Zener diode 30 volt marking. How does a zener diode work? Volt-ampere characteristic of a zener diode

The simplest block 0-30 Volt power supply for amateur radio.

Scheme.

In this article we continue the topic of circuit design of power supplies for amateur radio laboratories. This time we will talk about the simple device, assembled from domestically produced radio components, and with a minimum number of them.

So, circuit diagram power supply:

As you can see, everything is simple and accessible, element base is widespread and does not contain deficiencies.

Let's start with the transformer. Its power should be at least 150 Watts, the voltage of the secondary winding should be 21...22 Volts, then after the diode bridge on capacitance C1 you will get about 30 Volts. Calculate so that the secondary winding can provide a current of 5 Amps.

After the step-down transformer there is a diode bridge assembled on four 10-amp D231 diodes. The current reserve is of course good, but the design is quite cumbersome. The best option will be using imported diode assembly type RS602, with small dimensions it is designed for a current of 6 Amperes.

Electrolytic capacitors are designed for an operating voltage of 50 Volts. C1 and C3 can be set from 2000 to 6800 uF.

Zener diode D1 - it sets the upper limit for adjusting the output voltage. In the diagram we see the inscription D814D x 2, this means that D1 consists of two series-connected zener diodes D814D. The stabilization voltage of one such zener diode is 13 Volts, which means two connected in series will give us an upper limit for voltage regulation of 26 volts minus the voltage drop at the junction of transistor T1. As a result, you get smooth adjustment from zero to 25 volts.
The KT819 is used as a regulating transistor in the circuit; they are available in plastic and metal cases. The location of the pins, housing dimensions and parameters of this transistor can be seen in the next two images.

DIY 0-30 Volt power supply

There are so many interesting radio devices collected by radio amateurs, but the basis, without which almost no circuit will work - power unit. .Often one simply doesn’t get around to assembling a decent power supply. Of course, the industry produces enough high-quality and powerful stabilizers voltage and current, but they are not sold everywhere and not everyone has the opportunity to buy them. It's easier to solder it yourself.

Power supply diagram:

The proposed circuit of a simple (only 3 transistors) power supply compares favorably with similar ones in the accuracy of maintaining the output voltage - it uses compensation stabilization, startup reliability, a wide adjustment range and cheap, non-scarce parts.

After proper assembly, it works immediately, we just select the zener diode according to the required value of the maximum output voltage of the power supply unit.

We make the body from what is at hand. The classic option is a metal box from an ATX computer power supply. I'm sure everyone has a lot of them, because sometimes they burn out, and buying a new one is easier than repairing them.

A 100-watt transformer fits perfectly into the case, and there is room for a board with parts.

You can leave the cooler - it won't be superfluous. And so as not to make noise, we simply power it through a current-limiting resistor, which you will select experimentally.

For the front panel, I didn’t skimp and bought a plastic box - it’s very convenient to make holes and rectangular windows in it for indicators and controls.

We take a pointer ammeter - so that current surges are clearly visible, and put a digital voltmeter - it’s more convenient and beautiful!

After assembling the regulated power supply, we check its operation - it should give almost complete zero at the lower (minimum) position of the regulator and up to 30V at the upper one. Having connected a load of half an ampere, we look at the output voltage drop. It should also be minimal.

In general, for all its apparent simplicity, this power supply is probably one of the best in its parameters. If necessary, you can add a protection unit to it - a couple of extra transistors.

Stable salary, stable life, stable state. The last one is not about Russia, of course :-). If you look in an explanatory dictionary, you can clearly understand what “stability” is. On the first lines, Yandex immediately gave me the designation of this word: stable - this means constant, stable, not changing.

But most often this term is used in electronics and electrical engineering. In electronics, constant values ​​of a parameter are very important. This can be current, voltage, signal frequency, etc. Deviation of the signal from any given parameter can lead to incorrect operation of the electronic equipment and even to its breakdown. Therefore, in electronics it is very important that everything works stably and does not fail.

