A protection circuit for connecting AC220V equipment to AC380V

Abstract

The present invention proposes a protection circuit for connecting AC220V equipment to AC380V, which adopts a two-stage protection circuit. The first stage is an overvoltage detection circuit composed of a bidirectional transient voltage suppression diode V1, a voltage regulator diode V2, a field effect transistor V3, a resistor R1, a discharge resistor R2, and a delay capacitor C1, and the second stage is a main switch circuit composed of a voltage regulator tube V4, a main switch tube V5, a bias resistor R3, and an anti-interference capacitor C2. When the power supply voltage of the circuit of the present invention increases abnormally, the power supply of the subsequent power supply equipment can be quickly cut off, and when the power supply is normal, the power supply of the subsequent power supply circuit can be connected without distortion.

Description

Technical Field

[0001] The invention relates to a voltage protection circuit, in particular to a protection circuit for connecting an AC220V device to an AC380V device. Background Art

[0002] With the popularization of Internet of Things technology, various intelligent controllers have been widely used. However, in the transformation of some small-scale power distribution control systems and the debugging stage of building control systems, due to construction defects, especially in the wiring or use of 3-phase 4-wire circuit breakers, the ground wire is forgotten or the contact is poor, resulting in an unexpected increase in the single-phase AC220 of the Internet of Things controller, causing overvoltage damage to the power supply inside the controller, and the inability to complete the detection and protection of the power distribution system.

[0003] Under normal circumstances, the power supply voltage of electrical appliances A, B, and IoT controller C is rated at single-phase 220V. If the wires of the power supply circuit are not in good contact or are disconnected, in the actual circuit, the power of the IoT controller is much smaller than that of electrical appliances A and B, that is, the equivalent impedance inside the power supply is much larger than the impedance of electrical appliances A and B. The voltage between the three-phase power supply lines is AC380V. At this time, the voltage at both ends of the controller will be higher than the normal AC220V, and may even reach close to AC380V. If the switching power supply inside the controller cannot withstand the high-voltage input, the controller will be damaged. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a protection circuit for connecting AC220V equipment to AC380V, so as to solve the problem that when the power supply voltage rises abnormally, the power supply of the subsequent power supply equipment can be quickly cut off, and when the power supply is normal, the power supply of the subsequent power circuit can be connected without distortion.

[0005] The present invention discloses a protection circuit for connecting an AC220V device to an AC380V device, comprising a circuit input unit and a subsequent circuit, wherein the circuit input unit comprises an anode of a rectified input voltage and a cathode of a rectified input voltage, and the subsequent circuit is connected to the circuit input unit. The invention also comprises an overvoltage protection unit, wherein the overvoltage protection unit and the subsequent circuit are connected to the circuit input unit in parallel.

[0006] Preferably, the circuit input unit is a half-wave rectifier circuit or a bridge rectifier circuit.

[0007] Preferably, the overvoltage protection unit comprises an overvoltage detection circuit and a main switch circuit.

[0008] The overvoltage detection circuit is composed of a bidirectional transient voltage suppression diode V1, a voltage stabilizing diode V2, a field effect transistor V3, a resistor R1, a discharge resistor R2, and a delay capacitor C1.

[0009] One end of the bidirectional transient voltage suppression diode V1 is connected to the anode of the rectified input voltage, and the other end of the bidirectional transient voltage suppression diode V1 is connected to the upper end of the resistor R1, and the other end of the resistor R1 is connected to the gate g of the low-voltage and low-current field effect tube V3; a voltage regulator diode V2, a discharge resistor R2, and a delay capacitor C1 are connected in parallel between the gate g and the source s of the field effect tube V3; the discharge resistor R2, the upper end of the delay capacitor C1, and the cathode of the voltage regulator diode V2 are all connected to the gate of the field effect tube V3, and the discharge resistor R2, the other end of the delay capacitor C1, and the anode of the voltage regulator diode V2 are all connected to the source of the field effect tube V3, and are connected to the cathode of the rectified input voltage.

