I some other language literature I used to read it is common to find a text that translates directly into English as "transistor open" or "diode open". This means that transistor is conducting notable current between collector and emitter, for diode this means that forward voltage is applied and notable current is flowing through it. The same way, "transistor closed" means that there is no notable current between emitter and collector, for diode this means that reverse voltage is being applied (no notable current).

I have recently received some criticism on this terminology, saying that "closed" should mean conducting, and "open" should mean no current. Indeed, this is true for the switch or relay contact: the literature I used to read also uses the opposite terminology for these devices.

However also in English it is possible to say "the door is closed", "the gate is closed", "the bridge is closed" or "the road is closed". This means you cannot pass through, not the opposite.

Is it appropriate to say in English "the transistor is closed" in the case like in the diagram below? If this is not the right wording to use, that wording should be used instead?


simulate this circuit – Schematic created using CircuitLab

  • \$\begingroup\$ Comments are not for extended discussion; this conversation has been moved to chat. \$\endgroup\$ – Voltage Spike Oct 30 '20 at 19:02

The contacts in a switch or relay have a mechanical gap between them. The terms 'open' and 'closed' were adopted into general use a long time ago to mean 'contacts apart' and 'contacts together' respectively.

The terms 'open' and 'closed' have not been adopted for transistors, which happen to have no such mechanical gap. Nor were they used for valves, which have a gap between electrodes but is not a moving part in their operation. Transistors and non-diode valves are amplifying devices. Using them as a switch is using a subset of their full gain range (fully 'on' or fully 'off'). So the idea of an 'open' or 'closed' transistor isn't as descriptive or associated with what you see as with electrical contacts on a switch or relay.

There are mountains of examples in the English language of words that are only used with specific nouns or verbs. This case is far from alone.

  • \$\begingroup\$ I think you have the terms in your first sentence reversed. An open switch or relay has the contacts not touching so no current flow, while a closed switch or relay has the contacts touching, so current can flow. \$\endgroup\$ – Peter Bennett Oct 27 '20 at 16:09
  • \$\begingroup\$ @PeterBennett, oops, thanks, fixed. \$\endgroup\$ – TonyM Oct 27 '20 at 16:35

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