A PWM filter output analog signal protection circuit and a protection method thereof

Abstract

The application relates to the technical field of PWM filter output analog signals, in particular to a PWM filter output analog signal protection circuit and a protection method thereof, which comprises a PWM signal isolation module, the PWM signal isolation module is used for isolating and conveying a PWM signal output by an MCU; a low-pass filter module and a PWM signal protection module are connected to the output end of the PWM signal isolation module, the input end of the low-pass filter module is connected to the output end of the PWM signal isolation module, and the low-pass filter module is used for outputting a preset voltage signal; the PWM signal protection module is used for outputting a signal indicating whether protection is needed; the output ends of the low-pass filter module and the PWM signal protection module are both connected to a signal selection module, the signal selection module is used for selecting and outputting signals input by the low-pass filter module and the PWM signal protection module; and the output end of the signal selection module is connected to an output module.

Description

Technical Field

[0001] This application relates to the technical field of PWM filter output analog signals, and in particular to a PWM filter output analog signal protection circuit and its protection method. Background Technology

[0002] PWM (Pulse Width Modulation) is an analog control method that modulates the bias of the base of a transistor or the gate of a MOSFET according to the change of the corresponding load, thereby changing the conduction time of the transistor or MOSFET and thus changing the output of the switching power supply.

[0003] Currently, in low-cost circuit control, when analog output is required, a preset voltage signal is typically generated by filtering the PWM square wave signal generated by a microcontroller (MCU) through a low-pass filter. This voltage is usually the total voltage multiplied by the PWM duty cycle, and the generated voltage signal is used for subsequent circuit control. This solution eliminates the need for a dedicated digital-to-analog converter chip, effectively reducing system cost and complexity, and is commonly used in electric bicycles, electric motorcycles, and low-speed four-wheeled mobility scooters. However, when the MCU fails due to hardware malfunctions, the PWM square wave signal that should be output may exhibit a continuous high level. In this case, the output throttle signal will be a continuous full-throttle output (maximum output state), which can lead to serious consequences such as runaway, posing a serious safety threat to the driver, passengers, and the surrounding environment.

[0004] Although there are existing PWM protection circuits based on edge detection in the prior art (for example, the patent application document with application number CN220401422U), the output of this solution is still a digital PWM signal, which cannot meet the requirements of analog control systems for safe degraded voltage output. Summary of the Invention

[0005] To solve the above-mentioned technical problems, this invention provides a PWM filter output analog signal protection circuit and its protection method. The technical solution adopted by this invention is as follows: A PWM filter output analog signal protection circuit includes: A PWM signal isolation module is used to isolate and transmit the PWM signal output by the MCU. A low-pass filter module, wherein the input terminal of the low-pass filter module is connected to the output terminal of the PWM signal isolation module, and is used to output a preset voltage signal; A PWM signal protection module, wherein the input terminal of the PWM signal protection module is connected to the output terminal of the PWM signal isolation module, and is used to output a protection trigger signal when an abnormal PWM signal is detected; A signal selection module, wherein the input terminal of the signal selection module is connected to the output terminal of the low-pass filter module and the PWM signal protection module, and is used to select and output the signals input to the low-pass filter module and the PWM signal protection module; The output module has its input terminal connected to the output terminal of the signal selection module.

[0006] Furthermore, the PWM signal protection module includes a comparator U2, a PWM signal normal output unit, and a PWM signal abnormal output unit. Both the PWM signal normal output unit and the PWM signal abnormal output unit are connected to the input terminal of the comparator U2, and the output terminal of the comparator U2 is connected to the signal selection module. The PWM signal normal output unit controls the output voltage of the comparator U2 to be high, and the PWM signal abnormal output unit controls the output voltage of the comparator U2 to be low.

[0007] Furthermore, the signal selection module includes a switching unit and a comparison unit. The input terminal of the comparison unit is connected to the output terminal of the switching unit, and the input terminal of the switching unit is connected to the output terminal of the PWM signal protection module. The switching unit has two states: on and off, which are used to control the signal output of the PWM signal protection module.

[0008] Furthermore, the low-pass filter module employs a second-order active low-pass filter circuit for outputting the filtered signal.

