Physically the resistor is placed between the current source, be it a
battery, etc and the load, in your case the leds. The purpose is to limit
the current flow through the whole circuit, but more specifically the
applied current to the load, your leds. In doing this heat is dissipated at
the resistor and a voltage drop is developed across the resistor. Therefore
the applied voltage and currents applied to the load, your leds, will not
exceed the manufacturer specifications. As stated, without limiting the
current and voltage to the leds they will surely fail in a short period of
operation. Formulae I=E/R Current equals voltage divided by resistance, for
a purely resistive load.
Hope this helps kiddo, keep on asking questions, inquisitive minds are never
bored!! Cheers
"Reason" wrote in message
news:TdnFc.41411$l6.19925@clgrps12...

"Brian Gregory [UK]" wrote in message
...
"Buckshot" wrote in message

For example:

+-------------RESISTER----|-------|
LED LED
| |
-_____________________________

Leds wired parallel. I believe this diagram is right. What is the
need of the resister if:

Source Volts: 5
Draw per LED: 3.7V

What exactly is it doing. Sorry if Im sounding/looking amature I want
to learn though.

Buck

RESISTOR
AMATEUR

Without the resistor the LEDs would have 5V across them and they would
burn out in a fraction of a second.


Voltage is not load. Voltage is "electrical pressure." (in water, p.s.i.)
Amperage is "electrical flow." (in water, gal. per min.)
Resistance is the amount the "flow" is restricted by load.