Inverter power supply for soldering iron

Here is a simple, low-cost inverter power supply, which can be used to power a low-power soldering iron (25W, 35W, etc.) when the AC power is off. The power supply uses 8 transistors and several resistors and capacitors, as shown in the attached figure.

Transistors T1 and T2 (model BC547) form a multivibrator circuit to generate a 50Hz signal. The collectors of transistors T1 and T2 are complementary outputs. They are fed into a PNP Darlington driver composed of transistors T3 and T4, T5 and T6 (BC558 and BD140). The output of the driver is then fed into a push-pull circuit of transistors T7 and T8 (model 2N3055). Heat sinks of appropriate size should be added to transistors T5 to T8.

The circuit uses a 230V/AC, primary to secondary 2x10V, 4.5Ah transformer (x1). The center tap of the transformer secondary is connected to the battery (+12V, 7Ah) terminal, and the other two terminals of the secondary are connected to the collectors of power transistors T7 and T8 respectively.

When you turn on switch S1 to power the circuit, the primary of transformer x1 will generate 230V AC voltage, which can heat your soldering iron.

Install the circuit on a common PCB and then put it into a suitable small box. Use appropriate current-carrying wires to connect to the battery and transformer. Install the power switch S1 and a three-pin socket on the front panel of the small box to insert the soldering iron plug.

Note: The rated value of the battery, transistors T7 and T8, transformer, etc., should be adjusted according to the change of load (soldering iron power).