What is diode:
A diode is an electronics
component made from a combination of a (1) P-type and (2) N-type (3) semiconductor
material, known as a p-n junction, with leads attached to the two ends.
The lead
attached to the n-type semiconductor is called the cathode. Thus,
the cathode is the negative side of the diode. The positive side of the diode —
that is, the lead attached to the p-type semiconductor — is called the (6)
anode.
When a voltage
source is connected to a diode such that the positive side of the voltage
source is on the anode and the negative side is on the cathode, the diode
becomes a (7) conductor and allows current to flow. Voltage connected to the
diode in this direction is called forward bias.
But if you
reverse the voltage direction, applying the positive side to the cathode and
the negative side to the anode, current doesn’t flow. In effect, the diode
becomes an (8) insulator. Voltage connected to the diode in this direction is
called (9) reverse bias.
Forward bias
allows current to flow through the diode. Reverse bias doesn’t allow current to
flow. (Up to a point, anyway. As you’ll discover in just a few moments, there
are limits to how much reverse bias voltage a diode can hold at bay.)
This is the
schematic symbol for a diode:
Forward and
reverse bias can be illustrated with two very simple -
Note that in a
typical diode, a certain amount of forward voltage is required before any
current will flow. This amount is usually very small. In most diodes, this
voltage is around half a volt. Up to this voltage, current doesn’t flow. Once
the forward voltage is reached, however, current flows easily through the
diode.
This minimum
threshold of voltage in the forward direction is called the (10) diode’s forward
voltage drops. That’s because the circuit loses this voltage at the diode.
For example, if you were to place a voltmeter across the leads of the diode in
the forward-biased circuit, you would read the forward voltage drop of the
diode.
Then, if you
were to place the voltmeter across the lamp terminals, the voltage would be the
difference between the battery voltage (9 V) and the forward voltage drop of
the diode.
For example,
if the forward voltage drop of the diode was 0.7 V and the battery voltage was
exactly 9 V, the voltage across the lamp would be 8.3 V.
Diodes also
have a maximum reverse voltage they can withstand before they break down and
allow current to flow backward through the diode. This reverse voltage
(sometimes called PIV, for peak inverse voltage,
or PRV for peak reverse voltage) is an important
specification for diodes you use in your circuits, as you need to ensure that
your diodes won’t be exposed to more than their PIV rating.
Besides the
forward-voltage drop and peak inverse voltage, diodes are also rated for a
maximum current rating. Exceed this current, and the diode will be damaged
beyond repair.
·
In simple word: A diode is a
two terminal electronic component that conducts current primarily in one direction
(asymmetric conductance). It has low (Ideally zero) resistance in one
direction, and high (Ideally infinite) resistance in the other.
Symbol:
A
semiconductor diode, the most common type today, is a crystalline piece of
semiconductor material with a p–n junction connected to two electrical
terminals.Semiconductor diodes were the first semiconductor electronic devices.
2.2 Operating Principle of Diode
The crystal diode is a pn junction formed by
a p-type
semiconductor and an n-type semiconductor, and a space charge
layer is formed on both sides of the interface, and a self-built electric field
is built. When there is no applied voltage, the diffusion current caused by the
difference in carrier concentration on both sides of the pn junction is equal
to the drift current caused by the self-built electric field and is in an
electrical equilibrium state. When there is a forward voltage bias externally,
the external electric field and the self-built electric field inhibit each
other, which increases the diffusion current of carriers and forms a forward
current.
When there is a reverse voltage bias
externally, the external electric field and the self-built electric field are
further strengthened and reverse saturation current I0 independent of the reverse
bias voltage value is formed within a certain reverse voltage range. When the
applied reverse voltage is high to a certain extent, the electric field
strength of the space charge layer of the pn junction reaches a critical value,
a carrier multiplication process occurs, a large number of electron-hole pairs
are generated, and a large reverse breakdown current is generated. This is
called the breakdown phenomenon of the diode. The reverse breakdown
characteristics of the pn junction are Zener breakdown and avalanche breakdown.
2.3
Volt-ampere Characteristics of Diode
The volt-ampere characteristic of a
diode is the relationship between the voltage applied to the diode and the current
flowing through the diode. The curve used to qualitatively describe the
relationship between the two is called the volt-ampere characteristic curve.
The volt-ampere characteristics of the silicon diode observed with a transistor
plotter are shown in the figure below.
Figure 2.
V-A Characteristics Curve
2.4 Forward Characteristics of Diode
1) When the applied forward voltage is small,
the diode shows a larger resistance, and the forward current is almost zero.
The OA section of the curve is called the non-conductive area or dead zone.
Generally, the dead zone voltage of a silicon tube is about 0.5 volts, and the
dead zone voltage of a germanium tube is about 0.2 volts. This voltage value is
also called the threshold voltage.
2) When the applied forward voltage exceeds the
deadband voltage, the PN junction of the electric field is almost canceled, the
resistance of the diode is small, and the forward current begins to increase,
and enter the forward conduction area, but it is not proportional to the
voltage and current, for example, the AB section. As the applied voltage
increases, the forward current increases rapidly. For example, the
characteristic curve of the BC section is steep, and the volt-ampere
relationship is approximately linear, in a fully conductive state.
3) After the diode is turned on, the forward
voltage across both ends is called the forward voltage drop (or tube voltage
drop), which is almost constant. The pressure drop of the silicon tube is about
0.7V, and the pressure drop of the germanium tube is about 0.3V.
2.5
Reverse Characteristics of Diode
1) When the diode is subjected to a reverse
voltage, the internal electric field of the PN junction is strengthened, and
the diode exhibits a large resistance with only a small reverse current. In
practical applications, the smaller the reverse current, the greater the
reverse resistance of the diode, and the better the reverse cutoff performance.
Under normal circumstances, the reverse saturation current of silicon diodes is
less than tens of microamperes, the reverse saturation current of germanium
diodes is hundreds of microamperes, and high-power diodes are slightly larger.
2) When the reverse voltage increases to a
certain value, the reverse current sharply increases and enters the reverse
breakdown region. The corresponding voltage is called the reverse breakdown
voltage. If the current is too large after the diode breaks down, it will
damage the tube. Therefore, except for the Zener diode, the reverse voltage of
the diode must not exceed the breakdown voltage.
