The Class D audio amplifier - Filters (2/3)
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- Опубликовано: 22 июл 2022
- #165 In this video I continue looking at the class D audio amplifier, by focusing on the output filter. I look at the basic principles behind the single ended filter and then look in a bit more detail into the more complex BTL output filter.
Related videos:
Class A amplifier part 1 - • The Class A amplifier ...
Class A amplifier part 2 - • The Class A amplifier ...
Class B amplifier part 1 - • The Class B amplifier ...
Class B amplifier part 2a - • The Class B amplifier ...
Class B amplifier part 2b - • The Class B amplifier ...
Class C amplifier part 1 - • The RF Class C amplifi...
Class C amplifier part 2 - • The RF Class C amplifi...
Class D audio amplifier part 1 - • The Class D audio ampl...
Class D audio amplifier part 2 - • The Class D audio ampl...
Class D audio amplifier part 3 - • The Class D audio ampl...
Class D RF amplifier part 1 - • The Class D RF amplif...
Class D RF amplifier part 2 - • The Class D RF amplifi...
Further reading:
www.ti.com/lit/an/slaa701a/sl...
www.maximintegrated.com/en/de...
Datasheets and links used:
www.mouser.com/datasheet/2/11...
www.murata.com/en-eu/products...
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Very nice LC filter topic on Class-D amplifier
Excellent content!
Very interesting and well presented - thank you. LTSpice is such a great tool!
so is the Falstad online simular.
nice explanation :)
Please make videos on power supply filters and control topologies of switching converter....please
11:09: Why the Cg caps should be 10x smaller than the Cp? What is preventing me using a Type II filter only, even for a class BD modulation? That way I will get the most efficient CM filtering.
anyone has experience of sepic converter? how is the compensation done? for now i can only slow the loop down but still unstable, i am using tl494. and Type iii compensation.
Hi Fesz Electronics: How have you included the inductor model ?. I save lib file like your previous video about third models and in value field (inductor) i named as BLM21AG102BH1. Ltspice says "missing inductance". Also i put subckt model in .op field as spice directive.
You need to make the inductor into a subcircuit - hold Ctrl and right click on the inductor and change the prefix from "L" to "X"
@@FesZElectronics Thanks
I have done a multilevel class d with 4 halfbridges, 90 degree shift, get 5 levels. Unfortanely when I measure current over speaker in LTspice I get nice result with -100dB distortion level. But when I measure each bridge on on side of the speaker and the other 180 degree side, I get a very strange in fase distorted sinusoidal, using a emi filter do let it get better, so I think I deal with a common mode voltage? or differential voltage? Can I do something about it because otherwise the amp will be a 2 Mhz transmittor through the cables..
regards
Please make a series of Ltspice tutorial videos.
So when purchasing class D amplifier, we need to know what loading did the company assume the users to run? or the LPF might not work as desired
If the LPF is included into the amplifier then the output (speaker) impedance of the amplifier should also be specified.
I am wondering about the 100M resistor in your cm model. Can I ask why you put it there and why that value? You make great videos, by the way.
It’s for the DM. Basically forces an open circuit to ground in the simulation-forces all the DM current through the main differential LCR loop. LTSpice needs everything connected to ground to work. This solves that issue. High resistance value means basically no DM current would typically flow in that direction in real life
Why not Common-mode-choke + small earth caps against common-mode noise? Afaik, like beads, they typically use a core that is lossy at high frequencies, so no gain peaking..
Hello. I think there's something wrong with the Q factor. At the beginning you write sqrt(2)=1.414 at 6:00 then it's 1/sqrt(2)=0.707 at 6:35
BTW there's a TI paper on class D filtering slaa701a pdf
Hello! You are right, I said 0.707(1/sqrt(2)) but wrote only sqrt(2); I know that Ti paper, its really good! - I already included it in the description under "further reading"
Square root of 2 =1.414
Q=2^½ or 1/2^½
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High power class-d amplifier are almost always discrete circuits, chips are clipped at 350W due to silicon limitations and noise at this power level places demand on the die Ti has some the powerpath series that covers this (but with poor to average THD figures and weird speaker load conditions see fine print in the datasheet) these chips are meant for consumer grade "non-pro audio" sales volumes for obsolescence home products. It's almost exclusively beneficial to learn control structures, layout for high current applications and other areas of relevance, but this obviously reserved for people pushing into pro-audio/enthusiastic area OR engineer's from a switch mode power supply background designing high power systems.
About the filter:
In self oscillating there is a deliberate expectation to use the switching residual triangle (~1V) and the phase shift produced by the LC (90 degree) to close the loop to create a self oscillating at gain above 0db. It's been discovered recently that the BH curve of the LC inductor creates nonlinear behaviour at high power (also note the material used for class-d amplifiers use low permeability material cores with frequencies expiations of up to ~550KHz to 1MHz (high power) and 2.1MHz for smaller applications to reduce area size with reduced output power)
There are also capacitor grades used at the LC filter with exceptional qualities like a WIMA Polypropylene. (but this is another topic).
Can you please elaborate what you mean by "switching residual triangle (~1V) and the phase shift produced by the LC (90 degree) to close the loop to create a self oscillating at gain above 0db"
@@nbuzkila Self oscillation is technically an oscillator and a oscillator requires positive feedback to work. In order to get an amplifier to go into oscillation the sum of all the phase shifting amounts to 360 degrees also the gain needs to above zero dB. 1v is the oscillation at the speaker terminals is called residual switching it's very tiny in voltage 800mV up to 1volts and it's triangle in waveform shape this is used by the comparator circuit to generate PWM. To understand this you need to self study these concepts find the literature online.