What I have: 5VDC and / or 12VDC, a PIC micro
What I want: Floating 9VAC 50Hz, able to output 1A.
Googling details for this kind of inverter seemed to be a tricky case. There are a few DIY-pages that describe the innards of an inverter doing 5VDC -> 220VAC using a PIC, SPWM, and an H-bridge using four MOSFET with drivers. The common denominator for many of these is that they hook a low-pass filter to the MOSFET-outputs, and then to the load. But, applying the same theory, but for 9V, would mean not getting a floating 9VAC (18Vp-p) but an output with a 18Vp-p with a 9VDC offset. I do not understand how that would work.
Another solution for the output stage, instead of an LC-filter, is to add a transformer and let the MOSFET output feed the primary. However, I do not find any transformer that can work with sine pulsating 12V input and give 9VAC output. Digikey parameter search gave nothing but a 24-9-transformer at best. For proper 50Hz sinus replication, I would need a reference clock for the drivers. This can either be generated with an analog oscillator (using a couple of LM358), or using software controlled PWM (using variable duty cycles) with a PIC micro. Either way is fine for me, as this controls the output frequency.
What I'm still puzzled about is that I fail to understand how the output amplitude is controlled. If I use a transformer, then bombing it with pulsating 5V to let it transform it up (to whatever voltage) isn't the challenge, but if I don't use a transformer; what part / block in my circuit will be the one deciding the amplitude? Higher PWM-frequency, higher output amplitude?
In the case of not using a transformer, but an LP-filter instead, is there any way to get the output to "float" without DC-offsets? I know capacitors block DC, but I cannot see how that would work given that there are no negative reference voltages.
As you can see, I have quite a vague starting point for this experiment. I know what output I want, but I'm having a hard time finding what parts / topics I need to learn to reach my goal.
Question: Where do I start? What should I dive into first?