Q: How to deal with inductive kickback?
Dale Wellborn
First disclaimer: I'm a "mostly" software designer ;-)
Here goes ...
I have a battery powered uP which monitors the battery. When I connect the
charger (AC full-wave rectified, almost no filtering) I get a ground spike
which usually blows the uP out of the water! I've somewhat eased the
problem by using a zener diode *which stays with the charger*. Still, every
now and then the uP gets hit.
What is a poor boy to do?
I have been told that the problem is due to the collapsing magnetic filed
(field) in the transformer when the charger is connected. This causes a
voltage spike.
Currently I have a 10uF electrolytic across the power of the uP.
My need is area and cost sensitive. Also, power (I do sound like a
software person, don't I?)
Thanks (ladies and gents).
Dale
dwel...@drao.nrc.ca
--
Dale Wellborn
(604) 490-4357 (W) / (604) 493-7767 (FAX) / (604) 494-7216 (H)
dwel...@sol.drao.nrc.ca
Summerland, B.C., CANADA
Silas E. Cheeseman
>I have a battery powered uP which monitors the battery. When I connect the
>charger (AC full-wave rectified, almost no filtering) I get a ground spike
>which usually blows the uP out of the water! I've somewhat eased the
>problem by using a zener diode *which stays with the charger*. Still, every
>now and then the uP gets hit.
>I have been told that the problem is due to the collapsing magnetic filed
>(field) in the transformer when the charger is connected. This causes a
>voltage spike.
Inductive kick back is usually caused when power is _removed_ from the load.
However, to eliminate inductive kick back, simply place a diode in parallel
with your load, in the reverse bias direction. A 1N914 is commonly used.
From: nbs...@mailserv.nbnet.nb.ca
Silas E. Cheeseman
Saint John, NB, Canada
(506) 674-1321 Computer/FAX
"He will wipe away all the tears from their eyes"
- Revelation 21:4
Nirmalkumar Velayudhan
> Inductive kick back is usually caused when power is _removed_ from the load.
> However, to eliminate inductive kick back, simply place a diode in parallel
> with your load, in the reverse bias direction. A 1N914 is commonly used.
>
I've got a dumb question, sort of related. Why is a freewheeling (free-wheeling?)
diode called a freewheeling diode?
nkv
Richard Steven Walz
-------------------------------------------
Because it allows the current that is flowing to keep flowing in the
inductor, like a coaster brake on an old bicycle or any other one way
clutch, to keep going around in a circle through the diode until dissipated
through resistive decay rather than being suddenly dissipated in a sudden
spark or jerk of the suddenly collapsing field in the inductor. A current
in an inductor is analogous to a mass with inertia in the physical world,
it's the equivalent of an uphill slope on a descending mountain road for a
truck/lorry to stop on if its brakes go out. I would use something more
substantial on any coil of sixe than a 1N914, more like a 1N400x, where x
sets the peak inverse voltage withstood! See motorola manual or such. It
allows it to freewheel to a stop instead of being stopped with a stick in
the spokes! Think of the energy the stick and spokes receive as being the
voltage spike and its energy! remember to put the diode on in the direction
of current flow through the inductor and it if they were in a circle alone
with a current to dissipate energy from to stop it.
-Steve Walz rst...@armory.com
Silas E. Cheeseman
>I would use something more
>substantial on any coil of sixe than a 1N914, more like a 1N400x, where x
>sets the peak inverse voltage withstood!
Stopping inductive kick with a 1N400x series diode is probably futile. These
are rectifier diodes and don't have the frequency response required to dampen
a fast rising spike. Their PN junction is too wide. You need a high speed
switching diode such as a 1N914. Granted you should watch PIV rating.
Michael Silva
In article <nbschee.22...@mailserv.nbnet.nb.ca>, Silas E. Cheeseman (nbs...@mailserv.nbnet.nb.ca) writes:
>In article <CrCr9...@freenet.carleton.ca> al...@FreeNet.Carleton.CA (Dale Wellborn) writes:
>
>Inductive kick back is usually caused when power is _removed_ from the load.
>However, to eliminate inductive kick back, simply place a diode in parallel
>with your load, in the reverse bias direction. A 1N914 is commonly used.
>
>
Mike
Richard Steven Walz
Silas E. Cheeseman <nbs...@mailserv.nbnet.nb.ca> wrote:
>In article <CrDx5...@armory.com> rst...@armory.com (Richard Steven Walz) writes:
>>I would use something more
>>substantial on any coil of sixe than a 1N914, more like a 1N400x, where x
>>sets the peak inverse voltage withstood!
>
>Stopping inductive kick with a 1N400x series diode is probably futile. These
>are rectifier diodes and don't have the frequency response required to dampen
>a fast rising spike. Their PN junction is too wide. You need a high speed
>switching diode such as a 1N914. Granted you should watch PIV rating.
>From: nbs...@mailserv.nbnet.nb.ca
> Silas E. Cheeseman
Okay, Silas, I'll buy that the rectifier diodes are too slow, but an 1N914
is simply insubstantial to withstand more than small signals. I see PIV
ratings of a few tens of volts on them, when I KNOW these spikes hit MUCH
higher! Any ideas about a better diode than either so far mentioned?? I
have never seen a freewheeling diode on a fair-sized relay coil that was a
1N914, have you? And on bigger ones I see a fat rectifier type diode
coupled with a cap in parallel!
-Steve Walz rst...@armory.com
t...@hplb.hpl.hp.com
stop the current flowing through a coil, don't forget basic energy
conservation. The current flowing through the coil implies that energy is
stored in the coil. When the current is removed that energy has to go
somewhere, and in fact it is mainly dissipated in the diode.
The peak diode current and diode power dissipation can be reduced by inserting
a resistor in series with the diode, value (Vm-Vd)/Ic where Vm is the maximum
tolerable reverse voltage, Ic is the coil current and Vd is the voltage drop
across the diode when it is carrying Ic.
