throbscottle
Well-Known Member
I arrived at this design for my PSU's linear output stage and tweaked it in LTSpice until I got a nice linear rise in output as the control voltage is changed.
So what we're looking at is a mains transformer/rectifier/smoothing producing 49V, a switching stage (represented by V1 and V4) which tracks the output and produces around 5-35V, and this linear stage, which will eventually have an adjustable current limit. I didn't think it necessary to regulate the low voltage supply for the op-amp.The output is adjustable from 0 to around 30v
V2 represents a 1.2V reference (ICL8069DCZR because they were cheap on eBay) with a 47K multi-turn pot across it (again, cheap on eBay),
I chose TIP42 as the pass element again because of cost, and LM324 I already have. BC547's I have a lot of old ones, that's why I'm using those.
I think that Q2 and Q1 should be thermally coupled, but I'm not sure.
I found that putting in R2 makes the output more linear, but I don't understand why. Make it low enough and it stops a nasty kink appearing in the op-amp's output at about mid-range. So can anyone explain what is going on there?
Also, I arrived at values for C3 and C5 by trial and error. I'd like to know how to calculate what they should be - so can anyone help me with that?
So what we're looking at is a mains transformer/rectifier/smoothing producing 49V, a switching stage (represented by V1 and V4) which tracks the output and produces around 5-35V, and this linear stage, which will eventually have an adjustable current limit. I didn't think it necessary to regulate the low voltage supply for the op-amp.The output is adjustable from 0 to around 30v
V2 represents a 1.2V reference (ICL8069DCZR because they were cheap on eBay) with a 47K multi-turn pot across it (again, cheap on eBay),
I chose TIP42 as the pass element again because of cost, and LM324 I already have. BC547's I have a lot of old ones, that's why I'm using those.
I think that Q2 and Q1 should be thermally coupled, but I'm not sure.
I found that putting in R2 makes the output more linear, but I don't understand why. Make it low enough and it stops a nasty kink appearing in the op-amp's output at about mid-range. So can anyone explain what is going on there?
Also, I arrived at values for C3 and C5 by trial and error. I'd like to know how to calculate what they should be - so can anyone help me with that?