Step-down DC-DC conversion circuit

Abstract

The invention provides a step-down DC-DC conversion circuit, and the circuit comprises a power switch which is used for chopping an input DC voltage into a high-frequency voltage pulse sequence; the high-frequency transformer is used for converting the high-frequency voltage pulse sequence into primary side current and secondary side current and adjusting the voltage reduction capacity at the same time; the power diode is used for providing a follow current path for the two windings of the high-frequency transformer; and the energy storage capacitor is used for storing energy of the current sent by the two secondary windings of the transformer and outputting direct current voltage. According to the DC-DC converter, an inductor in an original DC-DC converter is transformed into the high-frequency transformer or the current transformer, a corresponding follow current circuit is designed, under the condition of the same proportion, lower output DC voltage is achieved, and the DC-DC converter has the advantages of being high in voltage reduction capacity, adjustable, low in output voltage ripple, easy to achieve and low in cost.

Description

Technical Field

[0001] This application relates to the technical field of power electronic converters, and specifically, to a buck DC-DC conversion circuit. Background Art

[0002] For a traditional Buck DC-DC converter, that is, a step-down DC-DC converter, it includes a power switch, an inductor, a freewheeling diode, and a storage capacitor. The conversion function is step-down output. That is, in the continuous current mode (CCM), the ratio of the output voltage to the input voltage (voltage conversion ratio) is the duty ratio d, that is, U o / U i = d. The conduction time t on of the power switch is the switching period multiplied by the duty ratio d, that is, t on = dT S . The magnitude of the output voltage ripple of the Buck DC-DC converter is inversely proportional to the square of the switching frequency and is suitable for high-precision power supply occasions. In the Buck DC-DC converter, the inductor current ripple expression is △i L = dU i T s / L, and the electrolytic capacitor voltage ripple expression is △U O = (1 - d)U O / 8f s 2 LC. However, for some occasions, a strong step-down ability is required. For example, in subway power applications, the input voltage is 1500V and the output voltage is 24V. Then, in CCM, d = 24 / 1500 = 1.6%. If the switching frequency is 100kHz, the switching period is 10μs, and the conduction time of the power switch is 0.16μs = 160ns. The switch is in an unfavorable situation of turning off before it is turned on. Therefore, the switching frequency should not be selected too high. Another example is in aviation power, where the input voltage is 270V and the output voltage is 28V. Then, in CCM, d = 28 / 270 = 10.37%. If the switching frequency is 100kHz, the switching period is 10μs, and the conduction time of the power switch is about 1μs, and the duty ratio is relatively low. For these two typical application occasions, due to the low duty ratio, the inductor current ripple is large and the ripple voltage amplitude is high.

[0003] The critical inductor expression is L C = dU i / 2f s I avg = U o / 2f s I avg , where I avgis the average value of the inductor current. It can be seen that when the output voltage is fixed and the output current, i.e., the average value of the inductor current, remains unchanged, when the switching frequency is not high, the required inductance needs to be increased, which increases the volume, mass, and cost of the inductor. To solve these problems of the high step-down ratio Buck DC-DC converter, the following improvements need to be made: (1) The traditional multi-stage cascaded scheme of the Buck DC-DC converter has the disadvantages of large volume, complex control, and low efficiency; (2) A single-switch Buck DC-DC converter with a voltage transformation ratio of d 2 has the disadvantages of more devices and complex structure; (3) A dual-switch Buck DC-DC converter with a voltage transformation ratio of d 2 has the disadvantage of large output voltage ripple. The research in the field of Buck DC-DC converters has not stopped, and new circuit topologies and corresponding modulation algorithms are needed.

[0004] After retrieval, it is found that: as shown in Figure 4 , a Watkins-Johnson converter, that is, a step-down Buck DC-DC converter, with a voltage transformation ratio of [(2d - 1) / d] ∈ [0.5, 1] and a voltage transformation range of 0 to U i , has the disadvantages of large output voltage ripple and a duty ratio d ∈ [0.5, 1], and it cannot adapt to high step-down ratio application scenarios, such as subway power supplies and civil aviation power supplies.

[0005] In view of this, it is very necessary to design a step-down DC-DC conversion circuit with a simple topology and strong adjustable step-down ability, suitable for the application occasions of high step-down ratio Buck DC-DC converters. Summary of the Invention

[0006] Aiming at the defects in the prior art, the purpose of this application is to provide a step-down DC-DC conversion circuit. By transforming the inductor in the original Buck DC-DC converter into a high-frequency transformer or a current transformer and designing a corresponding freewheeling circuit, under the same duty ratio, a lower output DC voltage can be achieved, which has the advantages of strong and adjustable step-down ability, low output voltage ripple, easy implementation, and low cost.

