Micropower DCDC converter and transformer thereof
By using a square ring core and winding design, combined with a resonant capacitor, the problems of low window utilization and poor consistency caused by winding slippage in micropower DC-DC converters are solved, achieving a product design with smaller size and higher consistency, while also improving the output voltage.
Patent Information
- Application Number
- CN202422952102.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-29
- Publication Date
- 2025-12-19
- Estimated Expiration
- 2034-11-29
AI Technical Summary
In existing low-power DC-DC converters, the transformer core structure leads to uncontrollable winding slippage, resulting in low core window area utilization, large product size, poor consistency, and high cost.
The magnetic core and winding design adopts a square ring structure, and the side posts are used to ensure that the input and output windings do not cross or overlap. The leakage inductance is improved by using a series resonant capacitor, thus forming an LC oscillation circuit.
It improves the utilization rate of the magnetic core window area, reduces product size, enhances isolation withstand voltage and leakage inductance consistency, reduces production costs, and improves output voltage through resonant capacitors.
Smart Images
Figure CN223692970U_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The utility model belongs to a kind of for medical equipment and photovoltaic energy storage industry Realization DC-DC conversion switching power supply, specifically related to the micro-power DCDC converter and its transformer in the occasion of high isolation voltage requirement. BACKGROUND
[0002] With the continuous development of medical and photovoltaic energy storage industry, the performance and consistency of micro-power 3W and below isolation converter power supply products are increasingly demanding. Figure 1 As shown in the circuit schematic diagram of a kind of micro-power DCDC converter commonly used at present, the circuit is a micro-power DCDC converter with 3W and below power and input-output isolation above 5000VDC / 4000VAC, the micro-power DCDC converter is a kind of micro-power high-isolation open-loop circuit with electrical isolation, which is composed of input capacitor C1, full-bridge micro-power drive chip U1, high-isolation transformer T, bridge rectifier circuit D and output capacitor C2. Wherein high-isolation transformer T includes magnetic core and two windings, two windings are input winding (wherein Lr and Lm are the equivalent schematic of the leakage inductance and excitation inductance of input primary winding respectively) and output winding. When the isolation voltage of product reaches 5000VDC / 4000VAC isolation or above, at least one side of the input winding or output winding of its transformer T needs to use three-layer insulation wire, and the input winding and output winding need to be wound separately on the magnetic core two ends without overlapping.
[0003] The magnetic core of the transformer of traditional product will select to use circular ring closed magnetic core, so when winding three-layer insulation wire with relatively thick diameter, the following situations will occur:
[0004] ① The circular ring structure will form a natural landslide, and the wire is prone to sliding during winding, which causes the wires to be unable to closely rely on each other, thereby reducing the utilization rate of the window area of the magnetic core, and this problem is particularly obvious when using three-layer insulation wire with relatively thick diameter;
[0005] ②As shown in Figure 2 Because the inner diameter of the circular ring is always smaller than the outer diameter, corresponding to the first layer of winding S1, even if the three-layer insulation wire of the inner diameter can closely rely on each other, but at the outer diameter, there will be a gap between the wires, when winding the second layer of winding S2, the wire material will inevitably fall into the outer diameter gap of the first layer, thereby extruding the first layer wire, making it slide outward, so part of the second layer wire will not overlap on the first layer, but will occupy the outer diameter and inner diameter position of the first layer wire, thereby further reducing the utilization rate of the window area of the magnetic core.
[0006] High isolation product needs input winding and output winding to be separated and not overlapped, ideal design is that each side winding layer is overlapped with each other, so as to reduce the line area, in fact, the winding is moved outward to increase the line area, which leads to the decrease of window area utilization, therefore, in order to avoid the input winding and the output winding from being overlapped, a larger magnetic core is selected, so that the product volume is increased.
[0007] In addition, since the winding sliding is uncontrollable, the sliding range of each product is different, so the consistency of the isolation voltage resistance, the isolation capacitance and the leakage inductance related to the winding is poor.
