Dual regulated power supply is needed in many digital and analog circuits.Operational Amplifier like UA741 needed dual regulated power supply to operate.In normal regulated power supply,only positive voltage is regulated this leads to ground loop coupling which produces noise when powering circuits like FM transmitters using IC555. That's why FM transmitter circuits are always powered using battery to eliminate noise.In digital circuits dual regulated power supply is used for safer operation of Analog To Digital Conversion without any error.
Step 1: Components Required
- LM 7805
- LM 7905
- 1000μF, 25V -------------------2
- 10μF, 50V-----------------------2
- Two pin screw terminal------3
- General Purpose PCB
- 12V-0-12V, 500mA
- Red Color
Step 2: Schematic Diagram
Step 3: Operation of Circuit
The four diodes are used to form bridge rectifier.The two terminals of secondary winding of transformer are connected to bridge rectifier to have pulsating DC.Ground is taken from the centre of secondary winding of transformer.One 1000μF capacitor is connected between the positive output of bridge rectifier with respect to ground.Another 1000μF capacitor is connected between the negative output of bridge rectifier with respect to ground.The capacitors are called as filter capacitors.It filter out AC voltage and allows only DC voltage. Here we have used Positive(LM7805) and Negative voltage regulators(LM7905) to have +5V and -5V.The purpose of using voltage regulators is to make a perfect straight line DC.The straight line DC will have 0Hz frequency,so it is called as straight line DC.The voltage regulators will also maintain constant DC voltage without any deviation.The 10μF capacitor at the output of voltage regulator is used to maintain stable voltage at output.The LED is used for indication purpose.
Step 4: Assembling the Circuit
I had soldered the +5v and -5V dual regulated power supply circuit in a general purpose PCB according to the schematic diagram.
Step 5: Result of the Circuit
The +5V and -5V are get added up and together shown as 10V in multimeter.The output of LM7805 is +5V and the output of LM7905 is -5V.Now it is ready to provide +5V and -5V to power up analog and digital circuits that requires dual regulated power supply to operate.