Author Topic: Basic circuit questions  (Read 1016 times)

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peteski

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Re: Basic circuit questions
« Reply #15 on: March 03, 2021, 09:52:59 PM »
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Should there also be a small value resistor connected between the capacitor and the photo-relay to limit the current to the 1.5A maximum specified in the datasheet?

Maybe they are depending on the internal lresistance of the MOSFET?   :D  But yes, adding a resistor would be prudent (and a bypass diode for when the capacitor is discharging its energy back to the decoder).  I think that the photo-relay should be installed in the resistor branch of the Keep-Alive resistor/diode circuit.

Actually, since the photo-relay will be conducting while the decoder is not being programmed, the relay can be installed in series with the resistor/diode combo.
I still think that adding a coil is much less complicated, and many reported that it works for them.
« Last Edit: March 03, 2021, 09:55:19 PM by peteski »
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RBrodzinsky

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Re: Basic circuit questions
« Reply #16 on: March 03, 2021, 10:19:26 PM »
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I was having real good success using the 100 uH inductor with the V4/Selects, but since the 5s came out, the inductor has no effect - cannot program with the caps attached
Rick Brodzinsky
Chief Engineer - JACALAR Railroad
Silicon Valley FreeMo-N

peteski

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Re: Basic circuit questions
« Reply #17 on: March 03, 2021, 11:34:57 PM »
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Interesting Rick - thanks!  That's good to know.
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Point353

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Re: Basic circuit questions
« Reply #18 on: March 04, 2021, 12:33:05 AM »
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Maybe they are depending on the internal lresistance of the MOSFET?   :D  But yes, adding a resistor would be prudent (and a bypass diode for when the capacitor is discharging its energy back to the decoder).  I think that the photo-relay should be installed in the resistor branch of the Keep-Alive resistor/diode circuit.

Actually, since the photo-relay will be conducting while the decoder is not being programmed, the relay can be installed in series with the resistor/diode combo.
I still think that adding a coil is much less complicated, and many reported that it works for them.
On resistance is specified as 0.2 Ω max. @ 1A.
Recommended maximum current is 1.3A.
The absolute maximum ratings also mention a pulsed current capability of 4.5A, using a signal with a 100ms period and 10% duty cycle - so a 10ms pulse.