[time-nuts] HP 105B Modification

Gerhard Hoffmann dk4xp at hoffmann-hochfrequenz.de
Wed Dec 9 20:27:08 UTC 2009


On Wed, 09 Dec 2009 15:08:15 +1300, you wrote:


>Another point is the LTSpice LED model isn't particularly accurate for 
>simulating the effects of temperature variations.
>Does anyone knows of more accurate LTSpice compatible LED models?
>
>The LED model voltage drop increases with temperature even at low 
>current, whilst the voltage drop across a real LED at low currents 
>decreases with temperature.
>In practice the variation in the LED forward drop tracks the variation 
>in the pnp Vbe quite well.

I have used this model and also this diode:

* from OSRAM TOPLED library
*
*
.MODEL LH_T676_typ D
+ IS=5.5621E-24
+ N=1.3448
+ RS=4.3842
+ IKF=17.186E-3

Comparing the current with a BC860 PNP and a 15 Ohm emitter resistor
worked quite nicely, so I had no reason to investigate the model.
(as you wrote, too)

I also tried to operate a power LED with the base bias divider current
of all 6 distribution channels combined(70 mA tot.) to recycle the current
but it seemed that the power LED had more Ohmic resistance than
6 times LHT676. Could be just my sample, and it was close to the max. specs.

Gerhard







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