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Gear / Technical Help => Remote Power => Topic started by: bagtagsell on October 06, 2005, 06:43:44 PM

Title: Help LM7805 Circuit
Post by: bagtagsell on October 06, 2005, 06:43:44 PM

In anticipation of a MT, I thought I would build a voltage regulator.  But its not working. 
Q: Did I wire the circuit right? (see picture)

Q: On page 1 on JB3 power2 thread, leegedy shows a schematic thats what I was trying to follow.  Can anyone explain this very slowly.

Title: Re: Help LM7805 Circuit
Post by: bagtagsell on October 06, 2005, 07:40:21 PM

picture coming soon.

Title: Re: Help LM7805 Circuit
Post by: Brian Skalinder on October 06, 2005, 07:55:45 PM

Pos (+) wire from battery to 7805 input pin.
Pos (+) wire from 7805 output pin to device's power plug.
Neg (-) wire from battery to ground (GND) pin, and from ground (GND) pin to device's power plug.

Title: Re: Help LM7805 Circuit
Post by: bagtagsell on October 06, 2005, 08:03:06 PM

(http://img335.imageshack.us/img335/1952/circuit8bh.jpg) (http://imageshack.us)

I think I messed up somewhere.

is this right?
(http://img368.imageshack.us/img368/812/circuitb4gx.png) (http://imageshack.us)
where do the other caps and resistors go?

Title: Re: Help LM7805 Circuit
Post by: Chuck on October 06, 2005, 08:26:59 PM

http://www.iguanalabs.com/7805kit.htm

Title: Re: Help LM7805 Circuit
Post by: bagtagsell on October 06, 2005, 09:29:24 PM

Thanks for the link chuck. 

Where should I put the resistors?

Title: Re: Help LM7805 Circuit
Post by: Chuck on October 06, 2005, 09:34:31 PM

Quote from: bagtagsell on October 06, 2005, 09:29:24 PM

Thanks for the link chuck. 

Where should I put the resistors?

Let me get my data books out.
If I remember right, you can set up a voltage divider with a couple resistors...
It's been a while... I'll get back to you.

Title: Re: Help LM7805 Circuit
Post by: Chuck on October 06, 2005, 09:43:25 PM

Here you go:

Title: Re: Help LM7805 Circuit
Post by: Chuck on October 06, 2005, 09:47:13 PM

I must've been thinking about a variable voltage regulator. The capacitors are used to filter and reduce ripple.

Title: Re: Help LM7805 Circuit
Post by: recordista on October 06, 2005, 10:55:21 PM

Check out the LM2940 (http://www.national.com/pf/LM/LM2940.html), which will work with lower battery pack voltages than the 7805 will.

Title: Re: Help LM7805 Circuit
Post by: bagtagsell on October 06, 2005, 11:30:48 PM

Update...

I removed all resistors.  I have one capacitor linking pins 2 and 3.

I have the pin of the battery going to pin 1 of the regulator

I have the sleeve of the battery going to pin 2

I have the pin of the output going to pin 3 on the regulator

I have the sleeve of the output going to pin 2 on the regulator

and I got nothing.

As I understand the capacitor is helping stablize the power?  I think if I removed it things might work, but I don't know.  If this is the right wiring is my regulator bad?