[0009] Furthermore, the PWM signal isolation module includes a dual-channel digital isolator, which is used for electrically isolated transmission.

[0010] When the PWM signal is output normally, comparator U2 will output a high level, and the output voltage of the low-pass filter module will be lower than the output voltage of comparator U2. Diode D3 will be in the off state, and the input voltage of comparator U3 will be the output voltage of the low-pass filter module, resulting in a normal output voltage. When the PWM signal is output abnormally, comparator U2 will output a low level, and the output voltage of the low-pass filter module will be higher than the output voltage of comparator U2. Diode D3 will be in the on state, and the input voltage of comparator U3 will be the voltage drop across diode D3, resulting in a low output voltage.

[0011] The abnormal output of the PWM signal also includes the fact that the output voltage of the low-pass filter module and the output voltage of comparator U2 are both low voltage, which is 0V, and the output voltage of comparator U3 is 0V.

[0012] In the signal protection module, when the PWM signal is output normally (with periodic alternation between high and low levels), capacitor C2 is intermittently charged and discharged, resistor R3 remains at a high level for a certain period of time, the voltage at the positive terminal of comparator U2 increases, the voltage at the positive terminal of comparator U2 is higher than the voltage at the negative terminal of comparator U2, and the output voltage of comparator U2 is high. When the PWM signal is continuously at a high level, after capacitor C1 reaches a fully charged state, the equivalent current does not flow through capacitor C2, capacitor C2 discharges through resistor R3, the voltage at the positive terminal of comparator U2 decreases, the voltage at the positive terminal of comparator U2 is lower than the voltage at the negative terminal of comparator U2, and the output voltage of comparator U2 is low. When the PWM signal changes from a high level to a low level or remains at a low level, capacitor C1 discharges through resistor R1, resistor R2 and diode D1, capacitor C2 also continuously discharges, the voltage at the positive terminal of comparator U2 decreases, the voltage at the positive terminal of comparator U2 is lower than the voltage at the negative terminal of comparator U2, and the output voltage of comparator U2 is low.

[0013] A protection method for the analog signal output of a PWM filter, applied to a PWM filter output analog signal protection circuit, includes the following steps: S1. The MCU sends the PWM signal to the PWM signal isolation module. The PWM signal isolation module receives the PWM signal and performs isolation processing before sending it to the low-pass filter module and the PWM signal protection module respectively. S2. Based on the low-pass filter module described in S1, the output voltage signal is sent to the signal selection module, and the PWM signal protection module outputs a protection signal to the signal selection module. S3. Determine whether the PWM signal is output normally. If the PWM signal is output normally, the PWM signal protection module outputs a protection signal that is not triggered, and the signal selection module selects the voltage signal output of the low-pass filter module to output a normal voltage. S4. If the PWM signal is not output normally, the PWM signal protection module triggers a protection signal, and the signal selection module outputs a low voltage based on the protection signal.

[0014] Furthermore, the specific steps for determining whether the PWM signal is output normally are as follows: When the PWM signal is output normally, and the PWM signal rises from low level to high level, the PWM signal protection module outputs a high voltage, and the low-pass filter module outputs a voltage lower than the PWM signal protection module output voltage. When the PWM signal is output abnormally and remains at a high level, the PWM signal protection module outputs a low voltage, and the low-pass filter module outputs a voltage higher than the PWM signal protection module output voltage.

[0015] Furthermore, if both the PWM signal protection module and the low-pass filter module output a low voltage, it is also determined that the PWM signal is an abnormal output, and the PWM signal drops from a high level to a low level or remains at a low level.

[0016] Furthermore, when the PWM signal is output normally, the PWM duty cycle is 10%–90%.

[0017] Furthermore, the PWM signal protection module sends a signal back to the MCU simultaneously with whether the protection signal is triggered, for early warning and diagnosis.

