Suggestion for Op Amp in Linear Power Supply 0-30V 0-5 Amp - Page 1
Forum section: electronics / beginners

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 05, 2023, 01:04:07 am
content: I am looking to furthering my understanding of operational amplifiers in a specific area of power supply design.I was wondering if the community would have a suggestion for an operational amplifier for a linear power supply design of 0-30V and 5 Amp.I have looked through a bunch of data sheets and found one that is appealing. The TLV930x family.https://www.ti.com/lit/ds/symlink/tlv9301.pdf?HQS=dis-dk-null-digikeymode-dsf-pf-null-wwe&ts=1699104993123The cost of the op amp is not really important, within reason (let’s say $10).Are there any better suggestions then the one referenced above?My goal in this exercise is to learn how to utilize an operational amplifier to control both voltage and current in a linear power supply.Besides a suggestion of a particular operational amplifier any knowledge shared on this particular subtopic of operational amplifiers is greatly appreciated.Any suggested technical reading on the subject is also welcomed.Thank you.

author: xavier60
author_rank: Super Contributor
timestamp: November 05, 2023, 02:05:55 am
content: Quote from: JJ_023 on November 05, 2023, 01:04:07 amAvoid designs that require the opamp to be powered from the full unregulated supply, but rather from some lower voltage regulated rail or rails.Where the opamp is powered from a single rail, it's common mode input range will likely need to include one of its supply rails. I see that it's both for TLV930x family.A commonly used opamp for linear PSUs is the LM358 or the LM324 quad version.I settled on theTL072TLC072 in my last PSU project. The only worthwhile advantage over the LM358 is a quicker current limiting response.https://www.eevblog.com/forum/beginners/lm324-power-supply-with-variable-voltage-and-current/msg3582664/#msg3582664

author: Konkedout
author_rank: Frequent Contributor
timestamp: November 05, 2023, 02:16:03 am
content: I can design a linear power supply, but the only way for me to explain how is to start designing based on target specifications. And.....during the design process it is likely that I will get part or all of the way through, then do some analysis and determine that I need to change something.When I was entering college for engineering in 1969, I was looking for some circuit design "cookbooks" and did not have any. I understand now that there are 100s or 1000s of steps, and identifying them is an individual and inductive (as opposed to deductive) process.When you say "an op amp" do you mean that you want to use only one op amp? If you do do it with op amps, it is likely that you will need several of them. The one you picked out may be OK, but it is also possible that you need more gain-bandwidth. This depends upon your objectives (target specifications).The first question is how much do you know about analog/power circuit design? If you think you may know enough, the second thing to do is to find a complete well-written power supply specification, and use it as a model to put together your own target power supply specification.Understand that if you want to build a completely linear bench power supply that can produce 0-30V at 0-5 Amps (for example), this thing will need to dissipate 150W or more of heat under some conditions. And that will not be small or easy. It is easy to run into that problem, and switching power conversion can save you a lot of trouble with that.... I have one cheap bench supply which I am pretty sure does transformer "tap switching". That means it switches between transformer output windings depending upon the output voltage, thus greatly reducing the power dissipation in the pass element. This is a nice scheme but would almost definitely require a custom transformer.One advantage of switching converters is that with smaller ferrite cores and les wire, it is easier to wind your own transformers or inductors. I do not recommend doing your own AC/DC transformers (linear or switching) unless you really know what you are doing.... There is the risk of electrocution....

author: coromonadalix
author_rank: Super Contributor
timestamp: November 05, 2023, 02:53:38 am
content: some google search would have given you loooots of designs ideas and explanationsyes a linear design will heat more when dissipating, the current limiter is the deciding factoreven lm324 classic op amps can do the job perfectly, unlees you want to play in the big game like ultra low noise, fast response etc ... yada yada

author: blackdog
author_rank: Frequent Contributor
timestamp: November 05, 2023, 12:33:02 pm
content: Hi,An opamp that is good for linear power supplies is the OPA202 series.This opamp has a very large phase margin which provides good stability for your power supply.The noise and offset are also good of the OPA202, but do not choose the feedback resistors too high in value,because then you get more trouble from the current noise, the OPA202 is not a FET opamp, but has a Super Beta input.There are more opamps with a good phase margin, but this one is really very good.And fast enough for a normal LAB power supply.For your power transistor, choose a model that has a Ft of 4 to 7 MHz.That will make your phase margin a bit better without getting instability of the transistors that have a Ft of 30 to 50MHz like the modern audio types.For robustness, do not let a power transistor dissipate more than 40-Watts.Make your cooling important in your design, don't skimp on it.If you stick to these tips, you can eventually lower the capacitor across the output terminals.Standard for a well-designed LAB power supply I use 40 to 50 uF per Ampere of current.Twist high current wires, Transformer wires, bridge to buffer capacitor, keep the transformer wires away from the electronic.Kind regards,Bram

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: November 05, 2023, 01:37:33 pm
content: I recently redesigned an old variable Lambda Linear PS. It is not for the faint of heart .I assume you are looking to design a variable supply. A one voltage supply is much easier.I stole designs from Lambda and anything else I could pirate.I ended up using three op amps and two zeners along with the transistors. One op amp for the reference voltage and one each for the volt and amp control.One (dual) LM 358 for two of them another old op amp for the reference.I also used a 3 pin volt regulator for the housekeeping voltage., which is 18 VoltsIf your concern is just learning to use op amps and you really do not care about micro volt tolerances don't bother with larger regulator IC like the LM 723. Get something like the LM 358 and order 10 or 20 of them. Cheap. Since you wish to learn about op amps you may wish to use some for other projects like oscillator etc.....Most of these lab grade linear PS use two power sources. one for the actual power out and one for "housekeeping". The housekeeping voltage powers the op amps and is separate from the power out source voltage, which may be higher than what the op amp can handle. There are two windings on the transformer, one for each voltage, then two rectifier bridges.The ICs that incorporate the reference zener in the IC itself for reference voltage are more stable since the temp is more stable. LM 723 is an example. Again if your goal is to learn about op amps don't bother with these devices, use your op amps.There is another recent post about linear PS here that I encourage you to read.( OOPS you already have) Also look up the schematics of some quality linear supplies like the Lambda.Bram's comments are well worth following.Oh, do you have a transformer? Or two? Gotta start somewhere.

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 05, 2023, 02:34:16 pm
content: Quote from: xavier60 on November 05, 2023, 02:05:55 amI understand this comment. Besides the fact that most op amps will not function well with an unregulated supply and will not operate at higher voltages are there any other reasons?QuoteWhat do you mean it’s both? Could you please elaborate.QuoteOften times “commonly used” is because of a lot of information or design concept based on that particular component already exist (which there’s nothing wrong with).However I’m trying to learn a little bit. So could you explain to me how LM358 or TL072 would be better or worse than the TLV930 family I found?I read the data sheets of both and TLV930x. To me it seems in most ways the TLV930x would be better. Am I missing something?

