Hysteresis Circuit for Power-Down Detection

Abstract

The present invention provides a hysteresis circuit for power-off detection, which relates to the field of circuit technologies and includes: a constant current module and a capacitor connected in parallel; a first or second load and drive module, connected in parallel to the constant current module, and the second load and drive module outputs a power-off fluctuation signal based on the change of the power parameter of the internal load; the first power-off judgment module directly monitors whether the constant current module is powered off, or the second power-off judgment module monitors whether the constant current module is powered off according to the power-off fluctuation signal; when the constant current module is powered off, the first or second power-off judgment module outputs a power-off prompt signal; a first or second controllable compensation load module, which connects an additional load in parallel to the constant current module according to the power-off prompt signal. Compared with the hysteresis generated by common methods such as modifying the threshold point inside the power-off module, the present invention can enhance the hysteresis effect of the system, improve the stability of the system, and improve the detection accuracy in the case of load change after the constant current module is powered off.

Description

Technical Field

[0001] The present invention relates to the field of circuit technologies, and in particular, to a hysteresis circuit for power-off detection. Background Art

[0002] As Figure 1 shown, in a circuit powered by a constant-current module, when the constant-current module loses power, other circuits in the system need to obtain information that the system is about to lose power, so as to record the power-off information of the system or make some adjustments to the load. A capacitor is used to provide electrical energy for other circuits in the system in the short term after the constant-current module loses power. Currently, many constant-current modules do not specifically output a power-off signal, so a module is needed to judge the situation that the system is about to lose power according to information such as node voltage or current. In this process, in order to obtain a reliable power-off judgment result, the power-off judgment module often adopts a hysteresis design, such as using a hysteresis comparator or switching the detection threshold according to the detection output. However, due to the existence of situations such as load changes (changes in the load and the driving module), this conventional method of generating hysteresis in the sampling means still has the problem of inaccurate detection; if a too large hysteresis detection window is designed to avoid unstable detection results, other problems will occur in application.

[0003] For example, when detecting power-off, if the voltage between the positive power supply line and the negative power supply line is less than a certain value, it is determined that the power is off (subsequently, the negative power supply line is regarded as the 0V reference point), and after detecting that the system has lost power, the load needs to be turned off. The load contains a module with a certain energy storage characteristic (such as a motor coil with inductance characteristics). For this situation, after the load is turned off, it will release residual electrical energy to the positive power supply line through a freewheeling diode, resulting in a short-term rise in the voltage of the positive power supply line and even exceeding the voltage of the positive power supply line during normal operation; if a large hysteresis window is selected, it will affect the detection of the power-off judgment module during normal power-on, and only the filtering time can be increased; however, increasing the filtering time will cause a decrease in the system state switching frequency, and in the case where the positive power supply line requires a load to maintain overvoltage, no load during too long a filtering time may bring the risk of device overvoltage damage.

[0004] In addition, when detecting power-off, if the current flowing through the current load (denoted as load A) is less than a certain value, it is determined that the power is off, and when detecting that the system has lost power, it is necessary to switch to another load (denoted as load B), but the current of load B is greater than that of load A under the same voltage. For this situation, after the system detects power-off (the load current is less than a certain threshold) and switches the load, the load current will increase; if a too large hysteresis window is selected, it will affect normal detection; if two specific hysteresis windows are designed according to two fixed loads, the applicable range of the circuit will be restricted; if the filtering time is set too long, the system state switching frequency will be restricted.

[0005] Therefore, a technical solution for a hysteresis circuit for power-off detection is needed. This technical solution can enhance the hysteresis effect of the system, improve the stability of the system, and increase the detection accuracy in the case of load changes after the constant current module loses power. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a hysteresis circuit for power-off detection, including:

[0007] A constant current module for providing a constant current;

[0008] A capacitor, connected in parallel across both ends of the constant current module, for providing electrical energy in the short term after the constant current module loses power;

[0009] A first load and drive module, connected in parallel across both ends of the constant current module, for operating under the drive of the constant current;

[0010] A first power-off judgment module, connected in parallel across both ends of the constant current module, for monitoring whether the constant current module is powered off, and outputting a power-off prompt signal through its output terminal when the constant current module is powered off;

[0011] A first controllable compensation load module, connected in parallel across both ends of the constant current module, and its control terminal is electrically connected to the output terminal of the first power-off judgment module, for paralleling an additional load across both ends of the constant current module according to the power-off prompt signal to enhance the hysteresis effect of the system.

[0012] In a possible implementation, the first load and drive module is provided with a control terminal;

[0013] The control terminal of the first load and drive module is electrically connected to the output terminal of the first power-off judgment module;

[0014] When the first load and drive module receives the power-off prompt signal, it controls the internal load to stop operating.

[0015] In a possible implementation, the first load and drive module includes a load control module and a load module;

[0016] The input terminal of the load control module serves as the control terminal of the first load and drive module, its output terminal is electrically connected to the control terminal of the load module, its working voltage terminal is electrically connected to the positive electrode of the constant current module, and its grounding terminal is electrically connected to the negative electrode of the constant current module;

[0017] The working voltage terminal of the load module is electrically connected to the positive electrode of the constant current module, and its grounding terminal is electrically connected to the negative electrode of the constant current module.

[0018] In a possible implementation, the first load and drive module further includes a first clamping module connected in parallel across both ends of the constant current module.

[0019] In a possible implementation, the first controllable compensation load module includes a first NMOS transistor and a first resistor;

[0020] The first NMOS transistor and the first resistor are connected in series and then connected in parallel across both ends of the constant current module, and its gate is electrically connected to the output terminal of the first power-off determination module;

[0021] The first NMOS transistor uses the first resistor as the additional load and connects it in parallel across both ends of the constant current module according to the power-off prompt signal.

