Reference voltage starting circuit, direct current residual current detection device and protection device

Abstract

The application provides a reference voltage starting circuit, a direct current residual current detection device and a protection device, wherein the reference voltage starting circuit comprises a voltage dividing circuit, an operational amplifier, a push-pull circuit and an output capacitor circuit; the voltage dividing circuit is used for voltage dividing a received power supply voltage signal and inputting a voltage divided signal to the operational amplifier; the operational amplifier performs voltage following on the current reference voltage output by the reference voltage starting circuit and the voltage divided signal to obtain a control signal; the push-pull circuit controls the charging or discharging of the output capacitor circuit according to the control signal, so that the reference voltage starting circuit outputs a constant reference voltage to a current transformer. The application enhances the current driving capacity by setting the push-pull circuit, and the push-pull circuit has no overcurrent protection and can quickly drive the output capacitor circuit to power on. Compared with the scheme of directly adjusting the reference voltage by the operational amplifier, the capacitor power-on time of the application scheme is shorter, which is beneficial to the fast and stable excitation system of the current transformer.

Description

Technical Field

[0001] This application relates to the field of residual current detection technology, and in particular to a reference voltage start-up circuit, a DC residual current detection device, and a protection device. Background Technology

[0002] In power systems, current imbalances can occur due to line or equipment failures or uneven loads, threatening the stable operation of the power system and potentially causing power system failures. Therefore, residual current monitoring of the power system is one of the most important protective measures.

[0003] In related technologies, current transformers are commonly used to detect residual DC current on power lines. A current transformer mainly consists of an iron core and a coil wound around the toroidal iron core. During operation, a reference voltage is provided to the coil by the starting circuit, which then charges and discharges the current transformer.

[0004] In scenarios with large residual DC current, current may flow from the current transformer to the starting circuit, causing fluctuations in the reference voltage. To ensure reference voltage stability, a large capacitor is used in the starting circuit to prevent changes in the reference voltage due to the charging and discharging of the current transformer. However, traditional starting circuits use operational amplifiers to directly regulate the reference voltage. Operational amplifiers typically have overcurrent protection, thus limiting their ability to drive large currents. Consequently, the capacitor charges slowly, further reducing the speed at which the reference voltage is brought up. For some protection devices requiring rapid tripping, a quick power-up is needed to rapidly stabilize the current transformer's excitation system, a requirement that existing starting circuits cannot meet. Utility Model Content

[0005] This application provides a reference voltage start-up circuit, a DC residual current detection device, and a protection device to enable the reference voltage start-up circuit to be powered on quickly and meet the requirement of the protection device to trip quickly.

[0006] In a first aspect, this application provides a reference voltage start-up circuit, which is electrically connected to a current transformer to jointly perform DC residual current detection. The reference voltage start-up circuit includes: a voltage divider circuit, an operational amplifier, a push-pull circuit, and an output capacitor circuit.

[0007] The voltage divider circuit's first terminal, the operational amplifier's power supply terminal, and the push-pull circuit's power supply terminal are used to receive the same power supply voltage signal. The voltage divider circuit's second terminal is grounded, and its third terminal is electrically connected to the operational amplifier's first input terminal. The operational amplifier's second input terminal is electrically connected to the output capacitor circuit's first terminal to obtain the current reference voltage signal. The operational amplifier's output terminal is electrically connected to the push-pull circuit's control terminal, and the push-pull circuit's output terminal is also electrically connected to the output capacitor circuit's first terminal. The output capacitor circuit's second terminal is grounded, and its first terminal serves as the output terminal of the reference voltage start-up circuit, providing a reference voltage to the excitation coil in the connected current transformer.

[0008] The voltage divider circuit is used to divide the power supply voltage signal and input the divided voltage signal to the operational amplifier;

[0009] The operational amplifier is used to perform voltage following on the received voltage divider signal and the current reference voltage signal to obtain a control signal, and transmit the control signal to the output of the push-pull circuit;

[0010] The push-pull circuit is used to control the output capacitor circuit to charge or discharge according to the received control signal, so that the voltage start circuit outputs a constant reference voltage to the excitation coil.

[0011] In some embodiments, the first input terminal of the operational amplifier is a non-inverting input terminal, and the second input terminal of the operational amplifier is an inverting input terminal;

[0012] The operational amplifier is specifically used to: reduce the voltage value of the output control signal when the voltage value of the reference voltage signal is higher than the voltage value of the supply voltage signal, so as to control the output capacitor circuit to discharge and reduce the voltage value of the reference voltage.

