A step-down isolation circuit suitable for medium power input high voltage

Abstract

The present application relates to the technical field of voltage reduction circuit, particularly relates to a voltage reduction isolation circuit suitable for middle power input high voltage V source , switch tube Q 1、 Q 2, voltage reduction transformer TX 1, voltage reduction transformer TX 2, rectifier diode D 3- D 10 , energy storage inductor L , output filter capacitor C 2, voltage reduction transformer TX 1, voltage reduction transformer TX 2 source end coil is connected in series, and is connected to DC power supply through switch tube Q 1、 Q 2 respectively V source ; two auxiliary end coils of voltage reduction transformer TX 1 are connected through rectifier diode D 3- D 6, energy storage inductor L , output filter capacitor C 2 constitute a loop; two auxiliary end coils of voltage reduction transformer TX 2 are connected through rectifier diode D 7- D 10 , energy storage inductor L , output filter capacitor C 2 constitute a loop.The circuit structure is relative to traditional double-tube forward circuit, saves one energy storage inductor and two sets of filter capacitors, and the stress of other circuit devices is not changed with equal power, is favorable to the miniaturization design of power supply product, compresses overall cost, and promotes product competitiveness.

Description

Technical Field

[0001] This invention relates to the field of step-down circuit technology, and in particular to a step-down isolation circuit suitable for medium-power input high voltage. Background Technology

[0002] In switching power supply applications with high input voltage and medium power output, the commonly selected circuit topologies include: active clamp forward converter, dual-transistor forward converter, half-bridge circuit, phase-shifted full-bridge, LLC, etc.

[0003] In a single-transistor forward converter, the MOSFET withstands twice the input voltage when turned off and requires an additional magnetic reset circuit. Common methods include LCD reset or transformer winding reset, with winding reset being more frequently used. However, the transformer reset time and the voltage stress on the switching transistor are contradictory design constraints.

[0004] Half-bridge circuits are hard-switching circuits, which carry a shoot-through risk and have low reliability. Phase-shifted full-bridge and LLC circuits offer simple symmetrical driving, high core utilization, and soft switching, but they suffer from high cost, the need for resonant inductors, large size, difficulty in achieving full-power-range soft switching, and complex software control.

[0005] The dual-transistor forward converter inherits the advantages of the single-transistor forward converter. By adding a MOSFET and a diode, it eliminates the need for a reset winding and reduces the voltage stress on the switching transistor to the input voltage. This topology is suitable for medium-power, high-voltage input applications, offering advantages such as low switching stress and resistance to transistor shoot-through. It is widely used in high-reliability applications such as military and aerospace.

[0006] In medium-power, high-voltage input applications, the two-transistor forward converter is typically used with a series input and parallel output configuration. Figure 1 This diagram illustrates a two-transformer forward converter circuit with two transformers connected in series at the source and in parallel at the secondary. This circuit configuration utilizes two energy storage inductors and a series-connected filter capacitor for circuit decoupling; inductors and capacitors are commonly used. Appropriately modifying the topology, reducing components, and lowering costs are the core issues that need to be addressed for this type of power supply. Summary of the Invention

[0007] This invention provides a step-down isolation circuit suitable for medium-power input high voltage, aiming to solve the problems of numerous components, large size, and high cost of the dual-transistor forward converter circuit in the above-mentioned application technologies.

[0008] This invention provides a step-down isolation circuit suitable for medium-power input high voltage, including a DC power supply V. source Switching transistors Q1 and Q2, step-down transformers TX1 and TX2, rectifier diodes D3-D4 10The energy storage inductor L and the output filter capacitor C2; the source coils of the step-down transformers TX1 and TX2 are connected in series and connected to the DC power supply V through switching transistors Q1 and Q2 respectively. source The two secondary coils of the step-down transformer TX1 form a circuit through rectifier diodes D3-D6, energy storage inductor L, and output filter capacitor C2; the two secondary coils of the step-down transformer TX2 form a circuit through rectifier diodes D7-D6. 10 The circuit consists of the energy storage inductor L and the output filter capacitor C2.

