Micropower DCDC converter
By adopting a combination of square ring structure transformer and resonant capacitors in a micro-power DCDC converter, the problem of inability to shrink and poor consistency in high isolation cases is solved, and higher core window utilization and better isolation performance are achieved, reducing production costs.
Patent Information
- Application Number
- CN202411741304.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-29
- Publication Date
- 2025-02-28
AI Technical Summary
In high isolation cases, the volume of existing micro-power DCDC converters cannot be further reduced, and the isolation voltage withstand voltage, isolation capacitor, and leakage inductance are poor, and the consistency of mechanical winding transformers is poor and the defect rate is high, and the cost is high.
A square ring structure transformer is adopted, and the core is formed as a ferrite material, forming four side pillars, and the two windings are wound on the two side pillars of the core, forming a non-crossing and overlapping layout positioning, and adding resonant capacitance to one end of the transformer to form an LC series oscillation circuit to weaken the leakage inductance voltage.
The utilization rate of the magnetic core window area is improved, the overall volume of high-isolation products is reduced, the consistency of isolation voltage withstand voltage, isolation capacitors, and leakage inductance is ensured, the product production cost is reduced, and the stability of the output voltage is improved through resonant capacitors.
Smart Images
Figure 00000000_0000_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a switching power supply for realizing DC-DC conversion in medical equipment and photovoltaic energy storage industries, and in particular to a micropower DCDC converter for applications with high isolation and voltage withstand requirements. Background Art
[0002] With the continuous development of the medical and photovoltaic energy storage industries, the performance and consistency requirements for micro-power 3W and below isolated converter power products are becoming increasingly higher. Figure 1 The figure shows the schematic circuit diagram of a commonly used micropower DC-DC converter. This circuit is for a micropower DC-DC converter with a power of 3W or less and input-output isolation of 5000VDC / 4000VAC or higher. This micropower DC-DC converter is a micropower, high-isolation open-loop circuit with electrical isolation. The circuit consists of an input capacitor C1, a full-bridge micropower driver chip U1, a high-isolation transformer T, a bridge rectifier circuit D, and an output capacitor C2. The high-isolation transformer T includes a magnetic core and two windings: an input winding (where Lr and Lm represent the equivalent leakage inductance and magnetizing inductance of the input primary winding, respectively) and an output winding. For products with an isolation withstand voltage of 5000VDC / 4000VAC or higher, at least one side of the input or output winding of the transformer T must use triple-insulated wire, and the input and output windings must be wound separately on opposite ends of the magnetic core without overlapping.
[0003] Traditional transformer cores use circular, closed cores. Therefore, when winding thicker triple-insulated wire, the following problems may occur:
[0004] ① The ring structure will form a natural landslide, and the wire will easily slip during the winding process, resulting in the wires not being able to be closely attached to each other, thereby reducing the utilization rate of the core window area. This problem is particularly obvious when using three-layer insulated wire with a thicker wire diameter;
[0005] ② If Figure 2 As shown, since the inner diameter of the ring is always smaller than the outer diameter, corresponding to the first layer of winding S1, even if the three layers of insulated wires can be tightly close together on the inner diameter, gaps will be left between the wires on the outer diameter. When the second layer of winding S2 is wound, some wires will inevitably fall into the outer diameter gaps of the first layer, thereby squeezing the first layer of wires and causing them to slide outward. Therefore, part of the second layer of wires will not overlap with the first layer, but will occupy the outer and inner diameter positions of the first layer of wires, thereby further reducing the utilization rate of the core window area.
[0006] High-isolation products require that the input and output windings be separated and non-overlapping. The ideal design is for the winding layers on each side to overlap, thereby reducing the wiring area. In practice, when this happens, the windings are moved outward, increasing the wiring area and reducing the window area utilization. Therefore, to avoid overlap between the input and output windings, a larger magnetic core should be selected, which increases the product volume.
