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Grounded Emitters and Grounded Collectors

Author: Leonard Krugman

The design and servicing of the transistor circuit is more complicated than that of the vacuum tube, because transistor input and output circuits are never inherently independent of each other. This makes it difficult for a newcomer to get the "feel" of the transistor. In the long run, however, these same complex characteristics provide for a more flexible device, one capable of many circuit applications beyond the range of the vacuum tube.

This chapter deals with the extension of the four-terminal characteristics developed for the grounded base to encompass the two remaining connections, the grounded emitter, and the grounded collector; a comparison of the major features of the three basic connections; limitations of the transistor; and transistor testing methods.


In the following analysis of transistor performance in the grounded emitter and grounded collector connections, the same typical point-contact and junction transistors discussed in Chapter 3 will be used for numerical examples. For the point-contact transistor in the grounded base connection, the parameters are:

r12 = 100 ohms = rb

r11 = 250 ohms = re + rb; then re = 150 ohms

r21 = 24,000 ohms = rm + rb; then rm = 23,900 ohms

r22 = 12,000 ohms = rc -f- rb; then rc = 11,900 ohms

For the junction transistor in the grounded base connection:

r12 = 500 ohms = rb

r11 = 550 ohms = re -f- rb; then re = 50 ohms

r21 = 1,900,000 ohms = rm + rb; then rm = 1,899,500 ohms

r22 = 2,000,000 ohms = rc + rb; then rc = 1,999,500 ohms

Notice that since rm and rc are so much greater in value than rb, particularly in the case of the junction transistor, for all practical purposes r21 = rm and r22 = rc.

Last Update: 2010-11-17