[0007] In one aspect of this application, a step-down DC-DC conversion circuit is provided, including: a power switch, a high-frequency transformer, an energy storage capacitor, and a power diode;

[0008] The power switch is used to chop the input DC voltage into a high-frequency voltage pulse sequence;

[0009] The high-frequency transformer is used to convert the high-frequency voltage pulse sequence into primary and secondary currents and simultaneously adjust the step-down ability;

[0010] The power diode is responsible for providing a freewheeling path for the two windings of the high-frequency transformer;

[0011] The energy storage capacitor is responsible for storing the current sent by the two windings of the secondary of the transformer and outputting a DC voltage.

[0012] Further, when the conversion circuit is composed of one power switch, one high-frequency transformer, one energy storage capacitor, two power diodes and one load resistor, it includes: a power switch S1, a high-frequency transformer T1, an energy storage capacitor C1, two power diodes D1, a second power diode D2 and a load resistor R1;

[0013] The drain d1 of the power switch S1 is connected to the positive pole of the input power supply Ui, and the source of the power switch S1 is connected to the primary terminal 1 of the high-frequency transformer T1 and the cathode of the second power diode D2; the gate g1 of the power switch S1 is connected to the driver output, and the primary terminal 2 of the high-frequency transformer T1 is connected to the secondary terminal 3, the anode of the second power diode D2, and the positive pole of the energy storage capacitor C1 to form an output positive pole, and at the same time is connected to one end of the load resistor R1. The secondary terminal 4 of the high-frequency transformer T1 is connected to the cathode of the first power diode D1, and the anode of the first power diode D1 and the negative pole of the energy storage capacitor C1 are connected to the negative pole of the input power supply to form an output negative pole, and at the same time are connected to the other end of the load resistor R1.

[0014] Further, the output terminal and the input terminal of the energy storage capacitor C1 are grounded together, and the output voltage polarity is the same as the input voltage polarity;

[0015] When the power switch S1 is turned on, the input voltage Ui is applied between the primary terminal 1 of the high-frequency transformer T1 and the negative pole of the DC voltage, and a current is formed through the inductance of the primary coil to charge the energy storage capacitor C1, forming a first current closed loop; at the same time, the induced voltage polarity of the primary coil of the high-frequency transformer T1 is positive on the left and negative on the right, and the induced voltage polarity of its secondary side is positive on the right and negative on the left. The formed current flows through the energy storage capacitor C1 and the first power diode D1, forming a second current closed loop, and at the same time the energy storage capacitor C1 supplies power to the load resistor R1;

[0016] When the power switch S1 is turned off, the primary coil of the high-frequency transformer T1 freewheels through the second power diode D2, and the voltage across the primary ends is approximately zero. The induced voltage on the secondary coil of the high-frequency transformer T1 is positive on the right and negative on the left, and the freewheeling direction remains unchanged. The formed current still flows through the energy storage capacitor C1 and the first power diode D1, and the energy storage capacitor C1 is charged; at the same time, the energy storage capacitor C1 supplies power to the load resistor R1;

[0017] Among them, the power switch S1 ensures the current continuity of the positive line at the front end of the energy storage capacitor C1; the amplitude of the voltage ripple of the energy storage capacitor is inversely proportional to the square of the switching frequency of the power switch S1.

[0018] Further, when the ratio d of the conduction time of the power switch S1 to the tube section time is a fixed value d ∈ [0, 1], by adjusting d and k 21 the magnitude, adjust the degree of reduction of the output voltage;

[0019] Among them, the ratio of the output voltage to the input voltage of the energy storage capacitor is

[0020] In the formula, U o is the output voltage; U i is the input voltage; n2 is the number of turns of the secondary coil of the transformer; n1 is the number of turns of the primary coil of the transformer; d is the ratio of the conduction time to the turn-off time of the power switch; k 21 is the ratio of the number of turns of the secondary coil to the number of turns of the primary coil.

[0021] Further, when the conversion circuit is composed of two said power switches, one said high-frequency transformer, one said energy storage capacitor, one said power diode and one said load resistor, it includes: input power supply Ui, first power switch S1, second power switch S2, high-frequency transformer T1, energy storage capacitor C1, power diode D1 and load resistor R1;

[0022] The drain d1 of the first power switch S1 is connected to the positive pole of the input power supply Ui, the source s1 of the first power switch S1 is connected to the primary terminal 1 of the high-frequency transformer T1 and the drain d2 of the second power switch S2, the gate g1 of the first power switch S1 is connected to the driver output, the primary terminal 2 of the high-frequency transformer T1 is connected to the secondary terminal 3, the source s2 of the second power switch S2, and the positive pole of the energy storage capacitor C1 to form an output positive pole, and at the same time is connected to one end of the load resistor R1. The gate g2 of the second power switch S2 is connected to the driver output. The secondary terminal 4 of the high-frequency transformer T1 is connected to the cathode of the power diode D1. The anode of the power diode D1 and the negative pole of the energy storage capacitor C1 are connected to the negative pole of the input power supply Ui to form an output negative pole, and at the same time are connected to the other end of the load resistor R1.

