I am trying to control two LEDs in reverse parallel, using a signal SIG
. SIG
is an open collector signal, so it is either high impedance or pulled to ground. The schematic looks as follows:
I am trying to calculate the resistor values such that the SIG
can light one LED or the other, and passes 2mA of current given a 2V drop across the LEDs. This gives two states for the circuit to be in:
SIG
is high impedance state, soR3
passes no current, andD1
lights:
SIG
is pulled to ground, andD2
lights:
Given VCC is 12V, is it possible to solve for resistor values such that the voltage and current drops through the LEDs hold true? After trying to set some values for a resistor and solving for the other values, I keep getting negative voltages or the currents don't add up. Is it possible that the currents through the diodes can't both be 2mA?
Best Answer
This works. Solved numerically. With R3=0, which is optimal for minimum wasted power, as suggested by Peter in a comment above.
simulate this circuit – Schematic created using CircuitLab