Sat Feb 5 09:50:00 EST 2011

3.3V from different regulator

I have a bunch of regulators, but no 3.3V ones.

If I recall there is a trick to get a different voltage from a linear
regulator by changing the feedback path..  How did that go?  See data
sheet [1].  That only shows how to raise the voltage though.  This
seems to be the default configuration for a component like [2] which
has a 1.25V reference.  The ARM board uses the L4931C33[3].

What about using a red LED to take the voltage drop/ That should be
about 1.8V?  ( Measured: the bright reds I have here are 1.67V which
is pretty close to perfect. )  So from 5V we go through the led to a
buffer cap.  Placing a resistor parallel to the buffer cap should
prevent the LED to turn off, which would lower its voltage, ultimately
charging the cap to 5V if there is no load attached.  Hmm.. There's
another problem: 5V across the LED when cap is not charged, so this
would need a current limiting resistor also.  But if the input also
has a cap, that problem is solved.

Seems quite a hack..  Ha, I found somebody suggesting it here[4].

Anyways.  I placed an order at Tayda.  Maybe visit RadioShack for some
3V3 regulators.  Other than that, I do have all components to solve my
most basic need.

[1] http://www.futurlec.com/Linear/78L05.shtml
[2] http://www.national.com/mpf/LM/LM317.html#Overview
[3] http://www.st.com/internet/analog/product/63164.jsp
[4] http://www.electro-tech-online.com/general-electronics-chat/88621-convert-5v-dc-3-3v-dc.html
[5] http://www.4uconnector.com/online/itemagrid.asp?seriesdesp=2.54+FEMALE+HEADER+PLUS+TWO+BASE+DIP+STRAIGHT+HEIGHT%3D13.59MM&seriesno=0197&GroupNo=01&groupdesp=Pin+%2F+Female+Header&itemnum=5324&sample=&seriesnum=96&