[0010] The main switch circuit is composed of a voltage regulator tube V4, a main switch tube V5, a bias resistor R3, and an anti-interference capacitor C2.

[0011] One end of the bias resistor R3 is connected to the anode of the rectified input voltage, and the other end of the bias resistor R3 is connected to the drain d of the field effect tube V3, and is also connected to the cathode of the voltage regulator tube V4, one end of the anti-interference capacitor C2, and the gate g of the main switch tube V5; the anode of the voltage regulator tube V4 is connected to the other end of the anti-interference capacitor C2, and is also connected to the source s of the main switch tube V5, and the source of the main switch tube V5 is connected to the cathode of the rectified input voltage; the drain d of the main switch tube V5 is connected to the low potential of the subsequent circuit of the overvoltage protection circuit.

[0012] Preferably, the voltage stabilization value of the voltage stabilizing diode V2 is 15V, so as to ensure that the voltage on the voltage stabilizing diode V2 does not exceed the gate safety voltage of the field effect transistor V3.

[0013] The discharge resistor R2 is a high-resistance resistor, which ensures that the gate voltage of the voltage-stabilizing diode V2 is at a low level when the power supply is normal, and does not affect the gate voltage of the field-effect transistor V3 when the input is overvoltage; the delay capacitor C1 is an anti-interference capacitor, and the value of the capacitor also determines the time delay of the overvoltage protection action. In order to ensure the overvoltage response speed, the value of the delay capacitor C1 should be relatively small.

[0014] The function of the voltage regulator V4 is also to clamp the gate voltage of the main switch tube, and the voltage regulation value is 15V; the anti-interference capacitor C2 and the bias resistor R3 determine the conduction delay of the second-stage field effect tube, and the capacity of the capacitor C2 is generally greater than the capacity of the delay capacitor C1.

[0015] Preferably, the rated AC input voltage is AC220V (the maximum voltage allowed by the mains is AC260V), so the peak voltage after rectification is about 367V. Therefore, a commercial TVS with a rated breakdown voltage of 400V (1mA) can be used as V1 to ensure that V1 will not break down and conduct under normal circumstances, and the overvoltage circuit will not operate; if the power input AC voltage unexpectedly increases, even to AC380V or higher, V1 will break down and conduct, and the overvoltage protection circuit will work; the resistor Select 1MΩ for R1, 2MΩ for bleeder resistor R2, and 2MΩ for bias resistor R3; select 0.01uF for delay capacitor C1, and 0.1uF for anti-interference capacitor C2; select 40V1A low-power field effect tube V3, and V5 is the main switch tube. The withstand voltage and current of V5 must be able to withstand the highest input voltage and the maximum current (related to the load power) of the circuit. Select a switch tube with a withstand voltage of more than 600V and a current of more than 5A. This withstand voltage value can ensure that the AC overvoltage reaches AC420V. Select 15V Zener diodes for Zener diodes V2 and V4.

[0016] Preferably, after the overvoltage protection unit takes effect, if the overvoltage disappears, the charge on the delay capacitor C1 is released after a delay of several tens of ms, the field effect tube V3 is turned off, the main switch tube V5 is turned on again, and the subsequent circuits of the overvoltage protection unit are powered and work normally.

[0017] As an alternative to the present invention, a diode connected in series with a voltage regulator or a single-phase TVS is used to replace the bidirectional transient voltage suppression diode V1. An IGBT (insulated gate bipolar transistor) can be used as the circuit of the main switch V5. The IGBT has better withstand voltage and current and is low in cost.

