The top circuit, in the diagram above, is a half-wave rectifier and you can see the circuit’s effects on a sinusoidal signal. What is the bottom circuit and how would it effect a sinusoidal input?

This circuit was designed to meet a medical application’s requirement to drive a laser diode with reasonable precision and a minimum of components and footprint (the device is now in clinical trials).

The polarity markings on LEDs (Light Emitting Diodes) seem to be a common cause of confusion. The polarity may be indicated by a flat section on one side of the body or by one lead being shorter than ...