Load detection circuit of digital power amplifier

Abstract

The invention relates to the field of load detection, in particular to a digital power amplifier load detection circuit. Comprising a digital power amplifier circuit and a load detection circuit, and the digital power amplifier circuit comprises a signal feedback circuit; the signal feedback circuit is used for outputting a feedback signal to the power amplifier circuit; the load detection circuit comprises a high-pass filter circuit, a rectification circuit and a logic judgment circuit, the high-pass filter circuit is connected with the rectification circuit, and the rectification circuit is connected with the logic judgment circuit; the load detection circuit is used for judging whether the digital power amplifier circuit has a load short circuit or not; the load detection circuit is connected between the digital power amplifier circuit and the output device. According to the invention, the influence of audio input, temperature change of a power device or dynamic change of horn impedance on load short-circuit fault detection can be avoided, static load short-circuit detection can be realized, and the reliability and efficiency of load short-circuit detection are greatly improved.

Description

Technical Field

[0001] The present invention relates to the field of load detection, and in particular to a load detection circuit for a digital power amplifier. Background Art

[0002] A power amplifier is a device used to amplify audio and drive speakers. While speakers may operate normally, they may also experience fault conditions such as short circuits, open circuits, and impedance variations. However, engineering applications, especially firefighting systems, require real-time monitoring of the speaker circuit status at the amplifier load end to prevent the speaker from malfunctioning during startup, potentially preventing normal operation.

[0003] In existing technologies, short-circuit detection for power amplifier loads often uses a threshold method to detect the sampled current. When the power amplifier detects that the sampled current exceeds the threshold, it initiates short-circuit protection. However, this method is limited in that it cannot determine whether the load is functioning properly when the power amplifier is in a static state and has no audio input (i.e., no output). To address this issue, some specific systems employ a control system that periodically applies an ultrasonic signal to the power amplifier to determine if a fault exists.

[0004] Existing technologies for determining whether there is a fault at the power amplifier output have many disadvantages. When there is no audio input or the audio input is very small, the short-circuit threshold cannot be reached, resulting in inaccurate short-circuit detection. The use of central control to apply ultra-audio detection is prone to cause harmonic audio distortion.

[0005] The terminal load of a power amplifier is typically a speaker. Speaker impedance varies dynamically with audio frequency. Furthermore, the current threshold of the power transistor also changes with temperature. Therefore, the speaker's impedance threshold can vary significantly under the combined effects of varying audio frequencies and temperatures. Consequently, the threshold value used in the determination method is typically the maximum value across the full frequency range, but this reduces the effectiveness of the power amplifier's load short-circuit protection. Summary of the Invention

[0006] The purpose of the present invention is to solve the above-mentioned related problems and design a digital power amplifier load detection circuit. To achieve the above-mentioned purpose, the present invention provides the following solutions: A digital power amplifier load detection circuit includes a digital power amplifier circuit and a load detection circuit, wherein the digital power amplifier circuit includes a signal feedback circuit; the signal feedback circuit is used to output a feedback signal to the power amplifier circuit; The load detection circuit includes a high-pass filter circuit, a rectifier circuit and a logic judgment circuit, wherein the high-pass filter circuit is connected to the rectifier circuit, and the rectifier circuit is connected to the logic judgment circuit; the load detection circuit is used to determine whether a load short circuit occurs in the digital power amplifier circuit; The load detection circuit is connected between the digital power amplifier circuit and the output device.

[0007] As a further improvement of the present technical solution, the digital power amplifier circuit includes a comparison circuit, a Class D power amplifier circuit, an LC filter circuit, and a feedback signal circuit. The comparison circuit is connected to the Class D power amplifier circuit, the Class D power amplifier circuit is connected to the filter circuit, the filter circuit is connected to the output device, and the signal feedback circuit is connected to the Class D power amplifier circuit and the comparison circuit.

[0008] As a further improvement of the present technical solution, the class D power amplifier circuit uses MOSFET as a power switch.

[0009] As a further improvement of the present technical solution, the digital power amplifier circuit adopts pulse width modulation control or space vector pulse width modulation control.

[0010] As a further improvement of the present technical solution, the sampling frequency of the digital power amplifier circuit is 300kHz to 400kHz.

[0011] As a further improvement of the present technical solution, the signal feedback circuit is an integration circuit.