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 05, 2023, 02:34:54 pm
content: Quote from: themadhippy on November 05, 2023, 02:10:17 amThank you for that. I have watched the full series.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 05, 2023, 02:57:55 pm
content: The TLV930x are in most parameters a small step up from the LM358 (a little faster, less bias, higher max supply, less offset - though not sure about the noise and the LF noise may even be higher):For a normal supply they are OK. For a accurate current regulation the drift and low frequency noise may be a bit limiting.Daves video series on the lab supply is not really covering the whole thing. Some of his choices are not that good - the µsupply kind of failed on the current regulation.Usually it is not a good idea to use a voltage regulator chip to make a lab supply. A voltage regulator is made for a different taske: a fixed, well behaved load and not that much need for precision and change in the voltage.Usually one starts the design with some kind of generic OP amp in mind ( e.g. universal OP-amp model in the simulation) and only near the end decides which OP-amp fits the circuit, not the other way around. Some details (need single supply ?, supply voltage) depend on the ciruit.Today there are plenty of choices and the amplifier are no longer a cost factor. The more relevant questions are more the general configuration (floating regulator or not), power transistors (BJTS or maybe MOSFETs), transformer(s) and the way transformer taps are switched.

author: xavier60
author_rank: Super Contributor
timestamp: November 05, 2023, 03:46:15 pm
content: Quote from: JJ_023 on November 05, 2023, 02:34:16 pmOne of the reasons to avoid designs that power the opamp from the main regulated supply is that the 40V or so it's likely to be isn't safe for most opamps.I had misread the spec for the TLV930X. The input common mode range only includes the negative supply rail, not both. I was looking at the Absolute Maximum Ratings.I made another mistake in my previous post, Tho opamp I used in my recent PSU is the TLC072.Although the TLV930X is faster than the LM358, the TLC072 is much faster again. As slow as the LM358 is, it's more than adequate for most designs. The transistors being controlled usually aren't very fast.A reason for not wanting to use a part from the TLV930X family is that there appears to be no DIP package available. Not the most convenient for experimenting with.The extra speed of the TLC072 made no significant improvement to the voltage regulation performance of my PSU. Only improved the CC response, the reasons for which should be left for later.

author: schmitt trigger
author_rank: Super Contributor
timestamp: November 05, 2023, 05:12:58 pm
content: As others have already mentioned, do not underestimate the thermal analysis. Thoroughly study and understand the thermal resistances involved and the derating considerations for ALL power components.Be aware that not only the power transistors are heat sources. The transformer itself, the bridge rectifier, the ballasting resistors, the drive transistors...all of them will heat up significantly and add to the ambient temperature.Speaking of fans, they do offer many thermal advantages. But they are also noisy and may bring dust into the circuit. The best approach is to include a thermal sensor of your choice which will turn the fan on only when a threshold temperature is exceeded. I once designed a supply with three thresholds: the first would turn on the fan, the second a yellow LED would warn me of overheating, and the last threshold would shut off the output.Lastly, add an output relay. It allows the supply to be turned on with the output disabled. This will ensure that the output voltage may be freely adjusted without danger of damaging a load. And it also will allow the output to be turned off when the thermal conditions are exceeded.

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 05, 2023, 06:16:44 pm
content: Quote from: Konkedout on November 05, 2023, 02:16:03 amWhat you described I think is part of almost any design process. When I prototype stuff outside of electronics it’s the same process. Start in CAD. Building a prototype. Then figuring out where it could be better and see if it performs to specification.QuoteNo absolutely not. From my understanding I would probably utilize several for different aspects of the circuit.So in my case, if building 0-30V 5A linear power supply with that particular op amp be a good choice in your opinion?I started this particular thread because in a previous thread op amps were recommended as a means of controlling voltage and current over a LDO.I also realized that I lack knowledge and experience with them even though I have read a lot about them and understand the broad strokes of them (Operational amplifiers). So I figured I would venture into this.The way I usually learn stuff is by applying what I learned, making a few screw ups, and unfortunately that’s where the real learning sets in. lolI also like to break things down into chunks. So since I have an interest in power supplies, and operational amplifiers encompass other areas as well I decided to just focus in applications specifically for voltage and current management and avoid other areas of op amps.QuoteI know some about power circuit design, mostly broad strokes. I have read a few very technical books on the subject but obviously lack a lot of knowledge even though I have read those books. (Like Power Electronics Handbook by Muhammad Rashid)QuoteAs stated in another thread. I would feel comfortable managing the heat. I have access to all sorts of aluminum and heat sinking capabilities as well as designing and controlling the flow of air through a cabinet. Efficiency here is not a concern to me nor is fan noise.QuoteI am very well aware of switching power supplies. The benefits of them. I am sure I will get into that rabbit hole at some point. Right now I just want to nail down a few things as far as understanding linear power supplies. So I am trying to keep a narrow scope.I could be wrong but I don’t think I would ever wind my own inductors. I rather just buy what I need. To me it’s a lot easier at this point where I am at.

author: Terry Bites
author_rank: Super Contributor
timestamp: November 05, 2023, 06:18:36 pm
content: What is the RAW DC supply?The opamp probably need to be able to cope with it plus a few volts of safe margin.Maybe a 44V part. eg OP07/77

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: November 05, 2023, 06:27:49 pm
content: This is just my opinion but in a regulated variable PS the op amp characteristic most valuable is temp stability not speed.The output transistors, BJT or FETs and output capacitance will really dictate the speed at which the PS can respond to changing output impedance.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 05, 2023, 08:16:02 pm
content: For a linear power supply for learning, I would start with a little smaller (e.g. 1-2 A and maybe a little lower voltage if that is what the parts allow for) for the start. Same principle, but less magic smoke when things go wrong.When doing it systematically a first step would be a simulation with a spice variant (e.g. LTspice). Quite a bit of the design is about the control theory and feedback loops. The cross over between voltage regulation and current regulation is a part where one leaves the simple standard theory. Another complication one has with a lab supply is that the load impedance is variable. So it is about a robust feedback system to work with different systems to control.Most circuit will work with no change with a large number of different OP-amps. Most OP-amp circuits are designed in a way that the actual properties don't enter very much and the OP-amp can be treated as some idealized version for much of the design. So the actual choice of the OP-amp type is than really one of the last things to do. It is about meeting requirements for the circuit (e.g. supply, CM range, min BW) and may be a few performance parameters like drift or noise. With a power supply those needs can often be quite moderate and even the old LM358 or µA741 OL TL072 may be good enough. One may still chose a more modern, maybe higher performance (e.g. lower noise or drift) type.There are only a few supply circuits to use special features like external compensation pins to really require a specific type (e.g. LM301).

author: alligatorblues
author_rank: Regular Contributor
timestamp: November 05, 2023, 09:38:17 pm
content: There are links to applications in the datasheet. Take a look at them. That's where I get a lot of my ideas. Op amps can be used in so many applications, and in so many configurations, if you want to learn how to use them you should learn the math first. Ootherwise, you'll be going by trial and error, which is expensive and time consuming.I also think a homemade DC PSU is one of the more dangerous things to have in the lab. They're so inexpensive to buy. And those have undergone testing and certification. If you're dead set on doing it yourself, by a 2lb halon fire extinguisher for your lab. Halon doesn't leave anything behind. It just extinguishes the fire and goes into the air.