2.6
Rectifier Circuit
2.6.1 One-way Half-wave Rectifier Circuit
The diode is like an automatic switch. When U2 is
a positive half cycle, the power supply is automatically connected to the load.
When U2 is a negative half cycle, the power supply and load are
automatically cut off. Therefore, as shown in the figure below, the pulsating
DC voltage U0 with the same direction and magnitude change on
the load is shown in the figure below. Since this circuit only outputs in the
positive half cycle of U2, it is called a half-wave rectification
circuit. If the polarity of the rectifier diode is reversed, a negative DC
ripple voltage can be obtained.
Figure 3.
One-way Half-wave Rectifier Circuit
2.6.2 Full Wave Rectifier
Circuit
Figure 4.
Full Wave Rectifier Circuit
- Rectification
Principle
Set the voltage on the secondary side of the
transformer to:
1) When U2 is a positive half
cycle, the potential at point A is the highest, the potential at point V is the
lowest, diodes V1 and V3 are turned on, V2 and V4 are turned off, and the
current path is A→V1→RL→V3→B.
2) When U2 is a negative half
cycle, the potential at point B is the highest, the potential at point A is the
lowest, diodes V2 and V4 are on, V1 and V3 are off, and the current path
is B→V2→RL→V4→A.
It can be seen that in a period of change of
u2, the current from top to bottom always flows through the load RL, and the
waveform of the voltage and current is a full-wave pulsating DC voltage and
current, as shown in the following figure.
Figure 6.
Full-wave Pulsating DC Voltage and Current
Ⅲ Diode Function
Diodes are one of the most commonly used electronic
components. Its biggest characteristic is unidirectional conduction, that is,
current can only flow through one direction of the diode. The function of the
diode includes a rectifier circuit, a detection circuit, a voltage regulator
circuit, and various modulation circuits. It is mainly composed of diodes. The
principle is simple. Because of the invention of diodes and other components,
we have the birth of our colorful world of electronic information. Since the
role of diodes is so great, how should we detect them? This component is
actually very simple. Just tap the resistance file with a multimeter and
measure the reverse resistance. If it is small, it means that the diode is
broken. If the reverse resistance is large, the diode is good. For such basic
components, we should firmly grasp our own operating principles and basic
circuits to lay a good foundation for future electronic technology learning.
Ⅳ
Main Parameters of Diode
A specification used to express the
performance and range of a diode is called a diode parameter. Different types
of diodes have different characteristic parameters. For beginners, you must
understand the following main parameters:
4.1 Maximum Rectifier Current (IF)
It refers to the maximum forward average current value
allowed by the diode in long-term continuous operation. This value is related
to the PN junction area and external heat dissipation conditions. When current
passes through the tube, the die heats up and the temperature rises. When the
temperature exceeds the allowable limit (about 141 for silicon tubes and about
90 for tubes), the mold overheats and is damaged. Therefore, under the
specified heat dissipation conditions, the diode should not exceed the maximum
rectified current value of the diode. For example, the commonly used
IN4001-4007 type germanium diode has a rated forward operating current of 1A.
4.2
Highest Reverse Working Voltage (Udrm)
When the reverse voltage applied across the
diode is high enough, the tube will break down and lose its unidirectional
conductivity. In order to ensure safe use, the highest reverse operating
voltage value is specified. For example, the IN4001 diode has a reverse
withstand voltage of 50V and the IN4007 has a reverse withstand voltage of
1000V.
4.3 Reverse
Current (Idrm)
Reverse current refers to the reverse current
and the highest reverse voltage flowing through the diode at normal temperature
(25°C). The smaller the reverse current, the better the unidirectional
conductivity of the tube. It is worth noting that the reverse current has a
close relationship with temperature and the reverse current doubles for every
10°C increase in temperature. For example, a 2AP1 germanium diode has a reverse
current of 250uA at 25°C, and a reverse current of 500uA when the temperature
rises to 35°C, and so on. At 75°C, its reverse current reaches 8mA. Not only
will it lose its unidirectional conductivity, but it will also overheat and
damage the tube. Another example is the 2CP10 silicon diode, which has a
reverse current of only 5uA at 25°C, and a reverse current of 160uA when the
temperature rises to 75°C. Therefore, silicon diodes have better
high-temperature stability than germanium diodes.
4.4
Dynamic Resistance (Rd)
The ratio of the change in voltage near the
static operating point Q of the diode characteristic curve to the change in the
corresponding current.
4.5 Highest Working Frequency (Fm)
Fm is the upper limit frequency of diode
operation. Since the diode is the same as the PN junction, its junction
capacitance is composed of blocking capacitance. Therefore, the size of the
frequency modulation mainly depends on the size of the PN junction capacitance.
If it exceeds this value, it will affect unidirectional conductivity.
4.6 Voltage
Temperature Coefficient (αuz)
Αuz refers to the relative change in the steady
voltage for every one degree Celsius increase in temperature. The temperature
stability of the Zener diode with a uz of about 6v is better.
4.7
Parameter Symbols
CT---barrier
capacitance
Cj---junction
(interelectrode) capacitance; indicates the total capacitance of the
germanium detection diode under the specified bias voltage across the
diode
Cjv---bias
junction capacitance
Co---zero bias
capacitor
Cjo---zero-bias
junction capacitance
Cjo/Cjn---junction
capacitance change
Cs---shell
capacitor or package capacitor
Ct---total
capacitance
CTV---voltage
temperature coefficient. The ratio of relative change in steady voltage to
absolute change in ambient temperature at test current
CTC---capacitor
temperature coefficient
Cvn---nominal
capacitance
IF---forward
DC (forward test current). Germanium detector diode passes the current between
the poles under the specified forward voltage VF; the maximum operating current
(average value) that the silicon rectifier and the silicon stack are allowed to
pass continuously in the sine half-wave under the specified use conditions, the
silicon switch The maximum forward DC that the diode is allowed to pass at
rated power; the current given when measuring the forward voltage of the Zener
diode
IF(AV)---forward
average current
IFM(IM)---forward
peak current (forward maximum current). The maximum forward pulse current
allowed through the diode at rated power. LED limit current.
