The Need : I would prefer to not to spend >$750 (Cdn) for a linear bench power supply if possible.
I need a bench power supply for IoT and embedded system work. 12v max is fine (driving motors, relays) and most commonly I use < 5v to drive components, accurate control of 3.3v is a high priority (Most of my stuff is 3.3v).
I have installed a ATX Breakout Board from Dangerous Prototypes that presents the PSU voltages to some binding posts. I believe this circuit ensures a proper "load" to the PSU to prevent it from overloading. This is ok but far from ideal.
Materials on hand:
I have some High quality (800+ watt) Computer Power supplies that I no longer use, but in great shape. These supplies are "Gold" standard efficiency, high quality etc. etc.
They provide +12V, -12V, +5V and +3.3V
I have 30+ Amps available on each 12V rail.
Goal: I would like to build a project which will use the output from the PSU and provide:
Some Points of clarification: (from post below)
I envision a 3 part system:
A) The computer PSU is the back end and is not opened or in any way tampered with, I expected to use the 24 PIN Molex as the Input connector (no wire cutting) it provides power to parts B & C.
B) Power Rail (+12v) This is a fused rail (or current limited supply) that provides power to mechanical components motors, actuators etc. (would be a separate battery in the real robot) The bulk of the PSU power would flow this was up to say ~300 Watts
C) Front end (the project) provides the variable voltages and currents for the electronics test bed
1) I expected to come off the PSU immediately into a circuit breaker / polyfuse as protection into the project.
2) The output of the project would be max 5 Amps on the 12v and 3 amps on the other output voltages. I could get away with less.
3) I was looking for a way to make sure any noise/ripple in the PSU was reduced within the project, and not passed to the outputs
4) I was hoping to find a way to make sure the front end was very precise since it controls the electronics
5) "Emergency" shut down capability from the project to shut off all power via solid state relays. Example: Big red Button and/or triggered from conditions on the outputs
So I look at it as if we have a constant voltage source to multiple precision power supplies.
Part C - The Front End cont'd
1) Constant Voltage output set by a variable resistor .. highest possible with the +/- 12v sources.
2) Variable Current limits on all voltages, essentially a variable fuse on each of the stock voltages (+12v, -12v, +5v, +3.3v)
3) Constant current output using the +12v & -12v sources, Ideally with a settable voltage <= the source.
4) Digital display of settings, (maybe digital control of voltages etc. via digital resistors.).
5) Avoid voltage spikes at all costs (I have spent too much already on blown materials)
6) Need through hole parts, I can't mount tiny things on boards
If anyone knows of an efficient robust design for this please provide a link so I can find it.
Background: It is not for lack of trying that I come to this request ...
I made a few "Internet Projects" that have failed dangerously, one in a spectacular fashion with an explosive mosfet! (parts bounced off my eyeglasses) others just overheated, smelt bad and ejected magic smoke.
So just "googling it" has presented a lot of "solutions" but, I do not have sufficient knowledge to choose between the alternatives. As-in what is a professional safe design vs some young players daydream. I have seen many .. many .. internet solutions based on LM317 or 78xx voltage regs but just as many conflicting opinions about using them. I have also seen folks say just use a transistor with no further detail, quite frankly if I understood what to do I would not need to make this post.
I have watched Dave's Videos for a PSU, but it seems the designs evolved so much that I am not sure what portions are applicable to my need. It may be that what I need is a sub-component of his design.
Finally, I am interested any pointers to a really solid and current educational resource on precision power supply. I have become so "confused now" and I can't see the forest for the trees.
Thanks in advance