Application analysis of field-effect transistors in audio digitization 4

(2) The output current of NOS power vehicle management line

As mentioned earlier, increasing the power supply voltage by only about ± 5V under the same circuit conditions does not enable the MOS power output stage to achieve the same power as bipolar transistors. We often underestimate the dynamic losses of MOS transistors during actual operation. Assuming a 100W rear stage, when the load is 8 ohms, the power supply voltage for the bipolar transistor is V_Gc (8P. × RL)+2 × [VcE (sat)+I() × RE, such as IcM=5A and vc at this time. 1．5V、RE=0．22Q， So VC85.2V (± 43V). For MOS transistors, V?=99.2V (± 50V) can also be calculated. Of course, this is a theoretical and maximum power value, and in practice, the no-load voltage when using a non regulated power supply is obviously higher.

In fact, the AC secondary power supply value of a 100W/8Q bipolar transistors amplifier is approximately AC33V × 2. When using AC38V × 2 as the usual method to power a MOS amplifier, P can only reach 70-80W, and the high R of Hitachi MOS tubes relies on the amplifier NFB network to improve the overall internal resistance. Therefore, the actual listening experience at high output lacks strength (which is even worse when the amplifier is designed without feedback). So various misunderstandings arose about MOS transistors , such as poor linearity at high currents being one of them.