Switching power supply printed circuit board and switching power supply

Abstract

The utility model provides a switching power supply printed circuit board and a switching power supply. The switching power supply printed circuit board comprises a bonding pad of a high-voltage pin HV, a bonding pad of a grounding pin GND and a first bonding pad provided with a high-voltage detection point. And the first bonding pad is also used for welding a synchronous rectification control chip. And the high-voltage detection point, the bonding pad of the high-voltage pin HV and the bonding pad of the grounding pin GND form a high-voltage detection loop through wires. The switching power supply comprises a synchronous rectification control chip and a switching power supply printed circuit board. And the synchronous rectification control chip is respectively connected with the bonding pad of the high-voltage pin HV and the bonding pad of the grounding pin GND. According to the switching power supply printed circuit board and the switching power supply provided by the utility model, on the premise of not increasing extra cost, the switching stress of a synchronous rectification transistor is effectively reduced, and the reliability of a device and a switching system is improved.

Description

Technical Field

[0001] The utility model belongs to the field of power electronics and relates to a printed circuit board of a switching power supply and a switching power supply. Background Art

[0002] Synchronous rectification technology (i.e., Synchronous Rectification, abbreviated as SR) is a technology that uses a metal-oxide-semiconductor field-effect transistor (abbreviated as MOSFET) to replace a rectifier diode to reduce rectification loss. Currently, it has been widely applied in fields such as industrial power supplies and consumer electronics.

[0003] The synchronous rectification transistor SR in a flyback circuit needs to be compatible with multiple operating modes, including the continuous current mode (abbreviated as CCM). However, in the CCM operating mode, the synchronous rectification transistor SR usually has a large turn-off negative current due to insufficiently fast turn-off speed, which in turn causes an overshoot of the MOSFET voltage stress and may even lead to device damage in severe cases. As Figure 1 shown, the flyback converter includes a primary circuit and a secondary circuit. The secondary circuit includes a synchronous rectification transistor SR. Combining Figure 1 and Figure 2 it can be known that for a flyback converter operating in the CCM state, when the primary control signal PWM for controlling the primary switch tube is at the first level (e.g., high level), the synchronous rectification control signal SR PWM for controlling the synchronous rectification transistor SR does not instantaneously become the second level (e.g., low level), but becomes the second level after a certain delay time Tdelay1. The parasitic parameters of the synchronous rectification transistor SR or the performance of the control circuit of the synchronous rectification transistor SR will determine the magnitude of the delay time Tdelay1. Due to the existence of the delay time Tdelay1, a negative overshoot current exists after the secondary freewheeling current normally freewheels to 0. This negative current directly determines the switching stress of the synchronous rectification transistor SR. The larger the absolute value of the minimum negative current Is_min1, the larger the maximum Vds_s stress Vds_s_max1. When Vds_s_max1 exceeds the BV breakdown voltage of the synchronous rectification transistor SR, it will cause device damage and abnormal system operation. And the magnitude of the delay time Tdelay1 directly determines the magnitude of Is_min1. The larger the delay time Tdelay1, the larger the absolute value of Is_min1, and the larger Vds_s_max1.

[0004] Therefore, in a flyback circuit, in the continuous conduction mode (CCM), the synchronous rectifier transistor SR requires a very fast turn-off speed, that is, to reduce the delay time Tdelay1. However, the turn-off speed is limited by the performance of the turn-off comparator, and improving the performance of the turn-off comparator will lead to an increase in the cost of the controller. Another technical solution is to select a metal-oxide-semiconductor field-effect transistor (MOSFET) with a smaller parasitic capacitance Ciss, but this will cause the on-resistance Rds_on of the MOSFET to become larger, resulting in lower efficiency. Or select a MOSFET fabricated with a more advanced process, so that both the capacitance value Ciss of the parasitic capacitance and the resistance value Rds_on of the on-resistance are smaller, but this will lead to an increase in the application cost. Therefore, in current applications, when reducing the CCM stress of the synchronous rectifier transistor SR in the flyback circuit, problems such as increased cost or reduced efficiency are usually encountered. Another solution is to select a controller with better performance and faster turn-off speed, but this will also increase the application cost.

