Electromagnetic compatibility-based PCB (Printed Circuit Board) layout and wiring design method of switching power supply circuit

Abstract

The invention relates to a PCB layout and wiring design method of a switching power supply circuit based on electromagnetic compatibility, and belongs to the field of PCB design. According to the method, the position of a switching power supply module on a PCB is determined, a large-current circuit in a switching power supply module principle block diagram is determined, the large-current circuit is a loop with very fast current conversion, the loop area is minimized, meanwhile, a ground plane is used for connecting an input capacitor, an output capacitor and the ground of the high-power current of a voltage stabilizer, and the ground is called the large-current ground; determining a low-current circuit, wherein the low-current circuit is separated from the high-current circuit in a region when being arranged; and determining a heating device on the switching power supply module, and considering the heat dissipation condition of the device during layout. According to the invention, the electromagnetic compatibility is improved, the signal integrity is improved, and the anti-interference capability is enhanced.

Description

Technical Field

[0001] The invention belongs to the field of PCB design, and in particular relates to a PCB layout and wiring design method for a switching power supply circuit based on electromagnetic compatibility. Background Art

[0002] A switching power supply is a voltage conversion circuit. Its main work is to step up and down the voltage. It is widely used in modern electronic products. Because the switching transistor always works in the "on" and "off" states, it is called a switching power supply. The switching power supply is essentially an oscillating circuit. This way of converting electrical energy is not only used in power supply circuits, but also in other circuits, such as the backlight circuit of LCD monitors, fluorescent lamps, etc.

[0003] Working principle of switching power supply: When the base of the transistor is at a high level, the transistor is saturated and turned on. The equivalent circuit is as follows: Figure 1 As shown, at this time, the inductor L stores energy and the capacitor C is charged. When the transistor base is at a low level, the transistor is cut off, and the equivalent circuit is as follows Figure 2 As shown, at this time, the inductor L releases energy and the capacitor C discharges. Usually, there are sampling circuits and feedback circuits on our PCB boards to adjust the duty cycle of the base control voltage to achieve the purpose of voltage regulation. At the same time, since the load and the transistor are connected in series, the output voltage is less than the input voltage, so it is also called a step-down switch circuit (buck switch circuit). The corresponding parallel switch circuit has a similar principle. At the same time, since the transistors are connected in parallel, the induced electromotive force generated by the inductor is superimposed on the voltage and acts on the load, so the output voltage will be higher than the input voltage.

[0004] Switching power supplies are widely used because of their low power consumption, high efficiency, significant energy-saving effects, small size, light weight, and wide input voltage range. However, switching power supplies also have obvious disadvantages: 1. Large electromagnetic interference. During operation, the switching power supply converts the voltage by controlling the on and off of the transistor. During this conversion process, peak currents and peak voltages will be generated, and these peak currents and peak voltages will cause relatively large electromagnetic interference and electromagnetic radiation, which will interfere with other circuits on the circuit board. This requires us to provide a reasonable method in the PCB layout and wiring process to reduce the interference caused by the switching power supply circuit to other circuits, and at the same time reduce the ripple and noise of the switching power supply itself, so as to avoid the power supply noise on the switching power supply circuit from entering other circuits through the power supply, causing timing and other problems. Summary of the invention

[0005] 1. Technical issues to be resolved

[0006] The technical problem to be solved by the present invention is how to provide a PCB layout and wiring design method for a switching power supply circuit based on electromagnetic compatibility to improve electromagnetic compatibility (EMC), enhance power supply efficiency, improve power supply stability, reduce thermal stress, simplify debugging and fault diagnosis, reduce size and cost, improve signal integrity: enhance anti-interference ability, thereby improving the core competitiveness of the product.

[0007] (II) Technical solution

[0008] In order to solve the above technical problems, the present invention proposes a PCB layout and wiring design method for a switching power supply circuit based on electromagnetic compatibility, the method comprising the following steps:

[0009] S1. Determine the position of the switching power supply module on the PCB. When determining the position, it should be placed away from the clock and interface sensitive devices, and then as close to the power end as possible, while considering heat dissipation and assembly;

[0010] S2. Determine the high-current circuit in the principle block diagram of the switching power supply module. The high-current circuit is a loop with very fast current conversion. Minimize the loop area. At the same time, use a ground plane to connect the input capacitor, output capacitor and the high-power current ground of the regulator. This ground is called the high-current ground.

[0011] S3. Determine the small current circuit. The small current circuit includes: sampling circuit, feedback circuit, comparison circuit and the filter circuit of the control circuit itself. The small current circuit should be separated from the large current circuit in terms of area during layout. Among them, the comparison circuit is placed close to the power chip, and the sampling circuit is placed between the output filter circuit and the comparison circuit. During layout, ensure that the sampling circuit is as close to the power chip pin as possible and close to the comparison circuit; the filter network and feedback circuit of the control circuit itself are placed as close to the corresponding control chip pin as possible.

[0012] S4. Identify the heat-generating components on the switching power supply module and consider the heat dissipation of the components during layout.

