What power supply to buy? - Page 1
Forum section: electronics / general

author: Andy
author_rank: Contributor
timestamp: March 27, 2012, 10:29:21 pm
content: Hi all,I have been in the market for a power supply for a couple of weeks. I am just a hobbyist that plays with microcontrollers, so I don't want to spend too much. My budget is approximately $300 including delivery. I am willing consider higher prices if necessary, though I am willing to buy a cheaper supply that will require some mods.So far, these are the requirements I have established:Minimum:0-20V DC0-1ADigital readout of both voltage and currentFine control of both voltage and current (I don't want only a single turn pot)Bonus:0-30V DC0-3AMultiturn pot or digital control (either keypad or rotary encoder) of voltage and current10mV/10mA accuracy of readout on displayLoad on/off switchReputable brandLinear regulated (I will consider SMPS, but prefer not to because of their unserviceability)ProgrammableDigital readout of wattageAustralian WarrantyAfter lots of research on the forums, I have found the following supplies:Vantek DSP3303P - My main concern is the getting a unit that has a power on spike like with the Quakko units.ATTEN APS3003Si - Concerned about getting a unit that doesn't have a temperature controlled fan. I don't like loud fans.ISO-TECH IPS405 - A switching power supply will not be easy to fix if something goes wrong, though ISO-TECH seem to be rebadging GW Instek, so the PSU should be of reasonable quality.GW Instek GPS-3030DD - Feature comparable to the ATTEN, but nearly three times the price.BK 1550 - Switching, decent brand, but nice and compact.I might also add that I am following Dave's PSU design, but honestly don't think that will be purchasable for another few months. And, at that time, I'll probably buy it so that I have two power suppliesDoes anyone have any comments or recommendations? How important is getting a linear power supply vs switching?Thanks for the help!Andy.

author: amspire
author_rank: Super Contributor
timestamp: March 28, 2012, 12:36:42 am
content: In general. Linear supplies will be much lower noise, and they can respond to load changes faster.To limit the voltage overshoot or undershoot, you often have to have fairly larger filter capacitors in a switching supply compared to what is possible for a linear supply. This can make the switching power supply a lot more sluggish, and if there is a short on the output, the extra charge in the bigger filter capacitors gets dumped into the load, regardless of the current limit settings.Overshoot when a load is switched off can be a real concern in a switching power supply. Basically when the supply is outputting full current, the magnetics have a lot of energy stored. If you switch off a load, that energy has to still go to the output, so you make the output filter cap big enough to absorb this energy without a dangerous spike. The size of the spike usually depends on the output voltage, so the spike can be a lot bigger with a 20 V output compared to a 2 V output.The only overshoot and undershoot problems for a linear supply are just due to the limits of the regulator speed, and usually you can get away with a much smaller output capacitor to prevent spikes during the 10uS or so that the regulator is taking to adjust. Again though, some companies still make linear supplies with large electrolytic caps on the output (maybe to cover up an ordinary regulator).That being said, the better designers have done a great job in their switching supply designs so my advice is if you want to go to a switching supply, have a good look at the specs and in particular, try and determine the undershoot and overshoot characteristics. I would be very suspicious about the less known brands of switching supplies. If the manufacturer is deliberately vague about these specs, it may be that they are pretty bad.Look also at the noise specs. If you want to use a 1mV/div oscilloscope with a load, then getting a supply that has 10mV of noise is not a good idea. The better switching supplies have output noise less then 1mV RMS. 10mV RMS of noise is 38mV peak to peak - that much would worry me for lab use.For a 1A lab supply, I look to a linear supply, but if I wanted something like 0-60V at 10A, I would definitely check out the switching supplies.Dave's supply, and the design I am working with in another thread are linear supplies with switching pre-regulators so you can get the best of both worlds.Richard.

author: Andy
author_rank: Contributor
timestamp: March 28, 2012, 12:46:28 am
content: Hi Richard,Thanks for the reply. Given what you said, I will rule out the SMPS. The two I had on my list were fairly cheap and did not have very good specs.Thanks,Andy.