This technique also ensures that the kickback transient dies away more
quickly
--
===============================================================================
Tom Gardner Hewlett Packard Laboratories, Filton Rd,
t...@hplb.hpl.hp.com Stoke Gifford, Bristol, Avon, BS12 6QZ, ENGLAND.
Fax: +44 272 228920 Tel: +44 272 799910 ext. 28192
Too many Heritage Centres make you go blind.
===============================================================================
Frank Powell
: I think a 1N400X is more common and more robust in these applications.
: Mike
Come on guys, think. You are suggesting that a diode
be placed across the windings of a transformer. What
is there that will stop the diode from blowing out?
Instead of a 1N400X type diode, place two zeners
back-to-back across the transformer winding. Make the
zeners a couple of volts higher than that needed from
the transformer.
--
|
I never met a cat I didn't like! | Frank PoWell
| pow...@slc.unisys.com
_______,,,^..^,,,_______ |
Silas E. Cheeseman
>Silas E. Cheeseman <nbs...@mailserv.nbnet.nb.ca> wrote:
>>Stopping inductive kick with a 1N400x series diode is probably futile.
These >>are rectifier diodes and don't have the frequency response required to
dampen >>a fast rising spike. Their PN junction is too wide. You need a high
speed >>switching diode such as a 1N914. Granted you should watch PIV rating.
>>From: nbs...@mailserv.nbnet.nb.ca
>> Silas E. Cheeseman
>Okay, Silas, I'll buy that the rectifier diodes are too slow, but an 1N914
>is simply insubstantial to withstand more than small signals. I see PIV
>ratings of a few tens of volts on them, when I KNOW these spikes hit MUCH
>higher! Any ideas about a better diode than either so far mentioned?? I
>have never seen a freewheeling diode on a fair-sized relay coil that was a
>1N914, have you? And on bigger ones I see a fat rectifier type diode
>coupled with a cap in parallel!
The voltage from removing a positive supply, from a coil, is a high
_negative_ going pulse. Having a diode across the coil will dampen the pulse
to about -0.6 volts. Since this is foward biasing the diode, PIV does not
enter the discussion.
I've used this on many many occasions and highly recommend it. If you use a
standard rectifier you risk having no dampening at all. I realize many
commercial designs use them and many say can all these manufactures be wrong.
Why not! I still stand by my argument. As soon as I locate some text that
agrees with my position, I'll post it.
From: nbs...@mailserv.nbnet.nb.ca
Silas E. Cheeseman
Silas E. Cheeseman
>Come on guys, think. You are suggesting that a diode
>be placed across the windings of a transformer. What
>is there that will stop the diode from blowing out?
>Instead of a 1N400X type diode, place two zeners
>back-to-back across the transformer winding. Make the
>zeners a couple of volts higher than that needed from
>the transformer.
We are not suggesting this at all. And our ideas about a diode dampening the
inductive kick of a coil is sound. It has been used for decades.
Silas E. Cheeseman
>When using a reverse-biassed diode to kill the inductive kickback when you
>stop the current flowing through a coil, don't forget basic energy
>conservation. The current flowing through the coil implies that energy is
>stored in the coil. When the current is removed that energy has to go
>somewhere, and in fact it is mainly dissipated in the diode.
The coil opposes the change in current by creating a very high negative going
_voltage_ spike. Currents are minimal. This conforms with any and all laws
of thermodynamics.
>The peak diode current and diode power dissipation can be reduced by inserting
>a resistor in series with the diode,
No sir, it cannot. If you insert a resistor in series with the coil-dampening
diode you will destroy its ability to dampen at all.
> value (Vm-Vd)/Ic where Vm is the maximum
>tolerable reverse voltage,
Who cares about reverse voltage when the pulse is negative going and reverse
biases the diode.
>Ic is the coil current and Vd is the voltage drop
>across the diode when it is carrying Ic.
>This technique also ensures that the kickback transient dies away more
>quickly.
No way!
From: nbs...@mailserv.nbnet.nb.ca
Silas E. Cheeseman
John Lundgren
Silas E. Cheeseman (nbs...@mailserv.nbnet.nb.ca) wrote:
: >I have a battery powered uP which monitors the battery. When I connect the
: >charger (AC full-wave rectified, almost no filtering) I get a ground spike
: >which usually blows the uP out of the water! I've somewhat eased the
: >problem by using a zener diode *which stays with the charger*. Still, every
: >now and then the uP gets hit.
: >I have been told that the problem is due to the collapsing magnetic filed
: >(field) in the transformer when the charger is connected. This causes a
: >voltage spike.
: Inductive kick back is usually caused when power is _removed_ from the load.
: However, to eliminate inductive kick back, simply place a diode in parallel
: with your load, in the reverse bias direction. A 1N914 is commonly used.
If the spike can burn out the uP, then it will certainly burn out the
1N914!! Use a several 3 or 6 amp diodes, and heavy wire, too. You might
consider putting some protection in the sensing leads, too. Use some lo
pass RC filters.
John Lundgren
: >I would use something more
: >substantial on any coil of sixe than a 1N914, more like a 1N400x, where x
: >sets the peak inverse voltage withstood!
: Stopping inductive kick with a 1N400x series diode is probably futile. These
: are rectifier diodes and don't have the frequency response required to dampen
: a fast rising spike. Their PN junction is too wide. You need a high speed
: switching diode such as a 1N914. Granted you should watch PIV rating.
I've seen transistor driven relays and solenoids where the only form of
transient protection across the coils was a large( 10 uF) electrolytic.
Something about Joules of charge comes to my mind.
So to my mind, the 1N4002, which has greater junction capacitance than a
1N914, would be much better, and more resistant to being destroyed by a
transient. The 1N914's have a breakdown voltage of less than 100V. All
the diode has to do is to dampen during the transient, and whether it does
this by diode conduction or by its capacitance doesn't seem important, to
me. Frequency response isn't a concern here.
