By using a cheap, readily available MOSFET, you can use a single-pole switch to turn a bipolar power supply on and off without consuming extra power. In Fig 1, the switch simply controls the MOSFET gate, which switches on the negative supply. Resistor R, which can be several megohms, is not necessary if the ±6V rails are permanently connected to a load, for example an op-amp circuit. Because the MOSFET's R_DS(ON) is a fraction of an ohm, power loss is minimal, and the circuit suits moderate-consumption, battery-operated circuitry. (DI #1360)