0-18V Pos/Neg 1A Current Limited

[CBETO3AP]

The truth is that I respond with fear, you're very reluctant to my comments and I need not bother you.
For me it is obvious that feedback must be in the output of the circuit. I suspected but was not so obvious that the C11, C12 are very large but audioguro corrected me and then I saw that could cause the problem.
  You need to know the why of each component in your circuit to reason and improve it. This is sometimes quite difficult, especially when you copied the outline of another without understanding. I'm not electronics guru, so I entered this community, to continue to learn from those who know more. Here I ended the conversation with you, you obviously do not need my help.

 

[liquibyte]

You can do a search for output decoupling caps to ground and you will find several references to 1uF to 2.2uF for the values in an effort to solve oscillation.  I used these because of that actual problem I was having.  I do understand each component in the circuit having studied it extensively and having modelled it in LTSpiceIV extensively to arrive at the circuit that I posted.  Bringing in linear regulators to the circuit added nothing to the conversation whatsoever.  I did not copy that other circuit, I based mine off of that configuration.  By the way, the 0-30V circuit uses the same principles and quite a bit of the same configuration.  I don't know if you've noticed but I posted a modified version of that circuit that I'm working on as well.  I removed the part of the circuit that was the negative regulator because it really added nothing to the circuit and introduced issues that has made it hard to fix.  We now have a 10V reference and a 0.1 ohm current sense resistor that suffers from much less heat than before.  Still think I don't understand what's going on?

 

[audioguru2]

I am glad that the value of the R7 heater has been reduced to 0.1 ohm. The original was 0.47 ohm which heated with (3A squared x 0.47 ohm=) 4.23W. The TL081 opamps that were used had a maximum input offset voltage of 15mV (!) so the minimum regulated current with an accuracy of 20% was 15mV/0.47 ohm x 1/5= 6mA but they claimed 2mA.

I do not think anybody needs current regulation less than 20mA (for an LED?).

 

[liquibyte]

I am glad that the value of the R7 heater has been reduced to 0.1 ohm. The original was 0.47 ohm which heated with (3A squared x 0.47 ohm=) 4.23W. The TL081 opamps that were used had a maximum input offset voltage of 15mV (!) so the minimum regulated current with an accuracy of 20% was 15mV/0.47 ohm x 1/5= 6mA but they claimed 2mA.

I do not think anybody needs current regulation less than 20mA (for an LED?).

I tried my best to fix a few of the more glaring issues that I had while I was testing.  The one thing that always bothered me was the current sense heater.  I felt like I should be using this as an on demand water heater.  I'm actively working on prototyping out the changes to see what works and what doesn't.  The one thing we lose is getting voltages close to 0V but I don't think anyone really needs that either.  I haven't looked at different op amp solutions yet because the TLE214x family worked so well but my guess is that a nice rail-to-rail could go in there now without issues due to the 36V regulator circuit and come close to addressing that issue.  My focus was on the transient issues and a better current sensing scheme.  I'm planning a voltmeter/ammeter for this using modern parts.  12bit ADC, Atmel microcontroller (up for debate but I've got some blank 328P-PU's), and a MAX7219 to drive the displays, and a 4-wire sense resistor.  Doing the meter is more for the educational value than anything else for me but some folks might find it useful so I plan on releasing everything all at once when testing is complete.