Intended as a replacement for generally poorly regulated `wall-type` ac/dc adapters, this circuit offers superior p
erformance to simple, unregulated adapters. Voltages of 3, 6, 9, and 12 V are available. The DPDT switch serves as a polarity-reversal switch. R2 through R6 can be replaced with a 2.5-kfl pot for a variable voltage of 1 to 12 V. R7 through RIO can be replaced by a fixed resistor of about 1 kfi if the LED1 brightness variation with output voltage is not a problem.