[0005] In view of this, a new structure or control method is needed to solve at least some of the above problems. Summary of the Utility Model

[0006] In view of one or more problems in the prior art, the present utility model provides a printed circuit board for a switching power supply and a switching power supply.

[0007] According to one aspect of the present utility model, a printed circuit board for a switching power supply is disclosed. The printed circuit board for a switching power supply includes a pad for a high-voltage pin HV, a pad for a ground pin GND, and a first pad provided with a high-voltage detection point. The first pad is also used for soldering a synchronous rectifier control chip for controlling a synchronous rectifier transistor. The high-voltage detection point, the pad for the high-voltage pin HV, and the pad for the ground pin GND form a high-voltage detection loop through wires.

[0008] In one embodiment, the high-voltage detection loop is on the same side of the freewheeling current axis, and the freewheeling current axis is the axis where the freewheeling current of the synchronous rectifier transistor is located.

[0009] In one embodiment, the first pad is provided with a preset area for soldering the drain pin of the synchronous rectifier control chip, and the distance between the preset area and the high-voltage detection point is not less than a preset distance.

[0010] In one embodiment, the area enclosed by the high-voltage detection loop is not less than a preset area.

[0011] In one embodiment, the first pad is provided with a preset area for soldering the drain pin of the synchronous rectifier control chip, or the printed circuit board for a switching power supply includes a pad for a gate pin.

[0012] In one embodiment, the printed circuit board of the switching power supply further includes pads for the power supply pin VDD, pads for the high-voltage pin HV, pads for the power supply pin VDD, and pads for the ground pin GND are arranged in sequence on one narrow side of the printed circuit board of the switching power supply.

[0013] In one embodiment, the first pad is located in the central area of the printed circuit board of the switching power supply. The first pad is provided with a preset area for soldering the drain pin of the synchronous rectification control chip. The preset area is close to the pad of the high-voltage pin HV, and the distance between the high-voltage detection point and the preset area is not less than the preset distance.

[0014] In one embodiment, the printed circuit board of the switching power supply is further provided with vias for connecting the first output terminal of the switching power supply, and vias for connecting the second output terminal of the switching power supply.

[0015] In one embodiment, the printed circuit board of the switching power supply further includes pads for the power supply pin VDD, pads for the high-voltage pin HV, pads for the power supply pin VDD, and pads for the ground pin GND are arranged in sequence on one long side of the printed circuit board of the switching power supply.

[0016] According to another aspect of the present invention, a switching power supply is disclosed. The switching power supply includes a synchronous rectification control chip and the printed circuit board of the switching power supply as described in any one of the above. The high-voltage pin of the synchronous rectification control chip is connected to the pad of the high-voltage pin HV, and the ground pin of the synchronous rectification control chip is connected to the pad of the ground pin GND.

[0017] In one embodiment, the drain pin of the synchronous rectification control chip is connected to the preset area of the first pad, or the gate pin of the synchronous rectification control chip is connected to the pad of the gate pin in the printed circuit board of the switching power supply.

[0018] The present invention proposes a printed circuit board of a switching power supply and a switching power supply. Among them, the printed circuit board of the switching power supply includes pads for the high-voltage pin HV, pads for the ground pin GND, and a first pad provided with a high-voltage detection point. The first pad is also used for soldering a synchronous rectification control chip for controlling a synchronous rectification transistor. The high-voltage detection point, the pad of the high-voltage pin HV, and the pad of the ground pin GND form a high-voltage detection loop through wires. The switching power supply includes a synchronous rectification control chip and a printed circuit board of the switching power supply. The high-voltage pin HV of the synchronous rectification control chip is connected to the pad of the high-voltage pin HV, and the ground pin of the synchronous rectification control chip is connected to the pad of the ground pin GND. The printed circuit board of the switching power supply and the switching power supply proposed by the present invention can effectively reduce the switching stress of the synchronous rectification transistor, reduce the risk of device damage, and improve the reliability of the device and the switching system by adjusting the layout of the printed circuit board without increasing additional costs. Description of the Drawings