[0007] In addition, since the winding sliding is uncontrollable, the sliding range of each product is different, so the consistency of winding-related indicators such as isolation voltage, isolation capacitance, and leakage inductance is poor.
[0008] At the same time, when winding thick wires such as three-layer insulated wires, mechanically wound transformers have poor consistency and high defective rates, and manual winding is often required, which is costly. Summary of the Invention
[0009] In view of this, the present invention aims to overcome the above-mentioned design problems of transformers in the prior art micro-power DCDC converters and provides a square ring structure transformer to solve the problems of further volume reduction and poor consistency of isolation withstand voltage, isolation capacitance, and leakage inductance in the application of high-isolation micro-power DCDC converter products.
[0010] In order to achieve the above object, the present invention adopts the following technical solutions:
[0011] A micropower DC-DC converter, suitable for open-loop circuit topologies with power of 3W or less and input-output isolation of 5000VDC / 4000VAC or above, includes a transformer, which includes a magnetic core and two windings. The magnetic core is a square ring structure, integrally formed from ferrite material, and has four side legs. The two windings are respectively wound around the two side legs of the magnetic core, forming a non-crossing and overlapping layout of the two windings.
[0012] Preferably, the magnetic core is a rectangular ring structure, and the two windings are respectively wound on two symmetrical short side columns; or the two windings are respectively wound on two symmetrical long side columns.
[0013] Preferably, the rectangular ring structure of the magnetic core has an aspect ratio between 7:3 and 5:5.
[0014] Preferably, the longest side column length of the magnetic core is less than 15 mm.
[0015] Preferably, at least one of the two windings uses a three-layer insulated wire.
[0016] Preferably, the wire diameters of the two windings are less than 0.25 mm, and the wire diameter of one winding is thicker than that of the other winding.
[0017] Preferably, the PCB circuit board is a carrier board for electronic components mounted with a DCDC converter circuit with a power of 3W or less and input and output isolation of more than 5000VDC / 4000VAC.
[0018] Preferably, the winding of the transformer is formed by mechanical winding.
[0019] Preferably, the circuit on the PCB circuit board is an open-loop circuit for DCDC conversion, one end of the transformer is first connected in series with a resonant capacitor and then connected to the circuit, and the resonant capacitor can form an LC series oscillation circuit with the leakage inductance of the transformer.
[0020] Preferably, the circuit on the PCB circuit board is an open-loop circuit for DCDC conversion, one end of the transformer is first connected in series with a resonant capacitor and then connected to the circuit, and the capacitance of the resonant capacitor is 10nF to 4.7uF.
[0021] The beneficial effects of the micropower DCDC converter of the present invention are:
[0022] ① The input winding and output winding are blocked by the two side columns without winding. The input winding and output winding are limited to the position on or near the winding side columns, so that the input winding and output can fully ensure that they do not cross and overlap. The two ends of each winding are stable in the position of the magnetic core and are not easy to slide. Therefore, multi-turn windings can be stacked in multiple layers, and the core window area utilization rate is high, so that smaller products can be made.
[0023] ② Since the input winding and the output winding do not cross or overlap, the isolation voltage, isolation capacitance, and leakage inductance are consistent.
[0024] ③ The winding side column is a straight line, which is more suitable for mechanical winding, not easy to slide, better consistency, and can reduce product production costs.
[0025] ④ The addition of resonant capacitors can improve the circuit and transformer structure by combining them to overcome the inherent circuit performance disadvantage of the square ring core transformer, which is that the leakage inductance is large due to unilateral changes in the structure, affecting the output voltage.
