A watchdog circuit with wide voltage adjustable reset time and electronic equipment

Abstract

The utility model discloses a kind of watchdog circuit and electronic equipment of adjustable reset time of wide voltage, belong to microcontroller monitoring technical field.The watchdog circuit includes timer chip, voltage adaptation module, timing module and dog feeding signal processing module.Voltage adaptation module is converted into the stable working voltage of the timer chip by voltage stabilizing tube and linear voltage stabilizing circuit, so that circuit can adapt the different system of 2V to 18V.Timing module is mainly composed of certain timing capacitor, and reset timeout can be linearly regulated by replacing the capacitance value of the capacitor.Dog feeding signal processing module receives the dog feeding pulse of MCU and discharges timing module to reset timing.The utility model circuit structure is simple, low in cost, realizes the beneficial effect that reset time is flexibly adjustable and wide voltage range adaptation, especially suitable for the scene that different voltage grade MCU needs to be monitored or program burned for a long time.

Description

Technical Field

[0001] This utility model relates to the field of microcontroller monitoring technology, specifically to a watchdog circuit and electronic device with a wide voltage adjustable reset time. Background Technology

[0002] In embedded systems, watchdog circuits are used to monitor the operating status of microcontrollers (MCUs) to prevent programs from crashing or entering infinite loops. When the microcontroller is working normally, it periodically sends a "feed" signal to the watchdog circuit; if the signal is not received within a preset time, the watchdog circuit outputs a reset signal to restart the system.

[0003] In existing technologies, commonly used watchdog chips (such as the MAX706 series) typically have the following shortcomings: First, their operating voltage is fixed (e.g., 3.3V or 5V), making it difficult to adapt to systems or monitored units with different voltage levels; second, their reset timeout time is usually fixed at the factory (typically 200ms), which cannot meet the needs of certain specific scenarios (such as time-consuming operations like program burning and system self-testing). Although there are some solutions that achieve adjustable time through complex logic circuits, these circuits are complex and costly, and they also do not solve the problem of wide voltage compatibility.

[0004] Therefore, how to provide a watchdog circuit that can adapt to a wide voltage input, flexibly adjust the reset time, and has a simple structure and low cost has become a technical problem that urgently needs to be solved in this field. Utility Model Content

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a watchdog circuit and electronic device that is simple in structure, low in cost, can operate in a wide voltage range, and has a flexible adjustable reset time.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This utility model provides a watchdog circuit with a wide voltage adjustable reset time, including: a timer chip, a voltage adaptation module, a timing module, and a watchdog signal processing module; The input terminal of the voltage adapter module is used to receive a wide range of DC input voltages, and its output terminal is connected to the power supply terminal of the timer chip to provide a stable operating voltage for the timer chip. The timing module is connected to the threshold and trigger terminals of the timer chip and is used to set the reset timeout time of the watchdog circuit. The input terminal of the watchdog feeding signal processing module is used to connect to the watchdog feeding signal output terminal of the MCU, and its output terminal is connected to the timing module to discharge the timing module when a valid watchdog feeding pulse is received, so as to reset the reset timeout time. The output of the timer chip is used to output a reset signal to the monitored MCU.

[0007] In one embodiment, the voltage adapter module includes a Zener diode and a linear voltage regulator circuit; The cathode of the Zener diode is connected to the wide-range DC input voltage through a first current-limiting resistor, and its anode is grounded; The linear voltage regulator circuit uses the cathode of the Zener diode as a reference to generate the operating voltage of the timer chip.

[0008] In one embodiment, the linear regulator circuit includes a first NPN transistor; The base of the first NPN transistor is connected to the cathode of the Zener diode, its emitter outputs the operating voltage through the first diode, and its collector is connected to the wide-range DC input voltage.

[0009] In one embodiment, the timing module includes a timing resistor and a timing capacitor; The timing resistor is connected between the output terminal of the voltage adapter module and the discharge terminal of the timer chip. One end of the timing capacitor is connected to the common node of the threshold and trigger terminals of the timer chip, and the other end is grounded.

