FLYBACK DC - DC Converter Theory And Example

if you ever opened a power supply of some sort you might have seen this kind of component and this is a transformer but used in a flyback configuration or sometimes called a coupled inductor you will also notice that the transformer doesn't have just one input and one output as common transformers do it has a lot more pins and we will see why in this video I will show you how far back DC to DC converter works we already seen the boost and the buck converters in some past tutorials but we still have one more to see and that is the fight back DC to DC converter I will show some examples of how you could regulate DC voltage using a transformer a simple circuit and the Arduino to generate a signal for this demonstration I will also explain all the theory behind this converter so you'll learn how it works and what to have in mind and the most important what advantages this flapper converter has against the boost and the buck converters but before we start make sure that you subscribe and activate the notification bell a huge thank you to all my patrons so let's get started the sponsor of this video is JAL CPCB thanks to all users feedback they are improving their services every day even this is your first time ordering PCBs is very easy and all you have to do is to upload the Gerber files to genesee PCB dot-com select the settings that you want and you could get five PCBs of any color for only $2 what's up my friends welcome back this component here is called a choke and it is used in switching supplies to black higher frequency while passing direct current but we could use it today as a one-to-one transformer because in the end that's what it is we have two windings one on each side with the same amount of turns and the FIR magnetic material passing through and that creates a transformer we could use this in today's experiment as a flyback transformer and create a DC to DC converter so I place this component on my breadboard I will use the Arduino to create a fast PWM pulse that will change its value according to this potentiometer as you can see now on the oscilloscope we will see later how this pulse can change the output voltage of our circuit I apply this post to some transistors that will be connected to the primary winding of the flyback transformer and at the secondary we have to place a diode a capacitor and a small resistor as a load now i supplied 12 volts at the input of this simple circuit and look what happens by changing the pwm signal we can change the output voltage just as with the buck or the boost converters from the past tutorials we can get a pretty decent control of the output I can easily set it to 5 volts for example using the potentiometer but instead of the potentiometer we could add a simple feedback connected to the Arduino analog input and set the voltage at a defined value let's say 5 volts and also the use coupled inductor doesn't have to be this big a small one would do the job as well as you can see with this other one we can still regulate the output they could come in all sorts of shapes and sizes so it's very simple to regulate DC voltage with this circuit but not just that we have a lot of other advantages using this setup so let's start and see how the slapback converter works it works kind of the same as the other converter the buck-boost DC to DC converter in that video we have seen this configuration and we saw that we must have the inductor to create a magnetic field and then collapse and as a result push voltage to the other side of the circuit and by that regulate the output but now we have this other setup which is kind of the same but the sell of the inductor we have the transformer but this will be used as a so-called coupled inductor so first let's see why this won't work as a transformer but as a couple inductor in a transformer we push current through the first winding and another current will pass through the secondary winding and a load attached to that and that's something basic but in a coupled inductor we will see later that because we have a diode as a secondary winding when we push current to the first one current won't be able to pass through the canary whining but that energy must go somewhere well the energy will be stored in the core of the inductor as a magnetic field just as in case of the boost or the back converter then in the second stage of the voltage conversion when we cut the current from the primary the magnetic field created will collapse and push current in the opposite way in the secondary winding that's why in this configuration our transformer acts as a coupled inductor but if you look at the current and voltage values the coupled inductor acts as a transformer so we could have a gain and the inductance ratio is given by this formula where the end is the amount of turns of each winding okay so let's get into more details this is our circuit now here we have the coupled inductor with a one to one ratio and the primary is connected to the power supply through a switch the secondary also has a switch connected in order to disconnect the load when we need to so let's say that we closed the first switch and open the second switch the secondary will now be in an open circuit so no current could pass through that coil so the energy will build up in the core of the coupled inductor then in a very fast instant we open switch 1 and we close switch to now the magnetic field that built up will collapse and the Cori will now flow towards the that of the secondary coil so voltage drop will be created in this way so we have reversed polarity so we can use this reverse polarity voltage in order to get rid of the second switch we know that a diode would let current pass only in one direction so we change the second switch with a diode and look what happens in this case when switch 1 is closed it will create a voltage of this polarity on the primary