[0026] The advantage of the micro-power DCDC converter of the present invention is that it utilizes the structure of the square ring magnetic core and is applied to high-isolation open-loop converters where the input winding and the output winding need to be completely separated, thereby improving the utilization rate of the magnetic core window area. At the same time, when a high number of turns and thick wire diameter are used, it ensures that the input winding and the output winding do not cross or overlap. The disadvantages of the square ring magnetic core are weakened by adding a series resonant capacitor, making it more suitable for applications in high-isolation situations. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] Figure 1 This is the circuit schematic diagram of the micropower DCDC converter;
[0028] Figure 2Schematic diagram of the transformer structure of the existing solution;
[0029] Figure 3 This is a circuit diagram of a micro-power DCDC converter according to the present invention;
[0030] Figure 4 Schematic diagram of the transformer structure of the present invention;
[0031] Figure 5 This is a schematic structural diagram of the square ring core transformer of the present invention assembled on a PCB circuit board;
[0032] Figure 6 This is a three-dimensional diagram of the square ring core transformer of the present invention assembled on a PCB circuit board;
[0033] Figure 7 This is a three-dimensional diagram of another structure of the square ring core transformer of the present invention assembled on a PCB circuit board.
[0034] The reference numerals in the above drawings are as follows:
[0035] 10. Magnetic core, 20. Winding, 201. Input winding, 202. Output winding, 2011.2012. Both ends of input winding 201, 30. PCB circuit board, S1. First layer winding, S2. Second layer winding DETAILED DESCRIPTION
[0036] like Figure 3 As shown in the figure, it is a circuit schematic diagram of the micro-power DCDC converter of the present invention. From the product circuit point of view, the circuit is a micro-power DCDC converter with a power of 3W or less and input and output isolation of more than 5000VDC / 4000VAC. The micro-power DCDC converter is a micro-power high-isolation open-loop circuit with electrical isolation. The circuit consists of an input capacitor C1, a full-bridge micro-power driver chip U1, a resonant capacitor Cr, a high-isolation transformer T (where Lr and Lm are equivalent schematic representations of the leakage inductance and excitation inductance of the input primary winding, respectively), a bridge rectifier circuit D, and an output capacitor C2.
[0037] like Figure 4 and Figure 5 Figure 1 shows a schematic diagram of the transformer unit and assembly structure of the micropower DC-DC converter of the present invention. From a product perspective, the high-isolation transformer T of the micropower DC-DC converter is assembled on a PCB circuit board 30 and includes a magnetic core 10 and two windings 20. The magnetic core 10 is a square ring structure transformer, integrally molded from ferrite material, and has four side legs. The two windings 20 are the input winding 201 and the output winding 202, respectively, wound around the two side legs of the magnetic core, forming a non-intersecting and overlapping layout for the two windings. Preferably, the longest side leg of the magnetic core 10 is less than 15 mm in length.
[0038] like Figure 3 、 Figure 5 and Figure 6 As shown, the transformer includes a rectangular annular closed magnetic core, an input winding, and an output winding. Preferably, the input winding 201 and the output winding 202 are respectively on the two symmetrical short side columns of the rectangular annular closed magnetic core 10, so as to physically form a longer isolation distance between the two windings and a larger mechanical winding operation window. The two ends 2011 and 2012 of the input winding 201 are electrically connected to the resonant capacitor Cr of the circuit input part and the full-bridge micro-power driver chip U1 through the pads of the PCB circuit board 30, and the output winding 202 is electrically connected to the rectifier circuit D. Figure 7 As shown, the input winding 201 and the output winding 202 are respectively on the two long side columns of the rectangular ring-shaped closed magnetic core 10 to obtain a larger winding area. The rectangular ring structure of the magnetic core 10 has an aspect ratio between 7:3 and 5:5.
[0039] like Figure 6 and Figure 7 As shown, at least one of the two windings of the transformer uses thick-diameter insulated wire, meaning one winding has a thicker wire diameter than the other. The preferred thick-diameter wire is triple-insulated wire with a diameter of less than 0.25 mm, which is used to achieve input and output isolation of 5000 VDC / 4000 VAC and above. The transformer windings can be mechanically wound.