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 06, 2023, 01:53:20 am
content: Quote from: blackdog on November 05, 2023, 12:33:02 pmI looked at the datasheet and was wondering why your suggestion would be better than The TLV930x family I found? I am asking this question not to challenge your suggestion but to understand the differences and why some are better than others.QuoteI understand what super Beta input is. Why is it relevant for controlling voltage and current, this is not an amplifier application?QuoteAs far as power transistors go I will probably start a specific thread asking on the benefits of power transistors versus MOSFETs. In that thread I will also ask for recommendations. Right now I am just trying to nail down the op amps. I know the voltage reference I will probably use.I have a bunch of transistors currently that I can play with. This is the datasheet for them. Any thoughts?https://www.onsemi.com/products/discrete-power-modules/general-purpose-and-low-vcesat-transistors/MJE3055TQuoteI never skimp on anything, it usually ends up costing more in the long run. As far as managing heat and being able to dissipate it, I feel quite confident in that regard. I don’t have size constraints for the power supply. I have access to tons of aluminum and can design heatsinks. I don’t have noise requirements and know how to create proper flow through an enclosed cabinet.QuoteI will keep that in mind, thank you. What happens if you use more in a linear power supply? I was going to use smaller capacitors in parallel in combination with an inductor to try to manage.QuoteThese are all great points. Easily overlooked. Thank you.

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 06, 2023, 02:02:55 am
content: Quote from: Wallace Gasiewicz on November 05, 2023, 01:37:33 pmThank you for additional information. I don’t know if you realize but I answered a lot of these questions in my previous post where you also commented graciously (I am the same poster).In that particular post somebody recommended a source for a toroidal transformer. I’m going to give them a shot as it seems like a good fit for what I have in mind. I’ll probably get the 1000 VA or the 1500VA toroidal transformer.

author: coromonadalix
author_rank: Super Contributor
timestamp: November 06, 2023, 02:09:12 am
content: i would not use the term housekeeping, the term is floating supply voltagethe regulator section float over the power section ... any surge or power cosumption / variations are not put / added in the floating section

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 06, 2023, 02:26:20 am
content: Quote from: Kleinstein on November 05, 2023, 02:57:55 pmThanks for the direct answer. So with a budget of $10 what would be a better choice than the TLV930X?What specific parameters in your recommendation would be better and are relevant for voltage control and current control in a linear power supply?QuoteGood to know I will keep that in mind for basic single voltage designs.QuoteThis kind of makes sense and at the same time it does not. If you have the broad strokes of your design worked out picking out higher grade components seems to make sense as the next step. I’m sure like every other design process nothing will play nice from the beginning and will require tweaking.I played around with some simulation software like LT-Spice, Q-Spice and a few others. I am not very proficient with them. I think where I get frustrated with them is being able to place specific components into the simulation. They seem to have limited choices for example in the op amp category. I generally pick up software fairly quickly so it’s not actually the interface that I have a hard time it’s more the lack of knowledge on a particular topic and the ability to select components that I want to simulate.QuoteAs stated in the previous response I will probably post a separate thread to discuss the selection of power transistors or MOSFETs.I did start discussing some transformer options and switching of taps in another post.What would be the benefits and cons of a floating regulator?

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 06, 2023, 02:38:39 am
content: Quote from: xavier60 on November 05, 2023, 03:46:15 pmIn the case of the TLV930X it should function in a 30 V supply, No?If you decided to create a separate rail for op amps, what voltage would you settle at and why?QuoteI understand the need for speed in a switch mode supply. What is the relevance of speed in a linear power supply?

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 06, 2023, 02:53:34 am
content: Quote from: schmitt trigger on November 05, 2023, 05:12:58 pmWhenever I design anything I always overcompensate so in the case of electronics I would definitely be derating as I went along.As far as thermals go I feel fairly comfortable. My plan is to have large aluminum heatsinks (which I can design and manufacture myself) , thermal paste and a well thought out fan system and enclosure that is roomy.QuoteNoise does not bother me. There are also very efficient fans that make very little noise. You can find some of those solutions in the PC market.Also if you utilize more than one fan you can create different pressures (compared to the outside) inside the enclosure which minimizes how much dust and debris is taken in.QuoteThis is a great suggestion and something that I touched upon in my previous post.I was also asking if there was a solution that would work better such as solid-state. My train of thought is that relays are a lot more harsh not to mention they add additional factors into the circuit such as capacitance and inductance.Any benefit of one over the other? Solid-state versus relays?

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 06, 2023, 02:56:07 am
content: Quote from: Terry Bites on November 05, 2023, 06:18:36 pmI am not sure what you mean by Raw DC supply?

author: xavier60
author_rank: Super Contributor
timestamp: November 06, 2023, 04:20:51 am
content: Quote from: JJ_023 on November 06, 2023, 02:38:39 amFor 30V output, a linear PSU's unregulated rail could easily reach 40V.A design that powers the opamp with the full unregulated supply usually means that the output of the opamp is expected to swing over the PSU's full output voltage range with the output transistors functioning as Emitter follower buffers to boost the output current capability.This type of topology has a low impedance, constant voltage output characteristic.The Harrison/HP topology which just about every store-bought linear bench PSU is based on, has a high impedance, constant current output characteristic. Each type has pros and cons. Without going any deeper, I prefer the high impedance output type topologies.With my most recent PSU project, I settled on 8V for the opamp supply which allows more than enough opamp output swing to drive the following stage. As the supply voltage is made unnecessarily higher, it increases the time taken for the CC opamp to take control of the PSU's output when a sudden overload occurs.While operating in CV mode, the CV opamp's job is to constantly compare a divided down sample of the PSU's output voltage to a reference voltage and make corrections to the drive of the output stage in an attempt to hold the PSU's output at some preset voltage.In practice, the output voltage will dip and over-shoot with abrupt changes in load current draw. The whole loop including CV opamp and output stage needs to have a fast enough response to keep the voltage fluctuation within acceptable limits. This is easy to achieve for most applications.

author: schmitt trigger
author_rank: Super Contributor
timestamp: November 06, 2023, 04:22:15 am
content: Mechanical Relays completely isolate the load when turned off. They can take significant amounts of abuse.On the other hand, solid state devices switch instantaneously and without contact bounce. They require less power to drive compared to a relay.In the end, it is a personal preference.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 06, 2023, 05:00:51 am
content: Quote from: JJ_023 on November 06, 2023, 02:38:39 amIf the speed is relevant depends on the circuit. In some cases the speed of the OP-amp used for the current control can matter, as it starts with a pretty small voltage at the shunt and may have to control the full voltage swing (if using the emitter follower configuration). The LM358 has the added complication with a rather large cross over range and thus added possible added delay when not used as a class A output.Because the needs vary with the circuit choosen it makes little sense to start with choosing an OP-amp. For the simulation the universal OP-amp type is perfectly fine to start with and possibly all the way to the end. If needed one can adjust the parameters from the default (e.g. 1 MHz GBW in LT spice AFAIR).Quote from: JJ_023 on November 06, 2023, 02:02:55 amStarting a first lab supply build with such a large transformer is not a good idea. It adds complications with inrush current and high power can get dangerous even at low voltage. I would even tend to the other extreme and first start really small, like maybe a 100 mA version with a 10 VA transformer.