author: Harvs
author_rank: Super Contributor
timestamp: March 28, 2012, 06:33:18 am
content: I've got a couple of switching supplies that due to noise, I cannot reliably program a run of the mill Atmel or PIC when powered from them (one came from Jaycar.)If I were you, I'd get on eBay, browse under the industrial then electrical section, filter by used and within 100kms of your post code. The other day I picked up a Tektronix PS280 that was new/old stock (came from a Defence lab that was shutting down and it had never been taken out of the wrapping.) I browse like this regularly and have picked up a number of high quality lab instruments for very reasonable prices.OK there's no Australian warranty, but if you're buying a older instrument from HP, Tektronix etc, then there's all the data available to repair if something does go wrong (in my belief this is better in some ways than a warranty.)I've seen a few supplies that easily fit your requirements (dual independent/tracking 30V@ 2-3A) for about half your budget in the last couple of weeks (Brisbane). However in most cases your going to need to be able to pick them up in person (often old guys getting rid of an excess of lab gear from their shed and don't want to be bothered posting heavy items.)

author: Andy
author_rank: Contributor
timestamp: March 28, 2012, 06:45:45 am
content: Funny you mention that Harvs, I just bought two used HP E3610A on eBay.I couldn't find any good deals locally, so I bought them from overseas. I made sure to get the 230VAC model.Including EMS shipping, they worked out to US$220 each.I hope I made the right decision

author: Harvs
author_rank: Super Contributor
timestamp: March 28, 2012, 11:51:35 am
content: Quote from: Andy on March 28, 2012, 06:45:45 amI'm sure they'll do very well for you and give years of service.If you're in the process of slowly collecting gear for your home lab, I'd still recommend occasionally browsing second hand gear in your local area on ebay. You'll find good local deals on all sorts of test gear over time. Because the volume isn't large in oz, you just can't expect to find what you want on any given day of the year, but over time...

author: deephaven
author_rank: Frequent Contributor
timestamp: March 28, 2012, 12:06:23 pm
content: I have one of thesehttp://uk.farnell.com/jsp/search/productdetail.jsp?SKU=1670775which serves me well.

author: saturation
author_rank: Super Contributor
timestamp: March 30, 2012, 10:18:14 pm
content: If you're in the Pacific, also check out linear supplies from the makers Trio, Kenwood, and Kikusui. Even 1970s and up units rival Agilent's current offering. Besides lower cost per unit and superb build quality, a key difference is much tighter V and A regulation, you can find their supplies at 0.0050% or less, i.e., 50ppm, compared to Agilent's 0.01% or 100 ppm. However, Agilents E series tends to have less noise, about 200-300uVrms versus under 500 Vrms for many Japanese brands. Transient response is similar, about under 50uS for test suites similar to Agilents. But used linear Kikusuis run ~ $50, excluding delivery, versus $100+ for an Agilent E3610. I just couldn't resist getting one recently for $20 and after testing, it blows all my newer PSU away easily. Research the particular model would help, to insure the service manual is available and that parts are not difficult to find or substitute.

author: Andy
author_rank: Contributor
timestamp: March 31, 2012, 12:18:11 am
content: Thanks for the tip. I'll keep an eye out.

author: kaz911
author_rank: Super Contributor
timestamp: March 31, 2012, 03:41:13 am
content: Quote from: Andy on March 28, 2012, 06:45:45 amMost HP/Agilent PSU are multi voltage - so you can change them between 110-130 to - 220 or 230-240. You will need to get a new fuse to be "safe" usually at 1/2 the amps of the US version. But the fuse in them will work since most fuses are 250v anyway. But it wont blow when it is supposed to :-)

author: Andy
author_rank: Contributor
timestamp: March 31, 2012, 03:48:26 am
content: I'm fairly certain that the E3610As have different transformers depending on which version is sold. There is no switch. Dave opens one up in EEVBlog #166.

author: kaz911
author_rank: Super Contributor
timestamp: March 31, 2012, 05:27:27 am
content: seems like 3610 and 3620 does not have to voltage switching as the larger models. Thanks for correcting me ! :-)