I've been into the electronics hobby for a while and my field of work is also closely related, and I've been watching EEVBlog videos for a while. Decided I would finally sign up on the forums and poke the forum brains a little for some ideas.
Believe it or not, I've gotten through all these years without a proper bench supply. I've literally got a whole pile of fixed-voltage power supplies I've been using. Cumbersome and a real pain in the butt.
Well, it's about time I get a proper bench supply. I could just go buy one, but what would be the fun in that?
Anyways, the specs I'm aiming for is 0-50V at up to 5A, linear. At these voltage and current levels power dissipation of a purely linear regulator will be an issue.
These are the possible solutions:
1) SCR-based tracking pre-regulator on primary side of transformer (kind of ugly, but it works, I've seen it done in some high current HP lab power supplies)
2) switchmode tracking pre-regulator before linear regulator
3) multi-tap transformer with relays to switch between taps
4) BIG BIG HEATSINK
5) Get creative?
A few considerations:
-I've got all the parts necessary to build several power supplies following option 1 or 2
-Option 2 would require careful design to avoid EMI/RFI being conducted through to the output.
-Option 3 would be more costly, as I would have to source and purchase transformers with multi-tap secondary
-Option 4 is absolutely ridiculous and there is absolutely NO WAY I will be doing it
As for "getting creative", I thought of perhaps using a series pass transistor between the bridge rectifier and filter capacitor. This transistor would be switched on until a comparator detects that the voltage on the capacitor reaches a certain level (Vout+5V for instance, arbitrary number for now), then turns the transistor completely off until the next cycle. Relatively simple, but in theory should be quite effective. Main problem with this setup is the large amount of 120Hz ripple at lower voltages and high currents, which would require a fairly substantial capacitance to keep the linear regulator in its "happy zone".
What do you think? I'm having trouble deciding which approach to take.