[0018] The beneficial effects of this invention are as follows: By setting up a PWM signal protection module and a signal selection module, during normal operation, when the PWM signal duty cycle is within the normal range of 10%-90%, the PWM signal protection module does not trigger the protection signal, and the signal selection module outputs the voltage signal output by the low-pass filter module, allowing the output module to output a normal voltage. When the MCU fails (malfunctions), the PWM signal duty cycle is less than 10% or greater than 90%, exceeding the normal range (PWM continuously high or low level). The PWM signal protection module triggers the protection signal, and the signal selection module outputs a low voltage, allowing the output module to output a safe voltage value. This achieves the protection effect by limiting the output voltage below the threshold voltage when the MCU fails and the PWM outputs abnormally. It also prevents the throttle signal from being continuously output at full throttle when the PWM signal is continuously high, thus preventing the actuator from unexpectedly operating at full power and significantly improving safety performance. This solution can automatically trigger protection at the hardware level without the intervention of the MCU (upper-level controller), forming a safety barrier independent of the software system and fundamentally solving the risk of loss of control that may occur due to MCU program crashes or other failures. Attached Figure Description

[0019] Figure 1 This is a flowchart of a PWM filter output analog signal protection circuit according to the present invention.

[0020] Figure 2 This is a circuit diagram of a PWM filter output analog signal protection circuit according to the present invention. Figure 3 This is a flowchart illustrating a method for protecting the analog signal output by a PWM filter according to the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will now be described in further detail with reference to the accompanying drawings and the following embodiments, so that the public can better understand the implementation method of this invention. The specific implementation scheme of this invention is as follows: Example

[0022] A PWM filtering output analog signal protection circuit includes a PWM signal isolation module for isolating and transmitting the PWM signal output by an MCU; the output terminal of the PWM signal isolation module is connected to a low-pass filter module and a PWM signal protection module respectively; the input terminal of the low-pass filter module is connected to the output terminal of the PWM signal isolation module for outputting a preset voltage signal; the PWM signal protection module is used to output a protection trigger signal when an abnormality in the PWM signal is detected; the output terminals of both the low-pass filter module and the PWM signal protection module are connected to a signal selection module, which is used to select the signals input to the low-pass filter module and the PWM signal protection module for output; the output terminal of the signal selection module is connected to an output module.

[0023] It should be noted that the PWM signal protection module includes a comparator U2, a PWM signal normal output unit, and a PWM signal abnormal output unit. Both the PWM signal normal output unit and the PWM signal abnormal output unit are connected to the input terminal of the comparator U2, and the output terminal of the comparator U2 is connected to the signal selection module. The PWM signal normal output unit controls the output voltage of the comparator U2 to be high, and the PWM signal abnormal output unit controls the output voltage of the comparator U2 to be low.

[0024] Specifically, the PWM signal protection module includes a comparator U1, resistors R1 and R2, capacitor C1, diodes D1 and D2, resistor R3, capacitor C2, and comparator U2. The input of comparator U1 is connected to the output of the PWM signal isolation module. One end of resistor R1 is connected to the output of comparator U1, and the other end is connected to capacitor C1. The other end of capacitor C1 is connected to the common terminal of the cathode of diode D1 and the anode of diode D2. The anode of diode D1 is connected to isolation ground, and the cathode of diode D2 is connected to resistor R3. The non-inverting input of comparator U2 is connected to capacitor C2, and the output of comparator U2 is connected to the signal selection module. The other end of capacitor C2 is connected to isolation ground. One end of resistor R2 is connected to the inverting input of comparator U1, and the other end is connected to isolation ground.

[0025] It should be noted that the signal selection module includes a switching unit and a comparison unit. The input terminal of the comparison unit is connected to the output terminal of the switching unit, and the input terminal of the switching unit is connected to the output terminal of the PWM signal protection module. The switching unit has two states: on and off, which are used to control the signal output of the PWM signal protection module.

[0026] Specifically, the signal selection module includes diode D3, comparator U3, and resistor R4; the switching unit is implemented through diode D3, and the comparison unit is implemented through comparator U3. The cathode of diode D3 is connected to the output terminal of comparator U2, and the anode of diode D3 is connected to the non-inverting input terminal of comparator U3. One end of resistor R4 is connected to the output terminal of comparator U3, and the other end of resistor R4 is connected to the inverting input terminal of comparator U3.

