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EPR-16 参数 Datasheet PDF下载

EPR-16图片预览
型号: EPR-16
PDF下载: 下载PDF文件 查看货源
内容描述: 对于EP- 16 2.75 W,充电器/适配器使用LNK501工程原型报告 [Engineering Prototype Report for EP-16 2.75 W Charger/Adapter Using LNK501]
分类和应用:
文件页数/大小: 36 页 / 1420 K
品牌: POWERINT [ Power Integrations ]
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17-May-04  
EPR-16 – LinkSwitch 2.75 W Charger/Adapter  
4.2 LinkSwitch Operation  
When power is applied to the supply, high voltage DC appears at the DRAIN pin of  
LinkSwitch (U1). The CONTROL pin capacitor C3 is then charged through a switched  
high voltage current source connected internally between the DRAIN and CONTROL  
pins. When the CONTROL pin voltage reaches approximately 5.7 V relative to the  
SOURCE pin, the internal current source is turned off. The internal control circuitry is  
activated and the high voltage internal MOSFET starts to switch, using the energy in C3  
to power the IC.  
As the current ramps in the primary of flyback transformer T1, energy is stored. This  
energy is delivered to the output when the MOSFET turns off each cycle.  
The secondary of the transformer is rectified and filtered by D6 and C5 to provide the DC  
output to the load.  
Control of the output characteristic is entirely sensed from the primary-side by monitoring  
the primary-side VOR (voltage output reflected). While the output diode is conducting, the  
voltage across the transformer primary is equal to the output voltage plus diode drop  
multiplied by the turns ratio of the transformer. Since the LinkSwitch is connected on the  
high side of the transformer, the VOR can be sensed directly.  
Diode D5 and capacitor C4 form the primary clamp network. The voltage held across C4  
is essentially the VOR with an error due to the parasitic leakage inductance.  
The LinkSwitch has three operating modes determined by the current flowing into the  
CONTROL pin.  
During start-up, as the output voltage, and therefore the reflected voltage and voltage  
across C4 increases, the feedback current increases from 0 to approximately 2 mA  
through R1 into the CONTROL pin. The internal current limit is increased during this  
period until reaching 100%, providing an approximately constant output current.  
Once the output voltage reaches the regulated CV value, the output voltage is regulated  
through control of the duty cycle. As the current into the CONTROL pin exceeds  
approximately 2 mA, the duty cycle begins to reduce, reaching 30% at a CONTROL pin  
current of 2.3 mA.  
If the duty cycle reaches a 3% threshold, the switching frequency is reduced, which  
reduces energy consumption under light or no load conditions.  
As the output load increases beyond the peak power point (defined by ½·L·I²·f) and the  
output voltage and VOR falls, the reduced CONTROL pin current will lower the internal  
current providing an approximately constant current output characteristic. If the output  
load is further increased and the output voltage falls further to below a CONTROL pin  
current of 1 mA, the CONTROL pin capacitor C3 will discharge and the supply will enter  
auto-restart.  
Power Integrations  
Page 9 of 36  
Tel: +1 408 414 9660 Fax: +1 408 414 9760  
www.powerint.com