Looking for first bench power supply project. - Page 1
Forum section: electronics / beginners

author: Grab_Chap
author_rank: Newbie
timestamp: June 13, 2017, 12:03:24 pm
content: I was watching the video "EEVblog #168 - How To Set Up An Electronics Lab" on YouTube, where he advised to make yourself a 15V 1A bench power supply, dual tracking, with multi turn knob, maybe with adjustable current. So I registered on the forum but I haven't found a similar project yet. I would appreciate if someone points me to a nice project with instructions how to do it. Thank you.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: June 13, 2017, 01:17:06 pm
content: These projects are a dime a dozen on the web. What makes them interesting is when you try and design one yourself. The core concept is not hard: Constant current and constant voltage requires nothing more than a voltage reference (that should make you think "zener diode"), a error amplifier (Oh wait, thats what we can use opamps for!) and a pass transistors (MOS or BJT, choice is yours!).To start of, it can be interesting to just use a regulator IC like the LM317 (or more modern, better in pretty much every way versions) and try and understand, truely understand, how it works. Then you can look at building the internals with discretes yourself. As a beginner, some boxes that just have some 5V, 3.3V and 12V regulators running of something like a laptop power brick can also be usefull (especially since they are cheap and youwillbreak them)

author: Grab_Chap
author_rank: Newbie
timestamp: June 13, 2017, 01:46:22 pm
content: QuoteSure thing. I guess I'll just have to google for it elsewhere.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: June 13, 2017, 01:47:13 pm
content: I'm sorry if this came accros blunt, but you can't expect people to keep on linking the same stuff again and again.

author: Grab_Chap
author_rank: Newbie
timestamp: June 13, 2017, 02:08:35 pm
content: Quote from: TheUnnamedNewbie on June 13, 2017, 01:47:13 pmOh, no that's absolutely okay. That doesn't matter where you find it. I was going to join an electronic forum anyways.

author: Grab_Chap
author_rank: Newbie
timestamp: June 13, 2017, 02:44:18 pm
content: I have just openned old laptop power supply. Hopefully that's a good point to start off and I could modify it into a benchtop version. It says the max output power - 20W.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: June 13, 2017, 02:54:54 pm
content: Just be carefull around mains (which will be on the inside of that supply). Usually laptop supplies are 20V out, a few amps (how much depends on the laptop). Since your's is rated at 20W, it'll probably be 1A.Also keep in mind that those laptop supplies can perform poorly in terms of switching noise. Adding a linear regulator after the supply can improve the performance (but ofcourse keep in mind the required power dissipation and such needed).

author: Kleinstein
author_rank: Super Contributor
timestamp: June 13, 2017, 03:25:55 pm
content: A laptop supply might be a good starting point for a low cost supply. However one would usually keep it as is and only add some linear regulation behind. The linear regulator makes it a variable voltage and might also add an adjustable / switchable current limit.Asking about projects, plans is not such a bad idea. Google finds a lot of such supply projects, however quite a large percentage of these are more like bad examples. Making just a voltage regulator with a kind of crude current limiting is relatively easy. Here ready made regulators like the LM317 might be a first try. A full featured lab supply with accurate adjustable current regulation is the more difficult one - here many projects from the web tend to fail.

author: rdl
author_rank: Super Contributor
timestamp: June 13, 2017, 03:27:14 pm
content: Use the laptop power supply as input to a basic LM317 circuit. It will get you started and probably be good enough for a long time. Most of what you will do while learning can be done with less than 20 volts and less than 500 milliamps. Current limiting is useful but you can get by without it until you start using more expensive parts. Get a cheap digital volt meter from ebay and you'll be good to go.http://www.ebay.com/itm/Green-Mini-DC-0-100V-LED-3-Digital-Diaplay-3-Wire-Voltage-Voltmeter-Panel-Meter-/401212598263

author: Vtile
author_rank: Super Contributor
timestamp: June 13, 2017, 03:34:01 pm
content: Also if you are not familiar with the "ohms law" V=R*I (R=V/I and I=V/R), here it is. It is the most basic tool for anything related to electricity, if you know two of the three you can calculate the third.Two parallel resistors have same voltage over them (voltage division). The lower valued one carries more current (current division).You can connect two resistors in series, the "new" resistor is the sum of the two and then the voltage is divided over the two as the parts of the sum.You can connect two resistors in parallel, the new resistor is the sum of inversed sum of the inverser values. (R_new = 1/((1/R1)+(1/R2))). The current is now divided between the the two parallel resistors with the magnitudes of the resistors (lower value carries more current). The new resistor have always smaller value than the smallest of the two resistors you combine.The combinations of these pairs can be combined again as invidual resistors.Power = Current * Voltage , P=V*IEnjoy.

author: schmitt trigger
author_rank: Super Contributor
timestamp: June 13, 2017, 04:10:32 pm
content: I agree;a DIY bench supply, is one of those projects that every electronics hobbyst should try at least once.Designing and building one will teach you so much about electronic circuits and assembly that is simply priceless.And, you can customize it any way you want. You may use for instance analog meters for a "retro" look, or a bargraph meter, or LCD or LED displays, to display the output voltage(s) and current(s). You can calculate the watts, amp-hours (for battery charging).You can add fan control and temperature protection, remote computer control, independent or tracking voltages (for dual supplies).Use switchmode, linear or hybrid approaches................the possibilities are endless.The best thing of all, this is a project that you'll be using constantly.

author: Grab_Chap
author_rank: Newbie
timestamp: June 13, 2017, 09:29:24 pm
content: QuoteOh my God, fortunately I have been digging through electromagnetism chapters during the past year. At least I am starting to like it rather than being upset. Today I am almost through with my textbook and I have got myself specialist level electrotechnics textbook - a university course. It really is scary but I feel there is no way I could work around it. All I hope for is that my basic knowledge will help me grasp the idea. It used to be so painful before, when I was lying and staring into ceiling, questioning every single word I read. Thank you for reminding

author: Microcheap
author_rank: Frequent Contributor
timestamp: June 13, 2017, 11:48:32 pm
content: As one of my first project I built this power supply:http://www.electronics-lab.com/project/0-30-vdc-stabilized-power-supply-with-current-control-0-002-3-a/it has worked fine and served me well for over 8 years now.You can even buy a Chinese version for around $5 (https://www.aliexpress.com/item/2016-NEW-Free-Shipping-Red-0-30V-2mA-3A-Continuously-Adjustable-DC-Regulated-Power-Supply-DIY/32660068947.html). But as others already suggested, you should built one yourself and try to understand how it works if you really want to learn.There is a post on the project forum page with nearly a hundred pages and thousands of messages discussing every section of this circuit and some improvements. If you have the will (and spare time) it is a good start point.There also this series of videos that you might find of interest:https://www.youtube.com/playlist?list=PLDBuVMDVJaX2wCN84B5sjFMKDsMbsS7jq