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 06, 2023, 03:31:36 pm
content: Quote from: alligatorblues on November 05, 2023, 09:38:17 pmI think that is a great suggestion. I actually look at a lot of data sheets. I enjoy reading them especially the Texas Instruments ones. In general I find Texas Instruments website to be a treasure trove of information. They have a lot of publications geared towards designing with their products.As far as math goes I agree that it's important and I feel fairly comfortable when it comes to math.I am very familiar with Halon and actually have few extinguishers that are Halon specific.

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 06, 2023, 03:48:28 pm
content: Quote from: xavier60 on November 06, 2023, 04:20:51 amThis makes sense to me.Why do you prefer the high impedance topologies?What are some of the cons associated with a high impedance topology design?QuoteSo I assuming you would use some sort of LDO circuit off of the unregulated rail that’s designed and fixed for 8 V to create a floating 8V rail?QuoteThis part I am aware of. As far as the voltage reference I was going to avoid a Zener diode and utilize a voltage reference such as.https://www.ti.com/lit/ds/symlink/tl431.pdf?HQS=dis-dk-null-digikeymode-dsf-pf-null-wwe&ts=1699056194193QuoteIt’s like most things I observed whether electronics or economics things and formulas predict an equilibrium and then the model constantly overshoots or under shoots needing further correction.

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 06, 2023, 03:52:11 pm
content: Quote from: schmitt trigger on November 06, 2023, 04:22:15 amI have worked with both in the past so the stuff you mentioned I am already aware of. I guess my question was poorly phrased.What I was trying to ascertain is which one would have less influence on the quality of the power supply in terms of noise and ripple?My previous applications never had any of those considerations.

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 06, 2023, 03:59:44 pm
content: Quote from: Kleinstein on November 06, 2023, 05:00:51 amThat makes sense.I always assumed that it would operate as a class A, is that not always the case in a linear power supply design?QuoteI understand exactly what you are saying. I guess I need to spend more time on LT spice and figure some of this stuff out.QuoteI really do appreciate everyone’s concern. I know that you don’t read all of my posts, but I feel fairly comfortable with voltages up to 400V, and have worked with mains voltages fairly often. I understand the risks. Thank you for your concern.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 06, 2023, 04:44:09 pm
content: The point with the LM358 is the output stage for the OP amp. Most OP amps have a more class AB like output stage, but the LM358 (and related) has a class B output stage with a rather large dead zone as part of the OP-amp. When used that the output goes from a positive to negative OP-amp ouput current this causes quite some delay from a limited slew rate (some 0.6 V/µs) and a dead zone of some 1.8 V. So while a common part it has it's quirks.The TLV9302 should at least not have such a large dead zone and the slew rate is higher (a common feature for FET parts compeared to similar GBW BJT based parts).Starting with a simulation is a more systematic, modern way. It works good with already some experience and knowledge. It allow virtual testing with many conditions, some hard to realize in real life.Others prefer a more hands on build, seeing oscillations and magic smoke in real life.Though still a relatively simple system, pure try and error can still be a long way and may not find a good solution. There are plenty of plans for the lab supply around. The difficilty is still to find a good one between many beginners first tries, that maybe kind of work under favorable conditions. The difficulty is in having the regulator to work (not oscillate, low output impedance and still reasonable fast) over a large range of load impedances and currents.

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 06, 2023, 08:40:22 pm
content: I agree with you that simulation is a great tool. I personally use several different simulators when I design stuff.I just have to I guess bear down on LT spice or Q -spice. You have a preference?

author: xavier60
author_rank: Super Contributor
timestamp: November 06, 2023, 10:44:52 pm
content: Quote from: JJ_023 on November 06, 2023, 03:48:28 pmHi-Z designs tend to have low drop-out voltage. It can be close to zero with Harrison/Hp type.It's 1V for mine,https://www.eevblog.com/forum/beginners/lm324-power-supply-with-variable-voltage-and-current/msg3582664/#msg3582664The specs of the transistors used can tend to have a greater effect on performance than they might with a Lo-Z design.As with LDOs, which are actually the Hi-Z type, the wrong type of output capacitor can cause instability. The capacitor needs to have a certain amount of ESR as electrolytic capacitors do, which would likely be chosen anyway. This needs to be aware of mainly for when simulating.QuoteI use an LM317 to regulate the 8V from the main unregulated supply, so it's not floating.Care needs to be taken as to what else should be powered from the 8V. An independent supply could be used instead, as other members have done with this design.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 07, 2023, 08:06:19 am
content: HIgh Z output stages have it a little easier with current control. The low Z (emiter follower type) vesion is a slightly easier with voltage control, but current regulation gets more tricky. A problem here is that the OP-amp needs to cover the whole voltage range and thus a limited maximum voltage. Already 30 V is hard this way. They get away with less capacitance at the output, but the slower reaction of the current limit looks like a simulated capacitance.Both systems need care to work over large range of load impedances, but if done right it works.The Harrison / HP topology with a floating regulator is kind of the standard found with most of the commercial lab supplies.

author: iMo
author_rank: Super Contributor
timestamp: November 07, 2023, 09:26:38 am
content: Here is a Harrison topology of a jelly bean HY1503 PSU (there are many variants for 15..30V and 3..5A, basically the same schematics). I've recently repaired one and been surprised how well it works.There are several minor improvements needed I would do when building my own based on that schematics (getting rid of the zeners for -6 and -12V in that wiring for example, also I would use some better opamps).So far I added a 4.7 (or was it 3.9?) ohm resistor in series with the 0.33ohm shunt which I do short with a switch mounted on the front panel, thus I get two CC ranges - 250mA and 3A.PS: the 741 there does the CV and the top left 324 does CC. The top right 324 does switching of the secondary transformer wiring with around 8V set.There are also two independent floating 9V power lines for a 7106 based floating LCD voltmeter and ammeter (not in the schematics).

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 08, 2023, 02:03:39 am
content: Quote from: xavier60 on November 06, 2023, 10:44:52 pmI assume that you would tend toward selecting capacitors with a lower ESR. Is this a correct assumption?QuoteI can make the enclosure any size within reason. So an independent supply is a direction that I would go in. Probably something like a 20 VA toroidal transformer with a center tap. To have 2 separate voltages. Does that sound like a good idea for an independent supplementary supply?

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 08, 2023, 02:07:13 am
content: Quote from: Kleinstein on November 07, 2023, 08:06:19 amThank you for the elaboration.Why is it hard to cover 30 V when the operational amplifier that I am looking at goes to 40 V?What is the name of the other Topology?