IH---constant
current, holding current.
Ii---; LED
flashing current
IFRM---forward
repeat peak current
IFSM---positive
peak current (surge current)
Io---rectifying
current. Operating current through specified frequency and specified voltage
conditions in a particular line
IF(ov)---forward
overload current
IL---Photocurrent
or steady current diode limiting current
ID---dark
current
IB2---single-junction
transistor
IEM---emitter
peak current
IEB10---Reverse
current between the emitter and the first base in a double-base single-junction
transistor
IEB20---Emitter
current in double base single-junction transistor
ICM---Maximum
output average current
IFMP---positive
pulse current
IP---peak
current
IV---valley
current
IGT---thyristor
gate trigger current
IGD---thyristor
control pole does not trigger current
IGFM---control
positive peak current
IR(AV)---reverse
average current
IR (In)---reverse
DC (reverse leakage current). When measuring the reverse characteristic, the
given reverse current; the silicon stack is in the sinusoidal half-wave
resistive load circuit, the current passed when the reverse voltage is
specified; the reverse polarity of the silicon switching diode plus the reverse
operating voltage VR The current passed through; the leakage current generated
by the Zener diode under reverse voltage; the leakage current of the rectifier
at the highest reverse operating voltage of the sine half-wave.
IRM---reverse
peak current
IRR---Thyristor
Reverse Repeated Average Current
IDR---thyristor
off-state average repeat current
IRRM---reverse
repeat peak current
IRSM---reverse
peak current (reverse surge current)
Irp---reverse
recovery current
Iz---stabilize
voltage and current (reverse test current). Given reverse current when testing
reverse electrical parameters
Izk---Stabilized
tube knee current
IOM---maximum
forward (rectifier) current. The maximum forward instantaneous current that can
withstand under specified conditions; the maximum operating current that allows
continuous conduction through the detection diode in a sinusoidal half-wave
rectification circuit with resistive load
IZSM---Zener
diode surge current
IZM---Maximum
regulated current. Current that the Zener diode allows passing at maximum
dissipated power
iF---forward
total instantaneous current
iR---reverse
total instantaneous current
Ir---reverse
recovery current
Iop---working
current
Is--- steady
current diode steady current
f---frequency
N---capacitance
change index; capacitance ratio
Q---good
value (quality factor)
Δvz---voltage
regulator voltage drift
Di/dt---on-state
current critical rise rate
Dv/dt---on-state
voltage critical rise rate
PB---withstand
pulse burnout power
PFT (AV)--- forward
conduction average power dissipation
PFTM---positive
peak power dissipation
PFT---positive
conduction total instantaneous power dissipation
Pd---dissipated
power
PG---gate
average power
PGM---gate peak
power
PC---control
pole average power or collector dissipation power
Pi---input
power
PK---maximum
switching power
PM---rated
power. The maximum power that a silicon diode can withstand no more than 150
degrees
PMP---maximum
leakage pulse power
PMS---maximum
pulse power
Po---output
power
PR---reverse
surge power
Ptot---total
dissipated power
Pomax---maximum
output power
Psc---continuous
output power
PSM---Do not
repeat surge power
PZM---Maximum
dissipated power. The maximum power that the Zener diode is allowed to
withstand for a given service condition
RF(r)---forward
differential resistance. In the forward conduction, the current exhibits
significant nonlinear characteristics as the voltage index increases. Under a
certain forward voltage, the voltage increases by a small amount ΔV, and the
forward current increases by ΔI, then ΔV/△I is called differential resistance.
RBB---base
resistance between double base transistors
RE---RF
resistance
RL---load
resistor
Rs(rs)----Series
resistance
Rth----thermal
resistance
R(th)ja----thermal
resistance from junction to environment
Rz(ru)---dynamic
resistance
R(th)jc---junction-to-shell
thermal resistance
r; δ---attenuation
resistance
r(th)---transient
resistance
Ta---ambient
temperature
Tc---shell
temperature
Td---delay
time
Tf---fall time
Tfr---forward
recovery time
Tg---circuit
commutation shutdown time
Tgt---gate gate
opening time
Tj---junction
temperature
Tjm---highest
junction temperature
Ton---opening
time
Toff---off time
Tr---rise time
Trr---reverse
recovery time
Ts---storage
time
Tstg---temperature
storage diode storage temperature
a---temperature
coefficient
Λp---luminescence
peak wavelength
△ ;λ---spectral half-width
η---single-junction
transistor divider ratio or efficiency
VB---reverse
peak breakdown voltage
Vc---rectified
input voltage
VB2B1---base
voltage
VBE10---emitter
and first base reverse voltage
VEB---saturated
pressure drop
VFM---maximum
forward voltage drop (forward peak voltage)
VF---forward
voltage drop (forward DC voltage)
△VF---positive pressure drop
difference
VDRM---off state
repeated peak voltage
VGT---gate
trigger voltage
VGD---gate does
not trigger voltage
VGFM---gate
positive peak voltage
VGRM---gate
reverse peak voltage
VF (AV)--- positive
average voltage
Vo---AC input
voltage
VOM---Maximum
output average voltage
Vop---working
voltage
Vn---center
voltage
Vp---peak
point voltage
VR---reverse
working voltage (reverse DC voltage)
VRM---reverse
peak voltage (highest test voltage)
V(BR)---breakdown
voltage
Vth---valve
voltage (threshold voltage, dead band voltage)
VRRM---reverse
repeat peak voltage (reverse surge voltage)
VRWM---reverse
working peak voltage
Vv---valley
voltage
Vz---stable
voltage
△Vz---voltage range voltage increment
Vs---to
voltage (signal voltage) or steady current tube to stabilize current and
voltage
Av---voltage
temperature coefficient
Vk---Knee
point voltage (steady current diode)
VL--- limit
voltage
If you have more interest in diodes, you can check
the
Diode Symbol
Ⅴ Types of Diode
There are many types of diodes: according to
materials, there are germanium diodes, silicon diodes, gallium arsenide diodes,
etc.; according to the manufacturing process can be divided into surface
contact diodes and point contact diodes; according to different uses can be
divided into rectifier diodes, detection diodes, Zener diodes, varactors,
photodiodes, light-emitting diodes, switching diodes, fast recovery diodes,
etc.; according to the type of connection can be divided into semiconductor
junction diodes, metal-semiconductor contact diodes, etc.; Conventional
packaged diodes, specially packaged diodes, etc. The following uses the
application as an example to introduce the characteristics of different types
of diodes.
