Isolation ACDC circuit with low cost and high performance

Abstract

The invention discloses a low-cost high-performance isolation ACDC circuit which comprises a rectifier bridge circuit, a first switch tube, a second switch tube, an energy transmission circuit and a rectification output circuit. The rectifier bridge circuit comprises first, second, third and fourth diodes, the cathodes of the first and second diodes are connected with the first end of the first switching tube, and the anodes of the third and fourth diodes are grounded; the anode of the second switch tube is connected with the second end of the first switch tube and the ground, and the cathode of the second switch tube is connected with the rectification output circuit through the energy transmission circuit. Through voltage reduction of the first switch tube and the second switch tube, all rear-end devices are ensured to be low-voltage devices, so that the rear-end circuit cost is reduced. According to the circuit, the switch transformer is optimized, the influence of flyback voltage of the switch transformer does not need to be considered, the cost of the same effect of the switch transformer is reduced, the energy transmission circuit is adopted to achieve the effect of energy isolation transmission, the energy isolation cost is reduced, meanwhile, the transformer is optimized, and the influence of strong magnetism on the circuit does not need to be considered.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit applications, and in particular, to an isolated ACDC circuit with low cost and high performance. Background Art

[0002] ACDC in an electric energy meter usually refers to the combination of alternating current (AC) and direct current (DC). In an electric energy meter, the ACDC function allows users to simultaneously measure and record the power consumption of alternating current and direct current.

[0003] However, the power supply in existing electric energy meters contains magneto-sensitive devices and is vulnerable to attacks: specifically, the ACDC in existing electric energy meters uses a high-frequency transformer for isolation, and the high-frequency transformer uses the inductance of a magnetic core for energy transfer, which is easily affected by magnetic fields. Especially when there is strong magnetic field interference, its power supply capacity decreases. Electric energy meters are legal metrology products and need to have the ability to prevent attacks. Strong magnetic interference is the most basic attack means, and the power supply design against strong magnetism is particularly important.

[0004] The cost of the power supply in the original electric energy meter is relatively high: in the ACDC isolation power supply of the original electric energy meter, several key devices, such as switching tubes and energy storage capacitors, need to have the ability to withstand high voltage, which greatly increases the cost. Especially for the switching tube, its voltage resistance not only needs to withstand the residual voltage of various lightning strikes but also needs to withstand the flyback voltage of the transformer, which greatly increases the cost of the switching tube; another device that affects the cost is the high-frequency transformer. When the electric energy meter needs multi-channel power supply, the transformer output needs multi-channel windings, which greatly increases the cost of the transformer, and the entire power supply needs to resist strong magnetism, further greatly increasing its cost. Summary of the Invention

[0005] The purpose of this application is to provide an isolated ACDC circuit with low cost and high performance to solve the problems in the prior art.

[0006] To solve the above technical problems, this application provides an isolated ACDC circuit with low cost and high performance, including:

[0007] A rectifier bridge circuit, a first switching tube, a second switching tube, an energy transfer circuit, and a rectified output circuit;

[0008] The rectifier bridge circuit includes a first diode, a second diode, a third diode, and a fourth diode. The negative electrodes of the first diode and the second diode are both connected to the first end of the first switching tube, and the positive electrodes of the third diode and the fourth diode are grounded;

[0009] The positive electrode of the second switching tube is connected to the second end of the first switching tube and the ground, the negative electrode of the second switching tube is connected to the energy transfer circuit, and the energy transfer circuit is connected to the rectified output circuit.

[0010] As a preferred embodiment, a low-cost and high-performance isolated ACDC circuit further includes:

[0011] A first polarized capacitor, the positive electrode of the first polarized capacitor is connected to the second end of the first switching tube, and the negative electrode of the first polarized capacitor is grounded.

[0012] As a preferred embodiment, in a low-cost and high-performance isolated ACDC circuit, the first switching tube is an N-channel field effect transistor;

[0013] Wherein, the source electrode of the first N-channel field effect transistor serves as the second end of the first switching tube, and the drain electrode of the first N-channel field effect transistor serves as the first end of the first switching tube.

[0014] As a preferred embodiment, in a low-cost and high-performance isolated ACDC circuit, the energy transfer circuit includes two non-polarized capacitors connected in parallel, namely a first non-polarized capacitor and a second non-polarized capacitor. One end of the first non-polarized capacitor and the second non-polarized capacitor is connected to the negative electrode of the second switching tube, and the other end of the first non-polarized capacitor and the second non-polarized capacitor is connected to the rectifier output circuit.

