A variable duty-cycle oscillator using a 555 IC applies the squarewave signal to the adjustment input of the LM350. When the output of the oscillator is low, the voltage at the output of the LM350 falls to 1.25 V (the internal zener reference).
When the voltage at the output of the 555 is high, the voltage at the output of the LM350 is given by the adjustment of Pl. Controlling the duty cycle of the signal generated by the 555 IC, it is possible to control the power applied to the load.
The LM350 must be mounted on a heat sink. The frequency of the 555 must be determined experimentally to suit the motor. This circuit doesn’t operate at high frequencies. The limit is given by the characteristics of the LM350T.
This circuit can be adapted to be controlled by a microcontroller such as the Arduino. MSP430 or PIC.