[0022] In a possible implementation, the first controllable compensation load module further includes a second NMOS transistor and a Zener diode;

[0023] The source of the first NMOS transistor is electrically connected to the negative pole of the constant current module, and its drain is electrically connected to the anode of the Zener diode;

[0024] The cathode of the Zener diode is electrically connected to the first end of the first resistor;

[0025] The second end of the first resistor is electrically connected to the source of the second NMOS transistor;

[0026] The gate of the second NMOS transistor is used to access a first reference voltage, and its drain is electrically connected to the positive pole of the constant current module.

[0027] The present invention also provides another hysteresis circuit for power-off detection, including:

[0028] A constant current module for providing a constant current;

[0029] A capacitor connected in parallel across both ends of the constant current module for providing electrical energy in the short term after the constant current module loses power;

[0030] A second load and drive module connected in parallel across both ends of the constant current module, for operating under the drive of the constant current and outputting a power-off fluctuation signal based on the change of the power parameter of the internal load;

[0031] A second power-off determination module, whose input terminal is electrically connected to the output terminal of the second load and drive module, for monitoring whether the constant current module loses power according to the power-off fluctuation signal, and outputting a power-off prompt signal through its output terminal when the constant current module loses power;

[0032] The second controllable compensation load module is connected in parallel to both ends of the constant current module, and its control end is electrically connected to the output end of the second power-off judgment module, and is used to parallel an additional load to both ends of the constant current module according to the power-off prompt signal to enhance the hysteresis effect of the system.

[0033] In a possible implementation manner, the second controllable compensation load module includes a third NMOS transistor and a second resistor;

[0034] The third NMOS transistor is connected in series with the second resistor and then connected in parallel to both ends of the constant current module, and its gate is electrically connected to the output end of the second power-off judgment module;

[0035] The third NMOS transistor uses the second resistor as the additional load and connects it in parallel to both ends of the constant current module according to the power-off prompt signal.

[0036] In a possible implementation manner, the second controllable compensation load module further includes a logic gate unit;

[0037] The source electrode of the third NMOS transistor is electrically connected to the first end of the second resistor, its drain electrode is electrically connected to the negative electrode of the constant current module, and its gate is electrically connected to the output end of the logic gate unit;

[0038] The second end of the second resistor is electrically connected to the negative electrode of the constant current module;

[0039] The first input end of the logic gate unit is used to access a first system signal, and its second input end is electrically connected to the output end of the second power-off judgment module;

[0040] Wherein, the logic gate unit can generate a control signal acting on the gate of the third NMOS transistor based on the power-off prompt signal.

[0041] In a possible implementation manner, the second load and drive module includes a drive and sampling module and n loads;

[0042] The positive electrodes of the n loads are respectively electrically connected to the positive electrode of the constant current module, and their negative electrodes are sequentially electrically connected to the n load interfaces of the drive and sampling module;

[0043] The power-off judgment communication interface of the drive and sampling module serves as the output end of the second load and drive module, and its grounding end is electrically connected to the negative electrode of the constant current module;

[0044] Wherein, n is an integer greater than 1.

[0045] The technical solution provided by the present invention has at least the following beneficial effects:

[0046] By applying the present invention, a hysteresis circuit for power-down detection applicable to a constant-current module can be obtained. After the power-down judgment module (the first power-down judgment module, the second power-down judgment module) gives a power-down prompt signal, an additional load is added across the constant-current module, thereby avoiding setting an overly large hysteresis window in the power-down judgment module and also avoiding an overly long filtering time in the power-down judgment module. It can enhance the hysteresis effect of the system, improve the stability of the system, and increase the detection accuracy in the case where the load changes after the constant-current module powers down. Description of the Drawings

[0047] Figure 1 It is the circuit diagram of power-down detection for a common constant-current module in the background art;

[0048] Figure 2 It is the circuit schematic diagram of the first hysteresis circuit for power-down detection provided by an embodiment of the present invention;

[0049] Figure 3 It is the circuit schematic diagram of the second hysteresis circuit for power-down detection provided by an embodiment of the present invention;

[0050] Figure 4 It is the circuit schematic diagram of the third hysteresis circuit for power-down detection provided by an embodiment of the present invention;

[0051] Figure 5 It is the circuit schematic diagram of a specific embodiment of a load control module and a load module provided by an embodiment of the present invention;

[0052] Figure 6 It is the circuit schematic diagram of the first controllable compensation load module provided by an embodiment of the present invention;

[0053] Figure 7 It is the circuit schematic diagram of the fourth hysteresis circuit for power-down detection provided by an embodiment of the present invention;

[0054] Figure 8 It is the circuit schematic diagram of the second controllable compensation load module provided by an embodiment of the present invention;

[0055] Figure 9 It is the circuit schematic diagram of the fifth hysteresis circuit for power-down detection provided by an embodiment of the present invention;

[0056] Figure 10 It is the circuit schematic diagram of the driving and sampling module provided by an embodiment of the present invention;

[0057] In the attached drawings, 10 is a constant current module; 11 is a capacitor; 12 is a first load and drive module; 13 is a first power-off judgment module; 14 is a first controllable compensation load module; 22 is a second load and drive module; 23 is a second power-off judgment module; 24 is a second controllable compensation load module; 121 is a load control module; 122 is a load module; 123 is a first clamping module; 221 is a first load; 222 is a second load; 223 is a third load; 224 is a second clamping module; 225 is a drive and sampling module. Detailed implementation mode

[0058] To deepen the understanding of the present invention, the present invention will be further described in detail below in conjunction with the attached drawings and embodiments. The embodiments are only used to explain the present invention and do not limit the protection scope of the present invention.

[0059] Please refer to Figures 1 to 6 , a hysteresis circuit for power-off detection provided by the present invention includes:

[0060] A constant current module 10 for providing a constant current;

[0061] A capacitor 11 is connected in parallel across both ends of the constant current module 10 and is used to provide electrical energy in the short term after the constant current module 10 loses power.

[0062] A first load and drive module 12 is connected in parallel across both ends of the constant current module 10 and is used to operate under the drive of the constant current.