[0018] Beneficial effects: The present invention adopts a two-stage protection circuit, the first stage is an overvoltage detection circuit composed of a bidirectional transient voltage suppression diode V1, a voltage regulator diode V2, a field effect transistor V3, a resistor R1, a discharge resistor R2, and a delay capacitor C1, and the second stage is a main switch circuit composed of a voltage regulator tube V4, a main switch tube V5, a bias resistor R3, and an anti-interference capacitor C2. When the power supply voltage of the circuit of the present invention increases abnormally, it can quickly cut off the power supply of the subsequent power supply equipment, and when the power supply is normal, it can connect the power supply of the subsequent power supply circuit without distortion. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the protection circuit of the AC220V device connected to AC380V of the present invention;

[0020] Figure 2 This is a schematic diagram of an overvoltage protection circuit using a thyristor as the main switch V5 (the waveform will be distorted);

[0021] Figure 3 Normal operating waveform of the main switch of field effect tube V5 (left: half wave, right: bridge type);

[0022] Figure 4 Normal working waveform of thyristor V5 as main switch (left: half-wave, right: bridge type);

[0023] Figure 5 Overvoltage protection waveform of field effect tube V5 as main switch (left: half wave, right: bridge type);

[0024] Figure 6 The overvoltage protection waveform of the field effect tube V5 as the main switch (left: half wave, right: bridge type);

[0025] Figure 7 The waveform is restored after the field effect transistor V5 acts as the overvoltage protection of the main switch (left: half-wave, right: bridge type). DETAILED DESCRIPTION

[0026] Example 1: Figure 1 As shown, a protection circuit for connecting an AC220V device to an AC380V device includes a circuit input unit and a subsequent circuit, wherein the circuit input unit includes an anode of a rectified input voltage and a cathode of a rectified input voltage, and the subsequent circuit is connected to the circuit input unit. An overvoltage protection unit is also included, and the overvoltage protection unit is connected to the circuit input unit in parallel with the subsequent circuit.

[0027] Preferably, the circuit input unit is a half-wave rectifier circuit or a bridge rectifier circuit.

[0028] Preferably, the overvoltage protection unit comprises an overvoltage detection circuit and a main switch circuit.

[0029] The overvoltage detection circuit is composed of a bidirectional transient voltage suppression diode V1, a voltage stabilizing diode V2, a field effect transistor V3, a resistor R1, a discharge resistor R2, and a delay capacitor C1.

[0030] One end of the bidirectional transient voltage suppression diode V1 is connected to the anode of the rectified input voltage, and the other end of the bidirectional transient voltage suppression diode V1 is connected to the upper end of the resistor R1, and the other end of the resistor R1 is connected to the gate g of the low-voltage and low-current field effect tube V3; a voltage regulator diode V2, a discharge resistor R2, and a delay capacitor C1 are connected in parallel between the gate g and the source s of the field effect tube V3; the discharge resistor R2, the upper end of the delay capacitor C1, and the cathode of the voltage regulator diode V2 are all connected to the gate of the field effect tube V3, and the discharge resistor R2, the other end of the delay capacitor C1, and the anode of the voltage regulator diode V2 are all connected to the source of the field effect tube V3, and are connected to the cathode of the rectified input voltage.

[0031] The main switch circuit is composed of a voltage regulator tube V4, a main switch tube V5, a bias resistor R3, and a capacitor C2.

[0032] One end of the bias resistor R3 is connected to the anode of the rectified input voltage, and the other end of the bias resistor R3 is connected to the drain d of the field effect transistor V3, and is also connected to the cathode of the voltage regulator tube V4, one end of the capacitor C2, and the gate g of the main switch tube V5; the anode of the voltage regulator tube V4 is connected to the other end of the capacitor C2, and is also connected to the source s of the main switch tube V5, and the source of the main switch tube V5 is connected to the cathode of the rectified input voltage; the drain d of the main switch tube V5 is connected to the low potential of the subsequent circuit of the overvoltage protection circuit.

[0033] Preferably, the voltage stabilization value of the voltage stabilizing diode V2 is 15V, so as to ensure that the voltage on the voltage stabilizing diode V2 does not exceed the gate safety voltage of the field effect transistor V3.

[0034] The discharge resistor R2 is a high-resistance resistor, which ensures that the gate voltage of the voltage-stabilizing diode V2 is at a low level when the power supply is normal, and does not affect the gate voltage of the field-effect transistor V3 when the input is overvoltage; the delay capacitor C1 is an anti-interference capacitor, and the value of the capacitor also determines the time delay of the overvoltage protection action. In order to ensure the overvoltage response speed, the value of the delay capacitor C1 should be relatively small.

