Linear Voltage Regulators (LM7805) | AO #17

when powering a circuit you need a stable power supply with the popularity of USB 5 volts has become pretty standard but what if you need 12 volts or 3.3 volts well then you can use a voltage regulator these devices take a voltage in on one side and output a different voltage on the other side in this episode of a domes we're going to talk about linear voltage regulators there are two major types of voltage regulators linear and switching linear regulators only need a small amount of components are simple to add to the board but are not very efficient switching regulators can be made to be very efficient for a particular circuit but can be difficult to design in this tutorial we're going to focus on linear regulators we will cover switching regulators in another Adam tutorial here is an lm7805 this regulator may be the most important integrated circuit in the history of electronics it's available in many different styles this is the to-220 which is the most popular why because they are super easy to put into a breadboard and can dissipate lots of heat more on that later let's talk about how linear voltage regulators were looking at a schematic for the lm7805 you can see it is pretty simple a voltage goes on one side and a smaller voltage comes out the other these are called decoupling capacitors this thing is the source which provides the input voltage it could be a battery another regulator or even USB the output is connected to a load the load is your device like an LED microprocessor or sensor for a linear voltage regulator to work the input voltage must always be more than the output usually the input voltage needs to be at least 2 volts greater than the output if the input voltage is too low the regulator will be unstable the lowest input voltage the regulator works at is known as the dropout voltage this value can be found in the regulators datasheet here's the value for the lm7805 in LDO can operate with less than two bolts of headroom so then what is an L do in L do is a linear regulator that has a low dropout voltage for example let's look at the data sheet for the NCP 11:17 it has a dropout range from 0.9 volts to 1.2 volts to get 5 volts out only 6 volts is needed now let's talk about current and how much heat gets generated the difference between the input and output voltage creates a voltage drop across the regulator the regulator's output current is the same as its input current knowing these two things we can then calculate power by multiplying the voltage drop by the current for example if we have 12 volts in 5 volts out and 1 amp of current this regulator would drop 7 volts multiplied by the 1 amp to get 7 watts of power settle watts might seem like a small number so let's figure out what the internal temperature of the silicon will be from the lm7805 datasheet I know the thermal resistance of the package is 65 degrees C per watt multiply that by seven watts and we get an enormous 455 degrees C does this mean the chip is going to burn itself up well no because linear regulators have thermal shutdown protection when you're getting started with electronics you're going to make mistakes you're going to create short circuits accidentally actually that's not entirely true whether you're just getting started or you have 10 years of experience you're still going to short things out after all a short-circuit is a path with little or no resistance which means a lot of current will flow when a lot of current flows through the regulator it heats up as it approaches its maximum junction temperature the regulator begins to shut down dropping the output voltage this is the most common reason the output voltage might be wrong the regulator is going into thermal shutdown however there is one more reason the output voltage might be wrong and that's the decoupling capacitors win the input voltage or the load changes there will be a change in the regulators output voltage without these capacitors the regulators output voltage might swing wildly on an oscilloscope you'd see ripple voltage while a multimeter might read the wrong voltage entirely decoupling capacitors help minimize this change the input capacitor decouples or separates the regulator from the supply voltage the output capacitor provides a small buffer or the load but you might be wondering what values the decoupling capacitors do you use well we check the regulator's data sheet for our lm7805 small values like 330 nano farad and 100 nano farad are suggested by this manufacturer and that's all you need for most applications almost every circuit contains at least one linear voltage regulator so I hope you understand them better now of course we couldn't cover everything relate its regulators so we'll have some future videos to cover them make sure you follow or subscribe to a domes to know when those become available if you have questions feel free to leave comments with this video or better yet go to forum Adams comm and leave questions there 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Channel: AddOhms

Views: 185,055

Rating: 4.9511876 out of 5

Keywords: regulators, LM7805, AddOhms, lm7805, linear voltage regulator, linear regulator, voltage regulator, electronics, tutorial, voltage regulator tutorial, voltage regulator ic, lm7805 how to use, lm7805 voltage regulator, linear voltage regulator tutorial, linear voltage regulator basics, linear voltage regulator wiring, linear voltage regulator 7805, electronics basics, lm7805 circuit, linear regulator vs switching regulator, voltage converter, lm7805 regulator

Id: OAoEWaGtQjs

Length: 6min 36sec (396 seconds)

Published: Tue Feb 23 2016