Here's a picture of the whole thing.

Attached Thumbnails

 

__________________

I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong.

Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.

 

Hi Hero,


Hey that's nice. I like the blue binding post too for the negative.

 

Just read through the last few pages.

Good project, I like the idea of using the case as a heat sink, does it get too hot though?

I was impressed with the way you tested the transient response.

Sorry for being picky but the paint job could be a bit better.

__________________
I am Hero999, I no longer visit here so if you want to contact me then my email address is
and I also post at www.silicontronics.com

 

I tested it with the output set to the minimum and drew 1.5A from each rail, it gets quite hot but not hot enough to burn.

The trouble was that the finishing on the enclosure isn't very good and no amount of sanding would make it smooth enough. I used spray paint which has the disadvantage of showing imperfections in the case, although it has the advantage of not having to worry about brush marks.

__________________

I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong.

Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.

 

Hey guys...I read through this whole thread and I decided I'd post my two cents if it is still active and anyone cares.

here is a pic of what I came up with when I considered making this type of PSU a long time ago. I never built it, but I did simulate it, and am in the process of actually working on it to build soon.

Now before anyone bashes me, it doesn't have any of the filtering caps of bypassing caps, this or that, bells or whistles. It's just simply showing you my idea of how to use the op-amp to track the positive rail.

My idea was to use it as an integrator and integrate the difference voltage of the rails at the 10k resistors junction. This way you slowly react to transients on the rails instead of causing an oscillation condition by using an opamp in an inverting setup in a negative feedback loop. Screams no no. Now whether this will achieve better phase margin and stability compared to the earlier design with appropriate compensation capactors. I cannot say right now.

However, from the start it was always my idea to intregrate the rail voltage difference. What do you all thing? You can adjust the "tracking" time by adjusting the integrators time constant.

 

As a followup, I do realize that the op-amp does not have a resistor on it's positive leg to counteract the input bias current as it should for a precision integrator. Obviously you'd want to use something like a JFET input op-amp with low input bias current and a resistor that on the positive leg that is equal to the equivalent resistance seen from the negative leg to mitigate integrator error.

Like I said previously, however, this is just a quick schematic for a proof of concept and the values don't really matter nor does it have all the trappings of something you'd want to build.

 

Jfice13, much of this thread is about stability and transient response. Read my post #11. It suggests adding the cap to make an integrator of the op amp.

__________________
Ron

 

Not obvious to me. The worst bipolar op amp I could find has a worst case bias current of 1.5µA. Even if you fail to put a resistor in the (+) input, the 6k ohm equivalent resistance could cause an offset error of only 9 millivolts. I would select an op amp based on input offset voltage, which rules out most JFET input op amps.

__________________
de KI6RWX