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  1. #1
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    E-C drain optocoupler

    Hello everybody,
    According to the attachment diagram, I want to completely separate a 5.4V power supply using an optocoupler regarding load . I extracted from a more complex scheme only the incriminated circuits and tested. When I energize firmly the relay it appears on the load R = 150 ohms an artifact. I want to remove this artifact and I can't succeed even if I coupled various capacitors between Point 1, Point 2 to ground. Photo 1 is from Point 1, and photo 2, 3.4 from point 2 with different time bases. I connected a capacitor of 100nF between 2 and 5 per relay, in Point 1 I had photo 5 and the artifacts on the load disappeared completely. I also did the following test. I connected in Point 1 a 3.3V source so that I have a switch between 3.3 and 5.4V, but the artifact on the load remains. Only the old method with the capacitor in parallel on contacts cancels the parasite. Why does this oscillation pass through C-E? I also tested opto 1N136 without success. Otherwise what can I replace the relay so that it does not produce these oscillations due to the contacts and at the same time I can very well isolate the optocoupler from the 5.4V source . Obviously, the opto has to be opened at a later stage, but for now I don't want to be like a resistor or a capacitor when the photo diode is not powered.

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    Re: E-C drain optocoupler

    Hi,

    I can not open .rar files on my old tablet...

    Klaus
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    Re: E-C drain optocoupler

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    Re: E-C drain optocoupler

    Phototransistor has large output capacitance in nF range created by Miller effect, the observed behaviour is quite expectable. You can try to switch the power supply more softly (reduced dV/dt), either using a transistor switch or a RC filter after the relays.


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  5. #5
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    Re: E-C drain optocoupler

    Hi,

    The relay contacts cause high dV/dt....and due to contact bouncing it will be multiple times with variable timing.

    You may filter at the optocoupler input(C) or output(E).
    You may also replace the relay with someting more soft switching.
    In this case it may be an improvement to reverse the order of components: supply --> optocoupler --> relay --> output.

    Currently the relay is switching the 5.4V...
    When reversed the relay is switching 0V (when the optocoupler is OFF. You may force the node to 0V with a pulldown)

    Does it make sense, or is there a need to connect a relay and an optocoupler in series? Can't you avoid it?

    Klaus
    Please don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.


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