In electronics and electrical engineering stabilize the voltage. The operation of electronic equipment depends on the voltage value. If it changes to a lesser extent, or even worse, to an increase, then the equipment in the first case may not work correctly, and in the second case it may even burst into flames.

In order to prevent voltage spikes and drops, various Surge Protectors. As you understand from the phrase, they are used to stabilize“playing” voltage.

Zener diode or Zener diode

The simplest voltage stabilizer in electronics is a radio element zener diode. Sometimes it is also called Zener diode. In the diagrams, zener diodes are designated something like this:

The terminal with a “cap” is called the same as that of a diode - cathode, and the other conclusion is anode.

Zener diodes look the same as diodes. In the photo below, on the left is a popular type of modern zener diode, and on the right is one of the samples Soviet Union

If you take a closer look at the Soviet zener diode, you can see this schematic designation on it itself, indicating where its cathode is and where its anode is.

Stabilization voltage

The most important parameter of a zener diode is, of course, stabilization voltage. What is this parameter?

Let's take a glass and fill it with water...

No matter how much water we pour into a glass, its excess will pour out of the glass. I think this is understandable to a preschooler.

Now by analogy with electronics. The glass is a zener diode. The water level in a glass full to the brim is stabilization voltage Zener diode. Imagine a large jug of water next to a glass. We will just fill our glass with water from the jug, but we don’t dare touch the jug. There is only one option - pour water from a jug by punching a hole in the jug itself. If the jug were smaller in height than the glass, then we would not be able to pour water into the glass. To explain it in electronics terms, the jug has a “voltage” greater than the “voltage” of the glass.

So, dear readers, the whole principle of operation of a zener diode is contained in the glass. No matter what stream we pour on it (well, of course, within reason, otherwise the glass will carry away and break), the glass will always be full. But it is necessary to pour from above. This means, The voltage we apply to the zener diode must be higher than the stabilization voltage of the zener diode.

Marking of zener diodes

In order to find out the stabilization voltage of the Soviet zener diode, we need a reference book. For example, in the photo below there is a Soviet zener diode D814V:

We look for parameters for it in online directories on the Internet. As you can see, its stabilization voltage at room temperature approximately 10 volts.

Foreign zener diodes are marked more easily. If you look closely, you can see a simple inscription:

5V1 - this means the stabilization voltage of this zener diode is 5.1 Volts. Much easier, right?

The cathode of foreign zener diodes is marked mainly with a black stripe

How to check zener diode

How to check the zener diode? Yes, just like! You can see how to check the diode in this article. Let's check our zener diode. We set it to continuity and attach the red probe to the anode, and the black probe to the cathode. The multimeter should show a forward voltage drop.

We swap the probes and see one. This means that our zener diode is in full combat readiness.

Well, it's time for experiments. In the circuits, a zener diode is connected in series with a resistor:

Where Uin – input voltage, Uout.st. – output stabilized voltage

If we look closely at the diagram, we get nothing more than a voltage divider. Everything here is elementary and simple:

Uin=Uout.stab +Uresistor

Or in words: the input voltage is equal to the sum of the voltages on the zener diode and the resistor.

This scheme is called parametric stabilizer on one zener diode. The calculation of this stabilizer is beyond the scope of this article, but if anyone is interested, google it ;-)

So, let's put together the circuit. We took a resistor with a nominal value of 1.5 Kilohms and a zener diode with a stabilization voltage of 5.1 Volts. On the left we connect the Power Supply, and on the right we measure the resulting voltage with a multimeter:

Now we carefully monitor the readings of the multimeter and power supply:

So, while everything is clear, let’s add more tension... Oops! Our input voltage is 5.5 Volts, and our output voltage is 5.13 Volts! Since the stabilization voltage of the zener diode is 5.1 Volts, as we can see, it stabilizes perfectly.

