A vehicle audio protection circuit and control method thereof

Abstract

This invention discloses an in-vehicle audio protection circuit and control method. The protection circuit includes an MCU, a MOS transistor control circuit, and a voltage detection circuit. Using common transistors and resistors and capacitors, the circuit can promptly cut off external high voltage, thereby protecting the internal power supply and achieving effective protection. The hardware implementation is simple. Furthermore, the MCU can quickly detect short-circuit conditions and protect the PA chip. The technical solution provided by this invention effectively resolves the problem of short-circuit damage at the audio output terminal and protects the PA chip in a T-box.

Description

Technical Field

[0001] The present invention belongs to the technical field of vehicle networking, and particularly relates to a vehicle-mounted audio protection circuit and a control method thereof. Background Art

[0002] As cars continue to evolve, they're gaining more and more additional features. The Internet of Vehicles (T-BOX), serving as a terminal device for automotive communications, comes with an independent audio amplifier system connected to speakers to provide call functionality during emergency rescue (ecall). To ensure the reliability of this audio system, short-circuit protection for the ports must be considered during design. Therefore, during the T-BOX design verification (DV) experiment, the two output terminals of the audio amplifier (PA) chip are short-circuited to a DC16V high-voltage power supply. The experiment requires that no audio output function be damaged after the experiment to confirm the reliability of the T-BOX audio circuit.

[0003] like Figure 1 As shown, the PA chip includes a PWM controller and four MOS transistors. Q1 and Q3 are P-type MOS transistors, and Q2 and Q4 are N-type MOS transistors. The gates of Q1 and Q2 are short-circuited and connected to the PWM controller. The source of Q1 is connected to VDD, the source of Q2 is grounded, and the drain of Q1 and Q2 are short-circuited, serving as output pin 1 of the PA chip. The gates of Q3 and Q4 are short-circuited and connected to the PWM controller. The source of Q3 is connected to VDD, the source of Q4 is grounded, and the drain of Q3 and Q4 are short-circuited, serving as output pin 2 of the PA chip. The two output pins of the PA chip are directly connected to the two ends of the speaker. When the system is operating normally, the PWM controller of the PA chip can drive the four MOS transistors inside the chip as needed, causing the speaker to produce sound.

[0004] In order to verify the reliability of the product, when doing DV experiment, it is necessary to add DC16V high voltage to the two output terminals of PA chip respectively. Figure 2As shown. First, the MOS transistor itself has a body diode, through which current can flow unidirectionally. The conduction condition requires a forward voltage greater than the conduction voltage of 0.7V. Therefore, when an external high voltage is applied to the common terminal of Q1 and Q2 (DC 16V), and the internal VDD of the PA chip is DC 4V, a forward voltage drop forms between the common terminal and VDD, and this voltage drop is greater than the diode conduction voltage of 0.7V. The direction of Q1's body diode meets the conduction condition, and current will flow there. However, Q2, because its body diode is oriented in the opposite direction, does not meet the conduction condition. The high voltage is blocked at Q2, and no current will flow. Similarly, Q3 will be turned on, and Q4 will be turned off. The external high voltage then flows into the PA chip, exceeding the operating voltage of 4V, damaging the PA chip's power supply and the chip itself.

[0005] In summary, the PA chip's output terminal contains four MOS transistors. Due to the presence of the MOS transistor's inherent body diode, when the output terminal is connected to the DC 16V high voltage in the DV experiment, short-circuit current will flow through the body diode to the PA chip's power supply terminal VDD. The VDD voltage is DC 4V. This will cause VDD to break down due to the high voltage, damaging the PA chip. Therefore, to protect the PA chip, it is necessary to design a protection circuit. Summary of the Invention

[0006] The purpose of the present invention is to provide a vehicle-mounted audio protection circuit and a control method thereof, which can protect the PA chip of a T-BOX.

