David asked in Science & MathematicsEngineering · 8 months ago

# How can these led Christmas lights be 3V or 2.5V bulbs but its connected to 120V supply with no transformer? Why doesn't it blow them out?

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• Steven
Lv 7
8 months ago

Multiple LEDs are wired in series and require a current limiting device for that string, which may be just a resistor.  Some LED lamps use a switching low voltage power supply. But it is important to understand that LEDs do not have resistance in the normal sense. They have a "forward voltage" below which they conduct nothing and above which they conduct an unlimited current and burn out, so the current must be controlled by a resistor or controller chip. LEDs also require a rectifier because their reverse voltage capability is not enough by themselves.

• roger
Lv 7
8 months ago

Because there are  40 of them  connected in  series.    They  drop   3  volts each.  there is also a   limiting  resistor in the string.

• 8 months ago

Each LED is 3V@~10mA= 300Ω.  120V/3v= ~40 LED's in the string of lights.

• M.
Lv 7
8 months ago

Series string to divide the voltage.

• 8 months ago

Because 40 - 50 of them are connected in series.  If you have 40 bulbs rated at 3 volts each in series, the applied voltage would need to be 40 * 3 = 120 V.

• ?
Lv 7
8 months ago

120v is the maximum available voltage. it doesn't mean that's what everything attached to it draws. Your house is connected to a water supply system that moves thousands of gallons an hour, that doesnt mean it all tries to come out your kitchen tap when you turn it on.

• 8 months ago

THEY ARE JOINED IN SERIES TO MAKE UP AS A 120V LIGHT BULB,. tHEN IT CAN BE POWERED DIRECTLY WITH 120V WITHOUT BURNING DOWN.

3V BULB*40 PIECES = 120V BULB