24-02-2018, 07:44 AM
(This post was last modified: 24-02-2018, 07:58 AM by Diabolical Artificer.)
Have read parts of Craig's articles and your comments Mark, what follows is me thinking out loud trying to assimilate all the info, so if I've missed some of the points you've made, I apologise. I'll need to re read everything a few ( a lot of) times before it coalesses.
The first PDF that Craig linked goes on about "power supply related noise" ripple yes? One thing I have noticed about the CCS I've been using is the large ripple. Have knocked up a test circuit - a phase splitter, but this is unsuitable if i want to measure Z out, as it's tricky to vary two loads at the same time. So thought about a simple common cathode gain stage instead. What I am uncertain about as regards a test circuit is whether I need a high voltage gain stage as part of the set up.
As I understand it at present (this might be a bit sketchy ) I need to test a CCS for 1) compliance - IE it stays at XmA over a differing voltage range. 2) Z out 3) frequency response 4) good ripple rejection? 5) not go bang : )
Therefore to test 1) I'd need a variable negative DC voltage supply ( though over not much of a range, say 10v? , to test 2) I need to measure V AC out at no load, then either compare to a load at 90% or measure V out with no load load then attach and lower load till Vout is half. Finally to measure 3) I need to measure V AC out from 20hz to 30khz say. The only way I can do this with a certainty of the result is to do a manual sweep but in steps of 1khz say. As regards 4) simples, scope it. 5) switch on and duck.
Been looking online at mosfets and Darlington's (have some TIP122's). Mosfets are tricky as they have no hFE, but transconductance, no worries there, it's like a valve, just more mental gymnastics.
Andy.
The first PDF that Craig linked goes on about "power supply related noise" ripple yes? One thing I have noticed about the CCS I've been using is the large ripple. Have knocked up a test circuit - a phase splitter, but this is unsuitable if i want to measure Z out, as it's tricky to vary two loads at the same time. So thought about a simple common cathode gain stage instead. What I am uncertain about as regards a test circuit is whether I need a high voltage gain stage as part of the set up.
As I understand it at present (this might be a bit sketchy ) I need to test a CCS for 1) compliance - IE it stays at XmA over a differing voltage range. 2) Z out 3) frequency response 4) good ripple rejection? 5) not go bang : )
Therefore to test 1) I'd need a variable negative DC voltage supply ( though over not much of a range, say 10v? , to test 2) I need to measure V AC out at no load, then either compare to a load at 90% or measure V out with no load load then attach and lower load till Vout is half. Finally to measure 3) I need to measure V AC out from 20hz to 30khz say. The only way I can do this with a certainty of the result is to do a manual sweep but in steps of 1khz say. As regards 4) simples, scope it. 5) switch on and duck.
Been looking online at mosfets and Darlington's (have some TIP122's). Mosfets are tricky as they have no hFE, but transconductance, no worries there, it's like a valve, just more mental gymnastics.
Andy.
