just watched psu#6. i'm concerned about the lt3080 burnt out. i had a situation of burnt npn power transistor that just simply short out the Vin to Vout, ie max voltage input=output. say we are powering 3.3V device and then poof the lt3080, if Vin something like 20V, then poof the device as well. so Dave, is there any protection/voltage sense on the output side to cut off supply in case the psu fails to regulate? or is it not necessary?
You have to ask yourself in what way can the circuit fail?
In essence, you can't really fully protect the output of a variable supply from circuit failure, because you don't know what the required output voltage the user has set, nor what maximum voltage the external circuit can tolerate.
You simply have to rely upon the voltage regulator working correctly and not failing in order to protect your circuit, there is little choice in that. That's the same with every supply, unless you designing some elaborate super redundant power supply for a 20 year life span on a space craft or something.
If the LT3080 suddenly shorts out for some reason then there isn't much you can do about it, the circuit you are powering won't get the regulated voltage any more. Not that the LT3080 is going to suddently "short out", as there usually has to be a deliberate external factor in order for that to happen.
If the supply was fixed then it would be easier of course, you could have a big zener on the output as additional fail-safe protection for example.
It is simply unrealistic to expect anything like this level of redundancy or protection from a regular variable bench power supply.
Dave.