: From: nbs...@mailserv.nbnet.nb.ca
: Silas E. Cheeseman
: Saint John, NB, Canada
: (506) 674-1321 Computer/FAX
: "He will wipe away all the tears from their eyes"
: - Revelation 21:4
--
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ John Lundgren - Elec Tech - Info Tech Svcs @ Standard @
@ Rancho Santiago Community College District @ disclaim- @
@ 17th St. at Bristol \ Santa Ana, CA 92706 @ ers apply.@
@ Voice (714) JOHN GAB \ FAX (714) JOHN FRY @ @
@ jlun...@pop.rancho.cc.ca.us\jlu...@eis.calstate.edu @ @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
Silas E. Cheeseman
Where do you come up with this stuff John? The spike will not even exist
with a diode present. The diode dampens it to about -0.6 volts. And 3 to 6
amps with heavy wire; common man, it's a high _voltage_ negative-going spike.
Current is minimal. I have used this method for years and it works great. If
you use a regular rectifier as a kick-back dampener you will have minimal
protection. Believe me, a 1N914 _is_ up to it.
Silas E. Cheeseman
>I've seen transistor driven relays and solenoids where the only form of
>transient protection across the coils was a large( 10 uF) electrolytic.
>Something about Joules of charge comes to my mind.
> So to my mind, the 1N4002, which has greater junction capacitance than a
>1N914, would be much better, and more resistant to being destroyed by a
>transient.
What transcient? The transcient won't exist John. The 1N914 would have
dampened it out. That's the point isn't it.
>The 1N914's have a breakdown voltage of less than 100V.
So what; the pulse is negative going. The 1N914 will be forward biased.
What's PIV got to do with it?
>All
>the diode has to do is to dampen during the transient, and whether it does
>this by diode conduction or by its capacitance doesn't seem important, to
>me. Frequency response isn't a concern here.
Frequency response certainly is a concern because the pulse has an extremely
fast rising slope.
Richard Steven Walz
Silas E. Cheeseman <nbs...@mailserv.nbnet.nb.ca> wrote:
>In article <CrJHF...@armory.com> rst...@armory.com (Richard Steven Walz) writes:
>
>>Silas E. Cheeseman <nbs...@mailserv.nbnet.nb.ca> wrote:
>
>>>Stopping inductive kick with a 1N400x series diode is probably futile.
>These >>are rectifier diodes and don't have the frequency response required to
>dampen >>a fast rising spike. Their PN junction is too wide. You need a high
>speed >>switching diode such as a 1N914. Granted you should watch PIV rating.
>>>From: nbs...@mailserv.nbnet.nb.ca
>>> Silas E. Cheeseman
>
>
>>Okay, Silas, I'll buy that the rectifier diodes are too slow, but an 1N914
>>is simply insubstantial to withstand more than small signals. I see PIV
>>ratings of a few tens of volts on them, when I KNOW these spikes hit MUCH
>>higher! Any ideas about a better diode than either so far mentioned?? I
>
>_negative_ going pulse. Having a diode across the coil will dampen the pulse
>to about -0.6 volts. Since this is foward biasing the diode, PIV does not
>enter the discussion.
>I've used this on many many occasions and highly recommend it. If you use a
>standard rectifier you risk having no dampening at all. I realize many
>commercial designs use them and many say can all these manufactures be wrong.
>Why not! I still stand by my argument. As soon as I locate some text that
>agrees with my position, I'll post it.
>From: nbs...@mailserv.nbnet.nb.ca
> Silas E. Cheeseman
Well, let's remember that we are dealing with a pulse that is in the
direction of the current that was removed that we have the reactive EMF.
I am not sure what you mean by a _negative_ going pulse. The inductor is a
reactive device which tried to first resist an imposed voltage and then
struggles to use its stored field energy to restore the falling voltage IN
THE CURRENT DIRECTION! If the inductor pulses through the diode, there may
still be quite enough energy stored on that very back swing to require
the diode to have a PIV substantially greater than simply be greater than
the originally applied voltage on the inductor, since it must resist being
trashed by the second induction, which IS against its reverse biased
direction! And I do indeed wonder why your diodes hold together on, say,
large relay coils for 5 to 12 volts. I wonder what you would use on a 24
volt relay or a 120VDC relay. I can understand that the fatter diode is
'slower' to turn-on, but I wonder whether this is important time-wise, or
whether Joules applied over a time is most important as a protective diode.
I suppose it depends on what we're protecting. I don't want us to draw this
out into a big nothing, Silas, but I hope we might both learn something
about this from someone who DOES know this!
-Steve Walz rst...@armory.com
Richard Steven Walz
Silas E. Cheeseman <nbs...@mailserv.nbnet.nb.ca> wrote:
>
>>Come on guys, think. You are suggesting that a diode
>>be placed across the windings of a transformer. What
>>is there that will stop the diode from blowing out?
>>Instead of a 1N400X type diode, place two zeners
>>back-to-back across the transformer winding. Make the
>>zeners a couple of volts higher than that needed from
>>the transformer.
>
>We are not suggesting this at all. And our ideas about a diode dampening the
>inductive kick of a coil is sound. It has been used for decades.
>From: nbs...@mailserv.nbnet.nb.ca
> Silas E. Cheeseman
Silas is right there. Zeners would be overdesign and our design is well
proven industrially. We were just discussing what diodes are needed for the
job. It was my contention that a 1N914 signal diode may be too small for
the "second" inductive kick in the reverse bias direction, while he
maintains, I believe, that such a crass animal as a 1N400x would be too fat
a pn junction to turn on quick enough!
