modified 8 years ago

Voltage divider that is not at dividing the voltage in half had to go to a thousand volts could have went higher to reduce to enough for a led to power on

00:52:08

Please someone explain my two blueprints, takes to much power with a voltage divider that is suppose to cut power in half 

published 8 years ago

tonyinselby

8 years ago

The resistance of the LED is not zero. So the total resistance of the right-hand part of the divider is "47000 in parallel with the LED", which is substantially less than 47000. Replace the LED with a simple resistor and try experimenting with various values.

tonyinselby

8 years ago

Apologies - I meant to say "the resistance of the LED is not infinite". In fact the total resistance of the LED/resistor combination is around 100Ω

jambo6984

8 years ago

Thanks everybody I'm just getting started with electronics although I've tinkered for years and it didn't make much since I bought a bunch of 47k and 22k resistors for a radio transmitter and was trying to use them for more stuff it just didn't make sense that I needed almost 2000 volts for it to bring it down to led level as a website told MD

jambo6984

8 years ago

Told me that a voltage divider will drop the voltage in half with two equal resistors

tonyinselby

8 years ago

Which it does - if the resistors are equal. However you can't treat them as being independent from what's connected to them. In your case you have a 47k resistor on the left and a 47k resistor *in parallel with an LED* on the right. The combination of resistor and LED has a resistance of about 95Ω, and the voltage divider is behaving accordingly.

eekee

8 years ago

At present, my biggest problem with electronics is learning to recognize and deal with the many interactions between voltage, current, and all the different components in a circuit. I like MOSFETs and op-amps because their very high input resistance means they just respond to voltage without changing the current, but even with MOSFETs the input voltage is relative to the substrate voltage which in some circuits varies depending on the input voltage, LOL!

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