RPS with from 0-30V and Current variable up to 3 A design Circuit Please.... - Page 1
Forum section: electronics / beginners

author: techguru
author_rank: Regular Contributor
timestamp: January 06, 2019, 05:54:31 pm
content: Dear all,For past three month i have been designing a variable power supply which gives 0-30V and Current variable up to 3 ampere from zero. can some can give working Schematic so that i would understand and complete my project. thank you all..

author: rstofer
author_rank: Super Contributor
timestamp: January 06, 2019, 06:17:13 pm
content: https://www.eevblog.com/forum/beginners/diy-0-30v-0-3a-again/See Reply #7Most of these projects fail to meet the specifications. Some can't get down to 0V because they don't have a negative supply for the op amps. Some can't handle low voltage with high current because there is too much voltage drop across the output transistors. None have transformers with taps to solve this issue.The Internet is full of circuits that don't work. If there was one that did, it should be posted as a 'sticky'.

author: David Hess
author_rank: Super Contributor
timestamp: January 06, 2019, 10:42:49 pm
content: 30 volts at 3 amps is a tough row to hoe without a lot of extra complexity. 90 watts worst case requires multiple transistors and 30 volts peak is marginal for common operational amplifiers which have an absolute maximum voltage rating of 36 volts. 20 volts at 1 amp is much easier.

author: techguru
author_rank: Regular Contributor
timestamp: January 07, 2019, 08:10:28 am
content: Hi to all,The above said opamp Vcc problem is true.What are the opamp whose Vcc greater than 40V and above in single supply operation. So that I could use it in my circuit.thank you all.

author: BravoV
author_rank: Super Contributor
timestamp: January 07, 2019, 08:18:01 am
content: Quote from: techguru on January 06, 2019, 05:54:31 pm3 months ? Its been almost a year Gurumurthy ... (this guy previous nick).The same guy that keeps haunting this forum for his 723 based PSU, as he keep posting another new thread "AGAIN AND AGAIN" if he does not have the component in his drawer as the circuit needs, and keeps nagging until someone give him a circuit that can do 30V 3A 723 based PSU with components that he owns.Reference ->https://www.eevblog.com/forum/projects/how-to-calculate-potentiometer-value/msg1237728/#msg1237728

author: not1xor1
author_rank: Frequent Contributor
timestamp: January 07, 2019, 08:25:18 am
content: Quote from: David Hess on January 06, 2019, 10:42:49 pmsince neither a zero ripple voltage unregulated DC source nor a zero drop voltage power device exist, in the real world, the worst case would require - at the very least - 100W (may be even 110-120W) of power dissipation

author: David Hess
author_rank: Super Contributor
timestamp: January 07, 2019, 09:19:02 am
content: Quote from: techguru on January 07, 2019, 08:10:28 amIf you do not mind paying a premium, the LT1006/LT1013/LT1014 (single/dual/quad) operational amplifiers are single supply and 44 volts replacements for the common 358/324. There are also newer low cost parts like the MC33171 and MC34171 series which I have never used.There are some higher voltage specialty parts but an alternative is to design the control circuits so they either float using the output voltage as ground or have a separate floating supply from another transformer winding. If the low voltage floating supply is bipolar, then any operational amplifier can be used.

author: techguru
author_rank: Regular Contributor
timestamp: January 07, 2019, 02:46:14 pm
content: Is it possible to construct my requirements with opamp and discrete components?give me some idea to construct the circuit.Kindly guide me in this direction.. thank you all...

author: xavier60
author_rank: Super Contributor
timestamp: January 08, 2019, 12:36:09 am
content: Yes, almost all audio power amplifiers are like a big op-amp. You will need only the transconductance part driving the output Darlington.There will be complications like adding current regulation and making it regulate down to zero, likely requiring a - rail. You will end up with a monster like most other designs out there.

author: techguru
author_rank: Regular Contributor
timestamp: January 08, 2019, 09:54:01 am
content: If any other possibility are there?Like Mr.bravo said I am trying this project for more than a year.now I came to know that linear mode that is class A mode of design is intractable.You all guide in design class s amplifier (smps), where my efficiency is nearly 100 percent. Buck topology.I think I am moving in right direction.help me in this regard.

