Real-time detection method for short circuit fault of class-d power amplifier output to power supply or ground

Abstract

The application discloses a real-time detection method for output short circuit to power or ground fault of a class-D power amplifier, real-time monitoring of respective currents of four MOS tubes of the class-D power amplifier, calculation of average values of the currents within a set time, and sequential judgment by a judgment module, so that the result can be quickly and effectively detected when the output short circuit to power or ground fault occurs, the detection method does not cause interference on a sound spectrum played by a loudspeaker, and the detection device is high in efficiency and low in cost.

Description

Technical Field

[0001] This invention belongs to the field of loudspeaker driving technology, specifically relating to a real-time detection method for a Class D power amplifier output short circuit to power supply or ground fault. Background Technology

[0002] The application of Class D audio amplifiers in car audio systems is becoming increasingly widespread. Typical characteristics of car audio systems include: 1) long speaker wires; 2) complex wiring; 3) high safety requirements for automotive electronics; and 4) with the increasing prevalence of vehicle-to-everything (V2X) connectivity, more and more modern smart cars are incorporating real-time fault monitoring. Class D audio amplifiers use PWM (Pulse Width Modulation) modulation for their music signals, with an external output LC (inductor and capacitor) filter to remove high-frequency PWM signals. Since the amplifier's circuitry is typically housed in a metal box, the probability of short circuits to the chip's external pins is extremely low. However, the speaker wires after the LC filter are prone to short circuits to the external power supply or ground (due to in-car wiring). If a strong short circuit occurs after the LC filter (a direct short circuit to the power supply or ground with a low impedance of less than 1Ω), a large current will flow at the moment the amplifier powers on or at the moment the external short circuit occurs, triggering the amplifier's overcurrent protection. This type of fault is generally handled by the Class D amplifier's mandatory protection (output shutdown). However, for subtle, weak short circuits (with short-circuit resistances >1Ω or even larger, such as the multilayer ceramic capacitors on the output LC filter easily short-circuiting due to vehicle vibration, the speaker wire being weakly short-circuited to the external vehicle chassis, or the speaker wire being weakly short-circuited to the external power supply line), the overcurrent protection of the Class D amplifier cannot be triggered. Under such weak short-circuit conditions, the current flowing through the Class D amplifier cannot reach the amplifier's overcurrent protection threshold. However, if this short circuit persists for a long time, the continuous high current heating will accelerate the aging of components, ultimately affecting reliability. It will also lead to increased system power consumption, further impacting system reliability.

[0003] Therefore, a real-time detection method for short circuits to power supply or ground faults in Class D power amplifier outputs is urgently needed. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a real-time detection method for short-circuit faults in the output of a Class D power amplifier to the power supply or ground.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] This invention provides a real-time detection method for a Class D power amplifier output short-circuit to power supply or ground fault, comprising the following steps:

[0007] S1. The current acquisition module acquires and records the current of the four MOSFETs in S1 to S4 of the Class D power amplifier, and then calculates the average current of each MOSFET over a set time period as the current value and outputs it.

[0008] S2. The first judgment module judges whether the current value of each MOSFET is 0. If yes, it means that there is no short circuit to the power supply or ground fault in the output. If no, proceed to step S3.

[0009] S3. The second judgment module judges whether the current value of each MOS transistor with a non-zero output value is greater than 0. If not, proceed to step S4; if yes, proceed to step S5.

[0010] S4. The third judgment module determines whether the absolute value of the current value of each MOSFET is greater than or equal to the short-circuit decision current threshold I. SHORT If yes, it indicates that a short circuit to ground fault has occurred; if no, it indicates that there is no short circuit to power supply or ground fault at the output.

[0011] S5. The fourth judgment module determines whether the absolute value of the current value of each MOSFET is greater than or equal to the short-circuit decision current threshold I. SHORT If yes, it indicates a short circuit to the power supply fault; if no, it indicates no short circuit to the power supply or ground fault at the output.

[0012] Preferably, in step S1, the average value is calculated within a time period of 500ms-1000ms.

[0013] Preferably, the short-circuit decision current threshold I in steps S4 and S5 SHORT The calculations were performed according to the following formula: ,

[0014] Where PVDD is the current power supply voltage of the power amplifier, R SHORT This is the external short-circuit resistance threshold.

[0015] Preferably, the first judgment module, the second judgment module, the third judgment module, and the fourth judgment module are comparators.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] This invention calculates the average current of the four MOSFETs within a set time period as the current value. After being judged sequentially by the judgment module, the result can be detected quickly and effectively in real time when a short circuit to the power supply or ground occurs. Moreover, this detection method does not interfere with the sound spectrum played by the speaker. The detection device is highly efficient and low in cost. Attached Figure Description

[0018] Figure 1This is a schematic diagram of the circuit structure of the Class D power amplifier of the present invention during normal operation;

[0019] Figure 2 This is a schematic diagram of the circuit structure of the Class D power amplifier of the present invention when the switching transistors S1 and S4 are turned on in the event of an external short circuit to the power supply.