[0013] Furthermore, when the voltage value of the reference voltage signal is lower than the voltage value of the power supply voltage signal, the voltage value of the output control signal is increased to control the output capacitor circuit to charge, thereby increasing the voltage value of the reference voltage.

[0014] In some embodiments, the push-pull circuit includes: an NPN transistor and a PNP transistor; the collector of the NPN transistor serves as the power supply terminal of the push-pull circuit to receive the power supply voltage signal, the emitter of the NPN transistor is connected to the emitter of the PNP transistor, the collector of the PNP transistor is grounded, and the bases of the NPN transistor and the PNP transistor serve as the control terminals of the push-pull circuit and are electrically connected to the output terminal of the operational amplifier;

[0015] When the voltage value of the reference voltage signal is higher than the voltage value of the voltage divider signal, the operational amplifier reduces the voltage value of the output control signal. The control signal drives the NPN transistor to turn off and the PNP transistor to turn on, so as to discharge the output capacitor circuit.

[0016] When the voltage value of the reference voltage signal is lower than the voltage value of the voltage divider signal, the operational amplifier raises the voltage value of the output control signal. The control signal drives the NPN transistor to turn on and the PNP transistor to turn off, so as to charge the output capacitor circuit.

[0017] In some embodiments, the output capacitor circuit includes a first capacitor and a second capacitor connected in parallel.

[0018] In some embodiments, the first capacitor is a tantalum capacitor and the second capacitor is a ceramic capacitor.

[0019] In some embodiments, the voltage divider circuit includes: a first resistor and a second resistor, wherein a first terminal of the first resistor receives the supply voltage signal, a second terminal is electrically connected to the first terminal of the second resistor, and a second terminal of the second resistor is grounded; the second terminal of the first resistor is electrically connected to the first input terminal of the operational amplifier.

[0020] Alternatively, the voltage divider circuit may be a reference voltage chip.

[0021] In some embodiments, the voltage divider circuit further includes a third capacitor; the third capacitor is connected in parallel across the second resistor.

[0022] In some embodiments, a current-limiting resistor is further provided between the output terminal of the operational amplifier and the control terminal of the push-pull circuit.

[0023] Secondly, this application provides a DC residual current detection device, comprising: a current transformer and a reference voltage start-up circuit as described in any one of the first aspects.

[0024] Thirdly, this application provides a protection device, including: a protection switch and the DC residual current detection device described in the second aspect, wherein the output terminal of the current transformer is electrically connected to the protection switch, and the protection switch performs a protection action based on the detection result output by the DC residual current detection device.

[0025] This application provides a reference voltage starting circuit, a DC residual current detection device, and a protection device. The reference voltage starting circuit includes a voltage divider circuit, an operational amplifier, a push-pull circuit, and an output capacitor circuit. The voltage divider circuit divides the received supply voltage signal and inputs the divided voltage signal to the operational amplifier. The operational amplifier performs voltage following processing by acquiring the current reference voltage output from the reference voltage starting circuit and the divided voltage signal to obtain a control signal. The push-pull circuit controls the output capacitor circuit to charge or discharge according to the received control signal, so that the reference voltage starting circuit outputs a constant reference voltage to the excitation coil in the current transformer. This application enhances the current driving capability by incorporating a push-pull circuit in the reference voltage starting circuit. Since the push-pull circuit has no overcurrent protection, it can quickly power on the output capacitor circuit. Compared to the traditional scheme where the operational amplifier directly adjusts the reference voltage, the power-on time of the output capacitor circuit using this application is shorter, which is beneficial for the excitation system of the connected current transformer to quickly reach stability, thereby meeting the rapid tripping requirements of the protection device. Attached Figure Description

[0026] Figure 1 A schematic diagram illustrating the application scenario of the reference voltage startup circuit provided in this application;

[0027] Figure 2 The structural diagram of the reference voltage startup circuit provided in this application;

[0028] Figure 3 for Figure 2 The waveform comparison diagram shown is between the reference voltage startup circuit and the traditional startup circuit.

[0029] Figure 4 A structural diagram of a reference voltage startup circuit provided in another embodiment of this application;

[0030] Figure 5 This is a structural diagram of the DC residual current detection device provided in this application;

[0031] Figure 6 A structural diagram of the protection device provided in this application.

