Zener diode and stabilizer
Zener diodes and stabilizers are semiconductor diodes designed for stabilization, i.e., maintaining a constant voltage in the power circuits of electronic equipment. The designs of zener diodes for widespread use are similar to planar rectifier diodes.
A stabistor is a semiconductor that stabilizes voltage through the direct branch of the current-voltage characteristic due to operation in the electrical breakdown mode.
The zener diode does not operate on the direct line, like rectifier or high-frequency diodes, but on that section of the reverse branch of the current-voltage characteristic, where a slight reverse voltage causes a significant increase in the reverse current through the device. The main parameters of high-power zener diodes and stabilizers are presented in the table below.
Table of parameters of zener diodes and high power stabilizers.
Its current-voltage characteristic will help you understand the essence of the action of a zener diode. Here, the reverse voltage is plotted on a certain scale along the horizontal axis, and the reverse current / reverse is plotted along the vertical axis down. The voltage is applied to the zener diode in reverse polarity, that is, it is turned on so that its anode is connected to the minus and the cathode to the plus of the power source. With this connection, reverse current flows through the zener diode /rev. As the reverse voltage increases, the reverse current increases very little - the characteristic runs almost parallel to the Urev axis. But at a certain voltage Urev pn the zener diode junction breaks through and a significant reverse current begins to flow through it. Now the current-voltage characteristic turns sharply and goes down almost parallel to the Irev axis. This section is the working section for the zener diode.
Breakdown of the pn junction does not lead to damage to the device if the current through it does not exceed a certain permissible value. A diagram of a possible practical application of a zener diode, with the help of which a stable (unchanging) voltage should be supplied to the load. With this connection, a reverse current Irev flows through the stabilizer D, created by the power source Upit, the voltage of which is not constant. Under the influence of this voltage, the current Irev flowing through the zener diode also changes, but the voltage on it, and therefore on the load Rн connected to it, remains practically unchanged. Resistor R limits the maximum permissible current flowing through the zener diode.
Zener diode and stabilizer.
The stabistor, like the rectifier diode, operates on the direct branch of the current-voltage characteristic. The stabistor opens at a low forward voltage Unp and an increasing forward current Ipr begins to flow through it. The direct branch of the current-voltage characteristic of the stabistor runs almost parallel to the Ipr axis; with a significant change in the forward current through the stabilist, the voltage drop across it changes very little. This is a property of a stabistor and is used to stabilize the voltage.
It will be interesting➡ What is a dinistor?
Look at the fig. 88.6, which shows a diagram of a possible practical application of a stabistor. In principle, such a device works in the same way as with a zener diode, only direct voltage is supplied to the stabilistor D. Here are the most important parameters (characteristics) of zener diodes and stabilizers: stabilization voltage Ust, stabilization current Ist, minimum stabilization current Istmin and maximum stabilization current Istmax. The parameter is the voltage drop that is created between the terminals of the stabilizer or stabilist in operating mode. Our industry produces silicon zener diodes for stabilization voltage Ust from several volts to 180 V, and stabistors for U within a few volts.
Job parameters.
The minimum stabilization current Istmin is: for a zener diode - the smallest current through the device at which stable operation in the “breakdown” mode begins (in Fig. 87, a - line Istmin); for a stabistor - the smallest forward current at which the slope of the current-voltage characteristic sharply decreases (in Fig. 88, a - at the level of the Ist.min line). As this current decreases, the devices no longer stabilize the voltage. The maximum permissible stabilization current Ist max is the highest current through the device (do not confuse it with the current flowing in the circuit powered by a voltage stabilizer), at which the temperature of its pn junction does not exceed the permissible value (in Fig. 87, a and 88, a - Istmax lines). Exceeding the current Ist.max leads to thermal breakdown of the pn junction and, naturally, to failure of the device.
The main parameters of some zener diodes and stabilizers, most often used in amateur radio designs, are given in the appendix. 3. In the power supply, for example, which I will talk about in the eighth conversation, a D813 zener diode will be used. The stabilization voltage of this zener diode (at Ist = 5 mA) can be from 11.5 to 14 V, Ist.min ~ 3 mA, Ist.max - 20 mA, maximum power dissipation Pmax (product of voltage Ust and current Ist.max) 280 mW
Schottky diode
The Schottky diode does not use a pn junction, but a metal-semiconductor rectifying contact. The symbolic graphic designation of a Schottky diode is shown in Fig. 1.44, b.
Let us turn to the corresponding band diagram (Fig. 1.47), which is useful to compare with the band diagram for a non-rectifying contact.
For an n-type metal-semiconductor rectifying contact, it is characteristic that the contact potential difference φmp = φm - φp is positive: φmp > 0.
Abrahamyan Evgeniy Pavlovich
Associate Professor, Department of Electrical Engineering, St. Petersburg State Polytechnic University
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The energy levels corresponding to the conduction band are more filled in a semiconductor than in a metal. Therefore, after connecting the metal and the semiconductor, some electrons will move from the semiconductor to the metal. This will lead to a decrease in the electron concentration in the n-type semiconductor. A region of the semiconductor will appear that is depleted of free carriers of electricity and has an increased resistivity. Space charges will appear in the transition region and a potential barrier will form, preventing the further transition of electrons from the semiconductor to the metal.
If you connect an external voltage source with a plus to the metal and a minus to an n-type semiconductor, then the potential barrier will decrease and direct current will begin to flow through the junction. With the opposite connection, the potential barrier increases and the current turns out to be very small.
