Modern day 723 and 78xx for new design - Page 1
Forum section: electronics / projects

author: tkamiya
author_rank: Super Contributor
timestamp: January 25, 2019, 04:46:05 pm
content: In old days, if one was making power supply, he/she used 723 or 78xx. But both of those series are quite dated. What's the modern day equivalent?I need a low noise/ripple 24V 3A power supply.

author: Wolfgang
author_rank: Super Contributor
timestamp: January 25, 2019, 06:21:42 pm
content: I had the same question. All the "good" new ICs are for lower voltages. If you find a *real* replacement for a 723, please tell me ! (but dont forget, I need 40V input, 150mA, ...).

author: SiliconWizard
author_rank: Super Contributor
timestamp: January 25, 2019, 06:59:43 pm
content: Quite a few. Just to mention LT/AD:https://www.analog.com/en/parametricsearch/11536Eg:https://www.analog.com/en/products/lt1084.htmlhttps://www.analog.com/en/products/adp7142.htmlNow for those saying they are too pricy, go have a look at Alpha&Omega stuff.

author: Wolfgang
author_rank: Super Contributor
timestamp: January 25, 2019, 07:12:50 pm
content: ... not even close.Where are the following 723 features:- reference can be filtered- long term drift spec- settable current limit- configurable compensation- flexilibility to be used a spositive, negative, floating, ... regulator.Why people still work with the 723 is:- extremely flexible- stable- cheap like hell. 10€Cents in quantities, all "replacements" are some €.

author: iMo
author_rank: Super Contributor
timestamp: January 25, 2019, 07:16:48 pm
content: 723 works as a switcher too..

author: Wolfgang
author_rank: Super Contributor
timestamp: January 25, 2019, 07:18:42 pm
content: ... thats correct. I have never seen it in the wild, however. A lot of (older) units use TL494 or SGxxx type ICs.

author: iMo
author_rank: Super Contributor
timestamp: January 25, 2019, 07:46:47 pm
content: This is a 723 switcher from a car charger (cigarette lighter adapter 14V->5V).

author: Giuss
author_rank: Contributor
timestamp: January 25, 2019, 09:04:49 pm
content: I think that the 723 is still a very good chip

author: Wolfgang
author_rank: Super Contributor
timestamp: January 25, 2019, 09:09:42 pm
content: Yeah, I use it a lot if I want something working and stable.See here:https://electronicprojectsforfun.wordpress.com/power-supplies/a-collection-of-proper-design-practices-using-the-lm723-ic-regulator/orhttps://electronicprojectsforfun.wordpress.com/silly-circuits/silly-circuits-a-heated-lm723-reference/

author: tkamiya
author_rank: Super Contributor
timestamp: January 25, 2019, 09:42:22 pm
content: LDP 7142 and LT1084 are like LM317. Not as cheap as 78xx and not as robust as 723. Hum.... hard to imagine not much happened in 30+ years...

author: schmitt trigger
author_rank: Super Contributor
timestamp: January 25, 2019, 10:13:18 pm
content: Quote from: imo on January 25, 2019, 07:46:47 pmWOW. A Harris semiconductor CA723. Nice vintage find.Of course, a metal can uA723 would be an even better vintage part.

author: Wolfgang
author_rank: Super Contributor
timestamp: January 25, 2019, 10:17:23 pm
content: The oldest ones I have are Harris military chips in CERDIP from 1986.Photo here:https://electronicprojectsforfun.wordpress.com/2018/09/18/not-all-lm723s-are-born-equal/

author: Hiemal
author_rank: Regular Contributor
timestamp: January 25, 2019, 10:31:45 pm
content: I got one!http://ww1.microchip.com/downloads/en/DeviceDoc/mic5156.pdfThese are quite pricey, but they have the advantage of being able to use N-channel mosfets. The 5158 version even has a built in charge pump to ensure proper gate drive, something that I feel is pretty unique.

