Method for overtemperature protection and audio apparatus

Abstract

The invention relates to a method for protecting a component (6) within an audio device (4) from the exceedance of a maximum internal temperature (TI), wherein a power loss (V) of the component (6) is determined, a measurement temperature (TM) is measured on the component (6), a temperature difference (DT) for the component (6) between the measurement temperature (TM) on the component and the internal temperature (TI) is determined from the power loss (V) by means of a thermal model (14) of the component (6), the internal temperature (TI) is determined as the sum of the measurement temperature (TM) and the temperature difference (DT), a permissible maximum value (VM) for the power loss (V) is determined on the basis of the internal temperature (TM) and known component data (16) of the component (6), and the component (6) is operated in a normal operating mode (N) if the power loss (V) does not exceed the maximum value (VM) or the component (6) is otherwise operated in reduced-power economy operating mode (S) such that the power loss (V) is limited to the maximum value (VM). An audio apparatus (2), having an audio device (4) that internally contains a component (6) that should be protected from the exceedance of a maximum internal temperature (TI), contains a protection module (8) for carrying out the method according to the invention.

Claims

1. A method for protecting a component (6) inside an audio appliance (4) against the exceeding of a maximum internal temperature (TI), the method comprising: determining a power loss (V) of the component (6), measuring a measured temperature (TM) at the component (6), determining a temperature difference (DT) for the component (6) between the measured temperature (TM) at the component and the internal temperature (TI) from the power loss (V) using a thermal model (14) of the component (6), determining the internal temperature (TI) as the sum of the measured temperature (TM) and the temperature difference (DT), determining a permissible maximum value (VM) for the power loss (V) using the internal temperature (TM) and known component data (16) of the component (6), limiting an audio signal (A) 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, wherein 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 as claimed in claim 1, wherein the power loss (V) is also determined on the basis of the internal temperature (TI) and the measured temperature (TM).

4. The method as claimed in claim 1, wherein at least one thermal time constant (pt) describing a dynamic thermal behavior of a thermal section (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 as claimed in claim 1, wherein 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 as claimed in claim 1, wherein, 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), by virtue of an audio signal (A) carried on the audio path (12) being 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) and having a protection module (8) for carrying out the method that follows, for carrying out the method as claimed in claim 1 including determining a power loss (V) of the component (6), measuring a measured temperature (TM) at the component (6), determining a temperature difference (DT) for the component (6) between the measured temperature (TM) at the component and an internal temperature (TI) of the component (6) using a thermal model (14) of the component (6) from the determined power loss (V), determining the internal temperature (TI) as the sum of the temperature difference (DT) and the measured temperature (TM) that is measured, determining a permissible maximum value (VM) for the power loss (V) on the basis of the internal temperature (TM) 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) as claimed in claim 7, characterized in that the audio appliance (4) and/or the audio device (2) is an audio amplifier.

9. The audio device (2) as claimed in claim 7, characterized in that the component (6) contains or is a semiconductor subassembly to be protected, and the internal temperature (TI) is a junction temperature in the semiconductor subassembly.

10. The audio device (2) as claimed in claim 7, 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).

11. The method as claimed in claim 1, wherein the power loss (V) is also determined on the basis of the internal temperature (TI).

12. The method as claimed in claim 1, wherein the power loss (V) is also determined on the basis of the measured temperature (TM).

13. The method as claimed in claim 1, wherein the internal temperature (TI) is an internal junction temperature.

14. The audio device (2) as claimed in claim 7, wherein the internal temperature (TI) is an internal junction temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features, effects and advantages of the invention will become apparent from the description of a preferred exemplary embodiment of the invention that follows and from the accompanying figures, in which, in a schematic outline:

(2) FIG. 1 shows an audio device according to the invention,

(3) FIG. 2 shows a diagram to explain the method according to the invention.

DETAILED DESCRIPTION

(4) FIG. 1 shows an audio device 2. This contains an audio appliance 4. Inside, that is to say in its interior, the audio appliance 4 contains a component 6. The component 6 has inside, i.e. in its interior, an internal temperature TI that is not open to direct measurement. The component 6 needs to be protected against the exceeding of a maximum internal temperature, that is to say that the internal temperature TI is not supposed to exceed a maximum value. The audio device 2 additionally contains a protection module 8. This is configured to carry out a protection method. The protection method is explained later on.

(5) The audio appliance 4 is an audio amplifier. The audio device 2 is therefore an amplifier device. The audio appliance 4 is an output stage. The component 6 is a semiconductor subassembly to be protected. The internal temperature TI is a junction temperature in the semiconductor subassembly. The protection module 8 contains an audio limiter 10. The audio limiter 10 is arranged in an audio path 12 upstream of the audio appliance 4. The audio limiter 10 is configured to limit an audio signal A which is supplied to the audio appliance 4 along the audio path 12 as an input signal, in an economy mode S, this being indicated by a downwardly directed arrow. The audio signal A is thus carried on the audio path 12. The protection module 8 performs the following protection method:

(6) The method is used to protect the component 6 inside the audio appliance 4 against the exceeding of a maximum internal temperature TI. The method involves a power loss V of the component 6 being ascertained, said power loss being depicted symbolically by a circle in FIG. 1. Furthermore, at or outside the component 6, a measured temperature TM is measured at a measurement location 13, in this case at a heat sink, not depicted, thermally coupled to the component 6. A thermal model 14 of the component 6, which model is stored in the protection module 8, is used to ascertain a temperature difference DT for the component 6 from the power loss V. The temperature difference DT describes the difference produced by the internal temperature TI minus the measured temperature TM. The internal temperature TI is then ascertained as a sum of the measured temperature TM and the temperature difference DT to give TI=TM+DT. The internal temperature TI and known component data 16 of the component 6, which are likewise stored in the protection module 8, are used to ascertain a permissible maximum value VM for the power loss V. In the event of a power loss V equal to the maximum value VM, a maximum permitted or desired internal temperature TImax would be reached. In the present case, there is the threat of an overload, for which reason the audio signal 4 and hence the maximum output power LA are reduced in comparison with the normal mode N, as a result of which although the internal temperature TI reaches its maximum value TImax, it does not exceed it.

