Right like I said stupid question. I didn't think that one through, just used to using one of the breadboard's bus lines as virtual ground so in my eyes it was output to virtual ground since I have a wire going from output to that bus.

Especially since tangent's schematic had a 1K resistor going from output to vgnd. So I tend to still think that way.

Which btw, that was an earlier question of mine. When hooking it up that way, the rails became unbalanced as they were before the op-amp. At this point I guess its just curiosity although I think I get the answer now.

 

I'm having you place a deliberate, calculated imbalance on the output of the L2722.

Without the UNO connected, the L2722 will have to source an extra 22.5mA through the 360 Ohm resistance to V- in order to keep the virtual ground centered between the rails.

The UNO draws about 45mA when connected. So, the 360 Ohm resistor will sink 22.5 mA, and the L2722 will sink the other 22.5mA, plus or minus a tad, to keep the virtual ground centered.

This cuts the load on the L2722 in half, so the power dissipation is cut in half as well.

 

I understand and I just measured it and the current draw by the resistor is 22.2mA so its working correctly.

I'm going to go ahead and order a proper valued resistor as well as the resistor needed for that bucherot cell you mentioned earlier.

Thank you for all your help, I hope this will be the last of it.

 

One last question. You mentioned early a resistor for the regulator heat. I measured the current going into the regulator as 82mA.

So using that I would need a resistor around 158ohms (160) rated at 2.132W (2.5W).

Now where would I put that resistor, you said in the post before to put it between the transformer and the rectifier. Is that correct?

 

160 Ohms at 2 Watts would be OK; a 3 Watt resistor would operate more cool, as it would have more surface area to radiate heat.

Put the resistor between the large filter cap and the input of the regulator.

 

Okay cool, digikey only had 160 @ 3W anyway though I didnt check for 2W only higher than 2W.

 

Quick question about that 3W resistor.

Right now I have a wire going from the large filter cap to the regulator input. Did you want me to replace that with the resistor or put the resistor parallel to that wire.

If I replace it then the resistor get pretty hot.

 

Replace the wire with the resistor. Since you are using linear regulators, about the only thing you can do is change the place that gets hot, or spread the power dissipation around to different components.

You're better off with an inexpensive resistor getting hot, than having the regulator getting hot.