[0027] When the PWM signal is output normally, comparator U2 will output a high level, and the output voltage of the low-pass filter module will be lower than the output voltage of comparator U2. Diode D3 will be in the off state, and the input voltage of comparator U3 will be the output voltage of the low-pass filter module, resulting in a normal output voltage. When the PWM signal is output abnormally, comparator U2 will output a low level, and the output voltage of the low-pass filter module will be higher than the output voltage of comparator U2. Diode D3 will be in the on state, and the input voltage of comparator U3 will be the voltage drop across diode D3, resulting in a low output voltage.

[0028] It should be noted that when the PWM signal is not output normally and the comparator U2 outputs a low level, it also includes the state in which both the low-pass filter module and the comparator U2 output a low voltage. In this state, the low voltage is 0V, and the output voltage is also 0V.

[0029] The PWM signal protection module monitors the duty cycle and voltage status of the PWM signal in real time through comparators U1 and U2. When the PWM signal is output abnormally, a protection signal is triggered, and comparator U2 outputs a low level to ensure safe operation.

[0030] Furthermore, the PWM signal in the PWM signal protection module includes three states: Specifically, as the PWM signal rises from a low level to a high level, capacitor C2 intermittently charges and discharges, resistor R3 remains at a high level for a certain period of time, the voltage at the positive terminal of comparator U2 increases, and the voltage at the positive terminal of comparator U2 is higher than the voltage at the negative terminal of comparator U2, so the output voltage of comparator U2 is high. In this state, diode D3 of the signal selection module is in the off state, the input voltage of comparator U3 is the output voltage of the low-pass filter module, and the output voltage is normal.

[0031] When the PWM signal remains high, after capacitor C1 reaches full charge, no equivalent current flows through it, and therefore no current charges capacitor C2. Capacitor C2 then discharges through resistor R3, causing the voltage at the positive terminal of comparator U2 to decrease. Since the voltage at the positive terminal of comparator U2 is lower than the voltage at the negative terminal, the output voltage of comparator U2 is low. In this state, diode D3 of the signal selection module is in the on state, and the input voltage of comparator U3 is the voltage drop across diode D3 when it is on. This on-state voltage drop is low, typically 0.6V.

[0032] When the PWM signal remains low, capacitor C1 discharges through resistors R1 and R2 and diode D1, and capacitor C2 also continues to discharge. The voltage at the positive terminal of comparator U2 decreases, and the voltage at the positive terminal of comparator U2 is lower than the voltage at the negative terminal of comparator U2. The output voltage of comparator U2 is low. In this state, both the low-pass filter module and comparator U2 output low voltage, and the input voltage of comparator U3 is low voltage (0V).

[0033] It should be noted that when the PWM signal is output abnormally, the output voltage is 0V or the voltage of the diode dropout.

[0034] In this embodiment, the PWM signal isolation module includes a dual-channel digital isolator, resistors R8 and R9, decoupling capacitors C6 and C7, and resistor R10. The dual-channel digital isolator is used for electrical isolation transmission. The dual-channel digital isolator includes eight pins: VDDA, VDDB, VI1, VO1, VO2, VI2, GNDA, and GNDB. The VDDA pin is connected to the main power supply Vcc, the VDDB pin is connected to the isolation power supply ISO, the VI1 pin is connected to resistor R8, and the other end of resistor R8 is connected to the PWM signal input terminal. The VO1 pin is the output, the VI2 pin is connected to resistor R9, and the other end of resistor R9 is connected to the feedback signal ACCE. The VO2 pin is the output, the GNDA pin is connected to the main ground GND, the GNDB pin is connected to resistor R10, and the other end of resistor R10 is connected to the VO1 output pin. One end of the decoupling capacitor C7 is connected to the isolation power supply ISO, and the other end of the decoupling capacitor C7 is connected to the GNDB pin. One end of the decoupling capacitor C6 is connected to the main power supply Vcc, and the other end of the decoupling capacitor C6 is connected to the main ground GND.

[0035] It should be noted that the low-pass filter module includes amplifier U4, resistors R5, R6, and R7, capacitors C3 and C4. One end of resistor R5 is connected to the output of the PWM signal isolation module, and the other end of resistor R5 is connected to the non-inverting input of amplifier U4 through resistor R6. Capacitor C3 is connected between the common node of resistors R5 and R6 and ground. Capacitor C4 is connected between the common node of resistor R6 and the non-inverting input of amplifier U4 and the output of amplifier U4. Resistor R7 is connected between the inverting input and output of amplifier U4. The low-pass filter module is a second-order active low-pass filter circuit used to output a filtered signal. The output of the low-pass filter module is connected to the common node of the anode of diode D3 and the non-inverting input of comparator U3.

