Diode voltage

[Pete the Elaner]

I plan to use frog polarity for route indication.

I have taken a feed from each bus back to the panel as well as a connection to each frog switch.

 

Do I need a resistor for every diode or would 1 between the each of the bus feeds & the diode matrix be sufficient?

From memory, I will have about 12 LEDs running from each bus.

[Paul-H]

Given how cheap resistors are I would go with one on each diode.

 

Paul

[John ks]

If your circuit is something like the top drawing then you might want to consider adding diodes (1N4004 or similar) as per the bottom drawing

 

 

 

DCC is an AC voltage

 

With an AC voltage across a LED on one half cycle the LED conducts & its current is limited by the resistor & the voltage across the LED is its rated voltage

 

On the other half of the cycle there is no current flowing through the resistor & therefore no voltage drop across the resistor, the result is you have the full DCC voltage across the LED & this could cause the LED to fail

 

John

[Pete the Elaner]

Given how cheap resistors are I would go with one on each diode.

 

Paul

True, I just wondered if that was actually necessary or if I could be a little lazy.

[Pete the Elaner]

 

If your circuit is something like the top drawing then you might want to consider adding diodes (1N4004 or similar) as per the bottom drawing

 

 frog powered led.png

 

DCC is an AC voltage

 

With an AC voltage across a LED on one half cycle the LED conducts & its current is limited by the resistor & the voltage across the LED is its rated voltage

 

On the other half of the cycle there is no current flowing through the resistor & therefore no voltage drop across the resistor, the result is you have the full DCC voltage across the LED & this could cause the LED to fail

 

John

 

Thanks for mentioning it, but I was already aware of & planning around.

My intention was not to use a plain diode for the reverse but a red LED, placing this on the line which was not chosen.

[Suzie]

 

This might be useful, you can use one or two 2-pin bi-colour LEDs to give the indication if required and the colour is not important - use whatever you can get hold of. You might need bigger resistors if the LEDs are too bright.