Constant voltage LED power supplies have isolated and non-isolated types. Non-isolated switching power supplies usually have basic working methods such as step-down and step-up:

1. Step-down circuit

① When the switch is off, the input value can be transmitted to the output;

② When the switch is closed, it will be cut off. This pulse-like energy transfer is converted and filtered to form a smooth voltage output. The pwm circuit converts its change into a pwm signal, which can manipulate the on-off time ratio of the switch to achieve stability.

2. Boost circuit

① When the switch tube Q1 is turned on, the choke coil L1 stores energy. il = uin / lt. Assuming that the current at the end of conduction is il, the energy storage is e = 0.5i21. After turning off Q1, il will decrease from il, and low left and high right self-induced electromotive force will be induced on L. The electromotive force is superimposed on uin through vd, and the two charging capacitors c are superimposed together and supply power to the load to obtain an output voltage higher than the input voltage.

②When Q1 is on, the capacitor MC1 only supplies power to the load. At this time, the anode potential of D1 is lower than the cathode and is in an off state, thereby preventing the capacitor from discharging in the opposite direction.

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