Please feel free to correct me, I don't want to learn the wrong things, but from what I understand, in using a flyback converter, a mosfet being used as a switch to create a square wave which can be multiplied through a transformer and then is filtered on the output to create DC. .....
....I've been learning and playing around with LTspice and its made me realise that I don't really know how to design a flyback converter at all. Are there any resources that can help in specifically designing one?
http://www.dos4ever.com/flyback/flyback.html - I often drop this link in when people mention flybacks, boost converters, or high voltage. It covers it well. I just deleted a very lengthy explanation.
You can think of a flyback simply as a boost converter, with an extra winding on the inductor. The key difference between this and simply considering it a 'transformer' is, in a flyback, the "transformer" stores energy, and current doesn't flow in the primary and the secondary (or secondaries if there's more than one) at the same time. This is why technically, its a coupled inductor. A true transformer shouldn't store energy, and simply transfers it from primary to secondary, at the same time, via its magnetic current.
So, say you had a boost converter that generated 30v from 5v. Now, if you added another winding on that inductor, with say, twice as many turns as the primary, and looked at the waveform on a scope you would see its voltage jump to 60V during the primary off-time (the primary will jump to 30). So, even though the ratio is only 1:2, you get 60V from 5V. The reason qutie a few ~300V flyback supplies have a 1:10 ratio is that it keeps the maximu primary voltage at 300 / 10 = 30V. This is the largest voltage the switch will have to cope with when it is off, and allows one to use very low on resistance MOSFETs (with a Vds of 40 max).
From what has been said, it is also possible to use it like a boost converter which lowers the multiplication needs of the transformer. For the switching waveform, would it be alright to use something simple like a 555 timer, or should I look into using a specialised PWM controller?
555 timers can be used, but... they were designed to simply create a delay or generate a square wave. Proper converters generally sense current in the primary, for current mode converters, and have many other features for the task (voltage reference for feedback, dead time etc..). Using the 555 for a boost converter can work, you just have to set the maximum on time based on the inductance and the peak current, and set the off-time to something sensible. Whilst its rather cool to use a cheap 555 - and the fact they are everywhere - these days, if you can, I would use a boost converter chip, still not easy, but less hassle trying to tweak with a 555.
With the royer oscillator, its converting the DC input to an AC sinusoid which is then multiplied through a transformer. That would then have to be filtered by a full bridge rectifier with a capacitor, right? I've been wondering about the royer oscillator, as its a DC to AC to DC conversion, would it be less efficient than the flyback converter? Also, from what I see, the royer oscillator requires a multiple input transformer, while the flyback requires a single input, it might be preferable to use a flyback not only to simplify finding a transformer, but also as a learning experience.
Again, more complicated. Sorry to resort to wiki... but its explanation isn't half bad.
https://en.wikipedia.org/wiki/Royer_oscillator It looks deceptively simple.
Here it really is a transformer, with two primaries.. or rather a single, centre tapped primary, and a feedback winding that drives the switching transistors. The positive feedback from this winding is what causes it to oscillate. It generally outputs a square wave (a high for one primary switching, and a low for the other) but the addition of a cap can create a form of resonance that greatly reduces the harmonics of the switching waveform. Its quite involved! In practical terms - its all about the transformer, the number of windings, the core material etc.. making it quite difficult to design from scratch. (its not just about turns ratio).