Spark
Loading...

BJT Transistors, Flip-Flops, and Op-Amps (C State/National)

A bipolar junction transistor (BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. In contrast, a unipolar transistor, such as a field-effect transistor (FET), uses only one kind of charge carrier. A bipolar transistor allows a small current injected at one of its terminals to control a much larger current between the remaining two terminals, making the device capable of amplification or switching. BJTs use two p–n junctions between two semiconductor types, n-type and p-type, which are regions in a single crystal of material.

Figures (10)

An SR latch (R1, R2 = 1 kΩ; R3, R4 = 10 kΩ)
A transparent latch circuit based on bipolar junction transistors
An SR latch constructed from cross-coupled NAND gates
NAND gated SR latch. Note the inverted inputs.
A gated SR latch circuit diagram constructed from AND gates (on left) and NOR gates (on right)
Schematic diagram
A gated D latch based on an SR NOR latch
A gated D latch in pass transistor logic that is write-enabled when CLK=1, similar to the ones in the CD4042 or the CD74HC75 integrated circuits
Earle latch uses complementary enable inputs: enable active low (E_L) and enable active high (E_H)
A positive-edge-triggered D flip-flop

Key Points

  • An NPN transistor comprises two semiconductor junctions that share a thin p-doped region, and a PNP transistor comprises two semiconductor junctions that share a thin n-doped region.
  • Biasing is the setting of the DC operating point of an electronic component.
  • Some basic circuits can be designed by assuming that the base–emitter voltage is approximately constant and that collector current is β times the base current.
  • Collector current and emitter current are related by Ic = α Ie with α ≈ 1, so the increase in emitter current with temperature is opposed, and the operating point is kept stable.
  • The common-emitter current gain is represented by βF or the h-parameter hFE; it is approximately the ratio of the collector's direct current to the base's direct current in forward-active region.
  • Unlike the JK flip-flop, the 11 input combination for the JK latch is not very useful because there is no clock that directs toggling.

Terms

Tap a term for a plain-language explanation.

Sources & licensing(4)