M
Mike
- Jan 1, 1970
- 0
I searched heavily on how to parallel 2 LM317 voltage regulators and I
think I found the answer but I need a little help . I'm new with
working with some of these components so please bear with me.
Here are the circuits I found, note that they have 3 LM317's but I'll
want to use 2 so just ignore one of them.
_______
| | 0.025 to
o--+--| LM317 |----- 0.25 ----------,
| | ___|___ |
| |___| | |
+----|-| LM317 |----- 0.25 ------+
| | | ___|___ |
| | |___| | | 5.0V
+----|---|-| LM317 |--+-- 0.25 --+--+---o 0 to 4A
| | | | | | |+
| | | |_______| | === 4.7uF
=== | | | R1 47 |
| | | | | gnd
| '---+---+--------+
gnd R2 | Vo = 1.25 (!+ R2/R1)
174 or 180 + n (R2 * 50uA)
|
gnd
Or to increase the accuracy and stiffen the output, add a jelly-
bean TL431 reference chip to servo the output voltage,
_____
| LM |
o--+-| 317 |--- 0.025 -----------,
| |_____| to 1.0, etc. |
| | _____ |
| | | | |
+----|-| 317 |--- 0.25 -------+ Vo = 2.5 (1 + R2/R1)
| | |_____| |
| | | _____ | 5.0V
+----|----|-| |--+- 0.25 -+-+----+---o 0 to 4A
| | | | 317 | | | |+
=== | | |_____| 470 | === 10uF
| | | | | 10nF | |
| '----+----+---+-+--||-, | gnd
gnd | | R2
__|__ 2.2k | 1.00k
| TL | | |
| 431 |----+----+
|_____| |
| R1 1.00k
gnd |
gnd
In Circuit#1 I don't understand the equation, how come it differs from
Circuit#2? Circuit#2 sounds better but I have no idea what a Jelly
Bean TL431 is. I searched and found different designes of the TL431
but I have no idea which one is this Jelly Bean . Most importantly
though I have no idea which pins of the TL431 to connect to. I have
no problems with the LM317, but the TL431 is a completely differnt
story. Looking at the circuit above, which pins are being connected?
By the way if you are wondering what I'm doing, I'm trying to convert
12->5V or 3.3V. I'm not quite sure which one yet, but it doesn't
matter as long as I use the equation to find the resistor values.
Although the equation of Circuit#1 makes no sense to me . I want to
combine both LM317's because they should give me a nice 3A, sure I can
use some other voltage regulator but I'm having problems locating some
with more ampage . Might aswell make use of what I got.
Thanks for he help, I really appreciated it.
think I found the answer but I need a little help . I'm new with
working with some of these components so please bear with me.
Here are the circuits I found, note that they have 3 LM317's but I'll
want to use 2 so just ignore one of them.
_______
| | 0.025 to
o--+--| LM317 |----- 0.25 ----------,
| | ___|___ |
| |___| | |
+----|-| LM317 |----- 0.25 ------+
| | | ___|___ |
| | |___| | | 5.0V
+----|---|-| LM317 |--+-- 0.25 --+--+---o 0 to 4A
| | | | | | |+
| | | |_______| | === 4.7uF
=== | | | R1 47 |
| | | | | gnd
| '---+---+--------+
gnd R2 | Vo = 1.25 (!+ R2/R1)
174 or 180 + n (R2 * 50uA)
|
gnd
Or to increase the accuracy and stiffen the output, add a jelly-
bean TL431 reference chip to servo the output voltage,
_____
| LM |
o--+-| 317 |--- 0.025 -----------,
| |_____| to 1.0, etc. |
| | _____ |
| | | | |
+----|-| 317 |--- 0.25 -------+ Vo = 2.5 (1 + R2/R1)
| | |_____| |
| | | _____ | 5.0V
+----|----|-| |--+- 0.25 -+-+----+---o 0 to 4A
| | | | 317 | | | |+
=== | | |_____| 470 | === 10uF
| | | | | 10nF | |
| '----+----+---+-+--||-, | gnd
gnd | | R2
__|__ 2.2k | 1.00k
| TL | | |
| 431 |----+----+
|_____| |
| R1 1.00k
gnd |
gnd
In Circuit#1 I don't understand the equation, how come it differs from
Circuit#2? Circuit#2 sounds better but I have no idea what a Jelly
Bean TL431 is. I searched and found different designes of the TL431
but I have no idea which one is this Jelly Bean . Most importantly
though I have no idea which pins of the TL431 to connect to. I have
no problems with the LM317, but the TL431 is a completely differnt
story. Looking at the circuit above, which pins are being connected?
By the way if you are wondering what I'm doing, I'm trying to convert
12->5V or 3.3V. I'm not quite sure which one yet, but it doesn't
matter as long as I use the equation to find the resistor values.
Although the equation of Circuit#1 makes no sense to me . I want to
combine both LM317's because they should give me a nice 3A, sure I can
use some other voltage regulator but I'm having problems locating some
with more ampage . Might aswell make use of what I got.
Thanks for he help, I really appreciated it.