Need Power Supply Precision 5mA (0-30V/or 60V). - Page 1
Forum section: electronics / beginners

author: SE
author_rank: Newbie
timestamp: August 27, 2023, 04:14:11 pm
content: Hello. I'm interested in buying a laboratory power supply. Inexpensive but high quality.I need precision current 5mA. Voltage 0-30V/or 60V. I need for precision electrolysis process.Different brands have different quality and different tolerances for the output current.Please recomended me which company offers this unit. Very important precision 5mA.Power supply with one output. Which brand respects the quality and such a current.Thanks for the help.

author: ledtester
author_rank: Super Contributor
timestamp: August 27, 2023, 04:37:30 pm
content: If you only need a fixed 5mA it seems you could just add on a constant current source/sink to an existing power supply.For instance like using a TL431 as described in this app note:Precision Current Sources and Sinks Using Voltage References - SNOAA46https://www.ti.com/lit/an/snoaa46/snoaa46.pdf

author: SuzyC
author_rank: Frequent Contributor
timestamp: August 27, 2023, 04:55:24 pm
content: TL431 will not handle 60V only 36V maxBut this device alone doesn't make a user/instrument interface/circuit to set/adj Iout of some yet unknown circuit to output up to 5mA within a 60V window of voltage compliance to create a workable constant-current source.

author: u666sa
author_rank: Frequent Contributor
timestamp: August 27, 2023, 04:59:47 pm
content: SPD1305X but really, for a few dollars more SPD3303X

author: TimFox
author_rank: Super Contributor
timestamp: August 27, 2023, 05:00:19 pm
content: Quote from: SuzyC on August 27, 2023, 04:55:24 pmIn that TI app note, there are several circuits using an external transistor with a TL431 for constant-current applications.An external transistor can easily handle 60 V.

author: ledtester
author_rank: Super Contributor
timestamp: August 27, 2023, 05:09:08 pm
content: Quote from: SuzyC on August 27, 2023, 04:55:24 pmThe power applied to the cathode of the 431 doesn't need to be the same as the power that is being current regulated, e.g.:https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/969722/tl431-tl431-use-as-a-constant-current-source

author: IanB
author_rank: Super Contributor
timestamp: August 27, 2023, 05:18:06 pm
content: This thread is funny.Normally, when people ask here about building a power supply, they get told it is not worth the trouble and to just buy one.Here, somebody is asking to buy one, and they are being told somehow to make one. It doesn't add up.There must presumably be precision, regulated, low current laboratory supplies made for specialized uses. Are we saying nobody makes such a thing?

author: TimFox
author_rank: Super Contributor
timestamp: August 27, 2023, 06:09:55 pm
content: I use the classic Keithley 225 when I need a current source in that range.I purchased it through eBay, and it only needed switch cleaning and calibration.Maximum output current 100 mA, maximum compliance voltage 100 V.Manual:https://xdevs.com/doc/Keithley/225/29039A%28Model225%29.pdf

author: SE
author_rank: Newbie
timestamp: August 27, 2023, 07:04:58 pm
content: Yes, you are right, I want to buy a ready block. only precisely so that it really gives out 5 milliamps. just different brands make big mistakes. It is written that the output is 5 milliamps, but in fact it produces 10 milliamps. I need a recommendation which brand would be best for me for my task. brands, models, confirmation that they really give out such current as it is written on the screen. I just don't know these brands, I have no such knowledge and no experience. you're a professional here. and it’s also good if there is a return signal on the block to control the output current. Thank you.

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 27, 2023, 07:13:28 pm
content: Quote from: SE on August 27, 2023, 04:14:11 pmIs this for hair removal?You're not specifying your requirements properly. It should be something like this:Current capability: 0-5mAPrecision: 50uA stepsAccuracy: 1%etc

author: SE
author_rank: Newbie
timestamp: August 27, 2023, 07:22:22 pm
content: thanks for correcting. I'm not an expert sorry.milliamp accuracy, ex. 1 milliamp.

author: SE
author_rank: Newbie
timestamp: August 27, 2023, 07:25:01 pm
content: this is for electrolysis, the hair will not be there)

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 27, 2023, 07:32:44 pm
content: Quote from: SE on August 27, 2023, 07:22:22 pmSo you don't care if it's adjustable at all? Just that it's limited at 5mA +-1mA.ie: Anything from 4mA to 6mA is OK.Search for a "precision current source"... Finding one that's both cheap & accurate will be the issue.

