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1N5439: Varactor Diode or Zener

But you opened the thread by telling us that it didn't always work. You need to work out how much more current a 11.9V diode would pass at 12.0V than a 12.0V diode at 12.0V.

The LTSpice zener model has an explicit entry for breakdown voltage. I've hand-edited Spice models in LTSpice 4, but when I just tried to do it in LTSpice XVII I couldn't get anywhere, which was frustrating.

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details the Spice model ON-Semiconductor uses for its Spice model. The breakdown voltage at the test current is given at the bottom of page 3.

Reply to
Anthony William Sloman
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I also said that I am using external serial resistors to flatten the curve and pre-sorting to match them better.

I would rather measure them with meters. It's just a matter of matching the curves, no matter what the curves are.

1N2976B DO-4 5A would probably work better than 1N5349B DO-15 0.4A.

But (vertically mounted) DO-4 would make a very tall board. Ideally, i want axial mounted DO-X (just a bigger version of DO-15 in metal casing), perhaps 2A limit.

Reply to
Ed Lee

I finally persuaded LTSpice XVII to produce a model. The relevant adjustable parameter in the zener diode model is BV and I changed is it from 7.750 to 7.950 between the two zener diodes. That's worth about 120mA. Here is the text version of the .asc file.

The model is for a slightly smaller zener diode, than the one you use.

Version 4 SHEET 1 3520 704 WIRE 32 -112 -96 -112 WIRE 160 -112 32 -112 WIRE 32 -32 32 -112 WIRE 160 -32 160 -112 WIRE -96 16 -96 -112 WIRE 32 112 32 48 WIRE 160 112 160 48 WIRE -96 256 -96 96 WIRE -80 256 -96 256 WIRE 32 256 32 176 WIRE 32 256 -80 256 WIRE 160 256 160 176 WIRE 160 256 32 256 WIRE -80 304 -80 256 FLAG -80 304 0 SYMBOL zener 48 176 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D1 SYMATTR Value KDZ12B SYMATTR Description Diode SYMATTR Type diode SYMBOL zener 176 176 R180 WINDOW 0 24 64 Left 2 WINDOW 3 -146 -1 Left 2 SYMATTR InstName D2 SYMATTR Value KDZV12.2B SYMATTR Description Diode SYMATTR Type diode SYMBOL res 16 -48 R0 SYMATTR InstName R1 SYMATTR Value 3R9 SYMBOL res 144 -48 R0 SYMATTR InstName R2 SYMATTR Value 3R9 SYMBOL voltage -96 0 R0 WINDOW 3 -163 -220 Left 2 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR Value PULSE(11 14 0 100ms 0 10ms 1110ms 1) SYMATTR InstName V1 TEXT -264 688 Left 2 !.tran 0 110ms 0ms TEXT -264 480 Left 2 !.model KDZV12B D(Is=6.1497E-15 N=1.0456 Rs=1.1352E-2 Ikf=.87678 Cjo=3.4156E-10 M=.36291 Vj=.72255 Isr=5.7166E-12 Nr=2.5200 Bv=12.750 Ibv=4.0000E-2 Tt=1.8755E-7 Nbv=0.5600 Tbv1=7.0000E-4 Nbvl=62.400 Ibvl=0.6000E-9 Vpk=13.5 mfg=Rohm type=Zener) TEXT -264 544 Left 2 !.model KDZV12.2B D(Is=6.1497E-15 N=1.0456 Rs=1.1352E-2 Ikf=.87678 Cjo=3.4156E-10 M=.36291 Vj=.72255 Isr=5.7166E-12 Nr=2.5200 Bv=12.950 Ibv=4.0000E-2 Tt=1.8755E-7 Nbv=0.5600 Tbv1=7.0000E-4 Nbvl=62.400 Ibvl=0.6000E-9 Vpk=13.5 mfg=Rohm type=Zener)

Reply to
Anthony William Sloman

Putting zeners in series would not run into problems.

Reply to
albert

Actually, it could. 12V "zeners" are avalanche diode. 6V zeners are half-way between breakdown diodes which rely on the Zener breakdown mechanism and avalanche diodes. The knee isn't as sharp , and you have two of the less sharp knees in series.

This might not be a problem, but it could be. Ed Lee isn't the world clearest thinker, so we don't really know what he is trying to do.

Reply to
Anthony William Sloman

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