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Posted by Tomi Engdahl (62.236.232.24) on December 24, 2001 at 10:19:50:
In Reply to: Droping voltage... posted by Bob on December 23, 2001 at 20:48:13:
: Hello :c)
: Im just starting to do simple electronic project and i need to drop the voltage from 4.75v to 3.3v. What size of resistor do i need.
You need a resistor which has the resistance
value of: (4.77V-3.3V) / takencurrent ohms
Where "takencurrent" is the current that 3.3V
load takes. If the current of that load is not
constant, then a simple resitor is not suitable
voltage dropping component, because the amount
of voltage it drops varied greatly depending on
the current flowing through it.
In case of varying load, methods like regulator
ICs (low voltage drop model in this application)
or series diodes are more suitable to think of.
: Now if i was to add a LED in this what would be the size of resistor would i need? the LED pakage have this info in the back:
: Power dissipation 60mV
: Forward current 20mA
: Forward voltage : 2.0v
Resistor = (psuvoltage-2.0V) / 0.020A
You just put the voltage you use to "psuvoltage".
In your applications is is propbaly that 4.75V
or 3.3V. You were not clear which one you planned
to use for this.