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 08, 2023, 02:18:13 am
content: Quote from: iMo on November 07, 2023, 09:26:38 amThank you for the schematic and the comments. What did you end up repairing?QuoteSo you would use a voltage reference instead?I have an operational amplifier in mind. What is your opinion of it?https://www.ti.com/lit/ds/symlink/tlv9302.pdf?ts=1699301328442&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTLV9302%253Futm_source%253Dgoogle%2526utm_medium%253Dcpc%2526utm_campaign%253Dasc-null-null-gpn_en-cpc-pf-google-wwe%2526utm_content%253Dtlv9302%2526ds_k%253DTLV9302%2526dcm%253Dyes%2526gclid%253DEAIaIQobChMIubSt2JawggMV4fTICh2B3w_EEAAYASAAEgIm1fD_BwE%2526gclsrc%253Daw.dsQuoteAre you doing this so that you have a finer control at the lower range?QuoteWhat is the purpose of D12 next to LM741?

author: xavier60
author_rank: Super Contributor
timestamp: November 08, 2023, 03:18:19 am
content: Quote from: JJ_023 on November 08, 2023, 02:03:39 amThe independent supply or Control supply can be from a separate transformer or a spare winding on the main transformer. It doesn't need to supply much power. 10mA or so for the PSU's control circuit plus for whatever else is added such as digital panel meters, microcontroller board and tap change relays.The actual output capacitor I used for two of my PSU projects is UCC KME series 47uF 100V. It's classed as general purpose, but the ESR measures rather low at 0.4Ω. At this stage, I wouldn't expect the ESR of any wet type of electrolytic capacitor to be low enough to cause problems. Keep in mind that this output capacitor issue applies to most LDO regulators including Harrison/HP types.Search on "LDO stability capacitor ESR"

author: Kleinstein
author_rank: Super Contributor
timestamp: November 08, 2023, 10:32:49 am
content: The difficulty from getting a high voltage in the emitter follower configuration comes from the limit output range of many OP-amps.Darlington transitors plus emitter resistors / shunts would need some 2 to 2.5 V of extra headroom. The combination with the current limit / current control often needs another extra 1-2 V. This than gets tricky with many OP-amps that only allow for a 36 V supply or don't have a rail to rail output. With the TLV9301 a 30 V range would be not too difficult as it allows 40 V and has near RR output.Adding a 2nd shunt resistor for a low current range is useful extension. Otherwise the accuracy for low current limits may be an issue. The dynamic range for currents is quite large and the normal shunt is low voltage (e.g. 200 mV at FS), especially for high maximum currents.The diodes D11 and D12 in the HY1503 circuit are the typical minimum circuit for combining the CC and CV controls. Either the CC or the CV regualtor turns down the output transistor.The zener diodes are used for supply regulation, the actual reference is the TL431.The circuit is the basic Harrison topology, but not a very good implementation. E.g. the voltage control with the variable series resisitor VR4 can lead to high voltage if the wiper gets bad. In addtion the loop gain / stability depends on the set voltage. It is better to get the votlage from the reference side even if this needs another OP-amp as voltage follower. Digital supplies do it this way anyway. There are also no provisions for windup limitation. Better ones would have back to back diodes at the LM741 inputs (or use an OP-amp with such diodes). For faster reaction and better trim of the stability there is usually a resistor in series to C9 and maybe C7.In many cases the shunt for the CC control can also be used for the measurement / display.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: November 08, 2023, 02:27:12 pm
content: Keinstein,I have a question.When building my experimental supply. I noticed a lot of ripple out of the 3 pin 18 V regulator I used for the "Control" (or housekeeping) supply. The original Lambda design only had one cap. I mitigated this with a resistor capacitor Pi filter before the 3 min 18 volt regulator. How important is a low ripple at this point?

author: Kleinstein
author_rank: Super Contributor
timestamp: November 08, 2023, 02:43:51 pm
content: Ripple before the regulator should not be that important. The 3 pin regulator usually have quite good ripple rejection. After all the ripple rejection is one of the main taks of the regulator. The PSRR of the OP-amps is usually also good.If there is plenty of voltage, one can use an extra resisistor, it even helps to get a better power factor.

author: MathWizard
author_rank: Super Contributor
timestamp: November 08, 2023, 03:02:58 pm
content: I copied and modified an old adjustable 30V-1A BJT PSU design. It used 2 differential pairs, 1 each for voltage and current control. Then I added more diff pair's for warning lights, shutdown's, and fan control.It had a floating floating supply rail. I adding some temperature controlled fans, and emergency shutdown's.I used 3 transformers I salvaged from stereo's. Then in a better version I made, I have a single transformer, with suitable winding's.It works pretty good, I hardly ever used it tho, but if I need the extra adjustable PSU, there it is.Soon I'll try an op-amp version of a linear PSU. I put a bunch of connectors on that big transformer I'm using, so I can plug it in and out of other circuits too. It can handle a lot more power too.

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 08, 2023, 03:58:03 pm
content: Quote from: xavier60 on November 08, 2023, 03:18:19 amI actually read a bunch about this topic from a few different sources 1 of which being Texas instruments design guideline for LDO.Basically from what I understood, to high an ESR or to low an ESR is not good because it will create a phase shift which could cause ringing and oscillations.As a matter of fact they attributed the majority of the oscillations to choosing the wrong ESR.As far as choosing a capacitor they recommend a solid tantalum capacitor.Anybody see anything wrong with the above? Just curious to see if I’m interpreting things correctly.

author: xavier60
author_rank: Super Contributor
timestamp: November 08, 2023, 04:09:04 pm
content: Quote from: JJ_023 on November 08, 2023, 03:58:03 pmI don't think tantalum capacitors are available in high enough voltage ratings. An electrolytic capacitor will do fine.To be sure, you could just get the same as what I have been using if available. I got mine from a surplus supplier many years ago.

author: themadhippy
author_rank: Super Contributor
timestamp: November 08, 2023, 04:24:03 pm
content: QuoteHow high do you want? 50V are widely available,and if you've deep enough pockets vishay will flog you 125v tants.

author: xavier60
author_rank: Super Contributor
timestamp: November 08, 2023, 04:35:37 pm
content: Quote from: themadhippy on November 08, 2023, 04:24:03 pmI had a quick look. Just the prices are enough reason to avoid them.The EKMG101ELL470MJC5S looks to be close to the caps I have been using. And they are getting scarce also.Edit: Plenty here,https://au.element14.com/chemi-con/ekmg101ell470mjc5s/aluminum-electrolytic-capacitor/dp/1304247

author: Kleinstein
author_rank: Super Contributor
timestamp: November 08, 2023, 04:38:09 pm
content: Tantalum caps are not so great for high power. With to powerfull a supply it may be enough to ignite the chemistry inside the cap and get a "nice" firework.With tantalum caps one may want a 3 x derating in the voltage - so 50 V types would be ok to maybe 20 V.For a regulator it helps if one has not just 1 capacitor but a combination of at least 2 capacitors in parallel: one smaller one with relatively low ESR - this could be a MLCC or film cap (e.g. 100 nF to 1 µF) and a 2nd larger (e.g. 10 x) with significant ESR, e.g. a normal electrolytic, possibly even with an extra series resistor of a few ohms. There was some sense to the old times typical 100 nF film + 10 µF electrolytic with an 78xx, even though they usually are not as critical as the LDOs.The difference between a 3 pin LDO and a lab supply is that the LDO is made to work with capacitors in a pretty limited range (capacitance and ESR), while a good lab supply should still work (not oscillating, though possible ringing at the extremes (usually high capacitance low ESR)) with essentially any realitic external capacitance.