[0019] The accompanying drawings are used to provide a further understanding of the present utility model, and together with the description, are used to explain the embodiments of the present utility model, and do not constitute a limitation to the present utility model. In the accompanying drawings:

[0020] Figure 1 It shows a schematic circuit structure diagram of a flyback converter of the prior art;

[0021] Figure 2 It shows a schematic diagram of the signal waveform of a flyback converter of the prior art;

[0022] Figure 3 It shows a schematic structure diagram of a printed circuit board of a switching power supply according to an embodiment of the present utility model;

[0023] Figure 4 It shows a schematic structure diagram of a printed circuit board of a switching power supply according to another embodiment of the present utility model;

[0024] Figure 5 It shows a schematic circuit structure diagram of a partial circuit of a switching power supply according to an embodiment of the present utility model;

[0025] Figure 6 It shows a schematic circuit structure diagram of a partial circuit of a switching power supply according to another embodiment of the present utility model;

[0026] Figure 7 It shows a schematic circuit structure diagram of a partial circuit of a switching power supply according to still another embodiment of the present utility model. Detailed implementation manners

[0027] In order to further understand the present utility model, the preferred implementation manners of the present utility model will be described below in conjunction with embodiments. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present utility model, rather than a limitation to the claims of the present utility model.

[0028] The description of this part only focuses on several typical embodiments, and the present utility model is not limited to the scope described in the embodiments. Combinations of different embodiments, mutual replacement of some technical features in different embodiments, and mutual replacement of the same or similar prior art means and some technical features in the embodiments are also within the scope of description and protection of the present utility model.

[0029] "Coupled" or "connected" in the specification includes both direct connection and indirect connection. Indirect connection is a connection through an intermediate medium, such as a connection through an electrical conduction medium like a conductor, where the electrical conduction medium may contain parasitic inductance or parasitic capacitance, or a connection through an intermediate circuit or component described in the embodiments of the specification; indirect connection may also include a connection through other active or passive devices based on achieving the same or similar functions, such as a connection through circuits or components like switches, signal amplification circuits, follower circuits, etc. "Plurality" or "multiple" means two or more. Additionally, in the present utility model, words such as first, second, etc. are mainly used to distinguish one technical feature from another technical feature, and do not necessarily require or imply a certain actual relationship or order between these technical features.

[0030] As Figure 3 shown, an embodiment of the present utility model discloses a printed circuit board for a switching power supply. The printed circuit board for the switching power supply includes a pad 11 of a high-voltage pin HV, a pad 12 of a power supply pin VDD, a pad 13 of a ground pin GND, and a first pad 14 provided with a high-voltage detection point 17. The first pad 14 is also used for soldering a synchronous rectification control chip for controlling a synchronous rectification transistor. In one embodiment, the synchronous rectification control chip is provided with a high-voltage pin, a power supply pin, a ground pin, and a drain pin. In another embodiment, the synchronous rectification control chip is provided with a high-voltage pin, a power supply pin, a ground pin, and a gate pin. As Figure 3 shown, the high-voltage detection point 17, the pad 11 of the high-voltage pin HV, and the pad 13 of the ground pin GND are connected by a wire to form a high-voltage detection circuit 18. The freewheeling current of the synchronous rectification transistor generates a changing magnetic field in space. The changing magnetic field in space can generate an induced current in the high-voltage detection circuit. The high-voltage detection circuit 18 is on the same side of the freewheeling current axis, and the freewheeling current axis is the axis where the freewheeling current of the synchronous rectification transistor is located.