[0007] In order to achieve the above object, the solution of the present invention is:

[0008] A vehicle-mounted audio protection circuit is used to protect a PA chip. The PA chip includes a PWM controller and first to fourth MOS transistors. The gates of the first and second MOS transistors are short-circuited and connected to the PWM controller. The source of the first MOS transistor is connected to VDD, the source of the second MOS transistor is grounded, and the drain of the first MOS transistor is short-circuited with the drain of the second MOS transistor and serves as the first output pin of the PA chip. The gates of the third and fourth MOS transistors are short-circuited and connected to the PWM controller. The source of the third MOS transistor is connected to VDD, the source of the fourth MOS transistor is grounded, and the drain of the third MOS transistor is short-circuited with the drain of the fourth MOS transistor and serves as the second output pin of the PA chip. The protection circuit includes an MCU, a MOS transistor control circuit, and a voltage detection circuit.

[0009] The MOS transistor control circuit includes a seventh and eighth MOS transistors and fifth and sixth transistors. The source of the seventh MOS transistor is connected to the first output pin of the PA chip, the drain of the seventh MOS transistor is connected to one terminal of the speaker, the source of the eighth MOS transistor is connected to the second output pin of the PA chip, and the drain of the eighth MOS transistor is connected to the other terminal of the speaker. The gates of the seventh and eighth MOS transistors are short-circuited and connected to the collector of the fifth transistor via a second resistor. One end of a third resistor and one end of a first capacitor are respectively connected between the short-circuited point of the seventh and eighth MOS transistors and the second resistor. The other end of the third resistor and the other end of the first capacitor are grounded. The emitter of the fifth transistor is connected to VCC, and the first resistor is further connected between its base and emitter. The base of the fifth transistor is connected to the collector of the sixth transistor, the emitter of the sixth transistor is grounded, a resistor is connected between the base and emitter, and the base is further connected to a control terminal of the MCU via another resistor.

[0010] The voltage detection circuit includes fourth to seventh resistors and second and third capacitors, wherein one end of the fourth resistor is connected between the seventh MOS transistor and the speaker, the other end of the fourth resistor is connected to one end of the fifth resistor, the other end of the fifth resistor is grounded, one end of the second capacitor is connected between the fourth and fifth resistors, the other end of the second capacitor is grounded, and the first detection end of the MCU is connected between the fourth and fifth resistors; one end of the sixth resistor is connected between the eighth MOS transistor and the speaker, the other end of the sixth resistor is connected to one end of the seventh resistor, the other end of the seventh resistor is grounded, one end of the third capacitor is connected between the sixth and seventh resistors, the other end of the third capacitor is grounded, and the second detection end of the MCU is connected between the sixth and seventh resistors.

[0011] The first and third MOS transistors are P-type MOS transistors, and the second and fourth MOS transistors are N-type MOS transistors.

[0012] The seventh and eighth MOS transistors are both N-type MOS transistors.

[0013] The fifth transistor is a PNP transistor, and the sixth transistor is an NPN transistor.

[0014] As described above, a method for controlling a vehicle audio protection circuit includes the following steps:

[0015] Step 1: cyclically sample the source voltages of the seventh and eighth MOS transistors. When the sampled voltage exceeds the operating voltage of the PA chip, it is determined to be a short circuit, and the short circuit count is increased by 1, and the process jumps to step 2; otherwise, the count is cleared and the process jumps to step 3.

[0016] Step 2: When the count reaches the set number of times, the MCU turns off the MOS tube to protect the PA; then the process of step 1 is repeated.

[0017] In step 3, when the sampling voltage does not exceed DC 4V during the execution, the MOS tube state is maintained or the MOS tube is turned on, and then step 1 is executed repeatedly.

[0018] In the above step 1, the method for cyclically sampling the source voltages of the seventh and eighth MOS transistors is as follows: the source voltages of the seventh and eighth MOS transistors are sampled respectively, and the MCU identifies the last sampling port. If it is the seventh MOS transistor, the sampling channel is switched to the eighth MOS transistor; if it is the eighth MOS transistor, the sampling channel is switched to the seventh MOS transistor, and the seventh and eighth MOS transistors are sampled cyclically.

