5 Ampere  Regulator using LM 317 or LM723 - Page 1
Forum section: electronics / projects

author: Gurumurthy
author_rank: Regular Contributor
timestamp: May 13, 2017, 04:46:44 pm
content: Hi to all..I want to design lab power supply with the transformer rating of 30V , 5 ampere using LM317 or LM723. Because after rectification it would give around 42V Pulsating DC, So both these IC could Handle voltage around 40V. Hence this is the reason for adapting to these ICs.At the initial stage started with LT1084 and LM338. Both went to break down condition and they are much costly then LM317 and LM723. I went outboard transistor for current boosting(for LM317) but my MJ4502 got hot and burned and also used TIP142/147,2N3055 etc. but all these circuit failed and I have used old 1ohm/25watt resistor for loading. I have taken output of secondary of transformer and connected 6A bridge and connected my regulator ICs(317 or723) but every thing failed.I want design power supply which should have control over voltage and current ,should be reliable in delivering power to load.Please help me in this regard.I have seen Video of Dave jones for constructing power supply. The problem is LT3080 is a current reference based regulator which is costly and not available in shops in chennai.Thanks Jones.

author: Paul Price
author_rank: Super Contributor
timestamp: May 13, 2017, 04:56:44 pm
content: To get some help, please show a schematic with component values and your output load.Your description suggests you have made design and connection errors.

author: Kalvin
author_rank: Super Contributor
timestamp: May 13, 2017, 05:02:09 pm
content: As a quick hack, you could use a linear pre-regulator or a simple transistor voltage regulator which will take the higher input voltage and output 30V feeding the L317 or LM723. In power efficiency-wise the result will be the same anyway, but in thermal management wise the situation will be easier to handle as there are two regulators sharing the thermal load.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 13, 2017, 05:18:09 pm
content: If the transformer is rated for 5 A (AC current) this would allow about an 3 A DC current without overloading the transformer, if no power factor correction is used.For a linear power supply it is normal the the transistor of other power element (like LM338) will get hot. A worst case 40 V times 3 A load is too much for a single TIP141 / 2N3055 / MJ4502 or similar. So one would need at least 2 of these, maybe even 3.The LM723 based circuit is good for voltage regulation, but not for a precise variable current regulation. Also the sometimes slightly more than 40 V can be a problem to the chips.So the circuit of choice is more like one based on OPs and power transistors. With 30 V this is just about at the upper limit where the emitter follower output stage can work with more normal OPs. The more flexible version is that with a floating regulator powered by a small second transformer. Many cheap Chinese supplies (and old HP supplies too) are build like these. Something like the HY1803 might be an inspiration. Plans for this supply are available in the net.

author: BravoV
author_rank: Super Contributor
timestamp: May 13, 2017, 05:25:25 pm
content: Quote from: Gurumurthy on May 13, 2017, 04:46:44 pmWent there once long time ago, basically the market is filled with counterfeit stuffs.Assuming you're using the right transformer to do the job, the right schematic and properly heat sunk ..... are you sure you're using the genuine stuffs ?

author: Zero999
author_rank: Super Contributor
timestamp: May 13, 2017, 07:06:32 pm
content: The LM338 will not be able to work up to 5A when the input-output differential is high.The LM317 is a floating regulator which means there's no upper voltage limit, just the voltage difference between the input and output. It's possible to add a couple of transistors and a zener diode to allow the LM317 to work at higher voltages. The main disadvantages are: more components, higher drop-out and you need to watch out for the current through D1 increasing the output voltage under light loads.

author: Zero999
author_rank: Super Contributor
timestamp: May 13, 2017, 09:43:59 pm
content: For completeness here it is again with a PNP pass transistor for higher currents.Quote from: Gurumurthy on May 13, 2017, 04:46:44 pmWhy not use a transformer with two 15V secondary windings? When higher output voltages are required, use both secondary windings but for lower voltages use a single 15V winding. The selection could be performed using a relay or transistor.

