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1.為什麼在設計POWER MOSFET時耐流要好幾百mA?
For DC-DC Boost type
Vout*Iout=Vin*Iin*effieciency
Assume Vin=3V,Vout=20, Effiieciency=80%,Iout(peak)=35mA
Iin=293mA
This is Iin average. ILX peak wil depend on 電感..I often reaches 500mA.
2.切換頻率越高 切換功率損失不也增加嗎?
為何 頻率 跟 效率 是成正比 ?
This is a tough question.
Power loss most on power FET loss(switching + IR),component loss(inductor+Diode), IC bias current and so on.
I deisgned couple LED drivers and I prefer to choos 500KHz to 1MHz. The efficiency is peak at 80%.
切換頻率 is not a major factor to improve 效率 for LED drive, a high voltage DCDC.
From my experiement, power FET loss(switching + IR) acounts for 5~8%, Inductor loss at least 10%.
頻率 跟 效率 是成正比 is more ture for Buck convertor. Higher frequency, less IR loss. |
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