection input245and/or the second thermal protection input255. The comparator340may be implemented, for example, with Analog Devices AD8565 operational amplifier.

FIG. 4is a flowchart illustrating one example method400for controlling the audio power circuit180. As illustrated inFIG. 4, the method400includes providing, with the battery260, a supply of power to the audio amplifier210(at block410). The supply of power is provided to the audio amplifier210through the first load switch225and the second load switch235. As described above, the first load switch225is controlled by the first current limiting control circuit220and the first thermal protection circuit240and the second load switch235is controlled by the second current limiting control circuit230and the second thermal protection circuit250.

The method400also includes outputting, with the thermal protection circuit300connected between the audio amplifier210and the speaker190, thermal protection signal (at block420). The thermal protection circuit300monitors the voltage between the positive terminal292and the negative terminal294of the speaker190at a non-inverting input IN+ (for example, a first speaker voltage input and a second speaker voltage input) of the comparator340. The comparator340compares the voltage between the positive terminal292and the negative terminal294of the speaker190with the reference voltage. The comparator340generates the thermal protection signal at the output VOUT of the comparator340which is provided to the first load switch225and/or the second load switch235.

The method400further includes controlling, with the control circuit270connected between the battery260and the audio amplifier210, supply of power to the audio amplifier210based on the thermal protection signal (at block430). The first thermal protection signal opens the first load switch225when the comparator340determines that the voltage between the positive terminal292and the negative terminal294exceeds the reference voltage. That is, the control circuit270disables the supply of power to the power input215of the audio amplifier210when the comparator340indicates that the speaker voltage exceeds the reference voltage. The first thermal protection signal closes the first load switch225when the comparator340determines that the voltage between the positive terminal292and the negative terminal294is below the reference voltage. That is, the control circuit270enables the supply of power to the power input215of the audio amplifier210when the comparator340indicates that the speaker voltage does not exceed the reference voltage. The second thermal protection signal operates similar to the first thermal protection signal to control the second load switch235.

In some embodiments, the thermal protection circuit300keeps the first load switch225and/or the second load switch235open until a hard reset is performed on the portable communications device100when the comparator340determines that the voltage between the positive terminal292and the negative terminal294exceeds the reference voltage. The hard reset may be, for example, removing and re-inserting a battery pack of the portable communications device. In some embodiments, the control circuit270may permanently open the first load switch225and the second load switch235when the comparator340determines that the voltage between the positive terminal292and the negative terminal294exceeds the reference voltage.

The speaker190may include an inductive coil that acts as a resistor to generate heat in a fault condition. In order to avoid the speaker190from getting too hot, the voltage provided to the speaker190may need to be limited in order to prevent the speaker190from getting hot. One conventional technique for limiting voltage provided to the speaker190may include inserting a pair of Zener diodes between the audio amplifier210output and the speaker190. In order to meet HAZLOC standards, high-power Zener diodes may be required which take up more space and clamp the audio voltage causing audio distortion and low level of audio output. Another conventional technique includes using polyswitches. At least two polyswitches may need to be added with one for each terminal of the speaker190. However, polyswitches add additional resistance on the audio path under normal operating conditions and may have varying trip current limits based on the radio operating temperature. As a consequence, the audio performance of the speaker190may be reduced and the trip current threshold may be hard to control.

One advantage of the above techniques over the Zener diodes and the polyswitches is that a faulty speaker is detected and prevented from generating excess heat with limited negative impact on the audio performance of the speaker190under normal operating conditions. The thermal protection circuit300detects the faulted speaker and opens the first load switch225or the second load switch235to prevent current flow to the speaker190without increasing resistance at the speaker output. This helps prevents the surface temperature of the portable communications device100from going above 90° Celsius while maintaining the audio performance.