[0032] Figure label:

[0033] 10. Reference voltage start-up circuit; 11. Current transformer;

[0034] 110 magnetic core; 111 excitation coil;

[0035] 20-voltage divider circuit; 30-operational amplifier;

[0036] 40° push-pull circuit; 50° output capacitor circuit;

[0037] R1 is the first resistor; R2 is the second resistor;

[0038] C1 is the first capacitor; C2 is the second capacitor;

[0039] C3 is the third capacitor; Q1 is the NPN transistor;

[0040] Q2 PNP transistor; 500V DC residual current detection device;

[0041] 600 protection device; R limit Current-limiting resistor. Detailed Implementation

[0042] In this application, "at least one" means one or more, and "more than one" means two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can mean: A alone, A and B simultaneously, or B alone, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one of a, b, or c alone can mean: a alone, b alone, c alone, a combination of a and b, a combination of a and c, a combination of b and c, or a, b, and c, where a, b, and c can be single or multiple. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0043] The terms “center,” “longitudinal,” “lateral,” “up,” “down,” “left,” “right,” “front,” and “rear,” etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0044] The terms "connected" and "connected" should be interpreted broadly. For example, in circuit structures, "connected" or "connected" can refer not only to physical connections but also to electrical or signal connections. This could be a direct connection (physical connection) or an indirect connection via at least one intermediate component, as long as the circuit is connected. It could also refer to the internal connection between two components. Similarly, a signal connection can refer to a connection via a circuit or a medium, such as radio waves. Those skilled in the art will understand the specific meaning of these terms in this application based on the specific circumstances.

[0045] To address the problem in related technologies where the starting circuit has poor current driving capability, resulting in slow charging of the capacitor at the output of the starting circuit and consequently preventing the current transformer's excitation system from quickly reaching stability, this application provides a reference voltage starting circuit. This application adds a circuit with stronger current driving capability between the operational amplifier and the capacitor to improve the charging speed of the capacitor at the output, thereby enabling rapid power-on of the current transformer, ensuring that the current transformer's excitation system quickly reaches stability, and obtaining accurate DC residual current detection results.

[0046] Next, we will introduce in detail the application scenarios of the reference voltage startup circuit. Figure 1 A schematic diagram illustrating an application scenario for the reference voltage startup circuit provided in this application. Please refer to [link / reference]. Figure 1 As shown, the system includes a reference voltage startup circuit 10 and a current transformer 11. The reference voltage startup circuit 10 includes an input terminal and an output terminal. The input terminal is connected to a power supply, and the output terminal is electrically connected to the current transformer 11. The current transformer 11 includes a magnetic core 110 and an excitation coil 111, with the excitation coil 111 wound around the magnetic core 110. The output terminal of the reference voltage startup circuit 10 is electrically connected to one end of the excitation coil 111, providing a constant reference voltage to the excitation coil 111; the other end of the excitation coil 111 receives a PWM signal. The reference voltage signal and the PWM signal together enable the excitation coil 111 to charge and discharge.

[0047] It should be noted that the current transformer 11 may also include other components or circuits, which are not limited in this application. For example, the excitation coil 111 is also directly or indirectly electrically connected to the controller, and the controller can obtain the detection result of the DC residual current by detecting the current on the excitation coil.

[0048] When performing DC residual current detection, such as Figure 1 As shown, the electric field lines are passed through the magnetic core 110. Figure 1 Taking a three-phase four-wire power line as an example, the specific details include... Figure 1In the diagram, lines A, B, C, and N represent the power line, which corresponds to the primary winding of current transformer 11, and the excitation coil 111, which corresponds to the secondary winding of current transformer 11. When a reference voltage signal and a PWM signal are applied to the two ends of the secondary winding, the excitation system formed by the primary winding, secondary winding, and magnetic core will oscillate self-excitedly. When there is no DC leakage in the power line, i.e., no residual DC current in the primary winding of current transformer 11, the excitation system can reach a balanced state, and the absence of residual DC current can be determined by analyzing the current in the secondary winding. When there is DC leakage in the power line, i.e., residual DC current in the primary winding of current transformer 11, the residual DC current will prevent the excitation system from reaching a balanced state. The change in magnetic flux caused by the residual DC current will induce a secondary current in the secondary winding, and the residual DC current can be detected by analyzing the secondary current in the secondary winding.

[0049] It should be understood that the current transformer 11 also includes other circuits, such as a current sampling circuit and an MCU, used to collect the current on the secondary winding and calculate the magnitude of the residual DC current. Figure 1 This part of the circuit is not shown.

[0050] Figure 2 A structural diagram of the reference voltage startup circuit provided in this application. Please refer to [link / reference]. Figure 2 As shown, the reference voltage start-up circuit 10 includes: a voltage divider circuit 20, an operational amplifier 30, a push-pull circuit 40, and an output capacitor circuit 50.

