power supply design

Thread Starter

richbrune

Joined Oct 28, 2005
106
Does anyone out there know how I might get the positive and negative supply voltage required to power a 741 or 1458 op amp from a transformer that is not center tapped? I am trying to amplify a small signal, but the signal goes from about zero to possibly as much as a volt, and sometimes it's not enough DC offset to get the amp to turn on at all, since the supply voltage to the op amp is zero and 12v DC positive. II need to power this circuit from a 24v RMS sine wave that goes positive and negative, but I'm only familiar with single supply (78xx) voltage regulators.
 

Thread Starter

richbrune

Joined Oct 28, 2005
106
Originally posted by Overclocked2300@Nov 6 2005, 07:06 PM
If you go from either side of the bridge rectifer you will find that One is positive and one is negative. Normally of the Positive Side the Caps are Facing Up (with the Plus sign facing towards the pos side), Basically Put 2 caps in series and make the point where they join ground (connect it to ground or chassis ground.)

Example:


Taken from:http://www.albertkreuzer.com/psu01.htm

(do a google search:http://www.google.com/search?hl=en&safe=off&q=Dual+Polarity+Power+supply&spell=1)
[post=11487]Quoted post[/post]​
So your saying that if I erase the line shown going from the secondary centertap to between c1 and c2 this circuit will still work?
 

kubeek

Joined Sep 20, 2005
5,719
If you need a little bit more stable source than the first one, use this.
And you can add some capacitors to the resistors and to the output, but they are not necessary.
 

Thread Starter

richbrune

Joined Oct 28, 2005
106
Originally posted by kubeek@Nov 7 2005, 11:47 AM
If you need a little bit more stable source than the first one, use this.
And you can add some capacitors to the resistors and to the output, but they are not necessary.
[post=11502]Quoted post[/post]​
Thanks for this, kubeek--- if it works the way it seems it will, it's brilliant. It seems as though it puts a 1/2 vcc bias to a signal I might want to apply to subsequent op-amps, using that 1/2 vcc point as ground--- Am I correct? I'm eager to try this one.
 

atferrari

Joined Jan 6, 2004
3,930
One caveat, though. If the op amp supply used is not able to deliver enough power you could get a misleading functioning.

But for opamps (few of them) dealing with signal only, should be OK.
 
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