KB6NU's Ham Radio Blog

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2020 Extra Class study guide: E7D - Power supplies and voltage regulators;
Solar array charge controllers

Posted: 20 Feb 2020 10:03 AM PST
http://feedproxy.google.com/~r/kb6nu...m_medium=email


Linear power supplies are a type of power supply used in amateur radio
stations. They are called linear power supplies because they use ICs called
linear electronic voltage regulator to maintain a constant output voltage.
The way they regulate the output voltage is to vary the conduction of
current through a control element, usually a transistor. The circuit shown
in Figure E7-2 below is a linear voltage regulator, and the control element
is Q1. Q1, often called the pass transistor, controls the current supplied
to the load, thereby keeping the output voltage constant even when the load
varies. C2 bypasses rectifier output ripple around D1.



QUESTION: What type of circuit is shown in Figure E7-2? (E7D08)

ANSWER: Linear voltage regulator
QUESTION: How does a linear electronic voltage regulator work? (E7D01)

ANSWER: The conduction of a control element is varied to maintain a
constant output voltage
QUESTION: What is the purpose of Q1 in the circuit shown in Figure E7-2?
(E7D06)

ANSWER: It controls the current supplied to the load
QUESTION: What is the function of the pass transistor in a linear voltage
regulator circuit? (E7D11)

ANSWER: Maintains nearly constant output voltage over a wide range of load
current
QUESTION: What is the purpose of C2 in the circuit shown in Figure E7-2?
(E7D07)

ANSWER: It bypasses rectifier output ripple around D1

Power supply designers typically use Zener diode as the voltage reference
in a linear voltage regulator. D1 in Figure E7-2 is a zener diode.
QUESTION: What device is typically used as a stable voltage reference in a
linear voltage regulator? (E7D03)

ANSWER: A Zener diode

There are two kinds of linear voltage regulators—the series regulator and
the shunt regulator. A series regulator is the type of linear voltage
regulator that usually makes the most efficient use of the primary power
source. A shunt regulator is the type of linear voltage regulator that
places a constant load on the unregulated voltage source.
QUESTION: Which of the following types of linear voltage regulator usually
make the most efficient use of the primary power source? (E7D04)

ANSWER: A series regulator
QUESTION: Which of the following types of linear voltage regulator places a
constant load on the unregulated voltage source? (E7D05)

ANSWER: A shunt regulator

An important analog voltage regulator specification is the drop-out
voltage, which is the minimum input-to-output voltage required to maintain
regulation. For example, if an analog voltage regulator has a drop-out
voltage of 2 V, the input voltage must be at least 11 V in order to
maintain an output voltage of 9 V.
QUESTION: What is the dropout voltage of an analog voltage regulator?
(E7D12)

ANSWER: Minimum input-to-output voltage required to maintain regulation

Power dissipation is also important when designing a power supply with a
series-connected linear voltage regulator. Excessive power dissipation
reduces the efficiency of the supply and could require that you use large
heat sinks to dissipate the power. The power dissipation by a series
connected linear voltage regulator is the voltage difference from input to
output multiplied by output current.
QUESTION: What is the equation for calculating power dissipated by a series
linear voltage regulator? (E7D13)

ANSWER: Voltage difference from input to output multiplied by output current
Switching power supplies

Nowadays, you are as likely to find a switching power supply in an amateur
radio station as you are a linear power supply. Switching power supplies
use a much different method of regulating the output voltage than a linear
supply. Instead of controlling the current through a control element, a
switching supply varies the duty cycle of the control element to produce a
constant average output voltage.
QUESTION: What is a characteristic of a switching electronic voltage
regulator? (E7D02)

ANSWER: The controlled devices duty cycle is changed to produce a constant
average output voltage

