KJ
Guest
Sat Feb 06, 2010 7:27 am
How viable is it to use a bleeder resistor rather than a direct
galvanic connection to try to cut down the transient induced by
static?
In our system we have moving paper that will generate occasional
discharges to a large metal plate which supports the mechanics.
Underneath that plate (~1 inch) there is a circuit board that has a
single connection to a post coming down from that plate. A flex
circuit is plugged into a connector which runs back up through that
plate up a tower to an LCD. Occasionally the discharge can disrupt
the LCD temporarily, basically resetting it. One thought was to try
to control this discharge by inserting some series resistance between
the post and where it would otherwise connect to the circuit board to
provide the 'earth' connection to the circuit board. Obviously this
would need to be a resistor capable of withstanding high volts and
impulse type events as well as PCB layout rules to support this. Does
anyone have any references to such a technique?
The alternative solution is a 27 cent ferrite around the flex circuit,
and cost is a concern with the product so exotic/expensive approaches
are out. Also investigating alternatives up near the LCD as well, but
just wondering if there is a good way to dissipate the static shock as
a bit of heat rather than disrupting the ground and everything at the
LCD that is sitting up on a perch..and do it for ~$0.25 USD or less.
KJ
Ban
Guest
Sat Feb 06, 2010 7:27 am
"KJ" <kkjennings_at_sbcglobal.net> schrieb im Newsbeitrag
news:b527773b-c8e9-4a4e-be29-dca4b2fdb53a_at_u9g2000yqb.googlegroups.com...
Quote:
How viable is it to use a bleeder resistor rather than a direct
galvanic connection to try to cut down the transient induced by
static?
In our system we have moving paper that will generate occasional
discharges to a large metal plate which supports the mechanics.
Underneath that plate (~1 inch) there is a circuit board that has a
single connection to a post coming down from that plate. A flex
circuit is plugged into a connector which runs back up through that
plate up a tower to an LCD. Occasionally the discharge can disrupt
the LCD temporarily, basically resetting it. One thought was to try
to control this discharge by inserting some series resistance between
the post and where it would otherwise connect to the circuit board to
provide the 'earth' connection to the circuit board. Obviously this
would need to be a resistor capable of withstanding high volts and
impulse type events as well as PCB layout rules to support this. Does
anyone have any references to such a technique?
The alternative solution is a 27 cent ferrite around the flex circuit,
and cost is a concern with the product so exotic/expensive approaches
are out. Also investigating alternatives up near the LCD as well, but
just wondering if there is a good way to dissipate the static shock as
a bit of heat rather than disrupting the ground and everything at the
LCD that is sitting up on a perch..and do it for ~$0.25 USD or less.
KJ
Better to use a separate ground connection with an extra wire to the
grounded frame or another low impedance point and isolate the bolt from your
circuit. Try it temporary first if it helps.
ciao Ban
Robert Baer
Guest
Sat Feb 06, 2010 8:22 am
KJ wrote:
Quote:
How viable is it to use a bleeder resistor rather than a direct
galvanic connection to try to cut down the transient induced by
static?
In our system we have moving paper that will generate occasional
discharges to a large metal plate which supports the mechanics.
Underneath that plate (~1 inch) there is a circuit board that has a
single connection to a post coming down from that plate. A flex
circuit is plugged into a connector which runs back up through that
plate up a tower to an LCD. Occasionally the discharge can disrupt
the LCD temporarily, basically resetting it. One thought was to try
to control this discharge by inserting some series resistance between
the post and where it would otherwise connect to the circuit board to
provide the 'earth' connection to the circuit board. Obviously this
would need to be a resistor capable of withstanding high volts and
impulse type events as well as PCB layout rules to support this. Does
anyone have any references to such a technique?
The alternative solution is a 27 cent ferrite around the flex circuit,
and cost is a concern with the product so exotic/expensive approaches
are out. Also investigating alternatives up near the LCD as well, but
just wondering if there is a good way to dissipate the static shock as
a bit of heat rather than disrupting the ground and everything at the
LCD that is sitting up on a perch..and do it for ~$0.25 USD or less.
KJ
Well...a resistor (normally) conducts current.
Since you are talking about electrostatic voltage / current, the
current is low and a resistor would bleed off the charge meaning little
or low net voltage.
