Re; I need creative ideas.....
Archiver
Posts: 46,084
Chis, I've lost track of the exact application you have
[noparse][[/noparse]if I ever knew!] - Sometimes it'sbest to dig ourselves
out of the hole we've designed ourselves into rather than
digging it deeper... :-) I recall something about boards
already made etc... so you've got a pretty deep hole..
However if you want to get rid of dissipation, even if
energy conservation is for wimps, one logical way to
go is pulses. Your 50usec timing implies you might
just set something with a 2us pulse and read that.
You could have an on pulse and an off pulse rather than
the continuous current to an optocoupler.
Another thing to do would be to get a much more sensitive
coupler so you could run at 1ma instead of 9ma taking you
down to a half watt resistor with 1/4 watt dissipation.
This would fit in the same board space....
You worry about the resistor getting hot - did you actually
measure the voltage across it? Watts = volts*volts/resistance.
You could at least see if that looks good.
If there were a HF signal it would have to be very high VOLTAGE
to dissiapte that extra power - seems unlikely unless you are
working with power RF unit. [noparse][[/noparse]In the case of a series capacitor
this would be an effect but not so much with a reisitor as you
have...].
Good luck running an opto with less current - a likely way
to go.... premena
Date: Sat, 30 Jun 2001 22:36:06 -0400
From: "Chris Loiacono (E-mail)" <chris01@t...>
>
Original Message
> From: Chris Loiacono [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=_xBjO60fK7d-1iceoSnsHsOQu2FIhNmNultQyma3PLZF1sKP6EHllEyyIt5HzLioZ1pr26YZz49I]chris@m...[/url
> Sent: Saturday, June 30, 2001 9:50 PM
> To: 'basicstamps@yahoogroups.com'
> Subject: RE: [noparse][[/noparse]basicstamps] Re: I need creative ideas.....
snippity...
> ago....It's just too slow. I need 50 usec response on and off
> here. It's also common practice to use a pair of
> inverse-parallel diodes to protect against reverse current,
> and I have used a pair of opto's LED's to accomplish this.
> The cap will give me a phase shift, will it not? That would
> mess up my timing again.
snippity...
> I just can't figure out why the resistor is getting so hot!
> I was targeting 60C or less, and even when I over size the
> resistor by 100%, it still goes over 105C.
> Could there be a constant HF signal on the line causing this,
> rather than random spikes??
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[noparse][[/noparse]if I ever knew!] - Sometimes it'sbest to dig ourselves
out of the hole we've designed ourselves into rather than
digging it deeper... :-) I recall something about boards
already made etc... so you've got a pretty deep hole..
However if you want to get rid of dissipation, even if
energy conservation is for wimps, one logical way to
go is pulses. Your 50usec timing implies you might
just set something with a 2us pulse and read that.
You could have an on pulse and an off pulse rather than
the continuous current to an optocoupler.
Another thing to do would be to get a much more sensitive
coupler so you could run at 1ma instead of 9ma taking you
down to a half watt resistor with 1/4 watt dissipation.
This would fit in the same board space....
You worry about the resistor getting hot - did you actually
measure the voltage across it? Watts = volts*volts/resistance.
You could at least see if that looks good.
If there were a HF signal it would have to be very high VOLTAGE
to dissiapte that extra power - seems unlikely unless you are
working with power RF unit. [noparse][[/noparse]In the case of a series capacitor
this would be an effect but not so much with a reisitor as you
have...].
Good luck running an opto with less current - a likely way
to go.... premena
Date: Sat, 30 Jun 2001 22:36:06 -0400
From: "Chris Loiacono (E-mail)" <chris01@t...>
>
Original Message
> From: Chris Loiacono [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=_xBjO60fK7d-1iceoSnsHsOQu2FIhNmNultQyma3PLZF1sKP6EHllEyyIt5HzLioZ1pr26YZz49I]chris@m...[/url
> Sent: Saturday, June 30, 2001 9:50 PM
> To: 'basicstamps@yahoogroups.com'
> Subject: RE: [noparse][[/noparse]basicstamps] Re: I need creative ideas.....
snippity...
> ago....It's just too slow. I need 50 usec response on and off
> here. It's also common practice to use a pair of
> inverse-parallel diodes to protect against reverse current,
> and I have used a pair of opto's LED's to accomplish this.
> The cap will give me a phase shift, will it not? That would
> mess up my timing again.
snippity...
> I just can't figure out why the resistor is getting so hot!
> I was targeting 60C or less, and even when I over size the
> resistor by 100%, it still goes over 105C.
> Could there be a constant HF signal on the line causing this,
> rather than random spikes??
________________________________________________________________
GET INTERNET ACCESS FROM JUNO!
Juno offers FREE or PREMIUM Internet access for less!
Join Juno today! For your FREE software, visit:
http://dl.www.juno.com/get/tagj.