sfields
Joined: 08 Dec 2006
Posts: 1
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 08 Dec 2006 6:39 Led indicator light problems |
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Here is another led issue... I need to connect one 5000mcd led to 110 volt as an inticator light. I need to do this in several locations, so I don't want to buy transformers to produce DC (I'm using lcd's for durability... transformers like to burn up). I have planned to use a 7.2k resistors (2w), followed up by a small diode to deal with the AC. Does this make sense? I'm assuming it would go: pos 110 voltage connected to resistor, then connected to the diode, then run to the positive side of the led. The neg side of the led would go back to the common side of the outlet. If this will work, does the diode have a direction it should go? how about the resistor? Is it correct to hook both of these up on the positive side?
Thank you so much,
Scott Fields
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fishkiller
Joined: 08 Dec 2006
Posts: 7
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| 08 Dec 2006 15:07 Re: Led indicator light problems |
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Hi,
Avoid to inject negative current in a LED.
To decrease the voltage you can use a capacitor
As you know Z=1/jCw
Z is the impedance of the circuit
C is the value of the capacitor
w = 2x3.14xFrequency (60Hz in USA, 50Hz in Europe)
j not used !
With the capacitor you won't have any problem with temperature compare to the resistor!
For 5mA / 110V / 60Hz you need Z=22k, so C=100nF
Prefere to use 2 capacitors for safety
Schematic:
110V o---||--- C=220nF -----(diode connect belove)-----(serial diode)--LED
110V o---||--- C=220nF ----------------*-------------------------------------LED
OK ?
Note capacitor must whistand at least 110V x 1.4 = 200V
Fishkiller
_________________
www.benito-design.fr
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