Overview: .. NCP1215A Low Cost Variable OFF Time Switched Mode Power Supply Controller
The NCP1215A is a controller for low power off−line flyback Switched Mode Power Supplies (SMPS) featuring low size, weight and cost constraints together with a good low standby power performance. The operating principle uses switching frequency reduction at light load by increasing the OFF Time. Also, when OFF Time expands, the peak current is gradually reduced down to approximately 1/4 of the maximum peak current to prevent from exciting the transformer mechanical resonances. The risk of acoustic noise is thus greatly diminished while keeping good standby power performance. A low power internal supply block also ensures very low current consumption at startup without hampering the standby power performance. A special primary current sensing technique minimizes the impact of SMPS switching on control IC operation. The choice of peak voltage across the current sense resistor allows dissipation to be further reduced. The negative current sensing technique offers advantages over a traditional approach by avoiding the voltage drop incurred by traditional MOSFET source sensing. Thus, the IC drive capability is greatly improved. Finally, the bulk input ripple ensures a natural frequency dithering which smooths the EMI signature.