I would use something between 1K and 10Meg depending on the severity
of generation.
I also would add a metallic or other conductive shield between the
generator and sensitive PC boards and directly connect it to the PCB
ground system, NO other connection (it can have insulation around it if
needed).
whit3rd
Guest
Sat Feb 06, 2010 10:13 pm
On Feb 5, 8:27 pm, KJ <kkjenni...@sbcglobal.net> wrote:
Quote:
How viable is it to use a bleeder resistor rather than a direct
galvanic connection to try to cut down the transient induced by
static?
In our system we have moving paper that will generate occasional
discharges to a large metal plate which supports the mechanics.
Underneath that plate (~1 inch) there is a circuit board that has a
single connection to a post coming down from that plate. A flex
circuit is plugged into a connector which runs back up through that
plate up a tower to an LCD. Occasionally the discharge can disrupt
the LCD temporarily, basically resetting it.
A bleeder resistor won't have any place to connect, will it? What you
really want, is a Faraday cage around the sensitive LCD (but it may be
awkward to put metal window-screen material over the face).
A frequently seen solution is a set of corona points (basically, tiny
little
lightning rods) next to the paper which carries the charge. Another
might
be some UV LEDs, which may create enough ionization to discharge the
paper. Radioactive strips in the old record-cleaner brushes performed
the same function.
legg
Guest
Sun Feb 07, 2010 10:42 pm
On Fri, 5 Feb 2010 20:27:11 -0800 (PST), KJ <kkjennings_at_sbcglobal.net>
wrote:
Quote:
How viable is it to use a bleeder resistor rather than a direct
galvanic connection to try to cut down the transient induced by
static?
In our system we have moving paper that will generate occasional
discharges to a large metal plate which supports the mechanics.
Underneath that plate (~1 inch) there is a circuit board that has a
single connection to a post coming down from that plate. A flex
circuit is plugged into a connector which runs back up through that
plate up a tower to an LCD. Occasionally the discharge can disrupt
the LCD temporarily, basically resetting it. One thought was to try
to control this discharge by inserting some series resistance between
the post and where it would otherwise connect to the circuit board to
provide the 'earth' connection to the circuit board. Obviously this
would need to be a resistor capable of withstanding high volts and
impulse type events as well as PCB layout rules to support this. Does
anyone have any references to such a technique?
The alternative solution is a 27 cent ferrite around the flex circuit,
and cost is a concern with the product so exotic/expensive approaches
are out. Also investigating alternatives up near the LCD as well, but
just wondering if there is a good way to dissipate the static shock as
a bit of heat rather than disrupting the ground and everything at the
LCD that is sitting up on a perch..and do it for ~$0.25 USD or less.
KJ
The reset is likely coincident with the discharge from the paper,
which you can't attach a resistor to - all you can do is provide a
more controlled discharge path that does not involve the victim
circuit, or prevent the charge from accumulating in the first place.
Otherwise, resistive bleeders across isolation barriers are safety
listed commodity components with values between 1/2 and 12 Meg. Pilkor
PPSR37 , PWSR37 and Phoenix HVR types come to mind. If this isn't a
safety barrier being crossed, then simply using parts of similar
construction would probably serve the purpose.
Frankly, US$0.27 does not strike me as a barrier in the cost of the
'system'.
RL
KJ
Guest
Mon Feb 08, 2010 3:36 am
On Feb 5, 11:56 pm, "Ban" <bans...@web.de> wrote:
Quote:
Better to use a separate ground connection with an extra wire to the
grounded frame or another low impedance point
The plate receiving the discharge is the frame.
Quote:
and isolate the bolt from your
circuit.
The bolt provides the electrical connection to provide the 'earth'
connection to the board. Isolating it would float the board relative
to an earth ground.
KJ
KJ
Guest
Mon Feb 08, 2010 3:40 am
Quote:
Since you are talking about electrostatic voltage / current, the
current is low and a resistor would bleed off the charge meaning little
or low net voltage.
Nominally low...except when the discharge comes along and now you have
a high transient voltage for a couple hundred ns.
Quote:
I would use something between 1K and 10Meg depending on the severity
of generation.
