Transistors are the fundamental building blocks of modern electronics and are mostly used as amplifiers or switches. There are two main categories of transistors: bipolar junction transistors (BJTs) and field-effect transistors (FETs). BJTs come in NPN or PNP types and function like a switch by using a small base current to control a larger collector current. Proper selection involves defining voltage and current requirements, referring to datasheets, and testing availability and performance. Datasheets provide critical parameters such as maximum voltage, current ratings, gain, and switching frequency. Common transistors include the 2N2222 and popular packages are TO-18, TO-92, TO-220, and TO-3.

1. TRANSISTORS
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2. TRANSISTORS
 Fundamental building block
of modern day electronics
 Used mostly as an amplifier
or switch
 Classified into two
categories:
 BJTs
 FETs
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3. TRANSISTORS: BJTS
 Bipolar Junction Transistors (BJTs) available in two
flavors
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4. TRANSISTOR ANALOGY
• Control a BIG flow of current with
a SMALL flow of current.
• Working as a Switch.
• Amount of current flow is Limited.
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5. NPN AS A SWITCH
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6. PNP AS A SWITCH
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7. TRANSISTORS
 How do we select the right transistor?
 Define and Calculate requirements
 Voltage
 Current
 Gain
 Refer datasheets
 Check availability
 Test
 Use
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8. TRANSISTORS
 How do we read transistor datasheets?
Decisive Parameters:
 Max collector-emitter voltage (Vce)
 Peak/Continuous collector current (Ic)
 DC current gain
 Transition frequency
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9. DATASHEET: PN2222
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10. TRANSISTORS
 Commonly available packages
TO-18 TO-92 TO-220 TO-3
Plastic package Metal package Plastic package Metal package
used for low used for low with heat-sink used for high
power power used mostly for power
transistors transistors with high power transistors
better thermal transistors
dissipation
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11. TRANSISTORS
 Commonly available transistors
Transistors Max Peak Collector DC current Cost Transition
Voltage Current (Ic) gain hFE(min) (Rs.) Frequency (Ft)
NPN PNP
(Vce)
2N2222 2N2907 30 800mA 100 2 300 MHz
2N3904 2N3906 40 200mA 100 2 300 MHz
BC546 BC556 65
BC547 BC557 45 100mA 300 2 100 MHz
BC548 BC558 30
TIP140 TIP145 60 10A 1000 40
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12. EXPERIMENTS
Transistor as a switch: 2N2222
Driving a LED
E B C
Rb = 1K
Rc = 500 to 1K
Calculations:
Ib= (Vin – 0.7)/Rb
Ic (max)= Ib X Hfe
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13. EXPERIMENTS
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14. ANY QUESTIONS?
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