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LM78XX is a family of positive voltage regulators used in electric circuits.
The 78xx (sometimes L78xx, LM78xx, MC78xx…) is a family of self-contained fixed linear voltage regulator integrated circuits. The 78xx family is commonly used in electronic circuits requiring a regulated power supply due to their ease-of-use and low cost. For ICs within the family, the xx is replaced with two digits, indicating the output voltage (for example, the 7805 has a 5-volt output, while the 7812 produces 12 volts). The 78xx line are positive voltage regulators: they produce a voltage that is positive relative to a common ground. There is a related line of 79xx devices which are complementary negative voltage regulators. 78xx and 79xx ICs can be used in combination to provide positive and negative supply voltages in the same circuit.
78xx ICs have three terminals and are commonly found in the TO220 form factor, although smaller surface-mount and larger TO3 packages are available. These devices support an input voltage anywhere from a few volts over the intended output voltage, up to a maximum of 35 to 40 volts depending on the make, and typically provide 1 or 1.5 amperes of current (though smaller or larger packages may have a lower or higher current rating).

  • 78xx series ICs do not require additional components to provide a constant, regulated source of power, making them easy to use, as well as economical and efficient uses of space. Other voltage regulators may require additional components to set the output voltage level, or to assist in the regulation process. Some other designs (such as a switched-mode power supply) may need substantial engineering expertise to implement.
  • 78xx series ICs have built-in protection against a circuit drawing too much current. They have protection against overheating and short-circuits, making them quite robust in most applications. In some cases, the current-limiting features of the 78xx devices can provide protection not only for the 78xx itself, but also for other parts of the circuit.

  • The input voltage must always be higher than the output voltage by some minimum amount (typically 2.5 volts). This can make these devices unsuitable for powering some devices from certain types of power sources (for example, powering a circuit that requires 5 volts using 6-volt batteries will not work using a 7805).
  • As they are based on a linear regulator design, the input current required is always the same as the output current. As the input voltage must always be higher than the output voltage, this means that the total power (voltage multiplied by current) going into the 78xx will be more than the output power provided. The difference is dissipated as heat. This means both that for some applications an adequate heatsink must be provided, and also that a (often substantial) portion of the input power is wasted during the process, rendering them less efficient than some other types of power supplies. When the input voltage is significantly higher than the regulated output voltage (for example, powering a 7805 using a 24 volt power source), this inefficiency can be a significant issue.

There are common configurations for 78xx ICs, including 7805 (5 V), 7806 (6 V), 7808 (8 V), 7809 (9 V), 7810 (10 V), 7812 (12 V), 7815 (15 V), 7818 (18 V), and 7824 (24 V) versions. The 7805 is common, as its regulated 5-volt supply provides a convenient power source for most TTL components. Each device in this series has minimal input voltage to be maintained to get regulated output.


Less common are lower-power versions such as the LM78Mxx series (500 mA) and LM78Lxx series (100 mA) from National Semiconductor. Some devices provide slightly different voltages than usual, such as the LM78L62 (6.2 volts) and LM78L82 (8.2 volts) as well as STMicroelectronics L78L33ACZ (3.3 volts)
Be advised, though, that though this voltage regulator can accept an input voltage of 36 volts, it is recommended to limit the voltage to 2-3 volts higher than the output regulated voltage. For a 5-volt regulator, no more than 8 volts should be applied as the input voltage. The difference between the input and output voltage appears as heat. The greater the difference between the input and output voltage, the more heat is generated. If too much heat is generated, through high input voltage, the regulator can overheat. If the regulator does not have a heat sink to dissipate this heat, it can be destroyed and malfunction. So the two options are, design your circuit so that the input voltage going into the regulator is limited to 2-3 volts above the output regulated voltage or place a heat sink in your circuit to dissipate the created heat.

Heat sink :
  • It is attached to the ground surface of the voltage regulator ic .
  • It increases the surface area of the ground of the ic where dissipate the heat generated.
  • If the supply voltage to the ic is more than above 2-3 volts to the regulated voltage then the ic will heat up and to prevent any malfunction or any damage to the regulator ic heat sink should attached to it.

Using LM7805 voltage regulator in the logic circuits :
For logic circuits the vcc supply needed is around 3.5V to 5.5V so we use LM7805 regulators in logic circuits for vcc supply.
The supply coming to the voltage regulators might not be a clean DC voltage it might contain some fluctuations in it and those fluctuations can lead error in logical outputs so to reduce these fluctuations from the regulated voltage an supply input pin is connected to the ground pin with help of a capacitor of 0.33μF and output pin is connected to the ground pin with the help of a 0.1μF capacitor .