Let's add some more volts. The input voltage is 9 Volts, and the zener diode is 5.17 Volts! Amazing!

We also add... The input voltage is 20 Volts, and the output, as if nothing had happened, is 5.2 Volts! 0.1 Volt is a very small error, it can even be neglected in some cases.

Volt-ampere characteristic of a zener diode

I think it wouldn’t hurt to consider the current-voltage characteristic (VAC) of the zener diode. It looks something like this:

Where

Ipr– forward current, A

Upr – forward voltage, IN

These two parameters are not used in the zener diode

Uarr– reverse voltage, V

Ust – Rated voltage stabilization, V

Ist– rated stabilization current, A

Nominal means a normal parameter at which long-term operation of the radio element is possible.

Imax– maximum zener diode current, A

Immin– minimum zener diode current, A

Ist, Imax, Imin – This is the current that flows through the zener diode when it operates.

Since the zener diode operates in reverse polarity, unlike a diode (the zener diode is connected with the cathode to the plus, and the diode with the cathode to the minus), then the working area will be exactly the one marked with the red rectangle.

As we see, at some voltage Urev our graph begins to fall down. At this time, such an interesting thing as a breakdown occurs in the zener diode. In short, it can no longer increase the voltage on itself, and at this time the current in the zener diode begins to increase. The most important thing is not to overdo the current, more than Imax, otherwise the zener diode will be damaged. The best operating mode of the zener diode is considered to be the mode in which the current through the zener diode is somewhere in the middle between its maximum and minimum values. This is what will appear on the graph operating point operating mode of the zener diode (marked with a red circle).

Conclusion

Previously, in times of scarce parts and the beginning of the heyday of electronics, a zener diode was often used, oddly enough, to stabilize the output voltage. In old Soviet books on electronics you can see this section of the circuit of various power supplies:

On the left, in the red frame, I marked a section of the power supply circuit that is familiar to you. Here we get DC voltage from AC voltage. On the right, in the green frame, is the stabilization diagram ;-).

Currently, three-terminal (integrated) voltage stabilizers are replacing stabilizers based on zener diodes, since they stabilize the voltage many times better and have good power dissipation.

On Ali you can immediately take a whole set of zener diodes, ranging from 3.3 Volts to 30 Volts. Choose to your taste and color.

Adjustablestabilizedpower supply – 0-24V, 1 – 3A

with current limitation.

The power supply unit (PSU) is designed to obtain an adjustable, stabilized output voltage from 0 to 24v at a current of about 1-3A, in other words, so that you don’t buy batteries, but use it to experiment with your designs.

The power supply provides so-called protection, i.e. maximum current limitation.

What is it for? In order for this power supply to serve faithfully, without fear of short circuits and not require repairs, so to speak, “fireproof and indestructible”

A zener diode current stabilizer is assembled on T1, that is, it is possible to install almost any zener diode with a stabilization voltage less than the input voltage by 5 volts

This means that when installing a VD5 zener diode, let’s say BZX5.6 or KS156 at the output of the stabilizer we get adjustable voltage from 0 to approximately 4 volts, respectively - if the zener diode is 27 volts, then the maximum output voltage will be in the range of 24-25 volts.

The transformer should be selected something like this: AC voltage the secondary winding should be approximately 3-5 volts more than what you expect to receive at the output of the stabilizer, which in turn depends on the installed zener diode,

The current of the secondary winding of the transformer must at a minimum be no less than the current that needs to be obtained at the output of the stabilizer.

Selection of capacitors by capacity C1 and C2 - approximately 1000-2000 µF per 1A, C4 - 220 µF per 1A

It is somewhat more complicated with voltage capacitances - the operating voltage is roughly calculated using this method - the alternating voltage of the secondary winding of the transformer is divided by 3 and multiplied by 4

(~ Uin:3×4)

That is, let’s say that the output voltage of your transformer is about 30 volts - divide 30 by 3 and multiply by 4 - we get 40 - which means the operating voltage of the capacitors should be more than 40 volts.

