uC controlled DC-to-AC inverter

[ edit 2016 03 27: modified post formatting ]

Greetings, forum.

I’m trying to build a DC-to-AC inverter. I set a course for Google, YouTube, and websites of well-informed engineers. Days of my personal R&D, and sifting the good information from the bad, I have developed the following schematic.

https://drive.google.com/file/d/0B8PLvK … sp=sharing

My original need for such a circuit was to create a 90VAC 20Hz signal–which would actuate an old Western Electric 500M rotary telephone’s ringer. I quickly realized, however, that such an inverter could be suitable for many other uses/designs.

By setting only pin A HIGH, I expect a normal signal (not inverted) at LOAD.

By setting only pin B HIGH, I expect an inverted signal at LOAD.

By alternating pin A and pin B, an alternating current SQUARE wave is generated. I believe, as this project advances, that I can use PWM to achieve an imperfect but usable SINE wave (or TRIANGLE, or SAW, etc (useful, perhaps, for music making)). The only LOAD that i have applied yet is my oscilloscope and a multimeter–which is hardly a load at all.

If V+ is greater than 0V, but less than 4V4, the AC peaks similar voltage (actually about a volt less than V+ (and of course the inverted V+).

If V+ is greater than 4V4 however, the AC voltage does not rise with increased V+. In addition, my power supply indicates “Current Limited”. That seems to confirm that I’m doing something wrong.

It seems that V+AC does not exceed 3V3 provided by either pin A or pin B. This indicates to me that I lack a thorough enough understanding of transistors, and how they can amplify a signal. Perhaps also, nearly every resistor set at 1Kohm is inappropriate.

In anticipation of helpful responses, I extend my thanks for your reading of this topic.

Did your days of R&D not find that there are telephone ringer ICs that will do that for under $1?