[GreenKeys] low Voltage Loop Supply

[ad7i]

Helloe Daniel --

I have something close, but not exactly what you are looking for.  I have a
TTY loop supply that runs from 12V DC.  It does have a boost converter to
create a second voltage source of about 45 VDC.  When the TTY line goes
marking the loop supply drives the magnets with 45 VDC and *no* loop series
resistor (however there still is the resistance of the magnets, the fuse,
the MOSFET switch and the current sense resistor).  With the 45 VDC applied
to the magnets the current rises linearly up to 60 mA (takes about 3.5 ms)
and then the microcontroller disables the MOSFET on the 45  V supply and
then switches in the MOSFET for the 12V supply with a loop resistor of such
a value as to cause 30 mA of current to flow through the magnets and stays
at 30 mA until the line goes spacing.  When the line goes spacing the
magnets are held active for another 2.5 ms to compensate for the 3.5 ms it
took to get to 60 mA on the front end, and then the 12V supply is removed
from the magnets.

If this is of interest I can send you the schematic.  The microcontroller
needs to be changed to another part because of the world wide silicon
shortage.  Have to move from a $1 MCU to a $2.25 MCU.  At least the $2.25
MCUs are still available.

Paul - ad7i




On Thu, Mar 24, 2022 at 2:10 PM Daniel Jones <djones at k6yic.com> wrote:

> I am looking to build a loop supply that can run off of 24vdc.  I run some
> old military stuff in the field and would like to be able to power a loop
> supply off of the same 24v battery’s.
>
> What would be some good suggestions?
>
> Daniel
> K6YIC
>
> Sent from my iPhone
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