The correct layout of the LED drive power supply is essential to ensure its long-term stability and compliance with electromagnetic interference (EMI) and electromagnetic compatibility (EMC) requirements. At present, LED drive power supply to printed circuit board (referred to as printed board or PCB) as the main assembly mode. A lot of practice has proved that even if the circuit design is correct, due to the unreasonable layout or wiring, it will have an adverse impact on the reliability of LED drive power supply. Therefore, the correct method should be used in the design of printed boards.
General principles for layout and wiring of LED drive power supply
General principles of LED drive power layout
(1) determine the size and shape of the printed board (PCB) when laying out the components. Because the isolated LED drive power supply is divided into input and output sides, and the two sides are required to achieve electrical isolation, the PCB is usually designed to be rectangular. The packaging of all components in the PCB is evenly arranged in a rectangular shape, with primary side components on the left and secondary side components on the right. Four mounting holes are reserved. Draw a rectangle on the forbidden wiring layer to surround all components and leave a certain safety boundary.
(2) the layout generally starts with high-frequency transformers. The high-frequency transformer is arranged in the middle of the printed board, the left side is the primary side and the right side is the secondary side. The input filter capacitor, primary winding and power switch constitute a circuit with large pulse current. Secondary windings, rectifying (or secondary) diodes and output filter capacitors form another circuit with a larger pulse current. The two loops should be compact with short leads. To reduce the leakage inductance, so as to reduce the loss of the absorption loop, improve the efficiency of the power supply. The space between components with primary side high pressure should be increased appropriately, and the size of PCB should be adjusted appropriately according to the need, and finally the whole layout of the printed board should be completed.
(3) the printed board size should be moderate, too large print line long, impedance increase, not only the ability to reduce noise, the cost is also increased; Too small size, heat dissipation is not good, but also easy to adjacent printed wire interference
2. Layout of key components
Reasonable layout of key components is also very important. For example, the grounding end of a detour end bypass capacitor must be a low-noise reference ground, connected to the ground end of a analog ground (AGND) and a sampling resistance voltage divider through only small signals, and as far away as possible from the power ground (PGND) through which a large current passes. It is very important to realize the isolation between low noise reference ground and high noise power ground. This layout prevents large switching currents from entering the battery or power supply through the analog circuit and causing interference.
The controller power circuit has two current paths, which are divided into two current paths
Do not train for the input loop and the output loop. Figure (a) shows the path of current through the input loop when MOSFET is switched on. Figure (b) shows the path of current through the output circuit when the MOSFET is turned off. By placing the components of the two circuits close to each other, the large current can be limited to the power circuit of the controller and kept away from the ground circuit of the low-noise components. C, L, MOSFET, VD and Co should be as close as possible. The use of short and wide printed wire wiring, can improve efficiency, reduce the ringing voltage, to avoid the interference of low noise circuit.
Compromise schemes are often used in the layout of the two current circuits. To determine which components in the loop are to be installed nearby, determine whether there is discontinuous current flowing through the components. The location of components with discontinuous current is very important to reduce the distributed inductance.