OVERTEMPERATURE PROTECTION METHOD AND AUDIO DEVICE

Description

State of the art

[0001] To ensure reliability in electronic devices and circuits, such as audio equipment, all components used within the audio device, e.g., semiconductors, must operate within the so-called safe operating area (SOA). Essentially, the SOA describes the amount of power dissipation that a component, e.g., a component, can withstand without being damaged. Outside this area, the component, e.g., the semiconductor, is overloaded, which would lead to its destruction.

[0002] From EP 0 135 870 A1, a method for overload protection of electrical power consumers is known, in which the consumer current and the temperature of the coolant acting on the power consumer are measured periodically, and the current and temperature values ​​measured after each period are fed to a circuit arrangement. In this arrangement, they are processed to simulate a temperature according to the algorithm of a thermal system, and the simulated temperature is compared with a predetermined limit temperature. Above this limit, a switch is actuated to interrupt the consumer current. The power consumer is assigned at least one thermal system, each with at least two system components. The losses of the system components of the thermal system are determined periodically. From the losses determined in this way, the periodically assigned value of the coolant temperature, and the heat capacities,

[0003] Based on the thermal conductivity values ​​of the system bodies of the thermal system, the temperature of each system body of the thermal system is determined, and the temperature thus determined for each system body of the thermal system to be protected is continuously compared with the limit temperature assigned to this system body.

[0004] A loudspeaker protection device is known from WO 2016 / 124896 A1. In this device, an amplification control block, based on a thermal impedance model and a predicted temperature rise, determines whether a temperature exceeds or will exceed one or more thresholds.

[0005] A thermal protection device for a loudspeaker is known from US patent 2017 / 0094408 A1. A controller generates a control signal for the amplification of the loudspeaker driver. The control signal is a function of: an indication of the loudspeaker voice coil temperature, an indication of the power consumption in the loudspeaker voice coil, and an indication of the temperature of a thermal reservoir for heat dissipation from the voice coil.

[0006] US Patent 6,014,059 discloses a power amplifier with a gain transistor. A module controls the amplifier's input signal. This module generates a control signal that follows the temperature of a transistor within a defined temperature range. The control signal does not exceed a predetermined value. This value corresponds to a predetermined transistor temperature equal to or below a maximum transistor temperature.

[0007] From US patent 2016 / 0119714 A1, a system and method for limiting audio power based on thermal modeling are known. Disclosure of the invention

[0008] Within the scope of the invention, a method with the features of claim 1 is disclosed. Preferred or advantageous embodiments of the invention, as well as of other categories of invention, will become apparent from the further claims, the following description, and the accompanying figures.

[0009] This method serves to protect a component located within an audio device. The component is protected from exceeding a maximum internal temperature or value. This internal temperature is not directly measurable, as it is the junction temperature within a semiconductor component.

[0010] The procedure determines the power dissipation of the component. Furthermore, a temperature measurement is taken at the component. "At the component" means at a metrologically accessible measurement point on the component or in its vicinity that is thermally coupled to the internal temperature, from which the internal temperature can therefore be inferred. A measurement point is, in particular, an electrical connection of the component, a heat sink with which the component is thermally coupled, a housing section of the component, etc.

[0011] Based on the power loss, a temperature difference for the component is determined. This temperature difference is the difference between the measured temperature at the component and the internal temperature within the component. The temperature difference is calculated using a thermal model of the component. The internal temperature is then determined as the sum of the measured temperature and the temperature difference.

[0012] Based on the internal temperature and known component data, a permissible maximum power dissipation value is determined. At this maximum power dissipation value, the maximum permissible or desired internal temperature is reached (the internal temperature reaches its maximum value), at which the component can still be operated without risk of damage, as is known from the known component data and behavior.

[0013] According to the procedure, the output power is reduced in such a way that the (temperature-dependent) maximum value of the power loss is never exceeded.

[0014] Specifically, the component operates in normal mode when the power loss does not exceed the maximum value. Alternatively, if the power loss would exceed the maximum value, the component operates in a reduced-power, energy-saving mode. In energy-saving mode, the power is reduced to such an extent that the power loss is limited to the maximum value.

