PROJECT REPORT SHEET
PROJECT DESCRIPTION: Special applications diodes
NAME: LEE(Leekung Jung)
STUDENT ID: C61193
· Clipper faults
· Clamper faults
· Voltage multiplier faults
· Varactor diode
· Transient Suppressors and Constant-Current Diodes
· Tunnel Diodes
· Schottky Diodes
· Pin Diodes
· Step-Recovery Diodes
1. Clipper faults
Clipper combines three parts which are a shunt resistor, a diode and a load resistor.
a. When shunt resistor is open anode of D1 dose not have voltages.
b. If D1 is broken and open, RL will be same as input signal waveform.
c. We do not know about faults in this circuit if the RS is short.
d. If D1 is short then the output is not appear in the RL.
2. Clamper faults
-Basic clamper
a. If C1 is broken then C1 is open in the circuit so the output signal is nothing.
b. The clamper dose not operates when D1 is open circuit.
c. If C1 is short then most current will go to diode D1 so D1 will be break down.
d. When C1 has problem then it is not enough charge so the output will be change.
f. If D1 is short then the current will be increase and output dose not appear.
-Biased clamper
a. Basically, most faults are same as basic clamper except potentiometer problems.
b. If potentiometer is short, biased function does not work so it dose not change.
c. The potentiometer is open, it will affect to diode D1, D1 is not working.
-Zener clamper
a. If D1 shorts, the clamper works as unbiased clamper.
b. The zener voltage is disappearing when the zener diode is short.
3.Voltage multiplier faults
a. Firstly, when the output dose not appear, we have to check the primary terminal
of transformer.
b. If the primary terminal is good, we take next step which is to check the secondary
terminal of transformer.
c. Secondly, we can check diode D1 and D2.
d. If the output voltage is still less than two times, we have to check capacitors.
4. Varactor diodes
In electronics, a varicap diode, varactor diode, variable capacitance diode, variable reactance diode or tuning diode is a type of diode which has a variable capacitance that is a function of the voltage impressed on its terminals.
Varicap schematic symbol
Typical circuit using a varactor diode for tuning
Varactors are operated reverse-biased so no current flows, but since the thickness of the depletion zone varies with the applied bias voltage, the capacitance of the diode can be made to vary. Generally, the depletion region thickness is proportional to the square root of the applied voltage; and capacitance is inversely proportional to the depletion region thickness. Thus, the capacitance is inversely proportional to the square root of applied voltage.
All diodes exhibit this phenomenon to some degree, but specially made varactor diodes exploit the effect to boost the capacitance and variability range achieved - most diode fabrication attempts to achieve the opposite.
In the figure we can see an example of a crossection of a varactor with the depletion layer formed of a p-n-junction. But the depletion layer can also be made of a MOS-diode or a Schottky diode. This is very important in CMOS and MMIC technology.
5. Transient suppressors and constant-current diodes
transient voltage suppression (TVS) diode is an electronic component used to protect sensitive electronics from voltage spikes induced on connected wires. It is also commonly referred to as a transorb, after the brand name TransZorb registered by General Semiconductor (now part of Vishay). STMicroelectronics sells them under the name Transil. The name Tranzil can also be seen.
The device operates by shunting excess current when the induced voltage exceeds the avalanche breakdown potential. It is a clamping device, suppressing all overvoltages above its breakdown voltage. Like all clamping devices, it automatically resets when the overvoltage goes away, but absorbs much more of the transient energy internally than a similarly rated crowbar device.
A transient voltage suppression diode may be either unidirectional or bidirectional. A unidirectional device operates as a rectifier in the forward direction like any other avalanche diode, but is made and tested to handle very large peak currents. The popular 1.5KE series allows 1500 W of peak power, for a short time.
A bidirectional transient voltage suppression diode can be represented by two mutually opposing avalanche diodes in series with one another and connected in parallel with the circuit to be protected. While this representation is schematically accurate, physically the devices are now manufactured as a single component.
A transient voltage suppression diode can respond to over-voltages faster than other common over-voltage protection components such as varistors or gas discharge tubes. The actual clamping occurs in roughly one picosecond, but in a practical circuit the inductance of the wires leading to the device imposes a higher limit. This makes transient voltage suppression diodes useful for protection against very fast and often damaging voltage transients. These fast over-voltage transients are present on all distribution networks and can be caused by either internal or external events, such as lightning or motor arcing.
Schematic symbols used to denote a bidirectional transient voltage suppression diode.
STMicroelectronics Transil devices. These devices are 1.5KE series, able to handle 1.5kW of peak power for a short period.
Constant current diode (also called CLD, current limiting diode, constant-current diode, diode-connected transistor or current-regulating diode) consists of a JFET with the gate shorted to the source, and it functions like a two-terminal current limiter or current source (analog to voltage limiting Zener diode). They allow a current through them to rise to a certain value, and then level off at a specific value. Unlike zener diodes, these diodes instead of keeping the voltage constant, keeps the current constant. These devices keeps the current flowing through them unchanged when the voltage changes.
6. Tunnel diodes
A tunnel diode or Esaki diode is a type of semiconductor diode which is capable of very fast operation, well into the microwave frequency region, by using quantum mechanical effects.
It was invented in August 1957 by Leo Esaki when he was with Tokyo Tsushin Kogyo (now known as Sony), who in 1973 received the Nobel Prize in Physics for discovering the electron tunneling effect used in these diodes.
These diodes have a heavily doped p–n junction only some 10nm (100 Å) wide. The heavy doping results in a broken bandgap, where conduction band electron states on the n-side are more or less aligned with valence band hole states on the p-side.
