Linear regulators can do it easily, if used in a constant-current driver configuration. That constant can be variable, so regulated-current might be a better na

Linear regulators can do it easily, if used in a constant-current driver configuration. That constant can be variable, so regulated-current might be a better name. Your classic LM317 linear regulator can do it pretty easily, with a potentiometer instead of a fixed resistor to set the output current. Section 9.3.3[1] of the datasheet describes the circuit, though in practice you might add a couple of capacitors for stability. There are also a number of discrete-transistor circuits. A current mirror with a rheostat is probably the simplest, though not generally ideal performance. [1]https://www.ti.com/lit/ds/symlink/lm317.pdf?ts=1734395381792#%5B%7B%22num%22%3A391%2C%22gen%22%3A0%7D%2C%7B%22name%22%3A%22XYZ%22%7D%2C0%2C464.4%2C0%5D https://www.ti.com/lit/ds/symlink/lm317.pdf?ts=1734395381792...