author: Jwillis
author_rank: Super Contributor
timestamp: August 28, 2023, 04:06:46 am
content: Quote from: SE on August 27, 2023, 04:14:11 pmThere hundreds of power supplies that match your requirements. So we can try to narrow down the choices.First up is programmable or manual operation.I suggest a programmable power supply for the chemistry lab. Almost all I have seen are 1mA resolution. And you can visually set the required current . A manual power supply might be to finicky for chemistry experiments for some people. I'm assuming this is for a chemistry lab.Next we have Switch mode or linear power suppliesAdjustable switch mode power supplies are cheaper, compact, efficient, and much lighter weight than the linear counterparts. Linear are better suited for radio and audio applications because they produce no RF noise. Not to say that switch mode supply can't be quiet, but extra filtering costs more.What's your budget. Cheaper models from Ebay or Aliexprees can be as low as $100. But theirs no guaranty that they will come with any warranty. Well known branded models like Rigol, Siglent, Keysight ect.ect. can range from a couple hundred to a a few thousand depending on requirements. You can get these from distributors such as Mouser, Digikey and Newark. Rigol supplies can be purchased direct from Rigol.Hope this helps some.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: August 28, 2023, 07:23:27 am
content: Straight from the EEVblog itself:https://youtu.be/0qjLx_HsKUQ?si=mbiL2qFHdMWJtoUr

author: SE
author_rank: Newbie
timestamp: August 28, 2023, 10:45:46 am
content: 1. programmable control.2. It is necessary for the electrolysis of silver in distilled water. To have the unit automatically control the 5mA output.3. Adjustable pulse will be ok.4. whenever possible cheaper and adequate quality.Thank you.

author: EPAIII
author_rank: Super Contributor
timestamp: August 28, 2023, 12:32:18 pm
content: 5 mA, +/-1 mA. And you say it needs to be accurate??That's +/- 20%! Hardly very precise. It is more likely the DEFINITION of inaccurate.Almost ANY lab style power supply will be, at the VERY, VERY LEAST, ten times more accurate than that. Look for one that will provide the Voltage you need and that is rated for between 10 mA and 1A ma with a current limit control and a current meter, preferably a digital current meter. It should work just fine for your project. Just short the output and adjust the current control until the meter reads 5 mA.Quote from: SE on August 27, 2023, 07:22:22 pm

author: Vovk_Z
author_rank: Super Contributor
timestamp: August 29, 2023, 08:09:39 am
content: Quote from: EPAIII on August 28, 2023, 12:32:18 pmI wasn't so sure. Working at the low end of a range is always trecky. Brand ones of cause are good but they seems too expensive for such an easy job (as for me).

author: EPAIII
author_rank: Super Contributor
timestamp: August 29, 2023, 09:40:03 am
content: Yes, the trick here is to avoid buying a 10 or 25 Amp supply and the built in control and meter become inaccurate at such a low current level. That's one good reason for building such a supply, but I don't know if SE can do that so I didn't suggest it.Quote from: Vovk_Z on August 29, 2023, 08:09:39 am

author: blackdog
author_rank: Frequent Contributor
timestamp: August 29, 2023, 10:35:19 am
content: Hi,Many here recommend standard LAB Power Supply as a current source.Actually, these Power Supply are a current limited voltage source, it is not a real Current Source.Across the output of an average LAB Power Supply is between 220uF to 1000uF capacitor.So this can never be a true Current Source! it is very slow, and especially at small output currents.So it is important to know if the load of the Current Source, shows dynamic behavior.And keep in mind the "Voltage Compliance" it should be sufficient for proper operation, but also not too high so that the load remains intact.Kind regards,Bram

