Many discrete and ICs need bipolar (dual or ± V) supplies. This can be easily accomplished with two three-terminal regulators, as illustrated in figure. Opposite-phase ac is provided by the transformer’s secondary and a grounded center tap. The single full-wave bridge converts these into positive and negative dc voltages (with respect to the grounded center tap). Filtering (with respect to ground) is provided by capacitors C1 and C2.

The LM 340 provides regulation of the positive voltage, while the LM 320 regulates the negative voltage. It is very important to mention here that LM 320 has a different pin configuration than the LM 340. The case of the LM 320 is not ground. So care is to be taken while mounting the negative regulator.

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