10W psu "no" ripple? - Page 1
Forum section: electronics / beginners

author: FriedMule
author_rank: Frequent Contributor
timestamp: July 08, 2021, 06:43:43 pm
content: I am in need of a power supply with variable 0-10V and variable current max 1A.My need is the ability to adjust in +/- 0.1mA and as little ripple as sanely possible, maybe 0.1 uA / mV.My problem is that I do not feel I am capable of designing the circuit, and I haven't found anything usable.Is it sanely possible?

author: MathWizard
author_rank: Super Contributor
timestamp: July 08, 2021, 07:03:52 pm
content: What sort of parts did u want to use, modern op-amps? or some older discrete design? I bet there are some pretty good old designs with schematics available, with low noise, but they also would have had all the parts matched just right, with all the spec's measured, etc, to really get low noise.IDK what/when would be the 1st PSU with the spec's you want, but I'd also like to make a low noise, low voltage PSU at some point.I'm just re-making an old Heathkit PSU, but with cheap parts. If it ends up close to the rated spec's I'll be happy,

author: FriedMule
author_rank: Frequent Contributor
timestamp: July 08, 2021, 09:33:39 pm
content: I have no preference in components, but maybe SMD and chips is easiest? Old components may be hard for me to mach perfect.

author: Warhawk
author_rank: Frequent Contributor
timestamp: July 08, 2021, 09:59:59 pm
content: Quote from: FriedMule on July 08, 2021, 06:43:43 pmStart looking at LT1970 and its applications. This would be my first starting point.

author: xavier60
author_rank: Super Contributor
timestamp: July 08, 2021, 10:48:07 pm
content: It's usual for most PSU designs to have some output ripple in CC mode. I think it's due to the very low value of the current sense resistor causing the CC loop gain to be low.This can be fixed with an active ripple filter. It can be a Darlington Emitter follower with an RC filtered voltage applied to the Base that's a few volts lower than the unregulated supply.

author: FriedMule
author_rank: Frequent Contributor
timestamp: July 09, 2021, 04:07:54 am
content: Do you mean i.e. 12V transformer and then maybe 10V as output will surf ice?What frequency do you think the filter shall work in?

author: xavier60
author_rank: Super Contributor
timestamp: July 09, 2021, 08:48:15 am
content: Because of the voltage drop across the active filter, say 4V, a 12VAC transformer might be cutting it close. Depending on its size.Do you already have transformers to try?Just the first part is applicable.The Emitter follower style filter works well with 100Hz ripple.

author: FriedMule
author_rank: Frequent Contributor
timestamp: July 10, 2021, 12:06:17 am
content: Thanks to you all did I find the following schematic, it sounds as a start point:Link to entire article:https://www.analog.com/en/technical-articles/high-performance-portable-dc-bench-power-supply.htmlI do not care if it can deliver above 10V or 1A, but ripple is paramount and fine adjustable. Could a 20+ turn pot be used?I do own an old 12V trafo but I'd rather buy a dedicated trafo for the project.EDIT: Saw the following text: "Linear regulators at the output suppress output ripple without requiring large output capacitors, resulting in a truly flat DC output and small size. At full power, 10mF cap will produce about ±1V ripple on the 34V DC input."2V p/p in ripple for a 34V PSU, does not sound as "truly flat" :-)

author: themadhippy
author_rank: Super Contributor
timestamp: July 10, 2021, 01:32:07 am
content: Off the wall idea,power the regulation circuit from a battery ,that gets charged when you switch the regulator off

author: FriedMule
author_rank: Frequent Contributor
timestamp: July 10, 2021, 02:09:08 am
content: Yes that is a possibility, maybe a super cap or more could also do it?Build it as some sort of double-sided UPS where one side charges until it is empty and the "UPS" switch to the other side?