[0035] The function of the voltage regulator tube V4 is also to clamp the gate voltage of the main switch tube, and the voltage regulation value is 15V; the capacitor C2 and the bias resistor R3 determine the conduction delay of the second-stage field effect tube, and the anti-interference capacitor C2 is greater than the value of the delay capacitor C1.

[0036] Preferably, the rated AC input voltage is AC220V (the maximum voltage allowed by the mains is AC260V), so the peak voltage after rectification is about 367V. Therefore, a commercial TVS with a rated breakdown voltage of 400V (1mA) can be used as V1 to ensure that V1 will not break down and conduct under normal circumstances, and the overvoltage circuit will not operate; if the power input AC voltage unexpectedly increases, even to AC380V or higher, V1 will break down and conduct, and the overvoltage protection circuit will work; the resistor Select 1MΩ for R1, 2MΩ for bleeder resistor R2, and 2MΩ for bias resistor R3; select 0.01uF for delay capacitor C1, and 0.1uF for anti-interference capacitor C2; select 40V1A low-power field effect tube V3, and V5 is the main switch tube. The withstand voltage and current of V5 must be able to withstand the highest input voltage and the maximum current (related to the load power) of the circuit. Select a switch tube with a withstand voltage of more than 600V and a current of more than 5A. This withstand voltage value can ensure that the AC overvoltage reaches AC420V. Select 15V Zener diodes for Zener diodes V2 and V4.

[0037] Preferably, after the overvoltage protection unit takes effect, if the overvoltage disappears, the charge on the delay capacitor C1 is released after a delay of several tens of ms, the field effect tube V3 is turned off, the main switch tube V5 is turned on again, and the subsequent circuits of the overvoltage protection unit are powered and work normally.

[0038] As an alternative to the present invention, a diode-in-series voltage regulator or a single-phase TVS is used to replace the bidirectional transient voltage suppressor diode V1, and a thyristor SCR is used as the circuit of the main switch V5.

[0039] The present invention adopts a two-stage protection circuit, the first stage is an overvoltage detection circuit composed of a bidirectional transient voltage suppression diode V1, a voltage regulator diode V2, a field effect transistor V3, a resistor R1, a discharge resistor R2, and a delay capacitor C1, and the second stage is a main switch circuit composed of a voltage regulator tube V4, a main switch tube V5, a bias resistor R3, and a capacitor C2. When the input voltage is within the normal range, the peak value of the DC voltage is less than the breakdown voltage of the bidirectional transient voltage suppression diode V1, the first stage circuit does not work, and only the working state of the second stage circuit is considered.

[0040] When the peak value of the rectifier output voltage exceeds the action voltage of the bidirectional transient voltage suppression diode TVS, V1 is turned on, the current flowing through R1 charges C1, and V3 is quickly turned on; at this time, the voltage on capacitor C2 has just changed a little bit. As V3 is turned on, the two ends of C2 are short-circuited by V3's d and s, and the charge on C2 is released instantly. The main switch V5 maintains the cut-off state or immediately enters the cut-off state, achieving overvoltage protection. At this time, the front and back of the overvoltage protection circuit are completely disconnected, and the voltage of the subsequent circuit remains zero, or the voltage on capacitor C3 is slowly discharged to zero. Thus, overvoltage protection is completed.

[0041] After the overvoltage protection circuit takes effect, if the overvoltage disappears, the charge on capacitor C1 is released after a delay of tens of ms, V3 is cut off, V5 resumes conduction, and the subsequent circuits of the overvoltage protection circuit are powered on and work normally again.

[0042] The overvoltage detection circuit and the main switch circuit complete the overvoltage protection and normal distortion-free functions.

[0043] Example 2: Figure 1 As shown,

[0044] The entire overvoltage protection circuit of the present invention is as follows Figure 1 In the dotted box, the input of the circuit can be a simple half-wave rectifier or a standard bridge rectifier circuit. The dotted box can be divided into two stages. The first stage is the overvoltage detection circuit composed of V1, V2, V3, R1, R2, and C1, and the second stage is the main switch circuit composed of V4, V5, R3, and C2.

