Self oscillating class d with BD modulation, it's possible!

Tekko

Banned
2005-01-01 3:33 pm

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Tekko

Banned
2005-01-01 3:33 pm
Read the paper, its constant switching frequency, its not changing. Also note in my sim that there IS a output filter used, i also do not like filterless.

Filterless is generally only used where the amp is within inches of the speaker.

I know you do not like self osc, i did so myself until i discovered the way to stabilize a self osc so that it does not vary in switching freq.
 
I see a pair of 22uH inductors on the output. All is good.

If you're building this amp, I'd recommend changing the two 470n caps to a single 220n film cap (with twice the voltage rating) connected between the two outputs. Use a pair of 22n capacitors to ground. This reduces the amount of ripple current flowing through the circuit ground, which is good from an EMI perspective.

Feed the output through a common mode filter before you bring it out of the case.
 
Also, a self-oscillating amplifier will not be constant frequency. It'll be maximum frequency at zero output, and the frequency will drop as it gets close to the rails.

Unless you're doing some sort of trick where you feedforward the audio signal and dynamically adjust the control loop with it, but I don't see that here.
 

Tekko

Banned
2005-01-01 3:33 pm
No you do not! They need to be synchronized so that they run at not only the exact same switching frequency, but also in phase with each other. Only the audio signal is 180deg out of phase, thats how you get the BD mode.

Also the hypex ucd modules suffer the exact same switching frequency drop as a fixed hysteretic window class d, but also the UcD can be compensated for a constant switching freq by using complex zeros in the feedback path and what not.
 

kASD

Member
2004-12-25 12:24 pm
N/A
No you do not! They need to be synchronized so that they run at not only the exact same switching frequency, but also in phase with each other. Only the audio signal is 180deg out of phase, thats how you get the BD mode.


Wrong...!!!

With the sync cap between 2 half bridge UCDs spk outputs + to + of both, the switching frequency becomes same and the phase also becomes same, only one has to feed out of phase audio signals at input.