author: Zero999
author_rank: Super Contributor
timestamp: January 08, 2019, 01:28:01 pm
content: I've never heard of a class S amplifier don't you mean class D?Why do you need a 0 to 30V, 0 to 3A PSU for an audio amplifier? I presume you want a general purpose bench power supply, rather than a dedicated audio amplifier PSU. A decent audio amplifier design shouldn't need a tightly regulated power supply. It should be designed to reject changes in the power supply voltage, without passing them through to the speakers.The problem with a constant voltage and constant current PSU is Ohm's law states that it can't be in both modes simultaneously. When the load resistance is above a certain point which would exceed the output voltage setting, it will be in constant voltage mode, then when the load resistance drops below the point when the current limit would be exceeded, it will switch to constant voltage mode. The problem is switching from constant current to constant voltage modes and back with minimal oscillation and current/voltage over/undershoot. Oscillation can be avoided, but it's actually impossible to prevent over/undershoot.Here's a simple constant VI regulator I lashed up in LTSpice. U1 needs to work with its inputs down to 0V and U2 with its inputs up to +V. V2 and V3 set the voltage and current limits respectively. D1 turns on when the regulator current limits, otherwise it's off. RL1/2/3 test the transient voltage and current response. RL1 applies a step load of 500mA, for 10ms. RL2 takes it into constant current mode and back again. RL3 as good as short circuits the power supply, when it's in the constant current mode.C2, C2, R8, R9 and R10 form phase compensation networks which reduce the oscillation.The transient response isn't great. Adding a capacitor across the output will cut down on the voltage over/undershot, at the expense of current overshoot and adding an inductor will improve the current mode, at the expense of the voltage mode.

author: techguru
author_rank: Regular Contributor
timestamp: January 08, 2019, 02:46:15 pm
content: Sorry it is class d amplifier. Thanks a lot. I will try to understand the schematic.

author: rstofer
author_rank: Super Contributor
timestamp: January 08, 2019, 06:02:46 pm
content: Quote from: techguru on January 08, 2019, 09:54:01 amIf there was a circuit out in the wild that would actually deliver 0-30V and 0-3A, it would be all over this forum. It would be a sticky on every forum. Everybody on the Internet would know where to find it. Instead of dozens of replies, the matter would be settled with a simple link and the comment to "build this".Alas, it's just a lot harder than it looks. Any design without 3 or 4 parallel pass transistors is probably not going to deliver 3A at 0.1V without transformer taps. High voltage op amp selection is a challenge. There's a reason that 'real' bench power supplies cost so much money. There's a lot of parts!If the power supply is for a fixed load, like an audio amplifier, the 0-30V 0-3A spec doesn't make sense. If it's for a bench PS then why in the world do you need anywhere near 3A? For that matter, why 30V? A 1A adjustable supply is perfectly reasonable for the bench and, in fact, adjustable voltage isn't a real requirement either. 5V, +-15V and, maybe, +12V fixed 1A supplies will probably cover just about every conceivable situation that is 'general purpose'. Sure, vacuum tube circuits clearly need other voltages but that arena is covered by dedicated fixed supplies.My view on the 0-30V 0-3A: Somebody wrote it down once and now it is the assumed standard in the industry. In fact, there are few DIY projects that succeed. Try audioguru's project and if it works out, it will be one of the few designs that actually delivers. But don't substitute parts! See Reply #6 here:https://www.eevblog.com/forum/beginners/diy-0-30v-0-3a-again/As a reference point, the Rigol DP832 PS costs about $500. It has 3 outputs that will presumably deliver up to 3A each, 2 at 0-30V and 1 at 0-5V. But it costs $500 and there's a lot of reasons why.There are a lot of cheap power supplies - they are all over the Internet.https://www.amazon.com/Lab-Power-Supplies/b?ie=UTF8&node=318022011

author: David Hess
author_rank: Super Contributor
timestamp: January 08, 2019, 06:09:26 pm
content: The first example below is a design which almost meets your requirements. I would not implement it as shown because it uses LM395 integrated power transistors but it could be modified to use normal transistors. It could also be modified to work without a negative supply. Notable features are very low output capacitance and fast transitioning between constant current and voltage modes.The second example below from theTektronix PS501is closer to what I would do. Notably:1. The current sensing is on the high side of the output making it more accurate. The current shunt in series with the output can be used to make the regulation loop more stable although that was not done in the PS501.2. For a high power supply, I would replace the output transistor with an integrated regulator like a 317 driving a set of big power transistors. This allows the integrated regulator to protect the output transistors however it also means that a negative supply is required to allow the output to get down to zero volts.3. I would add clamping to the error amplifiers to reduce transition time between voltage and current mode.

