Electrical – Can anyone explain what is doing this diode-capacitor branch on a Boost converter

Your topology very much resembles a standard PC PSU with active PFC. A boost stage followed by an isolated down-converter stage. Except that:

• the inductor in series with the transformer primary... that looks a little odd... what's the purpose?

• the FET in series with the "main stage" (the isolated transformer) is N-type in your design, which matches the typical topology, but yours is connected in "common collector" fashion to the + polarity of the "midway bulk capacitor". This would force you to implement high-side N-polarity driving circuitry in the primary PWM control block... This is normally done in a different way: the N-FET is hooked up as a low-side switch (common emitter) and is driven by a PWM controller IC which also uses the bulk cap's "-" as a common ground with the FET's emitter... What voltages are we talking about on the primary side?

By the transformer's winding end marks, your converter would be a "forward" converter. That's more typical than "an isolated flyback" (which is sometimes used for low-power SMPS, and has its own pitfalls - e.g. the primary FET must cope with higher voltage spikes if memory serves).

I think you're making a bit too much out of this, it is actually a very simple circuit.

The LMR62014 is also not required for this, almost any DCDC converter (buck or boost) can do this.

Have a look at these Voltage multiplier circuits, note how they all need a strong (it needs to provide power) AC signal (usually a square wave) at the input. Then the diodes and capacitors are used to make a high(er) DC output voltage.

If you flip the circuit "upside down" you would get a negative voltage.

The circuit you're looking at is basically only a one stage version of this. One for the positive voltage, one for the negative.

The Switcher IC, in combination with the inductor, is used to generate the squarewave signal that is needed.