[0010] In one embodiment, the watchdog signal processing module includes a second NPN transistor, an AC coupling capacitor, a pull-down resistor, and a discharge resistor; the base of the second NPN transistor is connected to the watchdog signal output terminal of the MCU through the AC coupling capacitor and grounded through the pull-down resistor; its collector is connected to the common node of the timing capacitor and the timer chip through the discharge resistor, and its emitter is grounded.

[0011] In one embodiment, the voltage regulation value of the Zener diode can be configured to adapt the operating voltage of the timer chip to different values ​​within the range of 2V to 18V, thereby changing the level amplitude of the output reset signal.

[0012] In one embodiment, the value of the timing capacitor can be configured to linearly adjust the reset timeout time of the watchdog circuit.

[0013] In one embodiment, the timer chip is a CMOS 555 timer.

[0014] This utility model also provides an electronic device, which includes an MCU and the above-mentioned wide voltage adjustable reset time watchdog circuit. The input terminal of the watchdog circuit's feed signal processing module is connected to the watchdog feed signal output terminal of the MCU, and the output terminal of the watchdog circuit is connected to the reset terminal of the MCU.

[0015] Beneficial effects Compared with the prior art, the present invention has the following beneficial effects: (1) Strong wide voltage adaptability: Through the simple design of Zener diode and linear voltage regulator circuit, the entire watchdog circuit can directly adapt to input voltage from 2V to 18V, and realize the monitoring of MCU or peripheral modules of different voltage levels by outputting a reset signal of corresponding amplitude, with a very wide range of applications.

[0016] (2) Flexible and intuitive reset time adjustment: The reset timeout is determined by the capacitance of an external timing capacitor, and the adjustment method is extremely simple, linear and low cost. Users can set it freely according to actual application needs (such as programming time) without modifying other parts of the circuit or relying on software programming.

[0017] (3) Simple circuit structure and low cost: The circuit uses a general-purpose 555 timer chip and a small number of discrete components. The overall circuit structure is simple and clear, and the production cost is much lower than that of a dedicated watchdog chip and also lower than that of a complex digital logic implementation scheme.

[0018] (4) Low power consumption and good state compatibility: The CMOS low power timer is adopted, and the circuit design ensures that when the MCU is in sleep mode, as long as the watchdog signal is valid, the watchdog can work normally without causing false reset, thus realizing reliable monitoring of the MCU's full working state. Attached Figure Description

[0019] Figure 1 This is a block diagram of the watchdog circuit with wide voltage adjustable reset time according to an embodiment of the present invention; Figure 2 This is a schematic diagram of a watchdog circuit with adjustable reset time and wide voltage range, according to an embodiment of this utility model. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this utility model clearer, the embodiments of this utility model will be described in detail below with reference to the accompanying drawings.

[0021] It should be noted that, unless otherwise defined, the technical or scientific terms used in this utility model should have the ordinary meaning understood by one of ordinary skill in the art to which this utility model pertains. The terms "first," "second," and similar words used in this utility model do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Words such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects.

[0022] Please see Figure 1 and Figure 2 This utility model provides a watchdog circuit with a wide voltage adjustable reset time, the core of which is a timer chip U1. In a preferred embodiment, the timer chip U1 is a CMOS 555 timer, such as the ICM7555, which has a wide voltage operating range and extremely low static power consumption. The watchdog circuit also includes a voltage adaptation module, a timing module, and a watchdog signal processing module.

[0023] The voltage adaptation module includes a Zener diode ZD1 and a linear voltage regulator circuit. The linear voltage regulator circuit generates the operating voltage VDD of the timer chip U1 with the cathode of the Zener diode ZD1 as a reference. Specifically, the linear voltage regulator circuit includes a first current-limiting resistor R1, a first NPN transistor N1, a first diode D2, a second diode D1, a first filter capacitor C1, and a second filter capacitor C2. The cathode of the Zener diode ZD1 is connected to a wide-range DC input voltage through the first current-limiting resistor R1, and the anode of the Zener diode ZD1 is grounded. The base of the first NPN transistor N1 is connected to the cathode of the Zener diode ZD1, its emitter outputs the operating voltage VDD through the first diode D2, and its collector is connected to a wide-range DC input voltage.

