lm7805 voltage regulator

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The 78XX voltage regulator

The 78XX voltage regulator is one of the most common components on electronic boards. There are several models depending on the voltage or current you want at the output.

This is called a linear regulator the last two digits give you the output voltage eg 7805 is a 5Vdc regulator, 7812 a 12Vdc regulator, their input voltage can go up to 35Vdc.

A regulator is a 3-terminal component used to regulate voltage in an electrical circuit.

Regulators are very useful in electrical circuits when you need a stable voltage. Indeed a regulator makes it possible to enter the output voltage very fixed, which is preferable for components such as microcontrollers.

7805 voltage regulator
7805 voltage regulator

For example for a + 5V regulator, you will have a maximum drop to + 4.97V for high currents. Which is much more precise than batteries or a power adapter.

 

7805 circuit

 

Above here is the usual circuit, the capacitors serving as an interference suppressor.

The minimum input voltage should be around Vout +2/3V due to the voltage drop.

For example for the 7805, Vin must be between 7V and 25V. For the 7824, Vin must be between 27V and 38V.

(Vout: -1mV/°C) You may have the regulator performance drop or deteriorate, due to the heat.

Calculation of the dissipated power

To calculate this power, we need to know the voltage drop between the input and the output of the regulator as well as the current you should use at the output.To calculate the voltage drop between input and output, subtract the supply voltage from the regulator voltage.

Example: if you supply your regulator with 24 Volts and you regulate at 12 Volts with a 7812, your voltage drop will therefore be:

24 - 12 = 12 Volts

To calculate the power, we must multiply the current that we will use at the output by this voltage drop.

Example:

if we use 100 mA

P = 12 x 0.1 = 1.2 Watt

In practice You need to get as close as possible to the voltage you need to limit overheating and therefore the loss of energy. It will still be necessary to remain 3 v above the output voltage for the regulator to work correctly.



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