This voltage controlled switch circuit operates when a voltage level which is previously adjusted is applied to the input. Circuit is designed for 24V supply but can be used in a range of 18V-36V.

Here is a simple but inexpensive inverter for using a small soldering iron (25W, 35W, etc) In the absence of mains supply. It uses eight transistors and a few resistors and capacitors. Transistors Q1 ...