Instant water heater. How to choose a flowing electric water heater for a faucet. Comparison of different heaters

In amateur radio practice, it often becomes necessary to use a sinusoidal generator. Its applications can be found in a wide variety of ways. Consider how to create a sinusoidal signal generator on the Wien bridge with a stable amplitude and frequency.

The article describes the development of a sinusoidal signal generator circuit. You can also generate the desired frequency programmatically:

The most convenient, from the point of view of assembly and adjustment, a variant of a sinusoidal signal generator is a generator built on the Wien bridge, on a modern Operational Amplifier (OA).

Wine Bridge

The Wien bridge itself is a bandpass filter consisting of two . It emphasizes the center frequency and suppresses the rest of the frequencies.

The bridge was designed by Max Wien in 1891. On a circuit diagram, the Wien Bridge itself is usually depicted as follows:

Image borrowed from Wikipedia

A Wien bridge has an output-to-input voltage ratio b=1/3 . This is an important point, because this coefficient determines the conditions for stable generation. But more on that later

How to calculate the frequency

Self-oscillators and inductance meters are often built on the Wien bridge. In order not to complicate their lives, they usually use R1=R2=R And C1=C2=C . Thanks to this, the formula can be simplified. The fundamental frequency of the bridge is calculated from the ratio:

f=1/2πRC

Almost any filter can be thought of as a frequency dependent voltage divider. Therefore, when choosing the values ​​​​of the resistor and capacitor, it is desirable that at the resonant frequency the complex resistance of the capacitor (Z) be equal to, or at least one order of magnitude with the resistance of the resistor.

Zc=1/ωC=1/2πνC

where ω (omega) - cyclic frequency, ν (nu) - linear frequency, ω=2πν

Wien bridge and operational amplifier

The Wien bridge itself is not a signal generator. For generation to occur, it should be placed in the positive feedback circuit of the operational amplifier. Such an oscillator can also be built on a transistor. But the use of an op-amp will clearly simplify life and give better performance.

C grade gain

Wien's bridge has a transmittance b=1/3 . Therefore, the generation condition is that the op-amp must provide a gain equal to three. In this case, the product of the transmission coefficients of the Wien bridge and the gain of the op amp will give 1. And the specified frequency will be generated stable.

If the world were ideal, then by setting the required gain with resistors in the negative feedback circuit, we would get a ready-made generator.

This is a non-inverting amplifier and its gain is given by:K=1+R2/R1

But alas, the world is not perfect. ... In practice, it turns out that in order to start generation, it is necessary that at the very initial moment the coefficient. the gain was slightly more than 3, and then for stable generation it was maintained equal to 3.

If the gain is less than 3, then the generator will stall, if more, then the signal, having reached the supply voltage, will begin to distort, and saturation will occur.

When saturated, the output will be maintained at a voltage close to one of the supply voltages. And random chaotic switching between supply voltages will occur.

Therefore, when building a generator on a Wien bridge, they resort to using a non-linear element in the negative feedback circuit that regulates the gain. In this case, the generator will balance itself and maintain the generation at the same level.

Amplitude stabilization on an incandescent lamp

In the most classic version of the Wien bridge generator on the op-amp, a miniature low-voltage incandescent lamp is used, which is installed instead of a resistor.

When such a generator is turned on, at the first moment, the lamp coil is cold and its resistance is low. This contributes to the start of the generator (K>3). Then, as it heats up, the coil resistance increases and the gain decreases until it reaches equilibrium (K=3).

The positive feedback loop in which the Wien bridge was placed remains unchanged. The general circuit diagram of the generator is as follows:

The positive feedback elements of the op amp determine the generation frequency. And the elements of negative feedback are amplification.

The idea of ​​using a light bulb as a control element is very interesting and is still used today. But the light bulb, alas, has a number of disadvantages:

• selection of a light bulb and a current-limiting resistor R* is required.
• with regular use of the generator, the life of the light bulb is usually limited to a few months
• the control properties of the light bulb depend on the temperature in the room.

Another interesting option is to use a directly heated thermistor. In fact, the idea is the same, only a thermistor is used instead of a bulb spiral. The problem is that you first need to find it and again pick it up and current-limiting resistors.

Amplitude stabilization on LEDs

An effective method for stabilizing the amplitude of the output voltage of a sinusoidal signal generator is the use of LEDs in the negative feedback circuit of the op-amp ( VD1 And VD2 ).

The main gain is set by resistors R3 And R4 . The rest of the elements ( R5 , R6 and LEDs) regulate the gain in a small range, keeping the generation stable. resistor R5 you can adjust the output voltage in the range of approximately 5-10 volts.