[0008] Meanwhile, when the thick wire such as three-layer insulated wire is wound, the consistency of the mechanical winding transformer is poor and the failure rate is high, so the artificial winding is often used, which has high cost. Practical new type content
[0009] Therefore, the utility model aims at overcoming the design problem of the transformer in the prior art micro-power DCDC converter, and provides a square ring structure transformer, so as to solve the problems of the further decrease of the volume and the poor consistency of the isolation voltage resistance, the isolation capacitance and the leakage inductance in the application of the high isolation micro-power DCDC converter product.
[0010] In order to achieve the above object, the utility model adopts the following technical scheme:
[0011] A micro-power DCDC converter is a 3W and below power module power supply, comprising a transformer, the transformer is composed of a magnetic core and two windings, the magnetic core is a square ring structure, is integrally formed by adopting ferrite material, and four edge columns are formed; the two windings are wound on two symmetrical edge columns of the magnetic core respectively.
[0012] Preferably, the magnetic core is a rectangular ring structure, and the two windings are wound on two symmetrical short edge columns respectively; or the two windings are wound on two symmetrical long edge columns respectively.
[0013] Preferably, at least one winding of the two windings uses three-layer insulated wire.
[0014] Preferably, the rectangular ring structure of the magnetic core has an aspect ratio of 7:3 to 5:5.
[0015] Preferably, the longest edge column of the magnetic core has a length of less than 15mm.
[0016] Preferably, the three-layer insulated wire used by the winding has a wire diameter of less than 0.25mm.
[0017] Preferably, the wire diameter of the two windings is less than 0.25mm, and the wire diameter of one winding is thicker than that of the other winding, so as to realize the input and output isolation of 5000VDC / 4000VAC and above.
[0018] Preferably, the PCB circuit board is a carrier board for electronic components of a DCDC converter circuit with a power of 3W or less and an input-output isolation of 5000VDC / 4000VAC or more.
[0019] Preferably, the winding of the transformer is mechanically wound.
[0020] Preferably, the circuit on the PCB circuit board is an open-loop circuit for DCDC conversion, and one end of the transformer is connected to the circuit in series with a resonant capacitor, and the resonant capacitor forms an LC series oscillation circuit with the leakage inductance of the transformer.
[0021] Preferably, the circuit on the PCB circuit board is an open-loop circuit for DCDC conversion, and one end of the transformer is connected to the circuit in series with a resonant capacitor, and the resonant capacitor has a capacitance of 10nF to 4.7uF.
[0022] The utility model also provides a transformer, be applicable to 3W and below power's DCDC converter, comprise magnetic core and two windings, the magnetic core is square ring structure, adopts ferrite material integral forming, forms four side columns.
[0023] Preferably, the magnetic core is a rectangular ring structure with an aspect ratio of 7:3 to 5:5.
[0024] Preferably, the magnetic core is a rectangular ring structure with a length of the long side column of less than 15mm.
[0025] Preferably, the two windings use three-layer insulation wire for at least one winding.
[0026] Preferably, the wire diameter of the two windings is less than 0.25mm, and the wire diameter of one winding is thicker than that of the other winding.
[0027] The utility model micro-power DCDC converter has the beneficial effects of:
[0028] ①The input winding and the output winding are blocked by the two side columns without winding, and the input winding and the output winding are limited to the winding side column or the position near the winding side column, so that the input winding and the output winding can be fully ensured not to cross and overlap, the two ends of each winding are stable at the position of the magnetic core and are not easy to slide, so that the multi-turn winding can be stacked in multiple layers, the window area utilization rate of the magnetic core is high, and thus a smaller volume product can be made.
[0029] ②Since the input winding and the output winding do not cross and overlap, the isolation voltage, the isolation capacitance and the leakage inductance have good consistency.
