This uses our basic opamp transconductance amplifier to provide an LED with 20 mA. It is a
Broadcom Limited HLMP-CE34-Y1CDD 3.2 V 20 mA cyan LED. Its forward voltage ranges from 2.8 V to 3.5 V.
The solver is not great, so you need to start with Vset = 0 V and ramp it up to 20 mV to get 20 mA. Then, you can mess with the LED's forward voltage and see how well the opamp maintains the output current using closed-loop negative feedback. Try lowering and raising the opamp open-loop gain to see how it affects the controlled current.