Switching power supplies are usually less expensive and lighter than a
linear power supply with the same output rating. Switching supplies are
also generally more efficient than linear power supplies. The main reason
that a high-frequency switching type high voltage power supply can be less
expensive, lighter in weight, and more efficient than a linear power supply
is that the high frequency inverter design uses much smaller transformers
and filter components for an equivalent power output. Butt, this comes at a
cost. Switching supply circuits are more complicated than the circuitry in
a linear supply and may generate RF noise.
QUESTION: What is the primary reason that a high-frequency switching type
high-voltage power supply can be both less expensive and lighter in weight
than a conventional power supply? (E7D10)

ANSWER: The high frequency inverter design uses much smaller transformers
and filter components for an equivalent power output
High-voltage power supplies

Most HF transceivers and VHF/UHF transceivers operate at a relatively low
voltage. This is normally around 12 – 15 VDC. Some devices, such as older
tube equipment and linear amplifiers need higher voltages to operate. These
power supplies are quite different than the low-voltage linear and
switching supplies describe above.

High-voltage supplies may also have a step-start circuit. The purpose of a
step-start circuit in a high-voltage power supply is to allow the filter
capacitors to charge gradually, thereby reducing the amount of current the
supply draws when turned on.
QUESTION: What is the purpose of a step-start circuit in a high-voltage
power supply? (E7D15)

ANSWER: To allow the filter capacitors to charge gradually

When several electrolytic filter capacitors are connected in series to
increase the operating voltage of a power supply filter circuit, resistors
should be connected across each capacitor. Doing this helps to equalize the
voltage drop across each capacitor, discharge the capacitors when the
supply is turned off, and provide a minimum load on the supply.
QUESTION: What is the purpose of connecting equal-value resistors across
power supply filter capacitors connected in series? (E7D14)

ANSWER: All these choices are correct



Equalize the voltage across each capacitor
Discharge the capacitors when voltage is removed
Provide a minimum load on the supply



Solar array charge controllers

Solar array charge controllers are voltage or current regulators that are
used when charging batteries from a solar array. The main reason to use a
charge controller with a solar power system is to prevent battery damage by
overcharging them. Most solar panels that are rated at 12 V actually output
16 to 20 V, and if that output is not regulated, batteries connected to the
solar panel may be damaged from overcharging.
QUESTION: What is the main reason to use a charge controller with a solar
power system? (E7D09)

ANSWER: Prevention of battery damage due to overcharge

The post 2020 Extra Class study guide: E7D – Power supplies and voltage
regulators; Solar array charge controllers appeared first on KB6NUs Ham
Radio Blog.


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2020 Extra Class study guide: E7C - Filters and matching networks: types of
networks; types of filters; filter applications; filter characteristics;
impedance matching; DSP filtering

Posted: 19 Feb 2020 01:25 PM PST
http://feedproxy.google.com/~r/kb6nu...m_medium=email


Because the impedance of inductors and capacitors vary with frequency, we
often make filters out of them. One of the most common is the T-network
filter, so called because it looks like the letter T. An example is shown
in figure E7C-1.
Figure E7C-1. T-network filter

This particular filter is a T-network high-pass filter. That is to say it
will pass frequencies above a certain frequency, called the cutoff
frequency, and block frequencies below that frequency. The reason the
circuit acts this way is that as the frequency of a signal increases,
capacitive reactance decreases and inductive reactance increases, meaning
that lower-frequency signals are more likely to be shunted to ground.
QUESTION: Which of the following is a property of a T-network with series
capacitors and a parallel shunt inductor? (E7C02)

ANSWER: It is a high-pass filter

A circuit containing capacitors and inductors can also form a low-pass
filter. A low-pass filter is a circuit that passes frequencies below the
cutoff frequency and blocks frequencies above it. The circuit shown in
figure E7C-2 is called a low-pass, pi filter because it looks like the
Greek letter π. The capacitors and inductors of a low-pass filter
Pi-network are arranged such that a capacitor is connected between the
input and ground, another capacitor is connected between the output and
ground, and an inductor is connected between input and output. The reason
the circuit acts as a low-pass filter is that as the frequency of a signal
increases, capacitive reactance decreases and inductive reactance
increases, meaning that higher-frequency signals are more likely to be
shunted to ground.
Figure E7C-2. Pi-network filter
QUESTION: How are the capacitors and inductors of a low-pass filter
Pi-network arranged between the networks input and output? (E7C01)