In the additional OS circuit, it is desirable to use low-resistance resistors ( R5 And R6 ). This will allow a significant current (up to 5mA) to pass through the LEDs and they will be in optimal mode. They will even glow a little :-)

In the diagram shown above, the Wien bridge elements are designed to generate at a frequency of 400 Hz, however, they can be easily recalculated for any other frequency using the formulas presented at the beginning of the article.

Quality of generation and applied elements

It is important that the operational amplifier can provide the necessary current for generation and has sufficient frequency bandwidth. The use of folk TL062 and TL072 as op amps gave very sad results at a generation frequency of 100 kHz. The waveform was hardly sinusoidal, rather it was a triangular signal. Using the TDA 2320 gave an even worse result.

But the NE5532 showed itself from the excellent side, giving out a signal very similar to a sinusoidal at the output. The LM833 also did an excellent job. So it is NE5532 and LM833 that are recommended for use as affordable and common high-quality op-amps. Although with a decrease in frequency, the rest of the op-amps will feel much better.

The accuracy of the generation frequency directly depends on the accuracy of the elements of the frequency-dependent circuit. And in this case, it is important not only to match the face value of the inscription element on it. More accurate parts have better value stability with temperature changes.

In the author's version, a resistor of the C2-13 ± 0.5% type and mica capacitors with an accuracy of ± 2% were used. The use of resistors of this type is due to the small dependence of their resistance on temperature. Mica capacitors also depend little on temperature and have a low TKE.

Cons of LEDs

On LEDs it is worth dwelling separately. Their use in a sine generator circuit is caused by the magnitude of the voltage drop, which usually lies in the range of 1.2-1.5 volts. This allows you to get a sufficiently high value of the output voltage.

After the implementation of the circuit, on the breadboard, it turned out that due to the spread of the parameters of the LEDs, the fronts of the sinusoid at the output of the generator are not symmetrical. It's a bit noticeable even in the photo above. In addition, there were slight distortions in the generated sine shape, caused by the insufficient speed of the LEDs for a generation frequency of 100 kHz.

Diodes 4148 instead of LEDs

The LEDs have been replaced with the beloved 4148 diodes. These are affordable fast signal diodes with switching speeds of less than 4 ns. At the same time, the circuit remained fully functional, there was no trace of the problems described above, and the sinusoid acquired an ideal form.

In the following diagram, the fault bridge elements are designed for an oscillation frequency of 100 kHz. Also, the variable resistor R5 was replaced with constant ones, but more on that later.

Unlike LEDs, the voltage drop at the p-n junction of conventional diodes is 0.6÷0.7 V, so the output voltage of the generator was about 2.5 V. To increase the output voltage, it is possible to turn on several diodes in series, instead of one, for example like this:

However, increasing the number of non-linear elements will make the generator more dependent on the external temperature. For this reason, it was decided to abandon this approach and use one diode at a time.

Replacing a variable resistor with constant ones

Now about the tuning resistor. Initially, a 470 ohm multi-turn trimmer was used as resistor R5. It allows you to accurately adjust the output voltage.

When building any generator, it is highly desirable to have an oscilloscope. The variable resistor R5 directly affects the generation - both the amplitude and the stability.

For the presented circuit, the generation is stable only in a small range of resistances of this resistor. If the resistance ratio is greater than required, clipping begins, i.e. the sine wave will be clipped at the top and bottom. If it is less, the shape of the sinusoid begins to be distorted, and with a further decrease, the generation stalls.

It also depends on the supply voltage used. The described circuit was originally assembled on an LM833 op amp with ± 9V power supply. Then, without changing the circuit, the op-amps were replaced with AD8616, and the supply voltage was ± 2.5V (the maximum for these op-amps). As a result of such a replacement, the sinusoid at the output was cut off. The selection of resistors gave values ​​​​of 210 and 165 ohms, instead of 150 and 330, respectively.

How to choose resistors "by eye"

In principle, you can leave a tuning resistor. It all depends on the required accuracy and the generated frequency of the sinusoidal signal.

For self-selection, you should, first of all, install a tuning resistor with a nominal value of 200-500 Ohms. By applying the output signal of the generator to the oscilloscope and rotating the tuning resistor, reach the moment when the limitation begins.

Then, lowering the amplitude, find the position in which the shape of the sinusoid will be the best. Now you can unsolder the trimmer, measure the resulting resistance values ​​​​and solder the closest values.

