Is it okay to get single output power supply as a beginner ?  - Page 1
Forum section: electronics / testgear

author: electronic_guy
author_rank: Regular Contributor
timestamp: November 26, 2021, 05:24:06 pm
content: Hi,I'm still preparing my home lab setup for electronics. I've seen the advice on getting, dual or triple output power supplies.Is it that bad to get a single output power supply ? I know this sounds like a no brainer, but l couldn't find a decent multiple output power supply from a reputable brand like Agilent or HP on used equipment market.My focus on start is to spend only about $ 250 on my first supply without shipping, and I will be working on getting experience of PCB prototyping and OPAMPs. My target is to reach RF circuit designs.Your advice on this would be supportive to me.Thanks.

author: Nusa
author_rank: Super Contributor
timestamp: November 26, 2021, 05:34:34 pm
content: Of course it's ok. And if you end up needing multiple voltages, there's no reason you can't get another one. Having multiple supplies in the same box is mostly a convenience, not a requirement.

author: 25 CPS
author_rank: Frequent Contributor
timestamp: November 26, 2021, 06:03:58 pm
content: You mentioned op-amps specifically so this is a bit of a tough situation.There's nothing inherently wrong with starting out using a single output power supply and it's by far better to have a single output power supply instead of no power supply and getting by using wall-wart adapters or batteries. When I was starting out, I ended up looking for a power supply pretty quickly after discovering how far 9 volt batteries went for powering circuits I was working on.Op-amps are definitely devices that typically work best with a dual +/- supply, ideally a dual tracking supply where one side follows the other for voltage in opposite polarity. Most supplies like this are two or three supplies in one cabinet as Nusa mentioned but this doesn't necessarily have to be the case. The idea I was kicking around my head for your situation was this: If you're stuck getting a single output supply, see if you can get a Hewlett-Packard power supply that has the full set of output, sense and programming terminals on the back. That'll get you started. Then when you save up a bit more, you can get a second one and then change the strapping on the terminals to operate them in multiple unit to get more current, more voltage, or a dual tracking, opposite polarity setup ideal for op-amps and end up with a two output supply but in two boxes bought at different times. It might be worth thinking about this idea depending on what's available on the used market in your area.

author: james_s
author_rank: Super Contributor
timestamp: November 26, 2021, 06:12:10 pm
content: I'll second that, if you have any interest in working with op amps then get at least a 2 channel power supply that is capable of tracking, even if you can't find one from an A-list brand. For years I used an old Heathkit triple power supply and it still lives on the shelf above my bench, it isn't the most feature rich thing but it does the job. Find some models you're interested in and then set up a saved search on ebay and something will turn up eventually. Or go ahead and buy a single output supply now and then keep looking for something with at least two channels, having extra power supplies is often nice.

author: David Hess
author_rank: Super Contributor
timestamp: November 26, 2021, 09:29:18 pm
content: I worked with a single output power supply for a long time, but quickly built a couple of fixed +/-15 volt power supplies using of 7815s and 7915s.

author: GerryR
author_rank: Frequent Contributor
timestamp: November 26, 2021, 11:41:53 pm
content: There are many linear triple-output supplies on Ebay, like BK Precision, Protek, etc. with switches for series/parallel operation, current limiting, with two variable outputs 0-30v @ 2.5-3.0A and a fixed 5v output, for well under $250.00. Power supplies are generally pretty bulletproof, and most reputable sellers have a good return policy. You might want to check some of them out.

author: David Hess
author_rank: Super Contributor
timestamp: November 27, 2021, 06:23:58 am
content: Also, it is relatively easy to make a simple variable bipolar tracking supply with a 317 and 337 for +/- 1.25 to 15 volts or higher, as shown below from the Linear Technology LT137 datasheet. Projects for simple test equipment are a good way to gain experience.Note that nothing prevents using the design shown below for a 2.5 to 40+ volt power supply.