[0045] One end of the bidirectional transient voltage suppression diode V1 (TVS) is connected to the "+" of the rectifier input, and the other end of V1 is connected to the upper end of the resistor R1, and the other end of R1 is connected to the gate (g) of the low-voltage and low-current field effect transistor V3; a voltage stabilizing diode V2, a discharge resistor R2, and a delay capacitor C1 are connected in parallel between the gate (g) and the source (s) of V3; the recommended voltage stabilization value of V2 is 15V, which is used to ensure that the voltage on it does not exceed the gate safety voltage of the field effect transistor V3; the resistor R2 is a high-resistance resistor, which ensures that the gate voltage of V2 is low when the power supply is normal, and has almost no effect on the gate voltage of V3 when the input is overvoltage; the capacitor C1 is an anti-interference capacitor, and the value of the capacitor also determines the time delay of the overvoltage protection action. In order to ensure the overvoltage response speed, the value of C1 should be relatively small. The upper ends of R2 and C1 and the cathode of V2 are all connected to the gate of V3, and the other ends of R2 and C1 and the anode of V2 are all connected to the source of V3 and to the “-” end of the input voltage.

[0046] Next, one end of the second-stage bias resistor R3 is connected to the "+" of the input voltage, and the other end of R3 is connected to the drain (d) of V3, and is also connected to the cathode of the voltage regulator tube V4, one end of the capacitor C2, and the gate (g) of the main switch tube V5; the anode of the voltage regulator tube V4 is connected to the other end of the capacitor C2, and is also connected to the source (s) of the switch tube V5, and the source of V5 is also connected to the "-" of the input power supply; and the drain (d) of V5 is connected to the low potential of the subsequent circuit of the overvoltage protection circuit. Figure 1 Capacitor C3 and resistor R5 are used to replace the subsequent circuit.

[0047] The function of the voltage regulator V4 is also to clamp the gate voltage of the main switch tube, and the recommended voltage regulation value is also 15V; the capacitor C2 and the bias resistor R3 determine the conduction delay of the second-stage field effect tube. Generally, we require that the delay of the second stage should be significantly greater than the delay of the first stage, that is, C2 should be significantly greater than the value of C1.

[0048] The working principle of the circuit of the present invention is as follows:

[0049] The overvoltage value of the protection circuit is determined by the breakdown voltage of the bidirectional transient voltage suppression diode V1. Assuming that the rated AC input voltage during normal operation is AC220V, and considering that the maximum voltage allowed is AC260V, the peak voltage after rectification is about 367V. Therefore, a commercial TVS with a rated breakdown voltage of 400V (1mA) can be selected as V1. In order to reduce the power consumption of the entire protection circuit, the resistor R1 can be selected as 1MΩ, the resistor R2 can be selected as 2MΩ, and the resistor R3 can be selected as 2MΩ; the capacitor C1 can be selected as 0.01uF, and the capacitor C2 can be selected as 0.1uF; the field effect tube V3 can be selected as a 40V1A low-power tube, and V5 is the main switch tube. All the currents of the subsequent circuits flow through it. Therefore, the voltage and current of V5 must be able to withstand the highest input voltage and the maximum current of the circuit. It is recommended to select a tube with a current of more than 600V and more than 5A. The voltage regulator tubes V2 and V4 can be selected as 15V voltage regulator tubes.

[0050] Normal operation:

[0051] When the input voltage is within the normal range, the peak value of the DC voltage is less than the breakdown voltage of the TVS, the first stage circuit does not work, and only the working state of the second stage circuit is considered. When the rated input voltage is AC220V, the peak value of the input rectified voltage (half-wave or bridge rectifier) ​​is 310V, and the conduction threshold of V5 is about 5V. At this time, the maximum charging current flowing through the current limiting resistor R3 is about: 300V / 2M=0.15mA, then the shortest time for C2 to charge to 5V is t2=0.1u×5V / 0.15m=3.3ms. In fact, the rectified voltage is a half-sine wave, the charging current will be less than 0.15mA, the charging time will exceed 3.3ms, and the longest is about 10ms (see Figures 2 and 3). At this time, the field effect tube V5 is turned on, and the large-capacity filter capacitor C3 and the switching power supply connected later enter the working mode.

