Dual supply ICs that aren't microscopic? - Page 1
Forum section: electronics / beginners

author: paulca
author_rank: Super Contributor
timestamp: February 06, 2018, 09:57:02 pm
content: I want to make a dual +-12V supply from a single input, Ideally 12V, but I can live with 5V. I can find switching regulator chips which do this from Linear, Maxim and TI, but they are all, so far, seem to be in the smallest little packages they can get. QFNs etc.Does anyone know of examples or more managable devices?The other option is a boost converter and an inverting boost converter as a pair.Of course this is where you tell me I'm barking up the wrong tree and these don't do what I expect anyway.

author: Tommy1984
author_rank: Regular Contributor
timestamp: February 06, 2018, 10:44:54 pm
content: ICL7660 for max 10 VICL7660A for max 12VOBS! I thought you need it to power an op amp!

author: Mr.B
author_rank: Unknown
timestamp: February 06, 2018, 10:59:32 pm
content: You don't mention your power requirements...muRata have a range of modules:MTU1D1212MC (+/-12vdc out, 10.8 to 13.2 in, 1W)https://nz.mouser.com/ProductDetail/Murata-Power-Solutions/MTU1D1212MC?qs=sGAEpiMZZMvGsmoEFRKS8EQfQWTYwRjY13tljw%252bH9s8%3dNCM6D1212C (+/-12vdc out, 12v in, 6W)https://nz.mouser.com/ProductDetail/Murata-Power-Solutions/NCM6D1212C?qs=sGAEpiMZZMvGsmoEFRKS8NGQWIL5m%2fkiSj4lVxi5VomTcB%252bcVdWoLw%3d%3d

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: February 06, 2018, 11:16:04 pm
content: LT8471 in a 20-Lead TSSOP?

author: Buriedcode
author_rank: Super Contributor
timestamp: February 07, 2018, 12:57:20 am
content: In addition to the previous replies:For lower current (<20mA) you can use a simple charge pump added to any boost converter - output won't be regulated though. Costs two diodes and two caps.For medium current you can use a coupled inductor on a buck converter - pseudo regulatedIf you can find those inductors with multiple windings, I forget the brand, but they have 5-6 separate windings all with the same inductance to mix'n'match you can use a boost converter with a center tapped secondary - pseudo regulated.QFN is indeed a bit of a bugger to prototype with (unless you use hot-air and adapter boards) but I'm sure there are MSOP/SSOP about which can be hand soldered fairly easily (flux'n'drag).

author: paulca
author_rank: Super Contributor
timestamp: February 07, 2018, 07:48:55 am
content: Sorry power requirements are to power a set of dual opamps, probably 7 or 8 of them with only 2 of them producing any power for headphones.So less than 100mA, call it 200mA to be safe if I add LEDs or some such.As this is audio, I suppose a further requirement is that the switching frequency is as high as possible. Certainly not a close multiple of audio frequencies like 60Khz.

author: paulca
author_rank: Super Contributor
timestamp: February 07, 2018, 07:55:44 am
content: Quote from: Neomys Sapiens on February 06, 2018, 11:16:04 pmLooks good until I get to the exposed base pad that would need hot air.I have no hot air gun. Also I will be prototyping with DIL/DIP adaptor boards.

author: Zero999
author_rank: Super Contributor
timestamp: February 07, 2018, 09:43:14 am
content: Is the +12V rail already well-regulated enough for your requirements? If so, then how about adding a buck-boost converter to get -12V?It can be done with the cheap MC34063, but there are better ICs available.http://www.ti.com/lit/ds/symlink/mc34063a.pdfHave you considered a virtual ground? The easiest way is to use the TLE2426.Do the LEDs really need to run off the regulated output?Can the circuit be redesigned to use a single rail?