[0015] Especially in semiconductors, the maximum permissible power dissipation depends on the internal junction temperature. Using the determined junction temperature, the maximum permissible power dissipation of the component to be protected can therefore be determined at any given time. With the method presented here, in the event of an impending overload of the component to be protected, the audio signal, in particular the output signal of the audio device, and thus the output power, is reduced to such an extent that the maximum permissible power dissipation of the component is not exceeded.

[0016] The determined maximum power dissipation means that the maximum internal temperature within the component is just reached, but not exceeded. According to the procedure, the power dissipation is only limited if it exceeds the permissible maximum value, which would lead to an increase in the internal temperature above the maximum permissible value. Specifically, in energy-saving mode, the power applied to the component is reduced compared to normal operation, thereby also reducing its power dissipation. If the maximum value is not exceeded, the component operates without restriction.

[0017] The component data is known primarily from, for example, the component's datasheet. The "maximum value" of the power dissipation can be the physically permissible value, exceeding which would result in immediate destruction of the component. However, the maximum value can also be a lower, desired maximum value if the maximum physically permissible internal temperature of the component is not to be fully utilized, but rather, for example, only 80, 90, or 95% of this temperature, or if it is to be kept 10, 15, or 20 degrees below this temperature. This provides a certain safety margin to protect the component from destruction.

[0018] According to this procedure, the component, and thus the audio device, continues to operate, albeit in a limited (energy-saving) mode, even if the internal temperature reaches or approaches its maximum value during normal operation. Only the power dissipation within the component is limited, and consequently, so is the output power of the component or audio device. The audio device remains operational and does not need to be completely switched off.

[0019] According to the invention, an audio device in the form of an amplifier delivers, for example, full output power (normal operation) for, say, 4 minutes, then the maximum output power is limited (power-saving mode). A reduction of, for example, 3 dB is perceptible, but not overly noticeable, which represents a halving of the output power, thus significantly reducing the load on the power electronics. The basic function is therefore maintained, unlike a complete shutdown.

[0020] In a preferred embodiment, the power dissipation is determined by ascertaining the component's output power and then calculating the power dissipation based on this output power and known component data. The output power is generally easier to determine than the power dissipation, for example, based on the component's output voltage and / or output current. The component data used for this purpose includes, for example, component characteristics or operating voltages. In this way, the power dissipation can be determined indirectly, but due to the correlation with the component data. Alternatively, an input power or other parameter can be determined from which the (internal) power dissipation of the component can be deduced based on the known component data.

[0021] In a preferred embodiment, the power loss is also determined based on the internal temperature and / or the measurement temperature. Both temperatures can influence the power loss in the component. Taking the respective temperatures into account thus leads to a more accurate determination of the power loss and therefore a more precise alignment of normal and economy operation with the power loss limit specified based on the maximum value.

[0022] In a preferred embodiment, at least one thermal time constant is used in the thermal model. This time constant describes the dynamic thermal behavior of a thermal path. The thermal path consists of the location of the internal temperature (where it occurs or is present) and the measurement location of the temperature (where the temperature is measured). Such a thermal model allows for a particularly reliable and accurate inference of the internal temperature from the measurement temperature.

[0023] In a preferred embodiment, a maximum permissible output power of the component is determined from the maximum permissible power dissipation. This is done, as described above, using the component data. In power-reduced, energy-saving mode, the component is operated in such a way that the output power is limited to the corresponding maximum value. The component's output power is generally more easily or directly controllable than the power dissipation. For example, the output power of the component is determined by a current and / or voltage applied to the component. This current and voltage can be easily influenced or controlled. This makes the method particularly easy to implement.

[0024] In a preferred embodiment, power dissipation during power-saving operation is limited to a maximum value using an audio limiter. The audio limiter is located in an audio path upstream of the component. An audio signal is carried along this path, and (at least a portion of) it is fed to the component as an input signal. Limiting is achieved by restricting the audio signal as an input signal compared to its waveform during normal operation. Audio limiters are particularly easy to implement and readily available on the market. Using an audio limiter makes the process especially simple. By limiting the audio signal, its volume or amplitude is reduced, meaning the component, e.g., a power amplifier, requires less power to process it and therefore generates less power dissipation.

