Semiconductor material application and motor controlling

1. Chapter III
Semiconductor Device & Motor Controlling

2. 3.1 Diode Application
This diode when forward biased emits photons. These can be in the visible
spectrum.
The forward bias voltage is higher, usually around 2-3V.

3. Diode Application
And/ or gate ( switching)
For ideal diode D1 & D2 what will be the current through R1 and R2?

4. Rectification;
• Converting ac to dc is accomplished by the process of rectification.
• Two processes are used:
• Half-wave rectification;
• Simplest process used to convert ac to dc.
A diode is used to clip the input signal excursions of one polarity to zero.

5. Full-wave rectification.
The dc level obtained from a sinusoidal input can be improved 100% using a process
called full-wave rectification.

6. CLIPPERS
• There are a variety of diode networks called clippers, that have the ability
to “clip” off a portion of the input signal without distorting the remaining
part of the alternating waveform.
• The half-wave rectifier is an example of the simplest form of diode clipper-
one resistor and diode.

7. CLAMPERS
• The clamping network is one that will “clamp” a signal to a different dc level.
• The network must have a capacitor, a diode, and a resistive element,

8. Steps to analyze clamping networks:
1. Start the analysis of clamping networks by considering that part of the input
signal that will forward bias the diode.
2. During the period that the diode is in the “on” state, assume that the
capacitor will charge up instantaneously to a voltage level determined by the
network.
3. Assume that during the period when the diode is in the “off” state the
capacitor will hold on to its established voltage level.
4. Throughout the analysis maintain a continual awareness of the location and
reference polarity for Vo to ensure that the proper levels for Vo are obtained.
5. Keep in mind the general rule that the total swing of the total output must
match the swing of the input signal.

9. Diode Arrays
Multiple diodes can be packaged together in an integrated circuit (IC) as
display.
Example: Seven segment display or LED displays
Diode Limitations

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3.2 Bipolar Junction
Transistors

11. Construction
• The BJT is, a semiconductor device, constructed with three doped
semiconductor regions separated by two p-n junctions
• The three regions are called emitter, base, and collector
• There are two types of BJTs
–NPN and PNP type

12. Transistor mode of Operation
• In order for a BJT to operate properly as an amplifier, the two p-n
junctions must be
• correctly biased with external dc voltages.
–The base-emitter junction forward biased
–The base-collector region reverse biased

13. Cont…
• To demonstrate the mode of operation of pnp transistor first let us consider the forward
bias base emitter P-N junction as shown in figure
• The depletion region has been reduced in width due to the applied bias, resulting in a
heavy flow of majority carriers from the p- to the n-type material.

14. Cont.…
• For the next case consider the reverse-biased base collector N-P
Junction only The flow of majority carriers is zero, resulting in a
minority-carrier flow, as indicated;
• The arrow in the graphic symbol defines the direction of emitter
current (conventional flow) through the device.

16. BJT Characteristics & Parameters
• The dc current gain of a transistor is the ratio of the dc collector current
(IC) to the dc base current (IB) and is designated dc beta (βDC ).
• The ratio of the dc collector current (IC) to the dc emitter current (IE) is
the dc alpha (αDC).

17. BJT Circuit Analysis
• Consider the basic transistor bias circuit configuration
• Three transistor dc currents and three dc voltages can be identified.
• IB: dc base current , IE: dc emitter current, IC: dc collector current
• VBE: dc voltage at base with respect to emitter
• VCB: dc voltage at collector with respect to base
• VCE: dc voltage at collector with respect to emitter

18. • When the base-emitter junction is forward biased, it is like a forward-
biased diode and has a nominal forward voltage drop of
• Since the emitter is at ground potential, applying KVL

20. Collector Characteristic Curves
• A curves show how the collector current, IC, varies with the
collector-to-emitter voltage, VCE, for specified values of base
current, IB.
• Assume that VBB is set to produce a certain value of IB and VCC
is zero.
• For this condition, both the base-emitter junction and the base-
collector junction are forward-biased because the base is at
approximately 0.7V while the emitter and the collector are at 0V.
• The base current is through the base-emitter junction because of
the low impedance path to ground and, therefore, IC is zero.