-Steve Walz rst...@armory.com
Michael Silva
In article <1994Jun17.0...@unislc.slc.unisys.com>, Frank Powell (pow...@unislc.slc.unisys.com) writes:
>Michael Silva (mjs...@ted.win.net) wrote:
>
>: I think a 1N400X is more common and more robust in these applications.
>
>: Mike
>
>Come on guys, think. You are suggesting that a diode
>be placed across the windings of a transformer. What
>is there that will stop the diode from blowing out?
>Instead of a 1N400X type diode, place two zeners
>back-to-back across the transformer winding. Make the
>zeners a couple of volts higher than that needed from
>the transformer.
>
Here are the first two lines of the original post:
>I have a battery powered uP which monitors the battery. When I connect
>the charger (AC full-wave rectified, almost no filtering) I get a
^^^^^^^^^^^^^^^^^^^^^^
I was really responding to the suggestion that a 1N914 is the diode of
choice for clamping inductive spikes (in DC circuits). Silas Cheeseman
says that a rectifier diode is too slow to be of much use. I don't
know about that, I just know that that's what I always see in these
circuits.
Mike
Silas E. Cheeseman
Michael Silva
In article <nbschee.23...@mailserv.nbnet.nb.ca>, Silas E. Cheeseman (nbs...@mailserv.nbnet.nb.ca) writes:
>In article <CrJLD...@hplb.hpl.hp.com> t...@hplb.hpl.hp.com () writes:
>
>>When using a reverse-biassed diode to kill the inductive kickback when you
>>stop the current flowing through a coil, don't forget basic energy
>>conservation. The current flowing through the coil implies that energy is
>>stored in the coil. When the current is removed that energy has to go
>>somewhere, and in fact it is mainly dissipated in the diode.
>
>The coil opposes the change in current by creating a very high negative going
>_voltage_ spike. Currents are minimal. This conforms with any and all laws
>of thermodynamics.
The initial current through the diode is exactly equal to the current
in the inductor at the moment the circuit was opened. Remember the
inductor relationship: V = L di/dt. di/dt must be finite.
>
>>The peak diode current and diode power dissipation can be reduced by inserting
>>a resistor in series with the diode,
>
>No sir, it cannot. If you insert a resistor in series with the coil-dampening
>diode you will destroy its ability to dampen at all.
Theoretically the peak diode current will be the same. In the real
world of imperfect components (esp. stray capacitance between
windings, etc) I'm not sure.
>
>> value (Vm-Vd)/Ic where Vm is the maximum
>>tolerable reverse voltage,
>
>Who cares about reverse voltage when the pulse is negative going and reverse
>biases the diode.
>
>>Ic is the coil current and Vd is the voltage drop
>>across the diode when it is carrying Ic.
>
>>This technique also ensures that the kickback transient dies away more
>>quickly.
>
>No way!
Yes, way. The only way we can get quicker current decay (higher di/dt)
is to allow the voltage to increase across the inductor. A resistor
does this. Imagining a perfect inductor and diode, the current would
*never* decay, it would just circulate. The decay is produced by the
diode drop and by circuit resistance. Remember, the time constant for
an LR circuit is L/R. If you integrate the power dissipated by the
diode and circuit resistance, it must equal the energy stored in the
magnetic field at circuit opening. The graph will be low (voltage) and
long (time) with low resistance, and high and short with high
resistance.
This still doesn't refute your statement that a rectifier diode is too
slow to prevent a large inductive spike. I don't know the answer to
that.
Mike
Randy Casciola
How can people be expected to seriously consider your technical
opinion WHEN YOU DON'T EVEN KNOW THE PROPER TERMINOLOGY. This
has bothered me for a long time:
Silas E. Cheeseman <nbs...@mailserv.nbnet.nb.ca> wrote:
>_negative_ going pulse. Having a diode across the coil will dampen the pulse
^^^^^^
and
>No sir, it cannot. If you insert a resistor in series with the coil-dampening
^^^^^^^^^
and
>We are not suggesting this at all. And our ideas about a diode dampening the
^^^^^^^^^
jlun...@news.kn.PacBell.COM (John Lundgren) wrote:
>the diode has to do is to dampen during the transient, and whether it does
^^^^^^
DAMPEN means to make or become moist. The only time you should use this
word when talking about electronics is when there is water on your circuit.
You DO NOT have a DAMPENING resistor. You have a DAMPING resistor. Un-
fortunately, the word DAMP could be a noun meaning humidity, an adjective
meaning moist, a verb (transitive) meaning to moisten, or a verb (transitive)
meaning (as we should be talking about here) to reduce oscillations.
Randy Casciola
Research Engineer
The Robotics Institute
Carnegie Mellon Univ.
Pittsburgh, Pa 15213
Silas E. Cheeseman
>How can people be expected to seriously consider your technical
>opinion WHEN YOU DON'T EVEN KNOW THE PROPER TERMINOLOGY. This
>has bothered me for a long time:
>Silas E. Cheeseman <nbs...@mailserv.nbnet.nb.ca> wrote:
>>_negative_ going pulse. Having a diode across the coil will dampen the pulse
>DAMPEN means to make or become moist. The only time you should use this
>word when talking about electronics is when there is water on your circuit.
>You DO NOT have a DAMPENING resistor. You have a DAMPING resistor. Un-
>fortunately, the word DAMP could be a noun meaning humidity, an adjective
>meaning moist, a verb (transitive) meaning to moisten, or a verb (transitive)
>meaning (as we should be talking about here) to reduce oscillations.
dampen 1. to make moist 2. to deaden, depress, reduce, or lessen.
- Websters Second College Edition c1986
Do you have anything of value to add to this discussion, Mr. Webster?
Bob Myers
> DAMPEN means to make or become moist. The only time you should use this
> word when talking about electronics is when there is water on your circuit.
