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[SOLVED] Compensate Voltage Drop

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Englewood

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Hi,

How can i compensate a volatge drop of 2V across a LED.

Im putting 9V through a temp switch through an LED but im only getting 7V out.

I would like 9v out to keep the voltage in and out the same.

Is this possible?
 

Audioguru

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A switch is on or off. An LED has a maximum allowed current that must never be exceeded.
Your circuit has switched 9V from the switch blowing up the LED because you have nothing in series to limit the current.

If you want to use the switched 9V to power something else then use it since the LED and its current-limiting resistor have nothing to do with the voltage.
 

SunnySkyguy

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Use the thermal cutout with 0V drop in series, then use the LED indicator in parallel on the output with a series current limiting Rs.

Rs=(9-2V)/If
for small forward diode current If, of say, 3 to 14mA or ~ Rs=2.2k to 470R 1/4W
 

Englewood

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Sorry i have used a resistor to limit the current to the LED.

I have 9V going through a 1k resistor through a LED through a thermo cut off switch.

I want the system to recieve 9V on the output.

Resistor VD is 2V
LED VD is 2V

Will the system see 9V on output? when swicth is closed or do i have to take the 4V of the 9V so the output is only 5V?

Im new to this :-(
 
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SunnySkyguy

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Show all part types or numbers incl. source and load or heat source and schematic


a switch should be 0 V drop

the resistor for LED should be 7V drop.
 

Englewood

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Sorry the resistor drop is 7V the switch is 0V

All sorted having a THICK moment.
 
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d123

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Thick = not intelligent. I think he may mean a momentary confusion probably common to beginners when we are overwhelmed where an issue with the circuit bamboozles the brain into not seeing something obvious or getting your knickers in a twist with a problem then seeing it. I never have such moments on a frequent basis, I just know some-one who does, honestly.
 
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