Loudspeaker load protection circuit

Abstract

The utility model discloses a loudspeaker load protection circuit, which relates to the technical field of loudspeaker protection, and utilizes the characteristics that when the temperature coefficient of a voice coil is higher, the temperature coefficient of a sampling divider resistor is very low, and the temperature rise of the voice coil of the loudspeaker does not exceed a set value, the direct-current voltage of the negative input end of a voltage comparator is higher than that of the positive input end of the voltage comparator; the voltage comparator outputs negative voltage; after the temperature rise of the loudspeaker voice coil exceeds a set value, the resistance value of the loudspeaker voice coil is increased, the voltage on the sampling divider resistor is reduced, the direct-current voltage at the negative input end of the voltage comparator is reduced, and when the direct-current voltage is reduced to be lower than the direct-current voltage at the positive input end, the output voltage of the voltage comparator is turned into positive voltage to trigger the protection execution unit to act; compared with the prior art, the utility model can timely execute protection operation (such as reducing power input and the like), and can more effectively prevent the loudspeaker from being burnt down due to overlarge power input.

Description

Technical Field

[0001] The utility model belongs to the technical field of loudspeaker protection, and in particular relates to a loudspeaker load protection circuit. Background Art

[0002] An electric speaker unit (hereinafter referred to as a speaker) includes a voice coil, a diaphragm, a frame and a magnet. The voice coil of the speaker is wound with metal wire and bonded with an adhesive. The voice coil is generally bonded to the frame with an adhesive. At the same time, the diaphragm and the frame are also bonded and shaped with an adhesive. The melting temperature of the adhesive is very low, generally between 100°C and 200°C, and the voice coil is generally made of metal materials such as copper, which has excellent thermal conductivity. Once an excessively high power load is input to the speaker, the temperature of the voice coil will quickly exceed 200°C, causing the adhesive on the voice coil, diaphragm and frame to begin to melt, causing the entire speaker to burn (the effect deteriorates or fails).

[0003] To prevent speakers from burning out due to excessive input power and high temperatures, existing speakers are often designed with parameter monitoring and protection measures. For example, some monitor the speaker's output voltage or output current, while others incorporate temperature sensors on the speaker's surface. If these parameters exceed set values, the speaker's input power is reduced or shut down to implement protection.

[0004] However, existing speaker parameter detection has many drawbacks. For example, when detecting the output voltage or output current of the speaker, when it is detected that the output voltage or output current exceeds the set value, the current exceeding the set value has already flowed through the voice coil, causing the adhesive on the voice coil, diaphragm and frame to begin to melt; similarly, there is a circle of magnets on the outer layer of the voice coil. By detecting the temperature, only the temperature of the magnets outside the voice coil can be detected, and the temperature of the voice coil cannot be reflected in a timely manner.

[0005] In summary, the existing parameter detection for speakers is not reasonable enough, and the parameter feedback is not timely enough, which results in a certain delay in the execution of protection measures. When the power input is too large, the speaker is still prone to burning out. Utility Model Content

[0006] In order to solve the problems in the prior art of unreasonable parameter detection and untimely parameter feedback of loudspeaker over-temperature protection, which result in failure to trigger protection execution elements in a timely manner, the present utility model aims to provide a loudspeaker load protection circuit.

[0007] The technical solution adopted by this utility model is:

[0008] A speaker load protection circuit includes a speaker, a first low-pass filter, a sampling voltage-dividing resistor, a second low-pass filter, a DC voltage amplifier, a voltage comparator, and a protection actuator. The input end of the speaker is connected to an external power amplifier, the output end of the speaker is connected to one end of the sampling voltage-dividing resistor, and the other end of the sampling voltage-dividing resistor is grounded. The input end of the first low-pass filter is connected to the common connection end of the power amplifier and the speaker, and the output end of the first low-pass filter is connected to the positive input end of the voltage comparator. The input end of the second low-pass filter is connected to the common connection end of the speaker and the sampling voltage-dividing resistor, the output end of the second low-pass filter is connected to the input end of the DC voltage amplifier, and the output end of the DC voltage amplifier is connected to the negative input end of the voltage comparator. The output end of the voltage comparator is connected to the protection actuator.