[0012] As a further improvement of the present technical solution, the high-pass filter circuit includes a capacitor C1, a coil circuit, and resistors R1, R2, and R3; The coil circuit includes a first coil side and a second coil side, the first coil side of the coil circuit includes coils T1A and T1B, and the second coil side of the coil circuit includes coils T1C and T1D; the capacitor C1 is connected to the coil T1A, and the coil T1A is connected to the resistor R1; the capacitor C1 and the resistor R1 are connected to the output device; The coil T1C and the coil T1D are connected in series, the resistor R2 is connected to the coil T1C, the resistor R3 is connected to the coil T1D, and the resistors R2 and R3 are connected to the rectifier circuit.

[0013] As a further improvement of the present technical solution, the coil circuit contains an iron core.

[0014] As a further improvement of the present technical solution, the rectifier circuit includes a bridge rectifier circuit composed of diodes D2, D3, D4 and D5; wherein the anode of the diode D2 is connected to the cathode of the diode D3, the anode of the diode D4 is connected to the cathode of the diode D5, the cathode of the diode D2 is connected to the cathode of the diode D4, and the anode of the diode D3 is connected to the anode of the diode D5 and is grounded; The electrostatic suppressor D1 is connected between the diodes D2 and D3 and the diodes D4 and D5; The cathodes of the diodes D2 and D4 are connected to the resistors R4 and R5 and then to the anodes of the diodes D3 and D5; a capacitor C2 is also connected in parallel between the cathodes of the diodes D2 and D4 and the ground; The diodes D2 and D3 are connected to the filter circuit; the resistors R4 and R5 are connected to the logic judgment circuit.

[0015] As a further improvement of the present technical solution, the logic judgment circuit includes a transistor Q1, a light-emitting diode D6, resistors R6 and R7, and a capacitor C3; The base and emitter of the transistor Q1 are connected to the rectifier circuit, the emitter of the transistor Q1 is connected to the ground, and the collector of the transistor Q1 is connected to a DC power supply via a resistor R7; The resistor R6 is connected between the collector of the transistor Q1 and the resistor R7, the resistor R6 is connected to the anode of the light emitting diode D6, and the cathode of the light emitting diode D6 is connected to the emitter of the transistor Q1; The capacitor C3 is connected between the DC power supply and the ground. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Various other advantages and benefits will become apparent to those skilled in the art by reading the detailed description of the preferred embodiment below. The accompanying drawings are only for the purpose of illustrating the preferred embodiment and are not to be considered as limiting the present invention; Figure 1 This is a structural diagram of a load detection circuit for a digital power amplifier according to the present invention; Figure 2 A schematic diagram of a high-pass filter circuit of a digital power amplifier load detection circuit of the present invention; Figure 3 A schematic diagram of a rectifier circuit of a digital power amplifier load detection circuit of the present invention; Figure 4 A schematic diagram of a logic judgment circuit of a digital power amplifier load detection circuit of the present invention; Figure 5 Another structural schematic diagram of a load detection circuit for a digital power amplifier of the present invention; Figure 6 The present invention provides a waveform diagram of a load detection circuit input signal and a rectifier circuit input signal of a digital power amplifier load detection circuit. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0018] Those skilled in the art will appreciate that, unless otherwise stated, the singular forms "a," "an," and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present invention refers to the presence of the stated features, integers, steps, operations, elements, and / or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0019] The present invention will be described in detail below with reference to the accompanying drawings.

[0020] Example 1 like Figure 1 As shown in the figure, a structural diagram of a digital power amplifier load detection circuit is shown.

[0021] This digital power amplifier load detection circuit includes a digital power amplifier circuit and a load detection circuit. The digital power amplifier circuit includes a comparison circuit, a Class D power amplifier circuit, an LC filter circuit, and a signal feedback circuit. The load of the digital power amplifier is a speaker. After an audio signal is input to the comparison circuit, it is compared with a high-frequency triangular wave signal input by the signal feedback circuit. When the voltage at the inverting terminal is higher than the voltage at the non-inverting terminal, the output is low; when the voltage at the inverting terminal is lower than the voltage at the non-inverting terminal, the output is high. The Class D power amplifier circuit uses metal oxide field-effect transistors (MOSFETs). MOSFETs have a faster response time and are therefore suitable for high-frequency operation. The Class D power amplifier circuit uses two MOSFETs, which can be fully switched between on and off in a very short time. When the MOSFETs are fully on, their voltage drop is very low; when they are fully off, the current flowing through them is zero. The two MOSFETs are connected in a half-bridge configuration, with one being an N-channel MOSFET (NMOS) and the other being a P-channel MOSFET (PMOS), and they operate alternately between on and off states. Because MOSFET switches very quickly, it is highly efficient and generates very little heat, so the Class D power amplifier circuit does not require an additional heat sink.

