An investigation of transistor current in npn and pnp bipolar junction transistors

WhatsApp Advertisement This bipolar transistor tester can indicate the type of the transistor as well as identify its base, collector and emitter pins. The circuit is very simple. The direction of current flow from the terminals of the transistor under test TUT is indicated by a pair of LEDs green-red. An NPN transistor produces a red-green-red glow, while a PNP transistor produces a green-red-green glow, depending on the test point that connects to the terminal of the transistor.

An investigation of transistor current in npn and pnp bipolar junction transistors

An investigation of transistor current in npn and pnp bipolar junction transistors

The width of the depletion region of the BE junction is small as compared to that of the CB junction. The forward bias at the BE junction reduces the barrier potential and causes the electrons to flow from the emitter to base.

This constitutes the base current, it flows due to recombination of electrons and holes Note that the direction of conventional current flow is opposite to that of flow of electrons. The remaining large number of electrons will cross the reverse biased collector junction to constitute the collector current.

Thus by KCLThe base current is very small as compared to emitter and collector current. Here, the majority charge carriers are electrons. The operation of a p-n-p transistor is same as of the n-p-n, the only difference is that the majority charge carriers are holes instead of electrons.

Only a small part current flows due to majority carriers and most of the current flows due to minority charge carriers in a BJT.

Hence, they are called as minority carrier devices. As a transistor has two p-n junctions, it is equivalent to two diodes connected back to back.

This is called as the two diode analogy of the BJT. Before knowing about the bipolar junction transistor characteristics, we have to know about the modes of operation for this type of transistors.

Characteristics is nothing but the graphical forms of relationships among different current and voltage variables of the transistor.

The characteristics for p-n-p transistors are given for different modes and different parameters. As the emitter - base junction is forward biased, therefore the graph of IE Vs VEB is similar to the forward characteristics of a p-n diode.

Output Characteristics The output characteristics shows the relation between output voltage and output current IC is the output current and collector-base voltage and the emitter current IE is the input current and works as the parameters.

The figure below shows the output characteristics for a p-n-p transistor in CB mode. These are three regions in the curve, active region saturation region and the cut off region. The active region is the region where the transistor operates normally. Here the emitter junction is reverse biased.

Now the saturation region is the region where both the emitter collector junctions are forward biased. And finally the cut off region is the region where both emitter and the collector junctions are reverse biased.

The characteristics are shown below The typical CE input characteristics are similar to that of a forward biased of p-n diode. But as VCB increases the base width decreases. The characteristics is shown below in the figure.

Like the output characteristics of common - base transistor CE mode has also three regions named i Active region, ii cut-off regions, iii saturation region. The active region has collector region reverse biased and the emitter junction forward biased. For cut-off region the emitter junction is slightly reverse biased and the collector current is not totally cut-off.

And finally for saturation region both the collector and the emitter junction are forward biased. BJT's are suitable for high frequency application also.

Another application of BJT can be stated as small signal amplifier, metal proximity photocell, etc.NPN Transistor vs. PNP Transistor NPN Transistor is the type of bipolar transistor consisting up of p-type semiconductor that is affixed in between two n-type semiconductors, whereas PNP is the type of bipolar transistor consisting up of n-type semiconductor attached in between two p .

Introduction To Bipolar Transistors The Bipolar Junction Transistor 6 of 19 The Designer’s Guide Community 4 The Bipolar Junction Transistor A transistor combines two junctions and has three terminals as shown in Figure 7. Bipolar transistor – three-ended (three electrodes), semiconductor electronic component having the ability to amplify the signals of direct current and alternative current, so every transistor is an amplifier.

The amplifier is a device, which can control more power with usage of less power. High-speed devices and integrated circuits group. Electrical Engineering Department, Institute of Electronics Engineering National Tsing Hua University, Hsinchu, Taiwan.

An investigation of transistor current in npn and pnp bipolar junction transistors

0 Shawn S. H. Hsu, Professor. Delta Bldg. Room , [email protected], 0. There are two basic types of transistors i.e. bipolar junction transistor or BJT and field effect transistor FET, that are used in two broad areas i.e.

linear amplifier to boost or amplify an electrical signal and as an electronic switch. Complementary NPN-PNP Silicon Power Bipolar Transistors Typical Current Gain Bandwidth Product PNP NJWG NPN NJWG IC, COLLECTOR CURRENT (A) 0 10 20 30 40 50 60 1 10 f Tau, CURRENT BANDWIDTH PRODUCT (MHz) a transistor; average junction temperature and secondary breakdown.

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