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Pspice transfer function

When i test the actual circuit, the output has a transition "hump" between the linear I/O part and the regulation part; it is about 900mV in amplitude. The Spice does not show it; why?

** Regulator.asc Version 4 SHEET 1 880 680 WIRE -400 208 -400 -32 WIRE -368 -32 -400 -32 WIRE -272 -32 -288 -32 WIRE -272 144 -272 -32 WIRE -240 144 -272 144 WIRE -32 144 -160 144 WIRE -32 144 -32 64 WIRE -32 176 -32 144 WIRE -32 336 -32 272 WIRE 64 -32 -272 -32 WIRE 64 144 -32 144 WIRE 64 224 32 224 WIRE 64 224 64 208 WIRE 112 64 -32 64 WIRE 112 64 112 32 WIRE 256 -32 160 -32 WIRE 256 64 256 -32 WIRE 256 224 64 224 WIRE 256 224 256 144 WIRE 256 272 256 224 WIRE 256 384 256 352 WIRE 336 384 256 384 WIRE 336 384 336 240 WIRE 368 -32 256 -32 WIRE 368 128 368 -32 WIRE 368 240 336 240 WIRE 368 240 368 192 WIRE 368 272 368 240 WIRE 480 -32 368 -32 WIRE 480 128 480 -32 WIRE 480 240 368 240 WIRE 480 240 480 208 FLAG -400 288 0 FLAG -32 400 0 FLAG 368 272 0 SYMBOL npn 64 32 R270 WINDOW 0 136 33 VRight 0 WINDOW 3 100 7 VRight 0 SYMATTR InstName Q1 SYMATTR Value ZTX849 SYMBOL Misc\\\\battery -400 192 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 38V SYMBOL res -272 -48 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R1 SYMATTR Value 1e-3 SYMBOL npn 32 176 M0 WINDOW 0 103 58 Left 0 WINDOW 3 77 24 Left 0 SYMATTR InstName Q3 SYMATTR Value FMMT459 SYMBOL zener -16 400 R180 WINDOW 0 24 72 Left 0 WINDOW 3 62 38 Left 0 SYMATTR InstName D1 SYMATTR Value BZX84C12L SYMBOL cap 48 144 R0 SYMATTR InstName C1 SYMATTR Value 150pF SYMBOL current -240 144 R270 WINDOW 0 -32 40 VBottom 0 WINDOW 3 32 40 VTop 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName I1 SYMATTR Value 1mA SYMBOL cap 352 128 R0 SYMATTR InstName C2 SYMATTR Value .01µF SYMBOL res 240 48 R0 SYMATTR InstName R2 SYMATTR Value 175K SYMBOL res 240 256 R0 SYMATTR InstName R3 SYMATTR Value 125K SYMBOL res 464 112 R0 SYMATTR InstName R4 SYMATTR Value 10K TEXT 304 -72 Left 0 ;N006 TEXT -96 -64 Left 0 ;N002 TEXT 144 248 Left 0 ;N005 TEXT -128 120 Left 0 ;N003 TEXT -328 -176 Left 0 !.dc V1 31 33 0.01 TEXT -328 -144 Left 0 !.LIB D:\\\\SPICE\\\\ZMODELS.LIB
Reply to
Robert Baer
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"Robert Baer" schrieb im Newsbeitrag news:kfWke.6344$ snipped-for-privacy@newsread3.news.pas.earthlink.net...

Hello Robert, Where did you uy the 1mA-current source? Type:? Manufacturer:?

Is it just a schematic simplification? Then please provide the real circuit(schematic) for this current source.

Is this Z-diode in the real circuit or is this also some kind of simplification for another device?

Have you tried to replace this crrent source with a simple 33k resistor. It would be very interesting how your real circuit behaves then compared to the simulation.

Best regards, Helmut

Reply to
Helmut Sennewald

The current source is a DMOSFET; the DN3545 and a 2.2K resistor. Do not know how to model that. This was tested using an E-B transistor junction (in reverse) for the zener; the transistor type was selected to have no negative R effects and have low noize at all currents from nanoamps to milliamps. The "hump" mentioned was measured not only with meters, but also seen on a curve tracer.

Reply to
Robert Baer

Hello Robert,

You could try to find a SPICE model of a similar device from another manufacturer.

