Programmable power supply with LM317

.This circuit can program output voltage by turn-on/off transistors.When transistor turn on the resistor R will be connected to ground for determine output voltage.The maximum voltage of this circuit is 27V when input voltage is 28V.

T1-T4 = 2N2222 or any NPN transistors

This is the output voltage when one of A-D connected to Vin

R	Vout
100	1.8
330	3.0
470	4.0
1K	7.3
2.2K	13.5
3.3K	18.0