[0031] In one embodiment, as Figure 3As shown, the first pad 14 is provided with a preset area 141 for soldering the drain pin of the synchronous rectification control chip. The distance between the preset area 141 and the high-voltage detection point 17 is greater than or equal to a preset distance, so that the distance between the drain of the synchronous rectification transistor and the high-voltage detection point is greater than or equal to a preset value. In another embodiment, the area enclosed by the high-voltage detection loop is a preset area. In yet another embodiment, the area enclosed by the high-voltage detection loop is greater than the preset area. The high-voltage detection loop 18 is on the same side of the freewheeling current axis. Therefore, a changing magnetic field in space can generate a relatively large induced current in the high-voltage detection loop. In one embodiment, the synchronous rectification control chip is provided with a drain pin, and the first pad 14 is provided with a preset area 141 for soldering the drain pin of the synchronous rectification control chip. In another embodiment, the synchronous rectification control chip is provided with a gate pin, and the printed circuit board of the switching power supply includes a pad for the gate pin. As Figure 3 As shown, in one embodiment, the pad 11 for the high-voltage pin HV, the pad 12 for the supply pin VDD, and the pad 13 for the ground pin GND are arranged in sequence on one long side of the printed circuit board of the switching power supply. A partial area 131 of the pad 13 for the ground pin GND on the side close to the pad 12 for the supply pin VDD is used for soldering the ground pin GND of the synchronous rectification transistor. The printed circuit board of the switching power supply is further provided with a via 15 for connecting the first output terminal Vo+ of the switching power supply, and a via 16 for connecting the second output terminal Vo- of the switching power supply.

[0032] Another embodiment of the present utility model discloses a printed circuit board of a switching power supply, as Figure 4 As shown, the printed circuit board of the switching power supply includes a pad 21 for the high-voltage pin HV, a pad 22 for the supply pin VDD, a pad 23 for the ground pin GND, and a first pad 24 provided with a high-voltage detection point 27. The first pad 24 is also used for soldering a synchronous rectification control chip for controlling the synchronous rectification transistor. In one embodiment, the synchronous rectification control chip is provided with a high-voltage pin, a supply pin, a ground pin, and a drain pin. As Figure 4 As shown, the high-voltage detection point 27, the pad 21 for the high-voltage pin HV, and the pad 23 for the ground pin GND form a high-voltage detection loop 28 through wires. The freewheeling current of the synchronous rectification transistor generates a changing magnetic field in space. A changing magnetic field in space can generate an induced current in the high-voltage detection loop. The high-voltage detection loop 28 is on the same side of the freewheeling current axis, and the freewheeling current axis is the axis where the freewheeling current of the synchronous rectification transistor is located. The pad for the high-voltage pin HV, the pad for the supply pin VDD, and the pad for the ground pin GND are arranged in sequence on one narrow side of the printed circuit board of the switching power supply.

[0033] In one embodiment, the first pad 24 is located in the central area of the printed circuit board of the switching power supply. The first pad 24 is provided with a preset area 241 for soldering the drain pin of the synchronous rectification control chip. The preset area 241 is close to the pad 21 of the high-voltage pin HV, and the distance between the high-voltage detection point 27 and the preset area 241 is greater than a preset distance. By comparing Figure 3 and Figure 4 it can be known that Figure 4 in one embodiment of Figure 4 the preset distance between the high-voltage detection point 27 and the preset area 241 is greater, and a larger area enclosed by the high-voltage detection loop can be obtained, thereby reducing the switching stress of the synchronous rectification transistor. In one embodiment as shown in Figure 4 , the first area 211 of the pad 21 of the high-voltage pin HV, the second area 221 of the pad 22 of the power supply pin VDD, and the third area 231 of the pad 23 of the ground pin GND are close to each other. The first area 211 is used for soldering the high-voltage pin of the synchronous rectification control chip. The second area 221 is used for soldering the power supply pin of the synchronous rectification control chip. The third area 231 is used for soldering the ground pin of the synchronous rectification control chip. The printed circuit board of the switching power supply is further provided with a via 25 for connecting the first output terminal Vo+ of the switching power supply, and a via 26 for connecting the second output terminal Vo- of the switching power supply.

