1. A short-circuit on the output will kill U1 and D1. Always use a 1 ohm 5w resistor,
or a 2.5A fast fuse on the 12v input lead.
2. Do not omit the LED (D2); It provides a visual indicator of a properly operating boost condition,
but more importantly, it also provides a minimum load for the output,
preventing an output “spike” which will otherwise
appear when the load is disconnected abruptly.
3. Keep the ratio of r2 and r3 to 22 or less to keep the output voltage
within the ratings of C4 (C4 on my board is rated at 35wvdc).
This ratio plus 1, multiplied times 1.25v, determines the output voltage.