author: xavier60
author_rank: Super Contributor
timestamp: July 10, 2021, 03:35:00 am
content: Quote from: FriedMule on July 10, 2021, 12:06:17 amI haven't put much thought into that design. If you want very fine current setting resolution, you also would want very stable setting accuracy, very little drift with temperature changes.I had hoped that you chose a simpler all linear design, keeping in mind what I said earlier.I just did a test on my most resent bench PSU project. It has 5mV p-p 100hz ripple while sourcing 1A into 10Ω.The CC loop can be bread-boarded using common components.The transformer I chose is medical grade with internal shield. I'm not certain how much it helps in reducing noise and ripple.https://au.mouser.com/datasheet/2/410/media-845752.pdfhttps://www.eevblog.com/forum/beginners/lm324-power-supply-with-variable-voltage-and-current/msg3582664/#msg3582664

author: FriedMule
author_rank: Frequent Contributor
timestamp: July 10, 2021, 03:24:52 pm
content: I think a linear design will be best, yes, but that part is before the displayed circuit. Great trafo you have chosen there, it looks like high quality, if I understand it correctly. :-)

author: Terry Bites
author_rank: Super Contributor
timestamp: July 10, 2021, 04:29:40 pm
content: You may want to see the datasheet for the opa549. There is a schematic for a 10a integrated psu.https://www.electronics-lab.com/project/1-2v-25v-10a-adjustable-power-supply-using-power-op-amp/

author: FriedMule
author_rank: Frequent Contributor
timestamp: July 10, 2021, 06:41:09 pm
content: I am happy for your comments and I have done my best to understand it all. My problem is that I do not have enough knowledge to determine the best circuit to reach my goal. The problem about temperature change could properly be solved by adding an oven and maybe keep the temperature at 40 deg C?My goal is to be able to fine adjust Voltage And max Current in as fine steps sanely possible, and have ripples well below that in both voltage and current.I do not care if I have to build a ridicules giant capacitor bank or if it will get large, only goal is precision, not accuracy, the accuracy can be read by a DMM.EDIT: Forgot to write: If I chose a circuit, let's just say the above, to make it easy and do not like the 2V ripple or think 34V 3A is too high, is it not "just" to select some components that is better to my goal, i.e. lower ripple but maybe max 11V 2A or whatever the right component can manage?Is there anything stupid, wrong or bad in just using one of your suggestions or the one I randomly found, I mean they sound fantastic, except from voltage or ripple?Can you please forgive me, but reading a circuit and determine its degree of usefulness is far beyond me! :-)

author: xavier60
author_rank: Super Contributor
timestamp: July 11, 2021, 11:26:37 am
content: There are ways to use 2 pots, one for coarse setting, the other for fine setting. Although good quality multi-turn pots are a good choice, one of thing to be aware of is that the wiper voltage does not change in a continuous way, rather in small steps. The may not be a practical problem.Hybrid pots were developed to correct this.

author: FriedMule
author_rank: Frequent Contributor
timestamp: July 11, 2021, 12:50:11 pm
content: Sounds interesting, I thought viper pots just had a continues resistive trace inside?To make usage of two pots, would you use one with fewer turns within the total value needed area and one with a small différance from max to min for the fine in series?

author: xavier60
author_rank: Super Contributor
timestamp: July 11, 2021, 01:07:08 pm
content: I should have mentioned that most multi-turn pots are the helical wire wound type,https://passive-components.eu/precision-potentiometers-type-1/One simple method is to have 2 pots of the same type connected to the same reference voltage with the wipers summed together with resistors where one is say 10 times larger than the other.

author: perieanuo
author_rank: Frequent Contributor
timestamp: July 13, 2021, 07:35:34 am
content: Quote from: FriedMule on July 08, 2021, 06:43:43 pmyepaccumulator>variable regulator>>load. no ripplebattery charged separate from this principle of variable psanyway, you're sure you really need this? all new designs (well, almost all consumer products) are smps-powered, TEST THEM with the smps used in real life after production.otherwise, it's just cheaptalk, chitchat, bla bla bla