author: Gurumurthy
author_rank: Regular Contributor
timestamp: May 14, 2017, 12:36:58 am
content: Thanks a lot for all. I want to design Lab power supply which is variabble from 0V to 30V . I found a circuit which is variable from old data sheet of LM317. I cant understand the operation of opamp with passive devices.Give clear functioning of circuit with good scenario. thank you all. i am attaching the circuit for your reference.

author: IanB
author_rank: Super Contributor
timestamp: May 14, 2017, 01:04:16 am
content: If you look at commercial linear power supplies that go from 0 to 30 V, they typically are limited to 1 or 2 A. Regulated linear power supplies that can go from 0 to 30 V and 0 to 5 A are very, very expensive. This might suggest to you that you are reaching beyond practical limits, especially if trying to make one from an LM 317.Maybe you should set your sights a little lower?

author: DBecker
author_rank: Frequent Contributor
timestamp: May 14, 2017, 01:14:46 am
content: Who would design a straight linear power supply in the modern era? The thermal challenge is just too much of a problem.For a quiet power supply you use a switching first stage with good output filtering, and use a quiet LDO final stage to remove switching noise and improve the transient response.

author: Gurumurthy
author_rank: Regular Contributor
timestamp: May 14, 2017, 04:56:48 am
content: Please find attachment.I can't understand the function of opamp which is acting as comparator with many passive devices. It would give insight ,if explained with some assumptions at circuit nodes.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 14, 2017, 06:37:50 am
content: Especially for a beginner, a linear supply is much easier than switched mode. It is also usually lower noise - especially common mode noise is difficult (or expensive) to avoid in switched mode supply. For a commercial product, the combination of switched mode and linear is definitely a good option, alone from saving on the heavy transformer and allowing for PFC.To save on the power loss one would tend to use at least 2 transformer taps, maybe even 4. This is at least what the cheap Chinese do. For the beginning 2 taps are a good start and that does not need a special transformer, but can use a more normal one with a split output winding (e.g. 2 times 15 V). With a fan, a power loss of 100 W is not that bad.In a linear regulator the OPs in the regulation loop are usually not working as comparators, but as linear amplifiers. Starting with voltage regulator chips looks easy at first, however it does not really help for a lab supply. These chips are made for a fixed current limit and a well behaved load - whereas a lab supply should be stable with any realistic load. So a voltage regulator isnota first step towards a simple lab supply. The LM317 would be used as a kind of transistor (small and relatively slow) with internal thermal protection.For the beginning, I would start at lower power to learn. Much of the design is the same, but much less magic smoke escaping if things go bad. I attached a PDF file for a simple lab supply design with a floating regulator. This is about as simple as it can get, if you leave out the optional transformer tap switching. It is probably good for about 1-1.5 A and sold by the Chinese as a 2 A supply.

author: Zero999
author_rank: Super Contributor
timestamp: May 14, 2017, 10:20:14 am
content: Quote from: Gurumurthy on May 14, 2017, 04:56:48 amJust posting it again won't help. You should post a PNG or GIF file and a link to the original source, rather than an M$ Turd document which hardly anyone will read.http://pdf.datasheetcatalog.com/datasheet/nationalsemiconductor/DS009063.PDFThe op-amp is not just acting as a comparator. It's a linear amplifier. Why not try building/simulating it?

author: Gurumurthy
author_rank: Regular Contributor
timestamp: May 14, 2017, 12:15:12 pm
content: Sure Sir. I will simulate.

author: technix
author_rank: Super Contributor
timestamp: May 14, 2017, 12:57:23 pm
content: Quote from: Gurumurthy on May 13, 2017, 04:46:44 pmAt this level of current it may be a better idea to use a switch-mode design so the heat output is manageable.42V/5A means 210W of total power. For a linear regulator this number is the sum of the power dissipation of your load the regulator itself. Assuming a short circuit at the output (e.g. when charging up supercaps at CC mode) your regulator need to dissipate this full 210W and it will fry the power elements very quickly.If you need the low ripple performance of linear regulators, You can add a 5A-capable switch-mode pre-regulator that tracks the actual output voltage, to cut the input voltage to the linear stage to somewhere slightly above the actual output, for example 2V above output, so the linear stage dissipates no more than 10W power.

