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As part of a college project I have to design a working Class-D audio amplifier.

One of the first challenges is to generate a triangular wave at a frequency arround 100kHz.

In order to do this I have in mind generating first a square wave (using a 555 timer in an astable configuration) and then integrate it. Then I encounter some problems:

  1. The device has to be single powered (5V taken from a USB plug)
  2. Becouse of that limitation I cannot use a simple Inverter Integration using an operational amplifier.

Any ideas on how to solve my problem?

Thanks in advance, and sorry for my bad english :/

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  • \$\begingroup\$ Maybe you can include a dcdc converter that provides -5V and simplify your design. Is this a possibility you thought of? \$\endgroup\$ – Vladimir Cravero Oct 16 '16 at 15:44
  • \$\begingroup\$ edn.com/design/analog/4312118/… \$\endgroup\$ – JIm Dearden Oct 16 '16 at 17:56
  • \$\begingroup\$ 100kHz is too low for a ClassD. Human hearing can be upto 22k, you really should aim for a decade higher to mitigate phase and amplitude distortion's \$\endgroup\$ – JonRB Oct 16 '16 at 18:50
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A class-D audio amplifier does not necessarily need a triangular wave generator, a good alternative could be a self-oscillating class-D amplifier (-> Google).

In case you have to use a carrier-based class-D you could use the following configuration for the carrier generation (link)

enter image description here

A 100kHz carrier frequency might be a little bit too low, I suggest to increase it to 200 or even 300kHz.

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  • \$\begingroup\$ This is part as a College project so we are forced to use a PWM modulation and not Sigma-Delta Also the solution you propose does not work in my case due to the power supply limitations. We are using a single power supply (5V) so I cannot use the inverting Integrator \$\endgroup\$ – jagjordi Oct 16 '16 at 15:43
  • \$\begingroup\$ @jagjordi - There are plenty of opamps that can perform an admirable job of making a working triangle wave generator. \$\endgroup\$ – Michael Karas Oct 16 '16 at 15:55
  • \$\begingroup\$ @jagjordi - This solution can be used with a single supply as well, shouldn't be too hard to find out how. There should be some effort on your part as well. \$\endgroup\$ – Mario Oct 16 '16 at 16:24
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The following circuit which you can simulate in LTSpice will generate a nice triangle waveform of ~200KHz which has a swing from about 0.5V to 4.5V.

enter image description here

Note that it is desirable to use an actual high speed comparator for the Schmidt trigger so that the triangle wave has well defined tips on its waveform. Using an opamp can cause the triangle waveform to get rounded off.

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I'll finally go for this design: enter image description here

Thank you for your help. I really apreciate it :-)

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