[0030] ③The winding side column is a straight line, which is more suitable for mechanical winding and is not easy to slide, has better consistency and can reduce the production cost of the product.
[0031] ④The addition of resonance capacitor can improve the inherent circuit performance disadvantage of the square ring magnetic core transformer due to the large leakage inductance caused by the unilateral change of the structure by the combination of the circuit and the transformer structure.
[0032] The micro-power DCDC converter has the advantages that the structure of the square ring magnetic core is utilized, is applied to a high-isolation loop converter in which input windings and output windings need to be completely separated, the utilization rate of the window area of the magnetic core is improved, the input windings and the output windings can be overlapped without crossing when high turns and thick wire diameter wire materials are used, and the disadvantages of the square ring magnetic core are weakened by increasing a series resonance capacitor, and the application is more suitable for high-isolation occasions. BRIEF DESCRIPTION OF DRAWINGS
[0033] Figure 1 It is a circuit schematic diagram of the micro-power DCDC converter;
[0034] Figure 2 It is a transformer structure schematic diagram of the prior art;
[0035] Figure 3 It is a circuit schematic diagram of the micro-power DCDC converter;
[0036] Figure 4 It is a transformer structure schematic diagram of the micro-power DCDC converter;
[0037] Figure 5 It is a structure schematic diagram of the square ring magnetic core transformer assembled on a PCB circuit board;
[0038] Figure 6 It is a perspective view of the square ring magnetic core transformer assembled on the PCB circuit board;
[0039] Figure 7 It is a perspective view of another structure of the square ring magnetic core transformer assembled on the PCB circuit board.
[0040] In the above drawings, the reference signs are as follows:
[0041] 10. Magnetic core, 20. Winding, 201. Input winding, 202. Output winding, 2011.2012. Two ends of the input winding 201, 30. PCB circuit board, S1. First layer winding, S2. Second layer winding DETAILED DESCRIPTION
[0042] As Figure 3The diagram shown is a circuit schematic of the micropower DC-DC converter of this utility model. From the product circuit, this circuit is a micropower DC-DC converter with a power of 3W or less and an 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 resonant capacitor Cr, a high-isolation transformer T (where Lr and Lm are equivalent schematic representations of the leakage inductance and magnetizing inductance of the input primary winding, respectively), a bridge rectifier circuit D, and an output capacitor C2.
[0043] like Figure 4 and Figure 5 The diagram shows the individual transformer and its assembly structure of the micropower DC-DC converter of this invention. From the product structure, the high-isolation transformer T of this micropower DC-DC converter is assembled on a PCB circuit board 30, including a magnetic core 10 and two windings 20. The magnetic core 10 is a square-ring structure transformer, integrally molded from ferrite material, forming four side posts. The two windings 20 are the input winding 201 and the output winding 202, respectively wound on the two side posts of the magnetic core, forming a non-overlapping layout of the two windings. Preferably, the longest side post of the magnetic core 10 is less than 15 mm.
[0044] like Figure 3 , Figure 5 and Figure 6 As shown, its 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 located on two symmetrical short pillars of the rectangular annular closed magnetic core 10, respectively, to physically create a greater 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 upper circuit input section and the full-bridge micropower driver chip U1 via pads on the PCB circuit board 30, respectively. 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 located on the two long pillars of the rectangular annular closed magnetic core 10 to obtain a larger winding area. The rectangular annular structure of the magnetic core 10 has an aspect ratio between 7:3 and 5:5.
[0045] like Figure 6 and Figure 7 As shown, the transformer has two windings, at least one of which uses a thicker insulated wire, meaning the wire diameter of one winding is thicker than that of the other. The preferred thicker wire is triple-insulated wire with a diameter of less than 0.25 mm, used to achieve input / output isolation at 5000VDC / 4000VAC and above. The transformer windings can be mechanically wound.