5.1
Rectifier Diode
The function of the rectifier diode is
to use the unidirectional conduction characteristic of the diode to rectify the
AC power source into a pulsating DC. Due to the large forward working current
of the rectifier diode, a surface contact structure is often used in this
process. The diode junction capacitance of this structure is relatively large,
so the operating frequency of the rectifier diode is generally less than 3khz.
Rectifier diodes are mainly available in
hermetic metal package and plastic package. Normally, the rectifier diode with
rated forward T current LF above l A is packaged in a metal case to facilitate
heat dissipation; the rated forward operating current is below 1A in an
all-plastic package. In addition, due to the continuous improvement of
T-technical technology, many high-power rectifier diodes are packaged in
plastic, which should be distinguished in use.
Since the rectifier circuit is usually a bridge
rectifier circuit, some manufacturers package four rectifier diodes together.
Such redundant components are usually called rectifier bridges or rectifier
full-bridge (referred to as a full-bridge).
When using a rectifier diode, the parameters
such as large rectification current, large reverse current, cutoff frequency
and reverse recovery time should be considered.
The rectifier diode used in the common series
stabilized power supply circuit does not require a reverse recovery time for the
cutoff frequency. As long as the rectifier current is selected according to the
requirements of the circuit, the rectifier diode (for example, the N series,
2CZ series, RLR series, etc.).
The rectifier
circuit used in the switching regulator power supply and
the rectifier diode used in the pulse rectifier circuit should use a rectifier
diode or a fast recovery diode with a higher operating frequency and a shorter
reverse recovery time.
5.2
Detection Diode
The detector diode is a device that detects a
low-frequency signal superimposed on a high-frequency carrier and has high
detection efficiency and good frequency characteristics.
The detection diode requires a small forward
voltage drop, high detection efficiency, small junction capacitance, and good
frequency characteristics, and its shape is generally EA glass package
structure. The general detection diode adopts a point contact type structure of
tantalum material.
When selecting a detector diode, the detector
diode with high operating frequency, small reverse current, and sufficient
forward current should be selected according to the specific requirements of
the circuit.
5.3
Switch Diode
Since the semiconductor diode has a positive
bias, the on-resistance is small. When the reverse bias is applied, the cutoff
is applied. The off-resistance is large, and the unidirectional conduction
characteristic of the semiconductor diode in the storage switching circuit can
turn on and off the current, so the semiconductor diode used for this purpose
is called a switching diode.
Switch diodes are mainly used in household
appliances and electronic equipment such as tape recorders, televisions, and
DVD players, such as switching circuits, detection circuits, and high-frequency
pulse rectifier circuits.
The 2AK series of common switch diodes can be
selected for the medium-speed switching and detection circuits. High-speed
switching circuits can be selected from RLS series, 1sS series, 1N series, 2CK
series high-speed switching diodes. The specific model of the switching diode
should be selected according to the main parameters of the application circuit
(such as forward current, high reverse voltage, reverse recovery time, etc.).
5.4 Zener Diode
The Zener diode is
characterized by the fact that the voltage of the PN junction reversely changes
without changing with the current to achieve the purpose of voltage regulation.
Because it can regulate the voltage in the circuit, it is called a Zener diode
(referred to as a voltage regulator). The Zener diode is classified according
to the breakdown voltage, and its voltage regulation value is the breakdown
voltage value. The Zener diode is mainly used as a voltage regulator or voltage
reference component. Zener diodes can be connected in series to obtain a higher
voltage regulation value.
The selected Zener diode should meet the
requirements of the main parameters in the application circuit. The stable
voltage value of the Zener diode should be the same as the reference voltage
value of the application circuit. The large current of the Zener diode should
be about 50% higher than the large load current of the application circuit.
5.5 Fast Recovery Diode
The Fast Recovery Diode is a new type of
semiconductor diode. This diode has good switching characteristics and short
reverse recovery time and is commonly used as a rectifier diode in
high-frequency switching power supplies.
The fast recovery diode has the
characteristics of short recovery time and is suitable for high frequency (such
as TV line frequency) rectification. The fast recovery diode has an important
parameter that determines its performance-reverse recovery time. The reverse
recovery time is defined as the diode falling from the output pulse to the zero
lines, and transitioning from the forward conducting state to the off state.
The time required for the reverse power supply to recover to 10% of the large
reverse current is represented by a symbol.
Ultra-fast recovery diodes (SRDs) are developed
based on fast recovery diodes, the main difference is that the reverse recovery
time is smaller. The reverse recovery time of a normal fast recovery diode is
several hundred nanoseconds, and the reverse recovery time of an ultra-fast
recovery diode (SRD) is typically several tens of nanoseconds. The smaller the
value, the higher the operating frequency of the fast recovery diode.
When the operating frequency is in the range of
tens to hundreds of k Hz, the change of the forward and reverse voltage of the
ordinary rectifier diode is slower than the recovery time, and the ordinary
rectifier diode cannot normally conduct unidirectional conduction and
rectification. At this time, it is necessary to use a fast recovery rectifier
diode to be competent. Therefore, the rectifier diodes powered by a switching
power supply (such as a color TV) are usually fast recovery diodes and cannot
be replaced by ordinary rectifier diodes. Otherwise, the device may not work
properly.
5.6 Schottky
Barrier Diode
This diode is an
abbreviation for Schottky Barrier Diode (SBD). It is a low-power, high-current,
ultra-high-speed semiconductor device produced in recent years. The reverse
recovery time is extremely short (can be as small as a few nanoseconds), the
forward voltage drop is only about 0.4 V, and the rectified current can reach
several thousand amperes. These excellent characteristics are unmatched by fast
recovery diodes.
A Schottky diode is a metal-semiconductor
device in which a noble metal (gold, silver, aluminum, platinum, or the like)
is used as a positive electrode, and an N-type semiconductor is used as a
negative electrode, and a barrier formed on the contact surface thereof has a
rectifying property.