[0024] ZD1 mainly serves as a voltage regulator; for example, its model is MM3Z5V6. The first current-limiting resistor R1 limits the current to prevent ZD1 from consuming a large current. For example, ZD1 keeps the base voltage of the first NPN transistor N1 at 5.6V, and the emitter output of the first NPN transistor N1 is 5.6V. After being stepped down by the first diode D2, the voltage is regulated to 5.3V to ensure that the power supply voltage of the timer chip is within the required range of 5V±10%.

[0025] The input terminal of the voltage adapter module receives a wide range of DC input voltages. The wide-range DC input voltage VIN (e.g., 2V to 18V) passes sequentially through the second diode D1 (for reverse connection protection or isolation) and the first current-limiting resistor R1, stabilizing the cathode of the Zener diode ZD1 at 5.6V. This voltage biases the base of the first NPN transistor N1, causing N1 to conduct. The emitter voltage of the first NPN transistor N1 is approximately 5.6V. This voltage then passes through the first diode D2 (generating a voltage drop of approximately 0.3V), resulting in a stable voltage of approximately 5.3V at the output terminal of the voltage adapter module. The output terminal of the voltage adapter module is connected to the power supply terminal VDD of the timer chip U1, providing a stable operating voltage for the timer chip U1. The first filter capacitor C1 is connected between VDD and ground, and the second filter capacitor C2 is also connected between VDD and ground. Both capacitors work together to decouple and filter the power supply, ensuring the stability of the operating voltage of U1.

[0026] By selecting different Zener diodes ZD1 with varying voltage regulation values ​​(e.g., MM3Z5V6 corresponds to approximately 5.6V, and MM3Z12 corresponds to approximately 12V), the operating voltage of the timer chip can be adapted to different values ​​within the range of 2V to 18V. This changes the amplitude of the output reset signal, allowing the entire circuit and the output reset signal to adapt to different system voltage requirements, achieving wide voltage adaptation from 2V to 18V. For example, replacing the Zener diode ZD1 with an MM3Z12 will generate a 12V supply voltage. The watchdog circuit will then operate at 12V, providing a 12V reset output signal. During reset, it outputs a low level (0V), and during normal watchdog locking, it outputs a high level (12V).

[0027] The timing module includes a timing resistor and a timing capacitor C5, used to set the reset timeout time of the watchdog circuit. The timing resistor is composed of a first timing resistor R2 and a second timing resistor R4 connected in series, and is connected between the output terminal of the voltage adapter module and the discharge terminal (DISCH, pin 7) of the timer chip U1. One end of the timing capacitor C5 is connected to the common node of the threshold terminal (THRES, pin 6) and the trigger terminal (TRIG, pin 2) of the timer chip U1, and the other end is grounded. The reset timeout time T is mainly determined by the product of (R2+R4) and C5, i.e., T≈(R2+R4)*C5. By selecting timing capacitors C5 with different values, the reset timeout time can be directly and linearly adjusted.

[0028] The watchdog signal processing module receives the watchdog signal (WDI) from the MCU and resets the timing when a valid signal arrives. It includes an AC coupling capacitor C3, a second NPN transistor N2, a first parallel resistor R5, a second parallel resistor R7, a pull-down resistor R8, and a discharge resistor R6. The input of the watchdog signal processing module is connected to the watchdog signal output of the MCU, and its output is connected to the timing module to discharge the timing module upon receiving a valid watchdog pulse, thereby resetting the reset timeout. The base of the second NPN transistor N2 is connected to the watchdog signal output of the MCU via the AC coupling capacitor C3, and its collector is connected to the common node of the timing capacitor C5 and the timer chip U1 via the discharge resistor R6. Its emitter is grounded. The output (OUT, pin 3) of the timer chip U1 outputs a reset signal to the monitored MCU. The first parallel resistor R5 and the second parallel resistor R7 are connected at one end to the AC coupling capacitor C3 and at the other end to the base of the second NPN transistor N2. This parallel design reduces the equivalent resistance of this branch, which helps to improve the response speed to fast pulses. The pull-down resistor R8 is connected between the base of N2 and ground. Its function is to clamp the base potential of N2 at a low level when there is no WDI pulse or the pulse is low, ensuring that N2 is reliably turned off and avoiding false triggering caused by noise interference, thereby greatly enhancing the anti-interference capability and stability of the watchdog circuit.