That's it. If you replace this "bad" device with a real Zener diode, the problem should go away. It's a very very bad idea to use the B-E breakdown as a Zener-diode for any serious application.

I rate the whole thing not as a problem to find a SPICE model for the B-E breakdown. It's simply a bad design practice to use this B-E breakdown as a reference voltage.

Best regards, Helmut

Reply to
Helmut Sennewald

Sorry, this particular transistor E-B junction is superior to any zener diode i have seen. Furthermore, if i add in the B-C junction in forward mode, i get a voltage reference good to 180C. Furthermore, when i replace it with a UCC2801 (zeners near 13.5V), i see exactly the same thing.

Reply to
Robert Baer

----------- SNIPped for brevity -----------

The "bump" is seen at any speed - curve tracer or manual input voltage increments. The "bump" is seen "at" the transition between the linear I-V from zero to the regulation at the output. I have experimented with various voltage dividers, the E-B-C transistor, the UCC2801 (which is what will be used) and a 15V zener. Depending on what i use, i see two different kinds of curves.

1) I-V slope abruptly changes to a lower value (higher R) during turn-on of the depletion mode MOSFET, then abruptly flat ("infinite" R) at regulation; no "bump". 2) I-V slope abruptly changes to a higher value (lower R) during turn-on of the depletion mode MOSFET, then abruptly flat ("infinite" R) at regulation; has "bump". I fiddled around with a few FETS in the library (there are no models for a depletion mode FET) to replace the current source. The result is similar to case #1 above, except the first transition is not abrupt (enhancement mode FETS are log Id VS Vgs, and maybe depletion mode FETS are loglog?).

-------------- Version 4 SHEET 1 880 680 WIRE -400 208 -400 -32 WIRE -368 -32 -400 -32 WIRE -272 -32 -288 -32 WIRE -272 144 -272 -32 WIRE -80 144 -96 144 WIRE -80 192 -112 192 WIRE -80 192 -80 144 WIRE -32 144 -80 144 WIRE -32 144 -32 64 WIRE -32 176 -32 144 WIRE -32 336 -32 272 WIRE 64 -32 -272 -32 WIRE 64 144 -32 144 WIRE 64 224 32 224 WIRE 64 224 64 208 WIRE 112 64 -32 64 WIRE 112 64 112 32 WIRE 256 -32 160 -32 WIRE 256 64 256 -32 WIRE 256 224 64 224 WIRE 256 224 256 144 WIRE 256 272 256 224 WIRE 256 384 256 352 WIRE 336 384 256 384 WIRE 336 384 336 240 WIRE 368 -32 256 -32 WIRE 368 128 368 -32 WIRE 368 240 336 240 WIRE 368 240 368 192 WIRE 368 272 368 240 WIRE 480 -32 368 -32 WIRE 480 128 480 -32 WIRE 480 240 368 240 WIRE 480 240 480 208 FLAG -400 288 0 FLAG -32 400 0 FLAG 368 272 0 SYMBOL npn 64 32 R270 WINDOW 0 136 33 VRight 0 WINDOW 3 100 7 VRight 0 SYMATTR InstName Q1 SYMATTR Value ZTX849 SYMBOL Misc\\\\battery -400 192 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 38V SYMBOL res -272 -48 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R1 SYMATTR Value 1e-3 SYMBOL npn 32 176 M0 WINDOW 0 3 106 Left 0 WINDOW 3 -80 133 Left 0 SYMATTR InstName Q3 SYMATTR Value FMMT459 SYMBOL zener -16 400 R180 WINDOW 0 24 72 Left 0 WINDOW 3 62 38 Left 0 SYMATTR InstName D1 SYMATTR Value BZX84C6V2L SYMBOL cap 48 144 R0 SYMATTR InstName C1 SYMATTR Value 150pF SYMBOL cap 352 128 R0 SYMATTR InstName C2 SYMATTR Value .01µF SYMBOL res 240 48 R0 SYMATTR InstName R2 SYMATTR Value 175K SYMBOL res 240 256 R0 SYMATTR InstName R3 SYMATTR Value 125K SYMBOL res 464 112 R0 SYMATTR InstName R4 SYMATTR Value 10K SYMBOL nmos -272 192 R270 WINDOW 0 69 11 VRight 0 WINDOW 3 -16 -37 VRight 0 SYMATTR InstName M1 SYMATTR Value IRL3915 SYMBOL Misc\\\\battery -208 192 R270 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 WINDOW 0 -53 3 VRight 0 WINDOW 3 -54 42 VRight 0 SYMATTR InstName V2 SYMATTR Value 4.25V SYMBOL res -80 128 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 -56 57 VTop 0 SYMATTR InstName R5 SYMATTR Value 2.2K TEXT 304 -72 Left 0 ;N006 TEXT -96 -64 Left 0 ;N002 TEXT 144 248 Left 0 ;N005 TEXT -56 40 Left 0 ;N003 TEXT -328 -176 Left 0 !.dc V1 10 25 0.001 TEXT -328 -144 Left 0 !.LIB D:\\\\SPICE\\\\ZMODELS.LIB