[0013] (III) Beneficial effects

[0014] The present invention proposes a PCB layout and wiring design method for a switching power supply circuit based on electromagnetic compatibility. The present invention provides a method for the layout and wiring of a switching power supply module on a PCB board. Experimental results show that the method works stably, achieves the expected effect, improves electromagnetic compatibility, improves signal integrity, enhances anti-interference ability, has a small power ripple, and has a significant effect in optimizing circuits. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is the equivalent circuit of the switch power supply on state;

[0016] Figure 2It is the equivalent circuit of the switching power supply in the cut-off state;

[0017] Figure 3 It is the overall block diagram of the switching power supply of the present invention;

[0018] Figure 4 It is a schematic diagram of the switching power supply chip of the present invention;

[0019] Figure 5 It is the switching power supply "high current" loop 1 of the present invention;

[0020] Figure 6 It is the switching power supply "high current" loop 2 of the present invention;

[0021] Figure 7 This is a PCB layout diagram of the switching power supply module of the present invention. DETAILED DESCRIPTION

[0022] In order to make the purpose, content and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below in conjunction with the drawings and examples.

[0023] The purpose of the present invention is to provide a PCB layout and wiring design method for a switching power supply circuit based on electromagnetic compatibility, which can improve electromagnetic compatibility (EMC), enhance power supply efficiency, improve power supply stability, reduce thermal stress, simplify debugging and fault diagnosis, reduce size and cost, improve signal integrity: enhance anti-interference ability, thereby improving the core competitiveness of the product.

[0024] The present invention provides a PCB layout and wiring design method for a switching power supply circuit based on electromagnetic compatibility. The layout and wiring method comprises two aspects: switching power supply module PCB layout and switching power supply module PCB wiring.

[0025] Generally speaking, the switch circuit in PCB mainly includes four main parts: input filter circuit, switch circuit, control circuit and output filter. Among them, the main current channel includes three important parts: input filter circuit, switch circuit and output filter. The rest is the control circuit, which includes four parts: sampling circuit, feedback circuit, comparison circuit and control filter circuit. Figure 3 shown.

[0026] The PCB layout of the switching power supply module includes the following steps:

[0027] S1. Determine the position of the switching power supply module on the PCB board. The switch is a strong source of EMI radiation. When determining the position, it should be placed away from sensitive devices such as clocks and interfaces, and then as close to the power end as possible, while considering factors such as heat dissipation and assembly.

[0028] S2. Determine the high current circuit in the principle block diagram of the switching power supply module. The main power supply channel of the switching power supply module includes: high current circuit and low current circuit. The high current circuit is a loop with very fast current conversion, minimizing the loop area. There are two high current loops in the switching power supply module. Figure 4 In the example shown, the red and blue lines are large current loops. Figure 5 As shown in the figure, the first loop is: the power supply end of the input capacitor to the switch tube, then to the inductor, and finally to the power supply end of the output filter capacitor; Figure 6 As shown, the second loop is: the ground of the output filter capacitor to the ground of the power chip, then to the current detection resistor Rs, then to the diode, then to the inductor, and finally to the output load.

[0029] S3. Determine the small current circuit. The small current circuit includes: sampling circuit, feedback circuit, comparison circuit and the filter circuit of the control circuit itself. The small current circuit should be separated from the large current circuit in terms of area during layout. In addition, in terms of details, the comparison circuit should be placed close to the power chip, and the sampling circuit should be placed between the output filter circuit and the comparison circuit. During layout, ensure that the sampling circuit is as close to the power chip pin and the comparison circuit as possible; the filter network and feedback circuit of the control circuit itself should be placed as close to the corresponding control chip pin as possible.

[0030] S4. Determine the heat-generating components on the switching power supply module. Some switching power supply chips have built-in switching tubes, which means that the chip itself generates heat. Some switching power supply chips have external switching tubes, which means that the switching tube and diode generate external heat. When laying out the switching power supply chip, you need to read the specific data sheet so that the heat dissipation of the device can be considered during layout.

[0031] When wiring the switching power supply module PCB, the following aspects should be considered:

[0032] First, minimize the loop area to reduce parasitic inductance and reduce noise. As mentioned earlier, in the switching power supply module, there are two loops with high current conversion speeds. One is: the power supply end of the input capacitor to the switch tube, then to the inductor, and finally to the power supply end of the output filter capacitor; the other is: the ground of the output filter capacitor to the ground of the power chip, then to the current detection resistor Rs, then to the diode, then to the inductor, and finally to the load. Minimizing the area of ​​these two loops can reduce parasitic inductance and reduce noise. If the loop is too large, it is easy to cause electromagnetic compatibility problems. In addition, it is recommended to use a ground plane to connect the input capacitor, output capacitor and the high-power current ground of the regulator (such as the attached Figure 7 This ground is called the high current ground.

