variable output boost converter

[tbj]

Hi everyone

I am currently quite interested in boost converter design (because it's fun, or I'm mad, or something like that.)

I'm trying to design a *variable output voltage* boost converter for use in a small variable power supply, and I have a question. Let's take a conventional boost converter, like so:

http://upload.wikimedia.org/wikipedia/en/9/9f/Boost_circuit.png

When the output capacitor has been charged to the desired voltage, if there's no load on the converter, it just sits there at that voltage, right?

Let's say you select a lower output voltage in the control system. The voltage at the output is suddenly too high.

So, what topology would you use if you wanted to dump the charge stored on that cap, to get down to a lower voltage, without putting a load on the output (or a low-value bleed resistor which would waste power)? Are there any widely accepted boost converter topologies that can do that for me?

Cheers

R

[Rerouter]

well when you think about it if the inductor stops being switched it then appears as an inductor between your higher voltage and your input voltage and will drain through that until it droops enough that the regulation loop starts switching again,

also you will want a load resistor even if large in value, as you will have issues and overshoot without it,

[SteveyG]

The feedback network could perform this function if you designed it this way. There's also not necessarily a need to use large capacitors on the output.