Deep anatomy of semiconductor diode and its application

Electronic circuit different from previously learned the main characteristics of the circuit is the circuit into a variety of electronic devices. Many types of led high bay light, is currently the most widely used semiconductor devices - diodes, voltage regulator, transistors, insulated gate field effect tube. Since the task is not to study these courses the physical processes inside the device, but rather discuss their application, therefore, in a brief introduction of these devices on the basis of external characteristics, discuss their application circuit.
4.1 PN junction diode and semiconductor
4.1.1 PN junction unidirectional conductivity
We already know in physics in purified tetravalent semiconductor crystal material (mainly silicon and germanium) the incorporation of trivalent trace (such as boron) or pentavalent (e.g., phosphorus) element, the conductivity of semiconductors will be greatly enhanced . This is due to the formation of a conduction current capability carriers. Pentavalent element incorporated in a semiconductor majority carriers is a free electron, referred to as electronic semiconductor or a N-type semiconductor. The trivalent elements incorporated in a semiconductor majority carriers is a hole, called a hole semiconductor or a P-type semiconductor. In doped semiconductors majority carriers (known as multi-sub) doping concentration determined by the number, while the minority carriers (known as birth rate) number and temperature, and the temperature rises, the number of minority carriers will increase.
On a semiconductor substrate by an appropriate semiconductor process technology can form a P-type semiconductor and N type semiconductor junction surface, called the PN junction. PN junction with unidirectional conductivity: When the PN junction forward voltage, P-potential higher than the N-terminal end, PN junction narrow, formed by a number of the current sub-region by the N-region flow P, shown in Figure 4-1 (a), and when the PN junction reverse voltage, N terminal side potential higher than P, PN junction becomes wider, formed by the minority carrier current is very small, as cut-off (non-conductive), see Figure 4-1 ( b).



4.1.2 semiconductor diode
Semiconductor PN junction diode is coupled by an electrode lead and the corresponding package from the shell. Led by the P region called the anode electrode, N area leads to the electrode called a cathode. Because unidirectional conductive PN junction diode conduction when the current direction through the interior of the tube from the anode to the cathode. Many different types of diodes, according to material points, the most commonly used silicon tube and a germanium tube two kinds; according to the structure of points, little contact type, surface contact type and silicon planar several; by use of points, there are ordinary diodes, rectifier diodes, zener diodes, and other.
Figure 4-2 is a common diode symbol, structure and shape of the Fig. Diode symbol in Fig 4-2 (a) in Fig. Arrows indicate the direction of forward current. Usually in the diode tube shell surface is marked with the symbol or color point color circle to indicate the polarity of the diode, solid arrow symbol on the left is commonly used in engineering notation, the right symbol for the new requirements of the symbols. From the process structure, point contact diode (usually germanium tube) Fig 4-2 (b) which is characterized by the junction area is small, so the junction capacitance is small, the current is allowed to pass through a small, led high bay light for detection or small current of the rectifier, is used as a digital circuit in the switching element; surface contact type diode (usually silicon tube) Fig 4-2 (c) which is characterized by a large junction area, junction capacitance is large, than allowed by the current , suitable for low-frequency rectifier; silicon planar diode Figure 4-2 (d), the junction area can be used for large power rectifier, junction area is small, suitable for pulse digital circuits for switching tube.
4.1.3 diode volt-ampere characteristics
Diode current and voltage curve I = f (V), is called the diode voltage characteristics. Its volt-ampere characteristic curve shown in Figure 4-3. Diode is the core of a PN junction, with unidirectional conductivity, the actual voltage characteristics and theoretical volt-ampere characteristics slightly different. Figure 4-3 shows the diode volt-ampere characteristic curve is nonlinear, can be divided into three parts: the forward characteristics, the reverse characteristics and reverse breakdown characteristics
1 Forward Characteristics
When the applied forward voltage is low, the majority of the tubes of the diffusion of carriers do not form, the forward current is almost zero. When the forward voltage exceeds a certain value, the only significant forward current, the voltage value is called dead zone voltage, usually dead zone silicon tube voltage of about 0.5V, germanium tube deadband voltage of about 0.2V, when Forward voltage is greater than the dead-band, the forward current rapid growth of the curve close to straight up, this part of the volt-ampere characteristic, when the current increases rapidly, the diode's forward voltage drop is small, the forward voltage drop of the silicon tube about 0.6 ~ 0.7V, germanium's forward voltage drop of about 0.2 ~ 0.3V. Diode voltage characteristics are sensitive to temperature, the temperature rises, the forward curve to the left, shown in Figure 4-3, which shows the same size corresponding forward current, forward voltage drop with the temperature rise decreases. Studies have shown that the temperature is increased 10C, the forward voltage drop decreases 2mV.



