Chapter 37 Quiz

Compare the normal current flow through a forward biased in reverse biased junction

2 voltage sources to foward bias the emitter base Junction and reverse bias the collector base junction

What reading should be expected if the junction is good and the emitter base junction of a bipolar junction transistor using a digital multimeter?

700mV in foward bias, OL in reverse bias

What is the operating current range of the base compared to that of the collector?

A few microamps to several milliamps

With reference to a properly biased complete bipolar junction transistor circuit, what determines the amount of collector current flow?

Amount of base current

In a JFET circuit why is the source current equal to the drain current?

Because it is in reverse bias. No current flows through it so all the current from the drain travels to the source

To what Junction of the UJT is the input signal applied?

Between the emitter and Base 1

What are the two main families of transistors?

Bipolar junction transistors(BJT) and field effect transistors (FET)

For what purpose is the base region used?

Control current flow through the transistor

What is the main advantage of the Darlington transistor?

Creates a transistor unit with a very high current amplification factor

What is the basic difference between the connection of an NP and a PNP bipolar function transistor circuit?

Direction of arrow on the emitter lead

In what ways is the unijunction transistor not like a true transistor?

Does not amplify

In MOSFET, what happens to the drain Current flow when a positive voltage is applied to the gate?

Drain flow increases

Name the two junction is found within a BJT

Emitter base Junction and collector base junction

State the type of bias used for each Junction in order to produce the required transistor action

Emitter is foward biased and collector is reverse bias

Compare the control of output current of a BJT with that of a FET

FET has almost no input current. Output current controlled by a varying "electric field" which is created through the application of voltage. BJT- current into or out of base of the transistor controls the larger current that flows between the emitter or collector (current driven device)

Why should an analog ohmmeter not ordinarily be used for testing MOSFETs?

Fragile nature of the oxide

What should be the normal resistance reading of the collector-to-emitter circuit of a BJT using an ohmmeter?

High ohms in one direction, low ohms in another direction

State three operating advantages of FETs over bipolar types of transistors

High switching speed, low driven power, no voltage loss or drop across the transistor due to its resistance

Explain the basics circuit configuration contained within a bipolar Darlington transistor

Hooking two or more bipolar transistors up so that a smaller transistor provides the best current for a larger transistor

In N-Channel enhancement, what happens to the drain Current flow when a positive voltage is applied to the gate?

Increases to the saturation point

The action of a P- channel JFET is complementary to that of anN- channel JFET. What does this mean?

It operates in exactly in the same manner except all current and voltages are reversed

What are the two main types of FETs?

JFET and MOSFET

JFET

Junction Field Effect Transistor

What special precaution is often taken for the packaging and shipping of MOSFETs?

Kept it static protection packages or with the leads shorted together until they are placed into a circuit

In what does a small increase in base current flow result?

Large increase in collector current

MOSFET

Metal Oxide Semiconductor Field Effect Transistor

State two ways in which power transistor packages is different from the small signal type

Mounted in a case or package

In MOSFET, what happens to the drain Current flow when a negative voltage to applied to the gate?

No current flow

What is the basic difference in construction between a JFET and a MOSFET?

No electrical contact with the source and drain

With no bass current flow how much collector current flows?

Open or no current flow

What are the normal for polarities of the drain and gate with respect to the source for an N-channel JFET?

Positive for drain. Negative for gate

In a JFET circuit, what gate-to-source biasing connection is normally used to prevent gate current flow?

Reverse bias

Assume a variable positive voltage is applied to emitter of an N-Type UJT. Describe what happens is is voltage is increased from zero

The base-to-emitter voltage increase to some peak value then decreases. When this leak value occurs, the B1-to-emitter junction conducts a Current

In N-channel enhancement, what happens to the drain Current flow when a negative voltage is applied to the gate?

The device is off and no drain current flows

Briefly explain how current flow through an N-channel JFET is controlled

The gate in channel form a PN junction similar to a PN Junction diode. A depletion region develops around the Junction. Size is controlled by the value of the reverse bias voltage that is applied between the gate and source. With no negative bias voltage applied, the depletion region is minimal and the resistance of the channel is low so max current flows between the source and drain.

In what way is the UJT symbol different from that of a JFET symbol?

The slant of the arrow

Explain how built in zener diodes can be used to protect MOSFETs against static charge

The zener diode voltage rating is less than the max gate-to-source voltage rating of the device, so zener diodes conducts to shunt the current before any damage to the thin layer occurs when connected in parallel to theMOSFET

Why are FETs said to be unipolar?

Their working current flows though only one type of semiconductor material

Why are JFETs classified as normally on devices?

They allow for current to pass between the drain in the source when the gate is not activated

Explain why MOSFETs can be damaged by the static charges?

Thin layer of silicone dioxide

In what two ways is the base region of a bipolar Junction transistor different from that of the emitter and collector

Thinner and has fewer doping atoms

Why is the N-channel of a MOSFET drawn as a solid line?

To signify that the circuit between the drain and source is normally complete and the device is normally on

Why is the N-Channel enhancement schematic drawn with broken lines?

To signify that the circuit between the drain and the source is normally open and that the device is normally off

State three ways in which transistors are used

Used as switch to turn current on/off, acts a variable resistor to vary current flow, and as amplifiers to increase current or voltage

State the basic function of the uniJunction transistor

Voltage controlled switch

Assume a variable negative voltage is applied to the emitter of an N-Type UJT. Describe what happens is voltage is increased from zero

When an emitter reaches a certain point (Vp) o. The curve, the emitter diode becomes foward bias and a small amount of Current begins to flow into the region between B1 and the emitter

Briefly explain how a phototransistor operates to control current

When the Junction is exposed to light through a lens opening in the transistor package, it creates a control current flow this which is the transistor on

What does pinch off mean applied to a JFET circuit?

When the depletion layer touch

Why can the MOSFET withstand a positive voltage at the gate without damage?

With zero gate bias voltage applied, drain current passes through the channel between the source and drink. Gate bias voltage can swing positive or negative with reference to zero