[0023] Further, when the first power switch S1 is turned on, the input power supply Ui is applied between the primary terminal 1 of the high-frequency transformer T1 and the negative pole of the DC voltage, and a current is formed through the inductance of the primary coil to charge the energy storage capacitor C1, forming a first current closed loop; at the same time, the induced voltage polarity of the primary coil inductance of the high-frequency transformer T1 is positive on the left and negative on the right, and the induced voltage polarity of its secondary side is positive on the right and negative on the left. The formed current flows through the energy storage capacitor C1 and the power diode D1, forming a second current closed loop, and the energy storage capacitor C1 supplies power to the load resistor R1.

[0024] When the first power switch S1 is turned off, the primary coil of the high-frequency transformer T1 continues to flow through the body of the second power switch S2, and the voltage across the primary terminals is approximately zero. The induced voltage polarity of the secondary coil of the high-frequency transformer T1 is positive on the right and negative on the left, and the direction of the continuous current remains unchanged. The formed current still flows through the energy storage capacitor C1 and the power diode D1, and the energy storage capacitor C1 is charged; at the same time, the energy storage capacitor C1 supplies power to the load resistor R1.

[0025] Further, when the conversion circuit includes two power switches, one high-frequency transformer, one energy storage capacitor, and one load resistor, it includes: an input power supply Ui, a first power switch S1, a second power switch S2, a high-frequency transformer T1, an energy storage capacitor C1, and a load resistor R1;

[0026] The drain d1 of the first power switch S1 is connected to the positive pole of the input power supply Ui, the source s1 of the first power switch S1 is connected to the primary terminal 1 of the high-frequency transformer T1 and the drain d2 of the second power switch S2. The gate g1 of the first power switch S1 is connected to the output of the corresponding driver. The primary terminal 2 of the high-frequency transformer T1, the secondary terminal 3, the source s2 of the second power switch S2, and the positive pole of the energy storage capacitor C1 are connected to form an output positive pole and are connected to one end of the load resistor R1. The gate g2 of the second power switch S2 is connected to the output of the corresponding driver. The secondary terminal 4 of the high-frequency transformer T1, the negative pole of the energy storage capacitor C1, and the negative pole of the input power supply Ui are connected to form an output negative pole and are connected to the other end of the load resistor R1.

[0027] Further, when the first power switch S1 is triggered to conduct, the second power switch S2 is turned off. The input power supply Ui is applied between the primary terminal 1 of the high-frequency transformer T1 and the negative pole of the DC voltage, and a current is formed through the inductance of the primary coil to charge the energy storage capacitor C1, forming a first current closed loop. At the same time, the induced voltage polarity of the primary coil inductance of the high-frequency transformer T1 is positive on the left and negative on the right, and the induced voltage polarity of its secondary side is positive on the right and negative on the left. The formed current flows through the energy storage capacitor C1 and through the secondary terminal 4 of the high-frequency transformer T1, forming a second current closed loop. At the same time, the energy storage capacitor C1 supplies power to the load resistor R1.

[0028] When the first power switch S1 is turned off, the second power switch S2 is triggered to conduct. The primary coil of the high-frequency transformer T1 continues to flow through the body of the second power switch S2, and the voltage across the primary terminals is approximately zero. The induced voltage polarity of the secondary coil of the high-frequency transformer T1 is positive on the right and negative on the left, and the direction of the continuous current remains unchanged. The formed current flows through the energy storage capacitor C1 and through the secondary terminal 4 of the high-frequency transformer T1. The energy storage capacitor C1 is charged. At the same time, the energy storage capacitor C1 supplies power to the load resistor R1.

[0029] Further, in the on and off states of the first power switch S1, the energy storage capacitor C1 is charged, and at the same time, power is supplied to the load resistor R1. A relatively stable output DC voltage is formed in the steady state. The output voltage is related to the ratio of the on-time to the off-time of the power switch and the turns ratio n2 / n1 of the high-frequency transformer.

[0030] Compared with the prior art, the present application has at least one of the following beneficial effects:

[0031] 1. By transforming the inductor in the original Buck DC-DC converter into a high-frequency transformer or a current transformer and designing a corresponding freewheeling circuit, the present application can achieve a lower output DC voltage under the same duty ratio, with the advantages of strong and adjustable bucking ability, low output voltage ripple, easy implementation, and low cost.

[0032] 2. For the buck DC-DC conversion circuit provided by the present application, regardless of whether the power switch is on or off, the current continuity of the positive line at the front end of the energy storage capacitor is ensured. Therefore, the voltage ripple of the energy storage capacitor is relatively low, and the ripple amplitude is inversely proportional to the square of the switching frequency of the power switch, capable of providing a high-quality output voltage.