[0015] It should be further noted in the solution that, in a low-cost and high-performance isolated ACDC circuit, the rectifier output circuit includes a fifth diode, a sixth diode, a seventh diode, an eighth diode, an inductance capacitor and a second polarized capacitor. The positive electrode of the fifth diode is connected to the positive electrode of the seventh diode. The negative electrode of the fifth diode is connected to the second non-polarized capacitor and the positive electrode of the sixth diode. The negative electrode of the seventh diode is connected to the first non-polarized capacitor and the positive electrode of the eighth diode. The negative electrode of the sixth diode is connected to the negative electrode of the eighth diode. One end of the inductance capacitor is connected to the negative electrode of the sixth diode, and the other end is connected to the positive electrode of the second polarized capacitor and the power supply. The negative electrode of the second polarized capacitor is connected to the positive electrode of the seventh diode and the ground.

[0016] Compared with the prior art, a low-cost and high-performance isolated ACDC circuit provided by the present invention includes a rectifier bridge circuit, a first switching transistor, a second switching transistor, an energy transfer circuit, and a rectifier output circuit. The rectifier bridge circuit includes a first diode, a second diode, a third diode, and a fourth diode. The cathodes of the first diode and the second diode are both connected to the first end of the first switching transistor, and the anodes of the third diode and the fourth diode are grounded. The anode of the second switching transistor is connected to the second end of the first switching transistor and the ground, and the cathode of the second switching transistor is connected to the energy transfer circuit, which is connected to the rectifier output circuit. By stepping down through the first switching transistor and the second switching transistor, it is ensured that all components behind the second switching transistor are low-voltage components, thereby reducing the cost of the backend circuit. This circuit optimizes the switching transformer, eliminates the need to consider the influence of the flyback voltage of the switching transformer, reduces the cost of the switching transformer with the same function, uses the energy transfer circuit to play the role of energy isolation and transmission, reduces the cost of energy isolation. At the same time, this circuit eliminates the transformer, reduces the electromagnetic interference generated by the transformer, and does not need to consider the influence of strong magnetism on the circuit, meeting the application scenarios of electric energy meters. Brief Description of the Drawings

[0017] In order to more clearly illustrate the technical solutions of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0018] Figure 1 Schematic diagram of a low-cost and high-performance isolated ACDC circuit provided by an embodiment of the present application. Detailed Embodiments

[0019] In order to enable those skilled in the art to better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings.

[0020] The core of the present application is to provide a low-cost and high-performance isolated ACDC circuit, which solves the problems in the prior art.

[0021] Figure 1 Schematic diagram of a low-cost and high-performance isolated ACDC circuit provided by an embodiment of the present application, as shown in Figure 1 shown.

[0022] Embodiment 1

[0023] A low-cost and high-performance isolated ACDC circuit includes a rectifier bridge circuit, a first switching transistor, a second switching transistor K2, an energy transfer circuit, and a rectifier output circuit;

[0024] The rectifier bridge circuit includes a first diode D1, a second diode D2, a third diode D3, and a fourth diode D4. The cathodes of the first diode D1 and the second diode D2 are both connected to the first end of the first switching tube. The anodes of the third diode D3 and the fourth diode D4 are grounded.

[0025] The anode of the second switching tube K2 is connected to the second end of the first switching tube and the ground. The cathode of the second switching tube K2 is connected to the energy transfer circuit, and the energy transfer circuit is connected to the rectifier output circuit.

[0026] Embodiment 2

[0027] Based on Embodiment 1, a low-cost and high-performance isolated ACDC circuit further includes:

[0028] A first polarized capacitor C1. The anode of the first polarized capacitor C1 is connected to the second end of the first switching tube, and the cathode of the first polarized capacitor C1 is grounded. The first polarized capacitor C1 can filter out the ripple voltage on the power line and provide a smooth DC output. The output voltage of the front-end second switching tube K2 is stored on the first polarized capacitor C1 at the back end with a low voltage (relative to the mains).

[0029] Based on Embodiment 2, for a low-cost and high-performance isolated ACDC circuit, the first switching tube is an N-channel field effect transistor K1. Among them, the source of the first N-channel field effect transistor K1 serves as the second end of the first switching tube, and the drain of the first N-channel field effect transistor K1 serves as the first end of the first switching tube. Due to the influence of semiconductor process manufacturing, it is difficult for P-channel field effect transistors to achieve a low internal resistance. For chips of the same size, the on-resistance of N-channel field effect transistors is lower than that of P-channel field effect transistors, and N-channel field effect transistors with the same rated current are cheaper than P-channel field effect transistors, that is, N-channel field effect transistors have a low cost. Therefore, in this embodiment, the first switching tube is selected as an N-channel field effect transistor.