2 Reverse Characteristics
Diode with reverse voltage, the formation of a small reverse current, and at a certain temperature, the number of its essentially unchanged, so that when reverse voltage is increased within a certain range, the reverse current is substantially constant size , regardless of the size with reverse voltage, it is called the reverse saturation current, generally low-power germanium tube reverse current up to tens of μA, while the low-power silicon tube reverse current is much smaller, usually in 0.1μA The following, when the temperature rises, the increase in the number of minority carriers, so that the reverse current increases, the characteristic curve down, studies have shown that the temperature is increased 100C, reverse current approximate doubling.
3 reverse breakdown characteristics
When the diode reverse voltage is greater than a certain value applied (reverse breakdown voltage), the reverse current suddenly increased dramatically called diode reverse breakdown. Reverse breakdown voltage is typically in the tens of volts or more
4.1.4 The main parameters of the diode
Except that the diode characteristic curve represents volt-ampere characteristic, the parameter also reflect the electrical properties of the diode, the device parameters are correct basis for selection and use of the device. Various device parameters given by the manufacturers product manuals, due to manufacturing process reasons, even if the same type of pipe, there are some parameters of dispersion, so manuals often give a range of parameters, the main parameters of a semiconductor diode There are several
1 Maximum rectified current IDM
IDM refers to the diode when the long-term work, allow the maximum average forward current. In use, if the current exceeds this value, the PN junction will overheat and burn the pipe
2 working peak reverse voltage VRM
VRM is not pipe the maximum allowable reverse breakdown voltage. Usually this parameter is the diode reverse breakdown voltage to half, if the reverse voltage exceeds this value, the tube will be a risk of breakdown.



3 Peak Reverse Current IRM
IRM is the diode reverse voltage VRM the reverse current value, IRM smaller diode unidirectional conductivity better. IRM greatly affected by temperature, used to be noted. Silicon tube reverse current is small, generally less in a few microamps, germanium tube reverse current is large, silicon tube tens to hundreds of times.
4. Maximum operating frequency ƒM
The applied high frequency AC voltage diode, since the PN junction capacitance effect, the role of uni-directional conducting degradation. ƒM unidirectional conducting means is a diode begins to significantly effect the frequency of the AC signal degradation.
4.1.5 Equivalent circuit of the diode and Application

