+/- 6-12v 100mA from +5v - suggestions? - Page 1
Forum section: electronics / projects

author: ahope
author_rank: Contributor
timestamp: February 01, 2021, 07:13:06 pm
content: Hi,I am building a small amplifier input control circuit where i need +/- 6-12V (or thereabouts) to drive a couple of op-amps after the digits.I was trying the MAX865, but that would not deliver enough current to drive the op-amps.I would like to run it from +3V or +5V supply.Any other suggestions for a charge-pump/reverse circuit or chip?Andreas

author: Benta
author_rank: Super Contributor
timestamp: February 01, 2021, 07:26:39 pm
content: Buy a small 1...2 W DC/DC module. Much easier. You can even get them with built-in LDOs for low noise.Example:https://www.tracopower.com/de/dc-dc-convertersNo affiliation.

author: ahope
author_rank: Contributor
timestamp: February 01, 2021, 09:23:44 pm
content: Good suggestion, thanks.That is the easy way out.Marginal, as with 5V it can at best deliver 41 mA +/- 12VPart of the fun was also to see if i could make my own to fit on my custom pcb.More suggestions welcome.

author: Dubbie
author_rank: Unknown
timestamp: February 01, 2021, 09:41:01 pm
content: Try using Ti webbench to design a custom solution.It generates you a BOM, schematic and layout.It's pretty brain dead simple and you don't need to know anything about anything to end up with a working board first try.

author: ahope
author_rank: Contributor
timestamp: February 02, 2021, 06:27:36 pm
content: Quote from: Dubbie on February 01, 2021, 09:41:01 pmThanks, I will give that. a try.

author: penfold
author_rank: Frequent Contributor
timestamp: February 02, 2021, 06:56:41 pm
content: The TI SN6505 is a pretty nice chip for applications like that, the push-pull config makes for a reasonably low noise output, if you need it regulated, then put an LDO at the output.If you want it super low noise, add some more filtering before an LDO - I wouldn't recommend relying on an LDO to eliminate switching noise, their rejection at that kind of frequency is generally pretty poor.

author: enz
author_rank: Regular Contributor
timestamp: February 02, 2021, 07:09:04 pm
content: The Texas Instruments TPS65130 is made for exactly this application. Works great, but not the most simplest solution in terms of parts count.

author: ahope
author_rank: Contributor
timestamp: February 04, 2021, 09:21:25 am
content: Quote from: enz on February 02, 2021, 07:09:04 pmThanks, this looks interesting. High parts count, but will do the job.

author: ahope
author_rank: Contributor
timestamp: February 04, 2021, 09:23:28 am
content: Quote from: penfold on February 02, 2021, 06:56:41 pmI am not able to see how this chip solves my problem.(I am not that pro )

author: penfold
author_rank: Frequent Contributor
timestamp: February 04, 2021, 10:52:25 am
content: The SN6505 is a power supply building block, you provide it with a transformer and secondary rectification, you pick the turns ratio and output configuration to suit your needs (look for fig 48 in the data sheethttps://www.ti.com/lit/ds/symlink/sn6505a.pdf). I suggested that one because its small, doesn't need any 'serious' PSU design beyond picking a transformer and being based around push pull topology allows much better noise performance for analogue stuff. You do sacrifice output regulation with that IC, but that's honestly rarely ever necessary with well designed opamp circuits, but you can address that by adding an LDO to each the positive and negative outputs.

author: ahope
author_rank: Contributor
timestamp: February 04, 2021, 12:43:47 pm
content: Quote from: penfold on February 04, 2021, 10:52:25 amHm, that's a new way of doing things to me. I need to spend some time looking into that. Thank you for the information.

author: Evan.Cornell
author_rank: Regular Contributor
timestamp: February 04, 2021, 03:16:49 pm
content: If you can take the cost and you can relax to +-50mA load current, take a look athttps://www.analog.com/en/products/ltc3265.htmlVery handy for bipolar bias supplies.