LED indicator

how should I drive an LED from a 38 volts power supply? The led wizard says I need a 1800 ohm, 2 watt resistor, but it also says' it'll disipate excessive heat. I recently took apart a surge protector and found that they drive an LED from a 120volt source by having a diode, LED and what appears to be either a 1 or 2 watt resistor. I need help driving an LED from a 38 volts power supply just as an indicator.

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tech-king10 years ago
the power supply works by using a zener diode to filter of extra voltage. heres a hard to understand diagram of what happens( for a better one, check the pics) :

zener diode rated to a turnover voltage of approx 100 volts

basically, a zener diode is a diode that conducts in both directions after the current passes a specific turnover voltage. by wiring it like in the above diagram, approximately 10 volts pass into the led's resistor.
gmoon, they sell 10 watts at 2 dollars in Montreal.
instructables 001.jpg
guyfrom7up (author)  tech-king10 years ago
are you taking an electronics course, and those your notes? What class are you taking, it looks like a good course
Forrest Mims puts out a wide range of books on the subject of electronics engineering in an easy to understand format.
hey :-), the book i got this diagram out of is from forest mims III.
Ahh, I made a "good guess then" :-) I thought I recognized that from somewhere
this is from his manual exclusively for radio-shack, when the shack still sold electronic components, and at reasonable prices. this book is copy write 1983
Yeah, about the time I was gathering books of that sort from all over. I was about 25 - 26 at the time. I have a few of his Op Amp workbooks too.
no. this is from a handwritten electronics manuel from the 1990's. although i am taking an electronics course.
NachoMahma10 years ago
. Use multiple resistors, such that each one handles only part of the load. Same amount of total heat, but you can spread it out.
gmoon NachoMahma10 years ago
In parallel, of course. And you won't need to pay the extra $$ for 2 watt resistors, just use four 1/2 watt.
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