Thanks Bill...Class D amps are the only way you are going to feed a sine wave through MOSFET and not get them hot. A plain unmodulated sine wave is analog, any analog signal generates heat because it is operating out of the modes described in post 14 that dissipate minimum wattage. As is stated in post 14, this is true of all transistors, not just MOSFETs.
You mean like this one?The circuit I drew in my second post (though I would merge it with the updated triangle wave generator show in post 10) would work with MOSFET, because it is fundamentally a digital circuit (a Class D amp).
Thanks Audioguru1) The first opamp's output is a square-wave, not a triangle-wave
Are you sure the Schmitt Trigger is not essential?I don't think op amp speed is critical, but if I'm wrong use a Schmitt Trigger (shown) to square up the edges.
This is your most fundimental power supply, a voltage follower. It allows me to use a single power supply, but makes the remaining op amps think it is a dual tracking supply. The output impedance of the op amp voltage follower is quite low, a few millohms at best. You'll note I'm not actually using a ground symbol, but something else. That something else is a virtual ground.I notice that in some of your schematics, you show what I assume is an unused opamp (1 of a quad) with a resistive divider from Vcc to ground, and with the + input connected to that divider. You also show the output of the opamp connected to the - input. But, why do you have the output of the opamp grounded? Won't this cause a lot of unnecessary dissipation in the opamp?
It would be more correct to say I don't think it is. This is an opinion, subject to change if the facts don't support it. Even the worst op amp (which the 741 qualifies even though I defend it occasionally) has a .7V/us slew rate, which means every microsecond the op amp can move a max of .7V. It's cousins, the LM324, a pretty decent quad, isn't much better. If you want to upgrade the op amp a LM353 would be a good route, we discussed a lot of these ideas in [url="http://forum.allaboutcircuits.com/showthread.php?t=11847]this[/url] thread, which I have bookmarked for future reference.Hi Bill
I redrew the ckt. again & I added the Sine wave Osc. but w/out the Schmitt Trigger.
Are you sure the Schmitt Trigger is not essential?
The extra opamp buffers the 'half the supply bias voltage" that biases the comparator. The opamp is not needed since the input of the comparator has an extremely low DC current.I notice that in some of your schematics, you show what I assume is an unused opamp (1 of a quad) with a resistive divider from Vcc to ground, and with the + input connected to that divider. You also show the output of the opamp connected to the - input. But, why do you have the output of the opamp grounded? Won't this cause a lot of unnecessary dissipation in the opamp?
The extra opamp buffers the 'half the supply bias voltage" that biases the comparator. The opamp is not needed since the input of the comparator has an extremely low DC current.
Thanks Audioguru...A PWM controller IC has everything that is needed. The TL494 PWM controller IC costs $.52US each at Digikey today. They have thousands in stock.
Class-D amplifier ICs are also available.
Thanks Bill...I have seen Class D amps go through transformers, this is a design decision. The switching delay could be a major problem which might be addressed with a combination of Schmitt Triggers and logic.