DC-DC converters are hard, but fun. The basic concept is that when you put current through an inductor for a while, then disconnect it, you get a big voltage spike. That's a classic auto ignition system. You can put that spike through a diode and use it to charge a capacitor to get DC out. The neat thing about switching power supplies is that there's very little resistance in the power path. That's why the efficiencies are so good. The not-neat thing is that they are a dead short across the input for part of the cycle, which is why failures can cause fires and why you may need an inrush current limiter and/or a fuse.
There are boost converters, buck converters, and ones with transformers. With a transformer you can isolate the input from the output, which is mandatory for safety if you're driving the thing from the AC power line.
Here's one of mine. USB 5VDC in, 120 VDC out, to operate antique teletype machines that need 60mA 120VDC.[1] The basic circuit is simple, but there are multiple surface mount ferrite beads and small capacitors to keep the spikes from coming out via the input USB, output, or as RF. LTspice simulation was needed to pick the values for those, so as to minimize noise in both voltage and current.
[1] https://github.com/John-Nagle/ttyloopdriver/blob/master/boar...
There are boost converters, buck converters, and ones with transformers. With a transformer you can isolate the input from the output, which is mandatory for safety if you're driving the thing from the AC power line.
Here's one of mine. USB 5VDC in, 120 VDC out, to operate antique teletype machines that need 60mA 120VDC.[1] The basic circuit is simple, but there are multiple surface mount ferrite beads and small capacitors to keep the spikes from coming out via the input USB, output, or as RF. LTspice simulation was needed to pick the values for those, so as to minimize noise in both voltage and current.
[1] https://github.com/John-Nagle/ttyloopdriver/blob/master/boar...