Above circuit is a inexpensive completely transistorised inverter circuit ideal for driving medium loads of the order of 40 to 60 watts working with battery of 12V, 15 Ah or bigger power capacity.
Transistors T1 and T2 (BC548) make a 50Hz multivibrator. For having proper frequency, the values of resistors R3 and R4 may have to be modified after testing. The complementary outputs from Collectors of transistors T1 and T2 are provided to PNP darlington driver stages formed by transistor pairs T3-T4 and T6-T7 (utilising transistors BD140 and 2N6107). The outputs from the drivers are given to transistors T5 and T8 (2N3055) connected for push-pull operation.
Considerably bigger wattage could be achieved by growing the drive to 2N3055 transistors (by lowering the value of resistors R7 and R8 while increasing their wattage). Appropriate heatsinks may be applied for that output stage transistors to prevent the transistor from overheating. Transformer X1 is really a 230V primary to 9V-0-9V, 10A secondary used in reverse.
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