Dual Rail Power Supply +/- 0 to 15V 1A by LM317,LM337
The dual rail supply which means there are two supply voltages, one positive, one negative, that are adjusted by a common potentiometer such that supply voltages are equal in magnitude. It is capable of supplying up to +/- 15V DC at up to 1A.
Two linear regulators are used, an LM317 on the positive side and an LM337 on the negative side. These regulators keep the supply voltage constant for a varying load up to a load current of around 1A. The voltage adjustment is achieved through potentiometers RV1 and RV2 in the positive side of the circuit. The clever part of this circuit comes from the mirroring of the positive voltage adjustment to the negative side via the op-amp U2 to give the circuit its tracking nature. The op-amp U2 has its positive input tied to ground via a 4k7 resistor. This means that, providing there is negative feedback around the op-amp, the op-amp will endeavour to make its negative input also at ground or 0V. The negative feedback is arranged by the output of the op-amp U2 driving the Adjust pin of the negative regulator U3 and by resistors R3 and R4. The op-amp U2 sets the voltage on the adjust pin of U3 such that the voltage at its negative input is 0V. Also as R3 and R4 are equal, the positive and negative regulated voltages must then be equal in magnitude.
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