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Thread: Avoiding relay use

  1. #11
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    Thanks again Brad, that looks a good tuition into FET's. I will have a good read.

    I just checked the current flow between the Picaxe output pin resistor and the switch it's putting a grouns on and it's 110uA, so I think that's safe enough.
    Regards

  2. #12
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    Quote Originally Posted by ZOR View Post
    Thanks again Brad, that looks a good tuition into FET's. I will have a good read.

    I just checked the current flow between the Picaxe output pin resistor and the switch it's putting a grouns on and it's 110uA, so I think that's safe enough.
    Regards
    Hello ZOR

    Yes, the tutorials on N&V are very good and not too complicated. Obviously things can be taken to a much greater depth, but, for most of us, understanding the general fundamentals is sufficient in most cases.

    110uA? No problems there. I believe that the PICs on which PICAXEs are based will tend to source/sink around 20mA.
    Darb

  3. #13
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    Quote Originally Posted by darb1972 View Post
    Here is some reading for you that might be of use and interest.

    http://www.nutsvolts.com/magazine/ar...ircuits_part_1

    Brad
    Thanks for that link. I was somewhat baffled by some of the early figures and descriptions until I reached the section entitled "THE IGFET/MOSFET" and realized that the text above was describing JFETs (as was clearly indicated, but I missed it).

  4. #14
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    A good survey article however i think input gate capacitance needs more emphasis as it's quite large for power FETs - capacitance from gate to drain - it's why you need drivers at high speed switching...

  5. #15
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    I don't if this will just confuse thing, but I used opto isolators for my camera remote shutter

    project here: http://www.picaxeforum.co.uk/showthr...ed-photography

  6. #16
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    Thanks oracacle, that was on the lines that I remembered seeing. Managed to sort this out okay now but thanks for comming in. Have a good one Regards

  7. #17
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    Hi guys/gals,

    Yes indeed FET's are terrific products in many respects. Only Micro amps are required to switch them on, where as a standard transistor has BASE current requirement. The link to N&V is definitely worth a read for those wanting to understand FETS.

    Doing a bit of research with good ole' Google for 'LOGIC LEVEL FETS' will be helpful for many using PICAXE as they only require 5V to turn them on FULLY.

    For required optically isolated switching in past applications I have found the IXYS/CLARE - CPC1981Y to do a great job. Of course there are similar others out there with perhaps more appropriately lower voltage thresholds.

    CPC1981Y datasheet link - https://www.arrow.com/en/products/cp...#Pdp-datasheet

    It may also be worth noting that in the past I have been burnt by purchasing cheap ones that were offered as genuine, but were in fact knock offs that did not at all function correctly so definitely worth purchasing from a reputable supplier.



    Regards,
    Morty.

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