[0051] The first terminal of the voltage divider circuit 20, the power supply terminal of the operational amplifier 30, and the power supply terminal of the push-pull circuit 40 are used to receive the same power supply voltage signal VCC. The second terminal of the voltage divider circuit 20 is grounded. The third terminal of the voltage divider circuit 20 is electrically connected to the first input terminal of the operational amplifier 30. The second input terminal of the operational amplifier 30 is electrically connected to the first terminal of the output capacitor circuit 50. The output terminal of the operational amplifier 30 is electrically connected to the control terminal of the push-pull circuit 40. The output terminal of the push-pull circuit 40 is electrically connected to the first terminal of the output capacitor circuit 50. The second terminal of the output capacitor circuit 50 is grounded.

[0052] In this application, the first terminal of the output capacitor circuit 50 is connected to the excitation coil in the current transformer as the output terminal of the reference voltage starting circuit 10, and is used to provide a constant reference voltage to the excitation coil. For specific connection details, please refer to... Figure 1 As shown, it will not be elaborated further here.

[0053] The voltage divider circuit 20 is mainly used to divide the supply voltage signal VCC and input the divided voltage signal to the operational amplifier 30. The voltage divider circuit 20 can be implemented by a series resistor circuit, and the voltage division coefficient of the voltage divider circuit 20 is related to the voltage division ratio of each resistor in the series resistor circuit.

[0054] In some embodiments, the voltage divider circuit 20 includes: a first resistor R1 and a second resistor R2, the first end of the first resistor R1 receives the supply voltage signal VCC, the second end of the first resistor R1 is electrically connected to the first end of the second resistor R2, and the second end of the second resistor R2 is grounded.

[0055] Based on this, the voltage divider signal Vout output by the voltage divider circuit 20 is VCC*R2 / (R1+R2). In this application, the voltage value of the voltage divider signal Vout is constant, which is also the set value that the reference voltage signal Vref needs to reach. Therefore, the voltage divider signal Vout is input to the operational amplifier 30 as the basis for determining whether the current reference voltage signal Vref has reached the set value.

[0056] Optionally, the voltage divider circuit 20 further includes a third capacitor C3, which is connected in parallel across the second resistor R2. This configuration filters out interference signals, preventing them from disturbing the voltage divider signal Vout, thus improving the stability and anti-interference capability of the reference voltage startup circuit.

[0057] For example, the capacitance of the third capacitor C3 can be greater than 20uF. The capacitance of the third capacitor C3 can be set according to the current range that the current transformer needs to sample; the larger the residual current to be sampled, the larger the capacitance of the third capacitor C3, and vice versa. For example, for a small residual current, the capacitance of the third capacitor C3 is approximately 20uF, and for a large residual current, the capacitance of the third capacitor C3 is approximately 100uF.

[0058] In other embodiments, the voltage divider circuit 20 is a reference voltage chip. A reference voltage chip is an electronic component that converts an input voltage into a stable output voltage. In this application, the power supply terminal of the reference voltage chip is used to receive the supply voltage signal VCC, and the output pin of the reference voltage chip is electrically connected to the operational amplifier 30. The reference voltage chip converts the supply voltage signal VCC into a stable divided voltage signal Vout and outputs it to the operational amplifier 30. Using a high-precision reference voltage chip ensures that the operational amplifier receives a stable divided voltage signal Vout.

[0059] The reference voltage chip can be, but is not limited to, TL431.

[0060] See Figure 2As shown, the first input terminal of operational amplifier 30 is electrically connected to the output terminal of reference voltage startup circuit 10, which is equivalent to forming a voltage follower, thereby acquiring the voltage value of the current reference voltage signal Vref in real time. Specifically, operational amplifier 30 is used to obtain a control signal Vc from the received voltage divider signal Vout and the current reference voltage signal Vref through voltage following, and outputs the control signal Vc to the control terminal of push-pull circuit 40 to control the two transistors on push-pull circuit 40 to conduct alternately.

[0061] Among them, the operational amplifier 30 can be of the following models: LM358, LM258, NCS2007, etc.

[0062] The push-pull circuit 40 is an output circuit formed by connecting two transistors of different polarities. For example, it can be a bipolar junction transistor (BJT) or a metal-oxide-semiconductor field-effect transistor (MOSFET). A BJT is also called a triode.

