12v to +-5v - Page 1
Forum section: electronics / beginners

author: RogerThat
author_rank: Regular Contributor
timestamp: January 12, 2023, 09:18:22 pm
content: As the topic says. I want to make a split supply, but which way is the best? I need only 100mA source/sink for a couple of op amps.

author: Benta
author_rank: Super Contributor
timestamp: January 12, 2023, 09:38:38 pm
content: Linear regulator from +12 V to +5 V (7805, LM317 or similar), followed by an LM2660 to generate -5 V.Can't be done much simpler.

author: Zero999
author_rank: Super Contributor
timestamp: January 12, 2023, 11:16:20 pm
content: Is it acceptable to have the reference somewhere in between 0V and 12V? If so a 10V LDO regulator and the TLE2426 might do.

author: Benta
author_rank: Super Contributor
timestamp: January 12, 2023, 11:22:27 pm
content: Quote from: Zero999 on January 12, 2023, 11:16:20 pmGood question.In that case, even a couple of "stacked" 5 V LDOs would do the job.

author: james_s
author_rank: Super Contributor
timestamp: January 12, 2023, 11:31:10 pm
content: It's hard to say what is the "best" way, but one easy and reliable way to do this is to get a DC-DC converter with the bipolar output you need. They are small potted blocks, most are even isolated.

author: mariush
author_rank: Super Contributor
timestamp: January 12, 2023, 11:53:44 pm
content: There's also the option of12v -> 7805 -> +5v12v -> charge pump converter to -12v -> 7905 -> -5vYou could do +5v -> charge pump -> -5v and save a 7905 regulator but most importantly because lots of such charge pump ics are rated for max 12v, so it's better to do 5v -> -5v and as added bonus you'd also put some minimal load on the 7805 regulator with this occasion.A cheap charge pump can do 20-50mA, maybe 100mA ... for more you'd probably have to use a switching regulator... MC33063/ *34063 are cheap.Here's a list of such charge pump regulators :https://www.digikey.com/short/5fcrpf42

author: Benta
author_rank: Super Contributor
timestamp: January 12, 2023, 11:54:22 pm
content: Quote from: james_s on January 12, 2023, 11:31:10 pmThought about that one myself, but the price!Try finding an unregulated type below $10, the regulated are at $15+.What on earth has happened the last few years? (Yeah, I know, chipageddon).

author: Psi
author_rank: Super Contributor
timestamp: January 13, 2023, 01:04:13 am
content: I recommend those little isolated modules you can get for around $1You decide what input range you want 5V 12V 24V etc. and then what output you want, 5V 12V 24V etcThen since they are isolated you can use 2 of them to turn 12V into -5 and +5 etc..Check datasheet to be sure they can do the current you need.(Some will produce more than 1 voltage but i like to keep things simple and use one type)They are more expensive on digikey than aliexpress and YMMV.And check the one you get is 'isolated' only some are.The key words to use on aliexpress is DCDC SIP

author: izen
author_rank: Newbie
timestamp: January 13, 2023, 01:07:27 am
content: 100ma is quite a lot. For opamps a sepic-cuk combined dc-dc with a linear post reg may be enough.

author: Psi
author_rank: Super Contributor
timestamp: January 13, 2023, 01:09:10 am
content: The $2 5V in 5V out isolated bricks will do 100mA, some 200mA

author: james_s
author_rank: Super Contributor
timestamp: January 13, 2023, 01:24:14 am
content: Quote from: Benta on January 12, 2023, 11:54:22 pm$15 doesn't seem too bad for a regulated one from a reputable brand. Those things have always been expensive, for a one-off hobby project it's not a huge investment.

author: Zero999
author_rank: Super Contributor
timestamp: January 13, 2023, 08:52:15 am
content: Quote from: Benta on January 12, 2023, 11:22:27 pmNo because the lower one would need to sink as well as source current and the 5V LDOs I've seen can only source.Quote from: RogerThat on January 12, 2023, 09:18:22 pmWhat do the op-amps do? Is just AC only, i.e. audio? If so, they can probably configured for single supply operation.Will a higher voltage do?

author: MarkL
author_rank: Unknown
timestamp: January 13, 2023, 03:48:09 pm
content: Take a look at the CUI VXO7805-500 non-isolated switching regulator:https://www.cui.com/product/dc-dc-converters/non-isolated/vxo78-500-seriesYou can get a pair of them and depending on how you wire it, it will output positive or negative 5V (negative output current is a little lower; 300mA vs. 500mA). USD $2.51 ea. at Digikey and the usual suspects, and lots in stock.Depending on your circuit and your opamp, you may need some supply filtering with any switching regulator solution.

author: Terry Bites
author_rank: Super Contributor
timestamp: January 13, 2023, 04:28:23 pm
content: For the cost of LM2660 you can get a dual rail DC-DC module. eg MPA1205S. You will have to manage input and output noise with any switcher.If you can, rearrange your circuit to be single supply then you only need one adjustable LDO. If you can live with 6V insted of 5V then you don't need any extra parts.Its hard to say what's without knowing the context.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: January 13, 2023, 06:34:56 pm
content: Quote from: izen on January 13, 2023, 01:07:27 amsepic-cuk?

author: Picuino
author_rank: Super Contributor
timestamp: January 13, 2023, 07:27:55 pm
content: https://core.ac.uk/download/pdf/162912855.pdf

author: RogerThat
author_rank: Regular Contributor
timestamp: January 13, 2023, 09:41:38 pm
content: Thanks for all the replies!I normally avoid negative supplies and make do with single supplies, but I see some great uses for it(like precision op amps that can go from GND and up). The LM2660 seams like a good go-to part, cheap and plentiful.

author: Zero999
author_rank: Super Contributor
timestamp: January 13, 2023, 10:18:17 pm
content: A standard buck regulator IC can be used to make a negative, as well as positive voltage, if used with a transformer, rather than a plain inductor.

author: SiliconWizard
author_rank: Super Contributor
timestamp: January 13, 2023, 10:25:58 pm
content: Now one of the main factors here will be whether you need the ground of your 12V supply to be the ground of your circuit - in other words, can/is the 12V supply floating? If so, Generating a middle point as "virtual" ground may be the easiest. It can be buffered with an adequate opamp for instance (one that can source and sink enough current.)If cost is not a factor, there is a pretty nice all-in-one solution with the LTC3260 (wide input range, integrated inverting charge pump, integrated post-reg LDOs). It's rather expensive though.

author: james_s
author_rank: Super Contributor
timestamp: January 14, 2023, 02:18:08 am
content: Quote from: Zero999 on January 13, 2023, 10:18:17 pmThat's a clever hack, I'm not sure I've ever seen it done that way although it's not too hard to see how it works.