Full Wave Bridge Rectifier + Capacitor filters + half wave rectifier

this is a full wave bridge rectifier it's used to power electronic circuits so we're going to learn in detail how they work in this video electricity is dangerous and can be fatal you must be qualified and competent to carry out any electrical work full bridge rectifiers look like this there are many shapes and sizes but they essentially consist of four diodes in a certain arrangement they are usually aligned in a diamond configuration but they can be aligned in other ways such as these we typically find them represented on engineering drawings like this this being the symbol for a diode the arrow points in the direction of conventional current this shows that ac electricity is the input and dc electricity is the output the full bridge rectifier converts ac alternating current into dc direct current why is that important because the power outlets in our homes provide ac but our electrical devices use dc so we need to convert the ac into dc electricity for example a laptop charger takes ac from the power outlet and converts this to dc to power the laptop if you look at the power adapter for your laptop and other electronic devices the manufacturer's label tells you is converting ac to dc in this example it states that it needs an input of between 100 and 240 volts with the symbol for aec electricity and this will draw 1.5 amps of current it will then output 19.5 volts of dc electricity and 3.33 amps of current notice that it also states 50 to 60 hertz this is the ac frequency and we'll look at that in just a moment in ac electricity the voltage and current constantly change direction between forwards and backwards that's because there's a magnetic field in the ac generator which essentially pushes and pulls electrons in the wires this is therefore changing between positive and negative values as it flows forwards and backwards the voltage is not constant even though the multimeter will make it look like it is if we plotted this we get a sine wave pattern the voltage changes between a peak positive and a peak negative value as the maximum intensity of the magnetic field passes the coils of wire inside the ac generator this example reaches 170 volts at its peaks so if we plotted these values we have positive and negative peaks of 170 volts if we took the average of these values we would get 0 volts that's not very useful so a clever engineer decided to use the root mean squared voltage that is what our multimeters calculate when we connect them to the electrical outlets to find the peak voltage we multiply the root mean squared voltage by the square root of 2 which is roughly 1.41 to find the rms voltage we divide the peak voltage by 0.707 for example here i have a north american british australian and european power outlets this multimeter shows basic waveforms and when i connect to any of these between the phase and neutral we see a sine wave which is indicating this is ac electricity notice that the british and european outlets are 230 volts the australian outlet is 240 volts but all three of these are at a frequency of 50 hertz however the north american outlets read 120 volts at a frequency of 60 hertz the frequency is measured in hertz but this just means the sine wave is repeating 60 times per second in the north american electrical systems and 50 times per second in the rest of the world the voltage is lower in the north american system at 120 volts whereas it's 230 to 240 volts in the rest of the world although there are some exceptions but we won't go into that in this video the peak voltage of each electrical system is therefore as follows in dc electricity the voltage is constant and in the positive region the electrons do not reverse they all flow in just one direction so if i measure this battery we see a flat line in the positive region at around 1.5 volts so this is dc electricity this solar panel also produces dc we can see it produces a flat line at around 4 volts on the multimeter we can use this adapter to measure a usb port we can see it's providing around 5 volts dc and if we plot this with the other multimeter we again see a constant flat line indicating this is dc electricity this is a four wave bridge rectifier on these input terminals we see around 12 volts ac with a sine wave and on these output terminals we see around 14 volts of dc so this device is converting ac to dc the voltage is slightly higher on the output because of the capacitor and we'll see why that is later on in this video now you need to remember that rectifiers will only convert ac to dc it cannot convert dc into ac for that we would need an inverter which uses special electronic components to achieve that but we won't cover that in this video by the way we have covered how power inverters work in detail in our previous video links can be found in the video description down below for that the rectifier consists of diodes a diode is a semiconductor device which allows current to flow through it but in only one direction so if we connect this lamp to a dc power supply it will illuminate we can reverse the leads and it will still illuminate if i place a diode on the red wire and connect this to the positive it will again illuminate but now when i reverse the leads the diode blocks the current and the lamp remains off so it only allows current to flow in one direction and we can therefore use this to control the direction of current in a circuit to form dc electricity let's see some different ways of how that's achieved if we looked at an ac supply with a step down transformer which simply reduces the voltage to a safer level the electrons are flowing forwards and backwards so the load experiences an ac sine wave the load could be anything from a resistor a lamp a motor etc if we inserted a diode the diode will only allow current to flow in one direction so the load now experiences a pulsating waveform the negative half of the sine wave is currently being blocked we can reverse the diode to block the positive half and only allow the negative half this is therefore a half wave rectifier the output is technically dc because the electrons only flow in one direction it's just not a very good dc output as it's not completely flat here i have a resistor which is connected to a low voltage ac supply we see on the oscilloscope the ac sine wave when i connect a diode in series with this the oscilloscope shows a pulsating pattern in the positive region if i reverse the diode the oscilloscope shows a pulsating pattern in the negative region if i connect two lamps in parallel one with a diode we see that the one without the diode is brighter because it's using the full waveform the other lamp is dimmer because it's only using half of this waveform the diode is blocking the other half if we view this in slow motion we can see that the diode connected lamp is flickering more because of the gaps in power therefore we can use this for simple circuits such as lighting or perhaps charging some simple batteries but we can't use this for electronics as the components need constant power otherwise they will not work correctly we can add a capacitor in parallel with the load to improve the output we'll look at that later on in this video a better improvement is to use a full wave rectifier and there are two main ways to do that we can create a four-way rectifier simply by using a center tap transformer and two diodes a center tap transformer just has another