Schottky diodes are commonly used in high
frequency, high current, low voltage rectifier circuits.
5.7 Transient Voltage Suppression Diode
This diode abbreviated as TVP tube
(transient-voltage-suppressor). It is a semiconductor device developed on the
basis of the process of the Zener diode and is mainly used in a fast
overvoltage protection circuit for voltage. It can be widely used in computers,
electronic instruments, communication equipment, household appliances, and onboard
or marine and automotive electronic equipment for field operations, and can be
used as a protection element for over-voltage shock caused by human operation
or an electric shock to equipment.
Transient voltage suppression diodes can be
classified into four categories according to their peak pulse power: 50 () w,
1000 W, 1500 W, 5000 w. Each class is divided into several types according to
its nominal voltage.
When the voltage at both ends is higher than
the rated value, the transient voltage suppression diode will turn on
instantaneously, and the resistance at both ends will change from high
resistance to low resistance at a very high speed, thereby absorbing a very
large current and the voltage across the tube. Clamp at a predetermined value.
5.8 Light
Emitting Diode
The English abbreviation for the light-emitting
diode is LED, which is a device made of
semiconductor materials such as gallium phosphide or phosphorus gallium
arsenide, which can directly convert electrical energy into light energy. In
addition to the unidirectional conduction characteristics of conventional diodes,
LEDs can convert electrical energy into light energy. When a forward voltage is
applied to the LED, it is also in a conductive state. When the forward current
flows through the mold, the LED emits light, which converts electrical energy
into light energy.
The color of the light-emitting diode is mainly
determined by the material of the tube and the type of impurities. At present,
the common LED light-emitting colors are mainly blue, green, yellow, red,
orange, white, and so on. Among them, white LED is a new type of product,
mainly used in mobile phone backlights, LCD backlights, lighting and other
fields.
The operating current of the LED is usually 2
to 25 mA. The operating voltage (ie, forward voltage drop) varies from material
to material: normal green, yellow, red, and orange light-emitting diodes
operate at approximately 2V; white LEDs typically operate at voltages greater
than 2.4V; blue LEDs usually work at a voltage higher than 3.3V. The working
current of the LED should not exceed the rated value too high, otherwise, there
is a danger of burning. Therefore, a resistor R is usually connected in series
in the LED circuit as a current-limiting resistor.
5.9 Avalanche
Diode
The avalanche diode is a microwave power device
developed based on the Zener process technology, which can generate
high-frequency oscillation under the action of an applied voltage.
The avalanche diode uses avalanche breakdown to
inject carriers into the crystal. Since it takes a certain time for the carrier
to pass through the semiconductor wafer, its current lags behind the voltage,
resulting in a delay time. If the passage time is properly controlled, the
current is a negative resistance effect that occurs in the voltage
relationship, leading to high-frequency oscillations. It is commonly used in
microwave communications, radar, tactical missiles, remote control, telemetry,
instrumentation and other equipment.
5.10 DIAC
The bidirectional trigger diode is also called
a two-terminal AC device (DIAC). It is a silicon bidirectional
voltage-triggered switching device. When the voltage applied across the
bidirectional trigger diode exceeds its breakdown voltage, both ends are turned
on, and conduction will continue until the current is interrupted or dropped to
a smallholding current of the device. Turn it off again. Bidirectional trigger
diodes are commonly used in overvoltage protection circuits, phase shifting
circuits, thyristor trigger circuits, and timing circuits.
5.11 Varactor
Diode
The varactor diode (English name
variable-Capacitance Diode, abbreviated as VCD) is a special semiconductor
device that uses reverse bias to change the PN junction capacitance. A varactor
diode is equivalent to a variable-capacity capacitor whose PN junction
capacitance varies between the two electrodes and changes with the magnitude of
the reverse voltage applied to the varactor diode. When the reverse voltage
applied to the varactor increases, the capacity of the varactor decreases.
Because varactors have this characteristic, they are mainly used in electrical
tuning circuits (such as high-frequency heads of color TVs), as an automatic
trimming capacitor that can be controlled by voltage.
When selecting a varactor, it should be
considered whether its operating frequency, high reverse operating voltage,
large forward current and zero-bias junction capacitance meet the requirements
of the application circuit. The junction capacitance should be changed greatly,
high Q value, reverse A varactor diode with a small leakage current.
Ⅵ Identification
and Detection of Diode
6.1
Diode Identification
The crystal diode is commonly used in the
circuit as a VD plus a digital representation, such as VD5 represents a diode
numbered 5.
The identification of the diode is simple: the
negative pole of the low-power diode is usually marked with a color ring on the
surface; some diodes also use the "P" and "N" symbols to
determine the polarity of the diode, "P" for the positive pole and "N"
for the negative pole. Metal-encapsulated diodes usually have a diode symbol
printed on the surface with the same polarity; LEDs usually use the length of
the pins to identify the positive and negative poles, the long legs are
positive, and the short legs are negative.
The surface of the rectifier bridge is usually
marked with the internal circuit structure or the name of the AC input and the
DC output. The AC input is usually indicated by “AC” or “~”; the DC output is
usually indicated by the “+” and “~” symbols.
Due to the variety of shapes of the chip
diodes, the polarity is also marked by a variety of methods: in the leaded chip
diode, the end of the tube with a white color ring is the negative electrode;
in the chip diode with lead and colorless ring, the longer end of the lead wire
is the positive electrode; in the leadless chip diode, the end of the ribbon or
the notched end is the negative electrode.
6.2
Diode Detection
When using an analog multimeter to test the
diode, one end of the black pen with a smaller value is the positive pole, and
the end connected to the red test pen is the negative pole. If the forward
resistance and reverse resistance are infinite, the diode is open; if the
forward resistance and reverse resistance are both 0, the diode is short-circuited.
Under normal conditions, the forward resistance of a germanium diode is about
1.6kΩ.
When measuring a diode with a digital
multimeter, connect the red pen to the anode of the diode and the black test
lead to the cathode of the diode. The measured resistance is the forward
conduction resistance of the diode, just like the pointer of a pointer
multimeter.