[0009] As a further improvement of the present invention, the step-down transformer TX1 includes secondary coils N2 and N3. The same-named terminal of the secondary coil N2 is connected to the anode of rectifier diode D3, and the opposite-named terminal of the secondary coil N2 is connected to the anode of rectifier diode D4 and the a terminal of energy storage inductor L, respectively. The cathode of rectifier diode D3 is connected to the cathode of rectifier diode D4 and the positive terminal of output filter capacitor C2, respectively. The same-named terminal of the secondary coil N3 is connected to the anode of rectifier diode D5, and the opposite-named terminal of the secondary coil N3 is connected to the anode of rectifier diode D6 and the negative terminal of output filter capacitor C2, respectively. The cathode of rectifier diode D5 is connected to the cathode of rectifier diode D6 and the b terminal of energy storage inductor L, respectively. The negative terminal of output filter capacitor C2 is connected to the ground of the secondary side of the step-down transformer TX1.

[0010] As a further improvement of the present invention, the step-down transformer TX2 includes secondary windings N5 and N6. The same-name terminal of the secondary winding N5 is connected to the anode of rectifier diode D7, and the opposite-name terminal of the secondary winding N5 is connected to the anode of rectifier diode D8 and terminal a of energy storage inductor L, respectively. The cathode of rectifier diode D7 is connected to the cathode of rectifier diode D8 and the positive terminal of output filter capacitor C2, respectively. The same-name terminal of the secondary winding N6 is connected to the anode of rectifier diode D9, and the opposite-name terminal of the secondary winding N6 is connected to the anode of rectifier diode D9. 10 The anode of the rectifier diode D9 is connected to the cathode of the output filter capacitor C2, and the cathode of the rectifier diode D1 is connected to the cathode of the output filter capacitor C2. 10 The cathode is the b terminal of the energy storage inductor L.

[0011] As a further improvement of the present invention, the circuit includes an input filter capacitor C1, a clamping diode D1, and a clamping diode D2. The step-down transformer TX1 includes a source coil N1, and the step-down transformer TX2 includes a source coil N4. The opposite-named terminal of the source coil N1 is connected to the same-named terminal of the source coil N4. The DC power supply V... source The power supply terminals are connected to the positive terminal of the input filter capacitor C1, the drain of the switching transistor Q1, and the cathode of the clamping diode D2, respectively, and the DC power supply V is connected to the DC power supply V. sourceThe ground terminal is connected to the negative terminal of the input filter capacitor C1, the source terminal of the switching transistor Q2, and the anode of the clamping diode D1. The source terminal of the switching transistor Q1 is connected to the cathode terminal of the clamping diode D1 and the same-name terminal of the source coil N1, respectively. The drain terminal of the switching transistor Q2 is connected to the anode terminal of the clamping diode D2 and the opposite-name terminal of the source coil N4, respectively.

[0012] As a further improvement of the present invention, the switching transistors Q1 and Q2 are MOSFETs.

[0013] As a further improvement of the present invention, the switching transistors Q1 and Q2 are simultaneously turned on or simultaneously turned off.

