Using Opto Isolators
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Posts: 46,084
I am building a large dc motor driver(still). I am using a PAK-V to
drive very large MOSFETs(100v 180amp rating, I'll be using 15vdc to
drive) and relays(12v 40amp). I would like to use a couple of Opto 22
modules that I have laying around. In the data sheet for the ODC5, it
shows using a N channel transistor. Has anyone used one of these
modules? Can I simplify and just send the positive signal? I would
assume that if i can, I can also use the same technique for the
Stamp's I/O's(switches,indicators,etc). Thanks.
Ian
drive very large MOSFETs(100v 180amp rating, I'll be using 15vdc to
drive) and relays(12v 40amp). I would like to use a couple of Opto 22
modules that I have laying around. In the data sheet for the ODC5, it
shows using a N channel transistor. Has anyone used one of these
modules? Can I simplify and just send the positive signal? I would
assume that if i can, I can also use the same technique for the
Stamp's I/O's(switches,indicators,etc). Thanks.
Ian
Comments
I haven't used the Opto modules in a while, but a Web search looks like
they draw 18mA max from the control input and need at least 3.7V. The
Stamp and the PAK both can drive 18mA, but maybe not all at one time.
Both chips have a maximum current rating for the total. So for the PAK,
you can have about 130mA passing through the chip. The chip itself draws
80mA or so. So that gives you about 40 or 50mA to play with. If you are
drawing 18mA per pin, then two or three pins would put you right at the
limit and you probably want some safety margin. On the other hand, our
ratings are relatively conservative and your duty cycle will be less
than 100%, but you still don't want to push the envelope too hard.
The Stamp has a similar specs, so while you might be able to draw 30mA
through each pin, you have a limit of 60mA total or some such.
I wonder if the opto draws much current when off (I can't imagine it
does, but that would be easy to test with a ammeter). If so, maybe you
could use a pull up resistor to supply the on current and then just
switch the Stamp output to ground or an input. That wouldn't help with a
PAK-V though.
Hope that helps.
Al Williams
AWC
* NEW: New kits!
http://www.al-williams.com/kits.htm
>
Original Message
> From: iphillipsca [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=meNx-yw3G67mfmLNxlpwDncT2XXItt7YRAvlX_PlJOddcngwjH9s1cWWRD_foIY6aC7eGgM5GINEaz1pW-cI4gg]iphillips@s...[/url
> Sent: Saturday, March 08, 2003 2:35 PM
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] Using Opto Isolators
>
>
> I am building a large dc motor driver(still). I am using a PAK-V to
> drive very large MOSFETs(100v 180amp rating, I'll be using 15vdc to
> drive) and relays(12v 40amp). I would like to use a couple of Opto 22
> modules that I have laying around. In the data sheet for the ODC5, it
> shows using a N channel transistor. Has anyone used one of these
> modules? Can I simplify and just send the positive signal? I would
> assume that if i can, I can also use the same technique for the
> Stamp's I/O's(switches,indicators,etc). Thanks.
> Ian
>
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negative side of the Opto would probably be the best idea then. I've
got a couple of IRL540n's left that I can use. Thanks again.
Ian.
--- In basicstamps@yahoogroups.com, "Al Williams" <alw@a...> wrote:
> Hi Ian,
>
> I haven't used the Opto modules in a while, but a Web search looks
like
> they draw 18mA max from the control input and need at least 3.7V.
The
> Stamp and the PAK both can drive 18mA, but maybe not all at one
time.
> Both chips have a maximum current rating for the total. So for the
PAK,
> you can have about 130mA passing through the chip. The chip itself
draws
> 80mA or so. So that gives you about 40 or 50mA to play with. If you
are
> drawing 18mA per pin, then two or three pins would put you right at
the
> limit and you probably want some safety margin. On the other hand,
our
> ratings are relatively conservative and your duty cycle will be less
> than 100%, but you still don't want to push the envelope too hard.
>
> The Stamp has a similar specs, so while you might be able to draw
30mA
> through each pin, you have a limit of 60mA total or some such.
>
> I wonder if the opto draws much current when off (I can't imagine it
> does, but that would be easy to test with a ammeter). If so, maybe
you
> could use a pull up resistor to supply the on current and then just
> switch the Stamp output to ground or an input. That wouldn't help
with a
> PAK-V though.
>
> Hope that helps.
>
> Al Williams
> AWC
> * NEW: New kits!
> http://www.al-williams.com/kits.htm
>