inductors IN amplifier circuits - Page 1
Forum section: electronics / projects

author: coppercone2
author_rank: Super Contributor
timestamp: December 08, 2024, 06:59:05 am
content: So this is taboo. Inductors are a hated counterpart to the capacitor in op-amp/amplifier circuits because of adherence to theory.But I was thinking, maybe, for some reason, it might make sense.Here is one snippet of a scenario like thishttps://www.researchgate.net/publication/279816959_Inductive_compensation_of_operational_amplifiers_in_feedback_circuitsAnyone got more?I don't mean simulated ones, I mean like someone putting a coil in there.

author: Analog Kid
author_rank: Super Contributor
timestamp: December 08, 2024, 07:29:00 am
content: No, don't have anything more (this is all over my head anyhow).But (as you probably know) inductors can be simulated in circuits without actually winding any wire around a core.They're called gyrators.Ah, didn't see your edit. So no simulations. OK.

author: Slh
author_rank: Regular Contributor
timestamp: December 08, 2024, 08:21:15 am
content: The main issue with using inductors is that they tend to be larger and less ideal than capacitors so if you want to make a small or precision design then you'll do better with capacitors than inductors. I wouldn't say that it's because they're hated, they just don't do as good a job so why bother if you don't have to.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 08, 2024, 09:26:11 am
content: With RF amplifiers it is not so uncommon to use inductors and also transformers in amplifiers.A problem with inductors, especially high values is that they couple to other fields (hum and other inductors). For new circuits there is also the size argument - higher value inductors tend to get physical large and capacitors are usually cheaper. I can fully understand why one would avoid inductors if possible.I know one example of a more lower frequency amplifier that uses inductors in the compensation of an amplifier: the input amplifier for the HP3458 DMM.

author: coppercone2
author_rank: Super Contributor
timestamp: December 08, 2024, 01:34:42 pm
content: Quote from: Kleinstein on December 08, 2024, 09:26:11 am...

author: mawyatt
author_rank: Super Contributor
timestamp: December 08, 2024, 01:49:25 pm
content: Having designed and utilized integrated inductors on ICs, they are to be avoided if possible because of mentioned size requirement which is precious on an IC, and are far from ideal with all sorts of undesirable characteristics.For discrete circuit use inductors seem to follow this same path of undesirability, except where they have no counterpoint like in SMPS use, but even here the larger bulky mains transformer has been replaced with a smaller "higher frequency" transformer to reduce size (and cost).Best

author: dobsonr741
author_rank: Frequent Contributor
timestamp: December 08, 2024, 02:16:19 pm
content: At what operational frequency? Audio - yes. RF and microwave - inductors are everywhere.

author: schmitt trigger
author_rank: Super Contributor
timestamp: December 08, 2024, 03:50:39 pm
content: Additionally, inductors usually have a wider tolerance, and the inductance value may also change with DC bias.

author: TimFox
author_rank: Super Contributor
timestamp: December 08, 2024, 05:30:13 pm
content: At radio frequencies, inductors are required. However, compared with capacitors, they are larger and have lowerQvalues. Ferromagnetic cores (e.g., toroids) are useful to reduce size, but can have problems with linearity and temperature dependence.

author: coppercone2
author_rank: Super Contributor
timestamp: December 08, 2024, 07:47:36 pm
content: there is also the odd case of sensor inductors inside of feedback loop for measuring inductance or measuring inductive sensors (position) that I know of, but they are not really acting like true circuit elements since they are sensors. And some chaotic oscillator circuits, which I don't know what they can use that for now.

author: TimFox
author_rank: Super Contributor
timestamp: December 08, 2024, 08:01:00 pm
content: For a position sensor, the inductor is part of the sensor impedance in series with the signal.

author: coppercone2
author_rank: Super Contributor
timestamp: December 08, 2024, 08:03:09 pm
content: They also have some weird differential one that measures induction difference between two coils or something with a moving somethingBut I swear, there must be more in circuit inductor circuits that might become realistic. I see you can actually get mu-metal shields now reasonably, alot of different core materials, with different core shapes and even odd wires like litz and approachable winding technologies even for low budget novices involving arduino etc. I wonder if there are high performance circuits that stand up to traditional topologies that were just not investigated because it was a total pita to get the materials you need to get higher utility from coils. And custom places and known techniques to make complex sheet metal shapes. I think magnetic technologies become more available because of switching converter and wireless charging proliferation.I can see problem with getting EE's to investigate something like 600 turns of fine wire on a small torroid core. The lower frequency inductors are a pain to make. Naturally it must have been totally avoided unless absolutely necessary.

author: TimFox
author_rank: Super Contributor
timestamp: December 08, 2024, 08:06:45 pm
content: Before I retired, we used "LVDT" sensors (linear variable differential transformer) to measure translation in one direction.They are essentially a transformer, normally excited with an audio frequency, where the effective primary-secondary ratio changes with displacement of the shaft.https://www.omega.com/en-us/resources/lvdt-sensors

author: coppercone2
author_rank: Super Contributor
timestamp: December 08, 2024, 08:09:19 pm
content: here I found onehttps://www.researchgate.net/figure/Modified-op-amp-based-differential-inductance-measuring-circuit_fig2_220410871

author: TimFox
author_rank: Super Contributor
timestamp: December 08, 2024, 09:08:46 pm
content: There are mechanical systems to wind fine wire on formers.I have seen them wind toroids at factories.Wirewound resistors (a simpler geometry) are not hand-assembled.Back in the day, hand assemblers (with small fingers) could achieve higher density of magnetic core memories than machine construction.

author: coppercone2
author_rank: Super Contributor
timestamp: December 08, 2024, 09:24:47 pm
content: I wonder if anyone setup those generic lab robot arms that were kinda getting popular to talk about for winding torroids by 'hand'. Or at least as a clumsy assistant

author: Kleinstein
author_rank: Super Contributor
timestamp: December 08, 2024, 10:53:09 pm
content: Even with a machine toroids are a bit difficult to wind. A reasonable alternative may be pot cores, that allow easy winding on a coil former and still a relatively well shielded ferrite core. Of cause some materials like nanocrystaline band are essentially only available as toroids.