Circuit knowledge

This Switch Selected Fixed Voltage Power Supply Circuit Diagram can serve as a battery eliminator for various devices (such as tape recorders, small radios, clocks, etc.). Si selects a resistance that is predetermined to provide a preselected output voltage. In this schema, various commonly used supply voltages produced by batteries were chosen, but any voltages up to the rating of Tl (approximately) can be produced by choosing an appropriate resistor. Remember to provide adequate heatsinking for Ul.