STK4101 internal circuit

The internal circuit structure of the STK series power amplifier IC is similar to the general discrete component quasi-complementary OCL circuit. The circuit is made using thick
film integration technology, and the components and workmanship used are sophisticated, so the circuit performance is easily guaranteed and has good consistency, which are
better than ordinary discrete component OCL power amplifier circuits.
    Figure 2-81 shows the internal circuit structure of the STK4101II4ioiv series power amplifier IC, and Figure 2-82 shows their typical application
circuit. In Figure 2-81, C1 is the input coupling capacitor, C2 is the high-frequency bypass capacitor, R2 is the input resistor, R3 and R4
are feedback resistors. The role of Rs, R6 and the island is to improve the transient response performance of the amplifier, and c5 is the DC blocking capacitor.
Pin 7 of STK4101II and other series devices is the e-pole terminal of the internal pre-amplifier bias control tube. Pin 7 is externally
connected to pin 4 (e-pole of the pre-amplifier bias tube) through R7, and the bias control tube b is the terminal of the STK4101II and other series devices. Pin 8 introduces
a negative voltage - Vc through № and R, so that the bias control tube is turned on, and the preamplifier stage is normally biased and works. The voltage of the B pole of the bias control tube is also
controlled by the squelch tube, and the B pole of the squelch tube is externally led to pin 6 through the current limiting resistor. When a negative voltage is applied to pin 6, the squelch tube is turned on,
allowing the bias control The tube is cut off and the preamplifier stage does not work, thus realizing the noise suppression function.
    C4 and C6 in the circuit. , turtle, C9, and clo are all decoupling capacitors. R is the preamplifier +Vc power supply decoupling
resistor in the device. Rio and C7 are RC phase correction networks, used to make the output load tend to be purely resistive to prevent high voltage at the load end
from damaging the power amplifier IC. This RC network also plays a certain role in suppressing high-frequency parasitic oscillations in the circuit.
    Pin 11 of the STK4101II4101V series device is the positive power supply + vc terminal. 9. Pin 14 is the negative power supply - Vc terminal, and
pin 16 is the ground terminal (power supply midpoint).
    STK series power amplifier rc is essentially an OCL amplifier. Direct coupling is used from input to output, and its
output midpoint is stable at zero potential. It is mainly guaranteed by the differential amplifier of the input stage and its constant current source. But when the circuit is powered on
or the preamplifier output level is unbalanced (when direct coupling is used between the preamplifier and the power amplifier circuit).
The output DC level will still be out of tune, which is likely to cause DC voltage to be generated at both ends of the speaker, possibly burning out
the speaker's voice coil. Therefore, when assembling and debugging this type of power amplifier circuit, you must pay attention to adjusting the output zero point of the pre-stage. If
a discrete component pre-stage is used, special attention should be paid to the matching of the characteristics of each differential stage tube. In addition, a soft-start
circuit can also be used to prevent the impact of instantaneous offset current on the speaker when power is turned on. The soft start circuit can use a delay switch or an
RC delay circuit, which is combined with the squelch control function in the circuit to realize the soft start of the circuit. The power supply of
    ST K series power amplifier LC generally does not require voltage stabilization and can be powered by a simple bridge rectifier plus capacitor filtering
. However, the power (current) capacity of the power supply must be sufficient, otherwise the output power of the circuit will be limited and cannot be used. Reach
rated output power.