> You DO NOT have a DAMPENING resistor. You have a DAMPING resistor. Un-
> fortunately, the word DAMP could be a noun meaning humidity, an adjective
> meaning moist, a verb (transitive) meaning to moisten, or a verb (transitive)
> meaning (as we should be talking about here) to reduce oscillations.
Fine, Randy. Now go back to your dictionary and look up PEDANTIC (adjective)
and/or PEDANT (noun). And as Silas already pointed out, "dampen" is just fine
in the above usage, although I would certainly agree that "damping diode"
is MUCH more common than "dampening diode."
Bob Myers KC0EW Hewlett-Packard Co. |Opinions expressed here are not
Advanced Systems Div. |those of my employer or any other
my...@fc.hp.com Fort Collins, Colorado |sentient life-form on this planet.
Randy Casciola
I looked up DAMPEN in a different dictionary and it did mention deadening and
depressing. But scientists and engineers don't use it when talking about
oscillations. They usually use DAMP. Using an online dictionary I looked up
DAMP, DAMPEN, DAMPING, and DAMPENING:
Word DAMP (damp) adj.
Definition --adj. -er, -est. 1. Slightly wet; moist. 2. Archaic. Dejected. --n. 1.
Moisture in the air; humidity. 2. Foul or poisonous gas that sometimes
pollutes the air in mines. 3. Lowness of spirits; depression. 4. A restraint
or check; discouragement. --tr.v. damped, damping, damps. 1. To make damp or
moist; moisten. 2. To extinguish (a fire, for example) by cutting off air. 3.
To restrain or check; discourage. 4. To provide (the strings of a keyboard
instrument) with dampers as a means of reducing the dynamic level. 5. Physics.
To decrease the amplitude of (a wave).
Usage Bot.
Etymology ME, poison gas, perh. < MLG, vapor.
Domain Music, Physics <-------------------------------------------------------------
Word DAMPEN (DAM'puhn) v.
Definition --v. -ened, -ening, -ens. --tr. 1. To make damp. 2. To deaden; depress:
dampen one's spirits. --intr. To become damp.
dampener --n.
Word DAMPING (DAM'ping) n.
Definition --n. The capacity built into a mechanical or electrical device to prevent
excessive correction and the resulting instability or oscillatory conditions.
Domain Botany
The word dampening had no definition in any dictionary I had.
The dictionary definition of the words DAMP and DAMPING both refer to science and/or
oscillations. Dampen, while its definition could be made to fit your usage, is
typically not used in that way. And DAMPENING doesn't even show up in any of 3
dictionaries I have.
Also, looking in the IEEE Standard Dictionary of Electrical and Electronics Terms, you
will find more than a page and a half of definitions of terms with the root DAMP in
them. While DAMP, DAMPING and DAMPED appear a total of at least 50 times (I skimmed
through while counting and may have missed some), DAMPEN, DAMPENED and DAMPENING don't
appear at all!!!
So, like it or not you are using the word inconsistently with the scientific and
engineering community.
Randy Casciola
Winfield Hill
In article <CrLnB...@armory.com>, <rst...@armory.com> writes:
> It was my contention that a 1N914 signal diode may be too small for
> the "second" inductive kick in the reverse bias direction, while he
> maintains, I believe, that such a crass animal as a 1N400x would be too fat
> a pn junction to turn on quick enough!
A 1N4002, etc. would work fine. However, the modern part to use, for coil
currents above 50 to 100mA, is a schottky diode, such as the 1N5819. It's
fast, can handle lots of current, small, cheap, ruggedly built and keeps a low
voltage drop to stay cool, etc.
The real problem with a simple "freewheeling-diode" clamp is it doesn't stop
the current flow very fast; you think you've turned off the device (e.g.
a dc-dc converter's transformer primary charging current) but current keeps
flowing! This is because dI/dt = - V/L is low since V is only a diode drop.
In many instances this is a problem. This is the reason for modern snubber
circuits. Here, the diode feeds a resistor-capacitor parallel pair, which are
at an equilibrium voltage, left from the previous snubbing operation less the
resistive discharge. Now V in the equation can be 20-30 volts (for low-V
circuits, to 180V (for ac-line powered converters), for a dramatically faster
(30 to 200x) current shutoff.
David Bashaw
service and are much faster than a diode. Just a suggestion.
Dave B
James C. Bach
In article <CrJHF...@armory.com>, rst...@armory.com (Richard Steven Walz) writes:
> In article <nbschee.23...@mailserv.nbnet.nb.ca>,
> Silas E. Cheeseman <nbs...@mailserv.nbnet.nb.ca> wrote:
> >In article <CrDx5...@armory.com> rst...@armory.com (Richard Steven Walz) writes:
> >>I would use something more
> >>substantial on any coil of sixe than a 1N914, more like a 1N400x, where x
> >>sets the peak inverse voltage withstood!
> >
> >Stopping inductive kick with a 1N400x series diode is probably futile. These
> >are rectifier diodes and don't have the frequency response required to dampen
> >a fast rising spike. Their PN junction is too wide. You need a high speed
> >switching diode such as a 1N914. Granted you should watch PIV rating.
> >From: nbs...@mailserv.nbnet.nb.ca
> > Silas E. Cheeseman
> --------------------------------
> Okay, Silas, I'll buy that the rectifier diodes are too slow, but an 1N914
> is simply insubstantial to withstand more than small signals. I see PIV
> ratings of a few tens of volts on them, when I KNOW these spikes hit MUCH
> higher!
Think about this for a second . . . the PIV rating is the Peak INVERSE Voltage
rating of the diode; in other words, the voltage the diode sees when it is
REVERSE biased (like when the coil is turned ON and connected to the power
supply), NOT the voltage of the spike you are trying to clamp.
YES, the spike voltage will go VERY HIGH if left unclamped, but, as soon as the
voltage get to Vf of the diode it will conduct and limit the voltage.