[0036] It should be noted that the output module includes a resistor R11 and a capacitor C5. One end of the resistor R11 is connected to the output terminal of the signal selection module, and the other end is connected to the isolation ground. One end of the capacitor C5 is connected to the output terminal of the signal selection module, and the other end is connected to the isolation ground. The resistor R11 and the capacitor C5 are connected in parallel.

[0037] When this circuit is applied to throttle control in electric bicycles, electric motorcycles, and low-speed four-wheeled mobility scooters, a minimum voltage threshold is typically set for throttle signal monitoring, usually 0.8V. When the output voltage is lower than the minimum threshold voltage, the throttle signal is 0. When the PWM signal is output abnormally, the PWM signal protection module outputs a protection signal, comparator U2 outputs a low level, and the signal selection module outputs a voltage lower than the voltage drop across diode D3, resulting in a final throttle output of 0. Example

[0038] A method for protecting the analog signal output of a PWM filter, the method being applied to the protection circuit for the analog signal output of the PWM filter, includes the following steps: S1. The MCU sends the PWM signal to the PWM signal isolation module. The PWM signal isolation module receives the PWM signal, performs isolation processing, and then sends it to the low-pass filter module and the PWM signal protection module respectively.

[0039] S2. Based on the low-pass filter module outputting voltage signal to the signal selection module, the PWM signal protection module outputs a protection signal to the signal selection module.

[0040] S3. Determine whether the PWM signal is output normally. If the PWM signal is output normally, the PWM signal protection module outputs a non-triggered protection signal, and the signal selection module selects the voltage signal output of the low-pass filter module to output a normal voltage.

[0041] Specifically, when the PWM signal is output normally, as the PWM signal rises from a low level to a high level, the PWM signal protection module outputs a high voltage, while the low-pass filter module outputs a voltage lower than that of the PWM signal protection module. In this state, the PWM signal protection module does not intervene, and the output module outputs a normal voltage.

[0042] S4. If the PWM signal is not output normally, the PWM signal protection module triggers a protection signal, and the signal selection module outputs a low voltage based on the protection signal.

[0043] Specifically, when the PWM signal is output abnormally, there are two possible scenarios: First, the PWM signal remains at a high level, triggering the PWM signal protection module to output a low voltage. In this case, the output voltage of the low-pass filter module is higher than that of the PWM signal protection module. Under these conditions, the diode D3 within the signal selection module conducts, forcing the signal selection module to output a low voltage (the voltage drop across diode D3). Second, the PWM signal remains at a low level, and both the PWM signal protection module and the low-pass filter module output low voltage. In this case, the signal selection module also outputs a low voltage.

[0044] It should be noted that when the PWM signal is output normally, the PWM duty cycle is 10%-90%; the output analog signal V = duty cycle * Vcc, where Vcc is generally 5V or 12V.

[0045] It should be noted that the PWM signal protection module may trigger a protection signal and simultaneously send a signal back to the MCU for early warning and diagnosis.

[0046] By configuring the PWM signal protection module and signal selection module, during normal operation, when the PWM signal duty cycle is within the normal range of 10%–90%, the PWM signal protection module does not trigger the protection signal, and the signal selection module outputs the voltage signal output by the low-pass filter module, ensuring the output module outputs a normal voltage. When the MCU fails (malfunctions), the PWM signal duty cycle is less than 10% or greater than 90%, exceeding the normal range (PWM continuously high or low level). The PWM signal protection module triggers the protection signal, and the signal selection module outputs a low voltage, ensuring the output module outputs a safe voltage value. This achieves the protection effect by limiting the output voltage below a threshold voltage when the MCU fails or the PWM outputs abnormally. It also prevents the throttle signal from being continuously output at full throttle when the PWM signal is continuously high, thus preventing the actuator from unexpectedly operating at full power and significantly improving safety performance.

[0047] This solution can automatically trigger protection at the hardware level without the intervention of the MCU (upper-level controller); it forms a security barrier independent of the software system, fundamentally solving the risk of loss of control that may occur when the MCU program runs away or crashes.

