chapter 37 Mr v.
State three operating advantages of FETs over bipolar type of transistors.
FETs do not have a thermal runaway as the temperature of the device increases. FETs have less voltage loss in a circuit than a BJT. FETs have higher input resistance.
Compare the normal current flow through a forward-biased and reverse-biased junction.
Forward bias will current flow, while reverse bias will have no current flow.
Brown
Helium
Briefly explain how a phototransistor operate to control current.
Light hits a lens opening in the transistor package which creates a current flow that turns the transistor on.
Draw the schematic symbol and identify the leads of a PNP and an NPN bipolar junction transistor (BJT).
NPN PNP
Black
Nitrogen
State the basic function of a unijunction transistor.
The Unijunction transistor functions as a voltage-controlled switch.
Explain how built-in Zener diodes can be used to protect MOSFETs against static charges.
The Zenner diode averts the current to protect the MOSFET.
With reverence to a properly biased, complete bipolar-junction transistor circuit; What determines the amount of collector for current flow?
The amount of collector current is determined by the amount of base current flow.
Why should an analog ohmmeter not ordinarily be used for testing MOSFETs?
The analog ohmmeter is not to be used because it destroys the fragile oxide insulation.
What is the operating current range of the base compared to that of the collector.
The base range current is smaller (micro- to milliamperes) than that of the collector current (mili to amperes).
What happens to the drain current flow when a positive voltage is applied to the gate?
The drain current flow increases and the channel becomes more conductive because there is a positive voltage at the gate.
In what two ways is the base region of a bipolar-junction transistor different from that of the emitter and collector?
The emitter and the collector have thicker walls than the base region. Also, the base region has fewer doping atoms.
State the type of biasing use for each junction in order to produce the required transistor action.
The emitter-base must be in forward biased with voltage and resistance values selected. While the collector-base junction must be in reverse bias and the biasing voltage must be higher than that of the emitter-base forward-biased voltage.
What can this MOSFET withstand a positive voltage at the gate without damage?
The gate can withstand positive voltage because it is insulated.
Why is this channel drawn as a broken line on this symbol?
The line is broken because the device is normally off until there is proper gate voltage on the gate and to tell that there is an open between the source and drain.
What is the main advantage of this configuration?
The main advantage of Darlingtons is that the manufacture can package them together so it becomes plug and play.
What is the basic difference in construction between a JFET and a MOSFET?
The main difference between MOSFET and JFET is that a MOSFET gate has no electric contact with drain and source.
purple
Waste air gas disposal
What is meant by the term pinch-off as it applies to a JFET circuit?
When a gate voltage goes negative the depletion zones will pinch off allowing current flow to stop between the drain and the source.
yellow
air
gray
carbon dioxide
Draw the schematic symbol and identify the leads of a three-lead NPN phototransistor.
get a picture.
Draw the schematic symbol and identify the leads of an N-channel depletion type MOSFET.
get drawing
blue
nitrous oxide
green
oxygen
Draw the schematic symbol and identify the leads of an N-channel and a P-channel JFET.
see Drawing there is no n type picture on the
Draw the schematic symbol and identify the leads of a standard N-type unijunction transistor.
see picture
In a JFET circuit, what gate-to-source biasing connection is normally used to prevent gate current flow?
A JFET gate is reversed-biased to prevent gate current flow.
Where FETs sad to be unipolar?
FETs are unipolar because working current flows through only one type of semiconductor material.
In what way is the unijunction transistor not like a true transistor?
Unijunction transistors do not amplify.
Explain why MOSFETs can be damaged by static charges. What special precautions is often taken for the packaging and shipping of MOSFETs?
Since the insulation layer is very thin it is very sensitive to any high voltage which static charges are high voltages. You need to keep MOSFETs in static protection packages or have their leads shorted together.
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vacuum
What are the normal polarity of the drain and gate with respect to the source of an N-channel JFET?
A positive Vpp that is fixed with supply voltage is connected between drain and source this allows for current to flow between source and drain. A negative variable Vgg with supply is connected between the source and the gate
In what does a small increase in base current flow result?