If you need an audio frequency sine wave generator, you can do without an oscilloscope. To do this, again, it is better to reach the moment when the signal, by ear, begins to distort due to clipping, and then reduce the amplitude. You should decrease until the distortion disappears, and then a little more. This is necessary because by ear it is not always possible to catch distortion even in 10%.

Additional Gain

The sine generator was assembled on a dual op-amp, and half of the microcircuit was left hanging in the air. Therefore, it is logical to use it under an adjustable voltage amplifier. This made it possible to transfer the variable resistor from the additional oscillator circuit to the voltage amplifier stage to adjust the output voltage.

The use of an additional amplifying stage guarantees a better matching of the generator output with the load. It was built according to the classical scheme of a non-inverting amplifier.

The specified ratings allow you to change the gain from 2 to 5. If necessary, the ratings can be recalculated for the required task. The stage gain is given by:

K=1+R2/R1

Resistor R1 is the sum of series-connected variable and fixed resistors. A fixed resistor is needed so that at the minimum position of the variable resistor knob, the gain does not go to infinity.

How to strengthen the exit

The generator was supposed to work on a low-resistance load of a few ohms. Of course, not a single low-power op-amp will be able to deliver the required current.

For power, a repeater on the TDA2030 was placed at the output of the generator. All the goodies of this application of this microcircuit are described in the article.

And this is how the circuit of the entire sinusoidal generator with a voltage amplifier and a follower at the output actually looks like:

The sine generator on the Wien bridge can also be assembled on the TDA2030 itself as an op amp. It all depends on the required accuracy and the selected generation frequency.

If there are no special requirements for the quality of generation and the required frequency does not exceed 80-100 kHz, but it is supposed to work on a low-resistance load, then this option is ideal for you.

Conclusion

The Wien bridge generator is not the only way to generate a sine wave. If you need high-precision frequency stabilization, then it is better to look towards oscillators with a quartz resonator.

However, the described scheme is suitable for the vast majority of cases when it is required to obtain a stable, both in frequency and amplitude, sinusoidal signal.

Generation is good, but how to accurately measure the magnitude of high-frequency alternating voltage? For this, a scheme called is perfect.

Material prepared exclusively for the site

Such a device will be very useful when testing the audio circuits of amplifiers of receivers, TVs and other industrial and home-made equipment. The generator circuit is given according to the book by V. G. Borisov "Young radio amateur" (from 145-146 in the 8th edition), with minor changes.

AF generator circuit

The generator is assembled on a K155LA3 chip (K555LA3 can be used), which is 4 2I-NOT elements. The generator itself is formed by series-connected logic elements DD1.1, DD1.2, DD1.3, connected by inverters. Capacitor C1, with a capacity of 0.47 uF, creates a positive feedback between the output DD1.2 and the input DD1.1. In principle, the signal can be taken from the output of DD1.3, element DD1.4 simply inverts them. The pulse frequency can be changed with a variable resistor R1. Resistor R2 serves as an output level regulator. Resistor resistance R1 680 Ohm, R2 10 kOhm, variable resistors can be of any type. With the parameters of the radio components indicated in the diagram, the pulse frequency can be changed within 500 - 5000 Hz. Diode VD1 serves to protect against power supply of the wrong polarity; any low-power diode, for example D220, is suitable as it. The circuit is mounted on a small breadboard. But due to the small number of parts, it is possible to carry out the scheme by surface mounting.

Complete generator

The nominal supply voltage of the K155 and K555 microcircuits is 5 V, but the generator is operable when the circuit is powered by a 4.5 V “square” battery (3336 type battery according to the old nomenclature), the voltage drop across the VD1 diode does not affect the operation of the device. The device can be used for audio frequency.

Low-frequency generators (LFGs) are used to obtain undamped periodic oscillations of electric current in the frequency range from fractions of a Hz to tens of kHz. Such generators, as a rule, are amplifiers covered by positive feedback (Fig. 11.7,11.8) through phase-shifting chains. To implement this connection and to excite the generator, the following conditions are necessary: ​​the signal from the output of the amplifier must be fed to the input with a phase shift of 360 degrees (or a multiple of it, i.e. 0, 720, 1080, etc. degrees), and itself the amplifier must have some gain margin, KycMIN. Since the condition for the optimal phase shift for the occurrence of generation can be satisfied only at one frequency, it is at this frequency that the amplifier with positive feedback is excited.