The volt-ampere characteristic of the diode is non-linear, in order to facilitate the analysis and calculation, in certain conditions, we can be linearized, as ideal components.
1 ideal diode equivalent circuit
In the circuit, if the diode forward voltage drop, and it is much smaller than the voltage of the series element, the diode is turned off in parallel with the reverse current is much smaller than the current element can be omitted when the forward voltage drop and reverse tube current of the diode is idealized as a switch, when the applied forward voltage, the diode conduction, the forward voltage drop is 0, the equivalent of the switch is closed, when the applied reverse voltage, the diode is off, the reverse current is 0, the equivalent switch off, ideal diode equivalent circuit shown in Figure 4-4. Represents the actual use of the ideal diode diode circuit analysis and calculation can be drawn satisfactory results, but has a slight error.
2 diode application circuit examples
Diode wide range of applications are mainly one-way use of its electrical conductivity. Here are a few application circuit.
(1) The limiter circuit: limiter function is to limit the output voltage amplitude.
Example 4-1 Figure 4-5 (a) is the use as a forward diode limiter circuit. Known vi = Vmsinωt, and Vm> VS, test analysis works, and make the output voltage vo waveform.
Solution: a) diode conduction condition is vi> VS, because D is ideal diode, D Once turned on, the pressure drop is zero, then vo = VS
b) where vi ≤ VS, the diode off, disconnect the branch, R is no current, the voltage drop is 0. So vo = vi
c) Based on the above analysis, the waveform may be made vo Figure 4-5 (b) shows, seen from the figure, the amplitude of the output voltage is limited to positive values ​​in the VS.
Note: The plotted, vo and vi waveform on the timeline to correspond, so as to properly reflect the change process vo.
(2) diode gate circuit
Gate circuit is a logic circuit, the input signal (condition) and the output signal (result) exists between a causal relationship between the logic. The logic circuit, usually symbols 0 and 1 represent two opposite logic state. Expressed with a high level, with 0 denoting a low called positive logic, and vice versa for negative logic.
There are three basic logical relationships: with logic, or logic, not logic. And this corresponds to the AND gate circuits have, or gate, NAND gate. Gates of these three basic compound can form a variety of other gates.
Example 4-2 Figure 4-6 shows the most simple and logical AND gate circuit diagram symbols. It is composed of diodes D1, D2 and resistor R and the power supply VCC components. Figure A, B are the two inputs, F is output. Let VCC = 5V, A, B input high (logic 1) is 3V, low (logic 0) to 0V, and ignore the diodes D1, D2 of the forward voltage drop. Try to analyze the circuit between input and output.
Solution: (1) When the input terminal A, B are low 0, i.e. VA = VB = 0V, the diode D1, D2 are forward biased and conduction, so that the output voltage VF = 0V F , the output terminal F 0 is low.
(2) When the input terminal A is low 0, B 1 is high, that is, VA = 0V, VB = 3V, D1 is the cathode potential of the cathode potential is lower than D2, D1 is turned on, the VF = 0V, therefore D2 Deadline for the reverse bias, the output F low 0.
(3) When the input terminal A is high 1, B 0 is low, i.e. VA = 3V, VB = 0V when, D1, D2 and the work (2) Conversely, the output remains low F 0.
(4) When the input A, B are high 1:00, that when VA = VB = 3V, D1, D2 are forward biased by conduction, so that the output voltage of F VF = 3V, the output F is a high end one.
From the above analysis, only when all inputs are high for 1, the output is high one, otherwise output are low 0. This "decision a result of the event only if all the conditions are met, the results just happen" logical relationship is called with (And) logic AND gate circuit meets with logic. Also called logical multiplication and logical, and computing. Generally with the symbol "*" indicates that, let A, B, F, respectively, is a logic variable, and the operation of the expression can be written as follows:
F = A · B or F = AB
F is equal to the formula reads as A and B. Logic means: only the input variables A, B is 1, the output variable F will be 1; if A, B has a to 0, F it is 0. In other words, that is, "There is 0 0, all one one." This conclusion is also suitable for the participation of multiple variables and computing.
Table 4-1 lists the circuit shown in Figure 4-6 Input and output logic level relationship. However, analysis of the logic circuit, usually used to describe a logic 0 input and output relationship between the truth tables as listed (i.e. logic state table). The AND gate truth table shown in Table 4-2.
In addition, Figure 4-7 shows the OR gate circuit and logic diagram symbols. It is also composed of a diode and resistor. Figure A, B are two inputs, F is the output terminal. Let A, B input high (logic 1) is 3V, low (logic 0) to 0V, and ignore the diodes D1, D2 of the forward voltage drop. By analyzing the (detailed process readers can analyze) shows that as long as A, B, there is a is high (logic 1) output is high (logic 1). Only when A, B at the same time is low (logic 0), the output is low (logic 0). This "in determining the outcome of an event in all conditions, as long as there is one or more satisfied results occurs," the logic name or (Or) logic. OR gate circuit meets or logic.



Also called logical sum or logical or arithmetic. Generally by the symbol "+" to that set A, B, F, respectively logic variable, or the operation of the expression can be written in the form:
F = A + B
F is equal to the formula reads as A or B. Logic or meaning is: only the input variables A, B has one or more of 1, the output variable F is 1; otherwise, only A, B are all 0, F only 0. In other words, that is, "There is a 1, the entire 0 0." This conclusion is also suitable for the participation of more than one variable or expression
Table 4-3 lists the circuit shown in Figure 4-7 Input and output logic level relationship. Table 4-4 of the OR gate truth table.
4.2 Special Diodes
In addition to the ordinary diode, there are some special diodes, such as zener diodes, photodiodes, light emitting diodes, etc., are described below.
4.2.1 regulator
The regulator is a special surface contact type semiconductor silicon diode, with a stable voltage. Figure 4-8 (a) as a regulator in the circuit connecting the right way; Figure (b) and Figure (c) is the regulator of the volt-ampere characteristics and graphic symbols. Zener diodes with common main difference is that the regulator is operated at a reverse breakdown PN junction state. Through the manufacturing process and the use of technical measures to limit the reverse current size, can guarantee the reverse breakdown state regulator will not damage due to overheating. From the regulator of the reverse characteristic curve can be seen, when the reverse voltage is small, the reverse current is almost zero, when the reverse voltage is increased to the breakdown voltage Vz (also zener voltage), the reverse current Iz (regulator operating current) increases dramatically, the regulator reverse breakdown. In characteristic curve ab segment, when Iz in a wide range of changes, the voltage across the regulator Vz essentially the same, with a constant voltage characteristics, use of this feature can play a role in stabilizing the voltage.



