Hi Guys,
I want to take the 5v from a molex plug and create 3.3volts.
1) How do i do this with resistors? Please provide details of how I calculate the 2 resistor values.
2) If i use a LM3940 regulator, do i need capacitors?
thx
if u use resistor to compensate some of the voltage, it will be unstable and the resistor will generate heat which is unnecessary for ur pc. same as the idea of using diode, because the voltage drop on the diode itself drift unevenly, hence u are not sure whether the output u get is exactly 3.3V or not..
its stil better to use a LMseries step down component in ur design, include some capacitor at the output to smoothen any ripple.
I'm fond of BAxxCC0FP/ BAxxCC0T (1A LDO voltage regulator). They have voltage drop of 0.3-0.5V that makes them very usable you have versions for all popular voltages (3.0, 3.3, 5, 7, 8, 9, 10, 12V). They are fairly cheap and accessible.
Compare the 0.3V typical (0.5V max) voltage drop to the voltage drop of L78xxACZ of 1.7V typical and I do not believe 78xxACZ was much cheaper.