(7) When the audio signal A is limited by an audio limiter 10, there is no “hard” distinction between normal mode N and economy mode S because the maximum output power LA is always limited. Only the value MA of the maximum output power LA is always reascertained on the basis of the present internal subassembly temperature TI and hence the limit value is also supplied to the audio limiter 10.

(8) The aforementioned method steps are performed periodically. As such, an internal junction temperature TI is ascertained periodically as explained above. The component data 16 are used to periodically ascertain the maximum permissible power loss VM of the component 6 and, from this, the maximum permissible (value MA) output power LA. From this value MA, a limit value is prescribed for the audio limiter 10. If the expected power loss V as a result of the audio signal A upstream of the limiter 10 is thus below the maximum permissible power loss VM, then no kind of reduction is attempted. The component 6 is then operated in a normal mode N again (indicated in dashes in FIG. 1). In the example, the audio signal A is then thus supplied to the audio appliance 4 and hence to the component 6 in unlimited form on the audio path 12.

(9) The power loss V is ascertained in the method by virtue of an output power LA of the component 6 being ascertained and the power loss V being ascertained on the basis of the output power LA and the known component data 16. In the example, the output power LA is the power of the audio signal A amplified by the component 6.

(10) The ascertainment of the power loss V in this case also includes the currently ascertained internal temperature TI (after it has been ascertained for the first time or e.g. has been estimated the first time, e.g. equal to the measured temperature TM).

(11) The component data 16 are used to ascertain a maximum value MA for the permissible output power LA of the component 6 from the maximum value VM for the permissible power loss V. In a reduced-power economy mode S, the component 6 is operated such that the output power LA has been limited or is limited to the maximum value MA.

(12) The power loss V or output power LA is thus limited in the economy mode S by limiting the audio signal A using the audio limiter 10. The limiting of the output power LA also limits the power loss V, which is related thereto by means of the internal structure or properties of the component 6. In a normal mode N, no limiting by the audio limiter 10 is effected. The audio signal A can thus pass through the latter without alteration, so that the audio appliance is operated in regular fashion, i.e. without limitations.

(13) FIG. 2 explains the invention specifically using the example of the semiconductor protection (protection of the component 6 in the form of a semiconductor) in the audio appliance 4 in the form of an audio power amplifier as shown in FIG. 1:

(14) 1. Ascertainment of the Power Loss

(15) (Indicated by a Dashed Frame)

(16) An output voltage Uout and an output current Iout are measured at the component 6. Together with static parameters such as subassembly properties and internal operating voltages in the form of the component data 16, the output current Iout and output voltage Uout are taken as a basis for ascertaining the power loss V. The output voltage Uout and the output current Iout are modified in this case using functions f(U) and f(I) that are not explained more specifically, and the results are summed with an idle power loss R. Moreover, the subassembly temperature ascertained (e.g. estimated the first time as explained above) is also included in this case in the form of the internal temperature TI, since it also affects the power loss V produced by the output current Iout. In this case, the internal temperature TI is multiplied by and likewise summed with a function f(I), not explained more specifically, of the output current Iout. Therefore, the ascertained junction temperature (internal temperature TI) is fed back to the power loss ascertainment.

(17) 2. Thermal Model

(18) The power loss V is used to calculate the heating in the form of the temperature difference DT using the thermal model 14. In this example, three time constants pt1-3 (with downstream thermal resistors R1-3, not explained more specifically) are used in order to describe the dynamic thermal behavior of a thermal section 18, i.e. the section from a junction in the component 6 (location of the internal temperature TI) to a temperature sensor, which is not depicted (measurement location 13 for the measurement of the measured temperature TM). In this case, the section 18 can be described sufficiently accurately using three time constants pt1-3. In other cases, more or fewer than three time constants pt can also be used in order to describe the dynamic thermal behavior of the section 18.

(19) In the thermal model 14, 3 thermal time constants pt1-3 and three thermal resistors R1-3 are thus used, which describe a dynamic, thermal behavior of the thermal section 18 extending between the location of the internal temperature TI and the location of the measured temperature TM (measurement location 13).

(20) 3. Temperature Measurement

(21) All in all, heating (temperature difference DT) and “ambient temperature” (measured temperature TM) result in the absolute junction temperature (internal temperature TI).

(22) 4. Ascertainment of the Maximum Permissible Output Power

(23) (Indicated by a Dashed Frame)

(24) From a datasheet of the component 6 (component data 16), it is inferred at what internal temperature TI how much power loss (maximum value VM) can be asked of the subassembly (component 6). Since, of course, it is known (from the component data 16) how the influence of the output variables (output current Iout and output voltage Uout) affects the power loss V in the subassembly (component 6), it is also possible to work out the maximum permissible output variables (maximum values for Uout, Iout) from a permissible power loss VM of the subassembly.

(25) 5. Reduction of the Output Power

(26) (Indicated by a Dashed Frame)

(27) The audio limiter 10 is used to limit the output power LA of the amplifier (audio appliance 4) such that the maximum permissible power loss VM in the semiconductor (component 6) is not exceeded. This is accomplished by transferring a threshold value, not explained more specifically, to the audio limiter 10.