[0040] Unlike the conventional use of circular magnetic cores, the magnetic core is a square ring structure, and the winding area of the four side columns is fixed and controllable. In this embodiment, the symmetrical narrow sides of the rectangular ring magnetic core are selected to wind the input winding and the output winding. Due to the physical barrier of the wide side columns that are not wound, if the number of winding turns is large and multi-layer winding is required, the layers will be stably superimposed within the narrow sides and will not slide to the opposite sides, thereby ensuring that the input winding and the output winding do not cross and overlap. This can not only improve the utilization rate of the core window area, thereby reducing the overall volume of high-isolation products, but also make the consistency of isolation withstand voltage, isolation capacitance, and leakage inductance better, and is suitable for mechanical winding of thick wire diameter windings, and is particularly suitable for micro-power products with high isolation withstand voltage requirements. Preferably, the square ring magnetic core used in the transformer can be rectangular or square, and its corners are allowed to be arc angles to facilitate core demoulding. If a rectangular ring structure is used, it can be preferably but not limited to winding on two symmetrical narrow sides, thereby increasing the isolation distance between the input winding and the output winding.
[0041] Since square ring cores do not need to consider the problem of reserving larger core space due to winding sliding, their volume can be smaller than circular ring cores. In actual product application, the product volume can be reduced from "length 19.65mm*width 9.80mm*height 12.50mm" to "length 19.65mm*width 7.90mm*height 10.16mm", reducing the overall product volume by about 34%.
[0042] On the other hand, since the input and output windings of the square ring core are blocked by the unwound side columns, its physical blocking effect is better and the blocking distance is longer than that of products using traditional circular ring cores. This means that the coupling between the input and output windings becomes worse and the leakage inductance becomes larger.
[0043] For an open-loop circuit (i.e., a circuit without a feedback loop, whose output voltage follows the input voltage and is affected by circuit parameters), leakage inductance will divide part of the voltage, causing the output voltage to drop.
[0044] Take a micropower high isolation DC-DC converter as an example. Figure 1 As shown, this converter consists of an input capacitor C1, a full-bridge micro-power driver chip U1, a high-isolation transformer T (where Lr and Lm are equivalent schematic representations of the leakage inductance and excitation inductance of the input primary winding, respectively), a rectifier circuit D (such as a bridge rectifier circuit), and an output capacitor C2.
[0045] To more concisely describe the issue of leakage inductance affecting output voltage, the circuit is assumed to be an ideal circuit, that is, ignoring the voltage drop of the power tube, the circuit wiring resistance, and the dead zone (that is, there is no dead zone, the duty cycle of the first half cycle and the second half cycle is 50%, and the total duty cycle is 100%). Then, according to the transformer principle, the output voltage of this open-loop converter can be obtained as:
[0046] Where Vo is the output voltage, Vin is the input voltage, Vr is the leakage inductance voltage, and N is the transformer turns ratio.
[0047] Assume that the input voltage of this converter is 5V, the output power is 1W (output voltage is 5V); the efficiency is 80%; the switching frequency is 300KHz; the primary inductance is 180uH, the leakage inductance accounts for 1% (ie, 1.8uH), and the turns ratio is 1:1 (ie, N=1).
[0048] Since the primary leakage inductance Lr cannot be coupled to the secondary side, the primary current will all flow through the leakage inductance and generate an induced electromotive force. The formula derived from Faraday's law can be used to calculate the voltage across the leakage inductance:
[0049] Where Vr is the leakage inductance voltage, Lr is the leakage inductance, P is the circuit power, η is the circuit efficiency, Vin is the input voltage, and f is the circuit frequency.
[0050] Substituting Vr into Formula 1, we can obtain the output voltage Vo = 4.865V.