>Any ideas about a better diode than either so far mentioned?? I
> have never seen a freewheeling diode on a fair-sized relay coil that was a
> 1N914, have you? And on bigger ones I see a fat rectifier type diode
> coupled with a cap in parallel!
> -Steve Walz rst...@armory.com
>
The thing that you want to look at for a clamping diode is it's current rating;
it needs to be >= the steady-state current of the coil at the time of turn-off
because THATs the amount of peak current that will flow thru the diode. The PIV
rating should exceed the supply voltage to avoid reverse breakdown.
NOW, that being said, what's a good diode to use? A 1N400x is good for a few
amps (30 to 50A surge according to my Digi-Key catalog). A 1N540x is good for
200A surges, a GI75x is good for 400A, etc. I've used 1N400x's on many different
types of relays with no problems. BTW a 1N914 is not surge rated in the catalog.
NOW, is this the BEST way to go clamping inductive kicks? Depends.
Do you care how FAST the energy in the coil is dissipated? If so, then you'll
want to have a bigger Vf than the 1.1-ish of a diode. Let's say you have a coil
that's connected to 12V on one end, and switched to ground (thru a transistor) on
the other end. When the switch transistor turns off the "now free" end of the
coil is going to go VERY positive unless you clamp it; if you don't, you run the
risk of breaking down the switch transistor. If you use a 1N400x diode across
the coil the voltage will be clamped to about 13V, and the time constant to dump
the energy will simply be the L/R tau of the coil. If, instead, you used say a
75V zener (presuming the breakdown voltage of the transistor could survive this)
from the output to ground, then the "Free end" could only swing to 75V; but the
equivalent resistance of that zener would be 75/Icoil at the moment of turn-off,
so the "R" term of the L/R tau would be much greater, and hence a quicker
turn-off. If you are using a discrete FET for your switch, you can simply run a
zener and 1N914 in series from the Drain to the Gate, and this will cause the FET
to turn back on when Vz is reached; thus, the FET does all the work, and you can
use a wimpy zener. BTW, depending upon the number of mJ (.5xLxIxI) you are
trying to dump, some FETs are "Avalanche Rated", meaning that they will
automatically "zener" when Vds gets to a particular voltage, and you might be
able to do away with the drain-gate diodes.
NOW, do you care about the AM-band RFI you are going to generate? Are you going
to turn these coils on/off rapidly? Then placing the diode at the coil is a BAD
idea, particularly if the coil is some distance from the driver. When you
turn-off the driver and the coils' internal diode starts to conduct all the
current that was flowing from the coil to the driver disappears; thus a BIG dI/dt!
BIG dI/dt and a long wire spells RFI. If the supression diode is inside the
controller, and the controller's V+ is connected to the battery via a path that
is in close proximity to the driver output wire, then the loop area is minimized,
and the dI/dt is minimized (because the current flowing to the controller is
STILL flowing to the controller at turn-off). If you want to further reduce the
dI/dt, then waveshape the output driver . . . take our FET driver example . . .
connect a capacitor from Drain to Gate . . . as driver turns off, the Drain
voltage starts to rise, impressing a current onto the Gate node (which has a
resistance back to the pre-driver) and thus will impose a voltage on the gate . .
. depending on the values of "R" and "C" you can get a really NICE linear dI/dt
and can force the slope to be about anything you want.
Bon apetite
--
James C. Bach Ph: (317)-451-0455 The views & opinions expressed
Advanced Project Engr. GM-NET: 8-322-0455 herein are mine alone, and are
Circuits Bldg Blocks Grp Amateur Radio: WY9F NOT endorsed, sponsored, nor
Delco Electronics Corp. Just say NO to UNIX! encouraged by DE or GM.
James C. Bach
In article <nbschee.23...@mailserv.nbnet.nb.ca>, nbs...@mailserv.nbnet.nb.ca (Silas E. Cheeseman) writes:
> In article <CrJLD...@hplb.hpl.hp.com> t...@hplb.hpl.hp.com () writes:
>
> The coil opposes the change in current by creating a very high negative going
> _voltage_ spike. Currents are minimal.
ERRRRR . . . wrong!
By definition an INDUCTOR prevents the instantaneous CHANGE in current,
so at turn-off time the current thru the inductor (and hence the diode)
will be the same as the current that was flowing thru the inductor just
prior to turn-off!
>
> >The peak diode current and diode power dissipation can be reduced by inserting
> >a resistor in series with the diode,
>
> No sir, it cannot. If you insert a resistor in series with the coil-dampening
> diode you will destroy its ability to dampen at all.
>
ERRRRR . . . Wrong again!
Adding a resistor in series with the diode WILL limit the current thru the diode.
It will also also decrease the effective L/R tau and allow FASTER turn-off of
the coil. Of course, it will also mean higher flyback voltages.
> > value (Vm-Vd)/Ic where Vm is the maximum
> >tolerable reverse voltage,
>
> Who cares about reverse voltage when the pulse is negative going and reverse
> biases the diode. =======
=========
ERRRRR . . . Wrong again!
If you point the diode in the RIGHT direction, then when the negative going pulse
(assuming you're switching the "hi side" of the coil) will FORWARD bias the diode!
The diode is reverse biased when the coil is being energized (voltage applied).
BTW
Another common "Kickback Clamping" method is to use a series RC network across
the coil. As the switch transistor turns off and the current coming out of the
diode wants to "go somewhere", it goes thru the resistor and into the cap. Of
course, this causes a damped oscillation to occur . . . pick "R" for the amount
of flyback voltage you can tolerate (i.e. Icoil * Rclamp = Vspike), chose "C" so
that it's terminal voltage doesn't get too big when the energy gets dumped into
it (NOT sure offhand how to figure that).