[0025] Within the scope of the invention, an audio device according to claim 7 is also disclosed. This device comprises an audio unit. A component is contained within the audio unit. As explained above, this component is to be protected from exceeding a maximum internal temperature. The audio device includes a protection module. The protection module serves to carry out, or is configured to carry out, the method according to the invention. The audio device and at least some of its embodiments, as well as their respective advantages, have already been explained in substance in connection with the method according to the invention.The audio device is thus assigned a protection module to protect the component that needs to be protected from exceeding a maximum internal temperature, where the internal temperature is not directly measurable, where the component contains or is a semiconductor device to be protected, and the internal temperature is a junction temperature in the semiconductor device, according to the procedure described above. In other words, the audio device is an audio device modified by the protection module. The protection module is configured to perform the following procedure: Determination of the component's power dissipation, measurement of a temperature on the component, at a metrologically accessible measurement point of the component or in its environment that is thermally coupled to the internal temperature, determination of an internal temperature within the component using a thermal model of the component based on the determined power dissipation and the measured temperature, determination of a permissible maximum value for the power dissipation based on the internal temperature and known component data, limitation of an audio signal in such a way that the power dissipation does not exceed a maximum value and / or the maximum internal temperature is not exceeded.

[0026] In a preferred embodiment, the audio device and / or audio assembly is an audio amplifier for amplifying the aforementioned audio signal. The audio amplifier is, in particular, a power amplifier stage. Audio amplifiers are generally especially susceptible to damage to their components due to internal overheating. The present method and / or protection module provide particularly effective protection for these components.

[0027] In a preferred embodiment, the component contains or is itself a semiconductor component to be protected. The internal temperature is then a junction temperature within the semiconductor component. Semiconductor components, in particular, are especially temperature-sensitive with respect to their junction. The present method or protection module provides particularly effective protection against damage to these components.

[0028] Alternatively, the component can also contain a capacitor, an inductor, a relay, a resistor, or a motor. The component can also be an assembly of several individual components. These individual components are, for example, the aforementioned semiconductors, capacitors, inductors, etc. These components, too, can be particularly sensitive to power dissipation or temperature and are thus especially effectively protected by the present method or protection module.

[0029] In a preferred embodiment, the protection module includes an audio limiter as described above. The audio limiter is located in an audio path upstream of the audio device. An audio signal is carried along this audio path and fed to the audio device, and thus also to the component, as an input signal. The audio limiter is configured to limit the audio input signal to the audio device during power-saving operation. The audio limiter is therefore also located upstream of the component in the audio path, resulting in the advantages mentioned above.

[0030] The invention is based on the following findings, observations, and considerations and includes the following embodiments. These embodiments are sometimes referred to simply as "the invention." The embodiments may also contain parts or combinations of the embodiments mentioned above, correspond to them, and / or may include previously unmentioned embodiments.

[0031] The invention is based on the following considerations: Ensuring the operation of a component within the SOA (Standard Operating Area) can be achieved in various ways: For example, in a device, the design itself ensures operation within the SOA for some of the semiconductors used (as components), and a user has little or no influence on the stress placed on the semiconductor. However, particularly in power electronics, the stress on individual semiconductors often varies considerably depending on the operating mode. If the user has significant influence on the stress on these individual components, special precautions must be taken to protect them. Designing the components for the worst-case scenario (e.g., a short circuit caused by the user) often amounts to completely oversizing them for normal operation.While an emergency shutdown of the device can protect the components in most cases, it is usually not preferable from the user's point of view.

[0032] A fundamental idea of ​​the invention is therefore to detect an impending overload and react by reducing the output power (or power loss) in order to limit the temperature increase. One approach is to detect an impending overload by measuring the output voltage and output current of the component and / or with a temperature sensor placed at a measuring point near the component or part to be protected, e.g., on the same heat sink. Thus, the temperature of the component (semiconductor) itself is not measured, but rather a temperature that is thermally coupled to the component temperature (semiconductor temperature) as closely as possible. Under a static load, the temperature difference is usually quite small. However, if a sudden, heavy load (or a potential overload) occurs, a certain amount of time elapses before the measuring point (e.g., heat sink) heats up.During this time, the temperature difference between the measured temperature and the actual component temperature (semiconductor temperature) can be very high. Therefore, to reliably protect the component (semiconductor) from damage based solely on the measured temperature, a considerable safety margin must be factored in to withstand these dynamic stresses. This also means, however, that the static maximum power output is significantly lower than the possible output power.