author: Gurumurthy
author_rank: Regular Contributor
timestamp: May 14, 2017, 01:07:50 pm
content: Dear Sir, you suggest me some pregulator circuits..Thank you sir..

author: Kalvin
author_rank: Super Contributor
timestamp: May 14, 2017, 01:15:21 pm
content: In order to achieve the best qualities of the linear power supply and the switched mode power supply, one could use a tracking switched mode pre-regulator which can be bypassed on light loads. In that way one can get a decent high current performance with reduced switching noise and good low current performance without switching noise, while minimizing the thermal problems.

author: technix
author_rank: Super Contributor
timestamp: May 14, 2017, 01:55:17 pm
content: Quote from: Kalvin on May 14, 2017, 01:15:21 pmI personally would like a mains-direct approach instead, using adjustable isolated mains switching regulator chained to the linear regulator. This allows the mains-side optimizations like power factor correction to be used.

author: Kalvin
author_rank: Super Contributor
timestamp: May 14, 2017, 02:10:47 pm
content: Quote from: technix on May 14, 2017, 01:55:17 pmTypically the mains switching power supplies have a Y-capacitor between the mains and the secondary causing sufficient leakage current which can damage sensitive electronics. The mains transformer can have multiple, isolated secondaries with adjustable regulators so one can get multiple isolated and independent outputs in addition to the better mains insulation. Also, using the mains smps one cannot achieve the low noise benefits of the linear power supply on lighter loads.

author: technix
author_rank: Super Contributor
timestamp: May 14, 2017, 03:39:07 pm
content: Quote from: Kalvin on May 14, 2017, 02:10:47 pmThat Y capacitor isn't necessarily required. I am designing not aiming at minimum ripple, but a compromise between ripple and efficiency. Maybe I cannot guarantee the 20uV ripple, but I can shoot for a 80 Plus Gold rating.

author: Kalvin
author_rank: Super Contributor
timestamp: May 14, 2017, 03:55:10 pm
content: Quote from: technix on May 14, 2017, 03:39:07 pmAgreed. Typically a design is a compromise between many different requirements.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 14, 2017, 07:56:03 pm
content: If the mains input includes PE, the Y-class capacitor is not a problem. It is only a problem it the input is only 2 wires, as than the capacitor is effectively at half the mains voltage. The Class Y capacitor has nothing to do with ripple, but it is about common mode voltage. With the capacitor there might be several 10s of volt of common mode voltage at the switching frequency.Still for a beginner, the SMPS part is way to complicated, especially starting from mains.With tap switching one can also reduce the worst case power dissipation. With 4 taps one might cut is to about 1/3.

author: Gurumurthy
author_rank: Regular Contributor
timestamp: May 15, 2017, 03:19:12 am
content: Dear all,please give me some reference to study the Study of Regulated power Supply and Various Pre regulator circuit using SMPS Techniques.

author: Zero999
author_rank: Super Contributor
timestamp: May 15, 2017, 10:06:24 pm
content: Quote from: Gurumurthy on May 15, 2017, 03:19:12 amhttp://bee.mif.pg.gda.pl/ciasteczkowypotwor/Noty%20aplikacyjne/Linear%20Technology/AN140fa.pdfhttp://www.ti.com/lit/an/snva559a/snva559a.pdfhttp://www.ti.com/lit/an/slva001e/slva001e.pdf

author: coromonadalix
author_rank: Super Contributor
timestamp: May 15, 2017, 10:20:24 pm
content: You have some good variable smps circuits on ebay going down to zero with decent protection, just add main transformer rectifier and capacitor