The level of current limitation at the output of the stabilizer depends on R6 at a minimum and R8 (at a maximum until shutdown)

When installing a jumper instead of R8 between the base of VT5 and the emitter of VT4 with a resistance of R6 equal to 0.39 ohms, the limiting current will be approximately 3A,

How do we understand “limitation”? It’s very simple - the output current, even in short circuit mode, will not exceed 3 A, due to the fact that the output voltage will be automatically reduced to almost zero,

Is it possible to charge a car battery? Easily. It is enough to set the voltage regulator, I apologize - with potentiometer R3 the voltage is 14.5 volts at idle (that is, with the battery disconnected) and then connect the battery to the output of the unit, and your battery will be charged with a stable current to the level of 14.5 V, Current as it charges will decrease and when it reaches 14.5 volts (14.5 V is the voltage of a fully charged battery) it will be zero.

How to adjust the limiting current. Set the idle voltage at the output of the stabilizer to about 5-7 volts. Then connect a resistance of approximately 1 ohm with a power of 5-10 watts to the output of the stabilizer and an ammeter in series with it. Use trimmer resistor R8 to set the required current. Correctly set limiting current can be checked by turning the output voltage adjustment potentiometer all the way to the maximum. In this case, the current controlled by the ammeter should remain at the same level.

Now about the details. Rectifier bridge - it is advisable to select diodes with a current reserve of at least one and a half times. The indicated KD202 diodes can operate without radiators for quite a long time at a current of 1 ampere, but if you expect that this is not enough for you, then by installing radiators you can provide 3-5 amperes, that's just what you need Look in the directory which of them and with which letter can carry up to 3 and which up to 5 amperes. If you want more, look at the reference book and choose more powerful diodes, say 10 amperes.

Transistors - VT1 and VT4 should be installed on radiators. VT1 will heat up slightly, so a small radiator is needed, but VT4 will heat up quite well in current limiting mode. Therefore, you need to choose an impressive radiator, you can also adapt a fan from the computer power supply to it - believe me, it won’t hurt.

For those who are especially inquisitive, why does the transistor get hot? Current flows through it and the greater the current, the more the transistor heats up. Let's do the math - 30 volts at the input, across the capacitors. At the output of the stabilizer, let’s say 13 volts. As a result, 17 volts remain between the collector and emitter.

From 30 volts we minus 13 volts, we get 17 volts (who wants to see mathematics here, but one of the laws of grandfather Kirgoff, about the sum of voltage drops, somehow comes to mind)

Well, the same Kirgoff said something about the current in the circuit, like what kind of current flows in the load, the same current flows through the VT4 transistor. Let's say about 3 amperes flow, the resistor in the load heats up, the transistor also heats up, So this is the heat with which we heat the air and can be called power that is dissipated... But let's try to express it mathematically, that is

school physics course

Where R is the power in watts, U is the voltage across the transistor in volts, and J- the current that flows through our load and through the ammeter and, naturally, through the transistor.

So 17 volts multiplied by 3 amperes we get 51 watts dissipated by the transistor,

Well, let’s say we connect a resistance of 1 ohm. According to Ohm's law, at a current of 3A, the voltage drop across the resistor will be 3 volts and the dissipated power of 3 watts will begin to heat the resistance. Then the voltage drop across the transistor is: 30 volts minus 3 volts = 27 volts, and the power dissipated by the transistor is 27v×3A = 81 watts... Now let’s look in the reference book, in the transistors section. If we have a pass-through transistor, ie VT4, say KT819 in a plastic case, then according to the reference book it turns out that it will not withstand the dissipation power (Pk*max) it has 60 watts, but in a metal case (KT819GM, analogue 2N3055) - 100 watts - this one will do, but a radiator is required.