[0022] The Class D power amplifier circuit uses pulse width modulation (PWM) mode. The audio signal output by the comparator is a series of switching signals, and PWM can be used to control the audio signal.

[0023] After being amplified by the Class D power amplifier circuit, the original audio signal is restored using an LC filter circuit. This LC filter is a low-pass filter with a cutoff frequency higher than the audio bandwidth to ensure that all signals within the audio range can pass through. Between the Class D power amplifier circuit and the LC filter circuit, the output signal of the Class D power amplifier circuit is fed back to the comparison circuit as a comparison signal. Since the output signal of the Class D power amplifier circuit is a switching signal, that is, a square wave signal, an integrator circuit can be used in the signal feedback circuit to convert the square wave signal into a triangular wave signal, which is the high-frequency triangular wave signal required by the comparison circuit.

[0024] The load detection circuit, connected between the LC filter circuit and the speaker, includes a high-pass filter, a rectifier, and a logic circuit. The high-pass filter passes a signal in the non-audio range of 300kHz to 400kHz. This signal is converted to a DC signal by the rectifier circuit. The logic circuit uses this DC signal to determine whether the load has a short circuit fault.

[0025] Example 2 like Figure 2 FIG. 1 is a schematic diagram of a high-pass filter circuit of a digital power amplifier load detection circuit.

[0026] The high-pass filter circuit includes a capacitor C1, a coil circuit, and resistors R1, R2, and R3.

[0027] The coil circuit is divided into a first coil side and a second coil side. The first coil side includes coils T1A and T1B, while the second coil side includes coils T1C and T1D. Coils T1A, T1B, T1C, and T1D have the same number of turns and contain an iron core to enhance inductance and magnetic field strength. Coil T1A, capacitor C1, and resistor R1 on the first coil side are connected in series, and this circuit is connected to the speaker at the output. Coil T1B on the first coil side is not connected to the circuit and is left floating. Coils T1C and T1D on the second coil side are connected in series, and then connected to resistors R2 and R3, respectively. Resistors R2 and R3 are then connected to the rectifier circuit. Since coils T1A, T1B, T1C, and T1D have the same number of turns and coil T1B is suspended, the ratio of the number of turns between the first coil side and the second coil side is 1:2. Since the voltage across the coil is proportional to the number of turns, the voltage across coil T1A is 1 / 2 of the voltage across the series coil consisting of coils T1C and T1D.

[0028] Example 3 like Figure 3 As shown, a schematic diagram of a rectifier circuit of a digital power amplifier load detection circuit.

[0029] The rectifier circuit includes diodes D2, D3, D4 and D5, an electrostatic suppressor D1, a capacitor C2, and resistors R4 and R5.

[0030] Diodes D2, D3, D4, and D5 are connected to form a rectifier bridge, which is used to rectify AC signals into DC signals. The anode of diode D2 is connected to the cathode of diode D3, the anode of diode D4 is connected to the cathode of diode D5, the cathodes of diodes D2 and D4 are connected, and the anode of diode D5 is connected to ground. An electrostatic suppressor D1 is connected between diodes D2, D3, D4, and D5 to protect the entire rectifier bridge circuit.

[0031] The anode of the diode D2 and the cathode of the diode D3 are connected to the high-pass filter circuit, the anode of the diode D3 and the anode of the diode D5 are connected to the high-pass filter circuit, and the anode of the diode D3 and the anode of the diode D5 are grounded.

[0032] The cathodes of diodes D2 and D4 are connected in series with resistors R4 and R5, which are then connected to the anodes of diodes D3 and D5. Both sides of resistor R5 are connected to the logic judgment circuit. R4 and R5 act as a voltage divider, feeding the voltage across R5 into the logic judgment circuit. Capacitor C2 is also connected in parallel between the cathodes of diodes D2 and D4 and ground to maintain voltage balance.

[0033] Example 4 like Figure 4 As shown, a schematic diagram of a logic judgment circuit of a digital power amplifier load detection circuit.

[0034] The logic judgment circuit includes a transistor Q1, a light emitting diode D6, resistors R6 and R7, and a capacitor C3.

[0035] The base and emitter of transistor Q1 are connected to the rectifier circuit, with the emitter grounded. The collector is connected to a 3.3V DC power supply via resistor R7. Resistor R6 is connected between the collector of transistor Q1 and resistor R7. Resistor R6 is connected to the anode of light-emitting diode D6, and the cathode of light-emitting diode D6 is connected to the emitter of transistor Q1. Capacitor C3 is connected between the DC power supply and ground to balance the voltage. An active-high short-circuit signal is generated between resistor R7 and the collector of transistor Q1, which alerts the control system if a short-circuit fault occurs in the digital power amplifier's load.