author: MarkF
author_rank: Super Contributor
timestamp: November 27, 2021, 08:12:22 am
content: I have several small single output supplies nowbut very quickly built a couple fixed +/- suppliesjust for the convince of not having to configure and set the voltages each time.I built a +/-12V and a +/-15V. Thinking the 15V for really old op-amps (741).But if I were to build just one, I would build a +/-12V.Then, you have a +12V output readily available for those battery operated projects.I just love these little HP supplies (I have four now. Brings back the old school days.):Can be had for $50 on eBay.But, I would lean toward aSiglent SPD1305Xand build a +/-12V from 7812 and 7912 regulators to get started.Sense lines. Plus USB & LAN available for automation testing.

author: Fungus
author_rank: Super Contributor
timestamp: November 28, 2021, 11:10:15 am
content: Quote from: electronic_guy on November 26, 2021, 05:24:06 pmYou really need two outputs for opamps (+/- rails).Quote from: electronic_guy on November 26, 2021, 05:24:06 pmIt should be easy in the USA, eg:https://www.ebay.com/itm/304190908203Or get two cheap supplies (eg. the ones suggested by MarkF) and stack them:Quote from: MarkF on November 27, 2021, 08:12:22 amOr ... get a fancy, modern single-output supply for the positive rail (ie. with functions like current limiting, etc) and one of those little supplies for the negative rail (all you need is something linear/low noise, current draw is minimal, almost anything will do).

author: m k
author_rank: Super Contributor
timestamp: November 28, 2021, 02:40:14 pm
content: Some years back I thought I need something not analog in one case.Can't remember why I have two 1803D designs and not 3005 versions.Maybe it was a need, maybe value.Not so long a go I tried to update those two and my auction skills are clearly inadequate.What I found was that 3010 seems to be SMPS.Few 3005 versions were also available but their weights were mostly suspicious, less than 2kg or so.One thing I'd like to note.Indicating vs. measuring.

author: ledtester
author_rank: Super Contributor
timestamp: November 28, 2021, 03:04:34 pm
content: Quote from: electronic_guy on November 26, 2021, 05:24:06 pmA lot of op-amps today only need a single rail. Op amps are generally not very power hungry devices, so for dual rail applications you could use two 9V batteries which will also give you very clean power.

author: Fungus
author_rank: Super Contributor
timestamp: November 28, 2021, 03:23:36 pm
content: Quote from: ledtester on November 28, 2021, 03:04:34 pmI once used a 9V battery for the negative rail on a project with the positive rail from a single-output power supply.OP-amp circuits only use a few mA so they last quite a long time.(...and $50 buys a lot of 9V batteries.)

author: electronic_guy
author_rank: Regular Contributor
timestamp: November 29, 2021, 02:55:52 am
content: Quote from: Fungus on November 28, 2021, 11:10:15 amThank you all for your regard to my problem and the knowledge shared.Going with what @Fungus proposed here, would those two supplies be a good selection that can cover my needs in general ?As a modern power supply for positive rail I can buy a HP/Agilent 3632A and for the negative rail I can get a HP/Agilent 3610A.Here I would not be having tracking for the dual supply. Would that be a big issue when it comes to OPAMPs ?

author: james_s
author_rank: Super Contributor
timestamp: November 29, 2021, 04:22:05 am
content: Tracking isn't strictly necessary, you can always adjust the two separately and most of the time you'll set it to a specific voltage and leave it there. It's just a convenience.

author: Shock
author_rank: Super Contributor
timestamp: November 29, 2021, 06:24:17 am
content: Not that it's entirely necessary to have a triple output power supply, it's the utility of having one or two of them replace a bunch of other supplies.