[0033] 3. A buck DC-DC conversion circuit provided by the present application can suppress or eliminate the zero-crossing crossover distortion of the inductor current, making the total current distortion tend to zero, obtaining a near unity power factor on the grid side, preventing harmonic current from polluting the grid; it has a slightly stronger boosting ability, so it can increase the output voltage range of the subsequent voltage source inverter, expand the constant torque range of the motor, and be able to drive a load with a larger power; the power switch S2 can be omitted, and it has a wide range of application scenarios and can be applied to the fields of commerce, home appliances, communication, charging piles, and wireless power transmission for automobiles. The circuit structure is simple and the operability is strong. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] By reading the following detailed description of the non-limiting embodiments with reference to the accompanying drawings, other features, objects, and advantages of the present application will become more apparent:

[0035] Figure 1 It is a topological schematic diagram of a buck DC-DC conversion circuit in an embodiment of the present application.

[0036] Figure 2 It is a topological schematic diagram of another buck DC-DC conversion circuit in an embodiment of the present application.

[0037] Figure 3 It is a topological schematic diagram of yet another buck DC-DC conversion circuit in an embodiment of the present application.

[0038] Figure 4 It is a topological schematic diagram of a traditional Watkins-Johnson converter in an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] The present application will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made. These all belong to the protection scope of the present application.

[0040] Referring to Figure 1 As shown, a buck DC-DC conversion circuit in an embodiment of the present application includes: a power switch, a high-frequency transformer, an energy storage capacitor, and a power diode.

[0041] The power switch is used to chop the input DC voltage into a high-frequency voltage pulse sequence; the high-frequency transformer is used to convert the high-frequency voltage pulse sequence into primary and secondary side currents and simultaneously adjust the bucking ability; the power diode is used to provide a freewheeling path for the two windings of the high-frequency transformer; the energy storage capacitor is used to store the current sent by the two windings of the secondary side of the transformer and output a DC voltage.

[0042] In the above embodiments of the present application, by transforming the inductor in the original Buck DC-DC converter into a high-frequency transformer or a current transformer and designing a corresponding freewheeling circuit, a lower output DC voltage can be achieved under the same duty ratio, and it has the advantages of strong and adjustable bucking ability, low output voltage ripple, easy implementation and low cost.

[0043] In some possible embodiments, the conversion circuit includes a power switch, a high-frequency transformer, a storage capacitor, two power diodes and a load resistor. Refer to Figure 1 As shown, at this time, the conversion circuit may include: a power switch S1, a high-frequency transformer T1, a storage capacitor C1, two power diodes D1, a second power diode D2 and a load resistor R1. The specific connections of these components are as follows:

[0044] The drain d1 of the power switch S1 is connected to the positive pole of the input power supply Ui, the source of the power switch S1 is connected to the primary terminal 1 of the high-frequency transformer T1 and the cathode of the second power diode D2; the gate g1 of the power switch S1 is connected to the driver output, and the primary terminal 2 of the high-frequency transformer T1 is connected to the secondary terminal 3, the anode of the second power diode D2, and the positive pole of the storage capacitor C1 to form the output positive pole, and at the same time is connected to one end of the load resistor R1. The secondary terminal 4 of the high-frequency transformer T1 is connected to the cathode of the first power diode D1, and the anode of the first power diode D1 and the negative pole of the storage capacitor C1 are connected to the negative pole of the input power supply to form the output negative pole, and at the same time are connected to the other end of the load resistor R1.

[0045] In the above embodiments of the present application, the output terminal and the input terminal of the buck DC-DC conversion circuit are grounded together, the output voltage polarity is the same as the input voltage polarity, the circuit structure is simple, and the high-frequency transformer T1 operates at a high frequency, having a small volume and a light mass.

[0046] Specifically, the output terminal of the storage capacitor C1 is grounded together with the input terminal, and the output voltage polarity is the same as the input voltage polarity.

[0047] In the above Figure 1 shown embodiments of the present application, for the buck DC-DC conversion circuit, its working principle is: in CCM, the power switch S1 has two working conditions:

[0048] When the power switch S1 is turned on, the input voltage Ui is applied between the primary terminal 1 of the high-frequency transformer T1 and the negative pole of the DC voltage. A current is formed through the inductance of the primary coil to charge the energy storage capacitor C1, forming a first current closed loop. At the same time, the induced voltage of the primary coil of the high-frequency transformer T1 has a positive polarity on the left and a negative polarity on the right, and the induced voltage of its secondary side has a positive polarity on the right and a negative polarity on the left. The formed current flows through the energy storage capacitor C1 and the first power diode D1, forming a second current closed loop, and at the same time supplying power to the energy storage capacitor C1 and the load resistor R1.