[0052] After V5 is turned on, the voltage behind the half-wave or bridge rectifier is maintained by a large-capacity capacitor and will gradually reach a DC voltage with a certain ripple voltage. In this way, the charging process of capacitor C2 will continue until the voltage regulation value of V4 (15V) is reached. The overvoltage protection circuit is in a continuous conduction state, realizing a lossless connection between the rectifier and the filter capacitor, and ensuring the distortion-free transmission of the rectified voltage. The normal working waveform of the field effect tube as the main switch is shown in the attached Figure 3 , the left side is half-wave rectification, the right side is bridge rectification circuit, the breakdown voltage of TVS in the test is 200V.

[0053] like Figure 2There are also circuits that use thyristor (SCR) to act as the main switch V5, but the working condition of this circuit is not satisfactory. This is mainly because SCR is a current-type control device, and the input impedance between the control electrode (g) and the cathode (k) is low. The larger the current, the lower the device impedance, which can even be as small as tens of ohms. In order to ensure reliable triggering of SCR, the resistance value of resistor R3 must be reduced accordingly to increase the triggering current, resulting in a significant increase in the power consumption of R3; in addition, if the current in the SCR does not exceed its own holding current, if the trigger disappears, the SCR that has just been turned on will return to the cut-off state. From the waveform ( Figure 4 ) It can be seen that the voltage waveforms before and after the overvoltage protection switch circuit are inconsistent, which means that this switch cannot guarantee the distortion-free transmission of voltage. As the resistance value of R3 decreases, the capacity of capacitor C2 must be greatly increased to meet the appropriate delay of the second stage; taking 1A SCR as an example, R3 can be 200K and C2 must be 22uF. The resistance and capacity of SCR with larger current need to be adjusted more. Figure 4 Represents the operating waveforms of the SCR switch in half-wave (left) and bridge rectification (right).

[0054] The overvoltage protection working process is as follows:

[0055] When the peak value of the rectifier output voltage exceeds the action voltage of the TVS, V1 is turned on, and the current flowing through R1 (1MΩ) charges C1 (0.01uF). Assuming that the input voltage peak reaches 510V (the peak value of AC380V), the maximum charging current is (510-400) / 1M=0.11mA, and the conduction threshold voltage of the field effect tube V3 is about 2V. The time for C1 to charge to 2V is: t1=(0.01u×2) / 0.11m=0.18ms. It can be seen that t1 is much shorter than t2, that is, V3 is quickly turned on when the overvoltage occurs for about 0.18ms; at this time, the voltage on capacitor C2 has just changed a little bit. As V3 is turned on, the two ends of C2 are short-circuited by V3's d and s, and the charge on C2 is released instantly. The main switch V5 maintains the cut-off state or immediately enters the cut-off state, achieving overvoltage protection. At this time, the front and back of the overvoltage protection circuit are completely disconnected, and the voltage of the subsequent circuit remains zero, or the voltage on capacitor C3 is slowly discharged to zero. Subsequently, the voltage on C1 will continue to rise, and the final voltage is determined by R1, R2, and V2. The voltage in the test is about 7V.

[0056] When the switch is disconnected before and after, the rectifier output voltage is an interval of half sine wave (half-wave rectification) or a continuous half sine wave (bridge rectification). It is the key to the reliable operation of the circuit to keep V3 on and the main switch off. This requires limiting the voltage of C1 to maintain V3 on within the half cycle (10ms) when the input rectified voltage drops or is zero (half-wave). We use a bidirectional TVS as V1 to ensure that there is only a directional charging current in V1 but no discharge current. Of course, we can also use a diode series voltage regulator or a single-phase TVS instead of a bidirectional TVS to achieve this goal. That is, after the rectified voltage drops to the TVS breakdown voltage, R1 and V1 do not participate in the charging and discharging process of C1. At this time, only R2 connected in parallel to C1 will briefly consume the charge in C1.

