White LED Spice Model
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From: Jim Thompson on 28 Jan 2010 13:39 On Thu, 28 Jan 2010 10:26:17 -0800, "Paul Hovnanian P.E." <paul(a)hovnanian.com> wrote: >Jim Thompson wrote: > >> On Wed, 27 Jan 2010 19:28:57 -0700, "Paul Hovnanian P.E." >> <Paul(a)Hovnanian.com> wrote: >> >>>I found my old HP-41C curve fit program card. Then I found my old >>>HP-41C. >>> >>>The model I get from your curve is: >>> >>>.MODEL MyWhiteLED D >>>+ IS = 4.4249E-9 >>>+ N = 8.3923 >>>+ RS = 7.7980 >>> >>>No subcircuits required. >> >> I'm not sure if that will work over temperature. >> >> It would be interesting if someone could take data at several >> different temperatures. It'll be tricky, you have to be quick or >> self-heating will screw up the result. Maybe with a plotting curve >> tracer? > >That's a good point. N is often used as a 'fudge factor' for Vt, so for wild >values of N (greater than 2.0 or less than 1.0) it would be reasonable to >expect that nVt may vary with temp (or other conditions) in some different >manner than kT/q. > >Where I've seen weird values of N pop up, SPICE started to fall apart for >anything other then approximate values. It was time to toss the standard >model and go with something cooked up by the physicists. > EG is also a variable of interest. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
From: Jim Thompson on 28 Jan 2010 13:42 On Thu, 28 Jan 2010 10:36:28 -0800, "Paul Hovnanian P.E." <paul(a)hovnanian.com> wrote: >Jim Thompson wrote: > >> On Wed, 27 Jan 2010 19:28:57 -0700, "Paul Hovnanian P.E." >> <Paul(a)Hovnanian.com> wrote: >> >>>I found my old HP-41C curve fit program card. Then I found my old >>>HP-41C. >>> >>>The model I get from your curve is: >>> >>>.MODEL MyWhiteLED D >>>+ IS = 4.4249E-9 >>>+ N = 8.3923 >>>+ RS = 7.7980 >>> >>>No subcircuits required. >> >> BTW: "your curve"? Whose curve? You clip too much, Paul. > >Sorry. I took your spice model from your post, ran it for 70 current points >and poked every tenth one into my program. I didn't have the table function >values (the PDF you posted in a.b.s.e which I assume were your original >measured data points). By the way, there appears to be an outlying data >point in your graph. > >So I was actually curve fitting to your curve fit. I finally figured that out ;-) I first thought someone I had filtered out, like from googlegroups, had posted some data ;-) The "outlying data point" is an unknown, so PSpice stops and _holds_ at the last PWL data point. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
From: Paul Hovnanian P.E. on 28 Jan 2010 16:35 Jim Thompson wrote: > > On Thu, 28 Jan 2010 10:26:17 -0800, "Paul Hovnanian P.E." > <paul(a)hovnanian.com> wrote: > > >Jim Thompson wrote: > > > >> On Wed, 27 Jan 2010 19:28:57 -0700, "Paul Hovnanian P.E." > >> <Paul(a)Hovnanian.com> wrote: > >> > >>>I found my old HP-41C curve fit program card. Then I found my old > >>>HP-41C. > >>> > >>>The model I get from your curve is: > >>> > >>>.MODEL MyWhiteLED D > >>>+ IS = 4.4249E-9 > >>>+ N = 8.3923 > >>>+ RS = 7.7980 > >>> > >>>No subcircuits required. > >> > >> I'm not sure if that will work over temperature. > >> > >> It would be interesting if someone could take data at several > >> different temperatures. It'll be tricky, you have to be quick or > >> self-heating will screw up the result. Maybe with a plotting curve > >> tracer? > > > >That's a good point. N is often used as a 'fudge factor' for Vt, so for wild > >values of N (greater than 2.0 or less than 1.0) it would be reasonable to > >expect that nVt may vary with temp (or other conditions) in some different > >manner than kT/q. > > > >Where I've seen weird values of N pop up, SPICE started to fall apart for > >anything other then approximate values. It was time to toss the standard > >model and go with something cooked up by the physicists. > > > > EG is also a variable of interest. Right. That kicks in when you model diode's temperature dependence. But here's a question: What happens to the original subcircuit based model, which is based on a 1N4148? The activation energy isn't specified, so you're going to get Spice's default (probably for a silicon diode). As we are dealing with a (probably) blue LED, the chemistry will be diffeent, and we probably should find a more appropriate value for EG. -- Paul Hovnanian mailto:Paul(a)Hovnanian.com ------------------------------------------------------------------ professor; n, One who talks in someone else's sleep.
