[GreenKeys] [External] Re: low Voltage Loop Supply

[Daniel Jones]

So I have finished this loop supply powered by 24vdc.  

It’s set at about 110v with a 10w 2k resistor and rests right at 60ma.  I have not had a chance to try it yet, I will have more time this weekend. 

Daniel
K6YIC 

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Sent from my iPhone

> On Mar 24, 2022, at 19:06, Jones, Douglas W <douglas-w-jones at uiowa.edu> wrote:
> 
> From: Jim Haynes [jhhaynes at earthlink.net] -- Thursday, March 24, 2022 5:31 PM
> 
>> I've seen some published circuits for a selector magnet driver that
>> takes advantage of the constant-current characteristics of a transistor
>> to make the loop current rise faster than it would with a simple
>> resistor. 
> 
> See here:
> -- https://homepage.divms.uiowa.edu/~jones/step/current.html
> 
> I wrote that on the subject of current limiting for motors, but the theory is exactly the same with current loop supplies.  Figure 4.2 shows the impact of different voltages on the rise and fall time in the motor (or loop) current with a series resistor used as a current limiter.  Figure 4.3 shows a simple saturating bipolar transistor current limiter, and Figure 4.4 shows the waveform you can get with it.
> 
> For a TTY current loop, I wouldn't bother with a switching limiter, either open loop or closed loop, but it could be done.
> 
>         Doug Jones
>         jones at cs.uiowa.edu
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