[0063] A first power-off judgment module 13 is connected in parallel across both ends of the constant current module 10 and is used to monitor whether the constant current module 10 is powered off. When the constant current module 10 is powered off, a power-off prompt signal is output through its output terminal.

[0064] A first controllable compensation load module 14 is connected in parallel across both ends of the constant current module 10, and its control terminal is electrically connected to the output terminal of the first power-off judgment module 13. It is used to parallel an additional load across both ends of the constant current module 10 according to the power-off prompt signal to enhance the hysteresis effect of the system.

[0065] In this embodiment, the constant current module 10 can adopt a constant current power supply of a conventional model. Its positive electrode is led out through a positive power line, and its negative electrode is led out through a negative power line and grounded. It provides electrical energy for the system in the non-power-off situation.

[0066] The capacitor 11 is located between the positive power line and the negative power line. After the constant current module 10 loses power, it provides electrical energy for other modules in the short term to maintain the normal operation of circuits such as the first power-off judgment module 13, the first controllable compensation load module 14, and part of the first load and drive module 12. The capacitance value C 11 can be 10 μF.

[0067] The first load and drive module 12 may be a module having energy storage characteristics (such as a motor coil having inductance characteristics), including an electrical load and a drive circuit thereof, and is located between a positive power line and a negative power line.

[0068] The first power-off judgment module 13 is located between the positive power line and the negative power line. It can judge that the constant current module 10 is powered off by the change of the positive power line voltage, and give a power-off prompt signal. For example: the first power-off judgment module 13 can output a high-level signal as a power-off prompt signal when the voltage of the positive power line is lower than a certain threshold, indicating that the system is about to power off (that is, the constant current module 10 has been powered off, and after the electric energy stored in the capacitor 11 is used up, the entire system will also be powered off). Specifically, when the voltage of the positive power line is lower than 20V, the first power-off judgment module 13 outputs a 5V high-level signal through its output end. The first power-off judgment module 13 supports a detection hysteresis of 0.5V. When power-off is detected, the voltage of the positive power line needs to reach 20.5V to release the power-off state; at the same time, the first power-off judgment module 13 can have a built-in filter circuit with a shorter filtering time (to simplify the analysis, ignore the filtering time).

[0069] The first controllable compensating load module 14 can change the on-resistance between the positive and negative electrodes of the module according to the signal (power-off prompt signal) input outside the module, so as to connect the additional load in parallel to both ends of the constant current module 10. The module can enhance the hysteresis effect of the system by changing the load between the positive power line and the negative power line according to the power-off judgment result and system requirements. For example: the first controllable compensating load module 14 can add a load between the positive power line and the negative power line after receiving the high-level signal (i.e., the power-off prompt signal) output by the first power-off judgment module 13, until the system no longer needs to add this additional load (for example, the power-off detection stage has ended).

[0070] Compared with the common hysteresis generated by modifying the threshold point inside the power-off judgment module, the implementation of this circuit can enhance the hysteresis effect of the system, improve the stability of the system, and improve the detection accuracy when the load changes after the constant current module 10 loses power.

[0071] In one possible implementation, Figure 3 , the first load and driving module 12 is provided with a control terminal;

[0072] The control end of the first load and driving module 12 is electrically connected to the output end of the first power-off determination module 13;

[0073] When the first load and driving module 12 receives the power-off prompt signal, it controls the internal load to stop operating.

[0074] In this embodiment, the first load and drive module 12 receives the power-off prompt signal output by the first power-off judgment module 13 through the set control terminal, and can control the load inside it to stop operating according to the power-off prompt signal.

[0075] In a possible implementation manner, such as Figure 4 , the first load and drive module 12 includes a load control module 121 and a load module 122;

[0076] The input terminal of the load control module 121 serves as the control terminal of the first load and drive module 12, its output terminal is electrically connected to the control terminal of the load module 122, its working voltage terminal is electrically connected to the positive electrode of the constant current module 10, and its grounding terminal is electrically connected to the negative electrode of the constant current module 10;

[0077] The working voltage terminal of the load module 122 is electrically connected to the positive electrode of the constant current module 10, and its grounding terminal is electrically connected to the negative electrode of the constant current module 10.

[0078] In this embodiment, the load control module 121 controls and drives the normal operation of the load module 122. The load control module 121 can adopt a conventional module for controlling the operation of a motor, and the load module 122 can adopt a conventional motor operation structure. In a specific implementation manner, such as Figure 5 , the load module 122 may include a motor M, a first PMOS transistor Qp1, a second PMOS transistor Qp2, a first NMOS transistor Qn1, a second NMOS transistor Qn2, a first diode D1, a second diode D2, a third diode D3, and a fourth diode D4. The output terminal of the load control module 121 includes 4 sub-terminals such as Gp1, Gp2, Gn1, and Gn2, which are respectively electrically connected to the gates of the first PMOS transistor Qp1, the second PMOS transistor Qp2, the first NMOS transistor Qn1, and the second NMOS transistor Qn2.

[0079] The sources of the first PMOS transistor Qp1 and the second PMOS transistor Qp2 are connected to the positive power supply line, and the sources of the first NMOS transistor Qn1 and the second NMOS transistor Qn2 are connected to the negative power supply line. The drains of the first PMOS transistor Qp1 and the first NMOS transistor Qn1 are connected to the positive terminal of the motor M, and the drains of the second PMOS transistor Qp2 and the second NMOS transistor Qn2 are connected to the negative terminal of the motor M. The positive and negative electrodes of the first diode D1 are respectively connected to the drain and source of the first PMOS transistor Qp1, the positive and negative electrodes of the second diode D2 are respectively connected to the source and drain of the first NMOS transistor Qn1, the positive and negative electrodes of the third diode D3 are respectively connected to the drain and source of the second PMOS transistor Qp2, and the positive and negative electrodes of the fourth diode D4 are respectively connected to the source and drain of the second NMOS transistor Qn2.

