Circuit using NCP1216 to drive LED

Using the NCP1216 control chip with a power MOSFET, an inductor and a few external passive components, a simple high-energy-efficiency, constant-current converter can be implemented on a single power stage circuit. Since the output usually does not need to filter 100/120Hz The frequency content of the mains supply, therefore, does not require the use of large electrolytic capacitors in the circuit. This not only reduces circuit size but also improves overall power supply reliability.

This circuit is the most basic implementation of a non-isolated converter circuit. In this specific circuit with an AC input of 90 to 135V, a simple feedback network consisting of parallel current sensing resistor R4, integrating circuits R6 and C6, and an optocoupler allows this circuit to operate in constant current output mode. Typically an optocoupler is not needed in a non-isolated design, but here it is used to shift the current sense signal at the top of the LED string. The special implementation of this circuit allows it to provide high power factor and constant current output. The buck input capacitor C2 must form a high impedance to the 120Hz full-wave rectification waveform appearing on the input bridge rectifier circuit, otherwise the power factor will be as high as the capacitor The input filter also suffers significant degradation. The typical value of this capacitor is 0.1~0.47uF, which mainly depends on the target output power of the circuit. The inductance value of L1 needs to be low enough to allow the buck converter to operate in discontinuous conduction mode, which is important for a high power factor of the circuit. In discontinuous conduction mode, the capacity of C4 can also be quite small, 1~5uF, because it only needs to be used to filter out high-frequency switching components in the current waveform. C4 should use a low-ESR polypropylene film capacitor.