[0033] The invention is based on the understanding that the power dissipation of a component, e.g., a part, is determined by the component's internal properties as well as by external operating conditions such as voltage and current. The component properties are known and should be fully specified in the datasheet. If the external operating conditions of the component are also known, the instantaneous power dissipation of the component, e.g., the semiconductor, can be calculated. For example, the operating voltage may be known and constant, while the current is variable but measured. If the power dissipation of the component to be protected is known, the current temperature within the component, e.g., the semiconductor, can be calculated using a thermal model. If the path between the component or semiconductor interior and the temperature measurement point (e.g., the thermal interface material) is determined using the thermal model (e.g., the Foster model), the current temperature can be calculated.By simulating a temperature sensor, the calculated temperature rise can be added to the measured temperature. This yields the internal temperature of the component, e.g., the junction temperature, of the component or part to be protected. The output power can then be reduced due to the relatively accurate knowledge of the internal or junction temperature within the component or semiconductor. Additionally, the information about the internal or junction temperature can be incorporated into the power dissipation calculation, provided it is relevant (e.g., RDSON for a MOSFET). Thus, higher output powers can be achieved with the same components while maintaining full operational reliability. Conversely, this method allows the use of less expensive components for the same output power.

[0034] In particular, the procedure essentially comprises 5 key points: 1. Determination of the power loss of the component or part to be protected, 2. Determination of the temperature increase using the calculated power loss and a thermal model, 3. Temperature measurement, 4. Determination of the maximum permissible power loss or output, 5. (If necessary) Reduction of the power loss or output.

[0035] Since the aforementioned method allows for the maximum permissible loss or...

[0036] Since the output power is derived directly from the destruction mechanism, namely overheating inside the component or semiconductor, the safety margin can be drastically reduced compared to conventional methods or those mentioned above. From the customer's perspective, the device therefore has higher output power.

[0037] Further features, effects, and advantages of the invention will become apparent from the following description of a preferred embodiment of the invention and the accompanying figures. These figures are shown in a schematic diagram: Figure 1 an audio device according to the invention, Figure 2 a diagram to illustrate the method according to the invention.

[0038] Figure 1Figure 2 shows an audio device 2. This device contains an audio unit 4. Inside, that is, within its core, the audio unit 4 contains a component 6. The component 6 has an internal temperature TI, which is not directly measurable. The component 6 must be protected from exceeding a maximum internal temperature; that is, the internal temperature TI should not exceed a maximum value. The audio device 2 also contains a protection module 8. This module is configured to execute a protection procedure. The protection procedure is explained below.

[0039] Audio device 4 is an audio amplifier. Audio device 2 is therefore an amplifier. Audio device 4 is a power amplifier. Component 6 is a semiconductor component requiring protection. The internal temperature TI is a junction temperature in the semiconductor component. Protection module 8 contains an audio limiter 10. The audio limiter 10 is located in an audio path 12 upstream of audio device 4. The audio limiter 10 is configured to limit an audio signal A, which is fed to audio device 4 along audio path 12 as an input signal, in a power-saving mode S, as indicated by a downward-pointing arrow. The audio signal A is thus routed along audio path 12. Protection module 8 performs the following protection procedure:

[0040] The method serves to protect component 6 within the audio device 4 from exceeding a maximum internal temperature TI. In this method, the power dissipation V of component 6 is determined, which is then Figure 1is symbolically represented by a circle. Furthermore, a measurement temperature TM is measured at or outside of component 6 at a measurement point 13, here at a heat sink (not shown) thermally coupled to component 6. Based on the power dissipation V, a temperature difference DT for component 6 is determined using a thermal model 14 of component 6, which is stored in the protection module 8. The temperature difference DT describes the difference between the internal temperature TI and the measurement temperature TM. The internal temperature TI is then calculated as the sum of the measurement temperature TM and the temperature difference DT: TI = TM + DT. Using the internal temperature TI and known component data 16 of component 6, which are also stored in the protection module 8, a permissible maximum value VM for the power dissipation V is determined. If the power dissipation V equals the maximum value VM, a maximum permissible orThe desired internal temperature TImax has been reached. In this case, an overload is imminent, which is why the audio signal 4 and thus the maximum output power LA is reduced compared to normal operation N, so that the internal temperature TI reaches its maximum value TImax, but does not exceed it.

