building regulated 5v dc power supply


Posted on Feb 6, 2014

A regulated 5 volt DC supply is essential for powering micro-controller and TTL based circuits. The output of most wall-warts and adapters is to rippled and impure for use in digital circuits. Lets build an inexpensive power supply using some discrete components and a fixed voltage regulator IC. The circuit consists of three main blocks, the recti


building regulated 5v dc power supply
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fier, filter and regulator. The rectifier is used to transform the mains AC voltage to a suitable DC voltage. The output of the rectifier is however an impure DC signal so we use a filter to clean the signal and finally a regulator to deliver precisely 5 volts, irrespective of the load connected to the output. It consists of a transformer and a diode bridge. The diodes are standard silicon 1N4007 diodes. We have chosen a 12V transformer because the regulator IC needs at-least 7. 5V of input voltage to function properly. We use a pi-filter here. The two 220 µF capacitors and resistor form the filter. Pi-filters are great for light load applications like digital circuits. Be sure to check the polarity of the capacitors before connecting them. The resistor shown above is one rated to dissipate up-to 5W of power across it. You may use smaller 3W resistors, but availability may be an issue. Don`t use the tiny 0. 25 W or 0. 5W ones though. The voltage is regulated by three terminal voltage regulator IC LM7805. This regulator provides stable 5V DC output against large fluctuations in input voltage and load. It also has internal protection circuits which `brownout` the device when overloaded. To decide the pin-outs, hold the regulator with its face towards you and legs pointing upward, the pin to the right is the input, middle pin is ground and left most pin is output. A 6. 3mm or 3. 5mm female mono TRS connector (tip, ring,...




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