Euch, once again no current protection or measurement or anything.
But I expect no less from Instructables: where plans go to die for ad revenue.
If you must have a basic circuit -- one not using an integrated controller -- consider this:
https://www.seventransistorlabs.com/Images/555%20Boost.pdfThis is a peak current mode control, so the transistor
will not die* from transient conditions, whether startup, short circuit or anything else that happens.
*I mean, I'm not guaranteeing anything. There are a lot of compromises to keep the parts count low. But it's a far sight safer than an open loop
microcontroller that can't possibly see what's going on, or keep up with it.
As you can guess from the number of support components (transistors, an op-amp..) needed, this is practically an abuse of the 555. The circuit is using it for the flip-flop and timer functions, to replicate most of the operation of a UC3843 -- which is no harder to understand and uses far fewer parts, with far better performance. I do suggest reading up on it, it's very good despite its age.
I wish people would forget about the 555 and learn the 3842 series instead; they're possibly as universal as the 555 to begin with. It's also not hard to understand that there are two variables in a switching converter, not just one: the output voltage (and the compensation required due to change in that voltage, drawing current through the output capacitor), AND the inductor current (and the compensation required for it).
Tim