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Ok, I know the basic function of an optocoupler is "turn on irLED, triggering a phototransistor and allowing current to flow"; an optical off then on switch.

Is there a reverse optocoupler, i.e. "turn on irLED, unknown component is triggered and stops/blocks current flow", an optical on then off switch?

Circuit A does something that includes a charging function then activates Circuit B. As long as Circuit B has [enough] power, Circuit A is removed from it's power source (turned off) by a signal from Circuit B. When Circuit B's power is gone/too low, signal is removed and Circuit A's power is returned and starts process over again.

I know how optical relays work (Circuit A on, Circuit B off, trigger on, Circuit A off, Circuit B on, trigger off, original condition). A standard optocoupler is essentially one half of this. I am wanting the other half.

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    \$\begingroup\$ Why not use it in a common emitter configuration instead of common collector? \$\endgroup\$ – Ignacio Vazquez-Abrams Jun 10 '15 at 16:54
  • \$\begingroup\$ @Ignacio: is the image on this page what you are talking about link? \$\endgroup\$ – James V. Fields Jun 12 '15 at 17:02
  • \$\begingroup\$ Yes. Those are the phototransistor equivalents of CE and CC. \$\endgroup\$ – Ignacio Vazquez-Abrams Jun 12 '15 at 17:05
  • \$\begingroup\$ Thank you for clarifying that. I have several PC817's, I can use them for both sides of my idea. \$\endgroup\$ – James V. Fields Jun 12 '15 at 20:59
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Yes, there are photovoltaic cells driving depletion-mode MOSFETs. They are very slow in comparison to most optocouplers (hundreds of microseconds or milliseconds rather than microseconds or nanoseconds) but they do perform the function you ask about. Here is an IXYS (née Clare) one.

In relay terms this is called a "Form B" contact.

enter image description here

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    \$\begingroup\$ I think this is what I am looking for (simple replacement for an optocoupler that is NC not NO). Thank you. Now that I have a name I can do further research. For what I need/want, timing isn't the issue. \$\endgroup\$ – James V. Fields Jun 10 '15 at 18:16
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Photoreceivers (such as photodiodes or phototransistors) work because incident light on the semiconductor excites electrons into the conduction band, forming free carriers (both electrons and holes). So it's more or less fundamental to the operation of the photoreceiver that conductivity is increased when light is applied.

If you want the opposite behavior, you can either invert the signal driving the LED, or use an external buffer at the optocoupler output. Since most optocouplers can only directly drive very light loads anyway, this is very common.

schematic

simulate this circuit – Schematic created using CircuitLab

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If you drive the LED in different ways, you can achieve either configuration.

schematic

simulate this circuit – Schematic created using CircuitLab

In the first circuit, you control the voltage. When V1 is LOW, the LED is off, and so Q1 is off. When V1 is HIGH, the LED is on, and so Q1 is on.

V1 must have enough current and voltage to drive the LED.

In he second circuit, you control the ground. When V1 is LOW, the LED is on, and so Q1 is on. When V1 is HIGH, the led is off, and so Q1 is off.

V1 must go to Vcc to ensure that the LED is off and must be able to sink the current (which shouldn't be problem anyways).

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