Johnny5
Guest
Mon Mar 08, 2010 8:53 pm
I am working on an ignition coil driver circuit. I have a fixture with
the load(spark plug) that is arcing in open air within feett of my
board. I know this is brief description, but essentially IGBT final
control with opto mcu driver.
The layout was with EMI in mind, decouplers, 100ohm series limiters,
opto, bat54's as well as tvs's all over.
I am getting +/- 50 to 250 volt pulses with 2-3nanosecond risetimes
when the coil collapses. I am using shielded tektronix probes as
well.
The frequencies I am driving this with are <1kHz.
The board has 10ft signal and power wires as well. Tried reducing the
length, adding a shield etc no fix.
I have floated the plugs(scope and supply) which helped me not kill
another power supply.
For some reason the earth ground seemed to be an antenna...
Are these signals injected into my circuit via inductive/capacitive
coupling? Common mode current?
I still have the problem with or without the probes hooked up. The mcu
does not die over time either (relatively speaking had it running for
24+ hrs) it just resets every time the coil collapses. I have tried
snubbers, beads, toroids, ptc's all with no avail.Could someone please
enlighten me any help would be greatly appreciated.
whit3rd
Guest
Tue Mar 09, 2010 12:29 am
On Mar 8, 10:53 am, Johnny5 <dirtylogicdesi...@gmail.com> wrote:
Quote:
I am working on an ignition coil driver circuit ...
I am getting +/- 50 to 250 volt pulses with 2-3nanosecond risetimes
when the coil collapses.
Is your 'coil' made with nonlossy core material? If it were laminated
iron, the risetimes might become more moderate. If you
can add a small winding with an RC snubber load, your
high-efficiency core can emulate a cheaper iron unit.
The stray inductance in series with the spark gap is also
important in keeping transients in check.
Quote:
For some reason the earth ground seemed to be an antenna...
Yes, of course a ground wire that carries high current at high
frequency
has magnetic coupling (not antenna coupling, exactly) to nearby wiring.
Johnny5
Guest
Tue Mar 09, 2010 3:09 am
On Mar 8, 4:29 pm, whit3rd <whit...@gmail.com> wrote:
Quote:
On Mar 8, 10:53 am, Johnny5 <dirtylogicdesi...@gmail.com> wrote:
I am working on an ignition coil driver circuit ...
I am getting +/- 50 to 250 volt pulses with 2-3nanosecond risetimes
when the coil collapses.
Is your 'coil' made with nonlossy core material? If it were laminated
iron, the risetimes might become more moderate. If you
can add a small winding with an RC snubber load, your
high-efficiency core can emulate a cheaper iron unit.
The stray inductance in series with the spark gap is also
important in keeping transients in check.
For some reason the earth ground seemed to be an antenna...
Yes, of course a ground wire that carries high current at high
frequency
has magnetic coupling (not antenna coupling, exactly) to nearby wiring.
Thank you very much for your feedback,
I cant find any info on the ignition coil as far as materials are
concerned.
(destructive testing with saw to follow )
So If the coil and wire inductance are equal to X and I must maintain
said length
and wire size how could I compensate for this to have minimal
transients?
By winding you mean a R-LC tank circuit? What could the configuration
be?
Would it be somewhat of an impedance matching circuit for less
reflection. Or just minimizing di/dt?
Also why are fast recovery diodes not conducting these -/+ V
transients fast enough
to keep the mcu in check.
Nemo
Guest
Tue Mar 09, 2010 9:18 pm
The most promising avenues to follow for reducing magnetic interference,
which this almost certainly is, are (1) slowing the risetimes - which
you're obviously aware of; and (2) reducing loop areas. Can you, for
example, twist the cables to / from the items of equipment?
Also someone posted here a few weeks ago: "Magnetic fields are dipole
fields, and therefore the field strength diminishes with the cube of the
distance. This means that quite modest separation increases attenuation
a lot."
The coil may be generating a non uniform (in space) magnetic field, you
could try rotating it 90 degrees to see if that helps.
Have you tried a ferrite bead in the earth return? Remember your ferrite
components need to be rated not to saturate with the current passing
through them, or they'll stop dissipating in an optimally lossy manner.
Mark
Guest
Wed Mar 10, 2010 5:36 am
On Mar 9, 3:18 pm, Nemo <z...@nospam.nospam.nospam.nospam.co.uk>
wrote:
Quote:
The most promising avenues to follow for reducing magnetic interference,
which this almost certainly is, are (1) slowing the risetimes - which
you're obviously aware of; and (2) reducing loop areas. Can you, for
example, twist the cables to / from the items of equipment?
