This design is a switching power supply constant current drive circuit, which is designed based on the second generation of enhanced high efficiency small power isolated switching power supply integrated circuit TNY268 introduced by Power Integrations.
First, the overall structure design of the circuit
1, the circuit principle block diagram, as shown in Figure 1.
Figure 1 circuit block diagram
2, the circuit schematic, as shown in Figure 2.
Figure 2 circuit schematic
Second, the working principle of the circuit
The input mains (AC ~ 220 V) passes through the AC-DC rectification and filtering circuit, and is connected to the power isolation transformer, the single-chip switching power supply chip TNY268P, and the secondary output voltage of the transformer passes through the output rectification and filtering circuit. D7 and Q1 are open circuit protection circuits.
TNY268P and power isolation transformer and C5 form the switching power supply circuit part. The secondary output of the power isolation transformer is rectified by D6, filtered by C6 and L3 to provide DC voltage to the load. The switching constant current power supply is an output current sampling, and the output current is stabilized by current negative feedback. That is, the current flowing through the load generates negative current feedback through R5 and R6, and the power output of the TNY268P is adjusted by the optocoupler PC817 to achieve the purpose of constant current.
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