A small increase in base current flow will result in a larger collector current flow.
Briefly explain how current flow thought an N-Channel JFET is controlled.
Because of the negative voltage at the gate, this allows resistance to increases which causes current flow to decrease. A positive fixed voltage at the supply will allow the current to flow
Why is the phototransistor more sensitive to changes in light insensitive that the photodiode?
Because of the use of transistors, the base current is higher which causes a higher output current at the emitter.
In a JFET circuit, why is the source current equal to the drain current?
Because the gate-source junction is operating in reverse bias there should be no current flows through it. This means that all current from the drain goes to the source. Making source current equal drain current.
Compare the control of output current of a bipolar junction transistor (BJT) with that of a field-effect transistor (FET).
Bipolar junction transistors are current driven and the input current controls the output current. Since a FET transistor doesn't require much input current. the output current output is controlled by a varying electric field.
A explain the basic circuit configuration contained within a bipolar Darlington transistor.
The Darlington transistor pair is a way of setting up two bipolar transistors to let the smaller transistor act as base current for the larger transistor.
State two ways in which power transistor packages differ from the small-signal type.
The case and semiconductor material are larger. The way you install them is also different.
A digital multimeter set for the diode function test is used to check the emitter-base junction of a bipolar junction transistor. what readings would expected if the junction is good?
The diode function test should read 700mV in a forward-bias direction and in reverse-bias direction should read over range.
What is the basic difference between the connection of a PNP and NPN bipolar-junction transistor circuit?
The main difference between an NPN transistor circuit and a PNP transistor circuit is the opposite voltages and currents that are involved.
What happens to the drain current flow when a positive voltage is applied to the gate?
The positive voltage at the gate has to get bigger until the threshold voltage can be applied which lowers the resistance and the drain current flow increases to saturation.
In what way is the UJT symbol different from that of a JFET symbol?
The slant of the arrow is what makes the UJT different from an N-channel JFET.
Why is the channel drawn as a solid line on this symbol?
The solid line is to represent the circuit between the source and the drain, which is normally complete and that the device is normally on.
What are the two main families of transistors?
The two main families of transistors are field-effect transistors (FETs) and bipolar-junction transistors (BJTs).
Name the two junctions found within a BJT.
There are two PN junctions.
What are the two main types of FETs?
There are two types of FETs MOSFET and JFET.
With no base current flow how much collector current flows?
There is none because there is an open.
For what purpose is the base region used?
This base controls the current flow through the transistor.
Why are JFETs classified as normally on devices?
This is because the JFETs allow full current to pass between the source and drain when the gate circuit is not activated.
State three ways in which transistors are used.
Transistors are used in three ways, to act as amplifiers to increases voltage or current, to be used as switches to turn off and on current, and to act like variable resistors to make the current flow very.
An analog ohmmeter is used to check the collector-to-emitter circuit of a BJT. What should be the normal resistance reading between these two points?
When testing a resistor you should use the collector-to-emitter test, the resistance should read infinite or very high.
What happens to the drain current flow when a negative voltage is applied to the gate?
When the Vgs is a negative value or zero, there is no drain current flow and the device is off.
What happens to the drain current flow when a negative voltage is applied to the gate?
When there is a negative voltage at the gate, the drain current flow decreases and the channel becomes less conductive.
Assume a variable positive voltage is applied to the emitter of an N-type UJT. describes what happens as this voltage is increased from zero.
When you apply a positive voltage to a UJT it will hit peak voltage then start decreasing but at the peak, it starts emitting current from the emitter which switches to a forward-biased diode
The action of a P-channel JFET is complementary to that of an N-channel JFET. what does this mean?
With N-channel and P-channel being complementary means that they operate the same but the currents and voltages are reversed.
Assume a variable negative voltage is applied to the emitter of an N-type UJT. describes what happens as this voltage is increased from zero.
You would get negative resistance because the transistor would be turned off.
To what junction of the UJT is the input signal applied?
You would put the input signal between base 1 and the emitter.
Draw the schematic symbol and identify the leads of an N-channel enhancement type MOSFET.
a picture