wire on the secondary side which is connected to the center of the transformer coil this allows us to use the full length of the transformer coil or just half of it because the current constantly reverses in ac electricity while in the positive or forward half the current flows through diode 1 and into the load and then back to the transformer via the center-tapped wire diode 2 is blocking the current so it can't return through here only half the transformer coil is therefore being used in the reverse or negative half the current flows through diode 2 through the load and then back to the transformer diode 1 is blocking the current the current flows in one direction through the load in either case the current flows in just one direction through the load so it is considered dc but it is not smooth it is still pulsating there are just no gaps the negative half has been converted into a positive half the waveform is not smooth so we need to apply some filtering such as a capacitor again we'll look in detail at that later on in this video the most common method used is the full wave bridge rectifier this uses four diodes the ac supply is connected between diodes 1 and 2 with the neutral between 3 and 4. the dc positive output is connected between diodes 2 and 3 and the negative between diodes 1 and 4. in the positive half of the sine wave the current flows through diode 2 through the load through diode 4 and then back to the transformer in the negative half the current flows through diode 3 through the load through diode 1 and then back to the transformer so the transformer is supplying an ac sine wave but the load is experiencing a rippled dc waveform because the current flows in just one direction in this example circuit we can see that rectified waveform on the oscilloscope but this is not a flat dc output so we need to improve this by adding some filtering using a rectifier will result in a ripple in the waveform to smooth this out we need to add some filters the basic method is to simply add an electrolytic capacitor in parallel to the load the capacitor charges during the increase in voltage and stores the electrons it then releases these during the decrease this therefore reduces the ripple the oscilloscope will show the peaks of each pulse but now the voltage doesn't decrease to 0. it slowly declines until the pulse charges the capacitor again we can further reduce this by using a larger capacitor or by using multiple capacitors in this simple example you can see the led turns off as soon as the power is interrupted but if i place a capacitor in parallel with the led it remains on because now the capacitor is discharging and powering the led during the interruptions in this circuit i have a lamp connected as the load the oscilloscope shows the rippled waveform when i add a small 10 microfarad capacitor we see that it makes very little difference to the waveform when i use a 100 microfarad capacitor we see the dip is no longer down to zero volts at one thousand microfarads the ripple is very small at 2200 microfarads it's nearly completely smooth this would be fine to use for many electronic circuits we could use multiple capacitors also here we have a 470 microfarad capacitor which has made some difference but if i use two capacitors in parallel we see the waveform is much more improved when using a capacitor we need to place a bleeder resistor across the output this is a high value resistor which will drain the capacitor when the circuit is off to keep us safe notice with this circuit that when i switch it on the capacitor charges quickly to over 15 volts but when i switch it off the dc output is still at 15 volts because there is no load so the energy is still stored in the capacitor this could be very dangerous if the voltage is high in this example i place a 4.7 kilo ohm resistor across the output we see the capacitor charges up to 15 volts and when i switch it off the capacitor quickly discharges the electrons are flowing through the resistor which discharges the capacitor we can also see that without a capacitor the output voltage is lower than the input voltage because of the voltage drop of the diodes here we have a simple full wave bridge rectifier on the input we see there is 12 volts ac on the output we have 10.5 volts of dc the voltage on the output is lower because of the diodes each diode has a voltage drop of around 0.7 volts if we look at this circuit with a diode and an led we can measure across the diode to see a voltage drop of around 0.7 volts the current in our full bridge rectifier must pass through two diodes on the positive half and two diodes on the negative half so the voltage drop combines and is around 1.4 to 1.5 volts so that is why the output will be reduced however if we were to connect a capacitor across the output we will see that the output voltage is now higher than the input voltage how is that possible that's because the ac input is measuring the rms voltage or the root mean squared this is not the peak voltage the peak voltage is 1.41 times higher than the rms voltage the capacitors are charged up to the peak voltage and then release there will be a small voltage drop because of the diodes so the output is less than the peak input but it will still be higher than the rms input for example if we had 12 volts rms on the input the peak voltage would be 12 volts multiplied by 1.41 which is 16.9 volts there will be a 0.7 volt drop here and here so 16.9 volts subtract 1.4 is 15.5 volts the capacitors are charged up to this voltage this is only the approximate answer though the amount of ripple and the actual voltage drop of the diodes will cause it to be slightly different in reality but we can see that the output is higher than the input another common filter is placing two capacitors in parallel with a series inductor between these this is used for circuits with larger loads the first capacitor smooths the ripple the inductor opposes the change in current and tries to keep it constant and the second capacitor which is much smaller will then smooth out the final remaining ripple additionally we can also connect a voltage regulator to the output this is very common and allows some variation to the input but it will provide a constant output voltage this again has capacitors on either side of the regulator to ensure a smooth dc output here we can see a real version which is connected to a 12 volt ac supply and we see it has an output of around 5 volts dc you can learn how to build your own voltage regulator in our previous tutorials links for this in the video description down below check out one of the videos on screen now to continue learning about electrical and electronics engineering as this is the end of this video you can follow us on facebook twitter instagram linkedin and of course the engineeringmindset.com

Channel: The Engineering Mindset

Views: 264,406

Rating: 4.9332061 out of 5

Keywords: full wave bridge rectifier, full wave rectifier project, center tapped full wave rectifier, half wave and full wave rectifier, half wave rectifier, full wave rectifier circuit, rectifier circuit, rectifier, bridge rectifier, analog electronics, linear power supply, peak inverse voltage, full wave center tapped rectifier, centre tapped rectifier, bridge circuit, capacitor filter, breadboard, power electronics, center tapped transformer, full wave rectifier, rectifier circuits, AC

Id: RiRyzLl4Y8U

Length: 18min 59sec (1139 seconds)

Published: Sun Mar 14 2021