I have a conceptual question about electrical elements' role in engineering control. Indeed elements such as resistors or capacitors are widely used in all sorts of circuits. However, there are more "advanced" elements such as diodes, switches, etc.

I'd like to know:

  • if these "advanced" elements, switches, for example, are fundamental. Fundamental in the sense that they are necessary for building a certain control circuit.
  • Or equivalently, are there any control targets out there that cannot be achieved without a switch, diode, etc?
  • Equivalently, can one build such "advanced elements" from more fundamental elements?

I'm not familiar with the technological process of building such elements. So please bear with me if the is a trivial question.

  • \$\begingroup\$ Welcome! Depends what you mean by fundamental. In terms of SPICE simulation, one would be inclined to agree that R, C and L are the fundamental items and all switches are built using often several and far more complicated building blocks to make up a switch. In the real world, a diode and a resistor can look mechanically identical but are made very differently and have also very different functions. Can you perhaps narrow down your question? \$\endgroup\$
    – winny
    Dec 13, 2022 at 10:18
  • \$\begingroup\$ Thanks, @winny . I'm mainly interested in the theoretical possibility of building such life-easing elements (what I called "advanced") from more simple ("fundamental") ones. The mechanical construction doesn't matter for me. I got my answer from your comment and will mark it if you post it as an answer. \$\endgroup\$
    – arash
    Dec 13, 2022 at 10:28
  • \$\begingroup\$ My comment only asked for clarification and went on a tangent is case you could limit your question to how it works in SPICE. If SPICE (basically any electronic simulator) is what you are after, please update your question and I'll answer accordingly. \$\endgroup\$
    – winny
    Dec 13, 2022 at 10:57
  • \$\begingroup\$ @winny Look at the logic in your comment. " switches are built using often several and far more complicated building blocks to make up a switch. A switch is fundamental, (mechanical or electrical or electromagnetic etc.). You cannot make it from a RLC or any more complex combination of RLC. Yet we call RLC linear and switches, non-linear \$\endgroup\$ Dec 13, 2022 at 12:58

1 Answer 1



All passive components include RLC and a switch in each model.

A cap has ESR (ohm) and SRF (MHz) which includes ESL (nH).

A choke, L has DCR and SRF (MHz) with Cp and DCR (ohms).

A resistor has L of about 0.3nH/mm and C depending on the area to the height of a ground plane.

OK, but what's all the gobbledegook about switches?

A switch is a conductor that is ON=1=closed or OFF=0=open and insulator. . . Logical right?

It also has parasitic inductance, L when closed or capacitance, C when open.

Otherwise, in logic, we just use the binary notation: 0,1.

But the real world including logic is all analog. For example, there is a time delay, rise times voltage margins to the threshold, ESD protection and power consumption or losses.

A semiconductor switch has capacitance specs for input, output and feedback (Miller effect).

A FET switch tends to have a constant Coss * RdsOn minimum with a small variation due to Vds max, and structural 3D geometry. These have extremely high conductance gain Zin/out but low gm and high capacitance.

Compared to BJTs which have very high gm very high hFE up to 5000 but 250 typically. gm =Is/Vbe is variable, just as in FETs but 10x higher but has very low input capacitance unless they have extremely low Rce in mohms.

Mechanical switch degradation affects Ron by several orders of magnitude. There are 2 basic classes. Gold plated up to 2A and silver alloy over 2A. Then there are Mil-Spec gold plated, and current switches>100A called "contactor" switches and HV (kV) rated switches in vacuum and SF6 used in the AC power distribution industry for kW and MW switches.

Low voltage switches can be solenoid activated such as car engine starters with a 20A relay powering a 1000 A solenoid with a low duty factor. But generally low voltage relays have a capacity current gain from 1000 to 5000.

There are other Fundamental elements too.

Transformer, spark gap, memristor, diode, LED, delay line, etc . etc.

  • \$\begingroup\$ This doesn’t answer OP’s question. \$\endgroup\$
    – winny
    Dec 13, 2022 at 10:14

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