[0063] In this application, the push-pull circuit 40 includes two transistors with different polarities. These two transistors conduct alternately, each responsible for waveform voltage tracking within one half-cycle. For example, please refer to... Figure 2 As shown, the push-pull circuit 40 includes an NPN transistor Q1 and a PNP transistor Q2. The collector of the NPN transistor Q1 serves as the power supply terminal of the push-pull circuit 40, receiving the power supply voltage signal VCC. The emitter of the NPN transistor Q1 is connected to the emitter of the PNP transistor Q2, and the collector of the PNP transistor Q2 is grounded. The bases of the NPN transistor Q1 and the PNP transistor Q2 serve as the control terminals of the push-pull circuit 40 and are electrically connected to the output terminal of the operational amplifier 30.

[0064] The output capacitor circuit 50 is mainly used to stabilize the output reference voltage signal Vref. It discharges when the voltage value of the reference voltage signal Vref increases and charges when the voltage value of the reference voltage signal Vref decreases, thereby preventing the reference voltage signal Vref from changing with the charging and discharging of the current transformer.

[0065] In some embodiments, the output capacitor circuit 50 includes a first capacitor C1 and a second capacitor C2 connected in parallel. The capacitance of the parallel capacitors is the sum of the capacitances of the individual capacitors, which can increase the total capacitance of the entire circuit. This characteristic can meet the requirement of this application to set a large capacitor at the output of the reference voltage start-up circuit 10 to ensure the stability of the reference voltage signal Vref.

[0066] For example, the first capacitor C1 can be a tantalum capacitor, and the second capacitor C2 can be a ceramic capacitor. Specifically, the first terminal of the first capacitor C1 is electrically connected to the first terminal of the second capacitor C2, and the second terminals of both the first capacitor C1 and the second capacitor C2 are grounded. The first terminal of the first capacitor C1 is the positive terminal, and the second terminal of the first capacitor C1 is the negative terminal. Ceramic capacitors are non-polarized capacitors and can be installed in any orientation during circuit connection.

[0067] It should be noted that the first capacitor C1 and the second capacitor C2 can also be other types of capacitors, and are not limited to tantalum capacitors and ceramic capacitors. For example, they can also be film capacitors, aluminum electrolytic capacitors, etc.

[0068] Among them, the capacitance of the first capacitor C1 can be greater than 20uF, and the capacitance of the second capacitor C2 can be greater than 100nF.

[0069] Please see Figure 4 As shown, in some possible designs, a current-limiting resistor R is also provided between the output of operational amplifier 30 and the control terminal of push-pull circuit 40. limit By increasing the current-limiting resistor R limit This limits the current between the input terminals of operational amplifier 30 and push-pull circuit 40 to prevent excessive current from damaging the components in push-pull circuit 40.

[0070] Next, taking a power supply voltage signal VCC = 5V and a voltage division factor of 0.5 in voltage divider circuit 20 as an example, we will illustrate the following. Figure 2 The working principle of the reference voltage start-up circuit 10 shown is as follows:

[0071] The DC residual current detection is initiated by supplying power to the reference voltage startup circuit 10, which in turn outputs a 5V supply voltage signal VCC to the power supply terminals of the voltage divider circuit 20, operational amplifier 30, and push-pull circuit 40. The voltage divider circuit 20 divides the supply voltage signal VCC, providing a 2.5V divided voltage signal Vout to the non-inverting input terminal of the operational amplifier 30. The operational amplifier 30 acquires the current reference voltage signal Vref in real time and inputs it to the inverting input terminal of the operational amplifier 30. During the initial startup phase, the voltage difference across the output capacitor circuit 50 is 0V (i.e., the reference voltage signal Vref = 0V), requiring charging to allow the reference voltage signal Vref to reach the set value as quickly as possible. Therefore, the operational amplifier 30 outputs a control signal Vc to cyclically drive NPN transistor Q1 and PNP transistor Q2 to conduct alternately. At the moment of power-on, NPN transistor Q1 is turned on while PNP transistor Q2 is turned off. At this time, NPN transistor Q1 is in saturation. The large current flowing through NPN transistor Q1 will quickly charge the first capacitor C1 and the second capacitor C2 in the output capacitor circuit 50, rapidly increasing the voltage difference across the output capacitor circuit 50, that is, rapidly increasing the voltage value of the reference voltage signal Vref.

[0072] After a period of time, the reference voltage signal Vref will reach the set value of 2.5V. At this time, the voltage values ​​of the non-inverting input terminal and the inverting input terminal of the operational amplifier 30 are the same, and the NPN transistor Q1 enters the amplification state from the saturation state, thus fine-tuning the reference voltage signal Vref.