author: coromonadalix
author_rank: Super Contributor
timestamp: January 25, 2019, 11:02:32 pm
content: Here is a very nice and well done project by vellemanThe K7200 kit 0-30v 0-10 amps power supplyThe 723 can make good psu's, it's still in productionhttps://www.velleman.eu/downloads/0/manual_k7200.pdf

author: tkamiya
author_rank: Super Contributor
timestamp: January 25, 2019, 11:27:47 pm
content: I think I'm going to use LM317. Load regulation 0.05% and ripple is 0.5%. That's about 1.n mV at 24V. Not bad for simple circuit. 7824 on the other hand is order of magnitude worse.

author: iMo
author_rank: Super Contributor
timestamp: January 25, 2019, 11:30:31 pm
content: What is the IC3 in the Velleman's kit?

author: iMo
author_rank: Super Contributor
timestamp: January 25, 2019, 11:41:50 pm
content: You will not get 3A out of an 317..

author: markce
author_rank: Regular Contributor
timestamp: January 26, 2019, 12:12:17 am
content: QuoteAnother 723

author: coromonadalix
author_rank: Super Contributor
timestamp: January 26, 2019, 04:06:25 am
content: yep dual 723 regulatorsone for voltage and one for current

author: DaJMasta
author_rank: Super Contributor
timestamp: January 26, 2019, 05:34:45 am
content: Quote from: imo on January 25, 2019, 11:41:50 pmSure you can, you just feed it the minimum voltage above dropout and put on a decent heatsink

author: mariush
author_rank: Super Contributor
timestamp: January 26, 2019, 06:29:53 am
content: No, most 317 regulators are advertised as 1.5A regulators and they have a "typical" current limit at around 2-2.2A ... maybe you can use an extra transistor to get 3A but just with the regulator alone, 3A ain't happening.

author: iMo
author_rank: Super Contributor
timestamp: January 26, 2019, 07:47:10 am
content: The 317 recommended max Iout is 1.5A. For 3A you need an extra pass transistor over it (plus some basic overcurrent protection), or to run 2x317 in parallel (with some care}, or to use the LM338 (5A version).

author: David Hess
author_rank: Super Contributor
timestamp: January 26, 2019, 10:51:05 pm
content: Nothing has replaced the 723 and it is still in production. The 317 is a general improved replacement for the 78xx series. Improvements over the 317 and 78xx series include the LT1086 which is available in fixed and variable versions.There have been other improved 78xx and 317 parts over the years but none caught on as much as the LT1086 and similar 3-pin parts.

author: Wolfgang
author_rank: Super Contributor
timestamp: January 26, 2019, 11:02:29 pm
content: People have tried to replace the 723 with better chips like the SG3532, ...they had thermal protection, lower voltage references, better current limiting, ...but they could not match the 10c per chip, so nobody bought them and the vanished from the market.

author: battmyrne216
author_rank: Newbie
timestamp: January 27, 2019, 06:00:51 am
content: nice example from an elenco power supply that used the 723. Edit: actually this schematic only uses the lm317. but the elenco I had happened to use the 723. Ive found its version schematic before but now im gonna have to find it.

author: battmyrne216
author_rank: Newbie
timestamp: January 27, 2019, 06:06:39 am
content: found the manual for mine. Which contains the 723 chips.

author: iMo
author_rank: Super Contributor
timestamp: January 27, 2019, 08:37:17 am
content: Interesting current limit wiring in the XP-581 schematics..

author: coromonadalix
author_rank: Super Contributor
timestamp: January 27, 2019, 12:29:01 pm
content: Nothing special, a 4 voltages outputs psu with no current adjustmentand one variable output voltage.The SG1532/SG2532/SG3532 may be more modern, BUT they start at 4.5vdc min up to 50vdc output, once again ou have to negate the output voltage to drop it to zeroYou have some "google" projects with 723 designs who go up to 70vdc and more

author: Wolfgang
author_rank: Super Contributor
timestamp: January 27, 2019, 01:04:28 pm
content: ... you can "float" your 723 if you need more than 40V out. I've seen HV supplies (1kV) with floating 723s (having a 12V float supply).