Zener diode for 30 volts domestic. How does a zener diode work

A zener diode is a semiconductor diode with unique properties. If a conventional semiconductor is an insulator when turned back on, then it performs this function until a certain increase in the magnitude of 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, stabilization can be achieved.

In the closed state, a small leakage current first passes through the zener diode. The element behaves like a resistor, the resistance value of which is large. During breakdown, the resistance of the zener diode becomes negligible. If we 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 it, 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 turned on, the characteristics are no different from a diode. When the plus is connected to the p-region, and the minus is connected to the n-region, the transition resistance is small and the current flows freely through it. It increases with increasing input voltage.

A zener diode is a special diode, connected mostly in the opposite direction. The element is first in the closed state. In the event of an electrical breakdown, the voltage zener diode maintains it constant over a large current range.

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

Characteristics

The parameters of the zener diodes are as follows:

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

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

The maximum allowable current is associated with a parameter often indicated in tables - dissipation power:

P max \u003d I st max ∙ U st.

The temperature dependence of the zener diode operation can be either positive or negative. When connecting elements in series with coefficients of different signs, precision zener diodes are created that do not depend on heating or cooling.

Switching 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, there is a violation of stabilization.

1. Supplying a high voltage to the stabilizer from a power source in the presence of a filtering capacitor at the output. Current surges when charging it can cause failure of the zener diode or destruction of the resistor R b.
2. Load shedding. When the maximum voltage is applied to the input, the current of the zener diode may exceed the allowable one, which will lead to its heating and destruction. Here it is important to observe the passport area of ​​safe work.
3. The resistance R b is selected small so that at the minimum possible supply voltage and the maximum allowable current at the load, the zener diode is in the working regulation zone.

To protect the stabilizer, thyristor protection circuits or

Resistor R b is calculated by the formula:

R b \u003d (U pet - U nom) (I st + I n).

The zener diode current I st is selected between the allowable maximum and minimum values, depending on the input voltage U pit and the load current I n.

Choice of zener diodes

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

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

• U pit \u003d 12-15 V - input voltage;
• U st \u003d 9 V - stabilized voltage;

The parameters are typical for devices with low power consumption.

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

R ∑ \u003d 12 V / 0.1 A \u003d 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 equiv \u003d 9 V / 0.1 A \u003d 90 Ohm.

Now you can determine the resistance of the ballast:

R b \u003d 120 Ohm - 90 Ohm \u003d 30 Ohm.

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

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

U R \u003d 15 - 9 \u003d 6 V.

Then the current through the resistor is determined:

I R \u003d 6/30 \u003d 0.2 A.

Since the zener diode is connected to it in series, I c \u003d I R \u003d 0.2 A.

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

According to the parameters obtained, a suitable Zener diode D815V is selected.

Symmetrical zener diode

A symmetrical diode thyristor is a switching device that conducts alternating current. A feature of its work is a voltage drop of up to several volts when turned on in the range of 30-50 V. It can be replaced by two counter-connected conventional zener diodes. 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 possibility of voltage regulation. For this, DC amplifiers with several stages can be used.

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

Zener diode marking

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 \u003d 9.1 V.

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

The dark ring on the case 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 a high level of voltage stabilization with a wide range of operating current changes, as well as simple connection schemes. To stabilize a small voltage, the devices are switched on in the forward direction, and they begin to work like ordinary diodes.

The simplest power supply 0-30 volts for a radio amateur.

Scheme.

In this article, we continue the topic of power supply circuitry for amateur radio laboratories. This time we will talk about the simplest device, assembled from domestic radio components, and with a minimum number of them.

And so, the schematic diagram of the power supply:

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

Let's start with the transformer. Its power must be at least 150 watts, the voltage of the secondary winding is 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 amperes.

After the step-down transformer, there is a diode bridge assembled on four 10-amp D231 diodes. The current margin is certainly good, but the design is quite cumbersome. The best option would be to use an imported diode assembly of the RS602 type, 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 microfarads.

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

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

But most often this term is used in electronics and electrical engineering. In electronics, the constant values ​​of a parameter are very important. It can be current, voltage, signal frequency and. Deviation of the signal from any given parameter can lead to incorrect operation of 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 voltage. The operation of electronic equipment depends on the voltage value. If it changes to a smaller, or even worse, to a larger side, then the equipment in the first case may not work correctly, and in the second case it may even sway with a bright flame.

