On Semi NCP1251 20W低成本离线开关电源解决方案.docx

On Semi NCP1251 20W低成本离线开关电源解决方案On Semi公司的NCP1251是高度集成的PWM控制器,电源电压高达28V,固定频率65kHz或100kHz电流模式控制,内部有可调的超功率保护(OPP)电路,内部有4ms的软起动,+300 mA /?500 mA 源/沉驱动能力,220VAC时的待机功耗小于100mW,EPS 2.0 兼容,主要用在TV,STB和打印机的AC/DC转换器,笔记本和上网本的离线适配器.本文介绍了NCP1251主要特性,方框图,典型应用电路以及20-25W低成本离线电源主要特性，指标和设计电路图与相应元器件数值.The NCP1251 is a highly integrated PWM controller capable of delivering a rugged and high performance offline power supply in a tiny TSOP?6 package. With a supply range up to 28 V, the controller hosts a jittered 65 kHz or 100 kHz switching circuitry operated in peak current mode control. When the power on the secondary side starts to decrease, the controller automatically folds back its switching frequency down to a minimum level of 26 kHz. As the power further goes down, the part enters skip cycle while limiting the peak current.Over Power Protection (OPP) is a difficult exercise especially when no?load standby requirements drive the converter specifications. The ON proprietary integrated OPP lets you harness the maximum delivered power without affecting your standby performance simply via two external resistors. A latched Over Voltage Protection (OVP) is combined on the same pin. For ease of implementation, a latched OVP also monitors the VCC line. They offer an efficient protection in case of optocoupler destruction or adverse open loop operation.Finally, a timer?based short?circuit protection offers the best protection scheme, letting you precisely select the protection trip point irrespective of a loose coupling between the auxiliary and the power windings.NCP1251主要特性:Fixed?Frequency 65 or 100 kHz Current?Mode Control OperationInternal and Adjustable Over Power Protection (OPP) CircuitFrequency Foldback Down to 26 kHz and Skip?Cycle in Light Load ConditionsInternal Ramp CompensationInternal Fixed 4 ms Soft?Start100 ms Timer?Based Auto?Recovery Short?Circuit ProtectionFrequency Jittering in Normal and Frequency Foldback ModesOption for Auto?Recovery or Latched Short?Circuit Protectio