[0034] Combined with Figures 3 - 5 it can be known that the secondary side freewheeling current Is (flowing from the source of the synchronous rectification transistor to the drain of the synchronous rectification transistor) in the flyback switching power supply will generate an induced magnetic field in space. According to Ampere's rule, on the left side of the axis of the freewheeling current, the magnetic field direction is perpendicular to the paper and outwards. The continuously changing secondary side freewheeling current Is generates a changing magnetic field. According to Lenz's law, the changing magnetic field in the closed loop will generate an induced current. When the switching power supply is in the CCM operating mode, at the moment when the primary control signal PWM of the primary switch tube just goes high, the slope of the falling edge of the secondary side freewheeling current is much greater than the slope in the normal freewheeling stage. The induced magnetic field generated by the secondary side freewheeling current changes sharply, and the magnetic force lines in the high-voltage detection loop also change sharply, resulting in an induced current IHV flowing to the high-voltage pin HV in the high-voltage detection loop (the current direction is Figure 5 counterclockwise in the top view of Figure 5 . The induced current IHV will accelerate the output flip of the comparator coupled to the HV pin in the synchronous rectification control chip, thereby reducing the turn-off delay time Tdelay1, and further reducing the CCM stress.

[0035] Specifically, since the secondary freewheeling current along the axis of the freewheeling current gradually decreases, the magnetic field generated by the secondary freewheeling current on the left side of the spatial central axis also gradually weakens. According to Lenz's law, a decreasing magnetic field in a closed loop will generate an induced current, and the magnetic field formed by this induced current will hinder the weakening of the original magnetic field. Therefore, as Figure 5 shown, the continuously weakening magnetic field on the left side of the axis will generate a counterclockwise induced current I HV, which will hinder the weakening process of the original magnetic field. In a general controller, a comparator is usually coupled inside the HV pin. When an induced current is injected into the HV pin, it will accelerate the response speed of the comparator, thereby reducing Tdelay1 and thus reducing the switching stress. Obviously, under the condition that other conditions are the same, the larger the area enclosed by the high-voltage detection circuit and the farther the high-voltage detection point is from the drain of the synchronous rectifier transistor, the more magnetic field lines are enclosed by the high-voltage detection circuit, the larger the induced current generated, and the smaller the delay time Tdelay1. In addition, to make full use of the changing magnetic field lines to generate an induced current, the high-voltage detection circuit must be located on one side of the axis of the freewheeling current. As Figure 5 shown, the high-voltage detection circuits are all on the left side of the axis of the secondary freewheeling current Is.

[0036] Combined with Figure 2 , the current Is_off is the magnitude of the secondary freewheeling current when the primary switch is turned on. At the moment when the primary control signal PWM of the primary switch just goes high, the slope of the secondary freewheeling current starts to change. When the slope of the secondary freewheeling current Is changes significantly, a large induced current is generated in the high-voltage detection circuit, which accelerates the turn-off of the synchronous rectifier transistor SR, reduces the delay time, further reduces the absolute value of the negative current of Is, and finally reduces the maximum stress borne by Vds_s of the synchronous rectifier transistor in the CCM operating mode, reduces the risk of device damage, and improves the reliability of the device and the switching system.

[0037] An embodiment of the present invention also discloses a switching power supply, as Figure 6As shown, the switching power supply includes a primary circuit and a secondary circuit. The primary circuit includes a primary switching transistor and a primary switching control circuit, and the primary switching control circuit is used to control the switching state of the primary switching transistor. The secondary circuit includes a synchronous rectification control circuit, and the synchronous rectification control circuit is used to control the switching state of the synchronous rectification transistor. The synchronous rectification control circuit includes a synchronous rectification control chip, and the synchronous rectification control chip is soldered on the printed circuit board of the switching power supply described in any of the above items. The synchronous rectification control chip is provided with a high-voltage pin, a power supply pin, and a ground pin. The high-voltage pin HV of the synchronous rectification control chip is connected to the pad of the high-voltage pin HV, the power supply pin VDD of the synchronous rectification control chip is connected to the pad of the power supply pin VDD, and the ground pin of the synchronous rectification control chip is connected to the pad of the ground pin GND.

[0038] In an embodiment as Figure 6 shown, the synchronous rectification control chip is further provided with a gate pin, and the gate pin is coupled to the gate of the synchronous rectification transistor. In an embodiment as Figure 7 shown, the synchronous rectification control chip is further provided with a drain pin, the synchronous rectification transistor is built in the synchronous rectification control chip, the drain pin of the synchronous rectification control chip is connected to a preset area of the first pad, and the drain pin is coupled to the high-voltage pin.

