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Can we use 5VDC LED in the AC line to show indication

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strameshkumar

Feb 23, 2012
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Hi All, I am creating this design . The LED is 5VDC and take 40mA current. 10K Resistor is 0.25W. can this LED glow when the fuse blown ? Or It will glow in all time ?
 

shrtrnd

Jan 15, 2010
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If that fuse blows, you'll have 208VAC across a 10K Ohm Resistor and an LED.
What do you think is going to happen?
Why don't you just use a neon bulb?
 

duke37

Jan 9, 2011
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The current will be about 20mA AC.
The power in the resistor will be 200*200/10000 = 4W so a >5W resistor will be appropriate.
The led will pass current in one direction and will burn out when the polarity changes. One way around this is to use two leds in inverse parallel.

If the fuse blows, then the circuit will not be isolated and will remain a danger.
 

Minder

Apr 24, 2015
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As per post#2 use a neon, this is how it is done in industrial fuse holders to indicate blown fuse.
M.
 
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AnalogKid

Jun 10, 2015
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In place of a 10 W resistor you can use a 0.5 uF film capacitor rated for the AC voltage. But you still need either another LED or a 1N4007 diode in reverse parallel with the LED. And the downstream devices still will be dangerous when the fuse blows.

ak
 

davenn

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Sep 5, 2009
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Hi All, I am creating this design . The LED is 5VDC and take 40mA current. 10K Resistor is 0.25W. can this LED glow when the fuse blown ? Or It will glow in all time ?

If you have to ask this, then you probably shouldn't be playing with mains voltages


thread closed for everyone's safety


Dave
 
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