author: paulca
author_rank: Super Contributor
timestamp: February 07, 2018, 10:05:24 am
content: I 'could' use a virtual ground. However I have run into problems before with virtual grounds on the output. I don't like connecting a 6V GND to another random mains powered device, it makes me uncomfortable. For example I connected my headphone amp input to an Arduino and it browned out and crashed. I measured the potential between the grounds and it was 8.5V. Arduino was running off a bench supply, I think the brown out was just the time it took the various capacitance to shift the ground, but I'm probably talking out of my hat here. Maybe my discomfort is unnecessary.As to regulation,ideallyI would like a rather broad input spec. The typical auto-motive spec of 9V to 15V so I can run it off an unregulated 12V battery or solar.I 'could' use a linear regulator to drop that to a fixed, stable input voltage, but that is unlikely to be 12V, more practically 9V or 6V.I can limit the LEDs to a power LED which I can put a 1k on and it will run on the unregulated input. A level meter strip of LEDs post pre-amp stage would be a nice addition, but not really necessary.

author: Benta
author_rank: Super Contributor
timestamp: February 07, 2018, 10:19:17 am
content: For low volume runs, I don't bother building a PSU myself, but use the Traco TMR 2 and TMR 3 modules. Available with 9...18 V input and +/-12 V regulated, isolated outputs. Not cheap, but dead simple and available at most of the catalog distributors..No affiliation.

author: paulca
author_rank: Super Contributor
timestamp: February 07, 2018, 10:41:53 am
content: Quote from: Benta on February 07, 2018, 10:19:17 amHmmm. £12-15, but the self build solution for a single run will cost about as much. Nice wide input range, +-12V output, 125mA, perfect. The TMR-3 has 75mV vpp ripple, but I'm not dealing with mic level, only line level inputs so this should be fine??Thereveals my problem in that I don't yet understand audio design criteria at the same time I'm not an audiophool and so it will probably be grand.

author: paulca
author_rank: Super Contributor
timestamp: February 07, 2018, 11:08:30 am
content: Quote from: Mr.B on February 06, 2018, 10:59:32 pmSorry I missed this. Just as good as the TMRs. I missed it as the Mouser links never seem to work, they ask me to select my country and dump me to the homepageThanks for the suggestion.

author: tszaboo
author_rank: Super Contributor
timestamp: February 07, 2018, 11:38:59 am
content: Quote from: Benta on February 07, 2018, 10:19:17 amThose are really really noisy for analog, which means you need to filter them. Designing a proper filter means measuring the unit, and in the end, you put the same effort in the filter, than the power supply. There is no free lunch.The reason that these are in QFN and similar packages is easy. If you have an IC which needs to deliver 200mA +/-12V, that is almost 5W. Even with 80-90% efficiency, you have 0.5-1W dissipation in the IC. And the volume application for this is for LCD, portable devices, so as small as possible.I would suggest the LT1945. Or hack a typical boost converter to work with negative output, and use the same IC for the positive.

author: paulca
author_rank: Super Contributor
timestamp: February 07, 2018, 11:49:23 am
content: Quote from: NANDBlog on February 07, 2018, 11:38:59 amHow noisy is noisy? Are we talking about obviously noticeable on an op amp output amplifying Line level 500mVpp by gain of 4 or 5 or are we talking about only noticeable on a scope while doing frequency analysis and characterization?

author: Benta
author_rank: Super Contributor
timestamp: February 07, 2018, 11:58:38 am
content: QuoteNot really, when we talk audio. Peak ripple is at the switching frequency (and harmonics), which is around 200 kHz upwards.I wouldn't worry about it, and it's easy to filter out.

author: tszaboo
author_rank: Super Contributor
timestamp: February 07, 2018, 11:59:41 am
content: Quote from: paulca on February 07, 2018, 11:49:23 amDepends on the PSRR of your Opamp. These work in the 50-150KHz region, and they have no regulation whatsoever. Meaning that the output voltage will change if you change the input voltage or the output current. They require minimum load and they dont like large capacitors on the output.https://www.tracopower.com/products/tmr2_application.pdfJust look at the curves and see the 100mV changes for a load change.

author: Benta
author_rank: Super Contributor
timestamp: February 07, 2018, 12:06:26 pm
content: So you're saying that building one yourself will give better results than the modules? Allow me to doubt that.

