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From: John Larkin on 4 Apr 2010 11:02


I recall somewhere, maybe in this ng, the procedure for making an
ideal diode in LT Spice. But I can't find it now. Help!

The ideal diode should be a stock pulldown part. I wonder why it's
not.

And why can't I change the voltage of one of their pull-from-the-list
zeners? That would sure be convenient.

John

From: Jim Thompson on 4 Apr 2010 11:34
On Sun, 04 Apr 2010 08:02:46 -0700, John Larkin
<jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote:

>
>
>I recall somewhere, maybe in this ng, the procedure for making an
>ideal diode in LT Spice. But I can't find it now. Help!
>
>The ideal diode should be a stock pulldown part. I wonder why it's
>not.
>
>And why can't I change the voltage of one of their pull-from-the-list
>zeners? That would sure be convenient.
>
>John

Perfect diode...

http://analog-innovations.com/SED/PerfectDiodeForChargerIsolation.pdf

Though I'd think one could conjure up a behavioral rendition. I'll
think on it ;-)

Make your own zener...

****
..SUBCKT MyZENER 1 2 PARAMS: BV=10 IBV=1m RS=1 IS=10f CJO=10pF
D1 1 2 DZ
..MODEL DZ D(
+ IS = {IS}
+ RS = {RS}
+ N = 1
+ EG = 1.11
+ BV = {BV}
+ IBV = {IBV}
+ CJO = {CJO}
+ VJ = 0.75
+ M = 0.33 )
..ENDS MyZENER
****

I have a configurable symbol in my symbol library.

...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 |

The only thing bipartisan in this country is hypocrisy
From: Jim Thompson on 4 Apr 2010 11:58
On Sun, 04 Apr 2010 08:34:53 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote:

>On Sun, 04 Apr 2010 08:02:46 -0700, John Larkin
><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote:
>
>>
>>
>>I recall somewhere, maybe in this ng, the procedure for making an
>>ideal diode in LT Spice. But I can't find it now. Help!
>>
>>The ideal diode should be a stock pulldown part. I wonder why it's
>>not.
>>
>>And why can't I change the voltage of one of their pull-from-the-list
>>zeners? That would sure be convenient.
>>
>>John
>
>Perfect diode...
>
>http://analog-innovations.com/SED/PerfectDiodeForChargerIsolation.pdf
>
>Though I'd think one could conjure up a behavioral rendition. I'll
>think on it ;-)
>

Sure there is, just open "CompliantParts.SLB" on the Subcircuits and
Symbols page of my website (it's plain text).

A current source with no reverse current and a finite curvature can be
thought of as the same as a (nearly) ideal diode.

It's TANH, so all derivatives are there and smooth, so it converges
nicely.

Just set a transition region and a max current to suit.

I'll generate something more understandable by Larkin when I have a
free moment :-)

Maybe a symbol with parameters to make it easy :-)

...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 |

The only thing bipartisan in this country is hypocrisy
From: Martin Riddle on 4 Apr 2010 12:32


"John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in
message news:a9ahr5t7ea0jdtp4r0mb3a1ro5p0ohg1tl(a)4ax.com...
>
>
> I recall somewhere, maybe in this ng, the procedure for making an
> ideal diode in LT Spice. But I can't find it now. Help!
>
> The ideal diode should be a stock pulldown part. I wonder why it's
> not.
>
> And why can't I change the voltage of one of their pull-from-the-list
> zeners? That would sure be convenient.
>
> John
>

You can add Capacitors to the database, but they left out the interface
to add a diode.
I think you can go into C:\Program
Files\LTC\LTspiceIV\lib\cmp\standard.dio and just add your own.
It might choke on multi-line model.

Cheers



From: John Larkin on 4 Apr 2010 12:44
On Sun, 04 Apr 2010 08:02:46 -0700, John Larkin
<jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote:

>
>
>I recall somewhere, maybe in this ng, the procedure for making an
>ideal diode in LT Spice. But I can't find it now. Help!
>
>The ideal diode should be a stock pulldown part. I wonder why it's
>not.
>
>And why can't I change the voltage of one of their pull-from-the-list
>zeners? That would sure be convenient.
>
>John

Never mind, I figured out the ideal diode.

Click the D thing and add a diode to the schematic. Rename it Didl.

Then add a spice directive string nearby...

..model Didl D(Ron=0.1 Roff=1G Vfwd=0)

with whatever values you think are close to ideal. For some reason, my
sim slows down if I use too low an Ron value. The 0.1 is good enough.

The ideal zener is then just a voltage in series with this diode.


I'm doing what the controls guys call a "high select", to create a
voltage that's the greater of two inputs, to switch my power supply
from constant-current to constant-voltage mode. I did a clever thing
with two switch elements, but it did funny things sometimes and was
too hard to think about.


John


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