What's your opamp dual supply from single supply jellybean solution? - Page 1
Forum section: electronics / projects

author: dusan
author_rank: Regular Contributor
timestamp: September 18, 2024, 03:15:35 pm
content: What's your opamp dual supply from single supply jellybean solution? If you need dual supply (either postive to negative, or positive to positive and negative) and maybe some extra regulation afterwards if you need it. My current consumption is few mA.

author: rvalente
author_rank: Frequent Contributor
timestamp: September 18, 2024, 03:33:35 pm
content: For my simple op-amp circuits: virtual ground (kinda inefficient, works ok for audio stuff) or voltage inverter with a TC7660 (noisy).Liked the topic, good stuff will come up from the seniors

author: langwadt
author_rank: Super Contributor
timestamp: September 18, 2024, 03:45:40 pm
content: this is clever,https://www.edn.com/efficient-voltage-doubler-is-made-from-generic-cmos-inverters/

author: pqass
author_rank: Super Contributor
timestamp: September 18, 2024, 04:00:45 pm
content: Three possibilities, seehere.

author: reboots
author_rank: Regular Contributor
timestamp: September 18, 2024, 06:04:44 pm
content: I have heard that the TI "rail splitter" ICs (e.g. TLE2426) are considered too noisy for some applications, and that there are discrete active virtual ground designs which perform better. But that's all I've heard about that.

author: ArdWar
author_rank: Frequent Contributor
timestamp: September 18, 2024, 09:08:45 pm
content: Quote from: reboots on September 18, 2024, 06:04:44 pmI'm not exactly sure why would anyone still use that today over the much more ubiquitous opamp and 2 resistors solution. It might have their merit back in the day (low area/part count, guaranteed stability?), but I don't think it offer much of an advantage today over BOM consolidation etc.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: September 18, 2024, 10:19:16 pm
content: Quote from: dusan on September 18, 2024, 03:15:35 pmYou have not given starting and end voltages.Already mention is the 7660, that is the classic 8-pin simple voltage inverter pump, made by many vendors.Less conventional is to use MAX202 / variants as a charge pump, that starts from 5V or 3v3 and gives RS232 supplies circa +/- 9V. These series parts are widely available and cheap.There are also LCD driver pumps similar, that take 3-5V and give +/- 5.75VTI have SOT23 parts that take 3-5V in and give negative mirror voltage.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: September 18, 2024, 10:28:29 pm
content: Quote from: ArdWar on September 18, 2024, 09:08:45 pmYes, thirty+ years ago, getting sub 1% typical and 25ppm in a single TO92 package had some appeal.These days, 1% or better, and 25ppm resistors are mainstream, and the TLE2426 now has a maintenance price.

author: reboots
author_rank: Regular Contributor
timestamp: September 19, 2024, 05:07:30 pm
content: Quote from: ArdWar on September 18, 2024, 09:08:45 pmThe "rail splitter" parts were widely promoted and used at one time, and might still seem like an obvious choice to a novice searching the Web for virtual ground solutions. Just a note for any such person who might be reading this thread.

author: voltsandjolts
author_rank: Unknown
timestamp: September 19, 2024, 05:13:35 pm
content: XL6012 example:https://www.eevblog.com/forum/testgear/juntek-dpa-2698-10mhz-signal-amplifier-digilent-analog-discovery/msg3649978/#msg3649978

author: rvalente
author_rank: Frequent Contributor
timestamp: September 19, 2024, 05:38:03 pm
content: Inverting regulator, like 34063https://www.onsemi.com/pdf/datasheet/mc34063a-d.pdf, there are better choices out there, as the 34063 is also noisy.Inverting charge pump, similar to TC7660 or MAX232 as suggested, but driven from a oscillator (often a uC pin) or simple 555https://blog.mbedded.ninja/electronics/components/power-regulators/charge-pumps/Possibilities are endless, i guess

author: dusan
author_rank: Regular Contributor
timestamp: September 19, 2024, 06:47:05 pm
content: Quote from: rvalente on September 19, 2024, 05:38:03 pmWhy driven from oscillator?

author: rvalente
author_rank: Frequent Contributor
timestamp: September 19, 2024, 06:56:29 pm
content: Lets say you have a simple board with a microcontroller and a simple LCD, that needs -3V for improved contrast (like a few HD44780 clones), you could use an output from a uC clocking at A few KHz and use a charge pump to creat a very cheap negative power supply with only a few caps and a fast diode.https://product.torexsemi.com/en/technical-support/techinfo/doc_2095

author: exmadscientist
author_rank: Frequent Contributor
timestamp: September 19, 2024, 07:05:13 pm
content: Quote from: pqass on September 18, 2024, 04:00:45 pmJust please don't make the idiot mistake of calling the output of a rail splitter "ground" like this article shows. It's not ground, unless it was floating and you bonded it to ground somehow.This needs to be called "common"or something equivalent. This can become critical to safety in certain circumstances, and is all too often critical to function and/or EMC.I am willing to overlook loose terminology when there's only one reference voltage in a circuit. But once there's more than one (and a rail splitter always creates another reference voltage, so there definitely is now), you need to get this right.Anyway, for heavier lifting, a sync buck controller rigged as an inverting buck-boost does excellent work for negative rail generation. But probably overkill for a few milliamps!