Reply to
Robert Baer

Hello Robert,

Is this "bump" a dynamic behaviour when the inut voltage is ramped up with a certain speed or is it also visible when you manually increase the input voltage very slowly?

Means this "bump" a higher or a lower voltage?

Best regards, Helmut

Reply to
Helmut Sennewald

----------- SNIPped for brevity -----------

Offending part: the UCC2801 has a *large* negative resistance "kink"; that is what caused the wierd curves seen. The compensation capacitor used was large enough, in combination to the gain loss in the feedback divider, allowed the regulator to operate smoothly at all measured points.

And that brings up the question as to how to model such a beastie...

Reply to
Robert Baer

"Robert Baer" schrieb im Newsbeitrag news:7Czle.1134$ snipped-for-privacy@newsread2.news.pas.earthlink.net...

Hello Robert,

You could add a resistor in series with a negative resistance, e.g. -200 Ohm. A more complex behaviour can be modeled with B-sources. Be warned, dealing with negative resistance always causes a lot of headache with convergence.

Btw, the DN3545 model is on the website of Supertex. It's a 4-pin subcircuit. This requires to change the Prefix in the instance of your "nmos4" to X. Don't change the original symbol!!! An instance is the already placed symbol in your schematic.

I have send my LTspice file to your email address. I can't attach it here because it contains too long lines. Only very experienced LTspice users could restruct these splitted lines. If somebody eles wants this file, then send me an email so I can send it to you.

Best regards, Helmut

PS: We are simulating here with LTspice and not wit PSPICE. LTspice is free and unlimited SPICE with a GUI. It's also named SwitcherCADIII. Download it from here:

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There is also an independent user group. It's a moderated group and it requires to register for access. There are over 6000 messages now there and hundreds of examples, links and other stuff.

formatting link

I am one of the two moderators of this group.

Supertex SPICE model

--------------------

*
  • MARCH 07, 2000
*
  • COMPOSITE MODEL FOR DN3545
  • ..SUBCKT DN3545 1 2 3 4
*
  • NODE 1 = DRAIN
  • NODE 2 = GATE
  • NODE 3 = SOURCE
  • NODE 4 = BODY
  • MOS1 11 2 3 4 ND_DMOS L=2.5E-06 W=58E-3 JFET 1 3 11 JMOD 1 DBODY 4 1 DMOS R 1 11 1E+6
  • ..MODEL ND_DMOS NMOS
  • LEVEL=3 UO=307 VTO=-1.829 NFS=5.0E+11
  • TOX=5E-08 NSUB=3.59E+15 NSS=0 VMAX=5E+04
  • RS=1E-06 RD=1E-06 RSH=5000 CGDO=1.96E-9
  • CGSO=1.5E-09 CGBO=0 CBD=4.0E-11 CBS=1.0E-15
  • MJ=0.5003 MJSW=0.33 IS=5E-13 PB=0.4507
  • FC=0.5 XJ=1.2E-05 LD=0 DELTA=0
  • THETA=0 ETA=1.0E-6 KAPPA=1.0E-6
  • ..MODEL DMOS D
  • IS=281.0E-15 N=0.950 RS=2.5
  • BV=450 IBV=1.0E-3 TT=1.0E-6
  • ..MODEL JMOD NJF
  • VTO=-3.5 BETA=0.100 IS=281E-15
  • RD=9.0 LAMBDA=0 ..ENDS
Reply to
Helmut Sennewald

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