Book 1 Chapter 4 - switching circuits

Question 1

What are the different leads of a transistor

Answer 1

Base, Collector, Emitter

Question 2

What is the rules we have for a transistor

Answer 2

If Vin < 0.7V, the transistor is off, Vbe = Vin
If Vin > 0.7V, the transistor is on, Vbe = 0.7V

Question 3

What happens when Vin reaches 0.7V

Answer 3

When Vin reaches 0.7V the transistor saturates and turns on

Question 4

What is the off region of a transistor

Answer 4

This part of the characteristic when VIN is between 0 and 0.7 V shows that when the transistor is completely switched off, no current flows through the base-emitter junction, no current flows through the collector, and the voltage across the collector-emitter junction of the transistor (VOUT) is equal to the supply voltage.

Question 5

What is the linear region

Answer 5

When the voltage VIN increases above 0.7 V a base current starts to flow. The transistor behaves as a current amplifier and the base current causes a larger amplified current to flow through the collector and load. As VIN increases further, more current flows into the base and this allows
a further increase in the collector-emitter current.

Question 6

What is the saturation

Answer 6

As VIN continues to increase, a point is reached where changes to VIN no longer cause any change to VOUT , and we say that the transistor is saturated.
The saturation point is reached just before the voltage across the load reaches the full voltage of the power supply and the voltage across the collector-emitter junction of the transistor VOUT is about 0.2 V (i.e. nearly = 0 V).

Question 7

Transistor rules

Answer 7

For VIN < 0.7 V: VBE = VIN and VCE = Supply voltage, For VIN > 0.7 V: VBE = 0.7 V and VCE = 0 V

Question 8

What is current gain

Answer 8

Current gain = Ic/Ib

Question 9

What are the different leads for a MOSFET

Answer 9

Gate (G), Drain (D), Source (S)

Question 10

How is the characteristic of a MOSFET different from a transistor

Answer 10

the linear region is very small

Question 11

MOSFET formula

Answer 11

Id = Gm(Vgs-3)

Question 12

Advantages of MOSFETs

Answer 12

MOSFETs can handle very large currents and some are able to provide currents of 100A or more.

Question 13

Voltage rules of voltage comparators

Answer 13

V+ > V- then Vout will be at the positive saturation voltage
V+ < V- then Vout will be at 0V