When a Schottky diode operates, there is no injection of minority carriers and the corresponding accumulation and resorption phenomena, therefore Schottky diodes are very fast devices; they can operate at frequencies up to tens of gigahertz (1 GHz = 1 × 109 Hz). A Schottky diode can have a low reverse current and a low forward voltage (at low forward currents) - about 0.5 V, which is less than that of silicon devices. The maximum permissible forward current can be tens and hundreds of amperes, and the maximum permissible voltage can be hundreds of volts.
As an example, let us depict the direct branches of the current-voltage characteristics (Fig. 1.48) of a KD923A silicon diode with a Schottky barrier (Schottky diode), intended for operation in pulsed devices.
For it ipr.max = 100 mA, urev.max = 14V (at t < 35°C), charge carrier lifetime - no more than 0.1 ns, constant reverse current at urev = 10 V and t = 25°C - no more than 5 µA.
Electronic air ticket
An electronic air ticket or e-ticket is an electronic form of air ticket offered instead of a regular form.
Itinerary Receipt
Your flight reservation is made in the standard way, but the travel information reflected on the ticket is not printed on a form, but is securely stored electronically in a special airline database.
An itinerary receipt is issued as confirmation of the purchase of an electronic ticket. After purchasing an electronic ticket, an itinerary receipt will be sent to the specified email address. Using the itinerary receipt, you can compare the purchase data with what was needed.
The itinerary receipt contains complete information about the route, form and details of payment for transportation, similar to a paper ticket. It is recommended that you print it out and have it with you throughout your trip. The most important information indicated on the itinerary receipt is the reservation number.
Source of information: S7 Airlines.
E-ticket. Questions and answers. Purchasing an electronic ticket
Currently, most leading airlines in all countries practice selling electronic tickets via the Internet.
Procedure for purchasing an electronic ticket:
1. Go to the website of the airline you are interested in.
2. Select the Booking or Web booking function, fill in the required fields (departure date, return ticket date, departure city and airport, arrival city and airport, number of passengers, class of service).
3. The result of the search will be a list of possible flights and their costs. Important!
Read carefully what is included in the ticket price, pay attention to whether it includes airport taxes. Please pay attention to the general conditions of transportation for this tariff (if you do not immediately see the link to this document, then in any case, at the payment stage, the system will automatically show the terms of transportation and ask you to confirm your agreement to all conditions).
4. After selecting a flight to purchase a ticket, you must register on the airline’s website (or log in under an already registered name). When registering, you must provide accurate information.
5. It is also necessary to provide reliable information about the passengers for whom the electronic ticket is purchased.
6. The registration form usually contains a “payment method” field. You can pay for your air ticket in the following ways:
1) using electronic payment systems (for example, WebMoney);
2) through a credit or debit card (most often, Visa payment systems are accepted - categories higher than Electron - , Mastercard, American Express);
3) as well as using a special virtual card (for example, “MasterCard Virtual for paying for services on the Internet”).
7. If everything is done correctly, then after the payment procedure you will receive an itinerary receipt to the specified e-mail. It is recommended to check the correctness of the specified data: full name, passport number, flight number, fare. Save and, if possible, print the itinerary receipt. Tips
1. To quickly find the best deals from airlines around the world and the cheapest tickets, use specialized sites, for example https://www.skyscanner.net.
2. The rule often works: the longer before the departure date you buy an electronic ticket, the less you pay for it.
It is more profitable to plan your flight and buy a ticket in advance, for example 1-2 months before the departure date. Procedure for checking in for a flight
In practice, when checking in for a flight, it is not necessary to have a printout of the receipt with you; it is enough to write out or remember the reservation number.
A passenger with an electronic ticket registers for a flight as follows.
You go to the registration window, show: a valid passport (with a visa if necessary) and a printout of the receipt (or simply give the reservation number). The operator finds you in the database using your reservation number and full name and issues you a boarding pass. And then everything happens as usual - checking in your luggage, checking your hand luggage and, if everything is in order, boarding the plane.
Source of information: personal experience of the author.
Advantages of an electronic ticket
Source of information: Aeroflot.
Web booking. Links on the topic
“Travel and Save” - an article in the electronic magazine “World Travel” is devoted to economical ways to travel, the article talks about electronic tickets and the first discount companies.
“There will be no more paper tickets” - article in the “Financial News” section. The article provides interesting statistics on the share of electronic tickets among all tickets sold by airlines, and also talks about the opinions of the management of leading Russian airlines regarding the introduction of electronic tickets.
Marking of zener diodes
Domestic and imported zener diodes in a metal case are marked simply and clearly. They are marked with the name of the device and the location of the anode and cathode in the form of a schematic designation.
Devices in a plastic case are marked with rings and dots of various colors on the cathode and anode sides. You can determine the type of device by the color and combination of symbols, but to do this you will have to look in reference books or use calculator programs. Both can be found on the Internet.
Sometimes stabilization voltage is applied to low-power zener diodes.
Main characteristics
When designing power supplies, you should be able to correctly calculate and select the required element based on the values. An incorrectly selected zener diode will immediately fail or will not maintain the voltage at the required level.
The main characteristics are:
- voltage Uct. stabilization;
- rated stabilization current Ist. flowing through the zener diode;
- permissible power dissipation;
- temperature stabilization coefficient;
- dynamic resistance.
These characteristics are determined by the manufacturer and are indicated in the reference literature.