author: electron_plumber
author_rank: Regular Contributor
timestamp: September 19, 2024, 08:06:36 pm
content: Yet another split rail solution, when isolation is needed, is the push/pull topology. Very simple to implement.

author: exe
author_rank: Unknown
timestamp: September 19, 2024, 08:30:13 pm
content: Quote from: reboots on September 18, 2024, 06:04:44 pmI don't think this is true. Switching regulators are noisy, but this one is linear.Quote from: PCB.Wiz on September 18, 2024, 10:28:29 pmI don't think precision is needed for a rail splitter that supplies opamps. Opamps don't care.Quote from: ArdWar on September 18, 2024, 09:08:45 pmMost opamps cannot drive capacitive loads.I used TL431 as a rail splitter (beware of capacitive load and stability regions, different TL) for "virtual ground", but I didn't need symmetrical split. I just needed to "lift" ground for 2V or so.For my next project I'd just use two positive LDOs: first to stabilize total output voltage (say, to 10V), and then the second one to split it (say, -5V from V+). Just beware most LDOs cannot sink current.

author: Phil1977
author_rank: Frequent Contributor
timestamp: September 19, 2024, 08:39:22 pm
content: If you allow using a boost converter you can do two setups:a) boosting e.g. 3.7V supply voltage to 15V. You can add a charge pump to the boost converter with two diodes and two capacitors that "mirrors" the output voltage to a negative -15V. It´s not very stable, but if the load on +15V usually is higher than on -15V it works.b) boosting e.g. 5V to 12V. Define the 5V potential as the virtual ground with relatively -5V and +7V. This setup delivers quite stable voltages if the boost converter is strong enough.

author: rvalente
author_rank: Frequent Contributor
timestamp: September 19, 2024, 08:43:56 pm
content: Quote from: electron_plumber on September 19, 2024, 08:06:36 pmI believe you could use an ethernet transformer for that, easy to source

author: HalFoster
author_rank: Frequent Contributor
timestamp: September 20, 2024, 08:58:08 am
content: Quote from: exmadscientist on September 19, 2024, 07:05:13 pmIt's not a mistake - "Ground" is simply a reference to a common potential. For bonding for safety reasons this is typically earth ground, power line or chassis ground. I agree that better naming is important for understanding the purpose of the reference potential (digital ground, analog ground or some other descriptive term) but they all only refer to some specific voltage level. There are distinct schematic symbols for things such as the earth, power line, chassis (defined by specification or at least convention) and other types of ground that indicate their typical use.

author: tooki
author_rank: Super Contributor
timestamp: September 20, 2024, 09:15:17 am
content: Quote from: exmadscientist on September 19, 2024, 07:05:13 pmTrying to get people tonotsay “ground” when it’s just the 0V reference in a circuit is… an uphill battle. That usage is thoroughly and deeply entrenched in electronics,and you know this.So I concur with HalFoster that this is not a mistake at all, never mind not an “idiot mistake”.What is absolutely true is that one needs to be more specificwhen it matters, as HalFoster also said. In the article, the author refers to the ground as an “artificial earth” and explains some limitations. If anything, what the article should probably say more explicitly is that the DC supply itself needs to be floating. Remember that that website’s focus is on audio circuits, and in the context of audio gear, it’s more likely than not that the grounds of different devices get connected, so the virtual ground created here will likely connect to a true ground somewhere, and thus the PSU must not already ground one of the outputs already.

author: HalFoster
author_rank: Frequent Contributor
timestamp: September 20, 2024, 01:56:58 pm
content: One of the most confusing issues, at least for me, is remembering that all of those different "grounds" are not necessarily at the same potential and can have significantly different impedances and other properties. For example, a single supply op-amp circuit that uses a artificial ground: I just sketched out a circuit a few days ago for a RF amplifier and caught myself about to bypass the power terminals of the op-amps to the generated ground. Oops (I was using another HF op-amp as a buffer for the V+/2). Anyway, there are some very good application notes floating around about (what is the best name? Artificial? Generated? Virtual to me is reserved for inverting op-amp circuits) the artificial grounds from TI, AD and others - there are a lot of subtleties that come into play depending on the application.On a completely unrelated note: ever notice that the slew rate youneedis always about 10-20% more than the slew rate of the op-amp that youhave?Sigh.Hal

author: jwet
author_rank: Frequent Contributor
timestamp: September 20, 2024, 02:49:04 pm
content: Just a note- several mentioned the 7660. This is a great problem solver for making a low current negative rail but has been improved mightily over the years. Unfortunately, these old devices ran at very low frequencies as low as 5Khz for some and required large caps, originally 10 uF. Newer pin compatible parts from all the standard sources run at much higher frequencies, use small caps and are available in SOT's, etc. A nice example is the ADI MAX1852/3 series, they run at 50/200 Khz, make 30 mA and use .68 uF caps and come in a SC-70. Go on DigiKey and do a search for Charge Pumps.

