標題: 電阻一問 [打印本頁] 作者: Jazz_Wan 時間: 2010-10-7 04:18 標題: 電阻一問 請問如果有粒LED最大係7.2V, 我要用一舊7.4 V LIPO去推, 咁我要加多OMH電阻呢?作者: G4guy 時間: 2010-10-7 08:54
150-200 Ohm作者: Jazz_Wan 時間: 2010-10-7 11:54
點計出黎架, 可唔可以教我呀?作者: nel3838 時間: 2010-10-7 19:33
V= I x R
Or ,Voltage = current x resistance
Or, R = V / I
Led typically can handle 50 mA max
So, R = 7.4 / 0.05 = 150 ohm, approx.作者: ryancmlam 時間: 2010-10-7 22:55
LED is in fact a non-linear device. If you make reference to the LED specification, you can check the forward voltage and current value. If I remember correctly, the typical forward voltage is around 3.2V with a forward current of 20ma. So, if the supply voltage is 7.4, the resistance R = (7.4-3.2)/20ma = ?? (no calculator on hand, do it youself then)作者: stanley_wwy 時間: 2010-10-8 22:04
voltage drop across the LED should be 7.4-7.2 = 0.2V in this case......