National Semiconductor’s LM317T is a commonly used adjustable voltage regulator that can provide an output voltage of 1.25V to 37V with a maximum current of 1.5A. The output voltage can be adjusted with a potentiometer. The circuit in Figure 1 replaces the potentiometer with an analog voltage, which can be controlled by a PWM (pulse width modulation) signal. This signal can be controlled by a microcontroller or any other digital circuit. The same microcontroller can also dynamically monitor and adjust the output of the LM317T.
Through an RC low-pass filter and an operational amplifier, the PWM signal can be converted to a DC level for adjusting the output voltage of LM317T. By changing the pulse width of the input signal, an analog voltage of 0V~5V can be generated at the output of the low-pass filter. The op amp multiplies the voltage to obtain the required voltage range.
Popular ic chip you may need:
74LS76
2SA1020
2MBI100N-060
VN66AFD
