HELP IN THE DESIGN OF LAB POWER SUPPLY - Page 1
Forum section: electronics / beginners

author: Abayomi
author_rank: Contributor
timestamp: July 21, 2020, 12:12:27 pm
content: Greetings to everyone here!I am a newbie in electronics, but at least I have background in electronics- like reading resistors, capacitors and recognising of other components.Also, I can read schematics, place them on breadboard, solder on perfboard and even take measurement with multimeters. My only problem is that I want to know how to design my own circuit from scratch. I decided to start with building my own lab power supply 0-30v, 0-5A with overloading and shortcircuit protection using LM723. I have searched online but I got confused with different theories each design was based on.Kindly help me out with the design process such that my design will start from 0V.Please be nice with me

author: MosherIV
author_rank: Super Contributor
timestamp: July 21, 2020, 12:29:15 pm
content: QuoteThis may be over ambicious for a beginner or first psu circuit. Definitely anything more than 1A will require high power dissipation.Both voltage control and current limit is no trivial design task.I suggest you start with a simple linear 0.2V to ?V 1A variable psu based on the classic LM317.Starting with switchers is much more difficult.Fyi current limit works by reducing the voltage output of the psu to maintain the current limit set. It is not possible to maintain both volt set point and current limit - Ohm's law !

author: Abayomi
author_rank: Contributor
timestamp: July 21, 2020, 12:42:29 pm
content: @MosherIV. If I should build with LM317 that means in the nearest future if I need more current I would build afresh. What range of power supply do you feel is good for beginner project?

author: dcbrown73
author_rank: Regular Contributor
timestamp: July 21, 2020, 01:56:44 pm
content: If you intend to do this as a first project, I would make sure you learn about and have equipment on hand to safely deal with mains voltages. (current limter, variac, protective gloves, class C fire extinguisher, etc)Mains voltages can kill.I don't believe starting with projects that deal with mains voltage is a good way to start into the electronics hobby. Producing the magic smoke is common in the hobby, don't make your first magic smoke come at mains voltages.

author: Abayomi
author_rank: Contributor
timestamp: July 21, 2020, 02:11:52 pm
content: @dcbrown.I know the risk involved infact I have built rectifier before. I know where to take more precautions in circuit.Please help me with LM723 Design tips

author: dietert1
author_rank: Super Contributor
timestamp: July 21, 2020, 03:48:00 pm
content: https://www.eevblog.com/forum/projects/good-quality-lm723-lab-power-supply/Regards, Dieter

author: Ground_Loop
author_rank: Frequent Contributor
timestamp: July 21, 2020, 05:29:47 pm
content: Quote from: Abayomi on July 21, 2020, 02:11:52 pmThank you. The safety ninnies on here seem to just sit primed and waiting to pounce.

author: MosherIV
author_rank: Super Contributor
timestamp: July 22, 2020, 07:59:37 am
content: QuoteYes, you may have to build another PSU.The LM317 (TO220 package) are normally rated for 1.5A. It is also possible to increase the output current by adding 'bypass' transistors (transistor in common emitter mode in parallel with the LM317).The point is to take little steps and learn as you go.Nothing wrong with a few psus around. I still use my early LM317 psus every now and then.Linear psus are very quite and good for analogue electronic work.Switcher psu are more noisey, ok for microcontrollers.You can start with LM723 if you want, but it is much more complicated and if it does not work, do you know how to debug the circuit ?For a beginner/first psu project up to 25V and 1A. The LM723 can achieve more but the circuit is more complicated. Voltage control is easy to figure out and understand.Understanding current limiting is much harder. First you have to measure the ouput current and compare it with a current limit. If the current limit is reached, it has to lower the output voltage. Do you know how to do that ?

author: xavier60
author_rank: Super Contributor
timestamp: July 22, 2020, 08:46:43 am
content: This is a simplified version of a design I used to build a 30V 3A bench supply with good performance.https://www.eevblog.com/forum/beginners/lm324-power-supply-with-variable-voltage-and-current/msg3089254/#msg3089254I doubt that a simpler design exists if both good CC and CV performance are wanted.I would not go much more than about 25V 1A without tap switching depending on heatsink capacity which can be difficult to determine.Mine is cooled by air drawn in through holes underneath, making the PSU very compact.https://www.eevblog.com/forum/projects/linear-lab-power-supply/msg2388873/#msg2388873

author: Doctorandus_P
author_rank: Super Contributor
timestamp: July 22, 2020, 10:56:03 pm
content: Making a simple LM317 based power supply is a fine beginners project.The next step up is to use an L200, and then add an adjustable amplifier over the current sense measurement feedback for adjustable current limit.Do not see projects like these as "I need a power supply", but as: "I am learning how this stuff works, and when finished I've got something actually useful.When a power supply like this is no longer adequate for your tinkering and you need a "better" one, it will still be useful for many more years, especially if you put it in some nice box with knobs and voltage and current readout. With power supplies it's just as with multimeters. One is not enough.