Power supply with voltage regulator schematic - Page 1
Forum section: electronics / beginners

author: nForce
author_rank: Frequent Contributor
timestamp: January 08, 2016, 08:58:02 pm
content: Hello,I have build this scheme with help from datasheet. I didn't find the inductor, so it has no value. The only resistor which I had found is 1K, so I changed the labels to other resistors value.I have added the LED for indication.The output of first lm2574 is 3.3 V, the second is 5 V, and the last is 12 V.So, is it going to work? Can someone add the libraries for other resistors?Thank you.

author: Zero999
author_rank: Super Contributor
timestamp: January 08, 2016, 09:13:27 pm
content: What software are you using?D4 has no current limiting resistor so may go pop.Why use potential dividers to power LEDs? Just use a single resistor.With switched mode power supplies the PCB layout is as important and without knowing that, there's no way to tell whether it'll work or not.

author: nForce
author_rank: Frequent Contributor
timestamp: January 08, 2016, 09:21:05 pm
content: It's Altium.How can I reduce the voltage with a single resistor?

author: Zero999
author_rank: Super Contributor
timestamp: January 08, 2016, 09:27:22 pm
content: You don't reduce the voltage with a single resistor- it's a current limiting resistor. The LED sets the forward voltage (see datasheet) and the resistor limits the current.

author: ice595
author_rank: Regular Contributor
timestamp: January 08, 2016, 10:30:52 pm
content: Quote from: Hero999 on January 08, 2016, 09:13:27 pmif that's the case, I am assuming it won't work on a breadboard then?

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 08, 2016, 11:10:38 pm
content: The inductor is a VERY CRITICAL part of a switch-mode power-supply (SMPS) circuit. The data sheet or app notes for the chip should specify exactly what brand/part-number is appropriate if it is available as a commercial product. Or they should specify EXACTLY what core and the winding specs if it is some custom design part. Attempting this circuit without a very good idea about the inductor isn't worth even starting the project, IMHO. If you don't know what inductor the circuit was designed for, you are dead in the water.The resistor values for the voltage dividers for the voltage sense circuit should be almost trivial to calculate based on the desired output voltage and the set-point voltage of the chip.Wiring an LED (D4) directly to any power supply without a current limit resistor is practically guaranteed to blow it up. Might as well just toss it directly in the trash bin than to wire it without a limiting resistor.It is not at all clear what is the purpose of R8 and R10? I have never before seen an LED wired this way. Remember than LED will drop a fixed voltage, and the purpose of the current limiting resistor (R7 and R9) is to drop the voltage difference between the supply and the LED. But you don't need a shunt resistor like R8 and R10.Even after you have the proper inductor, it is unlikely this will work on an ordinary breadboard. Because of the high frequencies, high currents, and close proximity of high sensitivity nodes (like "Feedback") and high current nodes (like "Output"), most data sheets for SMPS chips say that the PC board layout is VERY CRITICAL also. And they typically provide example PC board layouts in the data sheets or application notes. Unless you have considerable experience with SMPS, it is unwise to stray very far from the recommended PC layout.

author: nForce
author_rank: Frequent Contributor
timestamp: January 09, 2016, 03:25:19 pm
content: Thanks for all your replies.I have one question regarding Altium.I am trying to add 3d model to inductor symbol, which is generic symbol. I have double clicked on the symbol in schdoc. And in the models window i clicked "add PCB3D model". But I can only choose 3d models from libraries and not the " .step files".

author: nForce
author_rank: Frequent Contributor
timestamp: January 09, 2016, 06:09:54 pm
content: Another question:What values the resistors should be for 3.3V, 5V and 12 V, so the LED doesn't blow up?I know I have to use Ohm's law. But I want to use the standard resistors.

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 09, 2016, 06:14:32 pm
content: Quote from: nForce on January 09, 2016, 06:09:54 pmThere are many online calculators like this:http://ledcalc.com/QuoteSimply use the nearest standard value to the calculated resistance. Slight variations like that will have no practical affect.

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 09, 2016, 06:42:47 pm
content: Quote from: nForce on January 09, 2016, 03:25:19 pmThe recommended inductors from Pulse Engineering are simply rectangular boxes. Nothing magic.The recommended inductors from Renco are just large, cylindrical axial components like resistors or capacitors.The recommended inductors from NPI are surface-mount round components much like flat electrolytic caps.

author: nForce
author_rank: Frequent Contributor
timestamp: January 09, 2016, 06:51:56 pm
content: Where can I find these libraries? From Pulse enginnering, and Renco...All I did find is the official altium page with all the IC from companies. I don't need IC, I need inductors, resistors and so on.Do you use Altium? Can you add this components as an attachment?

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 09, 2016, 06:57:01 pm
content: I don't use Altium. I am suggesting that the 3D outline of those inductors are common, ordinary shapes like boxes and cylinders. Are you not able to create 3D outlines with basic shapes like that? Why is a 3D model so important anyway?

author: nForce
author_rank: Frequent Contributor
timestamp: January 09, 2016, 07:04:26 pm
content: This project is for the school assignment.So every component needs a footprint and 3D model.Where can I get these standard resistors then?

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 09, 2016, 07:09:11 pm
content: That is an Altium-specific question.You should ask that question in the Altium-specific forum.https://www.eevblog.com/forum/altium/

author: MarkF
author_rank: Super Contributor
timestamp: January 09, 2016, 09:21:09 pm
content: I've been getting my models from3D ContentCentral®. You must create an account; but it's free to download models afterward. There are many file formats available.

author: exe
author_rank: Unknown
timestamp: January 10, 2016, 06:11:46 pm
content: LM2574 is a very generic stuff, the datasheets are quite comprehensive and include inductor selection section as well:http://www.ti.com/lit/ds/symlink/lm2574.pdfI'm not sure if it really that important to have a super-duper inductor for this scheme because it's lowest frequency buck converter (~50KHz). So, take any with matching value. However, PCB layout is important, do not do this on breadboard and read the datasheet for more info.