In order to prevent ups and downs in voltage, various Surge Protectors. As you understand from the phrase, they are used to stabilize"playing" tension.

Zener Diode or Zener Diode

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

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

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

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

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 for preschoolers.

Now by analogy with electronics. The glass is a zener diode. The level of water in a glass full to the brim - this is stabilization voltage zener diode. Imagine a large pitcher of water next to the glass. With water from the jug, we will just fill our glass with water, but we do not dare to touch the jug. There is only one option - to pour water from a jug, punching a hole in the jug itself. If the pitcher were smaller than the glass, then we would not be able to pour water into the glass. If explained in the language of electronics - the jug has a "voltage" more than the "voltage" of the glass.

So, dear readers, the glass contains the whole principle of the zener diode. Whatever stream we pour on it (well, of course, within reason, otherwise the glass will blow 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.

Zener diode marking

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

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

Foreign zener diodes are marked easier. 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 a zener diode

How to check the zener diode? Yes, as well as! And how to check the diode, you can see in this article. Let's check our zener diode. We put on the dial and cling with a red probe to the anode, and black to the cathode. The multimeter should show the forward voltage drop.

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

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

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

If you look closely at the circuit, we got nothing more than 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 on the resistor.

This scheme is called parametric stabilizer on one stabilizer. The calculation of this stabilizer is beyond the scope of this article, but for those who are interested, in Google ;-)

So, we collect the schematic. We took a resistor with a nominal value of 1.5 Kiloom and a zener diode for a stabilization voltage of 5.1 Volts. On the left we hook Power supply, and on the right we measure the resulting voltage with a multimeter:

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

So, while everything is clear, we are still adding tension ... Oops! We have an input voltage of 5.5 Volts, and an output voltage of 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 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 is 5.2 Volts as if nothing had happened! 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 would not hurt to consider the volt-ampere characteristic (CVC) of the zener diode. It looks something like this:

Where

Ipr- direct current, A

Upr- forward voltage, V

These two parameters are not used in the zener diode.

Uobr– reverse voltage, V

Ust– rated stabilization voltage, V

Ist- rated stabilization current, A

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

Imax- maximum current of the zener diode, A

imin- the minimum current of the zener diode, A

Ist, Imax, Imin – is the amount of current that flows through the zener diode when it is operating.

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

As we can see, at some voltage Uobr, our graph starts to fall down. At this time, such an interesting thing as a breakdown occurs in the zener diode. In short, he can no longer increase the voltage on himself, and at this time the current strength in the zener diode begins to increase. The most important thing is not to overdo the current strength, more than Imax, otherwise the zener diode will come to a kerdyk. The best operating mode of the zener diode is considered to be the mode in which the current strength through the zener diode is somewhere in the middle between its maximum and minimum values. On the chart, this will be 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, the zener diode was often used, oddly enough, to stabilize the output voltage. In old Soviet books on electronics, you can see such a section of the circuit of various power sources:

On the left, in the red frame, I marked a familiar section of the power supply circuit. Here we get a constant voltage from an alternating one. On the right, in a green frame, is a stabilization scheme ;-).

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

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

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

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 the order of 1-3A, in other words, so that you do not buy batteries, but use it for experiments with your designs.

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

What is it for? In order for this PSU to serve faithfully, not being afraid of short circuits and not requiring repair, 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 VZX5.6 or KS156 at the output of the stabilizer, we get an adjustable voltage from 0 to approximately 4 volts, respectively - if the zener diode is 27 volts, then the maximum output voltage will be within 24-25 volts.

The transformer should be chosen something like this - the alternating voltage of the secondary winding should be about 3-5 volts more than what you expect to get 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 least not be less than the current that needs to be obtained at the output of the stabilizer.

The choice of capacitors by capacitance C1 and C2 - approximately 1000-2000 microfarads per 1A, C4 - 220 microfarads per 1A

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

(~ Uin:3×4)

T e - let's say that the output voltage of your transformer is about 30 volts - 30 divided by 3 and multiplied by 4 - we get 40 - then the operating voltage of the capacitors must be more than 40 volts.

