安森美公司的ncp101x系列集成固定频率电流模式控制器和700v的mosfet,能提供建立功能强大低功耗电源所需的一切,包括软起动,频率抖动,短路保护,跳频模式,最大峰值电流设定点和动态自供电等.本文介绍了通用输入电压(85-265vac),采用反激式输出功率5w的单片解决方案,包括ncp101x的主要性能,电路图以及主要的设计公式.
the ncp101x series integrates a fixed-frequency current-mode controller and a 700 v voltage mosfet. housed in a pdip7 package, the ncp101x offers everything needed to build a rugged and low-cost power supply, including soft-start, frequency jittering, short-circuit protection, skip-cycle, a maximum peak current setpoint and a dynamic self-supply (no need for an auxiliary winding).
unlike other monolithic solutions, the ncp101x is quiet by nature: during nominal load operation, the part switches at one of the available frequencies (65-100-130 khz). when the current setpoint falls below a given value, e.g. the output power demand diminishes, the ic automatically enters the so-called skip cycle mode and provides excellent efficiency at light loads. because this occurs at typically 1/4 of the maximum peak value, no acoustic noise takes place. as a result, standby power is reduced to the minimum without acoustic noise generation。
特性
built-in 700v mosfet with typical rdson of 11 or 22 ohms
large creepage distance between high-voltage pins
current- mode fixed frequency operation: 65khz - 100khz - 130khz
skip-cycle operation at low peak currents only: no acoustic noise!
dynamic self-supply, no need of an auxiliary winding
internal 1ms soft-start
auto-recovery internal output short-circuit protection
latched overvoltage protection with auxiliary winding operation
frequency jittering for better emi signature
below 100 mw standby power if auxiliary winding is used
internal temperature shutdown
direct optocoupler connection
spice models available for transient ac analysis
pb-free packages are available
fig1. 简化的内部电路图
the controller used in this application is a low cost monolithic design, the ncp1013. this, and the other members of the family, from the ncp1010 to the ncp1014, allow for the design of low cost, yet fully featured, switched mode powers supplies. they integrate many peripheral circuits, from start-up to current limit, whilst also adding the ability to run directly from the hv bus, thus obviating the need for a bias winding, and an overload feature ensuring low dissipation in overload and short –circuit.
the design comprises and input filter, bridge rectifier (using low cost 1n4007 diodes), bulk capacitors and line inductor in π-filter arrangement, the power stage, rectifier diode and smoothing capacitors. feedback is cvcc, constant current drive for the led’s with a constant voltage in the event of an open circuit output.
key features
wide input voltage range – 85 vac to 265 vac
small size, and low cost
good line regulation
high efficiency
overload and short circuit protection.