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 08, 2023, 11:18:57 pm
content: Quote from: Kleinstein on November 08, 2023, 10:32:49 amI specifically searched for an operational amplifier that would have the extra headroom, that is 1 of the reasons I settled on TLV930x series.So based on what you wrote do you know of a better option for an operational amplifier?QuoteI don’t fully understand this. But I will look into it.QuoteI don’t fully understand this. If you have a reference what is the need for the Zener diodes?QuoteI have a decent amount of experience with potentiometers. I usually go for the higher end MIL spec ones. For a power supply I would probably use a multi-turn. If you use an extremely high quality potentiometer would this still be the case? If so what is a better solution?QuoteI don’t fully understand this. I will get back to this when I ascertain a little bit more knowledge.For faster reaction and better trim of the stability there is usually a resistor in series to C9 and maybe C7.In many cases the shunt for the CC control can also be used for the measurement / display.Is there a specific value of resistor? Would a high ESR capacitor be utilized as well?

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 08, 2023, 11:20:15 pm
content: Quote from: Kleinstein on November 08, 2023, 02:43:51 pmHow would this give you a better power factor? Where would this resistor be placed?

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 08, 2023, 11:30:20 pm
content: Quote from: xavier60 on November 08, 2023, 04:09:04 pmThey actually do have a lot of tantalum capacitors above 60 V. They get somewhat expensive. Also I think we are talking about 2 different scenarios. The Texas Instruments application note was particularly in reference to LDO’s not output capacitors. Take a look at the application notes it is a super interesting read. Maybe I got something wrong?https://www.ti.com/lit/an/snva020b/snva020b.pdf?ts=1699463437316&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FLMS1587

author: xavier60
author_rank: Super Contributor
timestamp: November 09, 2023, 03:05:54 am
content: Ti calls the design type of my PSU, Quasi-LDO Regulator.

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 09, 2023, 03:57:40 am
content: Quote from: xavier60 on November 09, 2023, 03:05:54 amWhy did you choose that design, versus a pure LDO?In a linear power supply from mains you have a lot more headroom that could be built in. So the dropout voltage is not as big of an impact versus a battery type of design, and from what I understood from that application report is that a LDO design has more stability.Am I wrong?

author: xavier60
author_rank: Super Contributor
timestamp: November 09, 2023, 04:37:16 am
content: Quote from: JJ_023 on November 09, 2023, 03:57:40 amI didn't actually choose the design. It evolved as a series of improvements to a dysfunctional design another member had found on the internet.If it were to be altered back to the LDO type, Q1 would be dissipating much more power than the few milliwatts a BC546 can easily handle. The stability of this design isn't a problem. A lot of testing has been done by me and other members.To compensate for the typically higher dropout voltage of Emitter follower designs, the unregulated rail voltage needs to be designed higher. This adds significantly to heat dissipation at the output transistors, the resulting complications it can cause might become apparent later.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 09, 2023, 08:49:26 am
content: Quote from: JJ_023 on November 08, 2023, 11:18:57 pmThe way the adjustment is made with the pot as a variable resistor has 2 weak points:1) wiper open failure gives a higher voltage, less an issue with a good pot, but still not good.2) the resistor setting changes the feedback gain and thus the control loop. This adds one more variability and needs compromises. At least in the plan they have the parallel electrolytic capacitor and the variable loop part effect the lower frequency part only.The better alternative is keeping a fixed feedback divider and instead make the reference voltage side variable. So a pot as voltage divider with an OP-amp as follower. This configuration is natural if one uses a DAC for the set point. So newer supplies usually use this configuration.The voltage regulator is a kind of PID (the resistors in series to C7 and C9 would be D part) regulator from classic control theory. Using the ESR of C7 /C9 is not practical as one often wants something in the kOhm range and a value to trim / tweak with. One would normally do the simulation to get good values for C7,C9 and the resistors.One classic refinement of the PID regulator is anti windup. This is a method to avoid that the integrato part get unreasonable large when the regulator temporary hits it's limits. This is standard with digital regulator, but actually a bit tricky to implement analog as it is nonlinear. One should still avoid / reduce windup to get a better transistion between CC and CV mode.The regulator configuration that xavier60 used is not common for labe supplies, but it has a few nice points: one gets many of the features of the floating regulator, but does not need a 2nd transformer (or extra windings). As an inbetween the high and low impedance output stage it can also be a reasonable balance for getting both CC and CV mode relatively easy/good.I consider that plan a good solution for a simple lab supply, especially if one does not want a 2nd transformer (e.g. start with a laptop supply or similar to keep the main voltage out altogether).The main advanatges I still see with the floating regulator is lower voltage loss and the good flexibility.

author: iMo
author_rank: Super Contributor
timestamp: November 09, 2023, 09:29:10 am
content: The issue with the HY1503 shown above is it has indeed the CC/CV control made of potentiometers wired as the variable resistors (not as a voltage divider). Those are wired on the reference side, that is ok, but they change the load on the reference (TL431 in my case), what is also not good. That would be an another improvement I would do - to rewire it.The issue with lousy wiper contacts - the solution could be a higher value resistor wired from the wiper to a potential such it sets a safe voltage/current in case of the lost contact..

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 09, 2023, 12:06:57 pm
content: Quote from: xavier60 on November 09, 2023, 04:37:16 amThanks for the elaboration. This makes sense from what I understand.I know that heat is always an issue, the result is a derating of the total performance of components, as well as the values of those components. What I don’t understand is if you can heatsink and provide adequate airflow through several fans (I don’t really have size limitations on the enclosure) why can’t this be managed quite easily.I can make or buy heatsinks with the appropriate size. Thermal compounds are obtainable. I know how to set up fans to create airflow. What exactly am I missing in terms of real-world solutions to this particular scenario?

author: xavier60
author_rank: Super Contributor
timestamp: November 09, 2023, 12:30:22 pm
content: Quote from: JJ_023 on November 09, 2023, 12:06:57 pmThe main thing is the lack of practical designs. The only design I'm comfortable with is the one I have posted. I have never seen a Lo-Z Emitter follower design that I have liked.Although the Harrison type is capable of the best performance, I will not recommend it as a first PSU project.From the experience of having built one, I found the testing and tweaking rather challenging due to having to ground some test equipment to the plus output and some to the minus output. With Harrison, ground for all the functional blocks is actually the plus output.