[0014] As a further improvement of the present invention, when switching transistors Q1 and Q2 are turned on, the voltage at the same-named terminals of the source coil N1 of step-down transformer TX1 and the source terminal N4 of step-down transformer TX2 is positive, and the voltage at the opposite-named terminals is negative, and the DC power supply V... source After being filtered by the input filter capacitor C1, the power supply flows into the drain of the switching transistor Q1, from the source of the switching transistor Q1 into the same-name terminal of the source coil N1, from the opposite-name terminal of the source coil N1 to the same-name terminal of the source coil N4, from the opposite-name terminal of N4 to the drain of the switching transistor Q2, and from the source of the switching transistor Q2 back to the negative terminal of the input filter capacitor C1, forming a circuit. The negative terminal of the input filter capacitor C1 is connected to the source side ground, i.e., the DC power supply V. source The ground wire; through electromagnetic induction, the induced voltage at the same-name terminals of the secondary coils N2, N3, N5, and N6 is positive, and the induced voltage at the opposite-name terminals is negative. Rectifier diodes D3, D5, D7, and D9 conduct, and rectifier diodes D4, D6, D8, and D... 10 The circuit is cut off under reverse voltage. Current flows out from the same-name terminal of the secondary coil N2, into the anode of rectifier diode D3, from the cathode of rectifier diode D3 to the positive terminal of output filter capacitor C2, from the negative terminal of output filter capacitor C2 to the opposite-name terminal of secondary coil N3, from the same-name terminal of secondary coil N3 to the anode of rectifier diode D5, from the cathode of rectifier diode D5 to terminal b of energy storage inductor L, and from terminal a of energy storage inductor L back to the opposite-name terminal of secondary coil N2, forming a return circuit. The current flows from the same-name terminal of coil N5, into the anode of rectifier diode D7, from the cathode of rectifier diode D7 to the positive terminal of output filter capacitor C2, from the negative terminal of output filter capacitor C2 to the opposite-name terminal of secondary coil N6, from the same-name terminal of secondary coil N6 to the anode of rectifier diode D9, from the cathode of rectifier diode D9 to terminal b of energy storage inductor L, and from terminal a of energy storage inductor L back to the opposite-name terminal of secondary coil N5, forming a loop. At this time, the output voltage...

[0015] As a further improvement of the present invention, when the switching transistors Q1 and Q2 are turned off, the step-down transformers TX1 and TX2 are demagnetized. At this time, the voltage at the same-named terminals of the source coils N1 and N4 is negative, and the voltage at the opposite-named terminals is positive. Current flows from the opposite-named terminal of the source coil N1 to the same-named terminal of the source coil N4, from the opposite-named terminal of the source coil N4 to the anode of the clamping diode D2, from the cathode of the clamping diode D2 to the positive terminal of the input filter capacitor C1, from the negative terminal of the input filter capacitor C1 to the anode of the rectifier diode D1, and from the cathode of the rectifier diode D1 back to the same-named terminal of the source coil N1. Through electromagnetic induction, the induced voltage at the same-named terminals of the secondary coils N2, N3, N5, and N6 is negative, and the induced voltage at the opposite-named terminals is positive. Rectifier diodes D3, D5, D7, and D9 are reverse-voltage cutoff, and rectifier diodes D4, D6, D8, and D9 are cutoff. 10 When the circuit is turned on, the energy storage inductor L releases the energy stored when the switching transistors Q1 and Q2 are turned on, completing the freewheeling function when the switching transistors Q1 and Q2 are turned off. Current flows out from terminal a of the energy storage inductor L, into the anode of rectifier diode D4, then from the cathode of rectifier diode D4 to the anode of output filter capacitor C2, then from the cathode of output filter capacitor C2 to the anode of rectifier diode D6, and finally from the cathode of rectifier diode D6 back to terminal b of the energy storage inductor L, forming a loop. Current also flows out from terminal a of the energy storage inductor L, into the anode of rectifier diode D8, then from the cathode of rectifier diode D8 to the anode of output filter capacitor C2, and finally from the cathode of output filter capacitor C2 back to terminal b of rectifier diode D6. 10 The anode, from rectifier diode D 10 The cathode flows to terminal b of the energy storage inductor L, forming a circuit; at this time, the output voltage...