[0041] In the case of limiting the audio signal A by an audio limiter 10, there is no "hard" distinction between normal operation N and power-saving mode S, because the maximum output power LA is always limited. Only the value MA of the maximum output power LA is constantly recalculated based on the current internal component temperature TI, and thus the limiting value is always applied to the audio limiter 10.

[0042] The aforementioned process steps are performed periodically. As explained above, an internal junction temperature TI is determined periodically. Using component data 16, the maximum permissible power dissipation VM of component 6 is periodically determined, and from this, the maximum permissible output power LA (value MA) is calculated. A limit value is set for the audio limiter 10 based on this value MA. Therefore, if the expected power dissipation V due to the audio signal A before the limiter 10 is below the maximum permissible power dissipation VM, no reduction is attempted. Component 6 then resumes normal operation N (in Figure 1 (indicated by dashed lines). In the example, the audio signal A is then fed indefinitely along audio path 12 to audio device 4 and thus to component 6.

[0043] The power loss V is determined in this procedure by determining the output power LA of component 6 and calculating the power loss V based on the output power LA and the known component data 16. In this example, the output power LA is the power of the audio signal A amplified by component 6.

[0044] The determination of the power loss V also includes the currently determined internal temperature TI (after it has been determined for the first time or was estimated for the first time, e.g. equal to the measurement temperature TM).

[0045] From the maximum value VM for the permissible power loss V, a maximum value MA for the permissible output power LA of component 6 is determined using component data 16. In power-reduced economy mode S, component 6 is operated in such a way that the output power LA is limited to the maximum value MA.

[0046] The limitation of the power loss V or the output power LA in power-saving mode S is achieved by limiting the audio signal A using the audio limiter 10. Limiting the output power LA also limits the power loss V, which is related to the internal structure and properties of component 6. In normal operation N, there is no limitation by the audio limiter 10. The audio signal A can therefore pass through it unchanged, so the audio device operates normally, i.e., without restrictions.

[0047] Figure 2 explains the invention specifically using the example of semiconductor protection (protection of component 6 in the form of a semiconductor) in the audio device 4 in the form of an audio power amplifier according to Figure 1 : 1. Determination of the power dissipation (indicated by a dashed frame): An output voltage Uout and an output current lout are measured at component 6. Together with static parameters such as component properties and internal operating voltages in the form of component data 16, the power dissipation V is determined as a function of the output current lout and output voltage Uout. The output voltage Uout and output current lout are modified by functions f(U) and f(I) (not further explained), and the results are summed with a quiescent power dissipation R. Furthermore, the determined component temperature (estimated the first time, as explained above) in the form of the internal temperature TI is also included, as it contributes to the power dissipation V generated by the output current lout. The internal temperature TI is multiplied by a function f(I) of the output current lout (not further explained) and also summed.Thus, the determined junction temperature (internal temperature TI) is fed back into the power loss calculation. 2. Thermal Model Using the power loss V, the thermal model 14 calculates the heating in the form of the temperature difference DT. In this example, three time constants pt1-3 (with downstream thermal resistances R1-3, not further explained) are used to describe the dynamic thermal behavior of a thermal path 18, i.e., the path from a junction in component 6 (location of the internal temperature TI) to a temperature sensor (measuring point 13 of the temperature TM measurement), which is not shown. In this case, the path 18 can be described with sufficient accuracy using three time constants pt1-3. In other cases, more or fewer than three time constants pt can also be used to describe the dynamic thermal behavior of the path 18.In thermal model 14, three thermal time constants pt1-3 and three thermal resistances R1-3 are used, which describe the dynamic thermal behavior of the thermal path 18 that extends between the location of the internal temperature TI and the location of the measurement temperature TM (measurement location 13). 3. Temperature measurement: The heating (temperature difference DT) and the ambient temperature (measurement temperature TM) combined result in the absolute junction temperature (internal temperature TI). 4. Determination of the maximum permissible output power (indicated by a dashed frame): The datasheet for component 6 (component data 16) specifies the maximum permissible power dissipation (maximum value VM) for each internal temperature TI.Since it is known (from component data 16) how the influence of the output variables (output current lout and output voltage Uout) affects the power dissipation V in the component (component 6), the maximum permissible output variables (maximum values ​​for Uout, lout) can also be calculated from a permissible power dissipation VM of the component. 5. Reduction of the output power (indicated by a dashed frame) The audio limiter 10 limits the output power LA of the amplifier (audio device 4) so ​​that the maximum permissible power dissipation VM in the semiconductor (component 6) is not exceeded. For this purpose, a threshold value, which is not further explained, is passed to the audio limiter 10.

