50W thick film power amplifier circuit composed of STK084G

Figure (a) is a 50W output power amplifier circuit composed of STK084G thick film amplifier. STK084G is a thick film integrated chip with a distortion rate of 0.01% at 20kHz and 50W. Its internal equivalent circuit is shown in Figure (b). The input stage is a current mirror circuit composed of VT4 and VT5, which converts the differential output into a single-ended output and obtains a large gain at the same time. The intermediate stage can handle a large amplitude and determine the conversion rate. Its operating current should be as large as possible. The VT8 base grounding method is used to reduce the influence of the Miller effect on the high-frequency characteristics. VTl and VT6 are constant current bias circuits, which can suppress the influence of power supply changes on the circuit. VT7 is used for output transistor bias, eliminates the insensitive area of ​​the base-emitter voltage Ube, and performs temperature compensation. The output stage needs to output a large current, and the Darlington structure is used to increase the current gain.