[GreenKeys] New 60ma current loop driver board design

[Jeffrey D Angus]

On 10/27/2016 8:57 PM, drlegendre . wrote:
> So you're counting on the limited duty cycle to bridge the gap between 
> the 120 @ 60mA
> (7.5W) and the USB power of 5V @ 250mA (1.25W)? That seems like a 
> trick, but I can see
> how it might work - but the loop length will have to be fairly short, eh?
What makes it work is that it doesn't require the 120 volts @ 60 mA for
the entire bit duration.
The current required to hold the selector magnet in position is much less
that the current required to pull it into position. The need for 120 
volts is
only on the initial leading edge to overcome the inductance of the coil.

All in all, it's a really elegant approach.

Back "in the day" when I was playing with (model) trains, we would use
a series resistor to limit the current in a solenoid operated switch
machine. But we'd have a hefty capacitor on the coil side of the resistor.
The result, when you'd connect the coil across the cap was a nice crisp
SNAP of the actuator followed by a even nicer low power holding current.



-- 
Jeff-1.0
wa6fwi
http://www.foxsmercantile.com

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