The regulator of unusual simplicity (ROUS) in Fig 1 derives a low-voltage, low-current output from rectified 115 to 270V ac. Pass transistor Q1 is the regulator's only active component.
Design Ideas: March 16, 1995
The regulator of unusual simplicity (ROUS) in Fig 1 derives a low-voltage, low-current output from rectified 115 to 270V ac. Pass transistor Q1 is the regulator's only active component.
A small current through R1 starts the switching regulator oscillating. Once started, the circuit continues to oscillate, even if you remove R1. The circuit's operating frequency is ~170 kHz. Q1's rise and fall times are ~200 nsec, and its duty cycle is ~20%.
R2 senses the current output. Size R2 to suit your application. You can also select a zener diode for D2 that has a zener voltage ranging from 10 to 15V to vary the output current for a given value of R2. Shunt regulator D1 determines the circuit's output voltage.
You may connect C1 as Fig 1 shows or put it directly between Q1's source and gate. Either connection works well. (DI #1669)