I'm studying Rudy Severns eBook Snubber Circuits for Power Electronics; great read by the way.

In it he has the following figure, notice the phrase in the caption "including voltage and polarity conventions":

enter image description here

Should I take this to mean that there is a conventional orientation for the "opening" and "hinge", so to speak, of the switch symbol in a schematic? At least in a DC context where current would only be flowing the one direction?

I hadn't encountered that before and kind of have my doubts, but my engineering mind would like a convention that leads to a one-and-only-one right way to orient a symbol that otherwise has a degree of freedom to it.


No a switch doesn't normally have polarity, but when you implement a switch with semiconductors you have to worry whether they are one-quadrant, two-quadrant or four-quadrant, depending on what the rest of your circuit requires/imposes in terms of current and voltage. For example a BJT is good a 1st quadrant (or 3rd quadrant) switch and a diode as a 2nd quadrant (or 4th quadrant) switch. A MOSFET is good as two-quadrant switch if well chosen (body diode considerations). A good presentation of that topic is in Erickson's course.

  • \$\begingroup\$ Super helpful link, thanks for that, I think I'm going to watch that whole series :) Based on your response, I'm now interpreting that phrase in Rudy's book to mean something like: "... the polarity conventions of the voltage dropped across the switch, based on the direction of current flow, regardless of the orientation in which you draw the switch 'opening' and 'hinge'". \$\endgroup\$ – scanny Dec 11 '15 at 9:27

I have never seen or used any convention for polarity or current direction on a mechanical switch or relay contact.

You may have to pay attention to polarity or current direction with solid-state relays or transistor switching schemes.

It is generally recommended that switches be placed in the "hot" wire feeding a load, rather than on the ground side of the load.


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