[0046] Different from the conventional use of a circular magnetic core, the magnetic core is a square ring structure, and the winding area of the four edge columns is fixed and controllable. In the embodiment, the symmetrical narrow edges of the rectangular ring-shaped magnetic core are selected to wind the input winding and the output winding. Due to the physical blockage of the wide edge columns which are not wound, if the number of winding turns is large and requires multi-layer winding, the layers will be stacked in the narrow edge and will not slide to the opposite edge, which can ensure that the input winding and the output winding do not cross and overlap. This can not only improve the utilization rate of the window area of the magnetic core, reduce the overall volume of the high-isolation product, but also make the consistency of isolation withstand voltage, isolation capacitance and leakage inductance better, and be suitable for mechanical winding of thick wire diameter winding, especially 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 the corners are allowed to be arc corners for easy demolding of the magnetic core. For example, if a rectangular ring structure is used, the input winding and the output winding can be wound on two symmetrical narrow edges to increase the isolation distance of the input winding and the output winding.
[0047] Since the square ring magnetic core does not need to consider the problem of reserving more magnetic core space due to winding sliding, its volume can be smaller than that of the circular magnetic core. In practical application to products, the product volume can be reduced from "length 19.65 mm * width 9.80 mm * height 12.50 mm" to "length 19.65 mm * width 7.90 mm * height 10.16 mm", about 34% of the overall product volume.
[0048] On the other hand, the square ring magnetic core is blocked by the edge columns which are not wound, and compared with the product using the conventional circular magnetic core, the physical blockage effect is better and the blockage distance is longer, which means that the coupling between the input and output windings is worse and the leakage inductance is larger.
[0049] For an open loop circuit (i.e. a circuit without feedback loop, whose output voltage will change with the input voltage and be affected by circuit parameters), the leakage inductance will divide a part of the voltage, resulting in a decrease in the output voltage.
[0050] Taking a micro-power high-isolation DC-DC converter as an example, as shown in Figure 1 The converter is composed of an input capacitor C1, a full-bridge micro-power drive chip U1, a high-isolation transformer T (where Lr and Lm are the equivalent schematic of the leakage inductance and the magnetizing inductance of the input primary winding, respectively), a rectifier circuit D (such as a bridge rectifier circuit), and an output capacitor C2.
[0051] In order to more simply describe the problem of the influence of leakage inductance on the output voltage, the circuit is assumed to be an ideal circuit, i.e. the voltage drop of the power tube and the resistance of the circuit wiring and the dead zone (i.e. no dead zone, the duty cycle of the first half cycle and the second half cycle is 50%, and the total cycle is 100%) are ignored. Then according to the transformer principle, the output voltage of the open loop converter can be obtained as:
[0052] (Vo = Vin - Vr) (Equation 1), where Vo is the output voltage, Vin is the input voltage, Vr is the leakage voltage, and N is the turns ratio of the transformer.
[0053] Assuming the input voltage of this transformer 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 ratio is 1% (1.8uH), and the turns ratio is 1:1 (N=1).
[0054] Since the primary leakage inductance Lr cannot be coupled to the secondary side, the primary current will flow through the leakage inductance and generate an induced electromotive force. Using the formula derived from Faraday's Law, the voltage on the leakage inductance can be calculated as follows:
[0055] where Vr is the leakage 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.
[0056] Substituting Vr into Equation 1, we get the output voltage Vo = 4.865V.
[0057] The above example is for the case where the leakage ratio is only 1% of the primary inductance. If the ratio is further increased, the above method can be used to obtain:
[0058]
[0059] For an open-loop circuit, the leakage ratio seems small, but since the leakage cannot be coupled to the secondary side, the primary current will flow through the leakage and generate a high induced voltage, thus greatly affecting the output voltage.
[0060] Therefore, in high-isolation open-loop circuit applications, the leakage ratio of square ring magnetic core is relatively large compared to traditional circular magnetic core, so the output voltage is low. In practical applications, the number of transformer turns needs to be increased to compensate for the output voltage, but this will increase the cost and affect the circuit efficiency. This is a performance defect that cannot be overcome in the application of square ring magnetic core in micro-power DCDC converter.
