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Sci.Electronics.Basics -> What would you call this?
There are 21 messages in this thread.
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Author: DaveDate: 07:56 18-03-08
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"ehsjr" <ehsjr@bellatlantic.net> wrote in message
news:ykGDj.5726$sw3.1186@trnddc06...
> Dave wrote:
>> "Hammy" <spamme@hotmail.com> wrote in message
>> news:q9gst3lk7687n8jg31luig2837v8mlhjiv@4ax.com...
>>
>>>On Mon, 17 Mar 2008 04:22:08 GMT, ehsjr <ehsjr@bellatlantic.net>
>>>wrote:
>>>
>>>
>>>>Dave wrote:
>>>>
>>>>>"Hammy" <spamme@hotmail.com> wrote in message
>>>>>news:ju5qt39ouvqussmr45b48uhkt2cjbngdic@4ax.com...
>>>>>
>>>>>
>>>>>>On Fri, 14 Mar 2008 08:26:28 -0500, "Dave"
<db5151@hotmail.com> wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>>Aaahhh. Yes, I remember this from school. A circuit that
stays on
>>>>>>>even
>>>>>>>you
>>>>>>>try to turn it off... That's what I need. An SCR. Will
look into
>>>>>>>that.
>>>>>>>*Thank you, Michael.*
>>>>>>>
>>>>>>>Much appreciated.
>>>>>>>
>>>>>>>Dave
>>>>>>>
>>>>>>
>>>>>>The thing about an SCR is it needs an intiateing current even
the
>>>>>>2n5060 needs about 20mA .I found it to be higher on the ones I
have
>>>>>>anyway.Then it will hold on as little as 5mA.If all thats okay
then
>>>>>>fine.
>>>>>>
>>>>>>I have a similiar dilema only for a zero crossing detector.I
want it
>>>>>>to latch when the detector senses the zero crossing. I'm
looking at
>>>>>>something like this.
>>>>>>
>>>>>>http://rocky.digikey.com/weblib/ST%20Micro/Web%20Data/74V1T77.pd
f
>>>>>>
>>>>>>Cheap and tiny low power consumption.If you look you can
probably find
>>>>>>cheaper and lower power versions.
>>>>>>
>>>>>>Search for D-type transparent latches.
>>>>>>
>>>>>>Or depending on your application and what your willing to spend
there
>>>>>>are latching relays a little pricey though.
>>>>>
>>>>>
>>>>>Aaah, yes. Very interesting, but I think what I am going to do is
>>>>>build the
>>>>>equivalant of an SCR out of transistors, as my electronics textbook
>>>>>describes. This will allow me (I think) to select the parameters I
>>>>>want and
>>>>>tailer them to my exact needs. Or at least that's the present idea.
>>>>>Thank
>>>>>you for this pointer however. I may yet end up using it.
>>>>>
>>>>>Take it easy...
>>>>>
>>>>>Dave
>>>>>
>>>>>
>>>>
>>>>Gate current is no problem, at all. You can get sensitive gate
>>>>SCRs that will trigger well below 1 mA. For example, the 2N5060
>>>>mentioned in Hammy's post triggers at .2 mA (not 20 mA!)
>>>>
>>>>By all means, experiment with making your own from transistors.
>>>>You can have fun, and learn that way. But there is no problem
>>>>in getting one that will trigger at low current.
>>>>
>>>>Ed
>>>
>>>Hi Ed
>>>
>>>I didnt say that the 2n5060 needs 20mA gate trigger .What I said is
>>>that it needs an intial 20mA AK current.This is written in the
>>>datasheet.From my experience with them they usually need a bit more.
>>>
>>>Maybe I should have been clearer the intiating current I'm refering to
>>>is the Anode Cathode current,not gate current.You have to look for it
>>>in the datasheet but its there.
>>
>>
>> Hmmm. What about a sensitive gate that triggers at (lets say) .2mA, with
>> an AK current of similar proportions?
>
> Not likely to find an SCR with a 200 uA holding current.
> The one we are discussing - 2N5060 - needs a minimum of
> 5 mA to hold.
>
>> What I am wanting to do is switch a couple of leads from +5V (very low
>> current) to ground (essentially NO current) on a JK flip-flop, so that
>> the clock is thereafter ignored and the Q and not-Q outputs remain
>> unchanged. Any suggestions? Oh, and I need to do this with solid-state
>> devices, not a coil-of-wire relay.
>
> You can use an SCR as long as you provide a path that
> will allow it to hold, like a resistor from SCR anode
> to the + rail.
>
> +5 -------[1K]-----------+----> To flip-flop
> _|_
> \ /
> ---
> /|
> Signal---[1K]-----+ |
> |
> Gnd ----------------------+
>
>
> But if you are already using flip flops,
> is there a reason not to use another ff?
>
> Ed
>
>>
>> Thanks,
>>
>> Dave
>>
Thanks for the input, and the advice RE: an SCR unlikely to hold at 200 uA.
I believe I will actually have 5 mA holding current, which is a lot more
than I originally thought I would have, and the SCR I am thinking of using
fits that mold (the NTE5400).
'preciate it.
Dave
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