author: BigBoss
author_rank: Regular Contributor
timestamp: May 15, 2017, 11:42:06 pm
content: All those are old stuff..Look at this one.Discover the circuit because it has a ability to work in parallel to increase the supplied current.http://www.linear.com/product/LT3081http://www.linear.com/docs/45095

author: Gurumurthy
author_rank: Regular Contributor
timestamp: August 06, 2017, 05:21:47 pm
content: Dear all,Nothing went well for past 4 months with IC Regulators.So i decided to construct 30V @ 90 W it means 3A Load Current. Please Suggest me the circuit which could Do vary from 0-30V and 0-3A voltage and Current . I want to construct as a dual power supply with two separate transformers of 24V@3Ampere.Suggest me a circuit to Learn and Construct the circuit.Thousands of thanks to the members of the forum.

author: Zero999
author_rank: Super Contributor
timestamp: August 06, 2017, 10:05:17 pm
content: Quote from: Gurumurthy on August 06, 2017, 05:21:47 pmWhat have you being doing for the last four months?What problems have you had with IC regulators?Try the following schematic. It's also available in kit form but will need to be modified, in order to be reliable. If you want two outputs, then make two of them. You might be able to save some of the cost by using a transformer with two secondary windings, although you shouldn't expect the insulation between them to withstand more than 100VDC or so.https://www.eevblog.com/forum/beginners/bangood-psu-enhancements/msg897563/#msg897563

author: wasyoungonce
author_rank: Frequent Contributor
timestamp: August 06, 2017, 10:57:01 pm
content: If you search the OPs posts..he has been posting every few weeks asking for a Linear PSU design either LM723/LM317/LM338. He kinda either doesn't like what he's been told or doesn't understand it or doesn't have parts on hand (and wants us to substitute for him) ....thus keeps asking the same thing. He as also doesn't reply or explain what problems he is having...all very vague, then disappears only to start another thread.This same question has been posted over a dozen times by the OP so far and borders on spamming (he is know to double and triple cross post on different threads). Now no one minds helping but this is beyond a joke atm.Quote from: BravoV on May 19, 2017, 06:23:29 am

author: Zero999
author_rank: Super Contributor
timestamp: August 07, 2017, 03:32:17 pm
content: Quote from: wasyoungonce on August 06, 2017, 10:57:01 pmYes, I'm aware of this. I decided to make one last ditch effort to help. In future I'll just post links to what has already been advised.Some may argue that, you shouldn't post as you've done and that if you don't have anything helpful to say, then don't say anything but I'd disagree. If you warn others that someone is being unreasonable, then it helps them avoid wasting their time on them.

author: Gurumurthy
author_rank: Regular Contributor
timestamp: August 07, 2017, 04:50:29 pm
content: Thanks a lot to all.I need an solid understanding before constructing the circuit. If two much component is present, better we can simulate the circuit but it does not show temperature effects. just show the waveform of the circuit at various nodes.I must know to analyse the big circuit. i know i should use divide and conquer approach but my knowledge is not enough to understand which part does what operation. That is why i have fear in constructing circuit.I am college learner, where will i get sufficient time to understand huge chunk of circuit.I need both quantitative and qualitative analysis of circuit. No text book is good for this constructing of regulated power supplies. they does nt reveal the principle behind the operation. they hide principles and give schematics for constructing..what i have learnt from all these thread is ,there is a limit for Linear and Smps power supply.for low power go for Linear mode and for high power go for smps pregulator and LDO post regulator, this avoid over heating of LDO regulators.IC regulators have safer operating limits, so we cant expect required current at all conditions. this is where it fails.most of my initial design were with LM317 and LM723. these were selected merely due to its cost. I wont get 100 rupees as pocket money.This student is not arguing to make this mistake were resonable but this were the conditions which made to ask multiple threads.I never had an intention of ignoring all your advices. I swear for this... I respect all ur advices.