[0030] Based on Embodiment 1, a low-cost and high-performance isolated AC-DC circuit. The energy transfer circuit includes two non-polar capacitors connected in parallel, namely the first non-polar capacitor C2 and the second non-polar capacitor C3. One end of the first non-polar capacitor C2 and the second non-polar capacitor C3 is connected to the negative pole of the second switching tube K2, and the other end of the first non-polar capacitor C2 and the second non-polar capacitor C3 is connected to the rectifier output circuit. The energy stored in the first polar capacitor C1 causes the voltages of the first non-polar capacitor C2 and the second non-polar capacitor C3 to alternately change at high frequency, resulting in an alternating voltage appearing on the first non-polar capacitor C2 and the second non-polar capacitor C3. The energy is transferred to the rectifier output circuit at the back end through the first non-polar capacitor C2 and the second non-polar capacitor C3. The first non-polar capacitor C2 and the second non-polar capacitor C3 are symmetrically arranged, which can avoid the voltage difference change between the output section and the input section when the voltages of the first non-polar capacitor C2 and the second non-polar capacitor C3 alternately change, and form interference to the outside, and can effectively suppress the EMI (electromagnetic interference) of this circuit.

[0031] In this embodiment, a low-cost and high-performance isolated AC-DC circuit. The rectifier output circuit includes the fifth diode D5, the sixth diode D6, the seventh diode D7, the eighth diode D8, the inductance capacitor L1 and the second polar capacitor C4. The positive pole of the fifth diode D5 is connected to the positive pole of the seventh diode D7. The negative pole of the fifth diode D5 is connected to the second non-polar capacitor C3 and the positive pole of the sixth diode D6. The negative pole of the seventh diode D7 is connected to the first non-polar capacitor C2 and the positive pole of the eighth diode D8. The negative pole of the sixth diode D6 is connected to the negative pole of the eighth diode D8. One end of the inductance capacitor L1 is connected to the negative pole of the sixth diode D6, and the other end is connected to the positive pole of the second polar capacitor C4 and the power supply. The negative pole of the second polar capacitor C4 is connected to the positive pole of the seventh diode D7 and the ground.

[0032] The rectifier output circuit can convert the alternating voltage on the energy transfer circuit into direct current, and through the LC filtering of the inductance capacitor L1, finally form the power supply voltage required by the back-end circuit. In actual use, if multiple isolated outputs are required, multiple sets of energy transfer circuits and rectifier output circuits can be added.

[0033] To enable those skilled in the art to better understand this solution, the energy transmission principle of this circuit is described in detail below:

[0034] The key to energy transmission lies in three points: the capacitance of the first non-polar capacitor C2 and the second non-polar capacitor C3, the switching frequency of the first non-polar capacitor C2 and the second non-polar capacitor C3, and the supply voltage. The following only explains the principles of the designs of the three blocks of DC-to-AC switching, energy transfer, and rectifier output:

[0035] The calculation formula for energy transmission:

[0036] Note: In the following analysis, the voltage drops of the first switching transistor K1 and the second switching transistor K2 are ignored.

[0037] 1. When K2 conducts upward, the left side of C3 is grounded, and the voltage on the left side of C2 is VDD. After reaching equilibrium, the voltage values of C2 and C3 are: (VDD - VCC) / 2, where the voltage reference of VCC is the signal ground, and the signal reference of VDD is the power ground. The voltage of C2 is positive on the left and negative on the right, and the voltage of C3 is negative on the left and positive on the right.

[0038] 2. When K2 switches from conducting upward to conducting downward, the left side of C3 is grounded, and the voltage on the left side of C2 is VDD. After reaching equilibrium, the voltage values of C2 and C3 are: (VDD - VCC) / 2, but the voltage of C2 is negative on the left and positive on the right, and the voltage of C3 is positive on the left and negative on the right.

[0039] 3. When K2 switches from conducting downward to conducting upward, the voltage values of C2 and C3 are still (VDD - VCC) / 2, but the direction of the voltage changes.

[0040] As can be seen from the above:

[0041] When K2 switches once, the converted energy is calculated as follows:

[0042] The voltages on C2 and C3 change between (VDD - VCC) / 2 and -(VDD - VCC) / 2 once, and the voltage change amount is VDD - VCC. Then, in one cycle, the voltage change of C2 and C3 is 2*(VDD - VCC). 2 *C / 8 The voltage change amount is VDD - VCC, so in one cycle, the voltage change of C2 and C3 is 2*(VDD - VCC).

[0043] According to the formula for the energy stored in a capacitor: E = U*U*C / 2, when the voltages on C2 and C3 are (VDD - VCC) / 2, the stored energy E = (VDD - VCC) 2 *C / 8, then when the voltage changes from positive to negative once, the energy transfer on C2 and C3 is 2*E = (VDD - VCC) 2 *C / 4.

[0044] Then, every time K2 switches once, the total energy transferred by C2 and C3 to the backend is 4*E = (VDD - VCC) 2 *C / 2.

[0045] When K2 switches one cycle, the total energy transferred by C2 and C3 to the backend is 8*E = (VDD - VCC) 2 *C.

