Transistor Flashcards
What is a transistor?
a semiconductor device with three connections, capable of amplification in addition to rectification.
Which way does current flow in a NPN transistor?
Collector, base, emitter
Which way does current flow in a PNP transistor?
Emitter, base, Collector
If the base current is 0, what is the collector current?
Always 0 as the collector current is controlled by the base current
What does Vt (thermal voltage) equal?
kT/q
What does the collector current equal?
Ic= Is*e^(Vbe/Vt) Ic = beta Ib
Which part of the graph shows the active region?
The parts with the steepest slope, between saturation voltages (graph of x=Vbe against y=Vce)
How does a BJT amplifier work?
By using the base-emitter voltage to control the collector current.
Only possible in the active region otherwise it’s saturated
What happens to Vce when there is a small change in Vbe?
Large change
What does Vce equal?
Vce = Vs - IcR
What is gm?
The mutual conductance
What does gm equal?
gm = Ic/Vt
What is the small signal ratio between Vc and Ic?
Vc = -Rc * ic
= -(Ic/Vt)*Rc
What is the gain of a simple common-emitter amplifier?
A = - Rc * gm
Why is the gain unpredictable?
related to beta which has a very wide tolerance (50-200)