DIY Class D Audio Amplifier

in a previous video I showed you how [to] create a simple class AB audio amplifier that consists of the NE5554 op-amp and the Push-pull Bipolar junction Transistor output stage Now even though the circuit did work decently is there was one problem... its power loss We can identify it's cause by taking a look at the simplified functional block diagram Firstly our originally applied audio signal gets it's voltage amplified by an op-amp Since such Op amps can only supply very little power the next part of the circuit is a BJT output stage That modulates the supply voltage of 12 volts [to] become the audio signal that is not only voltage amplified, but can also supply a sufficient current for the speaker. The only problem is that the transistors work in the active region. Which means there exists a noticeable voltage drop across the collector-emitter path and thus power loss is created Which leads to an overall efficiency of around 50 to 60% To increase the efficiency though we can utilize another audio amp kinds, a class D amp to be precise. With an efficiency of up to 95%! So in this video. I will show you how such an audio amp works, and how we can create our own diy version Which consists of common components. Let's get started! [Intro music playing] First off let's have look at the simplified functional block diagram of the class D amp. On the left side we got our audio signal which is connected to the non-inverting inputs of a comparator. The inverting input however, gets connected to a triangle wave with a frequency up above 200 Kilohertz Now whenever the voltage of our audio signal is higher than the triangle voltage the output of the comparator gets pulled high, and Vice-versa. This way we basically modulated our audio signal with maximal frequencies of around 20 Kilohertz Into a high frequency square wave which then connects to a MOSFET driver the driver obviously, turns on and off two mosfets. The high side one according to the high voltage levels and the low side one according to the low voltage levels. This way, we get a powerful high frequency square wave at the MOSFET outputs. Which, since the mosfets were switched on and off in their ohmic region with a low drain to source voltage drop, created very little power losses. Now we can recreate the original audio signal by adding an LC Low-pass filter which like the name implies filters out all the high frequencies and leaves us with our original now amplified audio signal. As suitable components, we can use a 555 timer (IC), LM393, 74HC04 to create an inverted signal of the High frequency wear wave Which is mandatory for the IR2113 MOSFET driver and two IRLZ44N MOSFETS. Before we can solder a proper circuit though, I utilize the free, Easy EDA circuit design software to create an appropriate Schematic By utilizing the online component library, I imported all the required ICs and passive components And afterwards connected them all to one another according to the previously discussed functional block diagram. The only question left to answer was what kind of values should be used for the LC filter? According [to] a commercial class D amp that I had lying around, Inductances of 22uH should be suitable. The only inductors I had lying around though were 33uH ones. So I connected two of them in parallel in order to create a 16.5uH value and wrote down the two formulas to calculate inductance and capacitance* of a LC low-pass filter if We rearrange the inductor formula and insert the load impedance of 4 Ohms According to the speaker properties and the inductance of 16.5uH We can calculate a cut-off frequency of around 40 Kilohertz At which the original voltage amplitudes will be lowered by three decibel or 30% of the original amplitudes. By inserting this frequency into the capacitance* formula, we get a capacitance of around 1.03 uF Which I created by connecting 50.2 uF capacitors in Parallel and now that this schematic was complete, I gathered all the required components and started soldering them to a piece of perf board. As always, I try to utilise silvered copper wire for the most part but still had to use a bit of hook up wire at the end. And of course you can find reference pictures of my perf board layout as well as the schematic for this project in the video description aftert three hours of soldering the circuits was complete it was time to insert all the ICs connect A 15 volt power supply to the inputs and the speaker to the outputs As the first test, I hope that my function generator set to a sine wave with a frequency of only 1 Hertz to the audio inputs since the 555 timer, Created writing a voltage between around 1/3 and 2/3 of the supply voltage, We also have to use a potentiometer to add a DC offset to the Sine wave that is completely submerged Inside the triangle wave if we now take a look at the output of the comparator We can see how the slowly changing 1 Hertz sine wave creating modulated high frequency square wave and If we increase the frequency to a value that is closer to proper music The output definitely looks crazy and confusing, but the theory pretty much stays the same but by using lower frequencies We can [actually] create a lot of visible vibrations of the speaker cone which showcases that this class D amp is pretty damn powerful for its simplicity and As you would have expected it by increasing the frequency of the sine wave we produce higher tones Which means that the amp works without a problem. so I replaced the function generator with my smartphone and tested the music playback capabilities of the amp. As you can hear the music playback also worked like a charm, but the volume was a bit low The reason for that was that the music signal only features a peak to peak voltage of around half a volt while the fashion generator easily created Peak to Peak voltages of 4 volts So as an afterthought I added an LM386 op-amp in between the input audio signal and the comparator Which didn't even require complementary components Afterwards the Audio signal consisted of a peak to peak voltage of four volts as well Which was suitable to create a much louder playback of music through the class D audio amp. Now of course this circuit is definitely not perfect However the audio quality is pretty decent and more importantly, maybe you learnt something new! If so don't forget to like share and subscribe Stay creative, and I will see you next time!

Channel: GreatScott!

Views: 1,184,794

Keywords: class d, class, audio, amp, amplifier, diy, how to, tutorial, project, make, your, own, theory, powerful, operation, explain, class ab, ab, inefficient, efficient, comparison, 555, timer, comparator, lm393, inverter, 74HC04, MOSFET, mosfet, driver, ir2113, IR2113, IRLZ44N, bridge, lc, low pass, filter, test, experiment

Id: 3dQjIeYoIdM

Length: 7min 59sec (479 seconds)

Published: Sun Jun 04 2017