[0016] The beneficial effects of this invention are: in the design and application of power supplies with medium power input and high voltage, the new circuit structure of this invention, compared with the traditional dual-transistor forward circuit, eliminates one energy storage capacitor and two sets of filter capacitors, while the stress of other circuit components remains unchanged for the same power, which is conducive to the miniaturization design of power supply products, reduces overall costs, and enhances product competitiveness. Attached Figure Description

[0017] Figure 1 This is a circuit diagram of the dual-transistor forward converter topology in the prior art of this invention;

[0018] Figure 2 This is a circuit diagram of an isolated step-down circuit suitable for medium-power input high voltage;

[0019] Figure 3 This is a schematic diagram of the circuit conduction principle when switching transistors Q1 and Q2 are turned on in this invention;

[0020] Figure 4 This is a schematic diagram of the circuit conduction principle when the switching transistors Q1 and Q2 are turned off in this invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0022] like Figure 2 As shown, this invention constructs a step-down isolation circuit suitable for medium-power output with high-voltage input, including a DC power supply V. source Switching transistors Q1 and Q2, step-down transformers TX1 and TX2, rectifier diodes D3-D4 10 The energy storage inductor L, output filter capacitor C2, and the source coils of step-down transformers TX1 and TX2 are connected in series and then connected to the DC power supply V through switching transistors Q1 and Q2, respectively. source The two secondary windings of step-down transformer TX1 form a circuit through rectifier diodes D3-D6, energy storage inductor L, and output filter capacitor C2; the two secondary windings of step-down transformer TX2 form a circuit through rectifier diodes D7-D6. 10 The circuit consists of the energy storage inductor L and the output filter capacitor C2.

[0023] The step-down transformer TX1 includes secondary windings N2 and N3. The same-name terminal of the secondary winding N2 is connected to the anode of rectifier diode D3, and the opposite-name terminal of the secondary winding N2 is connected to the anode of rectifier diode D4 and terminal a of energy storage inductor L, respectively. The cathode of rectifier diode D3 is connected to the cathode of rectifier diode D4 and the positive terminal of output filter capacitor C2, respectively. The same-name terminal of the secondary winding N3 is connected to the anode of rectifier diode D5, and the opposite-name terminal of the secondary winding N3 is connected to the anode of rectifier diode D6 and the negative terminal of output filter capacitor C2, respectively. The cathode of rectifier diode D5 is connected to the cathode of rectifier diode D6 and terminal b of energy storage inductor L, respectively. The negative terminal of output filter capacitor C2 is connected to the ground of the secondary side of step-down transformer TX1.

[0024] The step-down transformer TX2 includes secondary windings N5 and N6. The same-name terminal of secondary winding N5 is connected to the anode of rectifier diode D7, and the opposite-name terminal of secondary winding N5 is connected to the anode of rectifier diode D8 and terminal a of the energy storage inductor L, respectively. The cathode of rectifier diode D7 is connected to the cathode of rectifier diode D8 and the positive terminal of output filter capacitor C2, respectively. The same-name terminal of secondary winding N6 is connected to the anode of rectifier diode D9, and the opposite-name terminal of secondary winding N6 is connected to the anode of rectifier diode D9. 10 The anode of the rectifier diode D1, the cathode of the output filter capacitor C2, and the cathode of the rectifier diode D9 are connected to the rectifier diode D1, D2, and D2, respectively. 10 The cathode is the b terminal of the energy storage inductor L.

[0025] The power input module includes an input filter capacitor C1, clamping diodes D1 and D2, a step-down transformer TX1 including a source coil N1, and a step-down transformer TX2 including a source coil N4. The opposite-named terminal of the source coil N1 is connected to the same-named terminal of the source coil N4. The DC power supply is V. source The power supply terminals are connected to the positive terminal of the input filter capacitor C1, the drain of the switching transistor Q1, and the cathode of the clamping diode D2, respectively, and the DC power supply V is connected to the DC power supply V. source The ground terminal is connected to the negative terminal of the input filter capacitor C1, the source terminal of the switching transistor Q2, and the anode of the clamping diode D1. The source terminal of the switching transistor Q1 is connected to the cathode terminal of the clamping diode D1 and the same-name terminal of the source coil N1, respectively. The drain terminal of the switching transistor Q2 is connected to the anode terminal of the clamping diode D2 and the opposite-name terminal of the source coil N4, respectively.

[0026] Switches Q1 and Q2 can be turned on or off simultaneously, and the power device type is MOSFET.