[0073] Once the reference voltage signal Vref reaches the set value, the excitation system in the current transformer also quickly reaches stability. In this way, the current transformer can obtain accurate DC residual current detection results when performing DC residual current detection.

[0074] Over time, leakage may occur in the power lines, causing an imbalance in the excitation system of the current transformer. Current will flow from the current transformer to the output of the reference voltage startup circuit 10, resulting in fluctuations in the reference voltage signal Vref. Since the inverting input of the operational amplifier 30 is electrically connected to the output of the reference voltage startup circuit 10, the voltage at the inverting input of the operational amplifier 30 will also change. Additionally, the reference voltage startup circuit may slightly discharge to the load, further causing fluctuations in the reference voltage signal Vref.

[0075] Specifically, when the reference voltage signal Vref rises above the voltage divider signal Vout, the voltage at the inverting input of operational amplifier 30 is higher than the voltage at the non-inverting input. At this time, operational amplifier 30 will reduce the level of the output control signal Vc. That is, operational amplifier 30 will quickly output a low-level control signal Vc to control PNP transistor Q2 to be in amplification mode and NPN transistor Q1 to be cut off. Since the voltage across the capacitor in the output capacitor circuit 50 will not change abruptly, and the output current of PNP transistor Q2 flows from the emitter to the collector and then to the ground terminal, the output capacitor circuit 50 will discharge, thereby reducing the voltage of the reference voltage signal Vref until it returns to the set value of 2.5V.

[0076] If the voltage value of the reference voltage signal Vref rises significantly, the PNP transistor Q2 will be in saturation for a rapid discharge, and then switch to amplification. When the voltage value of the reference voltage signal Vref is slightly lower than the set value, the NPN transistor Q1 will be turned on and the PNP transistor Q2 will be turned off. Then, when the voltage value of the reference voltage signal Vref reaches the set value, the two transistors will be turned on alternately.

[0077] When the reference voltage signal Vref drops below the voltage of the voltage divider signal Vout, the voltage at the inverting input of operational amplifier 30 is lower than the voltage at the non-inverting input. At this time, operational amplifier 30 raises the level of the output control signal Vc to control NPN transistor Q1 to be in amplification mode, PNP transistor Q2 to be cut off, and the output current of NPN transistor Q1 flows from the collector to the emitter and then into the output capacitor circuit 50. Thus, the output capacitor circuit 50 is charged, and the voltage at the output terminal of the output capacitor circuit 50 is clamped by NPN transistor Q1 at about Vref+0.7V, forming negative feedback, which causes the reference voltage signal Vref to rise continuously until it recovers to the set value of 2.5V and remains constant.

[0078] After the reference voltage signal Vref recovers to the set value, the voltage values ​​at the non-inverting and inverting input terminals of the operational amplifier 30 are the same. The operational amplifier 30 will output a control signal Vc to control the NPN transistor Q1 and the PNP transistor Q2 to conduct alternately.

[0079] It should be noted that during the operation of the reference voltage startup circuit, if the charging of the output capacitor circuit 50 by NPN transistor Q1 or the discharging of the output capacitor circuit 50 by PNP transistor Q2 exceeds the control range, such as consistently exceeding or falling below the set value, NPN transistor Q1 or PNP transistor Q2 will remain in a saturated state, potentially damaging either transistor. Therefore, such situations should be avoided to ensure the safety and reliability of the reference voltage startup circuit.

[0080] Figure 3 for Figure 2 The diagram shows a waveform comparison between the reference voltage startup circuit and a traditional startup circuit. Among them, Figure 3 In the diagram, channel C1 is a waveform diagram of the reference voltage signal in the reference voltage start-up circuit provided in this application, channel C2 is a waveform diagram of the excitation signal received by the current transformer connected to the reference voltage start-up circuit provided in this application, channel R1 is a waveform diagram of the reference voltage signal in a conventional start-up circuit, and channel R2 is a waveform diagram of the excitation signal received by the current transformer connected to the conventional start-up circuit.

[0081] The excitation signal refers to the PWM signal applied to one end of the excitation coil. The excitation signal can be generated by an MCU or through self-excitation, and it works together with the reference voltage signal Vref across the excitation coil.

[0082] Figure 3 In the waveform diagram shown, the reference voltage signals on channels C1 and R1 are acquired at a frequency of 200MHz, and the excitation signals on channels C2 and R2 are acquired at a frequency of 20MHz.