[0009] When the temperature rise of the speaker voice coil does not exceed the set value, the DC voltage at the negative input terminal of the voltage comparator is higher than the DC voltage at the positive input terminal, and the voltage comparator outputs a negative voltage; when the temperature rise of the speaker voice coil exceeds the set value, the resistance of the speaker voice coil increases, the voltage on the sampling voltage divider resistor decreases, and the DC voltage at the negative input terminal of the voltage comparator decreases accordingly. When it drops to a value lower than the DC voltage at the positive input terminal, the output voltage of the voltage comparator flips to a positive voltage, triggering the protection execution unit to operate.

[0010] Optionally, a bypass capacitor C3 is connected in parallel across the sampling voltage divider resistor.

[0011] Optionally, the power amplifier is an OCL power amplifier, which contains a DC drift voltage.

[0012] Optionally, the power amplifier is additionally superimposed with a DC bias voltage, and the AC audio signal of the power amplifier is mixed with the external DC bias voltage and then transmitted to the speaker.

[0013] Optionally, the first low-pass filter and the second low-pass filter are single-stage RC filters or multi-stage RC filters.

[0014] Optionally, the first low-pass filter and the second low-pass filter are source filters.

[0015] The beneficial effects of the utility model are:

[0016] The present invention actually utilizes the fact that the temperature coefficient of the voice coil is relatively high, while the temperature coefficient of the sampling voltage divider resistor is very low. When the temperature rise of the loudspeaker voice coil does not exceed the set value, the DC voltage at the negative input terminal of the voltage comparator is higher than the DC voltage at the positive input terminal, and the voltage comparator outputs a negative voltage. After the temperature rise of the loudspeaker voice coil exceeds the set value, the resistance of the loudspeaker voice coil increases, the voltage on the sampling voltage divider resistor decreases, and the DC voltage at the negative input terminal of the voltage comparator decreases accordingly. When it decreases to a value lower than the DC voltage at the positive input terminal, the output voltage of the voltage comparator flips to a positive voltage, triggering the action of the protection execution unit. Compared with the prior art, the present invention can execute protection operations (such as reducing power input, etc.) in a timely manner, and can more effectively prevent the loudspeaker from being burned due to excessive power input. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is the block diagram of the speaker load protection circuit.

[0018] Figure 2 This is a circuit diagram in which the sampling voltage divider resistor is connected in series with the negative pole of the speaker. At this time, the input end of the speaker is the positive pole.

[0019] Figure 3 This is a circuit diagram in which the sampling voltage divider resistor is connected in series between the speaker and the power amplifier. In this case, the input end of the speaker is the negative pole. DETAILED DESCRIPTION

[0020] The following combination Figure 1 and Figure 2 The technical solution of the utility model is further explained.

[0021] In this embodiment, if Figure 1 and Figure 2 A speaker load protection circuit is shown, which includes a speaker SP1, a first low-pass filter, a sampling voltage-dividing resistor R3, a second low-pass filter, a DC voltage amplifier IC1, a voltage comparator IC2, and a protection actuator; the input end of the speaker SP1 is externally connected to an OCL power amplifier, the output end of the speaker SP1 is connected to one end of the sampling voltage-dividing resistor R3, and the other end of the sampling voltage-dividing resistor R3 is grounded; the input end of the first low-pass filter is connected to the common terminal of the OCL power amplifier and the speaker SP1, and the output end of the first low-pass filter is connected to the positive input end of the voltage comparator IC2; the input end of the second low-pass filter is connected to the common terminal of the speaker SP1 and the sampling voltage-dividing resistor R1, the output end of the second low-pass filter is connected to the input end of the DC voltage amplifier IC1, and the output end of the DC voltage amplifier IC1 is connected to the negative input end of the voltage comparator IC2; the output end of the voltage comparator IC2 is connected to the protection actuator.

[0022] In normal operation, the resistance of sampling voltage divider resistor R3 is smaller than that of speaker SP1. The OCL amplifier converts the low-frequency electrical signal into a high-power signal to drive speaker SP1 and provide a DC voltage for detection. The first and second low-pass filters filter the AC signal and retain the DC voltage. Voltage comparator IC2 compares the voltages at the positive and negative input terminals and outputs the comparison result to the protection actuator.

[0023] When the signal (voltage or current) inputted at the positive terminal is large, the output signal of the voltage comparator IC2 is a positive voltage; conversely, when the signal inputted at the negative terminal is large, the output signal of the DC voltage amplifier IC1 is a negative voltage.