[0049] When the power switch S1 is turned off, the primary coil of the high-frequency transformer T1 continues to flow through the second power diode D2. The voltage across the primary terminals is approximately zero. The induced voltage of the secondary coil of the high-frequency transformer T1 has a positive polarity on the right and a negative polarity on the left, and the direction of the continuous current remains unchanged. The formed current still flows through the energy storage capacitor C1 and the first power diode D1, and the energy storage capacitor C1 is charged. At the same time, the energy storage capacitor C1 supplies power to the load resistor R1.

[0050] Among them, the power switch S1 ensures the current continuity of the positive line at the front end of the energy storage capacitor C1; the amplitude of the voltage ripple of the energy storage capacitor is inversely proportional to the square of the switching frequency of the power switch S1.

[0051] In this application, through the on and off of the power switch and the inductance effect of the high-frequency transformer, the effective step-down of the input voltage and the charging of the energy storage capacitor are realized. At the same time, the current continuity of the positive line at the front end of the energy storage capacitor is ensured, the amplitude of the voltage ripple of the energy storage capacitor is reduced (inversely proportional to the square of the switching frequency of the power switch), and the stability and quality of the output voltage are also improved.

[0052] In some specific embodiments, the conversion circuit can also be composed of two power switches, a high-frequency transformer, an energy storage capacitor, a power diode, and a load resistor. Refer to Figure 2 As shown, at this time, the conversion circuit includes: the input power supply Ui, the first power switch S1, the second power switch S2, the high-frequency transformer T1, the energy storage capacitor C1, the power diode D1, and the load resistor R1. The specific connections of these components are as follows:

[0053] The drain d1 of the first power switch S1 is connected to the positive terminal of the input power supply Ui. The source s1 of the first power switch S1 is connected to the primary terminal 1 of the high-frequency transformer T1 and the drain d2 of the second power switch S2. The gate g1 of the first power switch S1 is connected to the driver output. The primary terminal 2 of the high-frequency transformer T1 is connected to the secondary terminal 3, the source s2 of the second power switch S2, and the positive terminal of the energy storage capacitor C1 to form the output positive terminal. At the same time, it is connected to one end of the load resistor R1. The gate g2 of the second power switch S2 is connected to the driver output. The secondary terminal 4 of the high-frequency transformer T1 is connected to the cathode of the power diode D1. The anode of the power diode D1 and the negative terminal of the energy storage capacitor C1 are connected to the negative terminal of the input power supply Ui to form the output negative terminal. At the same time, it is connected to the other end of the load resistor R1.

[0054] Among them, the second power switch S2 can be the second power MOSFET S2.

[0055] In the above Figure 2 In the illustrated embodiment, the operating principle of the buck DC-DC conversion circuit is as follows: In CCM, the power switch S1 has two operating conditions:

[0056] When the first power switch S1 is turned on, the input power supply Ui is applied between the primary terminal 1 of the high-frequency transformer T1 and the negative terminal of the DC voltage, and a current is formed through the primary coil inductance to charge the energy storage capacitor C1, forming the first current closed loop. At the same time, the induced voltage polarity of the primary coil inductance of the high-frequency transformer T1 is positive on the left and negative on the right, and the induced voltage polarity of its secondary side is positive on the right and negative on the left. The formed current flows through the energy storage capacitor C1 and the power diode D1, forming the second current closed loop, and the energy storage capacitor C1 supplies power to the load resistor R1.

[0057] When the first power switch S1 is turned off, the primary coil of the high-frequency transformer T1 continues to flow through the body of the second power switch S2, and the voltage across the primary terminals is approximately zero. The induced voltage polarity of the secondary coil of the high-frequency transformer T1 is positive on the right and negative on the left, and the freewheeling direction remains unchanged. The formed current still flows through the energy storage capacitor C1 and the power diode D1, and the energy storage capacitor C1 is charged. At the same time, the energy storage capacitor C1 supplies power to the load resistor R1.

[0058] In some specific embodiments, the conversion circuit can also be composed of two power switches, a high-frequency transformer, an energy storage capacitor, and a load resistor. Referring to Figure 3 As shown, the conversion circuit includes: the input power supply Ui, the first power switch S1, the second power switch S2, the high-frequency transformer T1, the energy storage capacitor C1, and the load resistor R1. The specific connections of these components are as follows:

[0059] The drain d1 of the first power switch S1 is connected to the positive pole of the input power supply Ui. The source s1 of the first power switch S1 is connected to the primary terminal 1 of the high-frequency transformer T1 and the drain d2 of the second power switch S2. The gate g1 of the first power switch S1 is connected to the corresponding driver output. The primary terminal 2 of the high-frequency transformer T1 is connected to the secondary terminal 3, the source s2 of the second power switch S2, and the positive pole of the energy storage capacitor C1 to form the output positive pole, which is also connected to one end of the load resistor R1. The gate g2 of the second power switch S2 is connected to the corresponding driver output. The secondary terminal 4 of the high-frequency transformer T1 is connected to the negative pole of the energy storage capacitor C1 and the negative pole of the input power supply Ui to form the output negative pole, which is also connected to the other end of the load resistor R1.

