As mentioned earlier, the basic idea of a boost converter is to use the collapsing field in an inductor to generate a large voltage. To do this you need to be able to turn the current on and off. This is done using a transistor, usually a MOSFET.

This is the typical diagram used to explain this:

When the switch is closed, the current flows through the switch. When it is open, the field in the inductor collapses and generates an additional voltage in the same direction as that from the power source. The current can't flow through the switch, so it flows through the load. The capacitor provides current to the load while the switch is closed. The diode prevents this current from flowing back in to the inductor. After startup the diode blocks current flowing from the left side of the circuit while the switch is closed because the voltage on the right side is greater. This page gives one the best explanation of this I have seen.

As stated earlier, a flyback converter essentially replaces the inductor with a transformer, like this:

The rest is the same. This gives us two advantages:

1. We get the voltage multiplying effect of the transformer (at the expense of current, conservation of energy and all that).
2. The output is isolated from the input. With a boost converter, if the switch is left open the output voltage will be the same as the input voltage. Which is interesting, but not why we want to use one.

Generally, you want the switch to be closed longer than it is open. The longer it is closed, the more energy is pumped in to the magnetic field of the inductor, so the more power will come back out in the form of voltage (give that the current is constant), once we open the switch. This ratio of on to off is called the duty cycle. An 80% duty cycle means that the switch is closed 80% of the time. This on-off mechanism is also called PWM (Pulse Width Modulation). It is a square(ish) wave. In most documentation about boost converters, they will talk about small duty cycles - say 60%. In Nixie power supplies, 90% is not uncommon because we want to boost the voltage a lot!

In addition to this ratio, there is the period of the wave. After a certain amount of time, we will have pumped as much energy in to the inductor as it can take - the magnetic field won't get any stronger. There is no point pumping in any more. The larger the inductance, the more energy we can pump in. Unfortunately, large inductance and large physical size go hand in hand, and we want a small inductor. This effectively means that we need to switch the current faster so as to avoid saturating the inductor.

So smaller inductor => higher frequency.

If the frequency gets too high, circuits start behaving oddly, so we don't want to go too high. 600KHz seems like a recommended upper limit. Of course this also puts limits on how small the inductor can be.

This is all relevant to our design - we will be adjusting all of these things to try and come up with the best solution we can, given the actual products available to us.