[0036] When the base voltage of transistor Q1 is not 0, the base voltage of transistor Q1 is greater than the emitter voltage, R7 takes a larger value, transistor Q1 is in a saturated state, the branch composed of resistor R6 and light-emitting diode D6 is short-circuited, and the DC voltage 3.3V flows into the ground through resistor R7 and transistor Q1. At this time, the collector of transistor Q1 is in a low level state and will not send a short-circuit signal to the control system. At the same time, since the branch composed of light-emitting diode D6 is short-circuited, light-emitting diode D6 is off, which also indicates that the load is in normal working condition and no fault has occurred.

[0037] When the base voltage of transistor Q1 is 0, the base and emitter voltages of transistor Q1 are equal, and transistor Q1 is in the off state. Since no current flows through the collector in this off state, the collector of transistor Q1 is high, alerting the control system that a short-circuit fault has occurred in the load. The 3.3V DC voltage flows to ground through the loop formed by resistors R7, R6, and the LED. The LED, with forward current flowing through it, emits light, indicating that the digital power amplifier circuit is malfunctioning and the load is faulty.

[0038] Example 5 like Figure 5 FIG. 1 is another structural diagram of a load detection circuit for a digital power amplifier according to the present invention.

[0039] like Figure 6 As shown in the figure, a waveform diagram of a load detection circuit input signal and a rectifier circuit input signal of a load detection circuit of a digital power amplifier of the present invention.

[0040] The output of the digital power amplifier circuit is connected to a high-pass filter circuit consisting of a coil with an iron core. This high-pass filter circuit is rectified by a bridge rectifier and then connected to a logic judgment circuit. When audio input is present, the comparison circuit samples at a frequency between 300kHz and 400kHz, with an audio frequency range of 20Hz to 20kHz. The comparison circuit converts the audio signal into a square wave switching signal, which is amplified by the Class D power amplifier circuit to a more powerful square wave signal. This square wave signal passes through a low-pass LC filter circuit to restore the audio signal and is played through the speakers. The square wave output of the Class D power amplifier circuit is then converted to a triangle wave through the signal feedback circuit, which serves as the sampling signal for the comparison circuit.

[0041] When the load speaker is in normal working condition and there is an audio signal input, there is a signal at the output of the digital power amplifier circuit. This signal also serves as the input signal of the load detection circuit. It passes through the high-pass filter circuit composed of capacitors, resistors and coils and enters the rectifier bridge composed of diodes D2, D3, D4 and D5. Figure 6As shown in the figure, the yellow waveform represents the output signal at the output, and the green waveform represents the signal after passing through the high-pass filter circuit and entering the rectifier bridge. The rectifier bridge converts the AC signal into a DC signal, which flows through resistors R4 and R5, generating a voltage across resistor R5. This voltage serves as the input signal for the logic circuit. Since R5 is connected to the base and emitter of transistor Q1, transistor Q1 is saturated at this time, and its collector is low, thus not sending a short-circuit signal to the control system. The branch formed by LED D6 is short-circuited, and LED D6 turns off, indicating that the load is operating normally and there is no fault. When a loudspeaker short-circuit occurs, the load detection circuit loses input due to the load short-circuit. The base and emitter voltages of transistor Q1 are both zero, and transistor Q1 is off. However, the collector of transistor Q1 is high, alerting the control system that a load short-circuit fault has occurred. Forward current flows through LED D6, illuminating it, indicating that the digital power amplifier circuit is malfunctioning and the load is faulty.

[0042] When the load speaker is operating normally and no audio signal is input, the signal amplified by the Class D power amplifier circuit is only the carrier signal. A portion of the carrier signal, converted to a square wave, passes through the LC filter circuit and is input to the load. Because the carrier signal sampling frequency is well above the audio frequency range, no audible output is present at the output. This carrier signal also serves as the input to the load detection circuit. Passing through the high-pass filter circuit, the input signal is amplified due to the different turns on each side of the coil circuit, ensuring sufficient energy to drive transistor Q1 forward conduction, preventing a short-circuit signal from being sent to the control system and keeping LED D6 off. If a short-circuit occurs in the speaker and no audio signal is input, the carrier signal cannot be input to the load detection circuit due to the load short. Transistor Q1 shuts off, alerting the control system and lighting LED D6, indicating that the digital power amplifier circuit is operating abnormally and the load is faulty. This allows for detection of a load short-circuit even in the absence of an audio signal.

