Application analysis of field-effect transistors in audio digitization 6

① To achieve the same output power as a bipolar transistor in the same circuit, the power supply voltage of the MOS output stage should be more than ± 10V higher than when using a bipolar transistor. When reducing MOS transistor losses, voltage level and current level power supply can be adopted separately. At this point, the current level and voltage level are divided into Nl: k, and the bipolar transistor output level is high by ± 5V and ± 10V.

② Use multiple parallel output stages. Multi tube parallel connection is aimed at reducing the equivalent on state resistance of MOS power transistors, rather than improving the poor linearity of MOS transistors with high current. Parallel connection of multiple MOStransistors can not only increase current driving force, but also greatly reduce power loss, and improve the equivalent internal resistance of K135/J504 group in open-loop. When K135/J504 group is connected in parallel, the equivalent internal resistance is reduced to 1/4 of a single transistor, which is below 0.4Q, and the power loss of an 8-ohm load is correspondingly reduced from 20% to 5%. In addition, the parallel parameter error of MOS transistors can be appropriately relaxed compared to bipolar transistors, that is, a slightly larger parallel transistor error will not cause a deterioration in listening experience.

③ Adopting a common source output stage, which is the collector output form of bipolar transistors. This output method is more suitable for VMOS transistors because VMOS transistors have high current and low internal resistance. When the circuit design is reasonable, it can balance good efficiency, low distortion, and low output impedance. At this point, the power supply voltage only needs to be ± 3 to ± 5V higher than the bipolar transistor circuit.