Also someone posted here a few weeks ago: "Magnetic fields are dipole
fields, and therefore the field strength diminishes with the cube of the
distance. This means that quite modest separation increases attenuation
a lot."
The coil may be generating a non uniform (in space) magnetic field, you
could try rotating it 90 degrees to see if that helps.
Have you tried a ferrite bead in the earth return? Remember your ferrite
components need to be rated not to saturate with the current passing
through them, or they'll stop dissipating in an optimally lossy manner.
yes you can determine if it is magnetic by rotating the axis of the
coil to see if that changes the interference...
if so , try shielding with a copper strap like the way some power
transformers have a copper strap around them...
Mark
Johnny5
Guest
Wed Mar 10, 2010 3:51 pm
On Mar 9, 9:36 pm, Mark <makol...@yahoo.com> wrote:
Quote:
On Mar 9, 3:18 pm, Nemo <z...@nospam.nospam.nospam.nospam.co.uk
wrote:
The most promising avenues to follow for reducing magnetic interference,
which this almost certainly is, are (1) slowing the risetimes - which
you're obviously aware of; and (2) reducing loop areas. Can you, for
example, twist the cables to / from the items of equipment?
Also someone posted here a few weeks ago: "Magnetic fields are dipole
fields, and therefore the field strength diminishes with the cube of the
distance. This means that quite modest separation increases attenuation
a lot."
The coil may be generating a non uniform (in space) magnetic field, you
could try rotating it 90 degrees to see if that helps.
Have you tried a ferrite bead in the earth return? Remember your ferrite
components need to be rated not to saturate with the current passing
through them, or they'll stop dissipating in an optimally lossy manner.
yes you can determine if it is magnetic by rotating the axis of the
coil to see if that changes the interference...
if so , try shielding with a copper strap like the way some power
transformers have a copper strap around them...
Mark
Thank you all again for the suggestions. I tried rotating the coil
with no changes.
I minimized the power/signal lines as well, it reduced the transients
signifigantly
but they still remain around 10-20 volts. I have tried RCD snubbers
with no change,
and beads as well. Is there a way to mitigate these transients if I
have to have this length
of wire?
Winston
Guest
Thu Mar 11, 2010 12:06 am
On 3/10/2010 5:51 AM, Johnny5 wrote:
(...)
Quote:
Is there a way to mitigate these transients if I
have to have this length
of wire?
Try reducing the inductance of the wire
between the coil and your driver transistor.
This should turn your voltage pulse into
a current pulse.
First prize: Flat copper bar.
Second prize: Flat copper braid.
(Salvage from old, large diameter coaxial cable).
--Winston
Archimedes' Lever
Guest
Thu Mar 11, 2010 1:22 am
On Tue, 9 Mar 2010 19:36:34 -0800 (PST), Mark <makolber_at_yahoo.com> wrote:
Quote:
On Mar 9, 3:18 pm, Nemo <z...@nospam.nospam.nospam.nospam.co.uk
wrote:
The most promising avenues to follow for reducing magnetic interference,
which this almost certainly is, are (1) slowing the risetimes - which
you're obviously aware of; and (2) reducing loop areas. Can you, for
example, twist the cables to / from the items of equipment?
Also someone posted here a few weeks ago: "Magnetic fields are dipole
fields, and therefore the field strength diminishes with the cube of the
distance. This means that quite modest separation increases attenuation
a lot."
The coil may be generating a non uniform (in space) magnetic field, you
could try rotating it 90 degrees to see if that helps.
Have you tried a ferrite bead in the earth return? Remember your ferrite
components need to be rated not to saturate with the current passing
through them, or they'll stop dissipating in an optimally lossy manner.
yes you can determine if it is magnetic by rotating the axis of the
coil to see if that changes the interference...
if so , try shielding with a copper strap like the way some power
transformers have a copper strap around them...
Mark
Toroid core coils do not notably emit. The problem is elsewhere.
Archimedes' Lever
Guest
Thu Mar 11, 2010 1:23 am
On Wed, 10 Mar 2010 05:51:54 -0800 (PST), Johnny5
<dirtylogicdesigns_at_gmail.com> wrote:
Quote:
On Mar 9, 9:36 pm, Mark <makol...@yahoo.com> wrote:
On Mar 9, 3:18 pm, Nemo <z...@nospam.nospam.nospam.nospam.co.uk
wrote:
The most promising avenues to follow for reducing magnetic interference,
which this almost certainly is, are (1) slowing the risetimes - which
you're obviously aware of; and (2) reducing loop areas. Can you, for
example, twist the cables to / from the items of equipment?