It is more convenient to use the diode block
detection diode of the digital multimeter: put the digital multimeter in the
diode block, connect the negative pole of the diode to the black multimeter of
the digital multimeter, and connect the positive pole of the digital multimeter
to the red test lead. The forward voltage drop value of the diode. Diodes of
different materials have different forward voltage drop values: 0.55-0.7V for
silicon diodes and 0.15-0.3V for germanium diodes. If the display shows “0000”,
the tube is short-circuited; if “0L” or “overload” is displayed, it means that
the diode is open or in reverse state. At this time, the meter can be
re-tested.
Ⅶ
Frequently Asked Questions about LED Working Principle
1. What is a diode?
A diode is reverse biased when it acts as an
insulator and is forward biased when it allows current to flow. A diode has two
terminals, the anode and the cathode.
2. What is a diode used for?
Main functions. The most common function of a
diode is to allow an electric current to pass in one direction (called the
diode's forward direction), while blocking it in the opposite direction (the
reverse direction). As such, the diode can be viewed as an electronic version
of a check valve.
3. What is diode in basic
electronics?
A diode is a semiconductor device that
essentially acts as a one-way switch for current. It allows current to flow
easily in one direction, but severely restricts current from flowing in the
opposite direction.
4. What are the three main types of
diodes?
Types of diode
Backward
diode: This type of diode is sometimes also called the back diode.
BARITT
diode: This form of diode gains its name from the words Barrier Injection
Transit Time diode.
Gunn
Diode: Although not a diode in the form of a PN junction, this type of diode is
a semiconductor device that has two terminals.
5. What is diode equation?
I0 is the dark saturation current, q is the
charge on the electron, V is the voltage applied across the diode, η is the
(exponential) ideality factor.
6. What is the symbol of diode?
The basic schematic symbol for a diode looks
like an arrow head that points in the direction of conventional current flow
from its Anode (A) terminal to its Cathode (K) terminal. The schematic symbol
of a diode also shows that if forward-biased, current will flow through the
direction of the arrow.
7. What is diode characteristics?
Basic static characteristics of diodes are the
forward voltage VF and forward current IF, and the reverse voltage and current
VR and IR. The area surrounded by the orange dashed line in the diagram on the
right indicates the usable area of rectifying diodes.
8. What is ideal diode model?
An ideal diode is one kind of an electrical
component that performs like an ideal conductor when voltage is applied in
forward bias and like an ideal insulator when the voltage is applied in reverse
bias. So when +ve voltage is applied across the anode toward the cathode, the
diode performs forward current immediately.
9. What are diode parameters?
Peak Inverse Voltage, PIV: This diode
characteristics is the maximum voltage a diode can withstand in the reverse
direction. This voltage must not be exceeded otherwise the device may fail. ...
The diode can withstand a reverse voltage up to a certain point, and then it
will breakdown.
10. How do you read a diode value?
Diode Mode Testing Procedure
Connect
the red probe to the anode and black probe to the cathode. This means diode is
forward-biased. Observe the reading on meter display. If the displayed voltage
value is in between 0.6 to 0.7 (since it is silicon diode) then the diode is
healthy and perfect.
Questions and answer:
What is the main function of
a diode?
A diode is a device that allows
current to flow in one direction but not the other. This is achieved through a
built-in electric field. A diode is a device that allows current to flow in one
direction but not the other. This is achieved through a built-in electric
field.
What causes a diode to burn?
A diode typically fails to open
happens due to over current. This is called metallization burnout and can occur
from things like EOS (Electrical Over Stress). Over current causes excessive
heating and literally burns the metal away.
Can a diode go bad?
A bad (opened) diode does not allow
current to flow in either direction. A multimeter will display OL in both
directions when the diode is opened. A shorted diode has the same voltage drop
reading (approximately 0.4 V) in both directions.
How can you tell if a
diode is blown?
Turn the dial to “diode test”
mode. This level of current is high enough to produce a reading, yet not so
high that the diode will fail. It may also be labeled as “diode check” on your
multimeter and is usually indicated by a small diode symbol. The diode symbol
will look like a triangle pointing towards a line.
Can you bypass a diode?
Two types of diodes are available
as bypass diodes in solar panels and arrays: the PN-junction silicon diode and
the Schottky barrier diode. Both are available with a wide range of current
ratings.
What is the role of a bypass
diode?
The bypass diodes’ function is to
eliminate the hot-spot phenomena which can damage PV cells and even cause fire
if the light hitting the surface of the PV cells in a module is not uniform.
The bypass diodes are usually placed on sub-strings of the PV module, one diode
per up to 20 PV cells.
Do I need a blocking diode
with a charge controller?
Nowadays, most solar power
systems have a charge controller between the solar panel and the battery, and
this charge controller prevents this backflow of electricity, eliminating the
need for a blocking diode.
How many watts can a 40 amp
charge controller handle?
As a guide, the maximum number of
watts that a 40 amp PWM charge controller can handle is approximately 480W for
a 12 V battery system and 960W for a 24 V system provided it is mounted in a
well ventilated area to prevent overheating.
Is blocking diode necessary?
Blocking diodes will be of
benefit in any system using solar panels to charge a battery. Blocking diodes
are usually included in the construction of solar panels so further blocking
diodes are not required.
Can solar panel work
without diode?
Yes, you can remove the diodes.
But you need to be aware that the solar panel will act as a load itself when
the amount of light drops below a certain amount. If the panel were connected
to a battery bank and the charge controller doesn’t prevent reverse current
flow, the solar panel will discharge the battery.
What does the diode symbol
mean?
Diode, an electrical component
that allows the flow of current in only one direction. In circuit diagrams, a
diode is represented by a triangle with a line across one vertex.
Is amplifier a diode?
The diode amplifier which
combines the voltage and current ‘gain characteristics of the preceding
circuits is indicated in Figure 6. This circuit configuration has an output
impedance which is larger than its input impedance, and provides voltage gain
aimilar to a common base transistor amplifier.
Can zener diode be used as
rectifier?
Unlike the normal p-n junction
diode, a Zener diode has a low peak inverse voltage. This is an undesirable
property for the rectifier circuit. This is the reason why Zener diodes are not
used for rectification purpose but are mostly used in applications that require
voltage regulation.
Can a diode amplify voltage?