[0019] By adopting the above solution, the present invention can promptly cut off the external high voltage when a short circuit occurs in the PA chip, thereby protecting the internal power supply. By designing a protection circuit, the present invention uses common transistors and resistors and capacitors to achieve the protection effect. This hardware implementation is simple, requiring no special materials and without increasing sensitive costs. Furthermore, the present invention uses an MCU to quickly detect short-circuit conditions and protect the PA chip. Therefore, the present invention effectively solves the problem of audio output terminal short-circuit damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the functional block diagram of the output end of the existing PA chip;

[0021] Figure 2 This is a block diagram of the short-circuit current flow during the DV experiment;

[0022] Figure 3 is a circuit diagram of the present invention;

[0023] Figure 4 This is a schematic diagram of the MOS tube control circuit in the present invention;

[0024] Figure 5 This is one of the voltage detection circuit schematics in the present invention;

[0025] Figure 6 This is the second schematic diagram of the voltage detection circuit in the present invention;

[0026] Figure 7 It is a flow chart of the control method of the present invention. DETAILED DESCRIPTION

[0027] The technical solutions and beneficial effects of the present invention will be described in detail below with reference to the accompanying drawings.

[0028] like Figure 3As shown, the present invention provides a vehicle-mounted audio protection circuit. A MOS tube control circuit and a voltage detection circuit are added to the output end of the PA chip and controlled by an MCU. The MCU determines whether the output end of the PA chip is normal by detecting the voltage at the output end. When the voltage is normal, the MOS tube can be turned on to output the audio normally. When the voltage is abnormal, the MCU can be turned off to protect the PA chip and the internal power supply. These two circuits are introduced below.

[0029] like Figure 3 As shown, the MOS tube control circuit is set between the PA chip output end and the speaker, mainly including two MOS tubes Q7 and Q8. Q7 and Q8 control the two output ends of the PA chip respectively, and the gates of Q7 and Q8 are controlled by the transistor Q5. The base of Q5 is controlled by the transistor Q6. The base of Q6 is controlled by the MCU, that is, by controlling the base of Q6, the on and off of the PA chip output end can be controlled. Figure 4 As shown, the specific circuit connection relationship is as follows: Q7 and Q8 are both N-type MOS transistors, the source of Q7 is connected to the output pin 1 of the PA chip, the drain of Q7 is connected to one terminal of the speaker, the source of Q8 is connected to the output pin 2 of the PA chip, and the drain of Q8 is connected to the other terminal of the speaker; the gates of Q7 and Q8 are short-circuited and connected to the collector of transistor Q5 via resistor R2, and one end of resistor R3 and one end of capacitor C1 are respectively connected between the short-circuited point of Q7 and Q8 and R2, and the other ends of R3 and C1 are grounded; Q5 is a PNP transistor, its emitter is connected to VCC, and a resistor R1 is connected between its base and emitter; as mentioned above, the base of Q5 is connected to the collector of Q6, which is an NPN transistor, its emitter is grounded, a resistor is connected between its base and emitter, and the base is also connected to the control terminal MCU_Control of the MCU via another resistor.

[0030] Figure 4 In the control circuit shown, the analysis is as follows:

[0031] 1) Q6 is an NPN transistor, the base of which is controlled by the MCU. When MCU_Control is set to a high level, Q6 is turned on and the collector of Q6 is pulled low.

[0032] 2) Q5 is a PNP transistor. After the base is pulled low by the collector of Q6, Q5 is turned on.

[0033] 3) After VCC passes through R2, it pulls up the gates of Q7 and Q8, turning on Q7 and Q8, opening the PA output channel, and allowing the speaker to produce sound.