[0061] To fully utilize the advantages of square ring magnetic core and solve the performance defect problem of affecting the output voltage, it is optimal to add a resonant capacitor Cr at one end of the transformer, as shown in Figure 3 The selection of appropriate resonant capacitor Cr can form an LC series resonant circuit with the leakage inductance Lr. The voltage of the capacitor in the LC resonant circuit is opposite to the voltage of the inductor. By utilizing this characteristic, the resonant capacitor forms a voltage in the opposite direction in the circuit, which can weaken the leakage voltage. Therefore, for an open-loop circuit, the output voltage at this time is
[0062] (Equation 2), where Vc is the voltage drop of the resonant capacitor.
[0063] In addition, the self-resonance point of the leakage inductance and the resonance capacitor is In theory, if the resonance frequency fr of the leakage inductance is equal to the working frequency f of the circuit, the leakage inductance reactance = resonance capacitor reactance, the LC circuit is resistive, at this time the leakage inductance and the resonance capacitor form a sinusoidal voltage of opposite directions and equal amplitude, that is, at this time Vr and Vc can be completely offset, the input voltage is entirely added to the excitation inductance, and at this time the output voltage reaches the best state.
[0064] In practical applications, most of the primary micro-power drive chips used in open-loop circuits of micro-power DCDC converters are fixed-frequency, so the working frequency f of the chip adjustment circuit cannot be adjusted to make f = fr reach the best state. Therefore, in general cases, the size of the resonance capacitor needs to be adjusted to change the self-resonance point fr of the LC circuit, so that fr is equal to or close to the working frequency f to achieve the purpose. Usually, the resonance capacitor is a ceramic chip capacitor with a capacitance of 10nF~4.7uF.
[0065] Compared with the original circular ring magnetic core winding, due to the existence of natural landslide structure, and the inner diameter is smaller than the outer diameter, which leads to the gap of the outer diameter, it cannot guarantee the stable superposition between layers, which not only affects the utilization rate of the magnetic core window area, but also cannot guarantee its consistency, and even there is a risk of input winding and output winding sliding and overlapping. Therefore, in high isolation applications, it is often necessary to increase the magnetic core to reduce the risk of input winding and output winding overlapping, which leads to the fact that the volume of micro-power high isolation products is too large and cannot be further reduced, and the consistency of related isolation voltage, isolation capacitance, and leakage inductance performance is poor.
[0066] If a square ring magnetic core is used, the above problems can be avoided, because the side column is a straight line, and the winding position at the inner diameter and the outer diameter is symmetrical, relying on the physical barrier of the unwound side column, the winding can be stacked layer by layer, which can greatly improve the utilization rate of the magnetic core window area, so that a larger magnetic core is not needed, and accordingly, the volume of high isolation products is reduced. On the other hand, since the winding range of the input winding and the output winding is fixed and controllable, the consistency of the isolation voltage, isolation capacitance, and leakage inductance related to the winding is better. At the same time, the straight winding column of the square ring magnetic core is easier to meet the mechanical winding conditions, and the use of mechanical winding can improve the production efficiency and further reduce the product cost.
[0067] In addition, due to the good barrier effect of the square ring magnetic core, it brings advantages, but also reduces the coupling between the input winding and the output winding, thereby increasing the leakage inductance. For open-loop circuits, leakage inductance will cause voltage division, resulting in a decrease in output voltage. If the number of transformer turns is increased to adjust the output voltage, the cost will be increased and the circuit efficiency will be reduced.
