Single-Supply vs Split-Supply Op Amp Designs - What to Teach? - Page 1
Forum section: electronics / general

author: dieciduej
author_rank: Newbie
timestamp: October 10, 2025, 12:31:31 pm
content: Since I am a classically, early 80s, trained EE person most of op-amp circuit designs I dealt with were split/bipolar-supplies (±15 or ±12V). At that time rail-to-rail and single supply op amps were not cheap and most of the things plugged into a mains outlet. As time progressed rail-to-rail and single supply op amps became cheaper and better and batteries are doing more of the powering of circuits. Circuit/microcontroller power supplies are now +5, +3.3V or lower, no negative rail. In general, analog signals are bipolar and with bipolar op amps designs are relatively a piece of cake.Today most designs a powered by a battery or a wall-wart power supply, op amp circuits are somewhat forced into a single supply design. Again, I am trained in split/bipolar op amp circuits and looking at ways to redesign a split- into single-supply design a chore. Looking at various tech-notes on the web, the problems of proper biasing and AC signal coupling make it hard to come up with an easy way to do things.Now to one of the questions I have:What is done in industry?Has industry moved over to single-supply op amp designing or since DC-to-DC converters have come along way is that the method being used in the industry. The DC-to-DC converter would bring back the split-supply voltages, all be it with possibly noisy rails, but good filtering should quell that. But the key thing is it makes designing op amp and analog circuits easier. I have moved into the world of higher education and op amps are still taught the way I was taught. Is that what industry is looking for?I am just trying to find some guidance on how to steer the ship.Thanks for any light on the matter.CheersJoeD

author: PwrElectronics
author_rank: Regular Contributor
timestamp: October 10, 2025, 01:52:42 pm
content: At least in my industry (heavy duty ruggedized vehicle electronics) its all single supply. Nearly everything we do has a micro or FPGA of some type and any analog is just signal conditioning before it goes to a ADC.Right now, I am having the issue of trying to find a LDO type negative linear regulator for one of our product types that needs a negative rail (IGBT inverter gate drive). Not much out there to find so far. The current design is using a ancient old '7908 type non LDO regulator I would like to ditch for a LDO so the switcher pre-regulator can have lower output and we reduce the power (for a smaller package and space claim).

author: UnijunctionTransistor
author_rank: Frequent Contributor
timestamp: October 10, 2025, 02:09:11 pm
content: They are not mutually exclusive applications, each method has its space in the electronic universe.IMHO, learning about opamps should be done as ideal components first, allowing the students to understand its operation and allowing them to derive the proper transfer functions with different feedback methods.Then continue to learn the practical aspects of opamps, offset voltage, slew rate, bandwidth, output limitations, input CMR and biasing, the good stuff. And amongst those limitations is precisely the input CMR and how to bias the opamp for single supply operation.This is similar to logic gates: when one is studying truth tables and the different simplification methods, one is not initially concerned about fanout, noise immunity or propagation delays. However once someone has properly understood Karnaugh maps, one should delve into those topics.

author: dieciduej
author_rank: Newbie
timestamp: October 10, 2025, 03:37:10 pm
content: Hello UJT,One of the problems is that it is a 14 week all analog component course, i.e. diodes, BJTs, FET/MOSFET, and op amps. Trying to get it all in during the time frame is hard.Sorry to say we've dropped you, UJT, from the course.JoeD

author: rstofer
author_rank: Super Contributor
timestamp: October 10, 2025, 04:43:38 pm
content: I would start with bipolar because projects for that topology are all over the Internet. The only thing that changes with single supply is the need to bias the inputs to some midpoint between Vcc and Gnd.I would give more than a passing glance at integrators. They can be the real-time solution to differential equations. I really like analog computing.Attached is a MATLAB-Simulink depiction of the differential equations of motion for the Mass-Spring-Damper project common in every DE course. 1/s is an integrator and other op amps are used for summing, adding and inverting.MATLAB is one of my favorite toys. In the real world, most op amp integrators have inverted outputs so the arithmetic changes a wee bit. On a real analog computer, the project only requires 2 integrators, 1 summer and 1 inverter plus a couple of potentiometers to set up the constants.A great use for bipolar op amps.

author: UnijunctionTransistor
author_rank: Frequent Contributor
timestamp: October 10, 2025, 04:47:28 pm
content: Quote from: dieciduej on October 10, 2025, 03:37:10 pmAs long as you don’t drop the PUT, I won’t be offended.

