AC-powered LED 使用交流电的LED指示灯-----LED INDICATOR

本文来自下面的连接：http://www.turbokeu.com/myprojects/acled.htm

A long time ago I found a little schematic on internet on how to power a LED from an AC Line.
I tested and modified it a little so now it works great.
You could use it as an power-on indicator for your waterpump or so. Also it can be used with whatever LED-color you like.

I included the schematics for US or canadian 110-120V 60Hz AC lines, as well as european or australian 220-230V 50Hz AC lines.

电路如上图，分别工作在220V与110两种电压的参数，LED的平均工作电流在10毫安左右，适合任何LED使用。

电路中的电阻R1是为C1的放电提供回路，不可省略，否则容易被电击。

电路不隔离，在制作时要特别注意安全。

The capacitor is used to drop the voltage and the resistor to limit the inrush current.
Since the capacitor passes the current in both directions, a small diode is connected in parallel with the LED to provide a path for the negative half cycle and to limit the reverse voltage across the LED. The resistor value was chosen to limit the worst case inrush current to about 150mA which will drop to less than 30mA in a millisec as the capacitor charges.
The 0.47uF capacitor has an impedance of 5600 Ohms at 60Hz so the LED current is about 20mA half wave, or 10mA average (for the 220V version the impedance of the 0.33uF capacitor is 9600 Ohms at 50Hz which gives you also a LED current of about 10mA average)

Z = 1 / 2*Pi*f*C

Z = Impedance in Ohms

Pi = 3.14

f = frequency in Hertz

C = capacity in Farads)

A larger capacitor will increase the current and a smaller one will reduce it.
The capacitor must be a non-polarized type with a voltage rating of 250VDC or more for 110V AC-lines, or 400VDC or more for 230V AC-lines.
Resistor R1 discharges capacitor C1 in a few seconds after AC-line is disconnected. Remember that R1 must be able to withstand the full half wave peak AC-line voltage.

IMPORTANT: The circuit is powered from the AC line, so I will not be held responsible in any way for burned fingers, or melted fuses in your house. Isolate all connections with heat shrink.