Electro-Magnet drop out time

[demedeirosa]

I'm trying to decrease the amount of time it takes for an electromagnet to actuate. Currently we're driving it with two MOSFET's, to drop out both sides of the magnet. The MOSFET's im using are 300V, N-CH, link below. I am familiar with the idea of letting the inductive spike peak to decrease coil drop-out times, hence the reason for going with 300V MOSFET's with a 12V magnet. I was hoping that the 300V MOSFET would not clamp, therefore allowing my spike to quickly dissipate, but in reality I am clamping at roughly 16V.

Any one have any insight?

http://www.fairchildsemi.com/ds/FQ/FQP22N30.pdf

 

[OperaHouse]

Just what are you trying to accomplish with this, speed,rep rate, wattage if not achieved by removing
suppressor. The drive voltage seems low if you are also looking for fast on actuation too.

A few years back I was involved with a glue application manufacturer. I was design a driver to
place evenly spaced dots of glue with a speed of 2ms on and 2ms off. That required quite a bit of
playing with pressures and sprong ernsions and was no were near a saleable product. Of course the
stroke length was also next to nothing and it would run hot. This grew out of an initial request for
a fairly fast driver that would not heat up the solenoid and thus change glue characteristics. We
drove the 6V coil with nearly 50V and then PWM to a low hold in current after the plunger had pulled
in. There was a solenoid driver chip that did all this LM1949 and you could glean som ideas from the
application notes. The problem is that you run into mechanical speed limitations of the solenoid.
If the solenoid actually has some stroke, the actuation time can be seenby monitoring coil current
and looking for a change in slope. This can be easiest be seen by driving a relay for practice.
The closing of a relay creates a major change in inductance and thus an easily seen slope change.
This will give you the true speed of your mechanical device. Unless the core is a permenant magnet,
there is little you can do in electronics to speed up besides letting the coil see an open circuit.
We put a bunch of time in this as I wanted to add high speed solenoid drivers to our product line.
We were not being paid for any of this development work. We met with LEDEX, the supplier of solenoids
to the glue applicator company. We were both in agreement that the mechanical design chosen was
not optimal for the application. They had also developed high speed electronic drivers at the
English division but could not find a market for them. With that the plug was pulled on that
project. It was interesting work while it lasted.

Speeding up the turn on time with a higher initial voltage may make the turn off time less
critical in short pulse applications. One definite way way to speed turnoff is to lower
current once actuator has traveled to the hold in current. THe lower the magnetic field,
the faster the field will collapse. The LT high side driver is certainly slower. The statement
that the high side is driven by a JK indicates that it is an active output and not just a power
enable. It also makes it likely this is a not a microprocessor design, limiting options.

I was surprised that the 1949 is still in production. The darlington out looks like it could
easily be replaced with a FET lowering voltage losses. This chip is kind old school and even back
then it was cheaper to do it with a transistor and some gates. With a microprocessor this is
easy to do with no added cost. Currents generally are predictable and there is no need to sample
coil current We should all be using this technology when driving a relay or solenoud regardless
of speed to reduce power requirements and board heating. Power savings is easily 50%.

 

[IRstuff]

State of the art dispensers appear to be over 30 kdph:

http://news.thomasnet.com/fullstory...fers-gross-dot-placement-of-45-000-dph-466275

http://www.speedlinetech.com/docs/brochures/camalot/Camalot_FX-D_Brochure.pdf

https://www3.uic.com/wcms/images2.n...lder_Mask.PDF/$File/Effect_of_Solder_Mask.PDF

TTFN
faq731-376

 

[itsmoked]

Interesting stuff Opera! I had to build a glue dot controller that needed to pattern dots on a line that ran at 70MPH. The very next problem they had was getting the solenoids to run faster. This was for Grayco.

Keith Cress
kcress -

http://www.flaminsystems.com