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RPS with from 0-30V and Current variable up to 3 A design Circuit Please....

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rstofer:

--- Quote from: Zero999 on January 09, 2019, 12:57:47 pm ---
--- Quote from: David Hess on January 09, 2019, 12:35:19 pm ---
--- Quote from: Zero999 on January 09, 2019, 09:20:40 am ---He's right. It's not so much the current, but the voltage which is the problem. At 15V, an ordinary op-amp can be run from the unfiltered rectifier voltage. With 30V something more elaborate is required. The absolute maximum voltage rating of most standard op-amps is under 44V, which would be an AC voltage of just over 30V on the transformer secondary. A lower voltage transformer could be used, but that doesn't leave much headroom for voltage ripple.
--- End quote ---

So use a separate 40 volt low power regulator for the control circuits; it might be as simple as a zener shunt regulator.  Or configure the control circuits in a floating configuration with a low power negative regulator following the output voltage; this is more suitable for even higher voltage supplies.  With a floating design, low voltage operational amplifiers can be used.  The alternative to a floating design is to add high voltage level shifting between the operational amplifier and pass transistors which is a whole different set of problems; most new designers go this route.

--- End quote ---
My point was that none of that is necessary with a 0 to 15V supply.

--- End quote ---

I think this is the point I was trying to make.  The 0-30V 0-3A spec is nice to read but relatively difficult to achieve for a number of reasons.  Further, it isn't really necessary for the vast majority of bench type projects.

It isn't just finding a schematic, it's also having to make a PCB and, more important, lay it out properly.  Fewer parts is easier.

I wonder if the cheap supplies can actually deliver 3A at 0.1V.  In fact, I wonder how my DP832A would react to that.  The good news is that I don't have an electronic load to test it.  I'm not sure how it would come out.

not1xor1:

--- Quote from: Zero999 on January 09, 2019, 09:20:40 am ---
--- Quote from: not1xor1 on January 09, 2019, 07:48:42 am ---I do not think there is a lack of such schematic diagrams neither that it would be more difficult to design than e.g. a 0-15V 1A PSU.
4 large heatsinks and 8 TO3 BJTs can work for more than 120W of wasted power even without the help of fans.
It just does make little sense and would be more expensive than using a suitable multi-tap transformer based PSU.

--- End quote ---
Go on, post your design. . .

He's right. It's not so much the current, but the voltage which is the problem. At 15V, an ordinary op-amp can be run from the unfiltered rectifier voltage. With 30V something more elaborate is required. The absolute maximum voltage rating of most standard op-amps is under 44V, which would be an AC voltage of just over 30V on the transformer secondary. A lower voltage transformer could be used, but that doesn't leave much headroom for voltage ripple.

--- End quote ---

You must be kidding... nothing easier than that.  ;D

I made this from a quick copy & paste from other .asc files so there are likely some problems although it works flawlessly in the simulator.

BTW to play with it you need TL431 and BD140 models.

Zero999:

--- Quote from: not1xor1 on January 09, 2019, 07:04:22 pm ---
--- Quote from: Zero999 on January 09, 2019, 09:20:40 am ---
--- Quote from: not1xor1 on January 09, 2019, 07:48:42 am ---I do not think there is a lack of such schematic diagrams neither that it would be more difficult to design than e.g. a 0-15V 1A PSU.
4 large heatsinks and 8 TO3 BJTs can work for more than 120W of wasted power even without the help of fans.
It just does make little sense and would be more expensive than using a suitable multi-tap transformer based PSU.

--- End quote ---
Go on, post your design. . .

He's right. It's not so much the current, but the voltage which is the problem. At 15V, an ordinary op-amp can be run from the unfiltered rectifier voltage. With 30V something more elaborate is required. The absolute maximum voltage rating of most standard op-amps is under 44V, which would be an AC voltage of just over 30V on the transformer secondary. A lower voltage transformer could be used, but that doesn't leave much headroom for voltage ripple.

--- End quote ---

You must be kidding... nothing easier than that.  ;D

I made this from a quick copy & paste from other .asc files so there are likely some problems although it works flawlessly in the simulator.

BTW to play with it you need TL431 and BD140 models.

--- End quote ---
Many of those models are not in the standard LTSpice install, but I got it working eventually.

The only issue which immediately caught my attention is the rectifier diodes are underspecified, but that's easy to fix. No doubt it will work, after a bit of tweaking, but it's not a beginner project, like a PSU with a lower output voltage would be.

Please pay a bit more attention to the schematic layout: it's very hard to follow!

not1xor1:

--- Quote from: Zero999 on January 10, 2019, 09:29:49 am ---
--- Quote from: not1xor1 on January 09, 2019, 07:04:22 pm ---[...]
I made this from a quick copy & paste from other .asc files so there are likely some problems although it works flawlessly in the simulator.

BTW to play with it you need TL431 and BD140 models.

--- End quote ---
Many of those models are not in the standard LTSpice install, but I got it working eventually.

The only issue which immediately caught my attention is the rectifier diodes are underspecified, but that's easy to fix. No doubt it will work, after a bit of tweaking, but it's not a beginner project, like a PSU with a lower output voltage would be.

Please pay a bit more attention to the schematic layout: it's very hard to follow!

--- End quote ---

Yes I forgot a few other parts. I was in a hurry... otherwise I would have embedded at least the BJT models.
The schematic is a bit messy. I should have split at least the AC-DC + Vcc/Vee parts from the control circuit.

I'm in the process of designing a strip-board layout for a first low power version of the circuit (0-18V 1A) although I'm not sure when I'll be able to build it.

JohnPen:
I built  a PSU quite a few years ago from a circuit, I believe in the Wireless World you can tell how many years ago, that provided 2 x 22 volts at 2A.  It used separated windings on a 100 VA TFR to power the isolated sub PSU outputs.  Each sub PSU used a 78M12, directly from the rectified output, to power the control circuits consisting of 2 CA3140 (fet opamps).  The final regulator transistor was the good old 2N3055.   The voltage output was adjustable over ~ 0.5v to 22v.  It also has a adjustable current limit range ~20ma to just over 2A.  A separate overwind of a few turns on the TFR provided an extra low voltage AC feed to provide for a 7805 regulator to deliver a fixed 5v supply.  I felt at the time that it provided all the voltage/current/protection I would need for hobby use which included building a home computer.  Overall I found this PSU provided everything I wanted and only built one off dedicated supplies for projects such as Audio amplifiers that need higher voltages/current etc.  Out of curiousity I checked today what the lowest output voltage on one of the outputs could provide at ~2A and found it to be 0.5 volts with rapidly warming heatsink. :)

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