A member asked me to share some info on my class D amp project.
I have been working on it for some time time now & am currently at the point where I have a working prototype.
Circuit Details:
I use 2 opamps configured as a schmitt trigger & integrator to create a triangle waveform. This is compared to my audio signal using a quad comparator. The comparator drives two high & low side drivers which in turn drive the mosfets. Thus I have a full bridge. Dead time is inserted using RCD networks on the inputs of the mosfet drivers. This allowed me to adjust the (very small) dead time. I did this as I was concerned that the dead time provided by many IR driver ICs would be too large for the high frequency operation I was aiming for of 650kHz. When loaded I can't get it linear and symmetrical above 250kHz so have changed the design to include a buffer.
The circuit has been deliberately built using through hole components. The only surface mount parts are the two inductors in the output filter.
Upcoming tasks for me to do
-Measure the minimum dead time needed to avoid shoot through and compare it to the range of driver ICs available with dead time controls to see if it is feasible to change driver ICs, creating a simpler, more accurate & elegant dead time control.
-See how fast I can switch with improved pcb layout over the 1st revision board (the 100pF integrator cap was accidentally placed far from the integrator opamp)
-Reduce the quiescent current from 79mA @ 14V to <50mA.
-Build a final prototype
-Build a (already designed) speaker protection circuit for switch on
-Write up the entire project to share via my website (and on the forum)f
Attached are my schematics for all who are interested, feel free to comment. Note that this is a fully operational amplifier, not a conceptual one. Unfortunately the schematics have not yet been tidied after much tweaking & updating.
The scope photo shows my triangle wave working at nearly 0.5MHz.
I will try upload photos of the constructed circuit soon but my digital camera is stuffed so I'll have to find another way....
I have been working on it for some time time now & am currently at the point where I have a working prototype.
Circuit Details:
I use 2 opamps configured as a schmitt trigger & integrator to create a triangle waveform. This is compared to my audio signal using a quad comparator. The comparator drives two high & low side drivers which in turn drive the mosfets. Thus I have a full bridge. Dead time is inserted using RCD networks on the inputs of the mosfet drivers. This allowed me to adjust the (very small) dead time. I did this as I was concerned that the dead time provided by many IR driver ICs would be too large for the high frequency operation I was aiming for of 650kHz. When loaded I can't get it linear and symmetrical above 250kHz so have changed the design to include a buffer.
The circuit has been deliberately built using through hole components. The only surface mount parts are the two inductors in the output filter.
Upcoming tasks for me to do
-Measure the minimum dead time needed to avoid shoot through and compare it to the range of driver ICs available with dead time controls to see if it is feasible to change driver ICs, creating a simpler, more accurate & elegant dead time control.
-See how fast I can switch with improved pcb layout over the 1st revision board (the 100pF integrator cap was accidentally placed far from the integrator opamp)
-Reduce the quiescent current from 79mA @ 14V to <50mA.
-Build a final prototype
-Build a (already designed) speaker protection circuit for switch on
-Write up the entire project to share via my website (and on the forum)f
Attached are my schematics for all who are interested, feel free to comment. Note that this is a fully operational amplifier, not a conceptual one. Unfortunately the schematics have not yet been tidied after much tweaking & updating.
The scope photo shows my triangle wave working at nearly 0.5MHz.
I will try upload photos of the constructed circuit soon but my digital camera is stuffed so I'll have to find another way....
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