(As far as I remember, a voltage
exist BETWEEN two nodes). You can get amplification from an Esaki or tunnel
diode which exhibits a negative resistance on its characteristic curve.
Can we use zener diode as
amplifier?
The Zener diode is therefore
ideal for applications such as the generation of a reference voltage (e.g. for
an amplifier stage), or as a voltage stabilizer for low-current applications.
Another mechanism that produces a similar effect is the avalanche effect as in
the avalanche diode.
How is a Zener diode formed?
The Zener diode is made up of
heavily doped semiconductor material. The heavily doped means the high-level
impurities is added to the material for making it more conductive. The
depletion region of the Zener diode is very thin because of the impurities.
How do zener diodes work?
The Zener diode operates just
like the normal diode when in the forward-bias mode, and has a turn-on voltage
of between 0.3 and 0.7 V. As the reverse voltage increases to the predetermined
breakdown voltage (Vz), a current starts flowing through the diode.
How do you read a zener
diode?
Measure the reverse-biased
voltage on the Zener diode by switching the multimeter probes. Place the
positive lead on the marked or cathode side, and the negative lead on the
unmarked or anode side. You should get a reading indicating infinite resistance
or no current flow.
How do you fit a zener
diode?
To connect a zener diode is a
circuit and provide a voltage regulation, the zener diode should be connected
in reverse biased, in parallel on the power source which gives the zener diode
it s voltage, along the source connected to a resistor.
Explain
what is a zener diode?
Zener diode is a p-n junction diode specially designed for operation in the breakdown region in reverse bias condition.
Explain
what is zener voltage?
The voltage at which the zener diode breaks down is called the zener voltage.
Explain what is meant by the temperature coefficient?
The effect of temperature on zener voltage is given in terms of temperature coefficient which is defined as the percentage change in nominal zener voltage for each degree centigrade of change in junction temperature.
Explain
what happens to the series current , load current and zener current when the dc
input voltage of a zener regulator increases?
Zener current and series current increases while the load current remains unchanged.
Why is zener diode used as a voltage regulator?
Zener diode has the property of behaving like a dc battery in ‘on’ state (i.e. when the voltage across the zener diode exceeds its zener voltage rating VZ) . In ‘on’ state , the voltage across zener diode remains constant until the voltage across it deops less than VZ . This property of zener diode makes its use as a voltage regulator.
Explain
how zener diode maintains constant voltage across the load?
Zener diode has the property of behaving like a dc battery in ‘on’ state. If the zener diode is shunted across the load RL and the voltage across zener diode is more than the zener voltage VZ then zener diode is on ‘on’ state , and any variation in voltage across the zener diode due to variations either in supply voltage or in load resistance is not able to change the output voltage. Thus zener diode maintains voltage constant across the load.
Explain
what is tunnel diode?
Tunnel diode is a high conductivity two-terminal p-n junction doped heavily (about 1,000 times higher than a normal diode).
Explain
what is tunneling?
The mechanism of conduction in a semiconductor diode in which charge carriers (possessing very little energy) punch through a barrier directly instead of climbing over it is called tunneling.
Explain
what are the applications of tunnel diodes?
Tunnel diodes are used as amplifiers, oscillators or switching devices, being an exclusive high-frequency component because of its very fast response inputs.
Explain
what is PIN diode?
PIN is composed of three sections with a high resistivity intrinsic layer sandwiched between p and n regions. It offers a variable resistance (decreasing with the increase in the forward current) in the forward bias mode and infinite resistance in the reverse bias mode.
Eplain what is a varactor diode?
A
varactor diode is a specially fabricated p-n junction with proper impurity
concentration profile and operated under reverse-biased mode so as to give a
variable junction capacitance.
Which
device produces voltage variable capacitor? How the voltage variable
capacitance varies with the change in voltage across it?
The
varactor diode produces voltage variable capacitor. The junction capacitance of
a varactor diode varies inversely as the square root of the reverse bias
voltage in case of alloyed junction and varies inversely as the cube root of
reverse bias voltage for diffuse junction.
Explain
what is point contact diode?
Point
connect diode consists of an n-type germanium or silicon (preferably germanium)
wafer about 1.25 mm suare by 0.5 mm thick, one face of which is soldered to a
metal and the other face has a phosphor bronze or tungsten spring pressed
against it. Because of very low capacitance, point contact diode is very much
suitable for high freuency applications (of the order of 10 GHz).
Explain
what is a step-recovery diode and why is it so called ?
Step-recovery
diode is a voltage-dependent variable capacitor diode with graded doping
profile (concentration of charge carriers decreasing near the junction).
Because of step or sudden recovery from the reverse current ON to reverse
current OFF, it is called the step-recovery diode.
Explain
what is Schottky diode?
Schottky
diode is uite different in construction from the normal p-n junction diode. It
has metal (such as gold, silver, platinum , molybdenum, chrome or tungsten ) n
one side and n-type doped silicon on the other side of the junction. It has no
storage charge. The junction barrier is called the Schottky barrier.
Why is
Schottky diode called hot-carrier diode?
Since in
forward bias operation of the Schottky diode, the electrons on the n-side gains
enough energy to cross the junction and plunge into the metal with very large
energy, they are usually called into the metal with very large energy, they are
usually called hot carriers and the diode is called hot-carrier diode.
Explain
what is back diode?
Back
diode is similar to a tunnel diode except that tunneling effect is large but
only in the reverse direction. This is also called a unilateral diode.
Explain
what are power diodes?
The power
diodes are similar to p-n junction signal or low-power diodes but have large
power-, voltage-, and current-handling capabilities than those of conventional
p-n junction diodes. Power diodes find many applications in electronics and
electrical engineering circuits.’
Why the
current in power diode varies linearly rather than exponentially with voltage?
The large
magnitude of current in power diodes leads to ohmic drop that hides the
exponential part of the V-I characteristic curve.
Explain
what is photodiode?
Photodiode
is a two-terminal semiconductor p-n junction diode device and is designed to
operate with reverse bias.
How the
current is reduced to zero in a photodiode?
The
reverse saturation current I0 flowing through a photodiode is reduced to zero
by applying a forward bias voltage of magnitude eual to barrier potential.
Photodiode is a photovoltaic device or a photoconductive device or both?
