Test And Application of Diodes

Diode as the most basic transistor, ubiquitous in electronic circuit applications, the blogger in the circuit small class column inside the circuit summary, whether it is a level switching circuit, power automatic switching circuit, anti-reverse circuit, there are diodes shadow. Although the diode is very basic, compared with other transistors, it is simple, but his variety, different types of application scenarios are not the same, so in our usual circuit design how to choose the right diode, and understand the application of different kinds of diodes is very important. So since to say, then the blogger must be the same old, do not settle! Put it all in place, from principle to application. The core of this article is to understand the classification and application of diodes, explain the different applications of different diodes, some basic descriptions will use references, but the blogger will still make a summary of each part. <3 Diode voltammetry diagram <3 is the core of understanding diode application. First, diode basic knowledge. First, let's understand the diode, of course, this part is the basic introduction, and knowing and not knowing does not affect the application of the diode. The basic knowledge explanation is mostly a summary by quote, and the blogger will use summary language at the end of each subchapter. 1.1 What is a diode the basic noun explanation or have to use the official words: understand that the conductive ability of the substance between the conductor and the insulator is called a semiconductor. Common semiconductors are silicon (Si) and germanium (Ge). Diodes are made of semiconductor materials, including silicon diodes and germanium diodes. A <3 diode is an electronic component made of a semiconductor material that has unidirectional conductivity. 1.2 Composition of diode Diode is composed of a PN junction plus the corresponding electrode lead and tube shell package. The explanation of PN junction is as follows: Then the explanation of P-type semiconductors and N-type semiconductors, in a comprehensive understanding of MOS tubes, one article is enough, one article has been briefly introduced, here is the picture of the article: The <3 diode is composed of a PN junction formed by a P-type semiconductor and an N-type semiconductor, plus the corresponding electrode lead and the shell package. To clarify the working principle of the diode, we need to start with its fundamental PN junction, analyze the principle of PN junction formation, and analyze the formation of P-type semiconductors, N-type semiconductors, and so on. If you want to be really clear, at least need to be well illustrated, if you can have a video explanation is better, the blogger here refers to a large number of articles and videos on the Internet, recommend several bloggers that explain the more detailed articles and videos (the focus of this article is still on classification and application, this principle has a lot of good articles and videos) : diode working principle of the article: Diode working principle diode working principle video: explain the working principle of the diode working principle: <3 The principle of diode working principle is simply summarized as: PN junction plus forward voltage, low resistance, with a large forward diffusion current; PN junction has high resistance and small reverse drift current when reverse voltage is applied. PN junction has unidirectional conductivity. We use the volt-ampere characteristic diagram of the diode to analyze and explain some characteristics of the diode: forward characteristics (plus forward voltage, the positive half of the X coordinate in the figure above) When the forward voltage exceeds a certain value, the diode has obvious forward current, the voltage value is called the on-voltage. At room temperature, the Vth of the silicon tube is about 0.5V, and the Vth of the germanium tube is about 0.1V. The region greater than the on-voltage is called the on-zone. When the current I flowing through the diode is relatively large, the voltage at both ends of the diode is almost constant, and the silicon tube is about 0.6 ~ 0.8V (usually 0.7V), and the germanium tube is about 0.2 ~ 0.3V (usually 0.2V). In the range where the reverse voltage is less than the reverse breakdown voltage, the reverse current formed by a few carriers is small and basically independent of the magnitude of the reverse voltage. This section is the cut-off area. The forward and reverse characteristics of the diode can be intuitively seen: ① the diode is a nonlinear device; The diode has unidirectional conductivity. When the reverse voltage is increased to a certain value VBR, the reverse current increases sharply, which is called the reverse breakdown of the diode. Remember one sentence: <3 An increase in temperature will cause the forward characteristics to shift to the left (the on-voltage decreases, the forward voltage drop decreases) and the reverse characteristics to shift down (the reverse current increases). 2.3 About breakdown diode breakdown is divided into electrical breakdown and thermal breakdown, where the electrical breakdown process is reversible, and thermal breakdown needs to be avoided at any time. 1, electrical breakdown avalanche breakdown: PN junction doping concentration is low, the added reverse voltage is high, the breakdown voltage is inversely proportional to the concentration (generally need a relatively high voltage >6V). Zener breakdown: PN junction doping concentration is high, the reverse voltage added is low, the barrier layer is very thin, such as the voltage regulator (Zener diode) <3 to take the appropriate doping process, the avalanche breakdown voltage of silicon PN junction can be controlled at 8 ~ 1000V. The Zener breakdown voltage is less than 5V. 2, thermal breakdown in the process of using the diode, such as due to the reverse current and reverse voltage is too large, making the PN junction power consumption becomes larger, exceeding the allowable power consumption of the PN junction, the temperature rises until the phenomenon of overheating the PN junction breakdown is called thermal breakdown. The diode will be permanently damaged