[0024] In this embodiment, in a normal state, the DC voltage input to the negative terminal of the voltage comparator IC2 is greater than the DC voltage input to the positive terminal. At this time, the output of the voltage comparator IC2 is a negative voltage, and the protection actuator regards this signal as a safety signal; when the temperature of the speaker SP1 increases, the resistance of the speaker SP1 increases synchronously. Since the speaker SP1 and the sampling voltage divider resistor R3 are connected in series, as the resistance of the speaker SP1 gradually increases, the DC voltage at the speaker SP1 end becomes larger. When the resistance of the speaker SP1 exceeds the threshold set by the sampling voltage divider resistor R2, the DC voltage input to the positive terminal of the voltage comparator IC2 is greater than the DC voltage input to the negative terminal. At this time, the output signal of the voltage comparator changes to a positive voltage, and the protection actuator performs a protection action after receiving the positive voltage signal.

[0025] Specifically, voice coils are typically made of a material with good electrical conductivity, such as copper. Copper voice coils have a relatively high temperature coefficient of resistance (TCR) of approximately 0.00393°C (0.00393°F). This means that for every 100°C increase in temperature, the copper's resistance increases by approximately 39.3%. To minimize the impact of temperature changes on the resistance of the sampling voltage divider resistor R3 and improve measurement accuracy, the sampling voltage divider resistor R3 is typically made of a material with a low TCR. Therefore, in the present invention, the impact of temperature changes in the sampling voltage divider resistor on the final measurement result is negligible.

[0026] In this embodiment, the first low-pass filter and the second low-pass filter are single-stage RC filters, or may be multi-stage RC filters.

[0027] Specifically, the first low-pass filter is a first capacitor C1 and a first resistor R1 connected in series, or another low-pass filter circuit. The first low-pass filter can filter out AC signals and high-frequency voltages in the circuit, allowing only the DC voltage generated by the OCL power amplifier to enter the voltage comparator IC2 for comparison. This does not affect the power of the OCL power amplifier used to drive the speaker SP1, thereby preventing the protection circuit from affecting the normal operation of the speaker SP1.

[0028] In this embodiment, the sampling voltage divider resistor R3 is connected in parallel with a capacitor C3. The capacitor C3 provides a low-impedance path for the AC signal, so that the sampling voltage divider resistor R3 is not easily heated and the resistance value is stable and not easily changed.

[0029] The technical solution of the utility model is further described below in conjunction with specific data.

[0030] For example, in Figure 2 In the circuit diagram shown, it is assumed that the DC drift voltage generated by the OCL power amplifier is 11mV due to factors such as materials. After passing through the first low-pass filter, the AC audio signal is filtered out, and the 11mV DC drift voltage is directly sent to the positive input terminal of the voltage comparator IC2. At the same time, it is assumed that the amplification factor of the DC voltage amplifier IC1 is 15 times.

[0031] Under normal conditions, the resistance of speaker SP1 is 8Ω, the resistance of sampling voltage divider resistor R3 is 0.8Ω, and the voltage divider ratio is 10:1. After the DC drift voltage passes through speaker SP1 and sampling voltage divider resistor R3, according to the series voltage divider principle, the 11mV DC drift voltage is reflected as a DC voltage of 10mV on speaker SP1 and 1mV on sampling voltage divider resistor R3. This 1mV DC voltage is amplified 15 times by DC voltage amplifier IC1, becoming a 15mV DC voltage, which is then fed to the negative input of voltage comparator IC2. It should be noted that the AC voltage signal on sampling voltage divider resistor R3 has been filtered out by the second low-pass filter and is not fed to voltage amplifier IC1.

[0032] As known from the above, the voltage at the negative input terminal of the voltage comparator IC2 is higher than the voltage at the positive input terminal, so the signal output by the voltage comparator is a negative voltage, and the protection actuator recognizes the signal as a safety signal.