Zener diodes are not in general the same, it's reverse breakdown is reversible, do not exceed the permissible value regulator, PN junction will not overheat and damage, after the removal of the applied reverse voltage, the regulator to restore the original performance, so the regulator has a good breakdown characteristics repeated.
Regulator of the main parameters are:
1 stable voltage VZ. VZ regulated voltage regulator means normal operation, the voltage across the tube, due to the manufacturing process reasons, there is a certain voltage value dispersion, such as 2CW14 regulator is 6.0 ~ 7.5V.
(2) dynamic resistance rz. Dynamic resistance is the regulator within the normal operating range, the terminal voltage corresponding to the current amount of change of the ratio of the amount of change.



The reverse features the regulator steeper, rZ smaller, the better the performance regulator
3. Stable current IZ. Regulator of normal working hours of the reference current value, only I ≥ IZ, in order to ensure a better regulator regulator performance.
4 Maximum stable current IZmax. Allows the maximum reverse current, I> IZmax tube will be damaged by overheating.
5 The maximum allowable power dissipation PZM. Tubes thus preventing thermal breakdown of the maximum power dissipation PZM = VZ IZmax
6 Voltage Temperature Coefficient αV. 10C when the temperature changes, the regulated voltage is defined as the percentage change in the voltage temperature coefficient. Voltage temperature coefficient is smaller, the better temperature stability, typically silicon tube voltage VZ is lower than 4V has a negative temperature coefficient higher than 6V, have a positive temperature coefficient, VZ between the 4 ~ 6V, the temperature coefficient is small.
Regulator working conditions are two, one is working in reverse breakdown state, the second is the current regulator to stabilize between the current and the maximum allowable current. When the regulator is biased, it is equivalent to an ordinary diode. Figure 4-8 (a) the most common of the regulator circuit, when Vi changes, or RL, the regulator of the current changes, but in a certain range of changes in the terminal voltage is small, so the output voltage stabilizes effect. (The circuit analysis, see 4.4)
4.2.2 photodiode
Photodiode known photodiode. It's equipped with a glass tube shell window, in order to accept the light. Characterized in that, when light is irradiated on its PN junction, can be paired to generate free electrons and holes, the semiconductor in the concentration of minority carriers increased. These carriers at a certain reverse bias voltage can be generated under the action of drift current, reverse current increases. So it's the reverse current with light intensity increases linearly, then the photodiode is equivalent to a constant current source. When there is no light, the photodiode voltage characteristics as ordinary diode. The equivalent circuit is shown in the photodiode 4-9 (a), shown in Figure 4-9 (b) the sign of the photodiode.



Dark Current: without illumination of the reverse saturation current. General <1μA.
Photocurrent: refers to the nominal illumination reverse current, typically tens of milliamps.
Sensitivity: means at a given wavelength (eg 0.9μm) units of optical power, the photocurrent generated in the photodiode. General ≥ 0.5μA/μW.
Peak wavelength: the photodiode with the highest response sensitivity (light current maximum) of the optical wavelength. The peak wavelength of the photodiode generally in the visible and infrared range.
Response time: refers to the quantitative increase illumination, the light stability of the current value reaches 63% of the time, usually 10-7S.
Photodiode as light control element can be used to detect a variety of objects, photoelectric control, automatic alarm and so on. When made of a large area photodiode, can be used as a source of energy and called optical cell. At this point it does not require external power, the light energy directly into electricity.
4.2.3 Light Emitting Diode