[0034] 4) After MCU_Control is set to low level, Q6 is cut off, the collector of Q6 is floating, and then the voltage is pulled up to VCC by R1;

[0035] 5) The base of Q5 is also pulled up to VCC by R1, Q5 is cut off, the collector of Q5 is floating, and then pulled down to a low level by R2 and R3;

[0036] 6) The gates of Q7 and Q8 are pulled down to a low level by R3, Q7 and Q8 are cut off, the PA output channel is closed, the speaker cannot make any sound, and the external voltage cannot enter the PA;

[0037] 7) R2 and R3 form an attenuator that adjusts the voltage divider ratio based on the VCC voltage to keep the gate-source voltage of Q7 and Q8 within the operating range. C1 is a filter capacitor that acts as a voltage stabilizer, filtering out stray signals and stabilizing the gate voltage of Q7 and Q8, thereby stabilizing the conduction state of Q7 and Q8.

[0038] The voltage detection circuit consists of two parts, one at the output of Q7 and the other at Q8. The two parts have the same function and use resistors to divide the voltage to reduce it to the detectable range of the MCU, that is, the maximum voltage at the divider is 3.3V. The MCU then calculates the voltage at the output of Q7 and Q8 based on the voltage ratio and activates the protection mechanism when high voltage is detected, shutting down the output to protect the PA chip.

[0039] like Figure 5 As shown, it includes resistors R4, R5 and capacitor C2. One end of resistor R4 is connected between Q7 and the speaker, the other end of R4 is connected to one end of R5, and the other end of R5 is grounded. One end of capacitor C2 is connected between R4 and R5, and the other end is grounded. The MCU detection terminal MCU_ADC1 is connected between R4 and R5. R4 and R5 form an attenuator to reduce the output voltage of Q7 to the detection range of the MCU, that is, the maximum voltage at the voltage divider is 3.3V. The detection voltage upper limit is designed to be DC 16V, which meets the DV test requirements. C2 is a filter capacitor, which plays the role of voltage anti-shake, filters out stray signals, and provides a stable voltage level for MCU detection.

[0040] Cooperate Figure 6 , including resistors R6, R7 and capacitor C3. One end of resistor R6 is connected between Q8 and the speaker, the other end of R6 is connected to one end of R7, and the other end of R7 is grounded. One end of capacitor C3 is connected between R6 and R7, and the other end is grounded. The MCU's detection terminal MCU_ADC2 is connected between R6 and R7; among them, R6 and R7 form an attenuator, which reduces the output voltage of Q8 to the detection range of the MCU, that is, the maximum voltage at the voltage divider is 3.3V. The detection voltage upper limit is designed to be DC 16V, which meets the DV test requirements; C3 is a filter capacitor, which plays the role of voltage anti-shake, filters out stray signals, and provides a stable level for MCU detection.

[0041] When the present invention is working, after the output end of the PA chip is connected to high voltage, the voltage is detected by the MCU real-time voltage detection mechanism, triggering the MCU's high-voltage protection mechanism, and MCU_Control is set to a low level by the MCU, thereby protecting the PA and achieving a protection effect.

[0042] like Figure 7 FIG. 1 is a flow chart of the control method provided by the present invention, comprising the following steps:

[0043] Step 1: Identify the short circuit. After power-on and program initialization, start voltage sampling and begin loop execution. The voltages at the output terminals of the two MOS tubes, namely the sources of Q7 and Q8, need to be sampled separately. After sampling and reading the results, the MCU identifies the last sampled port. If it is Q7, the sampling channel switches to Q8. If it is Q8, the sampling channel switches to Q7. The sampling of Q7 and Q8 is repeated in a loop. When the sampled voltage exceeds the operating voltage of the PA, it is determined to be a short circuit, the short circuit count is increased by 1, and the process jumps to step 2. Otherwise, the count is cleared and the process jumps to step 3.

[0044] Step 2: When the count reaches 5 times (the number here can be determined according to the actual situation), the MCU turns off the MOS tube to protect the PA; then the step 1 is executed repeatedly;

[0045] During step 3, if the sampling voltage does not exceed DC 4V, the MOS tube state can be maintained or turned on, and then step 1 is executed repeatedly.