author: rstofer
author_rank: Super Contributor
timestamp: January 08, 2019, 10:31:31 pm
content: Quote from: David Hess on January 08, 2019, 06:09:26 pmThat National LB-28 design seems pretty nice. Minimal components, reasonable specs and the LM395 is still available albeit expensive ($4). Still, a quality supply just can't be built for a buck ninety five.Changing to normal transistors will be a challenge for a newcomer. The LM395s only take 10 uA of base current (3 uA typical) so the op amp can easily drive several. In addition, the LM395 has a lot of built-in protection, well beyond that of a 2N3055.I would be tempted to build the LB-28 as shown.http://www.ti.com/lit/ds/symlink/lm395.pdfIt's still going to take a pretty beefy heatsink!ETA: The LM395 also has a 0.1 Ohm ballast resistor to aid in current sharing across multiple devices.

author: David Hess
author_rank: Super Contributor
timestamp: January 08, 2019, 11:49:55 pm
content: Quote from: rstofer on January 08, 2019, 10:31:31 pmAlthough as shown it requires a -5 to -10 volt negative supply.QuoteCheck the schematic carefully; the LB-28 design uses 7 LM395s in parallel for 8 total although new big TO-3 power transistors are not much less expensive.QuoteI brought it up more as an example to study. What I might do is use one LM395 to drive a bunch of big current boosting transistors but like you said, this would be a challenge for a newcomer.

author: not1xor1
author_rank: Frequent Contributor
timestamp: January 09, 2019, 07:48:42 am
content: Quote from: rstofer on January 08, 2019, 06:02:46 pmI 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 heatsinksand 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.

author: Zero999
author_rank: Super Contributor
timestamp: January 09, 2019, 09:20:40 am
content: Quote from: not1xor1 on January 09, 2019, 07:48:42 amGo 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.

author: David Hess
author_rank: Super Contributor
timestamp: January 09, 2019, 12:35:19 pm
content: Quote from: Zero999 on January 09, 2019, 09:20:40 amSo 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.

author: Zero999
author_rank: Super Contributor
timestamp: January 09, 2019, 12:57:47 pm
content: Quote from: David Hess on January 09, 2019, 12:35:19 pmMy point was that none of that is necessary with a 0 to 15V supply.

author: rstofer
author_rank: Super Contributor
timestamp: January 09, 2019, 03:19:34 pm
content: Quote from: Zero999 on January 09, 2019, 12:57:47 pmI 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.

author: not1xor1
author_rank: Frequent Contributor
timestamp: January 09, 2019, 07:04:22 pm
content: Quote from: Zero999 on January 09, 2019, 09:20:40 amYou must be kidding... nothing easier than that.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.

author: Zero999
author_rank: Super Contributor
timestamp: January 10, 2019, 09:29:49 am
content: Quote from: not1xor1 on January 09, 2019, 07:04:22 pmMany 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!

author: not1xor1
author_rank: Frequent Contributor
timestamp: January 10, 2019, 02:21:47 pm
content: Quote from: Zero999 on January 10, 2019, 09:29:49 amYes 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.

author: JohnPen
author_rank: Regular Contributor
timestamp: January 11, 2019, 10:03:43 am
content: 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.

author: BravoV
author_rank: Super Contributor
timestamp: January 11, 2019, 10:07:45 am
content: With all excellent replies, advises, tips and even circuit, I guess the OP will not create, yet another new thread nagging for a new 723 based 30V 3A psu again, as this is the 5th one or 6th already ?Its just sad to see all goodwills and helps going to be wasted again if this happened.