Tunnel diodes were manufactured by Sony for the first time in 1957[1] followed by General Electric and other companies from about 1960, and are still made in low volume today.[2] Tunnel diodes are usually made from germanium, but can also be made in gallium arsenide and silicon materials. They can be used as oscillators, amplifiers, frequency converters and detectors.[3]
Tunnel diode schematic symbol
1N3716 tunnel diode (with jumper for scale)
A tunnel diode or Esaki diode is a type of semiconductor diode which is capable of very fast operation, well into the microwave
Under normal forward bias operation, as voltage begins to increase, electrons at first tunnel through the very narrow p–n junction barrier because filled electron states in the conduction band on the n-side become aligned with empty valence band hole states on the p-side of the pn junction. As voltage increases further these states become more misaligned and the current drops– this is called negative resistance because current decreases with increasing voltage. As voltage increases yet further, the diode begins to operate as a normal diode, where electrons travel by conduction across the p–n junction, and no longer by tunneling through the p–n junction barrier. Thus the most important operating region for a tunnel diode is the negative resistance region.
Reverse bias operation
When used in the reverse direction they are called back diodes and can act as fast rectifiers with zero offset voltage and extreme linearity for power signals (they have an accurate square law characteristic in the reverse direction).
Under reverse bias filled states on the p-side become increasingly aligned with empty states on the n-side and electrons now tunnel through the pn junction barrier in reverse direction– this is the Zener effect that also occurs in zener diodes.
Technical comparisons
A rough approximation of the VI curve for a tunnel diode, showing the negative differential resistance region
In a conventional semiconductor diode, conduction takes place while the p–n junction is forward biased and blocks current flow when the junction is reverse biased. This occurs up to a point known as the “reverse breakdown voltage” when conduction begins (often accompanied by destruction of the device). In the tunnel diode, the dopant concentration in the p and n layers are increased to the point where the reverse breakdown voltage becomes zero and the diode conducts in the reverse direction. However, when forward-biased, an odd effect occurs called “quantum mechanical tunnelling” which gives rise to a region where an increase in forward voltage is accompanied by a decrease in forward current. This negative resistance region can be exploited in a solid state version of the dynatron oscillator which normally uses a tetrode thermionic valve (or tube).
The tunnel diode showed great promise as an oscillator and high-frequency threshold (trigger) device since it would operate at frequencies far greater than the tetrode would, well into the microwave bands. Applications for tunnel diodes included local oscillators for UHF television tuners, trigger circuits in oscilloscopes, high speed counter circuits, and very fast-rise time pulse generator circuits. The tunnel diode can also be used as low-noise microwave amplifier. However, since its discovery, more conventional semiconductor devices have surpassed its performance using conventional oscillator techniques. For many purposes, a three-terminal device, such as a field-effect transistor, is more flexible than a device with only two terminals. Practical tunnel diodes operate at a few millamperes and a few tenths of a volt, making them low-power devices. The Gunn diode has similar high frequency capability and can handle more power.
Tunnel diodes are also relatively resistant to nuclear radiation, as compared to other diodes. This makes them well suited to higher radiation environments, such as those found in space applications.
Longevity
Esaki diodes are notable for their longevity; devices made in the 1960s still function. Writing in Nature, Esaki and coauthors state that semiconductor devices in general are extremely stable, and suggest that their shelf life should be "infinite" if kept at room temperature. They go on to report that a small-scale test of 50-year-old devices revealed a "gratifying confirmation of the diode's longevity".
7. Schottky diodes
The Schottky diode (named after German physicist Walter H. Schottky; also known as hot carrier diode) is a semiconductor diode with a low forward voltage drop and a very fast switching action. The cat's-whisker detectors used in the early days of wireless can be considered as primitive Schottky diodes.
A Schottky diode is a special type of diode with a very low forward-voltage drop. When current flows through a diode there is a small voltage drop across the diode terminals. A normal diode has between 0.7-1.7 volt drops, while a Schottky diode voltage drop is between approximately 0.15-0.45 volts. This lower voltage drop can provide higher switching speed and better system efficiency.
Schottky diode schematic symbol
Various Schottky barrier diodes: Small signal rf devices (left), medium and high power Schottky rectifying diodes (middle and right).
Construction
A Schottky diode uses a metal-semiconductor junction as a Schottky barrier (instead of a semiconductor-semiconductor junction as in conventional diodes). This Schottky barrier results in both very fast switching times and low forward voltage drop.
Reverse recovery time
The most important difference between p-n and Schottky diode is reverse recovery time, when the diode switches from non-conducting to conducting state and vice versa. Where in a p-n diode the reverse recovery time can be in the order of hundreds of nanoseconds and less than 100ns for fast diodes, Schottky diodes do not have a recovery time, as there is nothing to recover from. The switching time is ~100 ps for the small signal diodes, and up to tens of nanoseconds for special high-capacity power diodes. With p-n junction switching, there is also a reverse recovery current, which in high-power semiconductors brings increased EMI noise. With Schottky diodes switching essentially instantly with only slight capacitive loading, this is much less of a concern.
It is often said that the Schottky diode is a "majority carrier" semiconductor device. This means that if the semiconductor body is doped n-type, only the n-type carriers (mobile electrons) play a significant role in normal operation of the device. The majority carriers are quickly injected into the conduction band of the metal contact on the other side of the diode to become free moving electrons. Therefore no slow, random recombination of n- and p- type carriers is involved, so that this diode can cease conduction faster than an ordinary p-n rectifier diode. This property in turn allows a smaller device area, which also makes for a faster transition. This is another reason why Schottky diodes are useful in switch-mode power converters; the high speed of the diode means that the circuit can operate at frequencies in the range 200 kHz to 2 MHz, allowing the use of small inductors and capacitors with greater efficiency than would be possible with other diode types. Small-area Schottky diodes are the heart of RF detectors and mixers, which often operate up to 50 GHz.