Amplifier Teaching Aid (DED Philippinen, 86 p.) Bipolar Transistor II Lesson Plan (introduction...) Introduction Collector curves (output) Transistor power dissipation Transistor test Worksheet No. 3 Experiment No. 3

Amplifier Teaching Aid (DED Philippinen, 86 p.)

Bipolar Transistor II

Lesson Plan

Title: Bipolar Transistor II

Objectives:

- Able to analyze a base biased CE configuration
- Able to name the regions of operation in a collector curve
- Know how to test a transistor

Figure

Introduction

Base Curve (Input)

Fig. 3 - 1: Input curve, base biased CE connection

Calculate the Base Current: (see Fig. 2-7)

Fig. 3 - 2: Base biased CE connection

Approximation: V_BE = 0.7 V

Ex: Silicon Transistor

V_BE = 0.7V, V_BB = 10V, R_B = 100 KW

Collector curves (output)

Fig. 3-3: NPN transistor collector curve (2N3904)

Fig. 3-4: PNP transistor collector curve (2N3905)

Recall Kirchhoffs voltage law: (see Fig. 2-7)

V_CE = V_CC - I_C * R_C

Ex: Analyse the following circuit

Fig. 3-5: Base biased CE connection, b=100

I_C = b_dc * I_B = 6.2 mA

V_CE = V_CC - I_C * R_C = 15V - (6.2 mA * 1 KW) = 8.8V

Regions of Operation

Fig. 3-5: Regions of operation

Active region :	Normal operation Emitter diode forward biased Collector diode reverse biased ===> horizontal part of the curve
Breakdown region:	Transistor should never operate in this region
Saturation region:	VCE between 0V ----> 1V ===> rising part of the curve
Cutoff region:	IC approximately zero

Transistor power dissipation

P_D = V_CE * I_C

This power causes the junction temperature of the collector diode.

Important information from a data sheet:

Maximum power rating: P_{D (max.)}

Transistor test

- Out of circuit: With an ohmmeter.

* resistance between collector and emitter should be high in both direction.

===> diodes are back to back in series (see also Fig. 2-3)

* reverse and forward resistance of emitter collector diode (reverse/forward ratio) should be more than 1000: 1 (silicon)

- In circuit: With a voltmeter

* measure V_E and V_C, the difference V_E - V_E should be more than 1V but less than V_CC.

If V_CE is less than 1V:

----> transistor may be shorted

If V_CE equals V_CC:

---- > transistor may be open

Worksheet No. 3

Figure

No. 1 What is the base current ?

No. 2 If the current gain decreases from 200 to 100 what is the base current?

No. 3 What are the collector-emitter voltage and the transistor power dissipation?

No. 4 Suppose we connect a LED in series with the collector resistor. What does the LED current equal?

Experiment No. 3

Figure

Procedure:

Adjust V_CC in turn to every value of V_CE shown in the table. Observe and record the value of I_C for each value of V_CE. Monitor I_B, and readjust R1 if necessary.

From the data in the table, plot the collector characteristic curve (I_C over V_CE).

IB mA	IC mA
	VCE volt
	0	2.5	5	7.5	10	15	20	25	30
10
20
30
40
50