Regulator with reference input? - Page 1
Forum section: electronics / projects

author: cyberfish
author_rank: Regular Contributor
timestamp: October 15, 2010, 08:00:12 pm
content: Probably just having a brain fart but... are there regulators that takes a simple reference voltage input? I can't seem to find one.Eg. with input = 5V it will regulate at 5V.I know a BJT + op amp can do it, but I want something that regulates better and with lower component count.Thanks

author: Simon
author_rank: Unknown
timestamp: October 15, 2010, 08:05:51 pm
content: you need to explain your project better. if your looking for a variable regulator these exist in the form of chips like the LM317, these work with feedback resistors

author: Bored@Work
author_rank: Super Contributor
timestamp: October 15, 2010, 08:24:01 pm
content: Quote from: cyberfish on October 15, 2010, 08:00:12 pmIf you already have a stable 5 V reference, why do you want a regulator to put out 5 V? You already have 5 V. What you maybe want is a buffer or driver circuit.

author: cyberfish
author_rank: Regular Contributor
timestamp: October 15, 2010, 08:24:33 pm
content: This is for a DIY bench-top linear power supply, so I need a way to digitally control the output voltage. I thought DAC would be the easiest way, with some analog circuitry.Yeap, I know about LM317. That doesn't work unless I use a variable gain amplifier. But that's overkill and too few bits.

author: cyberfish
author_rank: Regular Contributor
timestamp: October 15, 2010, 08:25:59 pm
content: QuoteI guess that's another way of putting it.I need a buffer that can output about 4A. I thought people call them regulators (since regulators are just amplifiers with an internal reference, and I want to make the reference external).

author: JohnS_AZ
author_rank: Frequent Contributor
timestamp: October 15, 2010, 08:30:35 pm
content: Likethis?

author: Simon
author_rank: Unknown
timestamp: October 15, 2010, 08:31:14 pm
content: what about a non inverting power opamp with a gain of 1 ? or an opamp driving a power transistor, check out daves dummy load blog, you could adapt that as a buffer which is essentially what it is

author: cyberfish
author_rank: Regular Contributor
timestamp: October 15, 2010, 08:34:07 pm
content: Quote from: JohnS_AZ on October 15, 2010, 08:30:35 pmYeap! Exactly.Except with 4A output.

author: JohnS_AZ
author_rank: Frequent Contributor
timestamp: October 15, 2010, 08:39:46 pm
content: heheheI'd like to say I'm brilliant, but I just Googled "Tracking Regulator" and that was the first to pop up.That's an interesting idea, BTW. I have a shitload of DAC08's looking for an application.

author: Bored@Work
author_rank: Super Contributor
timestamp: October 15, 2010, 08:42:43 pm
content: Power transistor (darlington or the like) driven by an OpAmp. OpAmp compares output voltage with reference voltage. A schematic should be in any serious electronics textbook.

author: cyberfish
author_rank: Regular Contributor
timestamp: October 15, 2010, 08:45:05 pm
content: QuoteYeah I guess I'll have to build my own.Something this (attached) should work, but I'm not sure how well it will regulate in practice, hence wanting to just buy something designed by someone that knows what they are doing.

author: Simon
author_rank: Unknown
timestamp: October 15, 2010, 08:47:12 pm
content: @boredatwork - but it might be a hard find. I'm giving up on the art of electronics, it seems no american author can put a book together in what should be chronological progress of learning and topics allowing for looking up subjects in their logical places. I dearly miss my Italian school books and the electronics manual i had access to.

author: Bored@Work
author_rank: Super Contributor
timestamp: October 15, 2010, 09:11:01 pm
content: Quote from: JohnS_AZ on October 15, 2010, 08:39:46 pmThrow them away or sell them on eBay. They are nasty to interface. The 8 bit interface is eating up your valuable MCU pins. They have a current output (ok, can be helpful in some applications), and they need a dual power supply.

author: Bored@Work
author_rank: Super Contributor
timestamp: October 15, 2010, 09:41:23 pm
content: Quote from: Simon on October 15, 2010, 08:47:12 pmI really don't see your point. TaO Figure 2.75 (transistor version), and Chapter 6 contains umpteen variants.And serious, what logical order? There is simply no real logical order with circuits. Would you discuss a circuit with an OpAmp and a transistor under OpAmps, under Transistors, under Power Supplies, under Power Stages, under Feedback Loops, Voltage-Controlled Voltage Sources, Analog Circuits, Active Circuits, or whatnot?I have learned to become extremely wary of books looking too simple, trying to explain complex issues in a simple (usually too simple) way, trying to be a "For Dummies" guide or "Teach yourself Quantum Physics in 24 Hours", or trying to group everything in nice, non-overlapping groups. The later is typically only possible if you ignore important properties, to artificially make the subjects fit the category.

author: Frant
author_rank: Regular Contributor
timestamp: October 15, 2010, 09:47:10 pm
content: Quote from: cyberfish on October 15, 2010, 08:45:05 pmTry the OPA549 from Texas Instruments. I think that's what you need.

author: Simon
author_rank: Unknown
timestamp: October 16, 2010, 07:17:07 am
content: Quote from: BoredAtWork on October 15, 2010, 09:41:23 pmyes but putting in a paragraph saying: oh be careful of this when using fet, but we'll talk about it later with opamps and not actually say anything, that was just a waste of time, if it is relevant there and then, then explain it. I'm not looking for a dummies guide, I used to use a 2000 page electronics reference manual, it had everything in it but for MCU's and i could find anything in it because it was properly laid out and properly indexed.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: October 16, 2010, 02:22:12 pm
content: LT1021C-5MIN TYP MAX4.9975 5.000 5.0025Linear Technology Corporation1630 McCarthy Blvd., Milpitas, CA 95035-7417(408) 432-1900 ? FAX: (408) 434-0507 ?www.linear.com

author: scrat
author_rank: Frequent Contributor
timestamp: October 18, 2010, 02:05:36 pm
content: Quote from: Frant on October 15, 2010, 09:47:10 pmMaybe an integrated audio amplifier can be easier to find...Nice IC... Maybe an integrated audio power amplifier can be easier to find? Search for the TDA series...

author: cyberfish
author_rank: Regular Contributor
timestamp: October 19, 2010, 05:53:21 pm
content: Very cool suggestions! I never thought about using a power op amp.I even found one (OPA548) that has voltage controlled current limit. Exactly what I want.Thanks

author: Time
author_rank: Frequent Contributor
timestamp: October 19, 2010, 08:39:29 pm
content: Quote from: Simon on October 16, 2010, 07:17:07 amI don't think it has anything to do with nationality more so than it does with what you are comfortable with. When you are initially taught something for the first time the methodologies and thought processes built into the way material is presented by the author create a type of comfort zone for information absorption. As a practicing R&D engineer who always aspires to be creative, I think its essential to branch away from your normal references and materials and try to rid yourself of having this comfort zone all together. I guess in lesser words you just need to learn to be more resourceful.

author: Simon
author_rank: Unknown
timestamp: October 20, 2010, 06:06:00 am
content: hm no there is just a particular style to the writing I don't like. the general layout of the book speaks to me of someone that is not organised. how can you talk about digital circuits with fets and multiplexing before you've explained them ?, it seems to need to know many things before you even read the book to find out how fets work. No sorry every book I've read recently has been by and american and they are all in the same style. I had access to a 2000 page electronics manual in Italy and it was very logically laid out and contained everything, it was fine for the beginner that wanted to read it in order as it was ideal for the experienced person who wanted to jump into a chapter and freshen up on a certain aspect of electronics.