Basic circuit questions

[peteski]

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?     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.

[RBrodzinsky]

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

[peteski]

Interesting Rick - thanks!  That's good to know.

[Point353]

Maybe they are depending on the internal lresistance of the MOSFET?     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.