[0039] Those skilled in the art should know that in the logical control involved in the specification or drawings, logical controls such as "high level" and "low level", "set" and "reset", "AND gate" and "OR gate", "in-phase input terminal" and "inverting input terminal" can be interchanged or changed with each other, and the same functions or purposes as those in the above embodiments can be achieved by adjusting the subsequent logical control.

[0040] The description and application of the present invention here are illustrative, and it is not intended to limit the scope of the present invention to the above embodiments. The related descriptions of effects or advantages involved in the specification may not be reflected in actual experimental examples due to uncertainties in specific condition parameters or other factors, and the related descriptions of effects or advantages are not used to limit the scope of the invention. It is possible to make deformations and changes to the disclosed embodiments here, and substitutions and equivalents of various components are well known to those of ordinary skill in the art. Those skilled in the art should clearly understand that without departing from the spirit or essential features of the present invention, the present invention can be implemented in other forms, structures, arrangements, proportions, and with other components, materials, and parts. Other deformations and changes can be made to the disclosed embodiments here without departing from the scope and spirit of the present invention.

Claims

1. A printed circuit board for a switching power supply, characterized in that, The switching power supply printed circuit board includes pads for a high-voltage pin HV, pads for a ground pin GND, and a first pad provided with a high-voltage detection point. The first pad is also used for soldering a synchronous rectification control chip for controlling a synchronous rectification transistor. The high-voltage detection point, the pad for the high-voltage pin HV, and the pad for the ground pin GND form a high-voltage detection loop through a wire.

2. The printed circuit board of the switching power supply according to claim 1, wherein The high-voltage detection loop is on the same side of the freewheeling current axis, and the freewheeling current axis is the axis where the freewheeling current of the synchronous rectification transistor is located.

3. The printed circuit board of the switching power supply according to claim 1, wherein, The first pad is provided with a preset area for soldering the drain pin of the synchronous rectification control chip, and the distance between the preset area and the high-voltage detection point is not less than a preset distance.

4. The printed circuit board of the switching power supply according to claim 1, wherein The area enclosed by the high-voltage detection loop is not less than a preset area.

5. The printed circuit board of the switching power supply according to claim 1, wherein, The first pad is provided with a preset area for soldering the drain pin of the synchronous rectification control chip, or the switching power supply printed circuit board includes pads for gate pins.

6. The printed circuit board of the switching power supply according to claim 1, characterized in that, The switching power supply printed circuit board further includes pads for a supply pin VDD. The pads for the high-voltage pin HV, the pads for the supply pin VDD, and the pads for the ground pin GND are arranged in sequence on one narrow side of the switching power supply printed circuit board.

7. The printed circuit board of the switching power supply according to claim 6, wherein The first pad is located in the central area of the switching power supply printed circuit board. The first pad is provided with a preset area for soldering the drain pin of the synchronous rectification control chip. The preset area is close to the pad for the high-voltage pin HV, and the distance between the high-voltage detection point and the preset area is not less than a preset distance.

8. The printed circuit board of the switching power supply according to claim 6, wherein The switching power supply printed circuit board is further provided with vias for connecting a first output terminal of the switching power supply, and vias for connecting a second output terminal of the switching power supply.

9. The printed circuit board of the switching power supply according to claim 1, characterized in that, The switching power supply printed circuit board further includes pads for a supply pin VDD. The pads for the high-voltage pin HV, the pads for the supply pin VDD, and the pads for the ground pin GND are arranged in sequence on one long side of the switching power supply printed circuit board.

10. A switching power supply, characterized in that, The switching power supply includes a synchronous rectification control chip and the switching power supply printed circuit board according to any one of claims 1-9. The high-voltage pin of the synchronous rectification control chip is connected to the pad for the high-voltage pin HV, and the ground pin of the synchronous rectification control chip is connected to the pad for the ground pin GND.

11. The switching power supply according to claim 10, wherein The drain pin of the synchronous rectification control chip is connected to the preset area of the first pad, or the gate pin of the synchronous rectification control chip is connected to the pad for the gate pin in the switching power supply printed circuit board.

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