Best way to simulate a load in Circuit Simulator
There is no problem modeling a resistive load with a resistor. This circuit wil produce ~45mA current limit to any load (R2). As long as you have the 5V signal on the input, the circuit will provide the current to load limited to ~45mA. If the input voltage goes to 0V, the current will go to zero (ignoring any leakage currents). You should not need to go to a MOSFET at 45mA current but I used one in my illustration just so you can see how it behaves. Your original circuit runs at about 50mA with two 2N3904 transistors. Since the MOSFET that I used has a relatively high threshold voltage, the turn on characteristics are quite different.



simulate this circuit &ndash; Schematic created using CircuitLab