[0046] If the switching frequency of K2 is f, then the energy transferred in 1 s is 8*E*f = (VDD - VCC) 2*C*f, that is, the transmission power of the circuit is 8*E*f = (VDD - VCC) 2 *C*f.

[0047] The actual parameters of the transmitted energy are calculated as follows:

[0048] Assume that the front-end voltage VDD is 150V, the output voltage VCC is 12V, the capacitors C2 and C3 are 1nF, and the switching frequency f is 200kHz. Then the transmission power is (150 - 12) 2 *1nf*200k = 3.8W; when VDD is 200V, the transmitted power is 7W.

[0049] An isolation ACDC circuit with low cost and high performance provided by the present invention includes a rectifier bridge circuit, a first switching tube, a second switching tube K2, an energy transfer circuit, and a rectifier output circuit; the rectifier bridge circuit includes a first diode D1, a second diode D2, a third diode D3, and a fourth diode D4. The negative electrodes of the first diode D1 and the second diode D2 are both connected to the first end of the first switching tube, and the positive electrodes of the third diode D3 and the fourth diode D4 are grounded; the positive electrode of the second switching tube K2 is connected to the second end of the first switching tube and the ground, the negative electrode of the second switching tube K2 is connected to the energy transfer circuit, and the energy transfer circuit is connected to the rectifier output circuit. By stepping down through the first switching tube and the second switching tube K2, it is ensured that all devices behind the second switching tube K2 are low-voltage devices, thereby reducing the cost of the backend circuit. This circuit optimizes the switching transformer, does not need to consider the influence of the flyback voltage of the switching transformer, reduces the cost of the switching transformer with the same function, uses the energy transfer circuit to play the role of energy isolation transmission, reduces the cost of energy isolation. At the same time, this circuit optimizes away the transformer, reduces the electromagnetic interference generated by the transformer, and does not need to consider the influence of strong magnetism on this circuit, meeting the application scenarios of electricity meters.

[0050] Those skilled in the art will readily think of other embodiments of the present application after considering the specification and practicing the application disclosed herein. The present application is intended to cover any variations, uses, or adaptations of the present application, which follow the general principles of the present application and include the common general knowledge or conventional technical means in the technical field disclosed in the present application. The specification and embodiments are only regarded as exemplary, and the true scope of the present application is pointed out by the claims.

[0051] It should be understood that the present application is not limited to the exact structures described above and shown in the drawings, and various modifications and changes can be made without departing from its scope. The above-described embodiments of the present application do not constitute a limitation on the protection scope of the present application.

Claims

1. A low-cost, high-performance isolated ACDC circuit, characterized in that: include: A rectifier bridge circuit, a first switch tube, a second switch tube, an energy transfer circuit and a rectifier output circuit; The rectifier bridge circuit comprises a first diode, a second diode, a third diode and a fourth diode, the cathodes of the first diode and the second diode are connected to the first end of the first switch tube, and the anodes of the third diode and the fourth diode are grounded; The positive electrode of the second switch tube is connected to the second end of the first switch tube and the ground, the negative electrode of the second switch tube is connected to the energy transfer circuit, and the energy transfer circuit is connected to the rectifier output circuit.

2. The low-cost, high-performance isolated ACDC circuit according to claim 1, characterized in that: Also includes: A first polarity capacitor, wherein a positive electrode of the first polarity capacitor is connected to the second end of the first switch tube, and a negative electrode of the first polarity capacitor is grounded.

3. The low-cost, high-performance isolated ACDC circuit according to claim 2, characterized in that: The first switch tube is an N-channel field effect tube; The source of the first N-channel field effect transistor serves as the second end of the first switch transistor, and the drain of the first N-channel field effect transistor serves as the first end of the first switch transistor.

4. The low-cost, high-performance isolated ACDC circuit according to claim 1, characterized in that: The energy transfer circuit includes two parallel non-polar capacitors, namely a first non-polar capacitor and a second non-polar capacitor. One end of the first non-polar capacitor and the second non-polar capacitor is connected to the negative electrode of the second switching tube, and the other end of the first non-polar capacitor and the second non-polar capacitor is connected to the rectifier output circuit.

5. The low-cost, high-performance isolated ACDC circuit according to claim 4, characterized in that: The rectifier output circuit includes a fifth diode, a sixth diode, a seventh diode, an eighth diode, an inductor capacitor and a second polarity capacitor. The anode of the fifth diode is connected to the anode of the seventh diode, the cathode of the fifth diode is connected to the second non-polarity capacitor and the anode of the sixth diode, the cathode of the seventh diode is connected to the first non-polarity capacitor and the anode of the eighth diode, the cathode of the sixth diode is connected to the cathode of the eighth diode, one end of the inductor capacitor is connected to the cathode of the sixth diode, and the other end is connected to the anode of the second polarity capacitor and a power supply, and the cathode of the second polarity capacitor is connected to the anode of the seventh diode and ground.

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