The AC supply is fed to the transformer which is stepped down to 12V AC. Variable Power Supply with Digital ControlĪ variable power supply circuit is built with variable positive voltage regulator LM317, CMOS decade counter IC CD4017, timer IC NE555 and fixed negative voltage regulator LM7912. HVAC (Heating Ventilation Air Conditioning).The LM317 voltage regulator has many electrical applications. A variable resistance is connected across the ADJ pin of the regulator. Diodes are used to protect the regulator from excess flowing through if any voltage source is connected across the output terminals of the regulator. The capacitor C3 bypasses the ADJUST pin of a voltage regulator to ground to improve the ripple rejection capability. Capacitor C4 also prevents the LM317 voltage regulator to act as an oscillator. The capacitors C2 and C4 are used to eliminate the ripples if the filtering process is done away from the regulator. The smooth, non-pulsating DC signal is fed to the voltage regulator. Now the output with capacitance will be as shown below figure and further filtered to get pure DC. This pulsating DC also has some unwanted current (ripples) which makes it impossible for using in powering applications.Ī smoothing capacitor which acts as a filter is used to remove unwanted current (Ripples).
The polarity of the output cannot be inverted and has large ripples in it. The voltage from the step-down transformer is then fed to the bridge rectifier which generates a continuous pulsating DC signal. Finally, the voltage is regulated using a regulator IC. Then capacitors are used to filter the pulsating signal into a smooth non-pulsating DC. The bridge rectifier gives a continuous pulsating DC signal.
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