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 11, 2023, 01:19:07 am
content: Quote from: Kleinstein on November 09, 2023, 08:49:26 amI completely understand the 1st point. I guess you would mitigate that with a resistor in series in case the potentiometer fails to prevent a complete short.I understand your 2nd point as well.QuoteI assume you could use an Arduino with a DAC module as a setpoint, is this possible?Is there a better way to implement a DAC?QuoteIs it easier to implement a digital solution for some of my goals? I am not set on an analog only design.

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 11, 2023, 01:27:08 am
content: Quote from: iMo on November 09, 2023, 09:29:10 amCould you elaborate on how they change the load on the reference. Does the reference not compensate?

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 11, 2023, 01:37:56 am
content: Quote from: xavier60 on November 09, 2023, 12:30:22 pmI agree with you on the practical designs. I spent a lot of time looking.For me a better approach is reading and asking people that know more than me.

author: David Hess
author_rank: Super Contributor
timestamp: November 11, 2023, 01:48:35 am
content: There are plenty ofold and new 44 volt operational amplifiersto choose from.I would start with something smaller. 30 volts is fine but 1 amp, or even half an amp, is more suitable for general purpose use. I would rather have a positive and negative dual supply than high current.Quote from: JJ_023 on November 05, 2023, 02:34:16 pmOperational amplifiers have considerable power supply rejection so operate just fine from an unregulated supply as long as their maximum supply voltage is not exceeded. A zener shunt regulator is a good idea for protection though and provides more than enough regulation.Quote from: Terry Bites on November 05, 2023, 06:18:36 pmThose can work but have a very limited differential input voltage range which can be a problem. That kind of precision is rarely needed in a power supply.

author: xavier60
author_rank: Super Contributor
timestamp: November 11, 2023, 02:20:14 am
content: QuoteThis and other issues have already received attention in the design I have posted. Compensation resistor R5 is connected to the ORing node rather than the normally expected place at the output of the CV opamp. This simple modification, actually suggested by Kleinstein many years ago, greatly reduces voltage overshoot when the PSU transitions from CC to CV mode. There are other performance enhancements that are totally invisible to the casual observer.

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 11, 2023, 02:37:42 am
content: Quote from: David Hess on November 11, 2023, 01:48:35 amI appreciate the suggestion as I know it comes from a good place and experience. But I need higher voltage and amperage. I currently have an HP supply 623B that is not meeting my needs.QuoteI am looking at the following operational amplifier.https://www.ti.com/lit/ds/symlink/tlv9302.pdf?ts=1699301328442&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTLV9302%253Futm_source%253Dgoogle%2526utm_medium%253Dcpc%2526utm_campaign%253Dasc-null-null-gpn_en-cpc-pf-google-wwe%2526utm_content%253Dtlv9302%2526ds_k%253DTLV9302%2526dcm%253Dyes%2526gclid%253DEAIaIQobChMIubSt2JawggMV4fTICh2B3w_EEAAYASAAEgIm1fD_BwE%2526gclsrc%253Daw.dsI am looking at the following reference voltage.https://www.ti.com/lit/ds/symlink/tl431.pdf?HQS=dis-dk-null-digikeymode-dsf-pf-null-wwe&ts=1699056194193What are your thoughts on both?

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 11, 2023, 02:53:56 am
content: Quote from: xavier60 on November 11, 2023, 02:20:14 amI am that casual observer. But thank you for taking the time to share your knowledge.

author: David Hess
author_rank: Super Contributor
timestamp: November 11, 2023, 04:05:51 am
content: Quote from: JJ_023 on November 11, 2023, 02:37:42 amHigher voltages and currents are usually better satisfied with a separate fixed power supply. Like I have a 6 amp 24 volt frame supply for motor projects.QuoteThere is nothing wrong with that operational amplifier, but like I wrote, there are 44 volt parts available. It has low input bias current, wide differential input voltage range, and high slew rate. More advanced designs can take advantage of operational amplifiers which have external compensation pins.I like using LM329 type zener references for their lower noise (I do a lot of precision stuff), but the TL431 is easier to design with and the noise difference rarely matters.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 11, 2023, 09:39:46 am
content: Even if the final goal is a high power version, it still makes sense to start with a small one first. It is just less smoke and costs when parts blow up. One rarely has too many power supplies and often low power is sufficient.For the control a pot is easier to build and also not than bad to use. If digital control is wanted the PWM DAC with filtering is possible and defenitely a good low cost option. There are also DAC chips (12 bit range) that are not too expensive, but it gets expensive for higher resolution and low noise. With a DAC one naturally choses the configuration to adjust at the ref. voltage side and thus avoids the possible effect on the control loop. So it makes sense to use a pot in essentially the same way as a DAC and thus plan with both options in mind.The LM329 was a good option a few years back, when it was cheap - it got relatively expensive by now. Many DACs wants more like a 5 V reference anyway and there are plenty of 5 V references around and the requirements are usually not that high.While one usually does not need a precision amplifier like the OP07 for the voltage control, it can however make sense to have one with the current control part. A better amplifier can allow a lower value and lower power shunt and this way overall save money. Precision OP-amps are no longer than expensive anyway.A part that needs a bit more thought than one may fist think is the shunt resistor to regulate / measure the current. To get a reasonable adjustment range one does not want too small a resistance and thus has to fight with the self heating, especially with a higher current (e.g. 3 A or even more) version. 2 Current ranges are an option to consider too.For the OP-amps it depends on the general layout. A first step would be to decide on the needs and the general configuration. I would consider 3 general types :1) The Harrison, floating regulator type does not need OP-amps with a high supply and often has a +- supply for the OP-amps anyway.--> flexible, but need the extra supply / transfromer, a bit more difficult to understand, low drop possible2) The simple emitter follower type would need a high supply OP-amp and the CC loop amplifier also needs to be relatively fast. Without a negative supply one may need single supply amplifiers.--> can be simple in it's basic form, but limited in the max voltage. Gets a bit tricky with high current accuracy. Often slow CV-CC transition.3) Xaviers variant does not need high voltage amplifiers, but single supply parts if there is no negative auxiliary supply.--> a bit inbetween, still the shunt on the low side. No need for high voltage OP-amps.

author: iMo
author_rank: Super Contributor
timestamp: November 11, 2023, 11:04:21 am
content: Quote from: JJ_023 on November 11, 2023, 01:27:08 amA reference has a limited capability to compensate for changes in its output current (so called load regulation). With CC/CV potentiometers wired as "the variable resistors" the output current may vary significantly (like 1:2 for example) that creates a voltage drop at the reference output. How much it drops depends on the reference.With the potentiometers wired as the "the voltage dividers" the current change is almost zero, as the current taken by the opamp's input (off the pot's wiper) is negligible.

author: xavier60
author_rank: Super Contributor
timestamp: November 11, 2023, 12:07:32 pm
content: I would expect the Reference current to stay constant with the original rheostat arrangement because the voltage across R1 stays the same.Edit: changing from rheostat to pot will eliminate the reference current variation caused by the CC control.

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 12, 2023, 03:48:57 pm
content: Quote from: David Hess on November 11, 2023, 04:05:51 amI would agree with you based on my experiences with motor projects.QuoteI understand the advantages of having external compensation pins but could you elaborate as to why 44 V parts would be better than the 40 V part that I found when you are designing a 30 V linear power supply. What am I missing here?