22. TRANSISTOR AMPLIFYING ACTION
Let’s take common base configration
 For the common-base configuration the ac input resistance is quite small and
typically varies from 10Ω to 100Ω.
 The output resistance is quite high and typically varies from 50kΩ to 1MΩ.

23. • Using a common value of 20Ω for the input resistance and 100kΩ for output
resistance, we find that

24. • Typical values of voltage amplification for the common-base
configuration vary from 50 to 300. The current amplification
(IC/IE) is always less than 1 for the common-base configuration.
• This latter characteristic should be obvious since
IC= αIE
and α is always less than 1.

25. Operational Amplifiers
• Differential Amplifier
• Amplifies difference between inputs
Single-ended Amplifier

26. Operational Amplifier
• Output gain high
• A ~= 106
• Tiny difference in the input voltages result in a very large output
voltage
• Output limited by supply voltages
• Comparator
• If V+>V-, Vout = HVS
• If V+<V-, Vout = LVS
• If V+=V-, Vout = 0V

27. 3-stage Op-Amp
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28. • Sensor signals are often too weak or too noisy Op Amps ideally increase the
signal amplitude without affecting its other properties
Why are they useful?
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29. Inverting Op-Amp
Uses: Analog inverter
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30. Non-inverting Op-Amp
Uses: Amplify…straight up
Calculate the output voltage of a non inverting amplifier shown above for values of V1 2V,
Rf 500k, and R1 100k.
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31. Cont.…
• From the circuit shown above what will be the output has R1 =100k and Rf =500k, what
output voltage results for an input of V1 2 V?
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32. Cont.…
Differential amplifier realized with inverting connections
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33. Summation
Uses: Add multiple sensors inputs until a threshold is reached.

34. Motor Controlling
• Transistors are electronic devices that can act as either amplifiers or Switches
• We’ll be using them as switches that control the flow of power to the motor.
• Note how Digital Logic at the Base controls Power Flow in the other two ports

35. Motor Controlling
• By turning our transistors (switches) ON and OFF really fast, we change
the average voltage seen by the motor.
• This technique is called Pulse-Width Modulation (PWM).
• The higher the voltage seen by the motor, the higher the speed.
• We’ll manipulate the PWM Duty Cycle.

36. Motor Controlling

37. Motor Controlling
• If we switch our transistors too quickly, the current won’t have enough
time to increase.
• The period (not to be confused with duty cycle) of our PWM needs to be
long enough for the current to reach an acceptable level:

38. Motor Controlling

39. Motor Controlling
Direction Control using the H-Bridge
• The H-Bridge Chip has a “Direction Pin” that can be set using digital logic High/Low
This pin enables/disables flow through the transistors
• H-Bridges are used to control the speed and direction of a motor.
• They control the motor using Power Electronics… transistors to be precise.

40. DC motor speed controller
• LED provides a visual cue to the user that the microcontroller is running properly.
• The speed input device is a potentiometer which can be wired to produce a voltage input.
• The voltage signal is applied to a microcontroller which is decision making device to control a DC motor to
rotate at a speed proportional to the voltage comes from the pot.
• ADC and DAC in the system used to communicate between the analog and digital components.
• The power amplifier used to boost the voltage and source the necessary current to the motor.
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41. Stepper motor position and speed controller
• Controlling the position and speed of a stepper motor, which can be commanded to move in
discrete angular increments.
• Stepper motors are useful in position indexing applications, where you might need to move
parts or tools to and from various fixed positions (e.g., in an automated assembly or
manufacturing line).
• Stepper motors are also useful in accurate speed control applications (e.g., controlling the
spindle speed of a computer hard-drive or DVD player), where the motor speed is directly
proportional to the step rate.
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42. Stepper motor cont…
• The input devices includes a pot to control the speed manually, four buttons to
select predefined positions, and a mode button to toggle between speed and
position control.
• In position control mode, each of the four position buttons indexes the motor
to specific angular positions relative to the starting point (0, 45, 90, 180).
• In speed control mode, turning the pot clockwise (counter clockwise)
increases (decreases) the speed.
• The LED provides a visual cue to the user to indicate that the PIC is cycling
properly.
• ADC converter is used to convert the pot’s voltage to a digital value.
• A microcontroller uses that value to generate signals for a stepper motor driver
circuit to make the motor rotate.
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43. End of Chapter III