[0083] Figure 3 In the waveform diagrams shown, the horizontal axis represents time, and the vertical axis represents the voltage value of the reference voltage signal / excitation signal.

[0084] Comparing the waveform diagrams of the reference voltage signals shown in channels C1 and R1 respectively, when the reference voltage signal is set to 2.5V, the time taken for the reference voltage signal shown in channel C1 to reach 2.5V is shortened by approximately 10ms compared to the time taken for the reference voltage signal shown in channel R1 to reach 2.5V. Therefore, the power-on speed of the reference voltage startup circuit provided in this application is faster.

[0085] Comparing the excitation signals shown in channel C2 and channel R2 respectively, the excitation signal on channel C2 stabilizes to 50% duty cycle faster than the excitation signal on channel R2.

[0086] Please continue reading. Figure 3The diagram shows the waveforms of the excitation signals in channels C2 and R2, respectively. When the reference voltage signal is below 2.5V, the duty cycles of the excitation signals in both channels are much less than 50% in the initial power-on phase. As the reference voltage signal increases, the duty cycle of the excitation signal approaches 50%, and the excitation signal shown in channel C2 is approximately... Figure 3 The duty cycle at the 0ms position shown is close to 50%, while the excitation signal shown by channel R2 is basically at... Figure 3 The duty cycle reaches nearly 50% at the 10ms position shown. Therefore, the scheme of this application enables the excitation signal duty cycle to reach stability faster.

[0087] A low reference voltage signal or an unstable duty cycle in the excitation signal may lead to false leakage current detection, or necessitate extending the DC residual current calculation time. For example, with a smooth DC residual current of 10mA, the calculated excitation signal duty cycle is approximately 49.66%. Without DC leakage current, the duty cycle is approximately 50.01%. Unstable reference voltage will affect the stability of the excitation signal duty cycle, thus causing significant errors in the entire DC residual current detection system. For a rated residual operating current of 30mA, a low reference voltage during power-on may result in the detection of a particularly large leakage current, thus requiring a delay in leakage current detection.

[0088] The reference voltage start-up circuit provided in this application enhances the current driving capability and improves the power-on speed of the output capacitor circuit by adding a push-pull circuit, thereby meeting the requirement of rapid and stable excitation signal. This also avoids the problems of misjudgment of leakage current and leakage protection timeout caused by extending the DC residual current calculation time.

[0089] Furthermore, existing leakage current interruption test standards require that the leakage current interruption time not exceed 40ms when the DC or AC residual current is 150mA. In some scenarios, the requirements are even higher, possibly requiring the leakage current interruption time not to exceed 35ms. Considering the power-on time and MCU initialization time (approximately 15ms), rapid stabilization of the reference voltage is also necessary. The reference voltage startup circuit provided in this application can better meet this requirement.

[0090] The leakage current breaking time refers to the total time from the moment a leakage current is suddenly applied until the protected circuit is completely disconnected. It is an important technical parameter of the protection device, reflecting the speed at which the protection device disconnects the circuit after detecting a leakage current.

[0091] Based on the structure and waveform diagram of the reference voltage startup circuit described above, it can be seen that the reference voltage startup circuit provided in this application can be powered on quickly, enabling the excitation system of the current transformer to quickly reach stability.

[0092] This application also provides a DC residual current detection device. Please refer to... Figure 5 As shown, the DC residual current detection device 500 provided in this application includes: a reference voltage start-up circuit and a current transformer.

[0093] The reference voltage startup circuit can be: Figure 2 The reference voltage startup circuit shown can be referenced for its specific structure and operating principle. Figure 2 as well as Figure 3 , Figure 4 The detailed description of the illustrated embodiments will not be repeated here.

[0094] Current transformers can be, but are not limited to, zero-sequence current transformers.

[0095] This application also provides a protective device.

[0096] Please see Figure 6 As shown, the protection device 600 provided in this application includes: a DC residual current detection device and a protection switch. The output terminal of the DC residual current detection device is electrically connected to the protection switch.

[0097] Among them, the DC residual current detection device can be Figure 5 The DC residual current detection device in the illustrated embodiment.

[0098] When the DC residual current detection device detects the presence of DC residual current and the magnitude of the DC residual current exceeds the preset current threshold, it determines that leakage has occurred and then controls the protection switch to perform protection action. When the protection switch is a relay, the DC residual current detection device controls the relay to perform tripping action.

