It has long been known that the simple combination of a depletion-mode MOSFET (and before these were available, a JFET) and a resistor made a simple, serviceable current source such as that seen on ...

This design idea reprises another “1A, 20V, PWM controlled current source.” Like the earlier circuit, this design integrates an LM3x7 adjustable regulator with a PWM DAC to make a programmable 20 V, 1 ...