[0080] The load control module 121 controls the motor M by controlling the gate voltages of the first PMOS transistor Qp1, the second PMOS transistor Qp2, the first NMOS transistor Qn1, and the second NMOS transistor Qn2. The conduction voltage drops of the first diode D1, the second diode D2, the third diode D3, and the fourth diode D4 are 0.4V when a current of 1.3A flows through them, and the conduction voltage drops are less than 0.4V when a current of 1A flows through them. When the voltage of the positive power supply line is 20V, the current of the motor M is 1A; when the voltage of the positive power supply line is 25V, the current of the motor M is 1.3A; the inductance of the motor coil is 5mH.

[0081] In a possible implementation manner, the first load and drive module 12 further includes a first clamping module 123 connected in parallel to both ends of the constant current module 10.

[0082] In this embodiment, the first clamping module 123 can be implemented by a conventional clamping circuit, and starts to work when the voltage of the positive power supply line is 28V, responsible for protecting the circuit from overvoltage damage (if the motor M always operates during the time when the constant current module 10 is not powered off, and the system has the first controllable compensation load module 14, then this clamping module can be reduced or even removed).

[0083] In a possible implementation manner, as Figure 6 , the first controllable compensation load module 14 includes a first NMOS transistor Q1 and a first resistor R1;

[0084] The first NMOS transistor Q1 and the first resistor R1 are connected in series and then connected in parallel to both ends of the constant current module 10, and its gate is electrically connected to the output end of the first power-off judgment module 13;

[0085] The first NMOS transistor Q1 uses the first resistor R1 as the additional load and connects it in parallel to both ends of the constant current module 10 according to the power-off prompt signal.

[0086] In this embodiment, the first NMOS transistor Q1 can use a conventional NMOS transistor, and the first resistor R1 uses a resistor of a conventional model. When the power-off prompt signal is at a high level (such as 3.3V), the first NMOS transistor Q1 is turned on, and the first resistor R1 is connected in parallel to both ends of the constant current module 10 as an additional load.

[0087] In a possible implementation manner, the first controllable compensation load module 14 further includes a second NMOS transistor Q2 and a Zener diode Z1;

[0088] The source electrode of the first NMOS transistor Q1 is electrically connected to the negative electrode of the constant current module 10, and its drain electrode is electrically connected to the anode of the Zener diode Z1;

[0089] The cathode of the Zener diode Z1 is electrically connected to the first end of the first resistor R1;

[0090] The second end of the first resistor R1 is electrically connected to the source of the second NMOS transistor Q2;

[0091] The gate of the second NMOS transistor Q2 is used to access the first reference voltage Vref, and the drain of the second NMOS transistor Q2 is electrically connected to the positive electrode of the constant current module 10 .

[0092] In this embodiment, the second NMOS tube Q2 can adopt a conventional NMOS tube, and the Zener diode Z1 adopts a conventional model. In the specific implementation, the gate of the second NMOS tube Q2 can be connected to the first reference voltage Vref of 15V, its drain is electrically connected to the positive power line, and its source is connected to one end of the first resistor R1 of 5 ohms. The other end of the first resistor R1 is connected to the cathode of the Zener diode Z1 with a reverse breakdown voltage V_z1 of 5.2V. The source of the first NMOS tube Q1 is grounded. The voltage (Vgs_nm2) between the gate and the source of the second NMOS tube Q2 when a current of 1.56A flows is 2V, the on-resistance of the first NMOS tube Q1 is negligible, and the threshold voltage is 0.7V.

[0093] In a specific embodiment, Figures 4 to 6 , when the constant current module 10 outputs 1.3A current and the motor M rotates, most of the current flows through the motor M. At this time, the first PMOS tube Qp1 and the second NMOS tube Qn2 are turned on, and the main current flows to the negative power line through the channel of the first PMOS tube Qp1, the motor M, and the channel of the second NMOS tube Qn2. Ignoring the power consumption of the circuits other than the motor M, the first controllable compensation load module 14 and the first clamping module 123, the positive power line voltage is approximately 25V at this time.

[0094] When the constant current module 10 loses power, the voltage of the positive power line starts to drop. When the voltage of the positive power line drops to 20V, the first power-off judgment module 13 outputs a 5V high level (power-off prompt signal). At this time, the load control module 121 outputs a signal to close the conductive channel of the first PMOS tube Qp1 and the second NMOS tube Qn2. At this time, the coil current in the motor M cannot change suddenly, and the electric energy in the coil needs to be released, so the current direction is from the negative power line through the second diode D2 through the motor M and then through the third diode D3 to the positive power line.

[0095] In the above situation, if there is no first controllable compensating load module 14, the voltage of the positive power line will be charged to more than 20.5V, the system will think that the power failure is released and restart the motor M, and then the voltage of the positive power line will drop to less than 20V due to the start of the motor M, and then the detection result of the first power failure judgment module 13 will not be able to get rid of this abnormal detection state after multiple cycles between power failure and power failure release.

[0096] In the above case, if there is a first controllable compensation load module 14, after power-off, the first NMOS transistor Q1 in the first controllable compensation load module 14 is turned on, the first reference voltage Vref = 15V, the Vgs_nm2 of the second NMOS transistor Q2 is 2V, the reverse breakdown voltage V_z1 of the Zener diode Z1 is 5.2V, the turn-on voltage V_nm1 of the first NMOS transistor Q1 is 0, and the first resistor R1 = 5Ω. At this time, the current flowing through the branch where the first NMOS transistor Q1 is located is (Vref - Vgs_nm2 - V_z1 - V_nm1) / R1 = (15 - 2 - 5.2 - 0) / 5 = 1.56A. In this case, the voltage of the positive power line will not be charged to exceed 20.5V due to the residual current of the coil of the motor M, and the detection result of the first power-off judgment module 13 will not cycle multiple times between power-off and power-off release.