[0033] When the power delivered to speaker SP1 by the OCL amplifier increases, the temperature of speaker SP1 rises. After a 200°C increase, the copper or aluminum voice coil resistor increases by approximately 80%. At this point, speaker SP1's resistance is approximately 14.4Ω, while sampling voltage divider resistor R3 remains at 0.8Ω. The voltage divider ratio becomes 18:1, and the DC voltage across the sampling voltage divider resistor drops from 1mV to approximately 0.58mV. After being amplified 15 times by the DC amplifier, the DC voltage is 8.7mV. At this point, the voltage directly output from the OCL amplifier to voltage comparator IC2, which passes through the first low-pass filter, remains at 11mV at its positive input, while the voltage at its negative input is 8.7mV. The output voltage of voltage comparator IC2 switches from negative to positive, and the protection actuator recognizes this as an overtemperature condition for speaker SP1 and initiates actions such as reducing input power or shutting down the power supply.

[0034] In this embodiment, the power amplifier is an OCL power amplifier (ie Figure 2 The OCL power amplifier circuit contains a DC drift voltage. The power supply of this circuit can be taken from the AC audio signal output by the power amplifier.

[0035] In this embodiment, the DC drift voltage output by the OCL amplifier may be a negative voltage. In this case, an absolute value circuit is required at the output of the first and second low-pass filters. This absolute value circuit is a conventional technique used by those skilled in the art, and its function and principle are not further described here.

[0036] In other embodiments, when a power amplifier without a DC drift voltage is selected, a DC bias voltage may be added to the power amplifier, and the DC bias voltage is mixed with the AC audio signal of the speaker before being transmitted to the speaker.

[0037] In other embodiments, the sampling voltage divider resistor R3 can also be connected in series between the positive electrode of the speaker SP1 and the OCL power amplifier (eg Figure 3 As shown), the negative electrode of the speaker SP1 is grounded. At this time, the input end of the first low-pass filter is connected to the ground line of the speaker, and the input end of the second low-pass filter is connected to the parallel end of the speaker SP1 and the sampling voltage divider resistor R3. In this embodiment, the grounding of the first low-pass filter, the second low-pass filter, the capacitor C3, the DC voltage amplifier IC1 and the voltage comparator IC2 are all suspended ground ( Figure 3 The floating ground is referenced to the output of the OCL amplifier.

[0038] It should be noted that the protection execution element that performs operations such as reducing input power or shutting down power based on different feedback signals is a prior art.

[0039] In a possible embodiment, the protection execution element may be a relay provided between the loudspeaker SP1 and the OCL power amplifier. When the voltage comparator IC2 outputs a positive voltage signal, the relay disconnects the input circuit of the loudspeaker.

[0040] In this utility model, unless otherwise specified or limited, the terms "installed," "connected," "connect," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection; direct connection, indirect connection through an intermediate medium, internal communication between two components, or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in this utility model based on specific circumstances.

[0041] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0042] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are illustrative and cannot be understood as limitations on the present invention. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A speaker load protection circuit, characterized in that: It includes a speaker, a first low-pass filter, a sampling voltage-dividing resistor, a second low-pass filter, a DC voltage amplifier, a voltage comparator and a protection execution element; The input end of the speaker is connected to an external power amplifier, the output end of the speaker is connected to one end of a sampling voltage divider resistor, and the other end of the sampling voltage divider resistor is grounded; The input end of the first low-pass filter is connected to the common terminal of the power amplifier and the speaker, and the output end of the first low-pass filter is connected to the positive input end of the voltage comparator; The input end of the second low-pass filter is connected to the common terminal of the loudspeaker and the sampling voltage-dividing resistor, the output end of the second low-pass filter is connected to the input end of the DC voltage amplifier, and the output end of the DC voltage amplifier is connected to the negative input end of the voltage comparator; The output end of the voltage comparator is connected to the protection execution element.

2. The loudspeaker load protection circuit according to claim 1, characterized in that: A bypass capacitor C3 is connected in parallel across the sampling voltage-dividing resistor.

3. The loudspeaker load protection circuit according to claim 1, characterized in that: The power amplifier is an OCL power amplifier, and the OCL power amplifier contains a DC drift voltage.

4. The speaker load protection circuit according to claim 1, characterized in that: The power amplifier is additionally superimposed with a DC bias voltage, and the AC audio signal of the power amplifier is mixed with the external DC bias voltage and then transmitted to the speaker.

5. The loudspeaker load protection circuit according to claim 1, characterized in that: The first low-pass filter and the second low-pass filter are single-stage RC filters or multi-stage RC filters.

6. The loudspeaker load protection circuit according to claim 1, characterized in that: The first low-pass filter and the second low-pass filter are source filters.

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