[0027] The specific working principle of the circuit of this invention is as follows:

[0028] Switches Q1 and Q2 are turned on simultaneously, with both turn-on times being T. on The duty cycle and width are both Duty, abbreviated as D.

[0029] When switching transistors Q1 and Q2 are turned on, the circuit works as follows: Figure 3 As shown. The voltage at the source coil N1 of step-down transformer TX1 and the source coil N4 of step-down transformer TX2 is "+" at the same-name terminal and "-" at the opposite-name terminal. DC power supply V source The power supply, after being filtered by the input filter capacitor C1, flows into the drain of the switching transistor Q1. From the source of the switching transistor Q1, it flows into the same-name terminal of the source coil N1; from the opposite-name terminal of the source coil N1, it flows to the same-name terminal of the source coil N4; from the opposite-name terminal of the source coil N4, it flows to the drain of the switching transistor Q2; and from the source of the switching transistor Q2, it flows back to the DC power supply V. source The ground wire GND1 forms a circuit. Due to the principle of electromagnetic induction, the induced voltage at the same-name terminals of the secondary coils N2, N3, N5, and N6 is "+", and the induced voltage at the opposite-name terminals is "-". Rectifier diodes D3, D5, D7, and D9 are conducting, and rectifier diodes D4, D6, D8, and D9 are conducting. 10It is cut off under reverse voltage. Current flows from the same-name terminal of the secondary coil N2 to the anode of rectifier diode D3. From the cathode of rectifier diode D3, it flows to the positive terminal of output filter capacitor C2; from the negative terminal of output filter capacitor C2, it flows to the opposite-name terminal of secondary coil N3; from the same-name terminal of secondary coil N3, it flows to the anode of rectifier diode D5; from the cathode of rectifier diode D5, it flows to terminal b of energy storage inductor L; and from terminal a of energy storage inductor L, it flows back to the opposite-name terminal of secondary coil N2, forming a loop. Current flows from the same-name terminal of secondary coil N5 to the anode of rectifier diode D7. The current flows from the cathode of rectifier diode D7 to the positive terminal of output filter capacitor C2, from the negative terminal of output filter capacitor C2 to the opposite terminal of secondary coil N6, from the same terminal of secondary coil N6 to the anode of rectifier diode D9, from the cathode of rectifier diode D9 to terminal b of energy storage inductor L, and from terminal a of energy storage inductor L back to the opposite terminal of secondary coil N5, forming a circuit.

[0030] at this time

[0031]

[0032] In the formula V out V is the circuit output voltage. source The DC supply voltage is given, L is the inductance of the energy storage inductor, N1 to N4 are the number of turns of the transformer TX1 and TX4 coils, and i L This refers to the current flowing through the energy storage inductor.

[0033] When switching transistors Q1 and Q2 are turned off, step-down transformers TX1 and TX2 complete demagnetization. The circuit operation principle is as follows: Figure 4 As shown. At this time, the voltage at the same-name terminals of source coils N1 and N4 is "-", and the voltage at the opposite-name terminals is "+". Current flows from the opposite-name terminal of source coil N1 to the same-name terminal of source coil N4, from the opposite-name terminal of source coil N4 to the anode of clamping diode D2, from the cathode of clamping diode D2 to the positive terminal of input filter capacitor C1, from the negative terminal of input filter capacitor C1 to the anode of rectifier diode D1, and from the cathode of rectifier diode D1 back to the same-name terminal of source coil N1. Due to the principle of electromagnetic induction, the induced voltage at the same-name terminals of secondary coils N2, N3, N5, and N6 is "-", and the induced voltage at the opposite-name terminals is "+". Rectifier diodes D3, D5, D7, and D9 are cut off due to reverse voltage, while rectifier diodes D4, D6, D8, and D9 are cut off due to reverse voltage. 10The circuit is turned on. The energy storage inductor L releases the energy stored when the switching transistors Q1 and Q2 are turned on, completing the freewheeling function when the switching transistors Q1 and Q2 are turned off. Current flows from terminal a of the energy storage inductor L to the anode of the rectifier diode D4, from the cathode of the rectifier diode to the anode of the output filter capacitor C2, from the cathode of the output filter capacitor C2 to the anode of the rectifier diode D6, and from the cathode of the rectifier diode D6 back to terminal b of the energy storage inductor L, forming a loop. Current flows from terminal a of the energy storage inductor L to the anode of the rectifier diode D8, from the cathode of the rectifier diode to the anode of the output filter capacitor C2, and from the cathode of the output filter capacitor C2 back to terminal b of the rectifier diode D8. 10 The anode, from rectifier diode D 10 The cathode flows to terminal b of the energy storage inductor L to form a circuit.

