[GreenKeys] Loop power supplies

[Jeffrey Angus]

On 3/4/18 10:41 PM, drlegendre . wrote:
> @Jeff
>
> Ok.. so by using a tube as the pass element, they're eliminating
> the inductive rise time of the high-value rheostat(s) which would
> otherwise be in series with the output current. Is this the whole
> consequence?
Compared to the inductance of the selector magnet, the inductance
of the meter and 2K resistor is statistically zero.

On 3/4/18 12:33 PM, Nick England wrote:
> FWIW - here is the manual/schematic for the TMC constant-current
> loop supply, which uses a 6Y6 tube as the pass element.
> http://www.tmchistory.org/tmc_manuals/manuals_db/psp/tm_psp-1-2_2_1_59.pdf
Again, this is a regulated current supply, not a constant current supply.

On 3/4/18 10:51 PM, Bob kb8tq wrote:
> The big deal with a constant current source is that it keeps “full
> voltage” on the magnets longer than the equivalent resistor based
> loop.
Not exactly, they both have have full voltage available.
The difference is the source impedance of the voltage.
What causes the faster rise time is effectively having the high voltage
across the inductor with no current limiting until the circuit reacts and
increases the tube effective series resistance.
> A less significant benefit is that you *might* put a bunch of magnets
> in the loop and it would still stay at 60 ma. It would be slow, but it
> would have a 60 ma current at idle.
With a true constant current source, yes. But the above unit is a current
regulator. The current has to be set every time the load changes.



-- 
"I am a river to my people."
Jeff-1.0
WA6FWI
www.foxsmercantile.com