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

When a jumper is installed instead of R8 between the VT5 base and the VT4 emitter, with a resistance R6 equal to 0.39 ohm, the limiting current will be approximately at the level of 3A,

What is meant by "restriction"? Very simple - the output current, even in the short circuit mode at the output, will not exceed 3 A, due to the fact that the output voltage will be automatically reduced to almost zero,

Can a car battery be charged? Easy. It is enough to set the voltage regulator, I'm sorry - with the R3 potentiometer, 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 charge with a stable current up to the level of 14.5V, Current as it charges will decrease and when it reaches the value of 14.5 volts (14.5 V - the voltage of a fully charged battery) it will be equal to zero.

How to adjust current limit. 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. Trimmer resistor R8 set the required current. Correctly set limiting current can be controlled by unscrewing the output voltage adjustment potentiometer to the maximum until it stops. 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 choose diodes with a current margin of at least one and a half times, The indicated KD202 diodes can work without radiators for 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 all you need look in the directory which of them and with which letter can be up to 3 and which up to 5 amperes. I want more - look in the reference book and choose more powerful diodes, say 10 amperes.

Transistors - VT1 and VT4 installed on radiators. VT1 will warm up slightly, therefore, a small radiator is needed, but VT4, yes, in current limiting mode, will warm up pretty well. Therefore, you need to choose an impressive radiator, you can also adapt the fan from the computer's power supply to it - believe me, it won't hurt.

Particularly inquisitive - why is the transistor heating up? The current then flows through it and the greater the current, the more the transistor heats up. Let's count - at the input, on the capacitors 30 volts. 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 the math here, but somehow one of the laws of grandfather Kirchoff comes to mind, about the sum of voltage drops)

Well, the same Kirchoff said something about the current in the circuit, like what current flows in the load, the same current flows through the VT4 transistor. Let's say an ampere of 3 is flowing, the resistor in the load is heating up, the transistor is also heating up.

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 we multiply 17 volts 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 in the transistor is 27v×3A=81 watts... Now let's look at the reference book, in the transistors section. If we have a pass-through transistor te VT4, let's say KT819 in a plastic case, then according to the reference book it turns out that it will not withstand the power dissipation (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 at the expense of transistors it is more or less clear, let's move on to the fuses. In general, the fuse is the last resort that reacts to gross mistakes made by you and “at the cost of your life” prevents .... Let's assume that for some reason a short circuit occurred in the primary winding of the transformer, or in the secondary. Maybe because it overheated, maybe the insulation was leaking, or maybe just - the wrong connection of the windings, but there are no fuses. The transformer smokes, the insulation melts, the network wire, trying to perform the valiant function of a fuse, burns and, God forbid, if you have plugs with carnations instead of fuses on the distribution board instead of the machine.

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

Transformer. Perhaps the most expensive in the design Roughly speaking, the more massive the transformer, the more powerful it is. The thicker the wire of the secondary winding, the more current the transformer can give. It all comes down to one thing - the power of the transformer. So how do you choose a transformer? Again, a school course in physics, an electrical engineering section .... Again, 30 volts, 3 amperes, and as a result, 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 margin of at least 10 percent, and preferably all 30-50 percent. So 30 volts at a current of 4-5 amperes at the output of the transformer and your power supply unit will be able to give a current of 3 amperes to the load for hours if not for days.

Well, for those who want to get the maximum current from this PSU, let's say ampere 10 commercials.

The first is a transformer that meets your needs.

The second is a 15 amp diode bridge and on radiators

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

Fourth, it is desirable to increase the capacity, of course, but if the PSU is used as a charger, this is not critical.

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

Wiring diagram for parallel transistors instead of one

Do-it-yourself power supply 0-30 Volt

How many interesting radio devices are assembled by radio amateurs, but the basis, without which almost no circuit will work, is power unit. .Often, hands simply do not reach the assembly of a decent power supply. Of course, the industry produces enough high-quality and powerful voltage and current stabilizers, but they are not sold everywhere and not everyone has the opportunity to buy them. It's easier to solder with your own hands.

Power supply circuit:

The proposed circuit of a simple (only 3 transistors) power supply compares favorably with similar ones with the accuracy of maintaining the output voltage - compensation stabilization, start-up reliability, a wide adjustment range and cheap, non-deficient parts are used here.

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

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

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

The cooler can be left - it will not be superfluous. And so as not to make noise, we simply feed it through a current-limiting resistor, which you will select experimentally.

For the front panel, I was not stingy and bought a plastic box - it is very convenient to make holes and rectangular windows for indicators and regulators in it.

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

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

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