[0097] If the module that generates the first reference voltage Vref is also powered by the positive power line, then the first reference voltage Vref will still decrease as the positive power line drops after the positive power line is less than 15V (or higher). When the voltage difference between the source of the second NMOS transistor Q2 and the drain of the first NMOS transistor Q1 drops below the breakdown voltage 5.2V of the Zener diode Z1, the equivalent impedance of the first controllable compensation load module 14 will be very large. At this time, the circuit system can enter another stage, and the remaining electrical energy of the capacitor 11 can be provided to other working circuits to improve energy utilization efficiency.

[0098] As Figures 7 to 10 , the present invention also provides another hysteresis circuit for power-off detection, including:

[0099] A constant current module 10 for providing a constant current;

[0100] A capacitor 11 connected in parallel across both ends of the constant current module 10 for providing electrical energy in the short term after the constant current module 10 is powered off;

[0101] A second load and drive module 22 connected in parallel across both ends of the constant current module 10 for operating under the drive of the constant current and outputting a power-off fluctuation signal based on the change of the power parameter of the internal load;

[0102] A second power-off judgment module 23, whose input end is electrically connected to the output end of the second load and drive module 22, for monitoring whether the constant current module 10 is powered off according to the power-off fluctuation signal, and outputting a power-off prompt signal through its output end when the constant current module 10 is powered off;

[0103] The second controllable compensation load module 24 is connected in parallel to both ends of the constant current module 10, and its control end is electrically connected to the output end of the second power-off judgment module 23, and is used to parallel an additional load to both ends of the constant current module 10 according to the power-off prompt signal to enhance the hysteresis effect of the system.

[0104] In this embodiment, the constant current module 10 can adopt a constant current power supply of a conventional model. Its positive pole is led out through a positive power line, and its negative pole is led out through a negative power line and grounded, providing electrical energy for the system under non-power-off conditions, such as providing a 1.2 mA current. The second power-off judgment module 23 can be connected in parallel to both ends of the constant current module 10 or externally connected to a separate power supply to obtain the working voltage.

[0105] The capacitor 11 is located between the positive power line and the negative power line. When the second power-off judgment module 23 is connected in parallel to both ends of the constant current module 10, the capacitor 11 provides electrical energy for other modules in the short term after the constant current module 10 loses power to maintain the normal operation of circuits such as the second power-off judgment module 23, the second controllable compensation load module 24, and part of the second load and drive module 22. The capacitance value C 11 can be 20 μF.

[0106] The second load and drive module 22 adopts multiple loads (such as load one, load two, and load three), and monitors the change of the power parameter of the internal load (such as the change of load current or load terminal voltage and terminal current) based on the combination of functions such as clamping, drive disabling control, and voltage recognition, and outputs a power-off fluctuation signal accordingly, which is located between the positive power line and the negative power line.

[0107] When the second power-off judgment module 23 is connected in parallel to both ends of the constant current module 10, the second power-off judgment module 23 is located between the positive power line and the negative power line, and obtains the electrical energy required for operation from the positive power line. It judges whether the constant current module 10 loses power according to the power-off fluctuation signal received at the input end. For example: assuming that the power-off fluctuation signal is a voltage signal, when the currently used power-off fluctuation signal is lower than 5 V, it is determined that the constant current module 10 has lost power, and a high-level signal of 3.3 V can be output to the control end of the second controllable compensation load module 24 to indicate that the system is about to lose power (that is, the constant current module 10 has lost power, and after the electrical energy stored in the capacitor 11 is used up, the entire system will also lose power). The filtering time when judging system power-off is very short and is ignored in the following calculations. The filtering time when judging power-off release is 10 ms, and the power-off fluctuation threshold is 5.5 V, that is, when the power-off judgment signal is not lower than 5.5 V, it is determined that the power-off is released. It should be noted that the power-off fluctuation signal can also be a current signal or a power signal, etc., and can be specifically selected according to actual implementation needs.

[0108] The second controllable compensation load module 24 can change the on-resistance between the positive and negative poles of the module according to a signal (power-off prompt signal) input outside the module, so as to connect an additional load in parallel to both ends of the constant current module 10. This module enhances the hysteresis effect of the system by changing the load between the positive power line and the negative power line according to the power-off judgment result and system requirements. For example, the second controllable compensation load module 24 can add a load between the positive power line and the negative power line after receiving the high-level signal (such as 3.3V) output by the second power-off judgment module 23 until the system no longer needs to add this additional load (for example, the stage of detecting power-off has ended).

[0109] Compared with the common hysteresis generated by modifying the threshold point and other methods inside the power-off judgment module, implementing this circuit can enhance the hysteresis effect of the system, improve the stability of the system, and improve the detection accuracy when the load changes after the constant current module 10 loses power.

[0110] In a possible implementation, such as Figure 8 , the second controllable compensation load module 24 includes a third NMOS transistor Q3 and a second resistor R2;

[0111] The third NMOS transistor Q3 and the second resistor R2 are connected in series and then connected in parallel to both ends of the constant current module 10, and its gate is electrically connected to the output end of the second power-off judgment module 23;

[0112] The third NMOS transistor Q3 uses the second resistor R2 as the additional load and connects it in parallel to both ends of the constant current module 10 according to the power-off prompt signal.

[0113] In this embodiment, the third NMOS transistor Q3 can use a conventional NMOS transistor with a threshold voltage of 0.7V. The second resistor R2 uses a resistor of a conventional model with a resistance value of 256Ω. When the power-off prompt signal is at a high level (such as 3.3V), the third NMOS transistor Q3 is turned on, and the second resistor R2 is connected in parallel to both ends of the constant current module 10 as an additional load.