Claims

1. A method for protecting a component (6) inside an audio appliance (4) against the exceeding of a maximum internal temperature (TI), whereby the internal temperature (TI) cannot be measured directly, in which - a component (6) is protected that contains or is a semiconductor device to be protected and the internal temperature (TI) is the temperature of a barrier layer in the semiconductor device, - a power loss (V) of the component (6) is determined, - a measured temperature (TM) is measured at the component (6) at a measurement location of the component (6) that is accessible for measurement or in its vicinity, which is thermally coupled to the internal temperature (TI), - a temperature difference (DT) for the component (6) between the measured temperature (TM) at the component (6) and the internal temperature (TI) is determined from the power loss (V) with the aid of a thermal model (14) of the component (6), - the internal temperature (TI) is determined as the sum of the measured temperature (TM) and the temperature difference (DT), - a permissible maximum value (VM) for the power loss (V) is determined using the internal temperature (TM) and known component data (16) of the component (6), - an audio signal (A) is limited such that the power loss (V) does not exceed the maximum value (VM) and the maximum internal temperature is not exceeded.

2. The method as claimed in claim 1, characterized in that the power loss (V) is determined by virtue of the output power (LA) of the component (6) being determined and the power loss (V) being determined on the basis of the output power (LA) and the known component data (16).

3. The method according to any of the preceding claims, characterized in that the power loss (V) is also determined on the basis of the internal temperature (TI) and / or the measured temperature (TM).

4. The method according to any of the preceding claims, characterized in that at least one thermal time constant (pt) describing a dynamic thermal behavior of a thermal length (18) between the location of the internal temperature (TI) and the measurement location (13) of the measured temperature (TM) is used in the thermal model (14).

5. The method according to any of the preceding claims, characterized in that the component data (16) are used to determine a maximum value (MA) for a permissible output power (LA) of the component (6) from the maximum value (VM) for the permissible power loss (V), and the component (6) is operated in the reduced-power economy mode (S) such that the output power (LA) is limited to the associated maximum value (MA).

6. The method according to any of the preceding claims, characterized in that in the economy mode (S), the power loss (V) is limited to the maximum value (VM) using an audio limiter (10) arranged in an audio path (12) upstream of the component (6), in that an audio signal (A) carried on the audio path (12) is limited as an input signal into the component (6).

7. An audio device (2) having an audio appliance (4) that has a component (6) inside to be protected against the exceeding of a maximum internal temperature (TI), the internal temperature (TI) not being accessible to direct measurement, the component (6) containing or being a semiconductor device to be protected and the internal temperature (TI) being a temperature of a barrier layer in the semiconductor device, and having a protection module (8) for carrying out the method that follows, in particular for carrying out the method according to any of the preceding claims: - determining a power loss (V) of the component (6), - measuring a measured temperature (TM) at the component (6) at a measurement location of the component (6) that is accessible for measurement or in its vicinity, which is thermally coupled to the internal temperature (TI), - determining an internal temperature (TI) within the component (6) using a thermal model (14) of the component (6) from the determined power loss (V) and the measured temperature (TM), - determining a permissible maximum value (VM) for the power loss (V) on the basis of the internal temperature (TI) and known component data (16) of the component (6), - limiting an audio signal (A) such that the power loss (V) does not exceed a maximum value (VM) and / or the maximum internal temperature is not exceeded.

8. The audio device (2) according to claim 7, characterized in that the audio appliance (4) and / or the audio device (2) is an audio amplifier.

9. The audio device (2) according to any of preceding claims 7 to 8, characterized in that the protection module (8) contains an audio limiter (10) that is arranged in an audio path (12) upstream of the audio appliance (4) and that is configured to limit an audio signal (A) carried on the audio path (12) as an input signal into the audio appliance (4) in the economy mode (S).