Hi all, I've been unable to get sensible results from simulating the voltage spike inductors generate when their magnetic fields collapse. The only possibility I can think of for this failure is that the standard inductor models have insufficient parameters for this purpose and require an extended parameter set. Like many of y'all I use LTspice, btw. Any ideas?
Spice modelling of back EMF
Started by ●March 22, 2016
Reply by ●March 22, 20162016-03-22
On Tuesday, March 22, 2016 at 2:05:25 PM UTC-4, Cursitor Doom wrote:> Hi all, > > I've been unable to get sensible results from simulating the voltage > spike inductors generate when their magnetic fields collapse. The only > possibility I can think of for this failure is that the standard inductor > models have insufficient parameters for this purpose and require an > extended parameter set. Like many of y'all I use LTspice, btw. > Any ideas?you are doing something wrong in your simulation. THe spice stadard inductor model works fine for that. Connect a pulsed current source to an inductor.. the voltage will spike when the current shuts off Mark
Reply by ●March 22, 20162016-03-22
On 22/03/16 19:02, Cursitor Doom wrote:> Hi all, > > I've been unable to get sensible results from simulating the voltage > spike inductors generate when their magnetic fields collapse. The only > possibility I can think of for this failure is that the standard inductor > models have insufficient parameters for this purpose and require an > extended parameter set. Like many of y'all I use LTspice, btw. > Any ideas? >Show your circuit. LTspice's inductor model is plenty good for this. Jeroen Belleman
Reply by ●March 22, 20162016-03-22
On Tue, 22 Mar 2016 18:02:10 -0000 (UTC), Cursitor Doom <curd@notformail.com> wrote:>Hi all, > >I've been unable to get sensible results from simulating the voltage >spike inductors generate when their magnetic fields collapse. The only >possibility I can think of for this failure is that the standard inductor >models have insufficient parameters for this purpose and require an >extended parameter set. Like many of y'all I use LTspice, btw. >Any ideas?Add some shunt resistance and/or capacitance to avoid singularities. That's realistic anyhow. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●March 22, 20162016-03-22
On Tue, 22 Mar 2016 18:02:10 -0000 (UTC), Cursitor Doom <curd@notformail.com> wrote:>Hi all, > >I've been unable to get sensible results from simulating the voltage >spike inductors generate when their magnetic fields collapse. The only >possibility I can think of for this failure is that the standard inductor >models have insufficient parameters for this purpose and require an >extended parameter set. Like many of y'all I use LTspice, btw. >Any ideas?The standard inductor model deals only with current and voltage. If you are seeking a model that reflects behavior when you force an externally-induced field you'll need to write your own subcircuit. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | The touchstone of liberalism is intolerance
Reply by ●March 22, 20162016-03-22
Okay, gentlemen, thanks for the suggestions. I've found the problem - seems to be the box running LTS on Linux under WINE. No probs on the Windows installations, so nothing you fine people can assist me with. I'll post to a more appropriate Linux/WINE forum see if anyone there can figure it out. Thanks!
Reply by ●March 22, 20162016-03-22
On 22/03/16 20:50, Cursitor Doom wrote:> Okay, gentlemen, thanks for the suggestions. I've found the problem - > seems to be the box running LTS on Linux under WINE. No probs on the > Windows installations, so nothing you fine people can assist me with. > I'll post to a more appropriate Linux/WINE forum see if anyone there can > figure it out.That's even more reason to post your circuit! I'm runnning LTSpice under Wine in Linux. I see inductive spikes just fine. Jeroen Belleman
Reply by ●March 22, 20162016-03-22
On Tue, 22 Mar 2016 21:00:05 +0100, Jeroen Belleman wrote:> That's even more reason to post your circuit! I'm runnning LTSpice under > Wine in Linux. I see inductive spikes just fine. > > Jeroen BellemanI don't blame LT or Wine on reflection. I had an update for my Fedora installation a few days ago and something definitely got corrupted. I lost all my menus and have had to invoke applications from the command line in a terminal. I'd put money on these two things being connected, as various other things have been behaving rather oddly since as well.
Reply by ●March 22, 20162016-03-22
<makolber@yahoo.com> wrote in message news:f8802a61-8e23-476f-a750-5eae5dc9fcb1@googlegroups.com...> Connect a pulsed current source to an inductor.. > the voltage will spike when the current shuts offActually, it will always spike, going both up and down. If you set the risetime to zero, you'll even get a divide by zero error! (But then, SPICE doesn't *do* discontinuous functions, so that should be no surprise.) A real inductor has RLC elements around it, equivalent to loss and parasitic capacitance and stuff. This limits the voltage, even if an ideal CCS were applied. A real "current source" exhibits finite capacitance and resistance, and a finite compliance range, so tends to saturate for large voltage changes. The common case of e.g. a solenoid driver or flyback SMPS, is better seen as an impedance mismatch situation. If the drive impedance were always low, the voltage would always be well-defined (but the current will rise arbitrarily -- for a pure inductive load that is). If the drive impedance is switched*, then the voltage is well-defined when the switch is on (low resistance, load exposed to a constant voltage source), and only the current is well-defined when the switch is off (high resistance, load exposed to constant current source; that current being zero, usually). *A quite reasonable model of a switch, is something which goes from a high resistance state to a low resistance state fairly quickly. Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
Reply by ●March 22, 20162016-03-22
On Tue, 22 Mar 2016 18:04:17 -0500, Tim Williams wrote:> A real inductor has RLC elements around it, equivalent to loss and > parasitic capacitance and stuff. This limits the voltage, even if an > ideal CCS were applied.I've noticed the "parallel capacitance" of the inductor makes a BIG difference to the level of back emf produced; smaller = greater voltage. Is this "parallel capacitance" in LTS the same thing as *interwinding capacitance* in real life?
