Portable barcode label printer battery switching circuit

摘要

A portable barcode printer includes a circuit coupled between a main battery and a read/write memory of the printer to provide power to the memory from the main battery with a minimal voltage drop across the circuit. The circuit is also coupled between the main battery and a backup battery to prevent leakage current from the backup battery from flowing through the circuit. The circuit in includes a P-channel field effect transistor having a drain coupled to the main battery and a source coupled to the read/write memory. A N-channel field effect transistor having a source connected to ground has its drain connected to the gate of the P-channel field effect transistor so that when the N-channel field effect transistor is turned, on the P-channel field effect transistor is turned on and driven to saturation to allow a positive current flow from the drain to the source of the P-channel field effect transistor.