Single-inductor Circuit Generates Bipolar Supply Voltages

摘要

Many circuit techniques can generate bipolar supply voltages from a single positive voltage, but most of them require multiple inductors. In Figure 1, a single inductor and three Schot-tky diodes derive +15 V/-14 V from a +5-V source, while reducing the circuit size and minimizing cost. The circuit is capable of meeting the demands of most analog circuitry, including audio, instrumentation, and industrial applications. It provides output currents up to 200 mA with low output ripple (100 mV_(pp)), and drives several amplifiers drawing 5 mA to 10 mA each. A voltage-mode, step-up switchingrnconverter requiring no expensive current-sense resistors (U1) generates the +15-V output using a fixed on-time and minimum off-time. The negative rail is generated by an external charge pump consisting of D2, D3, C5 and C6. Because the negative rail is not regulated, it is not as stable as the positive rail, and varies with current drawn from the positive supply, Figure 2. Note also, that U1's latched-fault mode shuts down the controller in response to a short circuit.