author: colinza
author_rank: Contributor
timestamp: August 07, 2017, 05:29:57 pm
content: Don't try this at home, kids!So I have a prototype box where I play with power supply designs. The current iteration in it is surely insane but it works quite well, and is actually similar to this idea.It uses an LM317 but only to produce a low current 30V reference from 24V RMS transformer. I then use that to drive an LM358 way beyond spec and very close to exploding. The 358's input is a DAC with a 4v reference and then the opamp has a 10X gain and the a second stage provides the feedback from a TIP3055 to do the actual higher current linear regulation.Inefficient, very sketchy, needs short circuit protection added because high current surges will blow the opamp - luckily the DAC survives, and it needs to accept the fact that it can't really handle 30V output. I don't actually trust it, but it does provide negative rail tooSoftware side is an arduino mini, CC is currently in software (eek!). The LCD is a raspberry pi that controls the arduino via serial. The code is herehttps://github.com/calston/piwerlabBut the biggest purpose this serves in my lab is a set of touch screen controlled relays for 6x IEC AC connectors at the back which goes to my soldering iron, scope, etc.

author: Zero999
author_rank: Super Contributor
timestamp: August 07, 2017, 08:48:59 pm
content: I don't see a heat sink. Is the main power transistor hidden somewhere?

author: colinza
author_rank: Contributor
timestamp: August 08, 2017, 06:16:43 am
content: Quote from: Hero999 on August 07, 2017, 08:48:59 pmThey're off in the picture, or else you'd just see two big heatsinks and fans. Two CPU heatsinks clamp onto the top of the transistors which are oriented backwards as you can see

author: Gurumurthy
author_rank: Regular Contributor
timestamp: August 15, 2017, 03:45:14 pm
content: Dear All,I have attached L200 Schematic which is programmable voltage and current regulation.My doubt is the function of operational amplifier? the 0.1 ohm resistor is current sense resistor . when the load ia 1A it has a drop of 0.1V . Accordance to me , it is an difference amplifier which amplifies this o.1V.The output of OPamp Could be =(p1/R2)*0.1V.How L200 is going to do regulation by varying P1 resistor? What is the function of operational amplifier?

author: BigBoss
author_rank: Regular Contributor
timestamp: August 18, 2017, 03:00:47 pm
content: Another good-looking design..I have never checked but it seems principally working

author: Kleinstein
author_rank: Super Contributor
timestamp: August 18, 2017, 05:00:15 pm
content: Quote from: BigBoss on August 18, 2017, 03:00:47 pmThe circuit is a variation of the classic floating regulator.It uses a rather odd way to have a minimum load to the regulator. There is a simpler way using the upper auxiliary supply for this. The way of adjusting the voltage was common in the old days, but has the disadvantage of having regulator loop gain depending on the set voltage. It is usually better to do the adjustment from the reference voltage side - this comes naturally when you change to digital voltage adjustment. The way the extra sense inputs looks a little like an after-thought. It should work, but might cause trouble when higher impedance (e.g. open) and the 100 Ohms resistors would need to be high power, as they have no extra protection.Having the LEDs to do the min voltage function can be borderline on the reverse voltage rating, depending on the OPs used.

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: August 19, 2017, 07:09:31 pm
content: Quote from: coromonadalix on May 15, 2017, 10:20:24 pmUsed quite a few in the past. Like most Chinese stuff some are good, others not so. Most are only rated for up to 30v or 35v and 3A though, so pushing things a bit for this project. Also don't necessarily believe claims of higher ratings. Usually the same product from a dodgy seller, exaggerating.Basically if you want to handle that kind of power linearly, you need at least a couple of paralleled TO3 or TO247 devices on a decent h/s. Forget using TO220 devices, they have too high a chip-to-case thermal resistance. Also I would go for an opamp arrangement, a bit more work to build but better control than grafting power transistors onto a regulator chip."If you search the OPs posts..he has been posting every few weeks asking for a Linear PSU design either LM723/LM317/LM338."Point taken. Should have noticed that. Anyway, basically a case of trying to squeeze a quart out of a pint pot. Better to do the job with the right parts.