High efficiency 7.6 V 700 mA isolated LED driver design
First, the design features
1. Accurate primary side constant voltage/constant current controller (CV/CC) eliminates optocoupler and all secondary side CV/CC control circuits, eliminating the need for current sense resistors to achieve maximum efficiency; A low cost solution.
2, automatic restart protection function can reduce the output power to below 95% under the condition of output short circuit or open loop
3, hysteresis thermal shutdown function to prevent power supply damage
4. Meet CEC and ENERGY STAR 2.0 efficiency requirements:
5, green packaging: halogen-free and RoHS compliant
Second, the working principle
Figure 1 is a circuit diagram of a general-purpose input 7.6 V, 700 mA constant voltage/constant current flyback power supply designed using the LinkSwitch-II device LNK606PG for LED driver applications.
The LNK606PG (U1) integrates power switching devices, oscillators, CC/CV control engines, and startup and protection functions into the IC.
Diodes D1 through D4 rectify the AC input. Capacitors C1 and C2 filter the rectified AC. Together with inductors L1 and L2, these capacitors also attenuate differential mode conducted EMI noise. Resistors R1 and R2 can dampen the resonant oscillations that occur between these capacitors and the inductor. This design, combined with Power Integrations' transformer E-sheildTM technology, allows the power supply to easily meet EN55015 Class B conducted EMI requirements with a margin of greater than 10 dB without the need for a Y capacitor. The fusible resistor RF1 is used to limit the inrush current generated during startup and acts as a fuse when the component fails due to excessive input current.
This power supply design utilizes the constant current characteristics of U1 to drive the LED load and can operate at maximum output power in constant current mode. IC U1's constant voltage mode provides output overvoltage protection in the event of an open-circuit fault in any LED.
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