50W power amplifier circuit principle

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To date, almost monolithic and hybrid power ICs have not been able to achieve satisfactory high frequency characteristics. The circuit shown in Figure 1 is the application diagram of Sanyo thick film IC STK084G. Within 20KHZ, the output power is 50W. The distortion rate is only IC part of the main part of the circuit, so the external parts are mainly composed of large capacitance capacitors. Figure 2 shows the internal circuit of the STK084G. The input stage consists of a current mirror circuit consisting of VT4 and VT5. The PNP differential amplifier output is converted into a single-ended output, and a large gain is obtained at the same time. The intermediate stage processes a large amplitude and determines the amplifier conversion rate. Therefore, a large current should be used as much as possible. Driven, the common base circuit composed of VT8 eliminates the deterioration of high frequency characteristics caused by the Miller effect.
VT1 and VT6 are constant current source bias circuits that can resist the effects of power supply fluctuations. VT7 provides bias for the output transistor, eliminating the voltage V nonlinear transition between the base and emitter, and temperature compensation.
The output stage uses a Darlington connection to achieve higher current amplification. In order to output a large current, the STK084G is designed for audio amplifiers. Therefore, in other applications, in order to achieve high frequency characteristics, the values ​​of capacitors C1 and C4 should be appropriate on the basis of stability. cut back. C11 and R7 are impedance compensation circuits for inductive loads. The voltage gain is determined by the ratio of R6 to R5, which is about 34dB. If you want to change it, you need to adjust the phase compensation capacitor C3 and other components without special requirements, but the heat dissipation and power supply capacity should be taken seriously. The STK series can be used with aluminum plates or special heat sinks.

figure 1

figure 2