[0020] Figure 3 This is a schematic diagram of the circuit structure of the Class D power amplifier of the present invention when the switching transistors S1 and S3 are turned on in the event of an external short circuit to the power supply.

[0021] Figure 4 This is a schematic diagram of the circuit structure of the Class D power amplifier of the present invention when the switching transistors S2 and S4 are turned on in the event of an external short circuit to the power supply.

[0022] Figure 5 This is a schematic diagram of the circuit structure of the Class D power amplifier of the present invention when the switching transistors S3 and S2 are turned on in the event of an external short circuit to the power supply.

[0023] Figure 6 This is a schematic diagram of the circuit structure of the Class D power amplifier of the present invention when the switching transistors S1 and S4 are turned on in the event of an external short circuit to ground.

[0024] Figure 7 This is a schematic diagram of the circuit structure of the Class D power amplifier of the present invention when the switching transistors S1 and S3 are turned on in the event of an external short circuit to ground.

[0025] Figure 8 This is a schematic diagram of the circuit structure of the Class D power amplifier of the present invention when the switching transistors S2 and S4 are turned on in the event of an external short circuit to ground.

[0026] Figure 9 This is a schematic diagram of the circuit structure of the Class D power amplifier of the present invention when the switching transistors S3 and S2 are turned on in the event of an external short circuit to ground.

[0027] Figure 10 This is a flowchart of the real-time detection method for a Class D power amplifier output short circuit to power supply or ground fault according to the present invention. Detailed Implementation

[0028] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0029] Class D amplifiers, when operating normally, such as Figure 1 As shown, specifically, Figure 1 When the switching transistors S1 and S4 are turned on, the current flows through PVDD, OUTP, OUTN, and GND in sequence. The average current flowing through S1 is equal to the average current flowing through S4. Figure 1When the switching transistors S1 and S3 are turned on, the current flows in the following order: PVDD, OUTP, OUTN, PVDD. The average current flowing through S1 is equal to the current flowing through S3. Figure 1 When the switching transistors S2 and S4 are turned on, the current flows through GND, OUTP, OUTN, and GND in sequence. The average current flowing through S2 is equal to the current flowing through S4. Figure 1 When switches S3 and S2 are turned on, the current flows through PVDD, OUTN, OUTP, and GND in that order. The average current flowing through S2 is equal to the current flowing through S3. Therefore, in the absence of a short circuit at the output, the average current flowing through the four switches S1, S2, S3, and S4 is equal (the high-frequency ripple current has been filtered out by the LC low-pass filter), and the current flowing through the two power transistors that are turned on at the same time is equal. In this embodiment, current flowing into the MOSFET is defined as positive current, and current flowing out of the MOSFET is defined as negative current.

[0030] Generally, the single-ended output common-mode voltage of a Class D amplifier is PVDD / 2, and the voltage difference across the speaker is the actual audio AC signal (usually between 20Hz and 20kHz).

[0031] In the event of an external short circuit to the power supply, the voltage difference across the short-circuit resistor is PVDD / 2. Figure 2 When the switching transistors S1 and S4 are turned on, R SHORT The current flows back into S1, and the average current on S1 is PVDD / (2×R). SHORT ); Figure 3 When the switching transistors S1 and S3 are turned on, R SHORT The current flows back into S1, and the average current on S1 is PVDD / (2×R). SHORT ); Figure 4 When the switching transistors S2 and S4 are turned on, R SHORT The current flows back into S2, and the average current in S2 is PVDD / (2×R). SHORT ); Figure 5 When the switching transistors S3 and S2 are turned on, R SHORT The current flows back into S2, and the average current on S2 is PVDD / (2×R). SHORT Therefore, according to Figures 2-5 As shown, since the common-mode voltages on both sides of the speaker are equal (both are PVDD / 2), the short-circuit current flows through the MOSFET on the short-circuit side. When the upper MOSFET is on, the current flows into the upper MOSFET, and when the lower MOSFET is on, the current flows into the lower MOSFET. According to the definition of current direction mentioned above, when the power supply is short-circuited, this DC current flowing through the MOSFET is a positive current.

[0032] In the event of an external short circuit to ground, the voltage difference across the short-circuit resistor is PVDD / 2. Figure 6When the switching transistors S1 and S4 are turned on, R SHORT The short-circuit current is obtained from S1, and the value of S is PVDD / (2×R). SHORT ); Figure 7 When the switching transistors S1 and S3 are turned on, R SHORT The short-circuit current is obtained from S1, and the value of S is PVDD / (2×R). SHORT ); Figure 8 When the switching transistors S2 and S4 are turned on, R SHORT The short-circuit current is obtained from S2, and the value of S is PVDD / (2×R). SHORT ); Figure 9 When the switching transistors S3 and S2 are turned on, R SHORT The short-circuit current is obtained from S2, and the value of S is PVDD / (2×R). SHORT Therefore, according to Figures 6-9 As shown, since the common-mode voltages on both sides of the speaker are equal (both PVDD / 2), the short-circuit current flows through the MOSFET on the short-circuit side. When the upper MOSFET is open, the current flows out through the upper MOSFET, and when the lower MOSFET is open, the current flows out through the lower MOSFET. According to the aforementioned definition of current direction, when short-circuited to ground, this DC current flowing through the MOSFET is a negative current.

