Frank Boylan (boy@iol.ie) wrote: : Please view this in a fixed width font such as Monaco or Courier 9 or : 10. : I'd like to thank you all for your answers to my question. I found the : Class D evaluation board on the Harris site. It's very interesting but : there are a couple of things that have me puzzled. : This is the triangular wave generator. It uses three inverters.I always : thought that such inserters were logic in nature and therefore their : outputs would always be either high or low, in which case I can't figure : out how the output could be a triangular wave. : However ,if they are analog inverters, then what kind of characteristics : do they have? : In other words would this circuit produce a linear triangular waveform ? : Tri-Wave Generator 250kHz CD4069UB : ____ : | | : |\ |\ | _ |\ : __| \o____| \o___/\/\/\__|_/\/\/\__| \o_______o : | | / | / | | | / | : | |/ |/ | | |/ | : | | |---||---| : |_____/\/\/\/\__| | : |__________________/\/\/\__________________| A CMOS inverter such as the 4069 can be biased to operate in the linear mode. That is what the left-most resistor does. But they make lousy amplifiers, and no one would seriously use this circuit, however, as there are many better ones available (and in fact, it makes far more sense to use a proper PWM chip for modulating a class D amp). : My second question is: Is this an N channel or P channel MOSFET ? : RFP22N10s : D + : | : |--' : G ----||<-. : |--| : | : | : S - : In the circuit diagram, the output stage uses four of these Mosfets. : They are described as N channel Mosfets, but if so shouldn't the arrow : be facing the other way? That is an N channel FET. P channel FETs have the arrow pointing the other way. As you have drawn it, it makes perfect sense; the parasitic diode is reverse biased. If it were drawn the other way around (and connected with the same polarity) the diode would continuously be "on" and short out the drain to the source.
Date: 3 Sep 1996 19:52:24 GMT
Original Subject: Re: Harris Class D Amplifier