Schematic Rise

How to Build a Bipolar Power supply for Battery instruments. A bipolar power supply overcomes those limitations. Most importantly, it can provide both positive and negative voltages from a single pair of terminals. There are no relays to switch polarity, so a bipolar supply can move smoothly from positive, through zero, to negative voltages. 

It also regulates zero volts or other very small voltages. In this Bipolar Power supply for Battery instruments schema diagram to generate regulated ± 5-V supplies from a pair of dry batteries, the schema of Fig. 1 is commonly used. In order to give protection from inadvertent reverse connection of a battery, a diode in series with each battery would produce an unacceptable voltage drop. 

The more effective approach is to fit diodes Dl and D2 as shown in Fig. 2, in parallel with each battery. When the supply is switched off, there is the risk of a reverse bias being applied across the regulators, if there is significant inductance or capacitance in the load schema. Diodes across the regulators prevent damage. When the power supply is switched on, the two switches do not act in unison. 

There is a probability that one or the other regulators will be latched hard off by the other. To prevent this, D3 and D4 are Zener diodes so that ± 5-V rails are pulled up by the batteries until the regulators establish the correct levels.