James C. Bach
In article <nbschee.24...@mailserv.nbnet.nb.ca>, nbs...@mailserv.nbnet.nb.ca (Silas E. Cheeseman) writes:
>
> Where do you come up with this stuff John? The spike will not even exist
> with a diode present. The diode dampens it to about -0.6 volts. And 3 to 6
> amps with heavy wire; common man, it's a high _voltage_ negative-going spike.
> Current is minimal. I have used this method for years and it works great. If
> you use a regular rectifier as a kick-back dampener you will have minimal
> protection. Believe me, a 1N914 _is_ up to it.
And, so just what IS the surge current rating of a 1N914?
James C. Bach
In article <CrLn1...@armory.com>, rst...@armory.com (Richard Steven Walz) writes:
> Well, let's remember that we are dealing with a pulse that is in the
> direction of the current that was removed that we have the reactive EMF.
> I am not sure what you mean by a _negative_ going pulse. The inductor is a
> reactive device which tried to first resist an imposed voltage and then
> struggles to use its stored field energy to restore the falling voltage IN
> THE CURRENT DIRECTION! If the inductor pulses through the diode, there may
> still be quite enough energy stored on that very back swing to require
> the diode to have a PIV substantially greater than simply be greater than
> the originally applied voltage on the inductor, since it must resist being
> trashed by the second induction, which IS against its reverse biased
> direction! And I do indeed wonder why your diodes hold together on, say,
> large relay coils for 5 to 12 volts. I wonder what you would use on a 24
> volt relay or a 120VDC relay. I can understand that the fatter diode is
> 'slower' to turn-on, but I wonder whether this is important time-wise, or
> whether Joules applied over a time is most important as a protective diode.
> I suppose it depends on what we're protecting. I don't want us to draw this
> out into a big nothing, Silas, but I hope we might both learn something
> about this from someone who DOES know this!
> -Steve Walz rst...@armory.com
>
I don't believe the "Speed" of the diode is of concern here . . .
but if you DO care, use a "Fast Recovery Rectifier" . . .
James C. Bach
Children, children . . . let's not bicker over the English language . . .
everyone KNOWS that engineers aren't english majors!
What IS important here is that Mr. Silas is WRONG in just about
EVERYTHING he's said, other than that a rectifier is slower than a
small signal diode.
Henry Spencer
>I was really responding to the suggestion that a 1N914 is the diode of
>choice for clamping inductive spikes (in DC circuits). Silas Cheeseman
>says that a rectifier diode is too slow to be of much use. I don't
Well, let's take a look at what's happening here.
Initially, the diode is reverse-biased, at a voltage equal to the coil
current times the DC voltage of the coil. (I disregard transients, AC
operation, etc., here.) The diode has to be able to take that much
reverse bias. Shouldn't typically be much, the coil resistance is
usually pretty low.
Then the switch opens. Ignoring turn-on transients for the moment,
the diode is now forward-biased and is carrying the full coil current.
The diode has to be able to take that much current, at least briefly.
How briefly? Well, the current is decaying at a rate Vf/L, by the
definition of inductance (since the diode Vf is now the voltage across
the coil). Could take a while to reach zero, if you've got a lot of
inductance and quite a bit of current. Now, the 1N914's surge-current
rating is 500mA for 1s. Maybe you can fudge on this a bit... but I'd
worry.
Putting a resistor in series will not change the initial current,
although it will speed up the decay, at the cost of letting your
switch see more of the kick voltage. (In fact, the bottom line is
that *anything* you do to speed up the decay is going to increase
the voltage your switch sees. So the first thing you need to do is
to figure out how much kick your switch can stand, which will tell
you roughly how fast the decay can be.) No matter how you slice it,
your diode has to take that initial current briefly. I'd hesitate
to hit a diode with more current than the highest number in the
datasheet unless I understood its construction and device physics
well enough to predict its behavior. Surge failure modes often
differ from steady-state failure modes, so you can't just blindly
extrapolate steady-state limits: other limits may become dominant,
by starting from a lower base but rising with a steeper slope.
The transient aspect I'm less sure of. Until the diode turns on, the
coil is driving just the stray capacitance and other parasitic effects.
Could get exciting. :-) You should be able to make some guesses at
the magnitude of the effect, though.
If I was restricted to "old" diodes, and was worried about the transients,
and the coil current was more than 500mA, I think I'd cheat: put a 1N914
and a very small resistor in series, and then a 1N4004 in parallel with
that combination. That way the 1N914 handles the fast turn-on but drops
out as the rectifier starts to conduct. As others have pointed out,
though, more modern diodes combine fast turn-on with high current
capacity, and fancier snubber circuits do a better job than a lone diode.
--
"All I really want is a rich uncle." | Henry Spencer @ U of Toronto Zoology
- Wernher von Braun | he...@zoo.toronto.edu utzoo!henry
Bob Myers
> What IS important here is that Mr. Silas is WRONG in just about
> EVERYTHING he's said, other than that a rectifier is slower than a
> small signal diode.
Well, OK, there IS that aspect of all this as well....:-)
Bob Myers KC0EW | my...@fc.hp.com
Senior Engineer, Displays & Human Interface | Note: The opinions presented
Advanced Systems Division | here are not those of my employer
Hewlett-Packard Co., Ft. Collins, CO | or of any rational person.
Richard Steven Walz
Silas E. Cheeseman <nbs...@mailserv.nbnet.nb.ca> wrote:
>In article <Crp94y...@cs.cmu.edu> r...@ius4.ius.cs.cmu.edu (Randy Casciola) writes:
>
>>How can people be expected to seriously consider your technical
>>opinion WHEN YOU DON'T EVEN KNOW THE PROPER TERMINOLOGY. This
>>has bothered me for a long time:
>
>>Silas E. Cheeseman <nbs...@mailserv.nbnet.nb.ca> wrote:
>>>_negative_ going pulse. Having a diode across the coil will dampen the pulse
>
>>DAMPEN means to make or become moist. The only time you should use this
>>word when talking about electronics is when there is water on your circuit.
