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

[Daniel Jones]

So this little design works great.  Thanks for all the suggestions.  I put it in an old case I had laying around.  The total cost was $13 for the Dc-DC booster and junk I had in the parts drawer (basically the case and the 10w 2k Ohm resistor)

It runs on 24vdc so it can be powered by the same supply as my military gear.  

Daniel

Sent from my iPhone

> On Mar 31, 2022, at 15:39, Daniel Jones <DJones at k6yic.com> wrote:
> 
> 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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