author: Stray Electron
author_rank: Super Contributor
timestamp: August 29, 2023, 03:13:54 pm
content: Quote from: blackdog on August 29, 2023, 10:35:19 amExactly right. The OP needs to use a power supply that has a Constant Current mode. Here is an old HP 6294A power supply that does.https://www.ebay.com/itm/361550397867?epid=1607757779&hash=item542e1541ab:g:gt8AAOSwiYFXK63m&amdata=enc%3AAQAIAAAA4PaIytVTd0Ct7fwVXKCVXNP8RMRaUbOZgUxP7EdzUO7%2BaAjWWbjgcIiaQyAQJDMW5dUdNrQj5Vjbjjr2l4QoCSI%2FS7xE2p4TemUlkzXft08v0wSN7qlIRmaQqcRIUx8r3EZ%2FOCNIFdupBDXb4qlBvwm3VkKqUwHdx6ehkZ5o7B%2BpJ10b9DTggDDRfxgOUUI03BcO4FXGJ3%2F7HjAiAC8s%2BBCTT%2FVIWxmgk3NcflDSmPvt9AApbGYBYQN5%2BjhIvowK6RtagbPe2EN%2BRQKa7ulizppxjT%2B2l9BEWwXy2OCR%2BzXO%7Ctkp%3ABk9SR76_4pvIYg.The PS shown is used and in unknown conditions so I don't necessary recommend it, I just wanted to point out that there are well made PSs that do exactly what you want. HP made a series of similar power supplies and the manual gives the specs for all of them.To use simply set the output voltage to the desired voltage and then short the output terminals and adjust the Current to 5mA. Remove the short and connect the power supply to your device. After that, the power supply will deliver exactly 5mA to your device and will automatically increase or decrease the output voltage (up to the voltage the you set in step 1) to maintain that current. Do not add capacitance to the output, that will simply slow down the operation of the regulators in the power supply. And don't use a power supply that has a large current output, if you do then it won't be able to accurately regulate the small 5mA load.You can download the manual for the 6294 here, I suggest you read it and understand the difference between constant voltage output, and constant current output and between a constant current output and a current limited out put.https://xdevs.com/doc/HP_Agilent_Keysight/HP%206294A%20Operating%20%26%20Service.pdfOne of the nice things about the 6294 is that it has options for 10 turn pots for both the voltage control and the current control. I have one with the 10 turn voltage control and it works VERY well. If necessary there's no reason that you couldn't add those controls yourself.

author: TimFox
author_rank: Super Contributor
timestamp: August 29, 2023, 03:39:17 pm
content: The Keithley 225 I use (see my much earlier reply) is a true constant-current source with decade-switch programming, and can easily do 5 mA up to 100 V compliance.There are more modern lab instruments that do the same thing, and feature external digital programming.It sounds like overkill, however, if the application always requires 5 mA and a (variable) voltage compliance up to 60 V.Some of the 431-based circuits in the TI application note can do that.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: August 29, 2023, 04:50:47 pm
content: Quote from: IanB on August 27, 2023, 05:18:06 pmI find this quite logical. First, he wants a combination of "high quality" and "low cost" and those two do not go well together in commercial products.Second, he only needs a quite small current, which makes it much easier to DIY.

author: electr_peter
author_rank: Unknown
timestamp: August 29, 2023, 07:07:58 pm
content: There are plenty of options in high quality supplies with lower current range:BK PRECISION 1739AIM-TTI PLH250TDK-LAMBDA Z-650-0.32Key is to search for low output current. Low output current -> low output current like 5mA is above noise floor -> better current regulation.

author: TimFox
author_rank: Super Contributor
timestamp: August 29, 2023, 07:53:55 pm
content: The B&K only goes up to 30 V compliance.The other two go up much further in voltage compliance, and must be operated carefully since they will go up to hundreds of volts into an open circuit or high resistance unless the compliance is adjusted first before power on.What I like about my ancient Keithley 225 is that it has several full-scale range settings for current, plus the decade dials within that range.

author: electr_peter
author_rank: Unknown
timestamp: August 29, 2023, 08:34:35 pm
content: AIM-TTI has a function to "expand" voltage span from full range to smaller range, this should make it safer.Problem with this getting 30/60V 5mA precision supply is that it is very low power (<0.3W) and most lab PSUs are >100W. So solution is to get specialised dedicated supply, make something suitable from current sources yourself or use lab PSUs with more precise low current control.

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 29, 2023, 09:39:28 pm
content: I have no idea how much it costs, or how to buy this one, but:Here's an exampleof what you're looking for.

author: SE
author_rank: Newbie
timestamp: September 08, 2023, 06:37:50 pm
content: good example. I wonder if there are other similar proposals or if he is the only one. Maybe someone can show other companies similar power supplies. to have more choice.