dreed75 said:
I have looked all over for a chip or a schematic that allows me to
convert 12v to 6v and I can't find anything. I can find 12v to 5v
with no problem at all but I need 6v. Would a simple voltage divider
work? The load changes so I don't think a voltage divider will work
but I am not sure. The current will be up to 3A at some times but as
low as 500mA at other times. Thanks.
David
The LM317, LM350 and LM338 and two resistors will all do that.
The chips (on heat sinks) can handle up to 1.5 amps, 3 amps
and 6 amps, respectively.
The LM317 with a PNP pass transistor and a few resistors is
probably your best choice. Simpler, but more costly, would be
the LM250 or LM338. Here's the circuit with the pass xsistor:
PNP
2N2955
e c
+12 -----+------ ---------------------+
| \ / |
3[R1] ----- |
| | ------------ |
+--------+------|in LM317 out|---+--- Vout +6
| ref | |
------------ [R2]240
| |
+----------+
|
[R3] 910
|
Gnd
There will be a voltage drop across R1 (3 ohms) as the LM317
provides current to the load. The more current that is
drawn, the greater the voltage. The effect is to cause the
transistor to conduct when the current drawn is about 200 mA,
and the more current that is drawn, the harder the transistor
conducts. R2 (240 ohms) and R3 (910 ohms) form a voltage
divider that "programs" the LM317 to produce very close to
6 volts. If you need it to be precisely 6.00 volts, substitute
a 10 turn, 1000 ohm pot for R3 and adjust it to the exact voltage.
Consult the datasheet for the LM117/LM317 for more detail.
http://www.national.com/ds/LM/LM340.pdf
Ed