[0060] In the above Figure 3 In the shown embodiment, the working principle of the buck DC-DC conversion circuit is as follows: In CCM, the power switch S1 has two operating conditions:

[0061] When the first power switch S1 is triggered to conduct, the second power switch S2 is turned off. The input power supply Ui is applied between the primary terminal 1 of the high-frequency transformer T1 and the negative pole of the DC voltage, and a current is formed through the inductance of the primary coil to charge the energy storage capacitor C1, forming the first current closed loop. At the same time, the induced voltage polarity of the primary coil of the high-frequency transformer T1 is positive on the left and negative on the right, and the induced voltage polarity of its secondary side is positive on the right and negative on the left. The formed current flows through the energy storage capacitor C1 and through the secondary terminal 4 of the high-frequency transformer T1, forming the second current closed loop. At the same time, the energy storage capacitor C1 supplies power to the load resistor R1.

[0062] When the first power switch S1 is turned off, the second power switch S2 is triggered to conduct. The primary coil of the high-frequency transformer T1 continues to flow current through the body of the second power switch S2, and the voltage across the primary terminals is approximately zero. The induced voltage polarity of the secondary coil of the high-frequency transformer T1 is positive on the right and negative on the left, and the direction of the continuous current remains unchanged. The formed current flows through the energy storage capacitor C1 and through the secondary terminal 4 of the high-frequency transformer T1, and the energy storage capacitor C1 is charged. At the same time, the energy storage capacitor C1 supplies power to the load resistor R1.

[0063] Specifically, when the duty ratio d of the conduction time to the off time of the power switch S1 is a fixed value d ∈ [0, 1], by adjusting the size of d and k 21 the degree of reduction of the output voltage can be adjusted;

[0064] Among them, the ratio of the output voltage of the energy storage capacitor to the input voltage is

[0065] In the formula, U o is the output voltage; U iVin is the input voltage; n2 is the number of turns of the secondary coil of the transformer; n1 is the number of turns of the primary coil of the transformer; d is the ratio of the on-time to the off-time of the power switch; k 21 is the ratio of the number of turns of the secondary coil to the number of turns of the primary coil.

[0066] In all of the above embodiments, when the first power switch S1 is in the on and off states, it charges the energy storage capacitor C1 and supplies power to the load resistor R1 at the same time. When the circuit reaches a steady state, a relatively stable output DC voltage is formed. The magnitude of the output voltage depends on the ratio of the on-time to the off-time of the power switch and the turns ratio n2 / n1 of the high-frequency transformer.

[0067] When the first power switch S1 is in the on or off state, it can not only charge the energy storage capacitor C1 to ensure the storage and release of energy, but also continuously supply power to the load resistor R1. After the circuit reaches a steady state, a relatively stable output DC voltage is formed. The magnitude of the voltage mainly depends on two factors: one is the ratio of the on-time to the off-time of the power switch S1, which determines the energy transfer efficiency in the circuit; the other is the turns ratio n2 / n1 of the high-frequency transformer T1, which determines the voltage rise and fall amplitude. Therefore, by adjusting these two parameters, the magnitude of the output voltage can be accurately controlled.

[0068] In a specific application example, in the above step-down DC-DC conversion circuit, the parameter settings of each functional module and electronic component are as follows:

[0069] Input voltage: DC 1500V;

[0070] Output voltage: DC 24V;

[0071] Output power level: 200W, or not limited;

[0072] Switching frequency: 50kHz, or 100kHz, or others;

[0073] Power switches S1 and S2: SiC power MOSFET 35A@85°, 1700V:

[0074] Power diodes D1 and D2: Reverse fast recovery type, 35A@85°, 650V;

[0075] High-frequency transformer T1: Select the primary and secondary parameters according to the power level and switching frequency, including self-inductance, current-carrying capacity and turns ratio, such as 200μF / 200μF, n2 / n1 = 1:1 or others, AC withstand voltage 1500V;

[0076] Electrolytic capacitor C1: 220μF, withstand voltage 47V.

[0077] The buck DC-DC conversion circuit provided by the above embodiments in this application can suppress or eliminate the zero-crossing crossover distortion of the inductor current, making the total current distortion tend to zero, obtaining a near unity power factor on the grid side, preventing harmonic current from polluting the grid; it has a slightly stronger boost capability, so it can increase the output voltage range of the subsequent voltage source inverter, expand the constant torque range of the motor, and be able to drive a load with a greater power; the power switch S2 can be omitted, and it has a wide range of applications and can be applied to the fields of commerce, household appliances, communication, charging piles, and wireless power transmission for automobiles. The circuit structure is simple and the operability is strong.