[0029] The specific process of resetting the reset timeout is as follows: Timing capacitor C5 is charged through the first timing resistor R2 and the second timing resistor R4. When the charging of timing capacitor C5 reaches a value greater than ⅓VDD, the OUT output of timer chip U1 outputs a high level. When the charging reaches a value greater than ⅔VDD, the OUT pin will trigger a low level output, resetting the MCU connected to the watchdog circuit output. At this time, the MCU's WDI output pulse signal, after being blocked by AC coupling capacitor C3, is sent to the base of the second NPN transistor N2 through the parallel first resistor R5 and the second parallel resistor R7. During the high level of each WDI pulse, the second NPN transistor N2 is momentarily turned on. The charge accumulated on the timing capacitor C5 is quickly discharged to ground through the turned-on second NPN transistor N2 and the discharge resistor R6, thereby pulling down the voltage of C5 and resetting the timing cycle. This ensures that the voltage of C5 is within the range of greater than ⅓VDD and less than ⅔VDD, so that the OUT pin of U1 will be locked at a high level, ensuring that the MCU is not reset. Even when the voltage is discharged to less than ⅓VDD, the output of U1 is still high. That is, as long as the MCU (whether in normal, standby, or sleep mode) can continuously output a valid WDI pulse, the voltage of the timing capacitor C5 will never be able to charge to the flip threshold of U1 (2 / 3 VDD), and the output (OUT) of U1 will remain high, ensuring that the monitored MCU works normally and is not reset.

[0030] The output terminal (OUT, pin 3) of timer chip U1 is an open-drain output, connected to VDD via pull-up resistor R3, used to output a reset signal to the reset terminal of the monitored MCU. When the watchdog times out (i.e., C5 charges to 2 / 3 VDD), the internal discharge transistor of U1 turns on, and the OUT terminal is pulled low to ground, generating a low-level active reset signal to the peripheral MCU. The amplitude of this reset signal is the voltage value of VDD. For example, when VDD is 5.3V, the reset low level is 0V, and the normal high level is 5.3V; when VDD is adjusted to 12V, the amplitude of the reset signal changes accordingly to 0V and 12V.

[0031] In this embodiment of the invention, the capacitance value of capacitor C5 can be used to adjust the reset timeout time, and is generally selected between 10UF and 100UF. The voltage value of voltage regulator ZD1 can be used to adjust the amplitude of the reset level, and is generally selected between 3.3V and 18V, to ensure the normal operating voltage of timer chip U1, thereby meeting the power-on startup requirements of MCU and the time requirements for programming.

[0032] The following two examples illustrate the above operations: Example 1: When the device requires a watchdog circuit with a 5V reset signal for short-term monitoring, ZD1 is selected as MM3Z5V6, and C5 is 10μF. In this case, the reset timeout T ≈ 2MΩ * 10μF = 20 seconds. The MCU needs to feed the watchdog signal at intervals less than 20 seconds.

[0033] Example 2: When a 12V reset signal is required for long-term programming. Replace ZD1 with MM3Z12 and C5 with 100μF. At this time, the circuit operating voltage is approximately 12V, and the reset timeout time T≈2MΩ*100μF=200 seconds, which is sufficient to meet the needs of long-term programming, and outputs a 12V reset signal.

[0034] This utility model also protects an electronic device comprising the aforementioned watchdog circuit and MCU, wherein the input terminal of the watchdog circuit's feed signal processing module is connected to the watchdog feed signal output terminal of the MCU, and the output terminal of the watchdog circuit is connected to the reset terminal of the MCU. This watchdog circuit can effectively improve the reliability of the device under different voltage environments and operational requirements.