[0057] The time required for the C1 voltage to drop from 7V to 2V can be simply calculated as follows: the time constant of R2 and C1 is t3=2M×0.01u=20ms. This time has exceeded half a cycle of the input AC voltage (10ms). Therefore, even with half-wave rectification, the overvoltage protection circuit can still reliably maintain a protective isolation state without the phenomenon of being on and off for a while.

[0058] Figure 5 This is the waveform of the overvoltage sudden increase test when the field effect tube is used as the main switch. The left side is the half-wave rectification and the right side is the bridge rectification overvoltage protection waveform. The breakdown voltage of the TVS in the test is 200V.

[0059] Figure 6 This is the waveform of the sudden overvoltage test when the field effect tube is used as the main switch. The left side is the half-wave rectification and the right side is the bridge rectification overvoltage protection waveform. The breakdown voltage of the TVS in the test is 200V.

[0060] After the overvoltage protection circuit takes effect, if the overvoltage disappears, the charge on the capacitor C1 is released after a delay of several tens of ms, V3 is turned off, V5 is turned on again, and the subsequent circuits of the overvoltage protection circuit are powered on and work normally. This is the working principle of the complete distortion-free overvoltage protection circuit of the present invention.

[0061] Figure 7 This is the waveform when the overvoltage of the field effect tube as the main switch disappears and normal power supply is restored. The left side is the half-wave rectification and the right side is the bridge rectification recovery working waveform. The recovery response time is about 200ms. The breakdown voltage of the TVS in the test is 200V.

[0062] Experimental waveform:

[0063] Test circuit reference Figure 1 The rectifier circuits use the commonly used half-wave rectifier and bridge rectifier circuits. Figure 3 ,5 , 6, 7 use field effect tube as main switch; Figure 4 The comparison uses thyristor as the main switch and adjusts the values ​​of R3 and C2. It can be found that during normal operation, the waveforms before and after the switch are inconsistent.

[0064] The experimental waveforms were observed and recorded using a mutually isolated 4-channel oscilloscope and the waveform data was copied using a USB flash drive. The breakdown voltage of the TVS in the test circuit was 200V, and the input AC voltage was simulated by a voltage regulator to generate normal and overvoltage AC inputs.

[0065] Channel A (red) is the input rectified voltage, 100V / div;

[0066] Channel B (blue) is the output voltage of the protection circuit, 100V / div;

[0067] Channel C (black) is the gate voltage of the overvoltage detection tube V3, 5V / div;

[0068] Channel D (green) is the main switch V5 gate voltage, 10V / div.

Claims

1. A protection circuit for connecting an AC220V device to an AC380V device, comprising a circuit input unit and a subsequent circuit, wherein the circuit input unit comprises an anode of a rectified input voltage and a cathode of the rectified input voltage, and the subsequent circuit is connected to the circuit input unit, characterized in that: It also includes an overvoltage protection unit, which is connected in parallel with the subsequent circuit to the circuit input unit; The overvoltage protection unit includes an overvoltage detection circuit and a main switch circuit; The overvoltage detection circuit is composed of a bidirectional transient voltage suppression diode V1, a voltage stabilizing diode V2, a field effect transistor V3, a resistor R1, a discharge resistor R2, and a delay capacitor C1; One end of the bidirectional transient voltage suppression diode V1 is connected to the anode of the rectified input voltage, and the other end of the bidirectional transient voltage suppression diode V1 is connected to the upper end of the resistor R1, and the other end of the resistor R1 is connected to the gate g of the low-voltage and low-current field effect tube V3; a voltage stabilizing diode V2, a discharge resistor R2, and a delay capacitor C1 are connected in parallel between the gate g and the source s of the field effect tube V3; the discharge resistor R2, the upper end of the delay capacitor C1, and the cathode of the voltage stabilizing diode V2 are all connected to the gate of the field effect tube V3, and the other end of the discharge resistor R2, the delay capacitor C1, and the anode of the voltage stabilizing diode V2 are all connected to the source of the field effect tube V3, and are connected to the cathode of the rectified input voltage; The main switch circuit is composed of voltage regulator tube V4, main switch tube V5, bias resistor R3, and anti-interference capacitor C2; One end of the bias resistor R3 is connected to the anode of the rectified input voltage, and the other end of the bias resistor R3 is connected to the drain d of the field effect tube V3, and is also connected to the cathode of the voltage regulator tube V4, one end of the anti-interference capacitor C2, and the gate g of the main switch tube V5; the anode of the voltage regulator tube V4 is connected to the other end of the anti-interference capacitor C2, and is also connected to the source s of the main switch tube V5, and the source of the main switch tube V5 is connected to the cathode of the rectified input voltage; the drain d of the main switch tube V5 is connected to the low potential of the subsequent circuit of the overvoltage protection circuit.

