tailieunhanh - Introduction to Electronics - Part 5

Other FET Considerations Bảo vệ FET Cổng Trở kháng từ cổng đến kênh (đặc biệt là trong MOSFETs) có thể vượt quá 1 GΩ! Để bảo vệ lớp oxide cổng mỏng, zeners thường được sử dụng: | Other FET Considerations Introduction to Electronics 99 Other FET Considerations FET Gate Protection The gate-to-channel impedance especially in MOSFETs can exceed 1 GQ To protect the thin gate oxide layer zeners are often used 9D Fig. 151. Zener-diode gate protection of a MOSFET. Zeners can be used externally but are usually incorporated right inside the FET case. Many FET device types available with or without zener protection. Zener protection adds capacitance which reduces FET performance at high frequencies. The Body Terminal D AS Fig. 152. Normal MOSFET bodysource connection. In some rare applications the body terminal of MOSFETs is used to influence the drain current. Usually the body is connected to the source terminal or a more negative voltage to prevent inadvertently forward-biasing the channel-body parasitic diode . Basic BJT Amplifier Structure Introduction to Electronics 100 Basic BJT Amplifier Structure Circuit Diagram and Equations Fig. 153. Basic BJT amplifier structure. The basic BJT amplifier takes the form shown KVL equation around B-E loop VBB v in iBRB v BE 122 KVL equation around C-E loop VCC CRC VCE 123 Load-Line Analysis - Input Side Remember that the base-emitter is a diode. The Thevenin resistance is constant voltage varies with time but the Thevenin. Thus the load line has constant slope -1 RB and moves with time. Fig. 154. Load-line analysis around base-emitter loop. Basic BJT Amplifier Structure Introduction to Electronics 101 Fig. 155. Load-line analysis around base-emitter loop Fig. 154 repeated . The load line shown in red for vin 0. When vin 0 only dc remains in the circuit. This iB vBE operating pt. is called the quiescent pt. The Q-point is given special notation IBQ VBEQ Maximum excursion of load line with vin is shown in blue. Minimum excursion of load line with vin is shown in green. Thus as vin varies through its cycle base current varies from B max to B min . The base-emitter voltage varies also from vBE max to vBE min .