[0034] at this time

[0035]

[0036] Based on the volt-second product balance principle, combining equations (1) and (2), we obtain:

[0037]

[0038] Ignoring the saturation voltage drop of rectifier diodes D3 and D5, substituting equation (3) into (1) yields the inductance value of the energy storage inductor L:

[0039]

[0040] In the formula Δi L Let be the ripple current of the energy storage inductor L.

[0041] To illustrate the differences between this invention and a two-transistor forward converter in medium-power input high-voltage applications, a comparative evaluation is provided using examples. If the output power P of the two architectures... out Same, output voltage V source Similarly, the turns ratio of step-down transformer TX1 is N1:N2:N3=N:N:N, and the turns ratio of step-down transformer TX2 is N4:N5:N6=N:N:N.

[0042] Substituting into equation (3), we obtain the circuit output voltage V of the present invention. out =D·V source Comparison Appendix Figure 1 Output voltage

[0043] The current flowing through the energy storage inductor L in this invention is i L , attached Figure 1 The current flowing through inductor L1 is i L1 The current flowing through inductor L2 is i L2To maintain circuit consistency, the inductance values ​​of inductors L1 and L2 are assumed to be equal, i.e., L1 = L2. Then i L1 =i L2 Under the same power output conditions, we have:

[0044] i L =i L1 +i L2 =2i L1 (5)

[0045] To maintain the same output power, the energy in the energy storage inductor L should be equal to the sum of the inductors L1 and L2.

[0046]

[0047] In the formula, T is the switching period of Q1 and Q2.

[0048] Substituting equation (5) into equation (6), we obtain that the inductance of the energy storage inductor L is half that of the energy storage inductor L1.

[0049] L1 = L2 = 2L (7)

[0050] Current ripple Δi on energy storage inductor L L The current ripple Δi on inductors L1 and L2 L1 and Δi L2 Twice that of the previous value. To maintain a smaller current ripple, L = L1 = L2.

[0051] In this invention, the step-down transformers TX1 and TX2, clamping diodes D1 and D2, and rectifier diodes D3, D4, D5, D6, D7, D8, D9, and D1 are used. 10 Voltage, current, stress and attachment Figure 1 The same as in.

[0052] The circuit topology of this invention contains two transformers. The source coils of these two transformers are connected in series, and the secondary coils are connected in parallel, sharing the same energy storage inductor. This eliminates the two sets of filter capacitors found in a two-transistor forward converter, using only one output capacitor for filtering, resulting in a significant reduction in cost and size. This circuit offers advantages such as low stress on the switching transistors and diodes, and continuous current in the energy storage inductor. It is suitable for medium-power, high-voltage input applications, solving the problems of numerous inductors and capacitors, large size, and high cost inherent in such two-transistor forward converters.

[0053] Theoretically, the number of step-down transformers TX1 and TX2 in the circuit of this invention can be increased according to the input voltage and output power. However, in practical applications, the design and fabrication of the energy storage inductor L becomes extremely difficult as the power increases.