ANSWER: A capacitor is connected between the input and ground, another
capacitor is connected between the output and ground, and an inductor is
connected between input and output

Pi networks can also be used to match the output impedance of one circuit
to the input impedance of another or the output impedance of a transmitter
to the input impedance of an antenna. An impedance-matching circuit
transforms a complex impedance to a resistive impedance because it cancels
the reactive part of the impedance and changes the resistive part to a
desired value. One advantage of a Pi matching network over an L matching
network consisting of a single inductor and a single capacitor is that the
Q of Pi networks can be varied depending on the component values chosen.
QUESTION: How does an impedance-matching circuit transform a complex
impedance to a resistive impedance? (E7C04)

ANSWER: It cancels the reactive part of the impedance and changes the
resistive part to a desired value
QUESTION: What is one advantage of a Pi-matching network over an L-matching
network consisting of a single inductor and a single capacitor? (E7C12)

ANSWER: The Q of Pi-networks can be controlled

A Pi network with an additional series inductor on the output is called a
Pi-L network. They are often used for matching a vacuum-tube final
amplifier to a 50-ohm unbalanced output. One advantage a Pi-L-network has
over a Pi-network for impedance matching between the final amplifier of a
vacuum-tube transmitter and an antenna is that it has greater harmonic
suppression than a T network.
QUESTION: Which describes a Pi-L-network used for matching a vacuum tube
final amplifier to a 50-ohm unbalanced output? (E7C07)

ANSWER: A Pi-network with an additional series inductor on the output
QUESTION: What advantage does a series-L Pi-L-network have over a series-L
Pi-network for impedance matching between the final amplifier of a
vacuum-tube transmitter and an antenna? (E7C03)

ANSWER: Greater harmonic suppression

In addition to being used to control the frequency of oscillators,
piezoelectric crystals are used to build filters. A crystal lattice filter
is a filter with narrow bandwidth and steep skirts made using quartz
crystals. The relative frequencies of the individual crystals is the factor
that has the greatest effect in helping determine the bandwidth and
response shape of a crystal ladder filter. The narrowness of the bandwidth
and the steepness of the skirts are sometimes called the filter’s shape
factor. The shape factor affects a filter’s ability to reject signals on
adjacent frequencies.
QUESTION: What is a crystal lattice filter? (E7C09)

ANSWER: A filter with narrow bandwidth and steep skirts made using quartz
crystals
QUESTION: Which of the following factors has the greatest effect on the
bandwidth and response shape of a crystal ladder filter? (E7C08)

ANSWER: The relative frequencies of the individual crystals
QUESTION: Which of the following describes a receiving filters ability to
reject signals occupying an adjacent channel? (E7C11)

ANSWER: Shape factor

Different types of filters have different characteristics. For example, a
Chebyshev filter that has a sharp cutoff, but also ripple in the passband.
An elliptical filter, on the other hand, has an extremely sharp cutoff with
one or more notches in the stop band.
QUESTION: Which filter type is described as having ripple in the passband
and a sharp cutoff? (E7C05)

ANSWER: A Chebyshev filter

QUESTION: What are the distinguishing features of an elliptical filter?
(E7C06)

ANSWER: Extremely sharp cutoff with one or more notches in the stop band

Often, you’ll choose a filter type for a particular application. For
example, a cavity filter would be the best choice for use in a 2 meter
repeater duplexer.
QUESTION: Which of the following filters would be the best choice for use
in a 2 meter band repeater duplexer? (E7C10)

ANSWER: A cavity filter

The post 2020 Extra Class study guide: E7C – Filters and matching networks:
types of networks; types of filters; filter applications; filter
characteristics; impedance matching; DSP filtering appeared first on KB6NUs
Ham Radio Blog.