Question 7.1: (a) Show that Eq. (7–7) is valid from arguments of the stead...
(a) Show that Eq. (7–7) is valid from arguments of the steady state replacement of stored charge. Assume that \tau _{n} =\tau _{p} .
\frac{i_{c} }{i_{B} }=\beta =\frac{\tau _{p} }{\tau _{t} } (7–7)
(b) What is the steady state charge Q_{n} = Q_{p} due to excess electronsand holes in the neutral base region for the transistor of Fig. 7–4?
(a) In steady state there are excess electrons and holes in the base.The charge in the electron distributionQ_{n}is replaced every\tau_{p} seconds. Thus i_{B} = Q_{n}/\tau_{p} . The charge in the hole distribution Q_{p} is collected every \tau_{t} seconds, and i_{c} = Q_{p}/\tau_{t}. For space charge neutrality, Q_{n}=Q_{p} and
\frac{i_{c} }{i_{B} } =\frac{Q_{n}/\tau _{t} }{Q_{n}/\tau _{p}} =\frac{\tau _{p} }{\tau _{t} }
(b) Q_{n} = Q_{p} = i_{c} \tau _{t} = i_{B} \tau _{p} = 10^{-9} C.