Switch Mode boost Regulator
Rather than try something complex using a Linear mode regulator, might I suggest a Switch mode boost regulator instead. A boost regulator would be more accomidating to the wide voltage range you're looking for and would require significantly fewer parts. The problem with a linear circuit is the excess power losses, as the regulating transistor must drop the voltage from about 200V (your highest voltage output) to 50V your lowest value, a 150V difference.
One suggestion is to take a look at the LM3478 switching regulator configured in a Buck boost mode. In addition to easier implementation and fewer parts, you can use a low voltage input (perhaps 24V) that so that you don't expose yourself to dangerous voltage levels on the input side, while your testing your design.
http://www.national.com/images/pf/LM3478/10135501.pdf
Rather than try something complex using a Linear mode regulator, might I suggest a Switch mode boost regulator instead. A boost regulator would be more accomidating to the wide voltage range you're looking for and would require significantly fewer parts. The problem with a linear circuit is the excess power losses, as the regulating transistor must drop the voltage from about 200V (your highest voltage output) to 50V your lowest value, a 150V difference.
One suggestion is to take a look at the LM3478 switching regulator configured in a Buck boost mode. In addition to easier implementation and fewer parts, you can use a low voltage input (perhaps 24V) that so that you don't expose yourself to dangerous voltage levels on the input side, while your testing your design.
An externally hosted image should be here but it was not working when we last tested it.
http://www.national.com/images/pf/LM3478/10135501.pdf
That's a curious conception of "ease of implementation", and "fewer parts":
making a switching regulator work properly, from 0 to Inominal with a wide range of output voltage is not exactly trivial.
And I count 13 parts for this circuit, against 10 for the basic linear version.
Plus, I personally hate switching supplies for test gear: if you want to eliminate up to the last µV of differential and common mode noise, you have to go to extraordinary lengths of filtering, shielding, etc. And I don't like the relatively large output capacitors either: they have a good potential of destruction when something goes wrong.
But of course, all that is a matter of personal taste...
Elvee, I tried to run your file after downloading it and get a comment
'Can't find definition of model "BF469".
Because I am rather a newbee using LTspice: where can I find this
model and how can I implement this in the circuit diagram?
I see in the bottom left side of the diagram '.tran 0 60m 10m 1u'.
Has that something to do with this problem?
Sorry for the trouble.
Joe.
You can replace it with a 2N5551, it has an insufficient voltage rating and the collector capacitance is higher, but for the sim it should be OK (right-click and pick from the list, or simply edit the name)
No that's just the simulation statement, you can leave it as it is.
Note that the supply voltage and load current have heavy 100Hz and 1KHz ripple, it is intended to test the performances, but you can turn them off if you just want to examine the static operation.
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