[0054] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A step-down isolation circuit suitable for medium-power input high voltage, characterized in that, Including DC power supply V source Switching transistors Q1 and Q2, step-down transformers TX1 and TX2, rectifier diodes D3-D4 10 The energy storage inductor L and the output filter capacitor C2; the source coils of the step-down transformers TX1 and TX2 are connected in series and connected to the DC power supply V through switching transistors Q1 and Q2 respectively. source The two secondary coils of the step-down transformer TX1 form a circuit through rectifier diodes D3-D6, energy storage inductor L, and output filter capacitor C2; the two secondary coils of the step-down transformer TX2 form a circuit through rectifier diodes D7-D6. 10 The circuit consists of the energy storage inductor L and the output filter capacitor C2; The step-down transformer TX1 includes secondary windings N2 and N3. The same-name terminal of the secondary winding N2 is connected to the anode of rectifier diode D3, and the opposite-name terminal of the secondary winding N2 is connected to the anode of rectifier diode D4 and terminal a of energy storage inductor L, respectively. The cathode of rectifier diode D3 is connected to the cathode of rectifier diode D4 and the positive terminal of output filter capacitor C2, respectively. The same-name terminal of the secondary winding N3 is connected to the anode of rectifier diode D5, and the opposite-name terminal of the secondary winding N3 is connected to the anode of rectifier diode D6 and the negative terminal of output filter capacitor C2, respectively. The cathode of rectifier diode D5 is connected to the cathode of rectifier diode D6 and terminal b of energy storage inductor L, respectively. The negative terminal of output filter capacitor C2 is connected to the ground of the secondary side of step-down transformer TX1.

2. The step-down isolation circuit suitable for medium-power input high voltage according to claim 1, characterized in that, The step-down transformer TX2 includes secondary windings N5 and N6. The same-name terminal of secondary winding N5 is connected to the anode of rectifier diode D7, and the opposite-name terminal of secondary winding N5 is connected to the anode of rectifier diode D8 and terminal a of energy storage inductor L, respectively. The cathode of rectifier diode D7 is connected to the cathode of rectifier diode D8 and the positive terminal of output filter capacitor C2, respectively. The same-name terminal of secondary winding N6 is connected to the anode of rectifier diode D9, and the opposite-name terminal of secondary winding N6 is connected to the anode of rectifier diode D9. 10 The anode of the rectifier diode D1 and the cathode of the output filter capacitor C2 are connected to the cathode of the rectifier diode D9. 10 The cathode is the b terminal of the energy storage inductor L.

3. The step-down isolation circuit suitable for medium-power input high voltage according to claim 2, characterized in that, The system includes an input filter capacitor C1, a clamping diode D1, and a clamping diode D2. The step-down transformer TX1 includes a source coil N1, and the step-down transformer TX2 includes a source coil N4. The opposite-named terminal of the source coil N1 is connected to the same-named terminal of the source coil N4. The DC power supply V... source The power supply terminals are connected to the positive terminal of the input filter capacitor C1, the drain of the switching transistor Q1, and the cathode of the clamping diode D2, respectively, and the DC power supply V is provided. source The ground terminal is connected to the negative terminal of the input filter capacitor C1, the source terminal of the switching transistor Q2, and the anode terminal of the clamping diode D1, respectively. The source terminal of the switching transistor Q1 is connected to the cathode terminal of the clamping diode D1 and the same-name terminal of the source coil N1, respectively. The drain terminal of the switching transistor Q2 is connected to the anode terminal of the clamping diode D2 and the opposite-name terminal of the source coil N4, respectively.

4. The step-down isolation circuit suitable for medium-power input high voltage according to claim 3, characterized in that, The switching transistors Q1 and Q2 are MOSFETs.

5. The step-down isolation circuit suitable for medium-power input high voltage according to claim 3, characterized in that, The switching transistors Q1 and Q2 can be turned on or off simultaneously.

