This below circuit based in Intersil's ISL6719 can produce 1.5V to 20V DC at a current of 100 milli Amps from a unregulated DC source of 17 V to 100 V DC. The linear regulator used in this circuit is ISL6719 from Intersil Corp.
It uses very few external components and does not require any inductor.
C1 = 0.1 micro farads ceramic capacitor
C2 = 1 micro farad electrolytic or tantalum capacitor
C3 = 220 pico farad ceramic capacitor
R1 and R2 = Depends on the required output voltage (see the formula in the above picture)
For datasheet and further details visit