Also someone posted here a few weeks ago: "Magnetic fields are dipole
fields, and therefore the field strength diminishes with the cube of the
distance. This means that quite modest separation increases attenuation
a lot."
The coil may be generating a non uniform (in space) magnetic field, you
could try rotating it 90 degrees to see if that helps.
Have you tried a ferrite bead in the earth return? Remember your ferrite
components need to be rated not to saturate with the current passing
through them, or they'll stop dissipating in an optimally lossy manner.
yes you can determine if it is magnetic by rotating the axis of the
coil to see if that changes the interference...
if so , try shielding with a copper strap like the way some power
transformers have a copper strap around them...
Mark
Thank you all again for the suggestions. I tried rotating the coil
with no changes.
I minimized the power/signal lines as well, it reduced the transients
signifigantly
but they still remain around 10-20 volts. I have tried RCD snubbers
with no change,
and beads as well. Is there a way to mitigate these transients if I
have to have this length
of wire?
Your AC input should be a twisted pair once within the chassis, OR STP
(Sheilded Twisted Pair). All DC feed lines should ALSO be in twisted
pairs. The feed, and the return.
JosephKK
Guest
Thu Mar 11, 2010 1:24 am
On Wed, 10 Mar 2010 05:51:54 -0800 (PST), Johnny5 <dirtylogicdesigns_at_gmail.com> wrote:
Quote:
On Mar 9, 9:36 pm, Mark <makol...@yahoo.com> wrote:
On Mar 9, 3:18 pm, Nemo <z...@nospam.nospam.nospam.nospam.co.uk
wrote:
The most promising avenues to follow for reducing magnetic interference,
which this almost certainly is, are (1) slowing the risetimes - which
you're obviously aware of; and (2) reducing loop areas. Can you, for
example, twist the cables to / from the items of equipment?
Also someone posted here a few weeks ago: "Magnetic fields are dipole
fields, and therefore the field strength diminishes with the cube of the
distance. This means that quite modest separation increases attenuation
a lot."
The coil may be generating a non uniform (in space) magnetic field, you
could try rotating it 90 degrees to see if that helps.
Have you tried a ferrite bead in the earth return? Remember your ferrite
components need to be rated not to saturate with the current passing
through them, or they'll stop dissipating in an optimally lossy manner.
yes you can determine if it is magnetic by rotating the axis of the
coil to see if that changes the interference...
if so , try shielding with a copper strap like the way some power
transformers have a copper strap around them...
Mark
Thank you all again for the suggestions. I tried rotating the coil
with no changes.
I minimized the power/signal lines as well, it reduced the transients
signifigantly
but they still remain around 10-20 volts. I have tried RCD snubbers
with no change,
and beads as well. Is there a way to mitigate these transients if I
have to have this length
of wire?
Are you doing everything with twisted pairs or coax?
Archimedes' Lever
Guest
Thu Mar 11, 2010 1:24 am
On Wed, 10 Mar 2010 15:06:57 -0800, Winston <Winston_at_bigbrother.net>
wrote:
Quote:
On 3/10/2010 5:51 AM, Johnny5 wrote:
(...)
Is there a way to mitigate these transients if I
have to have this length
of wire?
Try reducing the inductance of the wire
between the coil and your driver transistor.
This should turn your voltage pulse into
a current pulse.
First prize: Flat copper bar.
Second prize: Flat copper braid.
(Salvage from old, large diameter coaxial cable).
--Winston
Or non-inpregnated solder braid.
Silver plated copper wire also makes good high current feeds for short
jumps.
Johnny5
Guest
Tue Mar 16, 2010 10:25 pm
On Mar 10, 7:24 pm, Archimedes' Lever <OneBigLe...@InfiniteSeries.Org>
wrote:
Quote:
On Wed, 10 Mar 2010 15:06:57 -0800, Winston <Wins...@bigbrother.net
wrote:
On 3/10/2010 5:51 AM, Johnny5 wrote:
(...)
Is there a way to mitigate these transients if I
have to have this length
of wire?
Try reducing the inductance of the wire
between the coil and your driver transistor.
This should turn your voltage pulse into
a current pulse.
First prize: Flat copper bar.
Second prize: Flat copper braid.
(Salvage from old, large diameter coaxial cable).
--Winston
Or non-inpregnated solder braid.
Silver plated copper wire also makes good high current feeds for short
jumps.
Thank you all for your help, absolutely the strangest case of RFI/EM
enduced cmos latchup I have ever seen.
No layout issues just some carefully placed bat54's.
