EDN Access — 03.16.95 Simple regulator has one active par

-March 16, 1995

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Design Ideas:March 16, 1995

Simple regulator has one active part

Kennan C Herrick,
ESI Electronics Corp, San Francisco, CA

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)

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