>>You DO NOT have a DAMPENING resistor. You have a DAMPING resistor. Un-
>>fortunately, the word DAMP could be a noun meaning humidity, an adjective
>>meaning moist, a verb (transitive) meaning to moisten, or a verb (transitive)
>>meaning (as we should be talking about here) to reduce oscillations.
>
>dampen 1. to make moist 2. to deaden, depress, reduce, or lessen.
> - Websters Second College Edition c1986
>
>Do you have anything of value to add to this discussion, Mr. Webster?
>
>From: nbs...@mailserv.nbnet.nb.ca
> Silas E. Cheeseman
Gee, Silas, he's almost as much of an asshole as I am!
-Steve Walz rst...@armory.com :)
Richard Steven Walz
Wow, Silas, this guy really *IS* more anal than *I* am!!!:)
Randy, you really should have that checked. I've heard that they have a
test now that can tell whether it'll finally reach up through your throat
and kill you!:)
-Steve Walz rst...@armory.com
P.S., I hear the de-caffeintated brands still have most of the flavor of
the fully caffeinated beans!
:)
And for Gawd's sake, can you please keep it to 70 columns or so!?? Makes
you look like a dip-shit.
-RSW
Claude Frantz
>NOW, is this the BEST way to go clamping inductive kicks? Depends.
>Do you care how FAST the energy in the coil is dissipated? If so, then you'll
>want to have a bigger Vf than the 1.1-ish of a diode. Let's say you have a coil
>that's connected to 12V on one end, and switched to ground (thru a transistor) on
>the other end. When the switch transistor turns off the "now free" end of the
>coil is going to go VERY positive unless you clamp it; if you don't, you run the
>risk of breaking down the switch transistor. If you use a 1N400x diode across
>the coil the voltage will be clamped to about 13V, and the time constant to dump
>the energy will simply be the L/R tau of the coil. If, instead, you used say a
>75V zener (presuming the breakdown voltage of the transistor could survive this)
>from the output to ground, then the "Free end" could only swing to 75V; but the
>equivalent resistance of that zener would be 75/Icoil at the moment of turn-off,
>so the "R" term of the L/R tau would be much greater, and hence a quicker
>turn-off. If you are using a discrete FET for your switch, you can simply run a
>zener and 1N914 in series from the Drain to the Gate, and this will cause the FET
>to turn back on when Vz is reached; thus, the FET does all the work, and you can
>use a wimpy zener. BTW, depending upon the number of mJ (.5xLxIxI) you are
>trying to dump, some FETs are "Avalanche Rated", meaning that they will
>automatically "zener" when Vds gets to a particular voltage, and you might be
>able to do away with the drain-gate diodes.
A driver circuit with FET protection is the subject of my US patent 3,896,367
issued July 22, 1975. Have a look on it.
--
Claude F. (cla...@bauv106.bauv.unibw-muenchen.de)
This message may contain opinions which are not shared by my employer.
The facts can speak for themselves.
Richard Steven Walz
------------------------
Winfield, thanks for that note. It was pretty much the high end consensus
if we wished to be strictly accurate. One thing you might wish to do is to
strip out your carriage returns from your post. They show up as ^M's on the
Internet/Usenet. If you are using a UNIX system, then all that's required
are line feeds as lineend separators.
In vi do: ESC :g/control-Vcontrol-M/s///g where control-V and -M are
actions you perform with the control key, and the rest is literal. The ^M
should appear in the place of control-Vcontrol-M .
-Steve Walz rst...@armory.com
Richard Steven Walz
Uh, no. They are like a fuse, they function by giving their life,
otherwise, they do nothing!
-RSW
Darin Latimer
Uh, no. They are not fuses, unless you use underrated MOV's. :)
MOV's will pass the current, but the voltage has to get to the rated voltage
for them to `turn on'. The predicament, in this particular case, is the kick
was to be conducted though the device as soon as the voltage drops negative
but the positive voltage was not to be conducted through the device. MOV's
don't care which way they are baised, thus the MOV `on' must be higher than
the highest positive voltage and the voltage will have to swing farther
negative than the largest positive voltage to be held off by the MOV before
it conducts.
Conceptually a MOV can be considered a Zener diode that works in both
directions. (i.e. a voltage difference across its terminals greater than
the required `on' voltage will cause the MOV to conduct, regardless of which
terminal is positive and which is negative.)
Darin
John Lundgren
Randy Casciola (r...@ius4.ius.cs.cmu.edu) wrote:
: How can people be expected to seriously consider your technical
Sorry about that!
--
John Lundgren
James C. Bach (jcb...@kocrsv01.delcoelect.com) wrote:
: In article <2u4jba$s...@tadpole.fc.hp.com>, my...@fc.hp.com (Bob Myers) writes:
: > Randy Casciola (r...@ius4.ius.cs.cmu.edu) wrote:
: >
: > > DAMPEN means to make or become moist. The only time you should use this
[deleted]
: Children, children . . . let's not bicker over the English language . . .
: everyone KNOWS that engineers aren't english majors!
But that doesn't give them license to misuse or abuse the language.
: What IS important here is that Mr. Silas is WRONG in just about
: EVERYTHING he's said, other than that a rectifier is slower than a
: small signal diode.
Amen!
: --
: James C. Bach Ph: (317)-451-0455 The views & opinions expressed
: Advanced Project Engr. GM-NET: 8-322-0455 herein are mine alone, and are
: Circuits Bldg Blocks Grp Amateur Radio: WY9F NOT endorsed, sponsored, nor
: Delco Electronics Corp. Just say NO to UNIX! encouraged by DE or GM.
--
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@ Rancho Santiago Community College District @ disclaim- @
@ 17th St. at Bristol \ Santa Ana, CA 92706 @ ers apply.@
@ Voice (714) JOHN GAB \ FAX (714) JOHN FRY @ @
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