author: j395
author_rank: Contributor
timestamp: January 11, 2019, 11:47:52 am
content: why not use something like LD1085 - much more robust for beginners due to built-in overcurrent/overheat protection ?to decrease heating, use cheap buck or buck/boost module as pre-regulator, LD1085 works at 1.3V dropout - only 4W wasted at 3A

author: rstofer
author_rank: Super Contributor
timestamp: January 11, 2019, 08:17:52 pm
content: Quote from: j395 on January 11, 2019, 11:47:52 amIt doesn't meet the "spec" in that the minimum output voltage is around 1.8V - see VoTable 3 or it could be as high as 2.5V from Table 4 but I didn't pursue the difference in #18 versus #25. In any event, the device can't get anywhere near the "spec" of 0V.Without a pre-regulator and in the situation where Vi-Vo is about 25V, the device can only deliver about 0.5A based on Short Circuit Current. But we want, perhaps, 35V as Vi and 0.1 as Vo so call it 35V across the regulator. The maximum output current won't be much = Figure 7.With a pre-regulator that can get Vidown to a reasonable level, the device can deliver the full 3A required by the "spec". But that adds a bit of complication. Transformer taps would be better (in my view).https://www.st.com/resource/en/datasheet/cd00001883.pdf"Specs" have consequences. It's a lot easier to write 0-30V than it is to achieve the 0V end of the spec. Same with the 0-3A. It's hard to deliver 0.1V at 3A from a fixed secondary transformer that is delivering enough voltage to produce 3A at 30V. I haven't seen a circuit for a linear supply served by a switching mode pre-regulator but I haven't really looked.

author: rstofer
author_rank: Super Contributor
timestamp: January 11, 2019, 08:26:49 pm
content: Quote from: BravoV on January 11, 2019, 10:07:45 amBut maybe some of the responders, like myself, are learning something about the problems created by the "specs". Yes, I have spent some time wandering around, bouncing off of other schematics and different approaches to the problem and, as a result, I have a new appreciation for the problem.If there was a simple design that had a decent bill of material, it would be a 'sticky' and served up as the universal answer to a DIY power supply. Alas, it isn't simple!As I see it, there are two choices: First, come up with a more realistic spec or, second, plan on finding a transformer with secondary taps. I don't know how hard it would be to wind a custom toroid. Maybe buy one, unwind the secondary and then rewind it with taps.There are a lot of commercial supplies that advertise to meet the spec and they tend to be in the $50-$60 range. I don't know that they actually meet the spec but I would tend to just buy one rather than try to build one.

author: dmills
author_rank: Super Contributor
timestamp: January 11, 2019, 11:02:32 pm
content: Hum, 2 * 9V dual secondary transformers, 4 bridge rectifiers and filter caps (That will only need to be 16V or so rated), and 4 NPN pass transistors plus 4 diodes and some small beer stuff, build an output stage class G style, almost right out of Doug Selfs book on audio power amplifiers (You only need half of it!)?At 3A with 12V across the pass device (more or less worst case with zero output voltage) you are looking at only 36W in the heatsink which is easily within the SOA of a single TO3P pass device, I would have thought a 1.5C/W convection cooled job would be fine.I think you could even wrap this around a 723 as the controller if you really wanted to, but there is nothing really wrong with a long tailed pair, Vas and some passives.The trick is that you hang a current source (a few mA or so) off the highest rail, then use a string of zenners to switch on the higher taps as the voltage comes up.I am not sure it is economic given what you can find a lab supply for on the used market, but I don't really see the difficulty, I might design if for shits and giggles.This is the basic concept :Zenners are 3.1V, transistors are probably darlingtons, current source is a few mA via the usual PNP transistor and a couple of diodes and resistors sort of affair.Regards, Dan.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 12, 2019, 10:56:06 am
content: The kind of linear cross over between separate transformer taps is a good option at intermediate power.It can be done even simpler, especially if the floating regulator circuit is used and only 2 taps.It may not be the most economic way, thought not that bad (mainly more filter caps). On the positive side it's simple and about half the worst case heat compared to the single tap way. So it's about as good as using relays for 3 transformer taps as one can go closer to the edge.It depends wether the reduced (about half) heat sink can make up for about 1.5 times the filter caps.There is a lab supply project using this system, though with MOSFETs:https://www.eevblog.com/forum/projects/diy-bench-power-supply-psl-3604/This supply could be a good option - at least a good point to learn from. For simplification one could use classical rectifier if a little more loss is acceptable.