I would too...but was wondering if anyone knew of any pitfalls
associated with. I wouldn't want to create an arc on the PCB as an
example.
Quote:
I also would add a metallic or other conductive shield between the
generator and sensitive PC boards and directly connect it to the PCB
ground system, NO other connection (it can have insulation around it if
needed).
That would probably cost more than the ferrite though
KJ
KJ
Guest
Mon Feb 08, 2010 3:45 am
Quote:
A bleeder resistor won't have any place to connect, will it?
Right now the large plate connects to the PCB with a post that touches
the PCB to provide the electrical connection to an 'earth' ground on
the board. What I was thinking was to get rid of the the PCB
connection to earth and insert a resistor between where the post comes
down and the earth ground net on the board.
Quote:
What you
really want, is a Faraday cage around the sensitive LCD (but it may be
awkward to put metal window-screen material over the face).
A frequently seen solution is a set of corona points (basically, tiny
little
lightning rods) next to the paper which carries the charge. Another
might
be some UV LEDs, which may create enough ionization to discharge the
paper. Radioactive strips in the old record-cleaner brushes performed
the same function.
The cage and LEDs would likely be more expensive than the ferrite.
The corona points would be a rework problem but might be useful for
new builds.
KJ
KJ
Guest
Mon Feb 08, 2010 3:56 am
Quote:
The reset is likely coincident with the discharge from the paper,
It is.
Quote:
which you can't attach a resistor to - all you can do is provide a
more controlled discharge path that does not involve the victim
circuit,
That's what I'm looking for, a way to control how the static hit to
the plate gets out of the system without disrupting the ground on the
board.
Quote:
or prevent the charge from accumulating in the first place.
There are some measures in the system to bleed off charge to the plate
before it gets too large...but apparently not quite enough.
Quote:
Otherwise, resistive bleeders across isolation barriers are safety
listed commodity components with values between 1/2 and 12 Meg. Pilkor
PPSR37 , PWSR37 and Phoenix HVR types come to mind. If this isn't a
safety barrier being crossed, then simply using parts of similar
construction would probably serve the purpose.
It is a safety connection.
I'll keep looking for any other app notes/concerns that might be
associated with separating 'frame' from 'earth' without creating other
issues.
Quote:
Frankly, US$0.27 does not strike me as a barrier in the cost of the
'system'.
The 27 cents was just the upper cost limit, since that's what the
ferrite that forms one possible solution costs. Actually slightly
more, since there would be some minor labor as well.
KJ
Jon Slaughter
Guest
Mon Feb 08, 2010 6:13 am
KJ wrote:
Quote:
How viable is it to use a bleeder resistor rather than a direct
galvanic connection to try to cut down the transient induced by
static?
In our system we have moving paper that will generate occasional
discharges to a large metal plate which supports the mechanics.
Underneath that plate (~1 inch) there is a circuit board that has a
single connection to a post coming down from that plate. A flex
circuit is plugged into a connector which runs back up through that
plate up a tower to an LCD. Occasionally the discharge can disrupt
the LCD temporarily, basically resetting it. One thought was to try
to control this discharge by inserting some series resistance between
the post and where it would otherwise connect to the circuit board to
provide the 'earth' connection to the circuit board. Obviously this
would need to be a resistor capable of withstanding high volts and
impulse type events as well as PCB layout rules to support this. Does
anyone have any references to such a technique?
The alternative solution is a 27 cent ferrite around the flex circuit,
and cost is a concern with the product so exotic/expensive approaches
are out. Also investigating alternatives up near the LCD as well, but
just wondering if there is a good way to dissipate the static shock as
a bit of heat rather than disrupting the ground and everything at the
LCD that is sitting up on a perch..and do it for ~$0.25 USD or less.
Your still going to have issues with static buildup if you do not find a way
to appropriately keep the charge from building up. This may or may not be an
issue depending on the saftey requirements. It seems you simply need to
properly ground the large metal plate and isolate the flex line and/or the
circuit board. This can be accomplished many ways. By providing a much lower
impedance path for the discharge through the plate to ground then you reduce
the voltage on the flex cable. By increasing the electrical isolation of the
flex cable you decrease it's susceptibility to the discharge.
If you fix the source of the problem then you won't have issues with the
other components. I assume the metal plate is not properly grounded?