[0046] The above embodiments are only for illustrating the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A vehicle audio protection circuit for protecting a PA chip, comprising a PWM controller and first to fourth MOS transistors. The gates of the first and second MOS transistors are short-circuited and connected to the PWM controller, the source of the first MOS transistor is connected to VDD, the source of the second MOS transistor is grounded, and the drain of the first MOS transistor is short-circuited with the drain of the second MOS transistor and serves as a first output pin of the PA chip. The gates of the third and fourth MOS transistors are short-circuited and connected to the PWM controller, the source of the third MOS transistor is connected to VDD, the source of the fourth MOS transistor is grounded, and the drain of the third MOS transistor is short-circuited with the drain of the fourth MOS transistor and serves as a second output pin of the PA chip. The circuit is characterized in that: The protection circuit includes an MCU, a MOS tube control circuit and a voltage detection circuit; The MOS transistor control circuit includes a seventh and eighth MOS transistors and fifth and sixth triodes, wherein the source of the seventh MOS transistor is connected to the first output pin of the PA chip, the drain of the seventh MOS transistor is connected to one terminal of the speaker, the source of the eighth MOS transistor is connected to the second output pin of the PA chip, and the drain of the eighth MOS transistor is connected to the other terminal of the speaker; The gates of the seventh and eighth MOS transistors are short-circuited and connected to the collector of the fifth transistor via the second resistor. One end of a third resistor and one end of a first capacitor are respectively connected between the short-circuited point of the seventh and eighth MOS transistors and the second resistor. The other end of the third resistor and the other end of the first capacitor are grounded. The emitter of the fifth transistor is connected to VCC, and the first resistor is further connected between its base and emitter. The base of the fifth transistor is connected to the collector of the sixth transistor, and the emitter of the sixth transistor is grounded. A resistor is connected between the base of the sixth transistor and the emitter of the sixth transistor. The base of the sixth transistor is further connected to the control terminal of the MCU via another resistor. The voltage detection circuit includes fourth to seventh resistors and second and third capacitors, wherein one end of the fourth resistor is connected between the seventh MOS transistor and the speaker, the other end of the fourth resistor is connected to one end of the fifth resistor, the other end of the fifth resistor is grounded, one end of the second capacitor is connected between the fourth and fifth resistors, the other end is grounded, and the first detection end of the MCU is connected between the fourth and fifth resistors; one end of the sixth resistor is connected between the eighth MOS transistor and the speaker, the other end of the sixth resistor is connected to one end of the seventh resistor, the other end of the seventh resistor is grounded, one end of the third capacitor is connected between the sixth and seventh resistors, the other end is grounded, and the second detection end of the MCU is connected between the sixth and seventh resistors; The first and third MOS transistors are P-type MOS transistors, and the second and fourth MOS transistors are N-type MOS transistors; The seventh and eighth MOS transistors are both N-type MOS transistors.

2. The vehicle audio protection circuit according to claim 1, wherein: The fifth transistor is a PNP transistor, and the sixth transistor is an NPN transistor.

3. The control method of a vehicle audio protection circuit according to claim 1, characterized in that The steps include: Step 1: cyclically sample the source voltages of the seventh and eighth MOS transistors. When the sampled voltage exceeds the operating voltage of the PA chip, it is determined to be a short circuit, and the short circuit count is increased by 1, and then the process goes to step 2; otherwise, the count is cleared and the process goes to step 3; Step 2: When the count reaches the set number of times, the MCU turns off the seventh and eighth MOS tubes, and then goes to step 1; In step 3, when the sampling voltage does not exceed DC 4V, the seventh and eighth MOS tubes are turned on, and then step 1 is executed repeatedly.

4. The control method according to claim 3, wherein: In step 1, the method for cyclically sampling the source voltages of the seventh and eighth MOS transistors is as follows: the source voltages of the seventh and eighth MOS transistors are sampled respectively, the MCU identifies the last sampling port, and if it is the seventh MOS transistor, the sampling channel is switched to the eighth MOS transistor; if it is the eighth MOS transistor, the sampling channel is switched to the seventh MOS transistor, and the seventh and eighth MOS transistors are sampled cyclically.

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