and that will create a voltage of this polarity on the secondary so current will want to flow opposite to the diode so by that the current flow will be blocked and that's exactly what the second switch was doing when it was open at this stage energy will be pushed into the core of the inductor just as before and now when we open the first switch the field will collapse if the current in the primary was going into the dot like this current in the secondary will go into the dot like this so now we have a current flow and we have a voltage drop on the load in this direction and that's how we get rid of the second switch using a diode and to get a positive voltage what we have to do is to invert the secondary coil so now that that will be placed at the bottom here and also to invert the diode so now we have a voltage at the output of this polarity and if we also add a capacitor we could smooth the output and store the voltage and basically that's how the five back converter works we close the first switch and build up energy in the inductor core then we open the switch and the magnetic field will collapse and the current will be induced in the secondary and that will create a voltage drop at the output the output voltage is given by this formula where n is the ratio of turns of the windings and Dion and D off are the time periods where the switch is turned on or turned off so as you can see the bigger is the D on the higher will be the output this time period is given by the PWM signal that we have seen before that will control the switch but in our example the switch will be a MOSFET and connected like this to the primary winding this is the schematic that I've made for this experiment the Arduino will control the D on in the D off time according to the potentiometer value the p mm signal is supplied to a small BJT transistor that will act as a mosfet driver and that is connected to the MOSFET gate the MOSFET is our switch that will control the voltage to the primary coil at the output of the secondary we have a diode a capacitor and a load and as we have seen before we can regulate the output voltage I have told both connected at the input the inductor in this case is a one-to-one ratio that's why the output voltage could only go from the input value to lower values but now I have this other transformer with bigger ratios as you can see now with the same 12 volts input I could now reach voltages up to 20 volts with a better main transformer you could get any other values according to the winding ratio and the Dion and the our values for example let's see how the switch DC power supply works we have the main input here of 230 volts AC we passed that first to a fuse for safety then we place a capacitor and a choke to block the higher frequencies we can see these components on the schematic as well and as you can see we then pass the 230 volts to a full bridge rectifier we can see four diodes on the power supply PCB as well and that is our bridge rectifier and together with this big capacitor of 400 volts we rectify the voltage and we get a high DC voltage then we use these two transistors and a small circuit as switch one and switch two to make the transformer regulate the output at 12 volts on the other side of the transformer we have the capacitors and that's how we get 12 volts DC from 230 volts ac be careful working with high voltages so what advantages do we have first we have isolation between the input and the output and that's very important for safety as you can see there is no direct connection between the primary and the secondary so high voltage could be on one side and no voltage on the other side for example in a switch power supply like this one the main input of 230 volts AC on one side and the output of 12 volt DC on the other side having a perfect isolation between these voltages is a very good safety feature another advantage is the use of multiple outputs remember at the beginning that we saw that one transformer had a lot of outputs and that because to the same primary inductor we could add multiple secondary coils with a different winding ratio in case of two outputs the energy that builds in the primary will then divide for two outputs and we could have different values at the output we could even have one positive and one negative output depending on the configuration that's why switch power supplies with multiple outputs like this one here will have a big transformer with multiple windings another Vantage is that we could use this as a boost or a buck converter because depending on the winding ratio we could increase or decrease the voltage or the boat at the same time a disadvantage of this converter is the output noise since we have a discontinuous current at the input and the output that will create a ripple and the output voltage will have noise but that is common with all switch voltage converters and we could just ignore that for everyday circuits for more precise voltage values you might want to look into other forms of regulating then switch supplies so guys that's how five back converter works be very careful if you work with high voltages as the small power supply because that could hurt you take a look at the links below for more information you could also find the schematic that I've used with the Arduino and also the code that you need I've also made a code and a schematic with a feedback so check that out as well and if you liked this tutorial consider subscribing and give a like to this video so thank you very much for your support to my patterns and to all my subscribers thanks again and see you later guys [Music]

Channel: Electronoobs

Views: 160,322

Keywords: flyback, converter, circuit, schematic, DC to DC, boost, buck, theory, how, explination, transformer, coupled, inductor, 220V, AC, 12V, voltage, power, Arduino, PWM, variable

Id: HOXgOWoN0EY

Length: 12min 8sec (728 seconds)

Published: Sun Oct 20 2019