[0078] The specific embodiments of this application have been described above. It should be understood that this application is not limited to the above specific implementation manners, and those skilled in the art can make various deformations or modifications within the scope of the claims, which does not affect the essence of this application. The above preferred features can be used in any combination without conflict.

Claims

1. A step-down DC-DC conversion circuit, characterized in that, It includes: A power switch, a high-frequency transformer, an energy storage capacitor, and a power diode; The power switch is used to chop the input DC voltage into a high-frequency voltage pulse sequence; The high-frequency transformer is used to convert the high-frequency voltage pulse sequence into primary and secondary side currents and simultaneously adjust the step-down ability; The power diode is used to provide a freewheeling path for the two windings of the high-frequency transformer; The energy storage capacitor is used to store the current sent by the two windings of the secondary of the transformer and output a DC voltage.

2. The step-down DC-DC conversion circuit according to claim 1, wherein When the conversion circuit includes one of the power switches, one of the high-frequency transformers, one of the energy storage capacitors, two of the power diodes, and one of the load resistors, it includes: a power switch S1, a high-frequency transformer T1, an energy storage capacitor C1, two power diodes D1, a second power diode D2, and a load resistor R1; The drain d1 of the power switch S1 is connected to the positive pole of the input power supply Ui, and the source of the power switch S1 is connected to the primary terminal 1 of the high-frequency transformer T1 and the cathode of the second power diode D2; the gate g1 of the power switch S1 is connected to the output of the driver, and the primary terminal 2 of the high-frequency transformer T1 is connected to the secondary terminal 3, the anode of the second power diode D2, and the positive pole of the energy storage capacitor C1 to form an output positive pole, and is simultaneously connected to one end of the load resistor R1. The secondary terminal 4 of the high-frequency transformer T1 is connected to the cathode of the first power diode D1, and the anode of the first power diode D1 and the negative pole of the energy storage capacitor C1 are connected to the negative pole of the input power supply to form an output negative pole, and are simultaneously connected to the other end of the load resistor R1.

3. A step-down DC-DC conversion circuit according to claim 2, characterized in that, The output terminal and the input terminal of the energy storage capacitor C1 are common ground, and the output voltage polarity is the same as the input voltage polarity; When the power switch S1 is turned on, the input voltage Ui is applied between the primary terminal 1 of the high-frequency transformer T1 and the negative pole of the DC voltage, and a current is formed through the inductance of the primary coil to charge the energy storage capacitor C1, forming a first current closed loop; at the same time, the induced voltage polarity of the primary coil of the high-frequency transformer T1 is positive on the left and negative on the right, and the induced voltage polarity of its secondary side is positive on the right and negative on the left. The formed current flows through the energy storage capacitor C1 and the first power diode D1 to form a second current closed loop, and at the same time, the energy storage capacitor C1 supplies power to the load resistor R1; When the power switch S1 is turned off, the primary coil of the high-frequency transformer T1 freewheels through the second power diode D2, and the voltage across the primary ends is approximately zero. The induced voltage of the secondary coil of the high-frequency transformer T1 is positive on the right and negative on the left, and the freewheeling direction remains unchanged. The formed current still flows through the energy storage capacitor C1 and the first power diode D1, and the energy storage capacitor C1 is charged; at the same time, the energy storage capacitor C1 supplies power to the load resistor R1; Among them, the power switch S1 ensures the current continuity of the positive line at the front end of the energy storage capacitor C1; the voltage ripple amplitude of the energy storage capacitor is inversely proportional to the square of the switching frequency of the power switch S1.

4. A buck DC-DC conversion circuit according to claim 3, characterized in that, When the ratio d of the conduction time of the power switch S1 to the tube section time is a fixed value d ∈ [0, 1], by adjusting d and k 21 magnitude, adjust the degree of reduction of the output voltage; Among them, the ratio of the output voltage of the energy storage capacitor to the input voltage is Where, U o is the output voltage; U i is the input voltage; n2 is the number of turns of the secondary coil of the transformer; n1 is the number of turns of the primary coil of the transformer; d is the ratio of the on-time to the off-time of the power switch; k 21 is the ratio of the number of turns of the secondary coil to the number of turns of the primary coil.