[0043] In summary, the digital power amplifier load detection circuit proposed in the present invention can avoid the influence of audio input size, power device temperature change or dynamic change of speaker impedance on load short-circuit fault detection. It responds immediately when a load short-circuit fault occurs and recovers automatically when the load short circuit is released. It has detection independence and reliability, can realize static load short-circuit detection, and greatly improves the reliability and efficiency of load short-circuit detection.

Claims

1. A digital power amplifier load detection circuit, characterized in that: It includes a digital power amplifier circuit and a load detection circuit, wherein the digital power amplifier circuit includes a signal feedback circuit; the signal feedback circuit is used to output a feedback signal to the power amplifier circuit; The load detection circuit includes a high-pass filter circuit, a rectifier circuit and a logic judgment circuit, wherein the high-pass filter circuit is connected to the rectifier circuit, and the rectifier circuit is connected to the logic judgment circuit; the load detection circuit is used to determine whether a load short circuit occurs in the digital power amplifier circuit; The load detection circuit is connected between the digital power amplifier circuit and the output device.

2. The digital power amplifier load detection circuit according to claim 1, characterized in that: The digital power amplifier circuit includes a comparison circuit, a class D power amplifier circuit, an LC filter circuit, and a feedback signal circuit. The comparison circuit is connected to the class D power amplifier circuit, the class D power amplifier circuit is connected to the filter circuit, the filter circuit is connected to the output device, and the signal feedback circuit is connected to the class D power amplifier circuit and the comparison circuit.

3. The digital power amplifier load detection circuit according to claim 2, wherein: The class D power amplifier circuit uses MOSFET as a power switch.

4. The digital power amplifier load detection circuit according to claim 1, wherein: The digital power amplifier circuit adopts pulse width modulation control or space vector pulse width modulation control.

5. The digital power amplifier load detection circuit according to claim 1, characterized in that: The sampling frequency of the digital power amplifier circuit is 300kHz to 400kHz.

6. The digital power amplifier load detection circuit according to claim 1, characterized in that: The signal feedback circuit is an integration circuit.

7. The digital power amplifier load detection circuit according to claim 1, characterized in that: The high-pass filter circuit includes a capacitor C1, a coil circuit, and resistors R1, R2, and R3; The coil circuit includes a first coil side and a second coil side, the first coil side of the coil circuit includes coils T1A and T1B, and the second coil side of the coil circuit includes coils T1C and T1D; the capacitor C1 is connected to the coil T1A, and the coil T1A is connected to the resistor R1; the capacitor C1 and the resistor R1 are connected to the output device; The coil T1C and the coil T1D are connected in series, the resistor R2 is connected to the coil T1C, the resistor R3 is connected to the coil T1D, and the resistors R2 and R3 are connected to the rectifier circuit.

8. The digital power amplifier load detection circuit according to claim 7, characterized in that: The coil circuit includes an iron core.

9. The digital power amplifier load detection circuit according to claim 1, characterized in that: The rectifier circuit includes a bridge rectifier circuit composed of diodes D2, D3, D4 and D5; wherein the anode of the diode D2 is connected to the cathode of the diode D3, the anode of the diode D4 is connected to the cathode of the diode D5, the cathode of the diode D2 is connected to the cathode of the diode D4, and the anode of the diode D3 is connected to the anode of the diode D5 and is grounded; The electrostatic suppressor D1 is connected between the diodes D2 and D3 and the diodes D4 and D5; The cathodes of the diodes D2 and D4 are connected to the resistors R4 and R5 and then to the anodes of the diodes D3 and D5; a capacitor C2 is also connected in parallel between the cathodes of the diodes D2 and D4 and the ground; The diodes D2 and D3 are connected to the filter circuit; the resistors R4 and R5 are connected to the logic judgment circuit.

10. The digital power amplifier load detection circuit according to claim 1, characterized in that: The logic judgment circuit includes a transistor Q1, a light emitting diode D6, resistors R6 and R7, and a capacitor C3; The base and emitter of the transistor Q1 are connected to the rectifier circuit, the emitter of the transistor Q1 is connected to the ground, and the collector of the transistor Q1 is connected to a DC power supply via a resistor R7; The resistor R6 is connected between the collector of the transistor Q1 and the resistor R7, the resistor R6 is connected to the anode of the light emitting diode D6, and the cathode of the light emitting diode D6 is grounded; The capacitor C3 is connected between the DC power supply and the ground.

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