[0033] Based on the above principles, this embodiment provides a real-time detection method for a short circuit to power supply or ground fault in a Class D power amplifier output. The detection mechanism for a short circuit to power supply or ground after the power amplifier output filter is as follows: Figure 10 As shown, the specific steps include:

[0034] S1. The current acquisition module acquires and records the current of the four MOSFETs in Class D power amplifier S1 to S4, then calculates the average current of each MOSFET over a 500ms period as the current value and outputs it.

[0035] S2. The first comparator determines whether the current value of each MOSFET is 0. If yes, it means that there is no short circuit to the power supply or ground fault at the output. If no, proceed to step S3.

[0036] S3. The second comparator determines whether the current value of each MOS transistor with a non-zero output value is greater than 0. If not, proceed to step S4; if yes, proceed to step S5.

[0037] S4. The third comparator determines whether the absolute value of the current value of each MOSFET is greater than or equal to the short-circuit decision current threshold I. SHORT If yes, it indicates that a short circuit to ground fault has occurred; if no, it indicates that there is no short circuit to power supply or ground fault at the output.

[0038] S5. The fourth comparator determines whether the absolute value of the current value of each MOSFET is greater than or equal to the short-circuit decision current threshold I.SHORT If yes, it indicates a short circuit to the power supply fault; if no, it indicates no short circuit to the power supply or ground fault at the output.

[0039] In this embodiment, the short-circuit decision current threshold I in steps S4 and S5 SHORT The calculations were performed according to the following formula: ,

[0040] Where PVDD is the current power supply voltage of the power amplifier, R SHORT This is the external short-circuit resistance threshold.

[0041] In this embodiment, the current of the four power MOSFETs is detected. In order to filter out the audio current and the high-frequency PWM ripple current, a 500ms average filter (equivalent to a 2Hz low-pass filter) is used for filtering.

[0042] In this embodiment, when an external short circuit to power failure occurs, the magnitude of the short circuit current is equal to PVDD / (2×R). SHORT When no short circuit occurs, the DC current flowing through the MOSFETs in a Class D audio amplifier playing audio signals (AC signals between 20Hz and 20kHz) will always be zero. However, in the event of a short circuit leading to a power supply failure, the output current of one of the output MOSFETs (high-side and low-side) will be a negative DC current for an extended period. The absolute value of this negative DC current is related to the magnitude of the short-circuit resistance and the current supply voltage; therefore, the threshold is set by the user.

[0043] In this embodiment, when an external short-circuit to ground fault occurs, the magnitude of the short-circuit current is equal to PVDD / (2×R). SHORT When no short circuit occurs, the DC current flowing through the MOSFETs in a Class D audio amplifier playing audio signals (AC signals between 20Hz and 20kHz) will always be zero. However, in the event of a short circuit to ground fault, the output current of one of the output MOSFETs (upper and lower transistors) will be a positive DC current for a long time. The absolute value of this current is related to the magnitude of the short circuit resistance and the current supply voltage, so the threshold is set by the user.

[0044] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A real-time detection method for a Class D power amplifier output short-circuit to power supply or ground fault, characterized in that, Includes the following steps: S1. The current acquisition module acquires and records the current of the four MOSFETs in S1 to S4 of the Class D power amplifier, and then calculates the average current of each MOSFET over a set time period as the current value and outputs it. S2. The first judgment module judges whether the current value of each MOSFET is 0. If yes, it means that there is no short circuit to the power supply or ground fault in the output. If no, proceed to step S3. S3. The second judgment module judges whether the current value of each MOS transistor with a non-zero output value is greater than 0. If not, proceed to step S4; if yes, proceed to step S5. S4. The third judgment module determines whether the absolute value of the current value of each MOSFET is greater than or equal to the short-circuit decision current threshold I. SHORT If yes, it indicates that a short circuit to ground fault has occurred; if no, it indicates that there is no short circuit to power supply or ground fault at the output. S5. The fourth judgment module determines whether the absolute value of the current value of each MOSFET is greater than or equal to the short-circuit decision current threshold I. SHORT If yes, it indicates a short circuit to the power supply fault; if no, it indicates no short circuit to the power supply or ground fault at the output.

2. The real-time detection method for a short circuit to power supply or ground fault in a Class D power amplifier output according to claim 1, characterized in that, In step S1, the average value is calculated over a period of 500ms-1000ms.

3. The real-time detection method for a short circuit to power supply or ground fault in a Class D power amplifier output according to claim 1, characterized in that, In steps S4 and S5, the short-circuit decision current threshold I SHORT Calculated according to the following formula: I SHORT =PVDD / (2×R) SHORT ), Where PVDD is the current power supply voltage of the power amplifier, R SHORT This is the external short-circuit resistance threshold.

4. The real-time detection method for a short circuit to power supply or ground fault in a Class D power amplifier output according to claim 1, characterized in that, The first, second, third, and fourth judgment modules are comparators.

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