Light emitting diode is a direct conversion of electrical energy into light energy of a semiconductor display device of the solid, referred to LED (Light Emitting Diode). And similar general diode, light emitting diodes but also by a structure of a PN. PN junction light emitting diode encapsulated in a transparent plastic case, form a square, rectangular and circular, etc.. Light-emitting diodes low drive voltage, current is small, has a strong anti-vibration and shock resistance, small size, high reliability, low power consumption and long life, etc., are widely used in signal indication circuits. Commonly used in the electronic digital control technology, is to use light-emitting diodes are arranged according to a certain composition



The principle of the light emitting diode and a photodiode opposite. When this forward bias current through the tube emits light, which is due to electron-hole recombination, when a direct result of energy released. Its relatively narrow spectral range, the wavelength used by the basic material may be. Type semiconductor material of the light-emitting diodes emit light of different colors, such as gallium arsenide phosphide (GaAsP) red or yellow material, gallium phosphide (GaP) red or green material, gallium nitride (GaN) materials blue light, silicon carbide (SiC) materials emit yellow, gallium arsenide (GaAs) material of not visible in the infrared.
Light-emitting diode symbol shown in Figure 4-10. Its similar volt-ampere characteristic and the general diode, the dead voltage is 0.9 ~ 1.1V, the forward voltage of 1.5 ~ 2.5V, operating current of 5 ~ 15mA. Reverse breakdown voltage is low, generally less than 10V.
4.3 diode rectifier and filter circuit
Circuit, typically requires a stable voltage DC power supply. The composition of low-power power supply Figure 4-11 can be said that it is by the power transformer, rectifier, filter and regulator circuit composed of four parts.



The power adapter is the AC mains voltage into the required voltage, and then the AC voltage by the rectifier circuit into a pulsating DC voltage. Because of this pulsating DC voltage also contain large ripple, must be filtered through a filter circuit to obtain a smoothed DC voltage. But also with the grid such that the voltage swings (generally about ± 10% fluctuations), load and temperature changes. Thus the rectifier filter circuit, the regulator circuit is also to pick up. The role of the regulator circuit when the voltage fluctuations, load, and temperature changes, the output DC voltage to maintain stability.
4.3.2 filter circuit
Although the AC rectifier circuit into led high bay light,  but the output is pulsating voltage. Pulsating voltage change of this size, in addition to containing the DC component, but also contains different frequency AC component, which can not meet the majority of electronic equipment for the power requirements. To improve the rectified voltage pulsation, improve the smoothness, the rectifying circuit in the filter will be added. Here are some commonly used filter circuit.
1 capacitor filter circuit
Capacitor filter circuit is the simple filter which is the output of the rectifier circuit in parallel with the load which consists of a capacitor C. Figure 4-15 (a) shows.



Filter capacitor is charged by the capacitor discharge to filter out the AC component. Figure 4-15 (b) a waveform diagram showing the waveform of the broken line half-wave rectified waveform. Into the capacitor C after v2> 0, D is turned on, the power supply at the same time to the RL, also the C rechargeable energy storage, since the charging time constant is small (winding resistance and diode forward resistance is very small) , charge quickly, with the output voltage vo v2 rise, when vC = after, v2 v2 vC began to decline when C has been charged vo = v2 rose again. Until v2



To achieve the formula (4-10) between the value, the output voltage obtained relatively straight, the general requirements



Where T is the period of the AC voltage supply.
In addition, since the diode conduction time is short (conduction angle is less than 1800), the average current of the capacitor is zero, showing the average diode current and the load current is equal to the average, so the diode current peak inevitably large, resulting in current impact, easy to damage the pipe.
Rectifier with capacitive filter diode in the circuit, the maximum reverse voltage of the half-wave and full-wave rectifier circuit is not equal. In the half-wave rectifier circuit, taking into account the most severe cases are output open circuit, capacitors filled with V2m, and v2 in the amplitude of the negative half-cycle, the time suffered 2V2 diode reverse voltage. It is compared with no filter capacitor, increasing doubled.
For single-phase bridge rectifier circuits, with or without a filter capacitor, diode maximum reverse voltage is V2.
About the filter capacitor values ​​should be selected depending on the size of the load current. Usually in the tens to thousands of microfarads microfarad capacitor voltage value should be greater than the maximum output voltage. Usually polar capacitors.

More info you can visit: www.lead-lighting.com