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Can someone please take a look at my circuit?

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mindctrl

New Member
Hi everybody,

I drew up what I think my circuit should look like today. I'm basically trying to flash LEDs using a transistor, and then power the transistors using a PIC. I'm going to be powering the whole thing off of 12V car power supply (lighter socket). I don't have any fancy circuit drawing programs to do this on, so I had to do it the old fashioned way, by hand on some graphing paper. :) Thanks in advance!

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jrz126

Active Member
You shouldnt run your leds in parrallel with only one limiting resistor. The LED's vary slightly when they are manufactured so one could draw more current and burn put quickly.

oops didnt see the double post... :roll:
 

gerty

Member
I don't think you'll have enough headroom for your 7812 regulator to work properly. If I'm not mistaken it needs about 15 volts in and your charging system should only get up to 13.8 to 14.2..
The 5 volt should be fine..
 

checkmate

New Member
1. You can run the LEDs of the 5V line as well, saving a regulator.
2. Regulators always have a drop-out voltage as mentioned above.
3. There's no reason to use 3 transistors as opposed to a single one. I've seen parallel transistors being used only in power supplies where high current support is needed.
4. I think you've drawn the transistors the opposite way.
5. You may consider using an LED drivers such as ULN2003. If not, as mentioned above, try wiring one resistor per LED.
 

panic mode

Well-Known Member
wait a second...

1. you cannot bring 12V into 12V reglator to get 12V output
2. transistors are not wired correctly (C and E swapped)
3. add one resistor in base circuit of each transistor.
4. even if you swap the C-E on thansistors it makes no sense to
power the thing with 12V. you will be just wasting lot's of energy
on warming those transistors. recommendation is to connect
emitters to negative supply, put the LEDs in collector circuit to the
positive supply (doesn't need 7812 regulator). put three leds
and one resistor in series to form one string. put two such
strings in parallel to be driven by same transistor. repeat the same
for the other two channels or connect everything to one transistor
if intention is to turn them all together.
5. you could drive LEDs of the 5V rail but this would mean more
parallel circuit, bigger current draw and more heat on the regulator.
in such case ditch the 5V regulator and use 3 AA batteries instead
of one 12V. if it is intention to power the circuit from 12V source,
use one 5V regulator for PIC and wire LEDs and transistor(s) as
described in previous point....
 
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