Tham khảo tài liệu 'refrigeration and air conditioning equipment cooling episode 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Figure 113. Two sections of P-type germanium and one section of N-type germanium. region. In the collector region the holes combine with electrons that enter the collector from the negative terminal of the base-collector battery. If holes that enter the base from the emitter-base junction avoid combination with electrons entering the base from the battery the holes are attracted to the collector by the acceptor atoms negative in the collector and the negative potential of the base collector battery. 24. To obtain maximum power gain in a transistor most of the holes from the emitter must diffuse through the base region into the collector region. This condition obtained in practice by making the base region very narrow compared the emitter and the collector regions. In practical transistors approximately 95 percent of the current from the emitter reaches the collector. 25. By using forward bias on the emitter-to-base junction there is a relatively low resistance whereas by using reverse bias on the collector-to-base junction there is a relatively high resistance. A typical value for the emitter-to-base resistance is around 500 ohms and around 500 000 ohms for the collector-to-base resistance. By Ohms law voltage is equal to current times resistance thus numerically stated Voltage gain current gain X resistance gain x - 500 950 26. Although the current gain 95 percent in this particular transistor circuit is actually a loss the ratio of resistance from emitter to collector more than makes up for this loss. Also this same resistance ratio provides a power gain which makes the transistor adaptable to many electron circuits. 27. N-P-N Junction Transistors. The theory of operation of the N-P-N is similar to that of the P-N-P transistor. However inspection and comparison of figures 115 and 116 will reveal two important differences The emitter-to-collector carrier in the P-N-P transistor is the hole. The emitter-to-collector carrier in the N-P-N transistor is the .
