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LM78xx Regulated Power Supply


It is very useful regulated power supply It is based on 78xx series ICs. We can use it for different output regulated voltages by choosing different IC numbers.



It is 78xx IC series based regulated DC supply. We can make different voltage level supplies by choosing different 78xx IC series number. For example we can choose

1) 7805 for 5V output.
2) 7808 for 8V output.
3) 7809 for 9V output.
4) 7812 for 12V output.

Vin is high level DC voltage that is provided through D1 to 78xx series IC for regulation. Diode D1 is used for blocking reverse voltage polarity applied by mistake and saves whole circuit from reverse polarity. capacitor C1-C4 are used for filtration purposes. LED D2 is an on/off indicator and resistance R1 limits the current through it. R1 can be changed according to input voltage. Diode D3 is used here to protect 78xx IC from reverse voltage across it’s output due to C4 when power is removed and also stops overcharging of capacitors C3, C4. At output pin 3 of 78xx we can get regulated DC supply that is at low level than input supply at pin 1 of 78xx. For better circuit performance and protection of 78xx IC input supply should be greater than output by 3V to 5V range. More voltage input than output will cause the 78xx IC to be hot and can damage the IC permanently. Because there will be more voltage drop across 78xx IC and so more wattage will be dissipated. Use heat sink for better performance of IC when there is more current requirement at output.

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