Principle Analysis of LED Lamp Driver Circuit

In the figure, F1 is a fuse, and L1, C11, L2, and C12 form a common mode and differential mode EMI filter. C2, C3, D3, D4, and D6 form a flow-by-flow circuit to implement power factor correction. After the flow-by-flow circuit, the flyback switching power supply circuit composed of T1, Q1, D1, and C5 completes the isolated output and the voltage transformation function, and the control chip U1 realizes the switching control function of the flyback switching power supply circuit. The flyback switching power supply circuit has the advantages of simple circuit structure, safe isolation and low cost, and is particularly suitable for the requirements of a small power LED driving power supply . The flyback switching power supply circuit adopting the primary side switching control mode eliminates the secondary side output constant current constant voltage detecting circuit and the optocoupler device, thereby further reducing the cost and improving the system reliability and cost performance.

In the figure, resistors R1 and R2 are the starting resistors of chip U1, which are connected to the VCC pin of the chip to provide a certain amount of starting current to the chip. D5, R11, C9 constitute the absorption circuit of the flyback switching power supply circuit, and absorb the spike voltage on the switch after the switch Q1 is turned off. Na is the auxiliary winding, and D2, R6, C4 form the power supply circuit of the chip U1. At the same time, the auxiliary winding voltage is divided by the resistors R10 and R9 and connected to the FB pin of the chip as the output voltage detection and open circuit protection circuit.

R5A, R5B is the current sense resistor of switch Q1. After R4, it is connected to the CS pin of the chip, that is, the current sampling pin of U1. The pin 1 of the chip U1 is the output driving pin, and after passing through the Zener diode Z1, the totem pole driving circuit is composed of Q2 and Q3 to amplify the driving energy and is connected to the gate of the MOS transistor Q1 to control the opening and closing of the switch Q1.

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