POWER AND LINEAR IC SOLUTIONS

PWM Controller is Heart of LED Ballast Design

The NCP1351 from ON Semiconductor is a current mode, variable off-time PWM controller designed for cost-critical applications. It is particularly suitable for use in LED ballast designs, providing small size, low cost and high efficiency.

ON Semiconductor can supply a complete design based on the NCP1351 for a universal input 20W LED ballast. Incorporating schematics, a bill of materials and full details of how to calculate external component values, the design has a target efficiency of 80% within a 125mm x 37mm x 35mm form factor.

Using a flyback topology with isolation, the design can accommodate an input voltage of 85V to 265V, producing an output of up to 33V and a nominal current of 700mA. It includes an input filter, bridge rectifier (using low cost 1N4007 diodes), bulk capacitors and line inductor in a π-filter arrangement, a power stage, rectifier diode and smoothing capacitors. Feedback is constant voltage, constant current.



The NCP1351 controller itself has a very low quiescent current, allowing high value resistors to be used as a start-up circuit direct from the HV rail. In addition, its low start-up current assists engineers whose designs require low standby current.

The device uses a fixed peak-current technique, decreasing its switching frequency as the load becomes lighter. As a result, any design using the NCP1351 naturally offers excellent no-load power consumption, with optimal efficiency in other loading conditions. When the frequency decreases, the peak current is gradually reduced to prevent transformer mechanical resonance and hence cut acoustic noise.

The device, which is supplied in an eight-pin SOIC, includes natural frequency dithering to improve its EMI signature. Integrated protection includes UnderVoltage LockOut (UVLO) and OverCurrent Protection (OVP) with optional dual trip points, facilitating the use of the NCP1351 in peak-power applications. As well as lighting circuits, the device can therefore be used in a wide variety of cost-sensitive power supply designs, such as printers, game stations, and low-cost power adapters.



Features: NCP1351

• Variable off time PWM controller
• Extremely low start-up and quiescent current consumption
• Peak current compression reduces transformer noise
• Frequency reduces at lighter loads
• Natural frequency dithering for improved EMI signature
• Undervoltage lockout
• SOIC-8 Package
• Choice of standard or dual trip point overcurrent protection, latched or auto-recovery

Features: LED ballast design

• Wide input voltage range: 85VAC to 265VAC
• Output voltage up to 33V
• Output power 20W
• Output current 700mA
• Small size 125mm x 37mm x 35mm
• Low cost
• Good line regulation
• High efficiency: 80%
• Overload and short circuit protection
• Design includes schematic, layout bill of materials

For further information, including a copy of the NCP1351 Datasheet, please click here