author: Benta
author_rank: Super Contributor
timestamp: February 07, 2018, 12:19:21 pm
content: QuoteYes, that corresponds to 1% of the output voltage, which is actually very good (and according to specs, which is +/-1.0% for a 0...100% or 100%...0 load step). I challenge you to do better with a homespun DC/DC converter.

author: Buriedcode
author_rank: Super Contributor
timestamp: February 07, 2018, 03:10:10 pm
content: Also note that, for opamp circuits - often the signal route isn't directly coupled to either rail, and all opamps have power supply rejection ratio (PSRR) in the order of >50dB. This means that, unless you have a resistor going from either rail to the signal path, opamps can be reasonably tolerant of power supply noise.What tends to be more problematic in my experience is radiated noise - EMI from switching converters coupling to high impedance inputs. This is why I lean towards either charge pumps - which are hard to get for >100mA working at less than -5V - or royer converters that have a more sinusoidal switching - narrower band of noise, easier to filter out.With that said I have made a headphone amp using a boost converter and coupled inductor for a bipolar power supply, that has no discernible noise, as the switching frequency is so high. This isn't a partocularly 'good' design' just an example that switching converters don't always cause problems.

author: Kalvin
author_rank: Super Contributor
timestamp: February 07, 2018, 03:19:17 pm
content: Have you checked these already:https://www.ebay.com/itm/DC-DC-Converter-Step-Up-Boost-3-3V-5V-12V-to-5V-9V-12V-15V-24V-Dual-Power/172765565537I have no idea how well these perform or how noisy they are, but they seem to be able to supply quite high positive and probably sufficient negative voltage from a single input supply. The price is not too bad either.Edit: The controller chip is XLSEMI XL6007E1:http://www.xlsemi.com/datasheet/XL6007%20datasheet.pdf

author: Benta
author_rank: Super Contributor
timestamp: February 07, 2018, 03:23:24 pm
content: Input voltage is too low and they're not isolated or regulated.

author: tszaboo
author_rank: Super Contributor
timestamp: February 07, 2018, 03:32:42 pm
content: Quote from: Benta on February 07, 2018, 12:06:26 pmYes. You dont need to doubt it, it is how it is.It is really easy to understand, if you think about it.The isolated converters are just a PWM signal fed into a transformer. The transformer is driven to saturation (EMI everywhere). There is absolutely no regulation. Meaning that if you do something on the output, draw current, your voltage will go down. And if your input voltage is only 4.5V for a 5V model, then your output is 10% lower. If your input has a 1KHz ripple, it goes to the output.Meanwhile if you take a boost-invert topology, there is immediately feedback if the output changes. The inductors are driven with just enough current and it is nice and silent.Also, you have 100mV noise where your signal is about 1 Volt. In frequency ranges where the opamp doesnt have any PSRR.Yes, you can filter it, but it is not smaller task than designing a proper (and not isolated) DC-DC.A homespun DC-DC doesnt have to be coming from the junk bin. I personally can solder QFN package with a chinese hot air station.

author: Benta
author_rank: Super Contributor
timestamp: February 07, 2018, 03:48:10 pm
content: QuoteI'm certain that cheap converter modules exist that are built as you say.But I think you're underestimating the modules I suggested. They are indeed regulated, check the data sheet.Like I said, I've used them myself to power opamps at +/-12 V and have had absolutely no noise problems or EMI. The high frequency ripple is killed in the end by the decoupling caps at the opamps.But you go to your church, I'll go to mine.

author: schmitt trigger
author_rank: Super Contributor
timestamp: February 07, 2018, 03:57:05 pm
content: I also suggest the use of charge pumps for opamp negative supplies.

author: David Hess
author_rank: Super Contributor
timestamp: February 07, 2018, 06:12:44 pm
content: Quote from: paulca on February 07, 2018, 07:48:55 amThat is high current for a simple charge pump. Many switching regulator topologies can produce a bipolar output by using either a dual inductor or an inductor to drive a charge pump. There is no requirement to use a specialized dual output switching regulator IC. The last examples in theLT1616 datasheetandLinear Technology design note 232show this.

