Contents
What is the difference between PNP and NPN transistors?
NPN Transistors are three-terminal, three-layer devices that can function as either amplifiers or electronic switches. In the previous tutorial we saw that the standard Bipolar Transistor or BJT, comes in two basic forms. An NPN (Negative-Positive-Negative) type and a PNP (Positive-Negative-Positive) type.
What is the relationship between base and emitter in NPN?
The voltage between the Base and Emitter ( VBE ), is positive at the Base and negative at the Emitter because for an NPN transistor, the Base terminal is always positive with respect to the Emitter. Also the Collector supply voltage is positive with respect to the Emitter ( VCE ).
What makes a bipolar NPN transistor a good amplifying device?
The value of β can be large up to 200 for standard transistors, and it is this large ratio between Ic and Ib that makes the bipolar NPN transistor a useful amplifying device when used in its active region as Ib provides the input and Ic provides the output. Note that Beta has no units as it is a ratio.
What are the properties of a bipolar junction transistor?
One of the most important properties of the Bipolar Junction Transistor is that a small base current can control a much larger collector current. Consider the following example. A bipolar NPN transistor has a DC current gain, ( Beta) value of 200. Calculate the base current Ib required to switch a resistive load of 4mA.
How to connect two transistors in series-electrical engineering stack?
Use PNP transistors instead of NPN. NPN won’t work ahead of load due to needing it’s emitter lower than it’s base. Replace the two 2n3904 with their PNP counterparts 2n3906, and move their base to ground. Move the load around. Place the Led and it’s current limiting resistor before the transistor collectors.
Which is the transistor gain in the common emitter configuration?
Beta is sometimes referred to as hFE which is the transistors forward current gain in the common emitter configuration. Beta has no units as it is a fixed ratio of the two currents, Ic and Ib so a small change in the Base current will cause a large change in the Collector current. One final point about Beta.