Full Member level 5
pwm class d
Can any1 introduce me some books or papers about High Power PWM amplifiers or Class D amplifiers?
Member level 5
555 class d amplifier
A few months ago there were a few aticles about this subject on Planet Analog Newsletter ( the EDN Newspaper)
So you can check this out.
Full Member level 3
Here are some papers on class D power amplifier
AES 4917 - Paralleled Phase Shifted Carrier Pulse Width Modulation (PSCPWM) Schemes - a Fundamental Analysis.
AES 4446 - A Review and Comparison of Pulse Width Modulation (PWM) Methods for Analog and Digital Input Switching Power Amplifiers.
AES 5039 - A Review and Comparison of Digital PWM Methods for Digital Pulse Modulation Amplifier (PMA) Systems.
/ Deleted, download from http://www.icepower.bang-olufsen.com/sw1062.asp
Full Member level 5
dc offset comparator pwm
Thank you for answering.
But i am beginner in this field and need some basic materilas.
Advanced Member level 5
karsten nielsen pwm
This idea has been around for several decades. One serious practical problem is is distortion. Another is the EMI radiation. This has been tried by many audio companies and they never brought the products to market. There are several main sources for distortion. One is the linearity of the triangle waveform generator. Another is the harmonicsidebands of the harmonics of the sampling frequency. Another is the errors in sampling by not using a sample and hold.
If you want something to play with try this. You need to have a triangular wave. For experimenting, the 555 timer capacitor voltage is close enough. Put this to one input of a comparator. Use an op amp to adjust the gain and DC offset of your audio signal so that it is always within the voltage swing range of the 555 capacitor. Put This to the other comparator input. The output should be the PWM signal. For crude experimenting, put a small speaker in series with a capacitor to the comparator output. Your ear and the speaker quality will provide the low pass filtering. You can experiment with the effects of 555 frequency. Notice how the distortion gets very bad when it gets near twice the audio frequency.
Full Member level 3
This should be an elementary introduction
Advanced Member level 1
audio power amplifiers pwm from dutch
here's a quick explanation.. hope it helps!
ok there are two ways that this is done.. PWM and PFM.. PWM is pulse width modulation - frequency is constant, much higher than the 20kHz upper limit of the ear. let's say 500kHz. If you have a steady signal, you will get a duty cycle that is equivalent to your voltage..
max output voltage of the system is 10v.. If your input signal is 1v, a class d amp is making 500kHz square waves at 10% duty cycle - full on for 10% of the time, full off for 90%. Into a slow network like the ear or a LRC of a speaker, this seems like just 1v.. Opposite side, if you have 9v signal, the PWM will be banging out square waves at 90% duty cycle, which equates to 9/10 or 9v..
To make a 1v-9v sine, you sweep from 10% to 90% duty and back again. The triangle wave explanation is a pretty good analogy, but I like saw waves..
take a comparator.. on one input you put your music or whatever, we will pretend it's a perfect sine wave from 0-10v (or 0-1v who cares!). On the other, you put a saw wave.. 500kHz, it ramps from 0-10 500k times a second. Every time the input is HIGHER than the saw, your comparator is on, giving a 1 output. when the saw ramps up to be higher (at 9v for the peak of the 1-9v sine) the comparator turns off.
Since it does this ramp 500k time a second, you get short pulses (10% duty) for low input signal like 1v, and long pulses (90% duty) for high input signal like 9v. as your music input wiggles up and down, this comparator keeps changing the duty cycle to match the input.
I'm sure you see a diagram like this when you learn about switchers or class D amps.. The reason it is very efficient is because you don't have to treat your power mosfet like a resisitor, varying the gate with the signal and wasting lots of power. In class D, you turn your power mosfet on all the way (maybe only 50mOhm RdsOn) for a little while, then turn it off completely once the saw wave passed the input signal. VERY NICE for minimizing switch loss!!!
PFM is pulse frequency modulation.. This guy only pulses for a very small fixed time (say 500ns - fastest output freq is 1MHZ) but when input is 9v, we are pulsing very very quickly over and over - again seems like 90% duty cycle, just made of many tiny pulses. 10% duty cycle for 1v output gives us the same size pulses, but farther apart.
PWM is much easier to implement, I don't know whether anyone has even made a PFM audio amp.. It's a more wasteful system but easier to control. It seems like PWM should be easiest, but you can run into trouble at high frequency if your signal to compare to has to go thru a slow network like a cheap amplifier or long wires. Now your PWM compares to something slow, and this mistake makes the next cycle have a bigger mistake. No way to escape this spiral once you hit it, but for audio you will never even see this case, 20kHz is no problem unless you have a mile of wire, or use 30kHz switcher (saw) frequency - below nyquist criterion (need at least 2x base frequency)
I say run the saw at 1-2MHz, you will have an extremely smooth system. Now your problem is the fact that headphones are inductors! All this switching will give you kickback ringing when you switch into an inductor. You can add a cheap RC filter between the switcher output and the speaker to make the speaker see DC, or there are more complicated, more "perfect" designs that compensate..
OK now i hope the tutorials take over.. Ask any questions if this seems confusing! Good luck!
13th December 2003, 18:47 #8
Advanced Member level 4
simple 555 pwm class-d
Here are some good articles from Bang & Olufsen ICEpower
Karsten Nielsen's Ph.D. thesis: Audio Power Amplifiers Techniques based on Efficient Power Conversion:
Member level 2
555 timer class d amp
I worked on class D amp before. My work is supposed to be based on Mark Smith's Class D audio amplifier.
In that specific design, an interesting nonlinear control scheme is proposed (one cycle control). Even today, I saw a paper on one cycle control (chip) DC-DC converter in the latest JSSC. In terms of performance, I don't see significant advantage over other traditional approach.
As explained by others, the main difficulty needs be tamed is THD. However, unless high switching freq is used (or the saw freq), there is not much room to play. Multiple level modulation is a possiblity. Some even proposed a combination of linear and class-D solution.
Since we are talking about power efficiency here, soft switch in general is helpful due to the increasing switching freq.
In terms of application, I believe it shall has huge market potential in places like subway, airport, train, plan, and even music hall.
5th March 2004, 16:32 #10
Member level 1
26th April 2004, 19:24 #11
Member level 4
pulse width modulation class-d -patent
This is a quite old paper but very useful for Class D amplifier design
Full Member level 2
class-d pwm ringing
This Document may helpful for You
21st April 2006, 01:31 #13
Newbie level 1
class d amplifier with lm555
HI, I worked for Infinity car & home audio amplifiers, check this amplifier out and see that it has less than 1% THD at 1300W RMS, ooo_http://www.infinitysystems.com/caraudio/product.aspx?ProdId='REF1211A'&Ser=REF&Cat=AMP, also other Amps full frequency range had less than 1% THD so problems of noise are cleared now, armonics? new filters on newer electronic components should take care about them.
Full Member level 2
I have seen 2 applications, They have more details, www.national.com and www.irf.com
Member level 3
class d distortion
now which company can design class-d amplifier?
Full Member level 3
Re: PWM-Class D Amplifers
Hello, i've done a school project in this area and it performs quite well. my work was based on a sigma-delta modulator with a max frequency of about 450KHz and i achieved 50dB SNR, and with just a few modifications i could get more out of it.
From the research i've done i got the idea that it is possible to make good and powerfull switched amplifiers but most of the techniques that allow a reduction in distortion and error are patented, anyway saw/triangle waves should be avoided because of the linearity required and the harmonic sidebands, just like flatulent said.