author: paulca
author_rank: Super Contributor
timestamp: February 08, 2018, 07:52:35 am
content: Hmm. I'm not sure I need 100 or 200mA. My headphone amp which has 2 dual op amps and a power LED shows as using less than 20mA even at full tilt. The rest of the opamps in my project will not be producing power for speakers/headphones, but just buffering and pre-amping.Maybe I can get away with a smaller output. It's hard to know. What is the standard way of assessing this? Do I add up the "absolute maximum current" for all the ICs or do I take a test such as the example headphone amp and multiple it by the extra amps?I do like the idea of the contained isolated (or even unisolated) potted PSUs linked to. Saves me the hassle and saves me the potential of ballsing up the PSU stage and getting horrid artifacts from a clipping switching regulator or similar. Also the switching regulator, self built will probably not be prototypable on a breadboard. I learnt that lesson recently, they don't like it, too much capacitance in the BB.An off board PSU to limit EMI is an option, but would mean more things flitting around my desk.Now I'm in procrastination mode. The potted PSU units are not cheap enough to buy to test and then reject. Where as the switching self build or switching IC build is a fair project in itself.

author: Kalvin
author_rank: Super Contributor
timestamp: February 08, 2018, 08:40:14 am
content: Is it going to be portable? If not, you should consider the plain old linear power supply as your power consumption is very small.For the portable device you probably want to use a switched mode psu - either charge pump or inductive - with good filtering. Filtering should be quite easy to do as your power requirement is quite modest and you do not require to have large magnetics.There are some mini 12V re-chargeable batteries available if you want to experiment a little. This would be a compromise between a linear psu and portability, but you would not have to struggle with the noise problems. However, you need to implement some sort of charging capability which will add some complexity. Just my 2c.

author: paulca
author_rank: Super Contributor
timestamp: February 08, 2018, 10:03:26 am
content: Quote from: Kalvin on February 08, 2018, 08:40:14 amI could go linear if I could get the operating voltage down to +-9V, as long as I can find LDO linear and inverting linear regulators.It's not portable persae but I want the option to run it off 12V nominal battery power. So that results in the standard automotive power range, 9V-15V. It just makes it easy to power from anything including a basic 12V wall wart, Lithium 3 series battery or a feed from a solar panel setup.The headphone amp I have which will form the basis of my amplifier design will run on such voltages and I don't notice any degradation of quality until it gets down to around 7 or 8V, but I haven't characterised that in anyway with a scope, just turning the voltage down until I noticed a sound quality change.

author: tszaboo
author_rank: Super Contributor
timestamp: February 08, 2018, 11:41:55 am
content: Quote from: Benta on February 07, 2018, 03:48:10 pmIt said on their website it is fully regulated... Probably only on the + for the dual version, that is why there is a 5% variation int the output. And it works at 0% load. OK. Looks like these are newer models, with more intelligence built in.

author: paulca
author_rank: Super Contributor
timestamp: February 08, 2018, 11:52:32 am
content: I'm thinking I might try one of those. It will make things a lot simpler and allow me to focus on the op amps which will be taxing enough.Still need to decide on how much power I actually need.The Maximum input current on the NE5532P is -10/10mA. I figure I need at most 8 of them. 3 input preamps, 1 mix down buffer, 2 aux output buffers and 2 as a current sharing pair for headphone output. They have current limiting outputs so I should be able to stay within the 10mA and thus my supply requirements would be 80mA.Adding a 25% grace gives me 100mA. The 4mA or so for a power LED is negligible. Does that sound reasonable? Do I need to accommodate loss in the passives?

author: David Hess
author_rank: Super Contributor
timestamp: February 08, 2018, 07:09:01 pm
content: Another way if regulation is not required is to use a 1:1:1 or N:1:1 transformer and drive it with a simple inverter. Some switching regulators can be configured to drive a transformer as part of an inverter. An inverter can also be regulated from either the input or output side to provide a constant output voltage. One nice thing about this is that the outputs may be completely floating. Coilcraft makes some off the shelf transformers for this.