[0099] Finally, it should be noted that the above embodiments are merely specific implementations of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions within the technical scope disclosed in this application should be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A reference voltage start-up circuit, characterized in that, The reference voltage start-up circuit is electrically connected to the current transformer to jointly perform DC residual current detection. The reference voltage start-up circuit includes: a voltage divider circuit, an operational amplifier, a push-pull circuit, and an output capacitor circuit. The voltage divider circuit's first terminal, the operational amplifier's power supply terminal, and the push-pull circuit's power supply terminal are used to receive the same power supply voltage signal. The voltage divider circuit's second terminal is grounded, and its third terminal is electrically connected to the operational amplifier's first input terminal. The operational amplifier's second input terminal is electrically connected to the output capacitor circuit's first terminal to obtain the current reference voltage signal. The operational amplifier's output terminal is electrically connected to the push-pull circuit's control terminal, and the push-pull circuit's output terminal is also electrically connected to the output capacitor circuit's first terminal. The output capacitor circuit's second terminal is grounded, and its first terminal serves as the output terminal of the reference voltage start-up circuit, providing a reference voltage to the excitation coil in the connected current transformer. The voltage divider circuit is used to divide the power supply voltage signal and input the divided voltage signal to the operational amplifier; The operational amplifier is used to perform voltage following on the received voltage divider signal and the current reference voltage signal to obtain a control signal, and transmit the control signal to the output of the push-pull circuit; The push-pull circuit is used to control the output capacitor circuit to charge or discharge according to the received control signal, so that the voltage start circuit outputs a constant reference voltage to the excitation coil.

2. The circuit according to claim 1, characterized in that, The first input terminal of the operational amplifier is a non-inverting input terminal, and the second input terminal of the operational amplifier is an inverting input terminal; The operational amplifier is specifically used to: reduce the voltage value of the output control signal when the voltage value of the reference voltage signal is higher than the voltage value of the supply voltage signal, so as to control the output capacitor circuit to discharge and reduce the voltage value of the reference voltage. Furthermore, when the voltage value of the reference voltage signal is lower than the voltage value of the power supply voltage signal, the voltage value of the output control signal is increased to control the output capacitor circuit to charge, thereby increasing the voltage value of the reference voltage.

3. The circuit according to claim 1 or 2, characterized in that, The push-pull circuit includes: an NPN transistor and a PNP transistor; the collector of the NPN transistor serves as the power supply terminal of the push-pull circuit, receiving the power supply voltage signal; the emitter of the NPN transistor is connected to the emitter of the PNP transistor; the collector of the PNP transistor is grounded; and the bases of the NPN transistor and the PNP transistor serve as the control terminals of the push-pull circuit, electrically connected to the output terminal of the operational amplifier. When the voltage value of the reference voltage signal is higher than the voltage value of the voltage divider signal, the operational amplifier reduces the voltage value of the output control signal. The control signal drives the NPN transistor to turn off and the PNP transistor to turn on, so as to discharge the output capacitor circuit. When the voltage value of the reference voltage signal is lower than the voltage value of the voltage divider signal, the operational amplifier raises the voltage value of the output control signal. The control signal drives the NPN transistor to turn on and the PNP transistor to turn off, so as to charge the output capacitor circuit.

4. The circuit according to claim 1, characterized in that, The output capacitor circuit includes a first capacitor and a second capacitor connected in parallel.

5. The circuit according to claim 4, characterized in that, The first capacitor is a tantalum capacitor, and the second capacitor is a ceramic capacitor.

6. The circuit according to claim 1, characterized in that, The voltage divider circuit includes: a first resistor and a second resistor, wherein a first terminal of the first resistor receives the supply voltage signal, a second terminal is electrically connected to the first terminal of the second resistor, and a second terminal of the second resistor is grounded; the second terminal of the first resistor is electrically connected to the first input terminal of the operational amplifier. Alternatively, the voltage divider circuit may be a reference voltage chip.

7. The circuit according to claim 6, characterized in that, The voltage divider circuit also includes a third capacitor; the third capacitor is connected in parallel across the second resistor.

8. The circuit according to any one of claims 1 to 7, characterized in that, A current-limiting resistor is also provided between the output terminal of the operational amplifier and the control terminal of the push-pull circuit.

9. A DC residual current detection device, characterized in that, include: A current transformer and a reference voltage start-up circuit as described in any one of claims 1 to 8.

10. A protective device, characterized in that, include: The protection switch and the DC residual current detection device according to claim 9, wherein the output terminal of the current transformer is electrically connected to the protection switch, and the protection switch performs protection actions according to the detection results output by the DC residual current detection device.

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