Re: Studying back EMFs in Spice

From: Mike Engelhardt (nospam_at_spam.org)
Date: 12/17/04 

Date: Fri, 17 Dec 2004 00:07:15 GMT

Paul,

> I've been messing about chopping the voltage supplied to an inductor
> in spice, hoping to see a sharp spike of x thousand volts as the
> magnetic field collapses. So far though, no joy. I can only imagine
> I've not contrived an appropriate circuit that would demonstrate the
> effect. Can anyone post a simple schematic that does illustrate this
> property of inductors?

This is the basis of "Boost" DC/DC converters. Below is an
LTspice schematic doing this open loop.

--Mike

Version 4
*** 1 1056 680
WIRE 160 384 160 368
WIRE 160 288 160 272
WIRE 160 160 32 160
WIRE 32 160 32 176
WIRE 32 256 32 272
WIRE 0 448 0 416
WIRE 0 336 0 304
WIRE 0 304 112 304
WIRE 160 272 224 272
WIRE 288 272 336 272
WIRE 160 272 160 256
WIRE 336 272 336 288
WIRE 336 352 336 384
WIRE 160 176 160 160
FLAG 32 272 0
FLAG 160 384 0
FLAG 112 352 0
FLAG 0 448 0
FLAG 336 384 0
SYMBOL ind 144 160 R0
SYMATTR InstName L1
SYMATTR Value 10µ
SYMBOL sw 160 384 M180
WINDOW 0 28 89 Left 0
WINDOW 3 23 20 Left 0
SYMATTR InstName S1
SYMBOL voltage 32 160 R0
WINDOW 3 27 94 Left 0
SYMATTR Value 5
SYMATTR InstName V1
SYMBOL voltage 0 320 R0
SYMATTR InstName V2
SYMATTR Value PULSE(0 1 0 1u 1u 4u 10u)
SYMBOL diode 224 288 R270
WINDOW 0 32 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName D1
SYMBOL cap 320 288 R0
SYMATTR InstName C1
SYMATTR Value 1µ
TEXT 432 416 Left 0 !.model SW SW(Ron=.1 Roff=10Meg Vt=.5 Vh=--.4)
TEXT 432 392 Left 0 !.model D D(Ron=1. Roff=10Meg)
TEXT 430 364 Left 0 !.tran 10m