[0114] In a possible implementation, the second controllable compensation load module 24 further includes a logic gate unit Logic;

[0115] The source of the third NMOS transistor Q3 is electrically connected to the first end of the second resistor R2, its drain is electrically connected to the negative pole of the constant current module 10, and its gate is electrically connected to the output end of the logic gate unit Logic;

[0116] The second end of the second resistor R2 is electrically connected to the negative pole of the constant current module 10;

[0117] The first input terminal of the logic gate unit Logic is used to access a first system signal, and its second input terminal is electrically connected to the output terminal of the second power-down determination module 23;

[0118] Wherein, the logic gate unit Logic can generate a control signal acting on the gate of the third NMOS transistor Q3 based on the power-down prompt signal.

[0119] In this embodiment, the logic gate unit Logic can be a single AND gate A1, or a logic gate combination with AND function composed of other logic gates (such as two NAND gates). When the logic gate unit Logic is a single AND gate A1, the AND gate A1 adopts a conventional design, and the first system signal Vs can adopt a 3.3V voltage (which can be provided by other structures outside the positive power supply line, as long as a stable 3.3V voltage can be provided). Assuming that the power-off fluctuation signal is determined to be a power-down of the constant current module 10 when it is lower than 5V, the second power-down determination module 23 outputs a 3.3V high-level signal to an input port of the AND gate A1 in the second controllable compensation load module 24 to indicate that the system is about to power down.

[0120] In a possible implementation manner, the second load and drive module 22 includes a drive and sampling module 225 and n loads;

[0121] The positive electrodes of the n loads are respectively electrically connected to the positive electrode of the constant current module 10, and their negative electrodes are sequentially electrically connected to the n load interfaces of the drive and sampling module 225;

[0122] The power-down determination communication interface of the drive and sampling module 225 serves as the output terminal of the second load and drive module 22, and its ground terminal is electrically connected to the negative electrode of the constant current module 10;

[0123] Wherein, n is an integer greater than 1.

[0124] In a specific implementation manner, as Figure 9 , n is taken as 3, the first load is the first load 221, the second load is the second load 222, the third load is the third load 223, the first load interface of the drive and sampling module 225 is the first load interface, the second load interface is the second load interface, and the third load interface is the third load interface. Thus, the positive electrodes of the first load 221, the second load 222, and the third load 223 are respectively electrically connected to the positive electrode of the constant current module 10, and their negative electrodes are sequentially electrically connected to the first load interface, the second load interface, and the third load interface of the drive and sampling module 225.

[0125] In this embodiment, the first load 221, the second load 222, and the third load 223 are all nonlinear loads of the same type, characterized by: when the current is 1 mA, the voltage difference across both ends is 10 V; when the current is 0.8 mA, the voltage difference across both ends is 9 V; when the current is 0.5 mA, the voltage difference across both ends is 6 V. The three loads are all composed of diodes in series, but the types, quantities, and parasitic parameters of the internal diodes are different. The positive electrodes of the first load 221, the second load 222, and the third load 223 are all connected to the positive power supply line. In specific implementation, a second clamping module 224 can also be connected in parallel across both ends of the constant current module 10.

[0126] When the constant current module 10 is powered normally, the driving and sampling module 225 connects the first load 221 in parallel across both ends of the constant current module 10 through a switching device, disconnects the lines where the second load 222 and the third load 223 are located through a switching device, and simultaneously outputs a low level to the second power-off judgment module 23; when the constant current module 10 is powered off, the driving and sampling module 225 disconnects the line where the first load 221 is located through a switching device, and connects the second load 222 and the third load 223 in parallel across both ends of the constant current module 10 respectively (that is, the second load 222 and the third load 223 are also connected in parallel), and simultaneously outputs a high level to the second power-off judgment module 23. The second clamping module 224 starts to work at 16 V and clamps the voltage of the positive power supply line at 16 V. The driving and sampling module 225 samples the voltages of the negative electrodes of the first load 221, the second load 222, and the third load 223 respectively, and determines whether to turn on the corresponding switching devices of the first load 221, the second load 222, and the third load 223 according to the sampled voltages.

[0127] In a specific implementation manner, such as Figure 9 and Figure 10 , the driving and sampling module 225 includes a driving disable control module, a voltage recognition module, a first current source S1, a second current source S2, a third current source S3, a first NMOS transistor Qn11, a second NMOS transistor Qn12, a third NMOS transistor Qn13, a first NMOS transistor Qn21, a second NMOS transistor Qn22, a third NMOS transistor Qn23, a first NMOS transistor Qn31, a second NMOS transistor Qn32, and a third NMOS transistor Qn33. The first current source S1, the second current source S2, and the third current source S3 are all conventional current sources, which are regarded as ideal current sources in this embodiment. The first NMOS transistor Qn11, the second NMOS transistor Qn12, the third NMOS transistor Qn13, the first NMOS transistor Qn21, the second NMOS transistor Qn22, the third NMOS transistor Qn23, the first NMOS transistor Qn31, the second NMOS transistor Qn32, and the third NMOS transistor Qn33 are all conventional NMOS transistors.

[0128] The first disabled drive signal interface G01 of the drive disabling control module is connected to the gate of the first NMOS transistor Qn11, its second disabled drive signal G02 is connected to the gate of the second NMOS transistor Qn21, and its third disabled drive signal interface G03 is connected to the gate of the third NMOS transistor Qn31.

[0129] The drain of the first NMOS transistor Qn11, the drain and gate of the second NMOS transistor Qn12, and the gate of the third NMOS transistor Qn13 are connected to the positive pole of the first current source S1.

[0130] The drain of the second NMOS transistor Qn21, the drain and gate of the second NMOS transistor Qn22, and the gate of the third NMOS transistor Qn23 are connected to the positive pole of the second current source S2.

[0131] The drain of the third NMOS transistor Qn31, the drain and gate of the second NMOS transistor Qn32, and the gate of the third NMOS transistor Qn33 are connected to the positive pole of the third current source S3.

[0132] The drive disabling control module is connected to the voltage identification module through a control line for transmitting voltage identification control instructions.

