Portable equipment that can operate from a battery pack or an external power source (such as a wall-adapter or external supply) needs to be able to smoothly switch between the two power sources. This application note describes a circuit (Figure 1) that switches power sources with good efficiency and without switching noise. Figure 1.
If you are making a battery substitute power connector for one of these devices then you might have to make separate 1.5 volt battery substitute connectors and supplies for each battery the device will use. A portable external power supply can be made using a bank of external cells wired in parallel to keep your device going all day.
A portable external power supply can be made using a bank of external cells wired in parallel to keep your device going all day. If you don't need portability as with studio type work a wall wort type power adapter with a minimum rating of 1 amp can be made using a transformer, bridge rectifier and a voltage regulator.
Default supply should be provided by an external power supply (1). In parallel, the connected power supply should charge the permanently installed battery (4) via a DC coverter (2) followed by charge controller/BMS (3) - depending on the applied accumulator technology. So the battery should be constantly fully charged.
Your power supply will need to be 13V2 to 13V8*, just put it in parallel with the battery and the load. Add a buck converter to get whatever lower voltages you need. You MUST put a fuse in one of the leads to the battery, as physically close to the battery as possible.
A similar version of this article appeared in the May 13, 2002 issue of Electronic Design magazine. Portable equipment that can operate from a battery pack or an external power source (such as a wall-adapter or external supply) needs to be able to smoothly switch between the two power sources.