Various diagram

The following inverter circuit can be used to supply soldering iron or other small electronic devices which need up to about 50W / 230V power supply.

Transistors T1 and T2 (each BC547) form an astable multivibrator that creates 50Hz signal. The complementary outputs from the collectors of transistors T1 and T2 are fed to pnp Darlington driver stages formed by transistor pairs T3-T5 and T4-T6 (utilising BC558 and BD140). The outputs from the drivers are fed to transistors T7 and T8 (each and every 2N3055) connected for push-pull operation. Use suitable heat-sinks for transistors T5 via T8.

A 230V AC primary to 12V-0-12V, 4.5A secondary transformer (X1) is utilised. The centre-tapped terminal of the secondary of the transformer is connected to the battery (12V, 7Ah), whilst the other two terminals of the secondary are connected to the collectors of power transistors T7 and T8, respectively.

Whenever you power the circuit making use of switch S1, transformer X1 produces 230V AC at its primary terminal. This voltage could be employed to heat your soldering iron.

Build the circuit on a standard purpose PCB and place it in a suitable cabinet. Hook up the battery and transformer with proper current-carrying wires. On the front panel of the box, fit power switch S1 along with a 3-pin socket for connecting the soldering iron.

Note that the ratings of the battery, transistors T7 and T8, and transformer could vary as these all depend on the load (soldering iron).