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| 安森美NCP1338电流模式控制方案 |
| 作者： 时间：2008-08-01 来源:eaw |
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安森美公司的NCP1338是用于自激准谐振操作的增强型电流模式控制器，包括了真正的电流模式调制器和去磁检测器，从而保证了任何负载条件下完全在边界线／临界导通模式以及在最低漏极电压时开关（准谐振操作）．变压器芯的重置检测由内部完成，不需要外界信号．工作频率内部限于130kHz，从而防止控制器工作在高于150 kHz CISPR-22 EMI．因此，NCP1338广泛应用在笔记本电脑的AC/DC适配器，离线电池充电器，消费类电子如DVD播放器，机顶盒，TV以及辅助电源如USB,TV和家用电器等．本文介绍了NCP1338的主要特性，内部电路架构和典型应用电路图．
The NCP1338 combines a true current mode modulator and a demagnetization detector which ensures full Borderline/Critical Conduction Mode in any load/line conditions together with minimum drain voltage switching (Quasi-Resonant operation). The
transformer core reset detection is done internally, without using any external signal, due to the Soxyless concept. The frequency is internally limited to 130 kHz, preventing the controller from operating above the 150 kHz CISPR-22 EMI starting limit.
By monitoring the feedback pin activity, the controller enters ripple mode as soon as the power demand falls below a predetermined level. As each restart is softened by an internal Soft-Skip_, and as the frequency cannot go below 25 kHz, no audible noise can be heard.
The NCP1338 also features an efficient protective circuitry which, in presence of an overcurrent condition, disables the output pulses and enters a safe burst mode, trying to restart. Once the default has gone, the device auto-recovers. Also included is a bulk voltage monitoring function (known as brown-out protection), an adjustable overpower compensation, and a VCC OVP. Finally, an internal 4.0 ms Soft-Skip eliminates the traditional startup stress. NCP1338 can be used in applications where the VCC supply voltage is delivered by an external dc voltage source.
NCP1338主要特性：
Free-Running Borderline/Critical Mode Quasi-Resonant Operation
Current-Mode
Soft-Skip Mode with Minimum Switching Frequency for Standby
Auto-Recovery Short-Circuit Protection Independent of Auxiliary Voltage
_Overvoltage Protection
_Brown-Out Protection
_Two Externally Triggerable Fault Comparators (one for a disable function, and the other for a permanent latch)
_Internal 4.0 ms Soft-Skip
_500 mA Peak Current Drive Sink Capability
_130 kHz Max Frequency
_Internal Leading Edge Blanking
_Internal Temperature Shutdown
_Direct Optocoupler Connection
_Dynamic Self-Supply with Levels of 12 V (On) and 10 V (Off)
_SPICE Models Available for TRANsient and AC Analysis
_These are Pb-Free Devices
NCP1338典型应用：
_Ac-dc Adapters for Notebooks, etc.
_Offline Battery Chargers
_Consumer Electronics (DVD Players, Set-Top Boxes, TVs, etc.)
_Auxiliary Power Supplies (USB, Appliances, TVs, etc.)
图１．NCP1338典型应用电路图
图２．NCP1338内部电路架构
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