author: Buriedcode
author_rank: Super Contributor
timestamp: September 20, 2024, 07:08:46 pm
content: Jellybean?Charge pumps, usually good for <15mA, couple of schottky diodes and caps driven from a TTL oscillator (74xx14) or 555 timer. That either gives positive, or negative or both. And if you don't connect the doubler to VCC you get fairly symetrical outputs. If you can accept lower currents, you can add two stages on the negative side for Vout = -(2*Vin - 2*DVf). I have a strip of 100 dual schottky diodes in SOT23 specifically for this - so 3 components (dual diode + 2 caps) gives me a negative rail good enough for a few opamp buffers.It's quick and simple, not great efficiency, but not bad EMI, and the output ripple is often fine for opamp circuits given their PSRR.There are however "better" solutions. The next step up is a boost converter with a charge pump for generating negative output, which is much more convenient than a negative buck-boost with a positive charge pump.

author: beenai2018
author_rank: Contributor
timestamp: September 22, 2024, 02:17:59 am
content: The attached idea pops up a few times in the EDN archives from Linear Technology .I have not tested it personally ..

author: beenai2018
author_rank: Contributor
timestamp: September 22, 2024, 02:40:34 am
content: Here is one more from the High-Priest . I imagine he said " Hold my beer"..Single inductor 5V to +- 15V.Full app notehttps://www.analog.com/en/resources/app-notes/an-29f.html

author: ArdWar
author_rank: Frequent Contributor
timestamp: September 22, 2024, 03:05:02 am
content: I feel 7660-style charge pumps are in the once great solution but now getting too expensive for what they offer. Today you can pick random cheap buck converter, wire it in inverting mode, and still end up with cheaper BOM and higher current capacity.Maybe if you already have something that oscillate in your circuit (free MCU pin, another DCDC, etc) you can build your own charge pump for "free".

author: Thomas
author_rank: Regular Contributor
timestamp: September 23, 2024, 11:06:08 am
content: LM2766 is a good one:https://www.digikey.com/en/products/detail/texas-instruments/LM2766M6X-NOPB/2514776More modern (?) and better than the 7660:2.7 - 5.5V200mA2MHz$1.12 in single quantities

author: dusan
author_rank: Regular Contributor
timestamp: September 23, 2024, 08:41:39 pm
content: Quote from: Thomas on September 23, 2024, 11:06:08 amBut that doesn't create negative voltage only doubles input voltage.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: September 23, 2024, 09:12:41 pm
content: Quote from: dusan on September 23, 2024, 08:41:39 pmCorrect.The cheapest way to get modest +/- OpAmp supplies is to use a x3232 (3v3-5V) or x232 (5V) UART transceiver, lcsc have those from as low as ~10c/500+

author: jasonRF
author_rank: Regular Contributor
timestamp: September 24, 2024, 12:18:04 am
content: If I don’t need to get down to DC (eg when doing audio) then I often don’t bother. I just use input and output caps, such as in figure 1 or 2 ofhttps://www.analog.com/en/resources/analog-dialogue/articles/avoiding-op-amp-instability-problems.htmlEspecially when I just need a buffer so there is no extra cap required for the feedback.

author: Thomas
author_rank: Regular Contributor
timestamp: September 24, 2024, 10:25:04 am
content: Brainfart lol. I probably meant LM2776:https://www.digikey.com/en/products/detail/texas-instruments/LM2776DBVR/5356685

author: Zero999
author_rank: Super Contributor
timestamp: September 25, 2024, 12:14:20 pm
content: I generally avoid it. Most of the time a dual supply isn't necessary. If it's audio, then go with AC coupled, single supply. If it's DC, then level shift and use differential outputs. That will enable you to have positive and negative input/outputs without a bipolar PSU.Here's an example of a Howland current source I designed to drive a valve with +/-7.5mA, using a +/-10V control signal, yet runs from a single 12V power supply.

author: rvalente
author_rank: Frequent Contributor
timestamp: September 30, 2024, 02:31:29 pm
content: Great share! Tks, I was looking for something similar, need to drive 120mA proportioning valve.For this 7.5mA, what op-amp did you use?

author: Zero999
author_rank: Super Contributor
timestamp: September 30, 2024, 10:04:45 pm
content: Quote from: rvalente on September 30, 2024, 02:31:29 pmI think it was the OP200 for U1 & U2 and a generic op-amp amp, such as the old '741 fro U3.The circuit actually has a differential input. If the negative input has a potential divider on it, a positive input voltage can be scaled to a current which goes negative. Here's an example showing a 0V to 5V to +/-120mA circuit.The current capacity of an op-amp can be increased by adding pass transistors. Here's an example of a similar circuit using ordinary op-amps to get 100mA out.

author: rvalente
author_rank: Frequent Contributor
timestamp: October 01, 2024, 11:51:55 am
content: Holly molly, you know the jazz when it comes to howland current pumps! Tks mate, ill base my design on yours.