I hope it’s more or less clear about transistors, let’s move on to fuses. In general, a fuse is the last resort, reacting to gross mistakes made by you and preventing it “at the cost of your life.” Let’s assume that for some reason a short circuit occurs in the primary winding of the transformer, or in the secondary. Maybe it’s because it’s overheated, maybe the insulation is leaky, or maybe it’s just an incorrect connection of the windings, but there are no fuses. The transformer smokes, the insulation melts, the power cable, trying to perform the valiant function of a fuse, burns, and God forbid if you have plugs with nails instead of fuses on the distribution panel instead of a machine.

One fuse for a current of approximately 1A greater than the limiting current of the power supply (i.e. 4-5A) should be placed between the diode bridge and the transformer, and the second between the transformer and the 220 volt network for approximately 0.5-1 ampere.

Transformer. Perhaps the most expensive thing in the design Roughly speaking, the more massive the transformer, the more powerful it is. The thicker the secondary winding wire, the more current the transformer can deliver. It all comes down to one thing - the power of the transformer. So how to choose a transformer? Again a school physics course, electrical engineering section.... Again 30 volts, 3 amperes and ultimately a power of 90 watts. This is the minimum, which should be understood as follows - this transformer can briefly provide an output voltage of 30 volts at a current of 3 amperes. Therefore, it is advisable to add a current reserve of at least 10 percent, and better yet 30-50 percent. So 30 volts at a current of 4-5 amperes at the output of the transformer and your power supply will be able to supply a current of 3 amperes to the load for hours, if not days.

Well, for those who want to get the maximum current from this power supply, let’s say about 10 amperes.

First - a transformer that matches your needs

Second - 15 ampere diode bridge and for radiators

Third, replace the pass-through transistor with two or three connected in parallel with resistances in the emitters of 0.1 ohms (radiator and forced airflow)

Fourth, it is desirable, of course, to increase the capacity, but in the event that the power supply will be used as Charger– this is not critical.

Fifth, reinforce the conductive paths along the path of large currents by soldering additional conductors and, accordingly, do not forget about the “thicker” connecting wires

Connection diagram for parallel transistors instead of one

A zener diode is a semiconductor diode with unique properties. If an ordinary semiconductor, when turned back on, is an insulator, then it performs this function until a certain increase in the applied voltage, after which an avalanche-like reversible breakdown occurs. With a further increase in the reverse current flowing through the zener diode, the voltage continues to remain constant due to a proportional decrease in resistance. In this way it is possible to achieve a stabilization regime.

In the closed state, a small leakage current initially passes through the zener diode. The element behaves like a resistor, the value of which is high. During breakdown, the resistance of the zener diode becomes insignificant. If you continue to increase the voltage at the input, the element begins to heat up and when the current exceeds the permissible value, an irreversible thermal breakdown occurs. If the matter is not brought to this point, when the voltage changes from zero to the upper limit of the working area, the properties of the zener diode are preserved.

When a zener diode is directly switched on, the characteristics are no different from a diode. When the plus is connected to the p-region and the minus to the n-region, the junction resistance is low and current flows freely through it. It increases with increasing input voltage.

A zener diode is a special diode, mostly connected in the opposite direction. The element is initially in the closed state. When an electrical breakdown occurs, the voltage zener diode maintains it constant over a wide current range.

Minus is applied to the anode, and plus is applied to the cathode. Beyond stabilization (below point 2), overheating occurs and the likelihood of element failure increases.

Characteristics

The parameters of the zener diodes are as follows:

• U st - stabilization voltage at rated current I st;
• Ist min - minimum current of the beginning of electrical breakdown;
• Ist max - maximum permissible current;
• TKN - temperature coefficient.

Unlike a conventional diode, a zener diode is a semiconductor device in which the areas of electrical and thermal breakdown are located quite far from each other on the current-voltage characteristic.