[0051] The above example shows that the leakage inductance only accounts for 1% of the primary inductance. If the proportion is further increased, the above method can be used to obtain:
[0052] Leakage inductance ratio 1％ 2％ 3％ 4％ 5％ Output voltage 4.865V 4.730V 4.595V 4.460V 4.325V
[0053] From an open-loop circuit's perspective, leakage inductance may seem to account for a small proportion, but since its leakage inductance cannot be coupled to the secondary side, the entire primary current will flow through the leakage inductance and generate a higher induced voltage, which has a significant impact on the output voltage.
[0054] Therefore, in high-isolation open-loop circuit applications, the leakage inductance of square ring cores is larger than that of traditional circular cores, resulting in a lower output voltage. In practical applications, the number of transformer turns needs to be increased to compensate for the output voltage, but this increases costs and affects circuit efficiency. This is an insurmountable performance defect of square ring cores in micropower DCDC converters.
[0055] In order to fully utilize the advantages of the square ring core and solve its performance defects that affect the output voltage, it is preferred to add a resonant capacitor Cr at one end of the transformer, such as Figure 3 As shown. Choosing the appropriate resonant capacitor Cr can form an LC series oscillation circuit with the leakage inductance Lr. The capacitor voltage in the LC oscillation circuit is opposite to the inductor voltage. By using this characteristic, the resonant capacitor forms a voltage in the opposite direction in the circuit, which can weaken the leakage inductance voltage. Then, for the open-loop circuit, the output voltage at this time is
[0056] Where Vc is the voltage drop of the resonant capacitor.
[0057] In addition, the self-resonance point of the leakage inductance and resonant capacitor is Theoretically, if the resonant frequency fr of the leakage inductance is equal to the operating frequency f of the circuit, the inductive reactance of the leakage inductance equals the capacitive reactance of the resonant capacitor, and the LC circuit becomes resistive. At this time, the leakage inductance and the resonant capacitor form equal-amplitude sinusoidal voltages in opposite directions. In other words, Vr and Vc can be completely offset at this time, and the input voltage is all applied to the excitation inductance. At this time, the output voltage reaches the optimal state.
[0058] In practical applications, the primary-side micropower driver chips used in open-loop micropower DC / DC converters are mostly fixed-frequency. Therefore, it's impossible to adjust the circuit's operating frequency, f, to achieve the optimal value of f = fr. Therefore, it's generally necessary to adjust the resonant capacitor to change the LC circuit's self-resonance point, fr, so that it equals or approaches the operating frequency, f. This is typically achieved using a ceramic chip capacitor with a capacitance range of 10nF to 4.7uF.
[0059] Compared to conventional toroidal core windings, due to their naturally sloping structure and the fact that the inner diameter is always smaller than the outer diameter, there are gaps in the outer diameter, making it impossible to ensure a stable stacking between layers. This not only affects the utilization of the core window area, but also cannot guarantee its consistency. There is even a risk that the input and output windings will slide towards each other and overlap. Therefore, in high-isolation applications, it is often necessary to enlarge the core to reduce the risk of the input and output windings colliding and overlapping. This results in the excessive size of micro-power high-isolation products, which cannot be further reduced. At the same time, the consistency of the related isolation withstand voltage, isolation capacitance, and leakage inductance performance is poor.
[0060] Using square ring cores can circumvent these issues. Because the side legs are straight, the windings are symmetrically positioned on both the inner and outer diameters. The physical barrier of the unwound side legs allows windings to be stacked layer by layer. This significantly improves the utilization of the core window area, eliminating the need for a larger core and, consequently, reducing the size of high-isolation products. Furthermore, because the input and output winding ranges are fixed and controllable, the isolation voltage, isolation capacitance, and leakage inductance associated with the windings are more consistent. Furthermore, the straight winding legs of square ring cores more easily meet the requirements of mechanical winding, resulting in higher production efficiency and further reductions in product costs.