[0133] The drive and sampling module 225 is also provided with a first load interface J1, a second load interface J2, a third load interface J3, a power-down judgment communication interface Jd, and a common ground terminal interface Jg.

[0134] Inside the drive and sampling module 225: The first load interface J1, the second load interface J2, and the third load interface J3 are sequentially connected to the drains of the third NMOS transistor Qn13, the second NMOS transistor Qn23, and the third NMOS transistor Qn33, and are sequentially connected to the three voltage sampling terminals of the voltage identification module. The power-down judgment communication interface Jd is connected to the voltage identification module. The negative poles of the first current source S1, the second current source S2, and the third current source S3, and the sources of the first NMOS transistor Qn11, the second NMOS transistor Qn12, the third NMOS transistor Qn13, the second NMOS transistor Qn21, the second NMOS transistor Qn22, the third NMOS transistor Qn23, the third NMOS transistor Qn31, the second NMOS transistor Qn32, and the third NMOS transistor Qn33 are all connected to the common ground terminal interface Jg.

[0135] Outside the drive and sampling module 225: The first load interface J1, the second load interface J2, and the third load interface J3 are sequentially connected to the negative poles of the first load 221, the second load 222, and the third load 223. The power-down judgment communication interface Jd is connected to the second power-down judgment module 23. The common ground terminal interface Jg is connected to the negative power supply line.

[0136] The drive and sampling module 225 limits the current to 1 mA when driving the load (generated by a current mirror in conjunction with a current source, the current source current is 100 μA, and the current mirror mirror ratio is 1:10). When each drive transistor drives the load, the drive current is within 1 mA, and the conduction voltage drop of the drive and sampling module 225 is negligible (directly approximated as 0 V in the following text). After the current reaches 1 mA, the conduction voltage drop depends on the load terminal voltage. When not driving the load, the corresponding disable drive signal for this path becomes high, and the gate of the drive transistor is pulled to about 0 V (less than the threshold voltage), and the drive transistor turns off. For example: The drive and sampling module 225 limits the current to 1 mA when driving the first load 221 (generated by a current mirror in conjunction with a current source, the current source (the first current source S1) current is 100 μA, and the current mirror mirror ratio is 1:10). When the drive transistor (the first triple NMOS transistor Qn13) drives the load (the first load 221), the drive current is within 1 mA, and the conduction voltage drop of the drive and sampling module 225 is negligible. After the current reaches 1 mA, the conduction voltage drop depends on the load terminal voltage (i.e., the voltage at the first load interface J1, which is also the voltage at the negative pole of the first load 221). When not driving the load (the first load 221), the corresponding disable drive signal for this path (i.e., the signal on the first disable drive signal interface G01) becomes high, and the gate of the drive transistor (the first triple NMOS transistor Qn13) is pulled to about 0 V (less than the threshold voltage), and the drive transistor (the first triple NMOS transistor Qn13) turns off.

[0137] In specific implementation, when the constant current module 10 is not powered off, the drive and sampling module 225 is only connected to the first load 221. The constant current module 10 outputs a current of 1.2 mA, and the current other than the second clamping module 224, the main load (i.e., the first load 221), and the second controllable compensation load module 24 is ignored. Then, 1 mA of current flows through the first load 221, 0.2 mA of current flows through the second clamping module 224, the positive power supply line voltage is 16 V, and the negative power supply line voltage is 0 V. At this time, the voltage at the negative pole of the first load 221 is 6 V, and the second power-off judgment module 23 does not detect that the constant current module 10 is powered off. The first system signal Vs is 3.3 V.

[0138] When the constant current module 10 loses power, no current flows through the second clamping module 224, and the voltage of the positive power supply line starts to drop. When the voltage of the positive power supply line drops to 15V, the negative voltage of the first load 221 drops to 5V, and the second power-off judgment module 23 outputs a power-off prompt signal of 3.3V (high level). At this time, the drive and sampling module 225 disconnects the first load 221 and connects the second load 222 and the third load 223, and shorts the negative electrodes of the second load 222 and the third load 223 (that is, connects the negative electrode of the second load 222 and the negative electrode of the third load 223). The second load 222 has a current of 0.5mA and a voltage drop of 6V; the third load 223 has a current of 0.5mA and a voltage drop of 6V; then the negative voltage of the second load 222 or the third load 223 is 9V, that is, the voltage of the positive power supply line (15V) minus the voltage drop v_load_b (6V) of the second load 222 or the third load 223.

[0139] At this time, if there is no second controllable compensation load module 24, the negative voltage of the second load 222 after a duration T = 10ms is:

[0140] 9 - I 11 ×T / C 11 = 9 - (I 222 + I 223 )×T / C 11 = 9 - (0.0005 + 0.0005)×0.01 / 0.00002 = 8.5V,

[0141] This value is higher than the power-off fluctuation threshold voltage of 5.5V, and the second power-off judgment module 23 will cancel the power-off prompt signal and set it to 0V (low level), where I 11 is the current of the capacitor 11, C 11 is the capacitance value of the capacitor 11, I 222 is the current flowing through the second load 222, I 223 is the current flowing through the third load 223; the drive and sampling module 225 will disconnect the second load 222 and the third load 223 and reconnect the first load 221. Then the power-off prompt signal will switch between low level and high level until the voltage at the negative electrode of the load is less than the power-off judgment threshold point regardless of which load is connected, and then a high-level signal of 3.3V will be stably output.