Associated with the maximum permissible current is a parameter often indicated in tables - power dissipation:

P max = I st max ∙ U st.

The dependence of the zener diode operation on temperature can be either positive or negative. By connecting elements in series with coefficients of different signs, precision zener diodes are created that are independent of heating or cooling.

Connection schemes

A typical circuit of a simple stabilizer consists of a ballast resistance R b and a zener diode that shunts the load.

In some cases, stabilization is disrupted.

1. Supplying a high voltage to the stabilizer from the power source with a filter capacitor at the output. Current surges during charging can cause failure of the zener diode or destruction of resistor Rb.
2. Load shedding. When the maximum voltage is applied to the input, the zener diode current may exceed the permissible value, which will lead to its heating and destruction. Here it is important to comply with the passport safe work area.
3. The resistance R b is selected small so that at the minimum possible supply voltage and the maximum permissible current on the load, the zener diode is in work area regulation.

To protect the stabilizer, thyristor protection circuits or

Resistor R b is calculated by the formula:

R b = (U pit - U nom)(I st + I n).

Zener diode current Ist is selected between the permissible maximum and minimum values, depending on the input voltage U supply and load current I n.

Selection of zener diodes

The elements have a large spread in stabilization voltage. To obtain the exact value of U n, zener diodes are selected from the same batch. There are types with a narrower range of parameters. For high power dissipation, the elements are installed on radiators.

To calculate the parameters of a zener diode, initial data is required, for example, the following:

• U supply = 12-15 V - input voltage;
• U st = 9 V - stabilized voltage;

The parameters are typical for devices with low energy consumption.

For a minimum input voltage of 12 V, the load current is selected to the maximum - 100 mA. Using Ohm's law, you can find the total load of the circuit:

R∑ = 12 V / 0.1 A = 120 Ohm.

The voltage drop across the zener diode is 9 V. For a current of 0.1 A, the equivalent load will be:

R eq = 9 V / 0.1 A = 90 Ohm.

Now you can determine the ballast resistance:

R b = 120 Ohm - 90 Ohm = 30 Ohm.

It is selected from the standard series, where the value coincides with the calculated one.

The maximum current through the zener diode is determined taking into account the load disconnection, so that it does not fail if any wire is unsoldered. The voltage drop across the resistor will be:

U R = 15 - 9 = 6 V.

Then the current through the resistor is determined:

I R = 6/30 = 0.2 A.

Since the zener diode is connected in series, I c = I R = 0.2 A.

The dissipation power will be P = 0.2∙9 = 1.8 W.

Based on the obtained parameters, a suitable D815V zener diode is selected.

Symmetrical Zener diode

A symmetrical diode thyristor is a switching device that conducts alternating current. A feature of its operation is the voltage drop to several volts when turned on in the range of 30-50 V. It can be replaced by two back-to-back conventional zener diodes. The devices are used as switching elements.

Zener diode analogue

When it is not possible to select a suitable element, an analogue of a zener diode on transistors is used. Their advantage is the ability to regulate voltage. For this purpose, DC amplifiers with several stages can be used.

A voltage divider with R1 is installed at the input. If the input voltage increases, at the base of transistor VT1 it also increases. At the same time, the current through transistor VT2 increases, which compensates for the increase in voltage, thereby maintaining it stable at the output.

Marking of zener diodes

Glass zener diodes and zener diodes in plastic cases are produced. In the first case, 2 numbers are applied to them, between which the letter V is located. The inscription 9V1 means that U st = 9.1 V.

The inscriptions on the plastic case are deciphered using a datasheet, where you can also find out other parameters.

The dark ring on the body indicates the cathode to which the plus is connected.

Conclusion

A zener diode is a diode with special properties. The advantage of zener diodes is high level voltage stabilization over a wide range of operating current changes, as well as simple circuits connections. To stabilize the low voltage, the devices are turned on in the forward direction, and they begin to work like ordinary diodes.