[0048] In the description of this invention, it should be understood that although the invention has been described with respect to a limited number of embodiments, those skilled in the art should understand from the foregoing description that other embodiments may be conceived within the scope of the invention described herein.

Claims

1. A PWM filter output analog signal protection circuit, characterized in that, include: A PWM signal isolation module is used to isolate and transmit the PWM signal output by the MCU. A low-pass filter module, wherein the input terminal of the low-pass filter module is connected to the output terminal of the PWM signal isolation module, and is used to output a preset voltage signal; A PWM signal protection module, wherein the input terminal of the PWM signal protection module is connected to the output terminal of the PWM signal isolation module, and is used to output a protection trigger signal when an abnormal PWM signal is detected; A signal selection module, wherein the input terminal of the signal selection module is connected to the output terminal of the low-pass filter module and the PWM signal protection module, and is used to select and output the signals input to the low-pass filter module and the PWM signal protection module; The output module has its input terminal connected to the output terminal of the signal selection module.

2. The PWM filter output analog signal protection circuit according to claim 1, characterized in that: The PWM signal protection module includes a comparator U2, a normal PWM signal output unit, and an abnormal PWM signal output unit. Both the normal PWM signal output unit and the abnormal PWM signal output unit are connected to the input terminal of the comparator U2, and the output terminal of the comparator U2 is connected to the signal selection module. The normal PWM signal output unit controls the output voltage of the comparator U2 to be high, and the abnormal PWM signal output unit controls the output voltage of the comparator U2 to be low.

3. The PWM filter output analog signal protection circuit according to claim 1, characterized in that: The signal selection module includes a switching unit and a comparison unit. The input terminal of the comparison unit is connected to the output terminal of the switching unit, and the input terminal of the switching unit is connected to the output terminal of the PWM signal protection module. The switching unit has two states: on and off, which are used to control the signal output of the PWM signal protection module.

4. The PWM filter output analog signal protection circuit according to claim 1, characterized in that: The low-pass filter module uses a second-order active low-pass filter circuit to output the filtered signal.

5. The PWM filter output analog signal protection circuit according to claim 1, characterized in that: The PWM signal isolation module includes a dual-channel digital isolator, which is used for electrically isolated transmission.

6. A method for protecting the analog signal output by a PWM filter, characterized in that, The method is applied to a PWM filter output analog signal protection circuit, and the specific steps include: The MCU sends the PWM signal to the PWM signal isolation module. The PWM signal isolation module receives the PWM signal, performs isolation processing, and then sends it to the low-pass filter module and the PWM signal protection module respectively. Based on the output voltage signal of the low-pass filter module, the signal selection module outputs a protection signal to the signal selection module; Determine whether the PWM signal is output normally. If the PWM signal is output normally, the PWM signal protection module outputs a non-triggered protection signal, and the signal selection module selects the voltage signal output of the low-pass filter module to output a normal voltage. If the PWM signal is not output normally, the PWM signal protection module triggers a protection signal, and the signal selection module outputs a low voltage based on the protection signal.

7. The method for protecting the analog signal output by a PWM filter according to claim 1, characterized in that: The specific steps for determining whether the PWM signal is being output normally are as follows: When the PWM signal is output normally, the PWM signal protection module outputs a high voltage, and the low-pass filter module outputs a voltage lower than the PWM signal protection module output voltage. When the PWM signal is output abnormally and remains at a high level, the PWM signal protection module outputs a low voltage, and the low-pass filter module outputs a voltage higher than the PWM signal protection module output voltage.

8. The protection method for the analog signal output by PWM filtering according to claim 7, characterized in that: Both the PWM signal protection module and the low-pass filter module output low voltage, which also indicates that the PWM signal is an abnormal output. The PWM signal drops from a high level to a low level or remains at a low level.

9. The method for protecting the analog signal output by a PWM filter according to claim 7, characterized in that: When the PWM signal is output normally, the PWM duty cycle is 10%–90%.

10. The method for protecting the analog signal output by a PWM filter according to claim 6, characterized in that: The PWM signal protection module sends a signal back to the MCU when the protection signal is triggered, for early warning and diagnosis.

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