[0033] like Figure 7As shown in the figure, the left side is the high current ground, and the right side is the low current ground, and the two are separated in the layout; the red line indicates the high current loop 1, and the purple line indicates the high current loop 2; the green circle indicates that the low current ground is directly punched into the ground layer of the PCB board, and is not connected to the high current ground copper foil next to it;

[0034] Second, good grounding: separate the large current ground from the small current ground to prevent the noise of the large signal from crosstalking to the small signal through the ground. Specifically, connect the small current ground of the small current circuit to the ground layer on the PCB board through vias, and do not directly connect it to the large current ground on the same layer.

[0035] Third, effective filtering on PCB: Using a multi-layer PCB design can effectively separate the signal layer and the ground layer, reduce interference and provide good electromagnetic shielding.

[0036] Fourth, the layout of the filter capacitor: the input filter capacitor and the output filter capacitor should be as close to the input and output terminals of the switching power supply chip as possible to reduce noise.

[0037] Fifth, avoid long traces: Try to avoid long signal traces, especially for high-frequency signals, as long traces will increase radiation and coupling.

[0038] Sixth, wiring width: choose the appropriate trace width according to the current size to reduce resistance loss and thermal effects.

[0039] Seventh, layout of decoupling capacitors: Place decoupling capacitors near ICs and sensitive components to provide a stable power supply.

[0040] Eighth, heat dissipation design: ensure that the switching components and high-frequency transformers have good heat dissipation design to avoid overheating.

[0041] Ninth, avoid parallel routing: Avoid running high-frequency signal lines and sensitive signal lines in parallel to reduce crosstalk.

[0042] The present invention provides a PCB layout and wiring design method for a switching power supply circuit based on electromagnetic compatibility. The method provides a method for layout and wiring of a switching power supply module on a PCB board. Experimental results show that the method works stably and achieves the expected effect, improves electromagnetic compatibility, improves signal integrity, enhances anti-interference ability, has small power ripple, and has a significant effect in optimizing circuits.

[0043] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A PCB layout design method for a switching power supply circuit based on electromagnetic compatibility, characterized in that: The method comprises the following steps: S1. Determine the position of the switching power supply module on the PCB. When determining the position, it should be placed away from the clock and interface sensitive devices, and then as close to the power end as possible, while considering heat dissipation and assembly; S2. Determine the high-current circuit in the principle block diagram of the switching power supply module. The high-current circuit is a loop with very fast current conversion. Minimize the loop area. At the same time, use a ground plane to connect the input capacitor, output capacitor and the high-power current ground of the regulator. This ground is called the high-current ground. S3. Determine the small current circuit. The small current circuit includes: sampling circuit, feedback circuit, comparison circuit and the filter circuit of the control circuit itself. The small current circuit and the large current circuit are separated in area during layout. Among them, the comparison circuit is placed close to the power chip, and the sampling circuit is placed between the output filter circuit and the comparison circuit. During layout, ensure that the sampling circuit is as close to the power chip pin as possible and close to the comparison circuit; the filter network and feedback circuit of the control circuit itself are placed as close to the corresponding control chip pin as possible. S4. Identify the heat-generating components on the switching power supply module and consider the heat dissipation of the components during layout.

2. The PCB layout and wiring design method of the switching power supply circuit based on electromagnetic compatibility as claimed in claim 1, characterized in that: There are two large current loops in the switching power supply module. The first loop is: from the power supply end of the input capacitor to the switching tube, then to the inductor, and finally to the power supply end of the output filter capacitor; the second loop is: from the ground of the output filter capacitor to the ground of the power chip, then to the current detection resistor Rs, then to the diode, then to the inductor, and finally to the output load.

3. The PCB layout and wiring design method of the switching power supply circuit based on electromagnetic compatibility as claimed in claim 2, characterized in that: The small current ground of the small current circuit is connected to the ground layer on the PCB board through vias, and is not directly connected to the large current ground on the same layer.

4. The PCB layout and wiring design method of the switching power supply circuit based on electromagnetic compatibility as claimed in claim 2, characterized in that: Use a multi-layer PCB design to separate signal and ground layers.

5. The PCB layout and wiring design method of the switching power supply circuit based on electromagnetic compatibility as claimed in claim 2, characterized in that: The input filter capacitor and output filter capacitor should be as close as possible to the input and output terminals of the switching power supply chip.

6. The PCB layout and wiring design method of the switching power supply circuit based on electromagnetic compatibility as claimed in claim 2, characterized in that: For high-frequency signals, try to avoid long signal traces.

7. The PCB layout and wiring design method of the switching power supply circuit based on electromagnetic compatibility as claimed in claim 2, characterized in that: Select the appropriate trace width according to the current size.

8. The PCB layout and wiring design method of the switching power supply circuit based on electromagnetic compatibility as claimed in claim 2, characterized in that: Place decoupling capacitors near ICs and sensitive components to provide a stable power supply.

9. The PCB layout and wiring design method of the switching power supply circuit based on electromagnetic compatibility as claimed in claim 2, characterized in that: Ensure that the switching components and high-frequency transformers have good heat dissipation design.

10. The PCB layout and wiring design method of the switching power supply circuit based on electromagnetic compatibility as claimed in claim 2, characterized in that: Avoid running high-frequency signal lines and sensitive signal lines in parallel.

Images