Low Power Inverter Circuit
IC ULN2004 (IC2) is a popular 7-channel Darlington array IC. Here, the three Darlington stages are paralleled to amplify the frequencies received from IC1. The output of IC2 is fed to transformer X1 via resistors R3 and R4.
Transformer X1 (9V-0-9V, 500mA secondary) is an ordinary step-down transformer that is used here for the reverse function, i.e., step up. That means it produces a high voltage. Resistors R3 and R4 are used to limit the output current from the ULN to safe values. The 230-250V AC output is available across the high-impedance winding of the transformer’s primary windings.
The article was first published in April 2005 and has recently been updated.