[0142] If there is a second controllable compensation load module 24 and the first system signal Vs is 3.3V, then: the power-off prompt signal is 3.3V, the first system signal Vs is 3.3V, and the output of the AND gate A1 is 3.3V; the current consumed by the branch where the third NMOS transistor Q3 is located is I Q3 = Vs - V Q3 / R 2=(3.3 - 1) / 256 ≈ 8.98 mA, where V Q3 is the threshold voltage of the third NMOS transistor Q3; after the duration T = 10 ms, the negative voltage of the second load 222 is approximately:

[0143] 9 - I 11 ×T / C 11 = 9 - (I 222 + I 223 + I Q3 )×T / C 11 = 9 - (0.0005 + 0.0005 + 0.00898)×0.01 / 0.00002 = 4.01 V,

[0144] This value is lower than the power-off fluctuation threshold voltage of 5.5 V, and at this time, there will be no problem of the power-off prompt signal switching multiple times between low and high levels. When the voltage of the positive power supply line further drops to 3.3 V, the first system signal Vs can become low level. At this time, the on-resistance of the third NMOS transistor Q3 branch becomes very large, and the system can supply the remaining electrical energy of the capacitor 11 to other working circuits, improving the energy utilization rate.

[0145] The above embodiments should not limit the present invention in any way. All technical solutions obtained by means of equivalent replacement or equivalent conversion fall within the protection scope of the present invention.

Claims

1. A hysteresis circuit for power failure detection, characterized in that: include: Constant current module, used to provide constant current; A capacitor connected in parallel to both ends of the constant current module, for providing electrical energy in a short period of time after the constant current module loses power; A first load and driving module is connected in parallel to both ends of the constant current module and is used to operate under the drive of the constant current; A first power-off judgment module is connected in parallel to both ends of the constant current module, and is used to monitor whether the constant current module is powered off, and output a power-off prompt signal through its output end when the constant current module is powered off; A first controllable compensation load module is connected in parallel to both ends of the constant current module, and a control end thereof is electrically connected to the output end of the first power-off judgment module, and is used to connect an additional load in parallel to both ends of the constant current module according to the power-off prompt signal to enhance the hysteresis effect of the system; The first load and drive module includes a load control module and a load module; The input end of the load control module serves as the control end of the first load and the driving module, the output end thereof is electrically connected to the control end of the load module, the working voltage end thereof is electrically connected to the positive electrode of the constant current module, and the ground end thereof is electrically connected to the negative electrode of the constant current module; The working voltage terminal of the load module is electrically connected to the positive electrode of the constant current module, and the grounding terminal of the load module is electrically connected to the negative electrode of the constant current module.

2. The hysteresis circuit according to claim 1, characterized in that: The first load and driving module are provided with a control terminal; The control end of the first load and driving module is electrically connected to the output end of the first power-off judgment module; When the first load and driving module receives the power-off prompt signal, the internal load thereof is controlled to stop operating.

3. The hysteresis circuit according to claim 1, characterized in that: The first load and driving module further includes a first clamping module connected in parallel to both ends of the constant current module.

4. The hysteresis circuit according to claim 1, characterized in that: The first controllable compensation load module includes a first NMOS tube and a first resistor; The first NMOS tube is connected in series with the first resistor and then connected in parallel to two ends of the constant current module, and a gate thereof is electrically connected to an output end of the first power-off judgment module; The first NMOS tube connects the first resistor as the additional load in parallel to two ends of the constant current module according to the power-off prompt signal.

5. The hysteresis circuit according to claim 4, characterized in that: The first controllable compensation load module also includes a second NMOS tube and a Zener diode; The source of the first NMOS tube is electrically connected to the cathode of the constant current module, and the drain of the first NMOS tube is electrically connected to the anode of the Zener diode; The cathode of the Zener diode is electrically connected to the first end of the first resistor; The second end of the first resistor is electrically connected to the source of the second NMOS tube; The gate of the second NMOS tube is used to access the first reference voltage, and the drain of the second NMOS tube is electrically connected to the positive electrode of the constant current module.

6. A hysteresis circuit for power failure detection, characterized in that: include: Constant current module, used to provide constant current; A capacitor connected in parallel to both ends of the constant current module, for providing electrical energy in a short period of time after the constant current module loses power; A second load and driving module is connected in parallel to both ends of the constant current module, and is used to operate under the drive of the constant current and output a power-off fluctuation signal based on the change of the electric quantity parameter of the internal load; A second power-off judgment module, whose input end is electrically connected to the second load and the output end of the driving module, is used to monitor whether the constant current module is powered off according to the power-off fluctuation signal, and output a power-off prompt signal through its output end when the constant current module is powered off; A second controllable compensation load module is connected in parallel to both ends of the constant current module, and a control end thereof is electrically connected to the output end of the second power-off judgment module, and is used to connect an additional load in parallel to both ends of the constant current module according to the power-off prompt signal to enhance the hysteresis effect of the system; The second load and driving module includes a driving and sampling module and n loads; The positive electrodes of the n loads are respectively electrically connected to the positive electrode of the constant current module, and the negative electrodes of the n loads are respectively electrically connected to the n load interfaces of the driving and sampling module in sequence; The power-off judgment communication interface of the driving and sampling module serves as the output end of the second load and driving module, and its ground end is electrically connected to the negative electrode of the constant current module; Here, n is an integer greater than 1.

7. The hysteresis circuit according to claim 6, characterized in that: The second controllable compensation load module includes a third NMOS tube and a second resistor; The third NMOS tube is connected in series with the second resistor and then connected in parallel to the two ends of the constant current module, and its gate is electrically connected to the output end of the second power-off judgment module; The third NMOS tube connects the second resistor as the additional load in parallel to the two ends of the constant current module according to the power-off prompt signal.

8. The hysteresis circuit according to claim 7, characterized in that: The second controllable compensating load module further includes a logic gate unit; The source of the third NMOS tube is electrically connected to the first end of the second resistor, the drain of the third NMOS tube is electrically connected to the negative electrode of the constant current module, and the gate of the third NMOS tube is electrically connected to the output end of the logic gate unit; The second end of the second resistor is electrically connected to the negative electrode of the constant current module; The first input end of the logic gate unit is used to access the first system signal, and the second input end thereof is electrically connected to the output end of the second power-off judgment module; The logic gate unit may generate a control signal acting on the gate of the third NMOS tube based on the power-off prompt signal.

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