[0035] The above embodiments are only used to illustrate the technical solution of this utility model, and are not intended to limit it. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solution of this utility model without departing from the spirit and scope of this utility model, and all such modifications and substitutions should be covered within the scope of the claims of this utility model.

Claims

1. A watchdog circuit with adjustable reset time and wide voltage range, characterized in that, include: Timer chip (U1), voltage adapter module, timing module, and dog feeding signal processing module; The input terminal of the voltage adapter module is used to receive a wide range of DC input voltage, and its output terminal is connected to the power supply terminal of the timer chip (U1) to provide a stable operating voltage for the timer chip (U1). The timing module is connected to the threshold and trigger terminals of the timer chip (U1) and is used to set the reset timeout time of the watchdog circuit. The input terminal of the watchdog feeding signal processing module is used to connect to the watchdog feeding signal output terminal of the MCU, and its output terminal is connected to the timing module to discharge the timing module when a valid watchdog feeding pulse is received, so as to reset the reset timeout time. The output of the timer chip (U1) is used to output a reset signal to the monitored MCU.

2. The watchdog circuit with wide voltage adjustable reset time according to claim 1, characterized in that, The voltage adaptation module includes a Zener diode (ZD1) and a linear voltage regulator circuit; The cathode of the Zener diode (ZD1) is connected to the wide-range DC input voltage through a first current-limiting resistor (R1), and its anode is grounded; The linear voltage regulator circuit uses the cathode of the Zener diode (ZD1) as a reference to generate the operating voltage of the timer chip (U1).

3. The watchdog circuit with wide voltage adjustable reset time according to claim 2, characterized in that, The linear voltage regulator circuit includes a first NPN transistor (N1). The base of the first NPN transistor (N1) is connected to the cathode of the Zener diode (ZD1), its emitter outputs the operating voltage through the first diode (D2), and its collector is connected to the wide-range DC input voltage.

4. The watchdog circuit with wide voltage adjustable reset time according to claim 1, characterized in that, The timing module includes a timing resistor and a timing capacitor (C5); The timing resistor is connected between the output terminal of the voltage adapter module and the discharge terminal of the timer chip (U1); One end of the timing capacitor (C5) is connected to the common node of the threshold and trigger terminals of the timer chip (U1), and the other end is grounded.

5. The watchdog circuit with wide voltage adjustable reset time according to claim 4, characterized in that, The dog-feeding signal processing module includes a second NPN transistor (N2), an AC coupling capacitor (C3), a pull-down resistor (R8), and a discharge resistor (R6). The base of the second NPN transistor (N2) is connected to the watchdog feed signal output terminal of the MCU through the AC coupling capacitor (C3), and grounded through the pull-down resistor (R8); Its collector is connected to the common node of the timing capacitor (C5) and the timer chip (U1) through the discharge resistor (R6), and its emitter is grounded.

6. The watchdog circuit with wide voltage adjustable reset time according to claim 2 or 3, characterized in that, The voltage regulation value of the Zener diode (ZD1) can be configured to adapt the operating voltage of the timer chip (U1) to different values ​​within the range of 2V to 18V, thereby changing the level amplitude of the output reset signal.

7. The watchdog circuit with wide voltage adjustable reset time according to claim 4, characterized in that, The value of the timing capacitor (C5) is configurable to linearly adjust the reset timeout time of the watchdog circuit.

8. The watchdog circuit with wide voltage adjustable reset time according to claim 1, characterized in that, The timer chip (U1) is a CMOS 555 timer.

9. An electronic device, characterized in that, The watchdog circuit includes an MCU and a wide voltage-adjustable reset time watchdog circuit as described in any one of claims 1 to 8, wherein the input terminal of the watchdog circuit's feed signal processing module is connected to the watchdog feed signal output terminal of the MCU, and the output terminal of the watchdog circuit is connected to the reset terminal of the MCU.

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