author: MarkF
author_rank: Super Contributor
timestamp: November 29, 2021, 02:32:48 pm
content: A lot of times, I find myself with a project that has a micro-controller and an op-amp.It's a nice convenience to just flip a switch (and not fiddling with adjusting voltages) for the op-amp power and a third supply for the MCU (3.3V or 5V).All having low power requirements.And then there are cases when you need a good variable output. Or need a single output with a higher current capabilities.IMHO.. Everyone builds a bunch of simple low power supplies and most projects only need a few 100 mA.But, higher output power (over 1A) is more difficult to build. I actually prefer a fixed dual supply for op-amp work.That's why starting with a supply with higher output power (i.e. 5A max) and a few small DIY supplies might be the way to go.Or spend more and get a triple output supply with more capabilities.You will always need more than one supply. So, it all boils down to personal preference. A triple supply, or a few single supplies, or some combination.

author: Fungus
author_rank: Super Contributor
timestamp: November 29, 2021, 05:36:15 pm
content: Quote from: MarkF on November 29, 2021, 02:32:48 pmOf course it'snice... but sometimes bench space and/or budget are limiting factors so we have to make do.

author: Tomorokoshi
author_rank: Super Contributor
timestamp: November 29, 2021, 06:56:00 pm
content: Quote from: 25 CPS on November 26, 2021, 06:03:58 pmExamples are the HP 6227B and 6228B. These tend to be in the $150 to $200 range on ebay.https://www.keysight.com/us/en/product/6227B/power-supply.htmlhttps://www.keysight.com/us/en/product/6228B/power-supply.htmlI hope that describing them as simultaneously bothrobustandrepairableisn't too much of a contradiction.

author: MarkF
author_rank: Super Contributor
timestamp: November 29, 2021, 07:19:31 pm
content: Quote from: Fungus on November 29, 2021, 05:36:15 pmExactly my point.To answer the OP original question:Modern projects will most likely consist of both an analog and a digital sections requiring 3 or even more voltages. You might need +/- voltages for an analog section and 5V and/or 3.3V for a digital control MCU section. You will typically only need one variable voltage and the rest are going to be fixed voltages.When just starting, the OP is not going to know what his evolving requirements will be. You can get a big triple output supply and still need more. Or save some money now by getting a single output lab supply and building a few cheap dual supplies. He can put the saved money toward other lab equipment. A second multi-meter for example.The physical bench space would be about the same for a bulky triple supply or a single lab supply with a small DIY dual supply. On my humble bench table (no shelving), I currently have 8 power supplies. Four lab supplies and four DIY supplies. I have only needed a higher power (30V @ 5A output) supply and the others have been fixed low power (500mA) voltages. But, everyone has different requirements.

author: tautech
author_rank: Super Contributor
timestamp: November 29, 2021, 07:25:27 pm
content: Quote from: MarkF on November 29, 2021, 07:19:31 pmThis ^^Some designs need power rails properly sequenced at power ON and a programmable multi channel PSU is required for that.Unlikely the novice will need such things initially but maybe one day.Decisions.......

author: nctnico
author_rank: Super Contributor
timestamp: November 29, 2021, 09:05:09 pm
content: Quote from: MarkF on November 27, 2021, 08:12:22 amThat is a lot of money for an old clunker if you compare it to the Korad PSUs you can buy new with better features. One of the things you'll want is adjustable current limit down the tens of mA. With a current limit you won't fry your circuit when it turns out it has a short or something isn't right.

author: YurkshireLad
author_rank: Frequent Contributor
timestamp: November 29, 2021, 09:15:24 pm
content: I'm an absolute beginner and I would say get a single bench power supply, like the Korad. Once you've worked out how deep you want to get into electronics, you can buy or build to meet your requirements and budget. I bought a Korad recently and it's perfect for my needs.

author: MarkF
author_rank: Super Contributor
timestamp: November 30, 2021, 02:35:11 am
content: Quote from: nctnico on November 29, 2021, 09:05:09 pmIt's a nostalgia thing for me and totally quiet (no fan).They are designed to be placed in parallel or series.By the way, you can set the current limit down in the tens of mA.F.Y.I. The max output of these power supplies is 500mA.Without taking time to go test them, I believe you could set the current limit to 1 or 2mA.Edit:Note that there are some reports of overshoot when switching on/off.https://www.eevblog.com/forum/repair/power-supply-overshoot-when-disabling-output/https://www.eevblog.com/forum/testgear/korad-kd3005d-bench-supply-power-on-spike/Edit #2:Just tested the old clunker. I found that with a steady hand, I can adjust the current in 100uA (yes. micro amp) steps, starting at 100uA. Test done at 6V plugged directly into a DMM.