From: Jim Thompson on 28 Jan 2010 17:27 On Thu, 28 Jan 2010 14:35:13 -0700, "Paul Hovnanian P.E." <Paul(a)Hovnanian.com> wrote: >Jim Thompson wrote: >> >> On Thu, 28 Jan 2010 10:26:17 -0800, "Paul Hovnanian P.E." >> <paul(a)hovnanian.com> wrote: >> >> >Jim Thompson wrote: >> > >> >> On Wed, 27 Jan 2010 19:28:57 -0700, "Paul Hovnanian P.E." >> >> <Paul(a)Hovnanian.com> wrote: >> >> >> >>>I found my old HP-41C curve fit program card. Then I found my old >> >>>HP-41C. >> >>> >> >>>The model I get from your curve is: >> >>> >> >>>.MODEL MyWhiteLED D >> >>>+ IS = 4.4249E-9 >> >>>+ N = 8.3923 >> >>>+ RS = 7.7980 >> >>> >> >>>No subcircuits required. >> >> >> >> I'm not sure if that will work over temperature. >> >> >> >> It would be interesting if someone could take data at several >> >> different temperatures. It'll be tricky, you have to be quick or >> >> self-heating will screw up the result. Maybe with a plotting curve >> >> tracer? >> > >> >That's a good point. N is often used as a 'fudge factor' for Vt, so for wild >> >values of N (greater than 2.0 or less than 1.0) it would be reasonable to >> >expect that nVt may vary with temp (or other conditions) in some different >> >manner than kT/q. >> > >> >Where I've seen weird values of N pop up, SPICE started to fall apart for >> >anything other then approximate values. It was time to toss the standard >> >model and go with something cooked up by the physicists. >> > >> >> EG is also a variable of interest. > >Right. That kicks in when you model diode's temperature dependence. But >here's a question: What happens to the original subcircuit based model, >which is based on a 1N4148? The activation energy isn't specified, so >you're going to get Spice's default (probably for a silicon diode). As >we are dealing with a (probably) blue LED, the chemistry will be >diffeent, and we probably should find a more appropriate value for EG. I agree. My subcircuit fit was accidentally fallen into while just noodling around ;-) If someone will take data at 3 or more temperatures, I'll try to fit it. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
From: Paul Hovnanian P.E. on 29 Jan 2010 16:06
Jim Thompson wrote: > On Thu, 28 Jan 2010 10:36:28 -0800, "Paul Hovnanian P.E." > <paul(a)hovnanian.com> wrote: > >>Jim Thompson wrote: >> >>> On Wed, 27 Jan 2010 19:28:57 -0700, "Paul Hovnanian P.E." >>> <Paul(a)Hovnanian.com> wrote: >>> >>>>I found my old HP-41C curve fit program card. Then I found my old >>>>HP-41C. >>>> >>>>The model I get from your curve is: >>>> >>>>.MODEL MyWhiteLED D >>>>+ IS = 4.4249E-9 >>>>+ N = 8.3923 >>>>+ RS = 7.7980 >>>> >>>>No subcircuits required. >>> >>> BTW: "your curve"? Whose curve? You clip too much, Paul. >> >>Sorry. I took your spice model from your post, ran it for 70 current >>points and poked every tenth one into my program. I didn't have the table >>function values (the PDF you posted in a.b.s.e which I assume were your >>original measured data points). By the way, there appears to be an >>outlying data point in your graph. >> >>So I was actually curve fitting to your curve fit. > > I finally figured that out ;-) I first thought someone I had filtered > out, like from googlegroups, had posted some data ;-) > > The "outlying data point" is an unknown, so PSpice stops and _holds_ > at the last PWL data point. Evidently the PSpice people haven't learned anything about dry-labbing and tossing undesirable data points out from the climatologists. ;-) -- Paul Hovnanian paul(a)hovnanian.com ---------------------------------------------------------------------- Have gnu, will travel. |