inverter
I would like to make an inverter from 12Vdc to 45Vac.
I am trying to simulate it into LTSpice but I can't get a Frequency of 60 Hz.
Here is the Schematic:
BOM:
Q1 & Q2 : 2N5877
R1 & R2 : 220ohm 2 W
Source : 12V+
TFO: ?
The question:
How can I figure what kind of transformer I need ?
Presently here is the output:
You say you're not familiar with digital oscillators yet, but I think it's worth looking into. Using a microcontroller with PWM output you can input the signal directly in the amplifier's format. So you won't need an A/D conversion at the amplifier's input stage.
The code for the microcontroller is very simple. Basically it's like this: you need a sine lookup table, and a timer interrupt generating your sample clock. This can be 5kHz, for instance, then you get 100 samples per cycle, which is enough for an inverter application; the transformer will work as a low-pass filter. Every 200\$\mu\$s you take the next value from the table and set the PWM register with this value. The output will be pulse-width modulated following the sine pattern.
This means that your class-D amplifier doesn't need the input stage with the triangle wave generator + comparator (this would otherwise be you A/D converter), so it only consists of the driver stage for driving the output MOSFETs.
You get a crystal precision frequency virtually for free.
PS: a center-aligned PWM signal will give you a cleaner sine approximation, but many microcontrollers only can generate edge-aligned PWM. This Freescale controller is available in an SOIC-8 package and is an example of a microcontroller which can do center-aligned PWM.
image from this document
Yes, at this input voltage a center tapped primary with low side switches on the ends seems like the way to go. For feedback, I'd look at opto-isolators first. Put something on the output side that can detect whether the voltage is above or below the regulation threshold and drive the opto accordingly. On the primary side, a simple control method is to simply stop the oscillations when the opto signal indicates the output is high. If you can live with some ripple, this should be effective, simple, and efficient.
Best Answer
Back in the dark ages, I have built this kind of oscillator with 2N3055 power transistors. It is used with a 50/60Hz steel or silicon steel core transformer.
You are going to have to use a nonlinear core model to get it to behave sensibly, because this type of oscillator depends on core saturation, but more likely it will oscillate a bit higher or lower than normal mains frequency, which typically isn't a problem.
If you want to know the theory, this was invented in 1954 by the eponymous George Royer and you can find the original patent US2783384A here