[0061] In addition, since the square ring core has a good barrier effect, while bringing advantages, it also reduces the coupling between the input winding and the output winding, thereby increasing the leakage inductance. For open-loop circuits, the leakage inductance will divide the voltage, causing the output voltage to drop. If you choose to use the number of transformer turns to adjust the output voltage, it will increase costs and reduce circuit efficiency.
[0062] In order to overcome the problem of rigid defects in the circuit performance of the square ring core, it is preferred to connect a resonant capacitor Cr in series at one end of the transformer so that the resonant capacitor Cr and the leakage inductance Lr form an LC oscillation circuit. The capacitance of Cr is adjusted, such as a typical value of 100nF, so that its self-resonant frequency fr is equal to or close to the operating frequency f of the circuit. At this time, the LC oscillation circuit is resistive or close to resistive, and the reverse voltage formed by the resonant capacitor offsets or greatly weakens the influence of the leakage inductance voltage. Finally, most of the input voltage is added to the primary side excitation inductance Lm, thereby coupling to the secondary side to form the optimal output voltage.
[0063] In summary, the combination of a square-ring structure transformer and a resonant capacitor, when used in a micro-power high-isolation open-loop converter, can fully utilize the structural advantages of the square-ring core to ensure that the input winding and the output winding are completely separated, while also utilizing the resonant capacitor to mitigate the disadvantage of the square-ring core causing greater leakage inductance and thus affecting the output voltage.
[0064] The above are merely preferred embodiments of the invention. It should be noted that the above preferred embodiments should not be construed as limiting the present invention, and its scope of protection should be determined by the scope defined in the claims. Persons skilled in the art will appreciate that improvements and modifications can be made without departing from the spirit and scope of the present invention, and such improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A micropower DCDC converter, suitable for open-loop circuit topology with power of 3W or less and input-output isolation of more than 5000VDC / 4000VAC, including a transformer, the transformer consisting of a magnetic core and two windings, characterized in that: The magnetic core is a square ring structure, made of ferrite material and formed into one piece, with four side columns; The two windings are respectively wound on the two side columns of the magnetic core, and the two windings are arranged and positioned in a non-crossing and overlapping manner.
2. The micropower DCDC converter according to claim 1, characterized in that: The magnetic core is a rectangular ring structure, and the two windings are respectively wound on two symmetrical short side columns; or the two windings are respectively wound on two symmetrical long side columns.
3. The micropower DCDC converter according to claim 1 or 2, characterized in that: At least one of the two windings uses a triple-layer insulated wire.
4. The micropower DCDC converter according to claim 2, characterized in that: The rectangular ring structure of the magnetic core has a length-to-width ratio between 7:3 and 5:
5.
5. The micropower DCDC converter according to claim 1 or 2, characterized in that: The longest side column length of the magnetic core is less than 15 mm.
6. The micropower DCDC converter according to claim 1 or 2, characterized in that: The wire diameters of the two windings are less than 0.25 mm, and the wire diameter of one winding is thicker than the wire diameter of the other winding.
7. The micropower DCDC converter according to claim 1 or 2, characterized in that: The PCB circuit board is a carrier board for electronic components installed with a DCDC converter circuit with a power of 3W or less and an input and output isolation of more than 5000VDC / 4000VAC.
8. The micropower DCDC converter according to claim 1 or 2, characterized in that: The winding of the transformer is formed by mechanical winding.
9. The micropower DCDC converter according to claim 1 or 2, characterized in that: The circuit on the PCB circuit board is an open-loop circuit for DCDC conversion. One end of the transformer is first connected in series with a resonant capacitor and then connected to the circuit. The resonant capacitor can form an LC series oscillation circuit with the leakage inductance of the transformer.
10. The micropower DCDC converter according to claim 1 or 2, characterized in that: The circuit on the PCB circuit board is an open-loop circuit for DCDC conversion. One end of the transformer is first connected in series with a resonant capacitor and then connected to the circuit. The capacitance of the resonant capacitor is 10nF to 4.7uF.