Contents
How can a BJT be used as a diode?
The emitter-base junction acts as a simple semiconductor diode. Simply connect the base of the transistor to its collector. Do not exceed the reverse-biased voltage rating of its base-emitter junction which is only 5V to 7V for silicon transistors.
How do you bias a diode?
Bias. A diode (PN junction) in an electrical circuit allows current to flow more easily in one direction than another. Forward biasing means putting a voltage across a diode that allows current to flow easily, while reverse biasing means putting a voltage across a diode in the opposite direction.
What is diode connected BJT?
Diode connected BJT aka “active diode” is simply a transistor which collector is connected to the base. Thus the collector-emitter part of the transistor is connected in parallel to its base-emitter junction so we can think of this combination as of a “reinforced diode”.
Is BJT a diode?
BJTs can be thought of as two diodes (P–N junctions) sharing a common region that minority carriers can move through. A PNP BJT will function like two diodes that share an N-type cathode region, and the NPN like two diodes sharing a P-type anode region.
What kind of bias does a diode have?
Diodes nominally conduct electricity in one direction, and the voltage they apply follows a so-called “forward bias” orientation. If the voltage moves in the opposite direction, we call that orientation a “reverse bias.” In reverse bias, current flow is nominally blocked as a sort of electronic check valve.
Why is a BJT off when the base voltage is low?
Remember that a typical silicon diode needs about 0.7 V to turn on and conduct. So, with less than 0.7 V on the base the transistor is off because the low voltage does not forward bias the BE diode. If we were to apply a negative voltage to the NPN BJT in figure 4 the situation worsens; the p-n junction between the base and emitter widens.
How does a BJT work in a bipolar junction transistor?
A BJT uses a small current at its base to control a much larger collector current. Before we go any further, it may be useful to define some important terms concerning the operation of a bipolar junction transistor.
How does the BJT work in saturation mode?
Saturation refers to a region of operation where maximum collector current flows and the BJT acts like a closed switch from collector to emitter. In this mode the BC junction forward biases and maximum current flows. The collector current cannot increase any more, even with an increase in base current.