after thermal breakdown. Third, the parameter description of the diode, the introduction of the parameters of the diode most of the articles on the Internet are paste copy, direct handling, and the blogger referred to the commonly used diode product manual, some are not on the = =! So here I use their own diode manual to explain, of course, only the general application needs to pay attention to the parameters. The parameters of the diode are described in the manual of each diode, here I use the commonly used 1N4148WS for a description: forward continuous current and average rectified current? In normal use, I generally only look at the average rectifier current parameter, I will not let their load design more than the average rectifier current of the diode. But now when it comes to the parameters, I do have a little question here, translated, what is this forward continuous current? Later, I carefully thought about it, and this forward continuous current is actually the maximum rectification current IF of the parameters said in other articles (please point out any errors). It's twice the average rectifier current. But in practice, if the design does not consider redundancy, the circuit is also prone to problems. My suggestion here is to take the average rectified current as a reference when designing. To solve this question, let's briefly explain the main parameters of the diode: 1. The parameter Io(PEAK Average Rectified Output Current) is not specifically explained in other articles, but I think in my practical application, more reference is made to this parameter for design. The current part is designed with direct reference to the average rectifier current design, so the maximum rectifier current described below will certainly not be reached. The diode in the image above is 150mA. 2, IF(maximum rectified Current Forward Continuous Current) is the forward continuous current in the surface diode parameter picture. The maximum forward current value that the diode is allowed to pass through during long-term continuous operation. I suggest using Io as a reference, so here is the reason to pay attention to the current is that the greater the current, the hotter the tube. Attention! Some diodes do not have this parameter IF, only Io, at this time Io can be considered to be the maximum rectification current. The diode in the image above is 300mA. Reverse repeat peak voltage and reverse repeat peak voltage? In the figure above, there is a Non-Repetitive Peak Reverse Voltage, my remarks are the highest reverse operating voltage, There's also a Peak Repetitive Peak Reverse Voltage, but what about those two voltages? For a brief note, Peak Repetitive Peak Reverse Voltage includes all repetitive transient voltages, excluding non-repetitive transient voltages. It's usually related to circuits, for example, AC signals are sinusoids, and each cycle will have a peak point, and that peak point can be said to be repeated peak voltage. Non-Repetitive Peak Reverse Voltage, usually caused by an external factor, any transient directional voltage occurring at either end of a semiconductor rectifier diode that does not repeat a maximum instantaneous value. It can be considered as the highest reverse operating voltage of the diode. First of all, from the application point of view, they are equal in the figure above, even if we do not know the details, we can normally use this diode. Even if they are not equal, we can choose the smallest one in the design. 3, VRM (maximum Repetitive peak reverse voltage) the maximum reverse voltage allowed to be applied at both ends of the diode. If the value is greater than this, the reverse current (IR) increases sharply, and the unidirectional conductivity of the diode is destroyed, resulting in reverse breakdown. Half of the reverse breakdown voltage (VBR) is usually taken as the VRM. The diode in the image above is 100V. 4. Reverse current (IR) Reverse current refers to the reverse current flowing through the diode under the specified temperature and reverse voltage. The reverse current under different reverse voltages must be different. The smaller the reverse current, the better the one-way guiding electrical performance of the tube. The reverse current is closely related to temperature, and about every 10 ° C increase in temperature, the reverse current doubles. Silicon diode has better stability at high temperature than germanium diode. The diode in the figure above has a reverse current of 1uA when the reverse voltage is 75V, and a reverse current of 25nA when the reverse voltage is 20V. 5, CT(junction capacitance) above the title is Capacitance between terminals, the size of the junction capacitance directly indicates the frequency characteristics of the Diode. Due to the presence of junction capacitance, when the frequency is high to a certain extent, the capacitance reactance is small enough to short-circuit the PN junction. Resulting in the diode to lose one-way conductivity, can not work, the larger the PN junction area, the larger the junction capacitance, the more can not work at high frequency. The current diode manual will tell you what the junction capacitance of the diode is under what circumstances, and will not directly give the operating frequency of this parameter. The diode in the figure above has a junction capacitance of 2pF under the condition of VR=0V and f=1MHz. 6, IFSM(Forward Surge Current) Surge current, is allowed to flow through the instantaneous current, more than this value will damage the diode. The diode in the figure above allows the maximum surge current of 2A current to not exceed 1us or 1A current to not exceed 1s. 7. When trr(Reverse recovery time) changes from the forward voltage to the reverse voltage, the current generally cannot be cut off instantaneously, and a little time is delayed. This time is the reverse recovery time. This parameter determines the switching speed of the diode. The diode in the figure above has a reverse recovery time of 4ns under the condition of IF=IR=10mA Irr=0.1XIR,RL=100Ω. <3 diode parameters are more than those listed above, but they are actually generally used, and knowing these parameters can already be safely designed for circuit design