Photodiode
is a photovoltaic device as well as a photoconductive device. When it is
operated with a reverse bias, it is photoconductive device and when operated
without the reverse bias, it is a photovoltaic device.
Explain
what is meant by LED?
LED
stands for Light Emitting Diode.
Explain
what precautions are reuired to be observed in the use of LEDs?
LEDs should neither be reverse-biased nor operated near their maximum current rating. The leads of an LED should never be bent closer than about 2 mm from the encapsulation.
SOME IMPORTANCE QUESTIONS -
Q1-In which devices
diode is used? And explain the few points about their devices?
we use diodes in many electronic devices as a
switch when in active region.
–
these works in forward direction.
–
they act as an open switch inn reverse direction.
Q2-In the p-n junction and photo transistor which diode is used?
ns- in pn junction –
it is simply a junction not not any special dide is needed to form a diode in
fact diode is the combination of both p-type & n-type semiconductor, which
form a diode. In photo transistor we use a photo diode for processing.
Q3-what is the main
purpose of diode used ? Explain?
Ans- the main
motive of a diode is to use as a switch for electronic devices like in
transistor .
Q4-can we replace
the avalanche diode any other diode? If yes or not ,give the logical
reason?
Ans- no we cant
replace an avalanche diode by any other diode because it give a constant output
in reverse bias condition .
Q5-Explain photo
transistor diode ?
Ans- photo
transistor basically works on the principal of photoelectric emission. In photo
transistor (either npn or pnp) which acts either in forward or reverse
direction by the photons falling on it , and make them activated for
transmission of electrons and working for amplification.
Q6-what is the main
function of pn diode? Explain.
Ans- the main
function of diode is biasing and acting like a switch close switch in forward
direction and open switch in revers direction.
Q7-In the pn
junction which diode is used?explain.
Ans- pn
junction form automatically a diode.
Q8-In any device if
we can get out the diode then what will happen?
Ans- if we take out
the diode there can be short ckt as the switching system is damaged, and that
can harm device at inverting the polarities of the source.
Q9-Types of
diode?explain.
Ans 2 type
npn and pnp
Q10-working of
diode?
Its simply that
P-Type with excess of Positive charges and N-Type , with excess of negative
charges , P-Type holes attract N Type electrons in hole.
QUESTIONS AND ANSWERS-
i) What is a pn
junction?
The 'P' side of a
pn junction diode is always positive terminal and is called as anode. Other
side which is negative is called as cathode. The symbol is shown in figure.
(iii) What is meant
by forward biasing of a pn junction?
If the anode is
connected to positive terminal of a battery and cathode to the negative
terminal, the set up is called forward bias.
(iv) What is meant
by reverse biasing of a pn junction?
When the positive
of the battery is connected to the N side and negative of the battery is
connected to the P side, then the diode is called to be reverse biased.
(v) What is forward
resistance of a diode?
A diode offers an
extremely small resistance (not equal to zero) when forward biased and it is
called a forward resistance of a diode.
(vi) Distinguish
between static and dynamic forward resistances of a diode.
When the diode is
forward biased, it creates a small resistance in the circuit. The static
resistance is defined as the ratio of DC voltage generated in the diode to the
DC current runs through it. Dynamic resistance otherwise called as AC
resistance is the reciprocal of the slope of the tangent of the characteristics
curve.
ie., Dynamic
resistance = change in voltage/resulting change in current = ΔV/ΔI
(vii) What is meant
by a semiconductor?
Semiconductors arc
substances having resistivity or conductivity lying between conductors and
insulators.
(viii) Give some
properties of a semiconductor?
i. It has covalent
bonding
ii. It is
crystalline in nature
iii. It has a
negative temperature coefficient of resistance.
iv. Its conductivity
increases with addition of impurities.
(ix) What is meant
by doping?
Doping is the
process of addition of a desirable impurity to a pure semiconductor in order to
increase its conductivity.
(x) What is meant
by forbidden gap?
The band separating
the valence hand and the conduction band is called forbidden gap.
(xi) What is meant
by a junction diode?
When a p-type
semiconductor is fixed with n-type semiconductor, it forms a junction diode.
(xii) What is
depletion region in p-n junction?
Depletion layer is
a thin layer formed amid p and n regions of junction diode devoid of free
electrons and the holes.
(xiii) Is Ohm's law
obeyed in a semiconductor or not?
In a semiconductor,
Ohm's law is valid only for low electric fields.
(xiv) What is a
rectifier?
Rectifier is a
device which converts AC into DC.
(xv) Aim of the PN
Junction Diode Experiment
To draw the static
current-voltage (I — V) characteristic of a junction diode in forward bias and
hence to calculate its ac and dc forward resistances.
(xvi) Apparatus of
the PN Junction Diode Experiment
The given junction
diode (ex: IN 4007), a 2-volt battery, voltmeter (a low range voltmeter reading
upto 1 V with 0.1 V per divisions), milliammeter, key, etc.
(xvii) Procedure of
the PN Junction Diode Experiment
Connections are
made as shown in the figure. A 2 volt battery is connected to a rheostat Rh.
The rheostat is used as a potential divider arrangement. The voltmeter V is
connected across the diode. The milliammeter m A is used to measure the diode
current. The potential difference across the diode is increased from
zero in steps of 0.1 V till the current increases steeply and becomes 25 to 30
mA. In each step the ammeter reading is noted. A mph is plotted with ammeter
readings in mA along the Y-axis and the voltmeter readings in volts along
X-axis. This gives the forward characteristic of the diode.
(a) To find static (dc)
forward resistance (Rf):
Static forward
resistance is the ratio of the direct voltage (V) applied at any point P on the
straight portion of the characteristic to the direct current (I) corresponding
to the point P. The voltage (V) and current (I) corresponding to the point P on
the straight portion (i.e., beyond the knee voltage) are noted. The static
forward resistance,
Rf =
V/I.
(b) To find dynamic
(ac) forward resistance (rf):
It is defined as
the ratio of a small change in the forward bias voltage to the corresponding
change in the forward current
rf =
(dV/dI)P
The reciprocal of the slope of the graph is determined at the point P. This gives the dynamic resistance of the diode in forward bias at the point P
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