A4988Power
Stepper motor driver
How the A4988 application circuit works — the bipolar stepper motor driver with microstepping and PWM current regulation.
Power
7805Power
High current regulator
How to get past the current limit of a 7805 regulator by adding a PNP pass transistor. Resistor Re, together with the MJ2955's VBE, sets when the transistor steps in to share the current, taking the output up to about 5 A.
7805Power
Constant current source
How to use a 7805 voltage regulator as a constant current source. A single resistor sets the output current at I = 5 V / R, taking advantage of the fixed 5 V the regulator keeps between its output and common pins.