5. A step-down DC-DC conversion circuit according to claim 1, characterized in that, When the conversion circuit consists of two of the said power switches, one of the said high-frequency transformers, one of the said energy storage capacitors, one of the said power diodes, and one of the said load resistors, it includes: input power supply Ui, first power switch S1, second power switch S2, high-frequency transformer T1, energy storage capacitor C1, power diode D1, and load resistor R1; The drain d1 of the first power switch S1 is connected to the positive pole of the input power supply Ui. The source s1 of the first power switch S1 is connected to the primary terminal 1 of the high-frequency transformer T1 and the drain d2 of the second power switch S2. The gate g1 of the first power switch S1 is connected to the driver output. The primary terminal 2 of the high-frequency transformer T1 is connected to the secondary terminal 3, the source s2 of the second power switch S2, and the positive pole of the energy storage capacitor C1 to form the output positive pole. At the same time, it is connected to one end of the load resistor R1. The gate g2 of the second power switch S2 is connected to the driver output. The secondary terminal 4 of the high-frequency transformer T1 is connected to the cathode of the power diode D1. The anode of the power diode D1 and the negative pole of the energy storage capacitor C1 are connected to the negative pole of the input power supply Ui to form the output negative pole. At the same time, it is connected to the other end of the load resistor R1.

6. A step-down DC-DC conversion circuit according to claim 5, characterized in that When the first power switch S1 is turned on, the input power supply Ui is applied between the primary terminal 1 of the high-frequency transformer T1 and the negative pole of the DC voltage, and a current is formed through the inductance of the primary coil to charge the energy storage capacitor C1, forming a first current closed loop. At the same time, the induced voltage polarity of the primary coil of the high-frequency transformer T1 is positive on the left and negative on the right, and the induced voltage polarity of its secondary side is positive on the right and negative on the left. The formed current flows through the energy storage capacitor C1 and the power diode D1 to form a second current closed loop, and the energy storage capacitor C1 supplies power to the load resistor R1; When the first power switch S1 is turned off, the primary coil of the high-frequency transformer T1 continues to flow through the body of the second power switch S2, and the voltage across the primary ends is approximately zero. The induced voltage polarity of the secondary coil of the high-frequency transformer T1 is positive on the right and negative on the left, and the direction of the continuous current remains unchanged. The formed current still flows through the energy storage capacitor C1 and the power diode D1, and the energy storage capacitor C1 is charged; at the same time, the energy storage capacitor C1 supplies power to the load resistor R1.

7. A step-down DC-DC conversion circuit according to claim 1, characterized in that, When the conversion circuit consists of two of the said power switches, one of the said high-frequency transformers, one of the said energy storage capacitors, and one of the said load resistors, it includes: input power supply Ui, first power switch S1, second power switch power S2, high-frequency transformer T1, energy storage capacitor C1, and load resistor R1; The drain d1 of the first power switch S1 is connected to the positive pole of the input power supply Ui. The source s1 of the first power switch S1 is connected to the primary terminal 1 of the high-frequency transformer T1 and the drain d2 of the second power switch S2. The gate g1 of the first power switch S1 is connected to the corresponding driver output. The primary terminal 2 of the high-frequency transformer T1 is connected to the secondary terminal 3, the source s2 of the second power switch S2, and the positive pole of the energy storage capacitor C1 to form the output positive pole and is connected to one end of the load resistor R1. The gate g2 of the second power switch S2 is connected to the corresponding driver output. The secondary terminal 4 of the high-frequency transformer T1 is connected to the negative pole of the energy storage capacitor C1 and the negative pole of the input power supply Ui to form the output negative pole and is connected to the other end of the load resistor R1.

8. A step-down DC-DC conversion circuit according to claim 7, wherein, When the first power switch S1 is triggered to conduct, the second power switch S2 is turned off. The input power supply Ui is applied between the primary terminal 1 of the high-frequency transformer T1 and the negative pole of the DC voltage, and a current is formed through the inductance of the primary coil to charge the energy storage capacitor C1, forming a first current closed loop. At the same time, the induced voltage polarity of the primary coil inductance of the high-frequency transformer T1 is positive on the left and negative on the right, and the induced voltage polarity of its secondary side is positive on the right and negative on the left. The formed current flows through the energy storage capacitor C1 and through the secondary terminal 4 of the high-frequency transformer T1, forming a second current closed loop. At the same time, the energy storage capacitor C1 supplies power to the load resistor R1. When the first power switch S1 is turned off, the second power switch S2 is triggered to conduct. The primary coil of the high-frequency transformer T1 continues to flow through the body of the second power switch S2, and the voltage across the primary terminals is approximately zero. The induced voltage polarity of the secondary coil of the high-frequency transformer T1 is positive on the right and negative on the left, and the freewheeling direction remains unchanged. The formed current flows through the energy storage capacitor C1 and through the secondary terminal 4 of the high-frequency transformer T1, and the energy storage capacitor C1 is charged. At the same time, the energy storage capacitor C1 supplies power to the load resistor R1.

9. A step-down DC-DC conversion circuit according to any one of claims 1-8, characterized in that, In the on and off states of the first power switch S1, the energy storage capacitor C1 is charged and the load resistor R1 is supplied with power at the same time. A relatively stable output DC voltage is formed in the steady state. The output voltage is related to the ratio of the on time to the off time of the power switch and the turns ratio n2 / n1 of the high-frequency transformer.

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