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Technically, every relay or transistor could be replaced by an ideal switch if there was such a thing.

However, I learned that those parts are satisfactory in most cases. Thus, I'm looking for a scenario where either:

  • a certain device can't be built because it would require such an ideal switch
  • the ideal switch would improve the performance (cost, efficiency, ...) of a device to such a degree that the alternative (relay/ transistor/ other switch) is no longer a meaningful option (assuming that the ideal switch costs the same as a relay/ transistor suitable for the same application)

Ideally, I'm looking for power-switching applications since I learned that RF-MEMS come close to the idea of an ideal switch. Thus HF/ RF applications are less suitable because the next best alternative (RF-MEMS) is already good.

I have already researched the following solution that could serve as an inspiration:

Electrical motor controllers use three-phase AC. They could technically be switched on by a TRIAC. However, the heat emission would be too much for most casings. On the other hand, a relay can't handle the current peaks that occur when the motor starts. Thus, they use the TRIAC to switch on the motor (to handle the current peak) and then short-circuit the TRIAC with a relay to avoid heat emissions. An ideal switch could replace the hybrid construction with one switch. (This should serve as an example - saving one component is too little impact to qualify as a solution, unfortunately. It has only a minor impact on the overall cost of the device).

Edit: An ideal switch has the following properties:

  1. if open, it is an open loop (infinite resistance)
  2. if closed, it has zero resistance (short-circuit)
  3. switching speed is (close to) infinite
  4. does not require energy to be operated (or very, very little)

It's size would be 10% of the next best alternative.

Alon
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  • First define "ideal switch", then we can discuss it's applications. – Eugene Sh. Jan 11 '23 at 21:46
  • Ideal switches don't exist except in simulators or in theory. What non-idealities are you likely to accept? – Andy aka Jan 11 '23 at 21:52
  • @EugeneSh. You're right, I edited the question. – Alon Jan 11 '23 at 21:53
  • So.. I guess you are talking about some kind of controlled switch, not manual? – Eugene Sh. Jan 11 '23 at 21:53
  • @Andyaka you're right. My question is geared towards justifying research to invent an (almost) ideal switch. However, I don't have specifications yet, thus I opted for the ideal switch as a proxy. – Alon Jan 11 '23 at 21:54
  • @EugeneSh. that is correct - it is an alternative to relays and transistors, not to manual switches. – Alon Jan 11 '23 at 21:55
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    Every power conversion application would benefit from an "ideal" or more ideal switch, some would benefit greatly. Let us know when you have samples available! – John D Jan 11 '23 at 21:56
  • @JohnD could you explain a little more? I studied CommTech, thus I can't think of an actual device that you refer to - are you talking about e.g. switch-mode power supply? – Alon Jan 11 '23 at 21:59
  • @Alon Yes, a switch-mode power supply, or DC-AC inverter, or even motor controllers, traction inverters, battery chargers, wireless power transmitters and receivers, etc. – John D Jan 11 '23 at 22:02
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    “every relay or transistor could be replaced by a . . . switch” No, in general a transistor used in an analog circuit could not be replaced with a switch. – George White Jan 11 '23 at 22:31
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    The possibility of achieving a Platonic ideal of a switch here in the physical plane presupposes the existence of a magic wand, and a magician to wave it. Such a person could just wave their magic wand and make the world so ideal that switches were no longer necessary. Therefor, the question is moot. – TimWescott Jan 11 '23 at 22:37
  • @TimWescott Does that mean that frictionless planes are out too? And the free energy motor-generator thing? – John D Jan 11 '23 at 22:45
  • Yes. Sorry if you've invested money... – TimWescott Jan 11 '23 at 22:46
  • Thanks for the sarcastic comments. I'm aware of those things and I'm hoping that your faith in science to achieve major improvements for incumbent technologies will be rekindled anytime soon. As you can read in previous comments, the question is a proxy for learning applications for an almost, but not entirely ideal switch with unknown specs. You can keep your wizard, please give me a competent engineer to answer my question. – Alon Jan 11 '23 at 22:48
  • @Alon Sorry, Alon, just a little ribbing due to your characterization of the switches as "ideal". If you had said "greatly improved" it probably wouldn't have generated the sarcastic comments. In fact today's FETs would probably seem almost ideal or magic to someone who only knew vacuum tubes (valves). Realize though that there are billions of dollars spent by countless engineers to wring out that extra bit of incremental performance from today's semiconductors. – John D Jan 11 '23 at 22:54
  • @JohnD thanks for your consideration! Yes, I'm aware of that. However, there are still problems to be solved: FETs switch slower than BJTs for example and both are damageable by radiation (just as an example). Assuming all the downsides of semiconductor switches/ relays were solved, what would you build? – Alon Jan 11 '23 at 23:02
  • Every improvement in on resistance and switching speed will benefit high power inverters - think power distribution, storage, EVs, the biggest and fastest evolving markets there are. That's why every semiconductor company is trying to improve on them. Never mind 10% of the next best, 80% of the next best would be an improvement worth redesigning for. So you are in good company, doing the right thing. But, I suspect, just hopelessly out-gunned in terms of investment into research, and understanding what the competition is doing. – Neil_UK Jan 12 '23 at 06:50
  • Do you have a technology in mind for your new, breakthough performance, switch? It would be interesting if you got the datasheet for a modern FET, and listed its parameters in your OP, showing which ones you could improve on, to what level of performance. – Neil_UK Jan 12 '23 at 07:06

2 Answers2

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A possible way to make an "ideal" switch is to enormously improve a real switch. This idea is implemented in the circuit of the so-called "precision diode rectifier" where the undesired forward voltage drop VF across a real diode switch is compensated by an equivalent voltage VF produced by the op-amp. As a result, an "ideal diode switch" with zero voltage drop across it is obtained.

See for example this recently asked question where, by the help of the op-amp A1, the real diodes D1 and D2 act as "ideal diodes".

In another answer of mine, you can see how an "ideal" transistor switch is made.

Circuit fantasist
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In most practical use cases you don't actually want an ideal switch.

Imagine that you have your ideal switch and some parasitic capacitance around it. What happens with the current when the switch is closed?

fraxinus
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  • Not to mention, what happens in a parasitic inductance, when an ideal switch opens in no time. – Justme Jan 12 '23 at 00:20