author: Zero999
author_rank: Super Contributor
timestamp: October 16, 2025, 08:02:54 pm
content: All you need to do is bias it with a potential divider, so that the output sits at half the supply voltage. It's a good idea to bypass the potential divider to the 0V rail, with a capacitor, to reduce the effect of supply fluctuations being passed to the output.For most op-amps you want the negative to be 0V, but in some applications, a negative supply (positive ground is preferable). If the op-amp's inputs' common mode range doesn't include the positive supply (the TL07x is a classic example) and can go into phase-inversion or latch up, if taken near the negative rail, then use a negative supplyRefer to the schematics below for how to properly design a single supply op-amp circuit.Credit: audioguru for the original.

author: Nominal Animal
author_rank: Super Contributor
timestamp: October 18, 2025 05:58:21 am
content: Quote from: Zero999 on October 16, 2025, 08:02:54 pmI know nothing of the subject, really, except that I have suffered from cheap powered computer speakers that used a simple voltage divider resistor pair between the rails to get the bias potential for opamps. That rejectsnoneof the supply noise, so that when there was no audio, the power supply hum/hiss/buzz can be heard.Remember, opamps reject power supply ripple and noise, and common-mode ripple and noise on the input; but not ripple and noise in only one of the inputs, like in the biasing scenario.For audio circuits, the bias voltage itself doesn't actually matter much, as long as it is not too close to either rail. Because the current draw on opamp inputs is so low, one could easily use a voltage divider followed by a low-pass RC or CLC ("Pi") filter to get a low-noise bias reference voltage. If designed in, it would only increase the cost of the circuitry by using a couple more resistors and capacitors, maybe an inductor (ferrite bead?), but would affect the quality of the end product a LOT.

author: Zero999
author_rank: Super Contributor
timestamp: October 18, 2025 07:16:02 am
content: Quote from: Nominal Animal onYesterdayat 05:58:21 amDid you read the rest of my post and look at the schematics?That's why I recommended bypassing the potential divider with a capacitor. This isn't necessary, if it's powered off a very stable voltage source i.e. a battery, with nothing else connected to it, but is essential in the case of a mains power supply.

author: Nominal Animal
author_rank: Super Contributor
timestamp: October 18, 2025 12:34:30 pm
content: Quote from: Zero999 onYesterdayat 07:16:02 amAsAnalog AN-581: Biasing and Decoupling Op Amps in Single Supply Applicationsfrom 2002 explains, that is not that effective especially for relatively low frequency supply ripple (and noise). The typical values used gives a low-pass cutoff at 30 Hz, so at 120 Hz the attenuation is just 12 dB, which means the ripple amplitude only gets quartered (×0.25). Even if you use a low-pass cutoff at 10 Hz, attenuation would be just 21.6 dB at 120 Hz, and ripple amplitude reduced by a factor of 0.083 (or about 1/12th). USB-powered speakers are particularly sensitive to this, because typical supplies have 50mV to 100mV of ripple and noise at the 5V rail.Using a cheap, low-power, low-noise linear regulator to get a suitable bias voltage gives you 50+ dB of power supply rejection, for example. See my point now?

author: Zero999
author_rank: Super Contributor
timestamp: October 18, 2025 05:16:41 pm
content: Quote from: Nominal Animal onYesterdayat 12:34:30 pmYes, I see your point.A downside of the regulator/zener diode is it will reduce the operating voltage range of the circuit, because the bias voltage is fixed and doesn't scale with the supply voltage, so the bias point gets nearer to the supply voltage, as the voltage drops, compared with a potential divider which is proportional to the supply voltage. If noise is a problem, then I would rather use a big capacitor for a cut-off of <1Hz , with multiple stages, if that's impractical.

author: Nominal Animal
author_rank: Super Contributor
timestamp: October 18, 2025 10:43:50 pm
content: Quote from: Zero999 onYesterdayat 05:16:41 pmYes, an excellent point.Quote from: Zero999 onYesterdayat 05:16:41 pmIn other words, the low-pass filter I also described, yes.As you see, we are in agreement and not in disagreement, and just rounding out the bias voltage approach with various implementation options, noting their benefits and downsides, and practical problems one might wish to consider when choosing which one to use.

author: ISO_mukund
author_rank: Newbie
timestamp: October 18, 2025 11:01:53 pm
content: I faced the same situation while designing a power supply for the electronic weighing scale. OP-07 instrumentation-grade Op-Amp required a dual power supply, which is no problem on mains, but for the battery backup, I had to use a negative voltage generator IC TL7660, i.e. supply voltage conversions from positive to negative.I have apostregarding dual v/s single power supply.