Types of circuit designs for LED constant current

A. Current Limit by Resistor
This design can provide constant current only when DC input and LED Vf both fixed. This design has very high risk because LED Vf is not a fixed value in common. This design can not assure the current constant and will cause LED damage or other quality problems. Therefore, this design is only implemented for simple flash lights and toys, not for general lighting purpose.

B. Constant Current by Driver IC
This design uses a Driver IC to provide constant current for single LED train. This design can solve LED Vf is not a fixed value problem. Its working principle is like an active variable resistor (VR). Therefore, this design can cause a lot of Power Loss when 1) Input DC voltage is much higher than LED Vf, and 2) to drive High-Power LED with large current.

C. Constant Current by Switching Power Converter (Buck Converter)
This design use a switching IC(PWM Converter), a Freewheel Diode, and a set of LC Filter. By switching and constant current filter working principle, this design can provide constant current for LED and there is almost no power loss. This is the reason why AOP implement Switching Power Converter design on all our popular products.