PNP transistor

A PNP transistor is depicted in figure 2 below.

The expressions are derived for a PNP transistor.

In a PNP transistor, emitter-base region is forward biased.

A correctly biased PNP transistor will conduct when the:

The diagram shows a schematic representation of a PNP transistor connected to two voltage sources.

PNP transistors have two layers of p-type semiconductors sandwiching an n-type semiconductor.

In fig. 45 we have a buffer, consisting of a compound emitter follower using two PNP transistors.

That is, a PNP transistor is "on" when its base is pulled low relative to the emitter.

To make a PNP transistor, the cathodes of both diodes are back-to-back connected to form a large N type base region.

PNP transistors work in the same manner, however, the polarities are opposite to those of the NPN device.

In the latest CMOS processes, β of vertical PNP transistors can even go below 1.

They developed complementary NPN and PNP transistors which could be used as a matched pair in a variety of circuit applications.

This configuration, which uses three NPN transistors and one PNP transistor, is advantageous because:

One mnemonic device for identifying the symbol for the PNP transistor is "'p'ointing i'n' 'p'roudly."

A mnemonic device for the PNP transistor symbol is "pointing in (proudly/permanently)", based on the arrows in the symbol and the letters in the name.

Consider the following:- The resistor can be replaced with a constant current device such as a self biased FET or a PNP transistor.

PNP transistors had the round, black "top hat" style body, while NPN transistors had oval, black "top hats".

The first transistor, tr5, drives the complementary pair, tr6 and tr7, which consists of an NPN transistor and a PNP transistor.

Some DTL designs used two power-supplies with alternating layers of NPN and PNP transistors to increase the fanout.

Normally it is not possible to manufacture NPN and PNP transistor types which are always used in the classic push-pull arrangement, with the same data and characteristics.

A series of bipolar linear semi-custom arrays, containing varying numbers of NPN and PNP transistors and sectional base resistors, is also offered.

Although the NPN devices on the top half are nominally complementary to the PNP transistors on the bottom half of the stage, there are some substantial differences.

By using two Darlington pairs, the designer is hoping that the combination of two NPN transistors will have similar characteristics of two PNP transistors.

Active high switching allows for maximum switching current, as the NPN transistor is also used to light the corresponding LED and switch the PNP transistor.

The modes of operation can be described in terms of the applied voltages (this description applies to NPN transistors; polarities are reversed for PNP transistors):