[0068] In order to overcome the hard defect problem of the circuit performance of the square ring magnetic core, preferably, a resonance capacitor Cr is connected in series at one end of the transformer, so that the resonance capacitor Cr and the leakage inductance Lr form an LC oscillation circuit, the capacitance of the Cr is adjusted, such as a typical value of 100nF, so that the self-resonant frequency fr is equal to or close to the working frequency f of the circuit, at this time, the LC oscillation circuit is resistive or close to resistive, the reverse voltage formed by the resonance capacitor offsets or greatly weakens the influence of the leakage inductance voltage, and finally most of the input voltage is added to the primary excitation inductance Lm, thereby coupling to the secondary side to form the optimal output voltage.
[0069] In summary, the combination of the square ring structure transformer and the resonance capacitor is applied in the micro-power high-isolation square ring transformer, which can fully utilize the advantages of the square ring magnetic core in structure, ensure that the input winding and the output winding are completely separated, and utilize the resonance capacitor to weaken the greater leakage inductance of the square ring magnetic core to affect the output voltage.
[0070] The above is only the preferred embodiment of the utility model, and it should be pointed out that the above preferred embodiment should not be regarded as a limitation of the present application, and the protection scope should be limited by the scope defined by the claims. For ordinary skilled in the art, several improvements and refinements can be made without departing from the spirit and scope of the application, and these improvements and refinements should also be regarded as the protection scope of the present application.
Claims
1. A low-power DC-DC converter, a modular power supply for 3W and below, comprising a PCB circuit board and a transformer mounted thereon, the transformer consisting of a magnetic core and two windings, characterized in that: The magnetic core has a square ring structure and is integrally molded from ferrite material, forming four side pillars; The two windings are respectively wound on two symmetrical side pillars of the magnetic core.
2. The low-power DC-DC converter according to claim 1, characterized in that: The magnetic core has a rectangular ring structure, and the two windings are respectively wound on two symmetrical short side posts, or the two windings are respectively wound on two symmetrical long side posts.
3. The low-power DC-DC converter according to claim 2, characterized in that: The rectangular ring structure of the magnetic core has an aspect ratio between 7:3 and 5:
5.
4. The low-power DC-DC converter according to claim 1 or 2, characterized in that: The longest side post of the magnetic core is less than 15 mm.
5. The micropower DC-DC converter according to claim 1 or 2, characterized in that: Of the two windings, at least one winding uses triple-insulated wire.
6. The low-power DC-DC 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 that of the other winding, in order to achieve input-output isolation at 5000VDC / 4000VAC and above.
7. The micropower DC-DC converter according to claim 1 or 2, characterized in that: The PCB is a carrier board for mounting electronic components of a DC-DC converter circuit with a power of 3W or less and an input-output isolation of 5000VDC / 4000VAC or higher.
8. The micropower DC-DC converter according to claim 1 or 2, characterized in that: The circuit on the PCB is an open-loop DC-DC converter. One end of the transformer is connected in series with a resonant capacitor before being connected to the circuit. The resonant capacitor and the leakage inductance of the transformer can form an LC series oscillation circuit.
9. The low-power DC-DC converter according to claim 1 or 2, characterized in that: The circuit on the PCB is an open-loop DC-DC converter. One end of the transformer is connected in series with a resonant capacitor before being connected to the circuit. The capacitance of the resonant capacitor is between 10nF and 4.7uF.
10. A transformer suitable for DC-DC converters with power ratings of 3W and below, comprising a magnetic core and two windings, characterized in that: The magnetic core has a square ring structure and is integrally molded from ferrite material, forming four side pillars.
11. The transformer according to claim 10, characterized in that: The magnetic core is a rectangular ring structure with an aspect ratio between 7:3 and 5:
5.
12. The transformer according to claim 10, characterized in that: The magnetic core is a rectangular ring structure, with the length of its long side column being less than 15 millimeters.
13. The transformer according to claim 10, characterized in that: Of the two windings, at least one winding uses triple-insulated wire.
14. The transformer according to claim 10, characterized in that: The wire diameter of the two windings is less than 0.25 mm, and the wire diameter of one winding is thicker than that of the other winding.