Electronics > Beginners

lab power supply

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tooki:

--- Quote from: EEVblog on December 15, 2019, 11:58:15 am ---
--- Quote from: tooki on December 13, 2019, 06:22:20 am ---It never came to fruition, but instead morphed into the still unfinished μSupply portable PSU project.

--- End quote ---

It has always been the uSupply portable USB PSU project.

--- End quote ---
Well then what’s this, then? It makes no mention of portable or USB:

https://youtu.be/CIGjActDeoM

It wasn’t until part 11 that you expressly mention wanting to make it portable:
https://youtu.be/xa9Lyb45oJM


And not until part 14 did you name it uSupply.

So while it might have always been envisioned in your mind as the uSupply, anyone watching the PSU series from the beginning (as I did) would see it as morphing from a more traditional PSU design into the uSupply. And for sure, for someone looking for how the “lab PSU” series continues, it’s not self-evident from the video titles that the uSupply is the continuation. Looking for “PSU part 14” comes up dry.

David Hess:

--- Quote from: not1xor1 on December 15, 2019, 06:03:27 am ---
--- Quote from: David Hess on December 15, 2019, 02:29:28 am ---Below is the lab power supply schematic that I would emulate from National Semiconductor linear brief 28.  Instead of using expensive LM395 integrated power transistors, the power pass element could be replaced with suitable integrated regulators or bare transistors or some combination of the two.
--- End quote ---

that's a nice circuit (unlike the other ones >:D) but it looks like LM308 is no longer available and LM101 is hard to find and very expensive, although there are cheap LM301 in sot8 package from onsemi.

replacing those opamps with modern parts would require a different compensation network and careful selection of parts complying with the same input range (and other features) of the original ones or mirroring the design (regarding polarity) to rather use the so-called single power supply opamps that usually include the negative rail as input range.
--- End quote ---

The LM101 is the military temperature range version of the LM301 and the LM301 can be replaced with the LM301A which is readily available.  (1) The LM308 as used here may be replaced with practically any device although the LT1008 from Linear Technology is an improved direct replacement.  The LT1012 and LT1097 are also improved replacements which include internal compensation.

The LM301A would be very difficult to replace in this circuit because:

1. Its input common mode range includes the positive supply making it especially suitable for a high side current sense amplifier or in this case, a high side current error amplifier.  There are many modern rail-to-rail input parts and several older JFET input parts which meet this requirement however ...
2. Its external compensation pin can is used here to clamp its output to improve overload recovery time.  The list of modern operational amplifiers which can support this mode of operation is very short.  The aforementioned LT1008, LT1012, and LT1097 are the only common modern possibilities I am aware of.  Analog Devices makes some parts which might be able to do this but since they do not publish schematics, there is no way to know without reverse engineering them.

I mostly listed this example circuit as something to study because it includes many lessons in practical design like low output capacitance, active pull-down, and direct high side current sensing.  There are ways to externally clamp an internally compensated operational amplifier however they get complicated very quickly so it is very rare.

(1) The LM301A is an LM301 with improved input bias current over temperature.  The LM301 was only produced for a very short time before being replaced with the A version.

glinjik:
progress so far well used the 2 tanilum caps i think they are called and works great so far very stabe of course no load no heating up but anyway its cool so far

Jwillis:
The yellow caps you showed don't look like tantalums . They look more like monolithic ceramics . I could be wrong . If they are indeed tantalums there should be a marking on them that shows a polarity.Monolithic Ceramics will just have a number code. If they are monolithic ceramics it won't be a problem using them in your circuit.

glinjik:
thank you for clearing that up you are correct not tantalums that bit of the circuit worked fine yesterday untill i put a 5w resister load to see what amps im getting and my 4 1000mf caps went up in a kind of smoke cloud lol i just dont have a big enough cap for this at the moment oh i think the two 2n3055 transistors blew as well cant complain at least i only fryed a few components and not myself this time at least the fuse didnt blow  :palm:

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