切換式升壓電路的電流

happybull

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.

happybull

電感 v=L*dI/dt
電流总是线性变化,LX电压会有瞬间变化.一些SYCHRONIZE BOOST mos 会被击坏是高压加电流.

我做的几个LED DRIVER 电流保护在700mA 左右,可以驱动6个LED ,MAX 35mA.