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 12, 2023, 04:03:30 pm
content: Quote from: Kleinstein on November 11, 2023, 09:39:46 amThis makes sense to me.QuoteI read through the datasheet and looked up the part. It’s not crazy expensive at $5. I’m going to do a little bit more reading on it besides the datasheet.QuoteWhat you say makes sense. What I still don’t understand is why the operational amplifier you suggested is better than the one I found.I am not disputing that it is, I am just trying to learn where to look in the datasheet to understand why your recommendation is better than the one I found.QuoteI think this is probably easily overlooked but it does make total sense to as that is the sensing part of the circuit and a lot of things will be based off this.How would you implement current ranges. I assume similar to different voltage ranges. Utilizing relays or solid-state for switching.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 12, 2023, 04:26:59 pm
content: Different current ranges could be made with a relay, just a simple mechnical switch or 2 MOSFETs for switching. The MOSFETs may even have a secondary use as emergency off in cause of a fault.The LM329 was at some $0.80 a few years ago. In the $5 range there are plenty of good references to chose from that may be better suited. It is still not too bad.For the amplifiers one would likely want more precision parts. So while OK for a CMOS part the TLV9301 still has quite some 1/f noise and possibly drift that could be an issue. It can still be good enough for most tasks, but maybe not so much for the shunt. At the shunt it is about the low frequency noise and drift. If a high voltage or signle supply operation is needed depends on the circuit.Most of the 44 V OP amps are not single supply of rail to rail out. So while they may work with 44 V this would not give much more useful range than a 40 V rail to rail part. Anyway, the better circuit don't need OP-amps for a high voltage, 16 V parts may be good enough. So forget about the OP-amps, decide on the configuration and circuit first. The deails of the part choice comes later, when things are 75% done, so probably not in this year anymore.

author: xavier60
author_rank: Super Contributor
timestamp: November 13, 2023, 12:08:36 am
content: The preferred opamp for my design, TLC072,has gone EOL butstill available. It's replaced by the TLV9162, not available in DIP.It's claimed to be rail to rail, in and out.The slew rate has near double to 33V/µs, which I'm expecting to quicken the PSU's current limiting response.I'll get some for testing with my next Mouser order.https://www.ti.com/product/TLV9162

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 13, 2023, 01:20:29 am
content: Quote from: iMo on November 11, 2023, 11:04:21 amOkay this makes sense to me. Thank you for taking the time and making a schematic and the explanation that goes with it.

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 13, 2023, 01:26:24 am
content: Quote from: Kleinstein on November 12, 2023, 04:26:59 pmOkay this makes sense to me. Thank you.

author: JJ_023
author_rank: Frequent Contributor
timestamp: November 13, 2023, 01:51:57 am
content: Quote from: xavier60 on November 13, 2023, 12:08:36 amSo I read the datasheet. This particular operational amplifier gets damaged at anything above 20V. How would it be used in a 30 V power supply?

author: xavier60
author_rank: Super Contributor
timestamp: November 13, 2023, 02:05:48 am
content: Quote from: JJ_023 on November 13, 2023, 01:51:57 amThe 16V rating isn't a problem for Harison and LDO type designs where the opamp is powered from low voltage regulated control rails.I added an edit to Reply #69.

author: David Hess
author_rank: Super Contributor
timestamp: November 13, 2023, 08:22:38 am
content: Quote from: Kleinstein on November 12, 2023, 04:26:59 pmI tend to avoid using rail-to-rail inputs over their full input voltage range because of performance limitations, but single supply inputs are useful when a negative supply is not available, or a rail-to-rail input can be used over a limited range as a "single supply" part at the positive or negative rail.QuoteSometimes I design like that, and at other times I start with the parts because of what is available or because of a limited budget. There are some "universal" modern parts which can do it all, but they start at like $5 each, and even there the rail-to-rail input parts are at a performance disadvantage.Quote from: xavier60 on November 13, 2023, 12:08:36 amBut the TLV9162's 11 MHz bandwidth means that it will require external frequency compensation for stability which will reduce its 33 volt/microsecond slew rate.If fast slew rate is needed then there are better parts which have lower bandwidth, or the circuit can be designed with clamping for faster recovery. Integrated regulators use operational transconductance amplifiers because their current outputs have essentially unlimited slew rate when switching between constant voltage and constant current, but that is difficult to duplicate in discrete designs because of lack of suitable parts.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 13, 2023, 08:47:26 am
content: For the OP-amps it can make sense to look at a set of common / basic types and try to get away in the design by using those types. This could be a list like LM358, OP07, TL072, MCP6001, TLC272, OP27 (already relative expensive), NE5532 , if you want add the TLV9301. Most of them are yelly-bean parts and expected to be around for longer also in the future. The final design may end up using different parts, but these would be a good start.Starting with the parts is a thing if one needs special performance. Most lab supply circuit don't need special OP-amps. A few use external compensation pins and thus need specific parts (e.g. LM301).I totally agree with no using the full rail to rail input range with most parts. There can be quite some glitch from input cross over, usually some 1-2 V from the positive supply. With AZ OP-amps it is still usually OK as the chopper part usually also corrects for this, though with some delays.

author: David Hess
author_rank: Super Contributor
timestamp: November 13, 2023, 08:49:45 am
content: Quote from: xavier60 on November 13, 2023, 02:05:48 amWith modern operational amplifiers more likely to be limited to low voltages, Harrison or floating designs are more desirable, but enough modern still support simplified designs up to 30 volts.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 13, 2023, 09:02:05 am
content: Even the floating regulator design gets a bit more demanding with higher voltage (e.g. above some 30-50 V): many power transistor show a break in the SOA and thus need extra care, like use less power per part or use power transistors in series / electronic tap switching instead (or in addition to) mechanical with relays.The 30 V class is a kind if standard size. A more hidden advantage is that even of the power transistors fail short the maximum output is usually less than 50V and this within safe limits for electrical shock.Even the low cost lab supplys (e.g. the HY1503 show earlier) usually use the floating regulator. The extra supply winding for the regulator part can also power a digital display. The otherwise slightly simpler circuit with the emitter follower type may need an extra supply for the display. Once you add a digital display or set point the floating regulator is no longer really more effort.

author: xavier60
author_rank: Super Contributor
timestamp: November 13, 2023, 10:00:49 am
content: Quote from: xavier60 on November 13, 2023, 12:08:36 amAlthough the TLC072 and TLV9162 have about the same high GBW, the regulation performance is not much better than it would be with an LM358.When there's a sudden overload, the high slew rate shortens the time it takes for the CC opamp to slew down from being pinned to the 8V rail down to where it can take control from the CV opamp which at the same time is trying to increase output drive as fast as possible.High output current also allows the CC opamp to quickly discharge the compensation cap through D5, resulting in fast CC settling time.This is one of those invisible performance enhancements.The TLV9162 contains a Slew Booster stage. It could actually make things worse somehow, so Ill test it.