Full bridge class d amp using 555 timer

Posted on Feb 5, 2014

So here is another improvised model circuit that will eliminate the unwanted DC offset voltage from the output that affect the previous one discussed. By the way, all previous circuits that I discussed were intended as low power  class d amp source that is adequate to drive head phones via a coupling capacitor. This means DC offset is ignored due to the added capacitor.

Full bridge class d amp using 555 timer
Click here to download the full size of the above Circuit.

The schematic shown below is a reference design with added DC offset adjust pot and a high power fet driver from MICREL but I used it as a power fet substitute to simplify the amplification and cost. With this approach, there`s no need for costly fet driver with level shifter because the PWM source requires same rail supply as with the output fet. Although chip maker MICREL mentioned that MIC4451 have built-in cross-conduction minimizer, I still provide an option to include it with the use of CD4030 exclusive or gate for added safety. This will also act as phase splitter as required by the two power switchers wired in full bridge topology. I also assumed that the would be  builder of this circuit understand several subjects like, ringings, RFI, EMI, etc. so adequate power supply by-pass capacitors and short traces of copper tracks must be implemented. Well, building a class d amp from scratch contain lots of challenge and requires courage but for some adventurous hobbyist who are bored with linear, this is worth a try. The schematic shown above requires minor tweaking on the 555 timer side due to the changes in supply voltage which is at 12 volts now. Here, aside from added offset adjust pot (50% adjust pot via R3), attention must be focused to pin 5 as well because this is the inverting input of the internal comparator which is tied-up from the voltage divider that requires tweaking also. Adjusting R1 pot will also help...

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