6. The step-down isolation circuit suitable for medium-power input high voltage according to claim 5, characterized in that, When switching transistors Q1 and Q2 are turned on, the voltage at the source coil N1 of step-down transformer TX1 and the source coil N4 of step-down transformer TX2 is positive, and the voltage at the opposite-named terminals is negative. The DC power supply V... source After being filtered by the input filter capacitor C1, the power supply flows into the drain of the switching transistor Q1, from the source of the switching transistor Q1 into the same-name terminal of the source coil N1, from the opposite-name terminal of the source coil N1 to the same-name terminal of the source coil N4, from the opposite-name terminal of N4 to the drain of the switching transistor Q2, and from the source of the switching transistor Q2 back to the negative terminal of the input filter capacitor C1, forming a circuit. The negative terminal of the input filter capacitor C1 is connected to the source side ground, i.e., the DC power supply V. source The ground wire; through electromagnetic induction, the induced voltage at the same-name terminals of the secondary coils N2, N3, N5, and N6 is positive, and the induced voltage at the opposite-name terminals is negative. Rectifier diodes D3, D5, D7, and D9 conduct, and rectifier diodes D4, D6, D8, and D... 10 The circuit is cut off under reverse voltage. Current flows out from the same-name terminal of the secondary coil N2, into the anode of rectifier diode D3, from the cathode of rectifier diode D3 to the positive terminal of output filter capacitor C2, from the negative terminal of output filter capacitor C2 to the opposite-name terminal of secondary coil N3, from the same-name terminal of secondary coil N3 to the anode of rectifier diode D5, from the cathode of rectifier diode D5 to terminal b of energy storage inductor L, and from terminal a of energy storage inductor L back to the opposite-name terminal of secondary coil N2, forming a return circuit. The current flows from the same-name terminal of coil N5, into the anode of rectifier diode D7, from the cathode of rectifier diode D7 to the positive terminal of output filter capacitor C2, from the negative terminal of output filter capacitor C2 to the opposite-name terminal of secondary coil N6, from the same-name terminal of secondary coil N6 to the anode of rectifier diode D9, from the cathode of rectifier diode D9 to terminal b of energy storage inductor L, and from terminal a of energy storage inductor L back to the opposite-name terminal of secondary coil N5, forming a loop. At this time, the output voltage...

7. The step-down isolation circuit suitable for medium-power input high voltage according to claim 5, characterized in that, When switching transistors Q1 and Q2 are turned off, step-down transformers TX1 and TX2 are demagnetized. At this time, the voltage at the same-named terminals of source coils N1 and N4 is negative, and the voltage at the opposite-named terminals is positive. Current flows from the opposite-named terminal of source coil N1 to the same-named terminal of source coil N4, from the opposite-named terminal of source coil N4 to the anode of clamping diode D2, from the cathode of clamping diode D2 to the positive terminal of input filter capacitor C1, from the negative terminal of input filter capacitor C1 to the anode of rectifier diode D1, and from the cathode of rectifier diode D1 back to the same-named terminal of source coil N1. Through electromagnetic induction, the induced voltage at the same-named terminals of secondary coils N2, N3, N5, and N6 is negative, and the induced voltage at the opposite-named terminals is positive. Rectifier diodes D3, D5, D7, and D9 are reverse-voltage cutoff, while rectifier diodes D4, D6, D8, and D9 are cutoff. 10 When the circuit is turned on, the energy storage inductor L releases the energy stored when the switching transistors Q1 and Q2 are turned on, thus completing the circuit freewheeling operation when the switching transistors Q1 and Q2 are turned off. Current flows out from terminal a of the energy storage inductor L, into the anode of rectifier diode D4, then from the cathode of rectifier diode D4 to the anode of output filter capacitor C2, from the cathode of output filter capacitor C2 to the anode of rectifier diode D6, and from the cathode of rectifier diode D6 back to terminal b of the energy storage inductor L, forming a loop. Current also flows out from terminal a of the energy storage inductor L, into the anode of rectifier diode D8, then from the cathode of rectifier diode D8 to the anode of output filter capacitor C2, and from the cathode of output filter capacitor C2 back to terminal b of rectifier diode D4. 10 The anode, from rectifier diode D 10 The cathode flows to terminal b of the energy storage inductor L, forming a circuit; at this time, the output voltage...

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