author: rstofer
author_rank: Super Contributor
timestamp: January 12, 2019, 03:11:24 pm
content: Quote from: Kleinstein on January 12, 2019, 10:56:06 amIt might be a little over the top for a newcomer.If we had a sticky thread for PSs, this should certainly be a candidate.

author: techguru
author_rank: Regular Contributor
timestamp: January 12, 2019, 05:34:10 pm
content: Quote from: not1xor1 on January 09, 2019, 07:04:22 pmSir,How to analyse this schematic. Where to start my analysis to understand the circuit?What is the book to learn to develop Understanding skill for Discrete or Integrated circuit?

author: BravoV
author_rank: Super Contributor
timestamp: January 12, 2019, 05:45:25 pm
content: Quote from: rstofer on January 11, 2019, 08:26:49 pmI am a electronics hobbyist, totally understand your point above, nothing against it what so ever.Its just you don't realize what the OP's have been done here, hint, just read from the bottom the list of threads created since the beginning, no need to read the thread's content, just the title ...The OP's created threads list ->https://www.eevblog.com/forum/profile/?area=showposts;sa=topics;u=154644Actually the current nick is his second, as he re-registered here to get a fresh new nick, as before, his old nick where he felt no one could give him satisfaction, btw, he admitted it already.Again, just read the thread's title to get a clue ...Previous abandoned nick threads list , started from mid 2017->https://www.eevblog.com/forum/profile/?area=showposts;sa=topics;u=138516The point, he will nag until someone come with a full schematic that uses 723 with 30V 3A capable, and also must utilizes components that are available in his drawer, if not, he will make another thread again, or re-register as new user when most "helpful & friendly" people exhausted on his nick.He does not have technical problem at all, nor language barrier, he has really bad netiquette and bad attitude.

author: techguru
author_rank: Regular Contributor
timestamp: January 12, 2019, 06:07:55 pm
content: Quote from: BravoV on January 12, 2019, 05:45:25 pmMr Bravo,I totally deny you. may be my specification may be to high for a beginner and Now i feel There is no need to built a circuit which can deliver 100W of power. Neither i could go for LT3080 which could control both voltage and Control regulation with dissipation of Nearly 30W. This is what i would understand from this forum.I cannot analyse big circuit. I donot know where to start my analysis.Here i could not get the component which we have discussed in this thread. What ever is available here i could use it.I could not order from online website because i am student of electronic engineering. my economy wont allow me.A simple LM723 cost ten rupee which is affordable my me. So i was searching for circuit with LM723. This is the reason for those those thread.I respect every one in this forum, Sorry If i hurted you all. Thank you all .

author: BravoV
author_rank: Super Contributor
timestamp: January 12, 2019, 06:47:29 pm
content: Quote from: techguru on January 12, 2019, 06:07:55 pmYou've been told, gently assisted, repeatedly mentioned, yet, you are stubbornly deny any good intentions and helps offered, and keep spamming again and again ... oh ... again.Quote from: techguru on January 12, 2019, 06:07:55 pmYep, again .. you've been told, explained and "sympathized" on the limitation of common Indian's budget limitation, with circuit designs that of course limited, but fit into your budget and component availability, and very likely available to you at your country as they're common jellybean components, yet, you ignored and stubbornly create anothersameidentical request at new thread ... again.. again.. and again... oh ... forgot ... again.Quote from: techguru on January 12, 2019, 06:07:55 pmAgain ... geezz... I'm tired typing this word, you've been assisted, gently informed (as people were aware of price sensitive for Indians and worry that might offend you) for "alternative" circuits that don't use 723, but still ...... you keep spamming with new thread asking to people to spoon feed you in "designing" a 723 based pcu .. oh .. again..again ... and again.Quote from: techguru on January 12, 2019, 06:07:55 pmWhatever, just DO NOT make a new same new discussion thread, or worst re-register a new nick and launch the same nagging again.Show appreciation for those generous people who helped you, don't just ignore and abandon the ongoing thread when every times you don't like it, and create another identical thread ... again.

author: techguru
author_rank: Regular Contributor
timestamp: January 13, 2019, 11:45:27 am
content: Quote from: BravoV on January 12, 2019, 06:47:29 pmHi..I forgot my Old login password ,So i created my New account. Thats all.I have not used both login in parrallel. A college boy will not mature enough to accept things. But From now onwards i will use single thread to get advices. thanks Bravo sir.