2. The protection circuit for connecting AC220V equipment to AC380V according to claim 1, characterized in that: The circuit input unit is a half-wave rectifier circuit or a bridge rectifier circuit.

3. The protection circuit for connecting AC220V equipment to AC380V according to claim 1, characterized in that: The voltage stabilization value of the voltage stabilizing diode V2 is set to 15V to ensure that the voltage on it does not exceed the gate safety voltage of the field effect transistor V3; The bleeder resistor R2 is a high-resistance resistor, which ensures that the gate voltage of the voltage-stabilizing diode V2 is at a low level when the power supply is normal, and does not affect the gate voltage of the field effect transistor V3 when the input is overvoltage; the delay capacitor C1 is an anti-interference capacitor, and the value of the capacitor also determines the time delay of the overvoltage protection action. In order to ensure the overvoltage response speed, the value of the delay capacitor C1 should be relatively small; The function of the voltage regulator V4 is also to clamp the gate voltage of the main switch tube, and the voltage regulation value is 15V; the anti-interference capacitor C2 and the bias resistor R3 determine the conduction delay of the second-stage field effect tube, and the capacity of the anti-interference capacitor C2 is greater than that of the delay capacitor C1.

4. The protection circuit for connecting AC220V equipment to AC380V according to claim 1, characterized in that: The rated AC input voltage is AC220V-AC260V, so the peak voltage after rectification is 367V. Therefore, a commercial TVS with a rated breakdown voltage of 400V is used as V1 to ensure that V1 will not break down and conduct under normal circumstances, and the overvoltage circuit will not operate; if the power input AC voltage unexpectedly increases, even reaching AC380V or higher, V1 will break down and conduct, and the overvoltage protection circuit will work; the resistor R1 is selected as 1MΩ, the bleeder resistor R2 is selected as 2MΩ, and the bias Select 2MΩ for resistor R3; select 0.01uF for delay capacitor C1, and 0.1uF for anti-interference capacitor C2; select 40V1A low-power field effect tube V3, and V5 is the main switch tube. The voltage and current resistance of V5 must be able to withstand the highest input voltage and the maximum current flowing through the circuit, which is related to the load power. Select a switch tube with a voltage resistance of more than 600V and a current of more than 5A. The voltage resistance value ensures that the AC overvoltage reaches AC420V; select 15V Zener diodes for Zener diodes V2 and V4.

5. The protection circuit for connecting AC220V equipment to AC380V according to claim 1, characterized in that: After the overvoltage protection unit takes effect, if the overvoltage disappears, the charge on the delay capacitor C1 is released after a delay of tens of ms, the field effect tube V3 is turned off, the main switch tube V5 resumes conduction, and the subsequent circuits of the overvoltage protection unit are energized and resume normal operation.

6. The protection circuit for connecting AC220V equipment to AC380V according to claim 1, characterized in that: A diode connected in series with a voltage regulator or a single-phase TVS is used to replace the bidirectional transient voltage suppression diode V1.

7. The protection circuit for connecting AC220V equipment to AC380V according to claim 1, characterized in that: An insulated gate bipolar transistor IGBT is used as a circuit for the main switch V5.

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