author: Fungus
author_rank: Super Contributor
timestamp: November 30, 2021, 11:56:22 am
content: Quote from: nctnico on November 29, 2021, 09:05:09 pmHere's one for $35:https://www.ebay.com/itm/304190918453I might buy it if I was in the USA but I'm not, so... I'll let you guys fight over it.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: December 01, 2021, 12:19:47 am
content: There are several bench supplies available in Indianapolis IN at a radio shop. If you are near you can go and check them out, Plug them in and measure voltage etc.Includes a triple and some singles.I cannot quote prices as they are not mine but they are cheap.Also lots of Linear supplies for 14 Volt and at least one for 28 Volt.If anyone is interested PM me. I will give you location.

author: MarkL
author_rank: Unknown
timestamp: December 01, 2021, 02:28:56 am
content: I would get a triple supply to start, and I would make sure the third output is adjustable. A lot of supplies have the third output fixed at 5V, which is not so useful since most logic and microcontrollers are now 3.3V.An often overlooked triple supply is the Lambda LPT-7202-FM:0-7V @ 5A2x 0-20V @ 1.5A500uV RMS ripple and noise0.01%+1.0mV no-load to full-load regulationAll channels isolated (so you can series/parallel as desired)The 20V sections can be adjusted into the range of <10mA (tested).The going price on ebay is around $100 for a working one. Avoid units with bent or missing binding posts. The unit is heavy (24lbs/11kg) and the binding posts stick out.(Image taken from ebay.)

author: m k
author_rank: Super Contributor
timestamp: December 01, 2021, 07:09:41 am
content: I just saw China goods where third output had a selector.(5, 3.3, 2.5)The very fist thing I miss is output on/off.

author: maxwelllls
author_rank: Contributor
timestamp: December 01, 2021, 07:52:06 am
content: Quote from: electronic_guy on November 29, 2021, 02:55:52 amThe E3632A is a good choice, there are no drawbacks except that it is a bit heavy（12Kg）, about $150 on the second-hand market

author: tautech
author_rank: Super Contributor
timestamp: December 01, 2021, 08:24:29 am
content: Quote from: m k on December 01, 2021, 07:09:41 amYes, all stand features on SPD3303X/X-E.

author: nctnico
author_rank: Super Contributor
timestamp: December 01, 2021, 10:23:01 am
content: Quote from: MarkF on November 30, 2021, 02:35:11 amThat first link looks like a serious issue indeed so that needs some investigation whether that got fixed in the models you can buy today. The second link starts of with a measurement error but shows that actual power on/off behaviour is good for a certain model (no overshoot).Either way; no matter the brand, it is always good to verify power on/off behaviour of a power supply. Even the A-brands can slip up every now and then. Nowadays there are many opamps that are powered from 5V (+/- 2.5V) so an -for example- 8V spike is enough to kill such opamps.

author: Electro Fan
author_rank: Super Contributor
timestamp: December 02, 2021, 04:44:00 am
content: 1. It’s ok to start with a single output power supply, you can add another if/when you need one.2. Look at a Korad KA3005D, about $110 at Amazon.3. Pretty good consensus you might want a 2nd PS for op amp work; in which case you can add a 2nd Korad.4. If you ever need a power supply in a 2nd location you can take one unit there and leave the other unit on your bench.

author: m k
author_rank: Super Contributor
timestamp: December 02, 2021, 11:47:51 am
content: From beginners beginning point of view I'd say a single PS is a must.Making a missing miniature one is a best way to educate one's W and dt, maybe even SNR.Unfortunately China surplus has LM2596 boards.