To shift the signal in phase, RC and LC circuits are used, in addition, the amplifier itself introduces a phase shift into the signal. To obtain positive feedback in the generators (Fig. 11.1, 11.7, 11.9), a double T-shaped RC bridge was used; in generators (Fig. 11.2, 11.8, 11.10) - Wien's bridge; in generators (Fig. 11.3 - 11.6, 11.11 - 11.15) - phase-shifting RC chains. In generators with RC chains, the number of links can be quite large. In practice, to simplify the scheme, the number does not exceed two or three.

Calculation formulas and ratios for determining the main characteristics of RC-generators of sinusoidal signals are given in Table 11.1. For ease of calculation and simplification of the selection of parts, elements with the same ratings were used. To calculate the generation frequency (in Hz), the values ​​​​of resistance expressed in Ohms are substituted into the formulas, and capacitances - in Farads. For example, let's determine the generation frequency of an RC oscillator using a three-link RC positive feedback circuit (Fig. 11.5). At R \u003d 8.2 kOhm; C \u003d 5100 pF (5.1x1SG9 F) the operating frequency of the generator will be equal to 9326 Hz.

Table 11.1

In order for the ratio of the resistive-capacitive elements of the generators to correspond to the calculated values, it is highly desirable that the input and output circuits of the amplifier covered by the positive feedback loop do not shunt these elements and do not affect their value. In this regard, to build generator circuits, it is advisable to use amplification stages with high input and low output resistance.

On fig. 11.7, 11.9 shows the "theoretical" and simple practical schemes of generators using a double T-bridge in a positive feedback circuit.

Wien bridge generators are shown in fig. 11.8, 11.10 [R 1/88-34]. A two-stage amplifier was used as a ULF. The amplitude of the output signal can be adjusted with potentiometer R6. If you want to create a generator with a Wien bridge, tunable in frequency, in series with resistors R1, R2 (Fig. 11.2, 11.8) include a dual potentiometer. The frequency of such a generator can also be controlled by replacing the capacitors C1 and C2 (Fig. 11.2, 11.8) with a double variable capacitor. Since the maximum capacitance of such a capacitor rarely exceeds 500 pF, it is possible to tune the generation frequency only in the region of sufficiently high frequencies (tens, hundreds of kHz). The generation frequency stability in this range is low.

In practice, to change the generation frequency of such devices, switched sets of capacitors or resistors are often used, and field-effect transistors are used in the input circuits. In all the above schemes, there are no output voltage stabilization elements (for simplicity), although for generators operating at the same frequency or in a narrow range of its tuning, their use is not necessary.

Sinusoidal signal generator circuits using three-link phase-shifting RC chains (Fig. 11.3)

shown in fig. 11.11, 11.12. The generator (Fig. 11.11) operates at a frequency of 400 Hz [R 4/80-43]. Each of the elements of a three-link phase-shifting RC chain introduces a phase shift of 60 degrees, with a four-link - 45 degrees. A single-stage amplifier (Fig. 11.12), made according to the scheme with a common emitter, introduces a phase shift of 180 degrees necessary for the generation to occur. Note that the generator according to the circuit in Fig. 11.12 is operable when using a transistor with a high current transfer ratio (usually over 45 ... 60). With a significant decrease in the supply voltage and a non-optimal choice of elements for setting the transistor mode for direct current, the generation will fail.

Sound generators (Fig. 11.13 - 11.15) are similar in construction to generators with phase-shifting RC chains [Рl 10/96-27]. However, due to the use of inductance (telephone capsule TK-67 or TM-2V) instead of one of the resistive elements of the phase-shifting chain, they work with a smaller number of elements and in a larger range of supply voltage changes.

So, the sound generator (Fig. 11.13) is operational when the supply voltage changes within 1 ... 15 V (current consumption 2 ... 60 mA). In this case, the generation frequency changes from 1 kHz (upit = 1.5 V) to 1.3 kHz at 15 V.

Sound indicator with external control (fig. 11.14) also works at 1) supply=1...15 V; the generator is turned on / off by applying logic levels of one / zero to its input, which should also be within 1 ... 15 V.

The sound generator can also be made according to another scheme (Fig. 11.15). The frequency of its generation varies from 740 Hz (consumption current 1.2 mA, supply voltage 1.5 V) to 3.3 kHz (6.2 mA and 15 V). The generation frequency is more stable when the supply voltage changes within 3 ... 11 V - it is 1.7 kHz ± 1%. In fact, this generator is no longer made on RC, but on LC elements, moreover, the winding of a telephone capsule is used as an inductance.

The low-frequency generator of sinusoidal oscillations (Fig. 11.16) is assembled according to the "capacitive three-point" scheme characteristic of LC generators. The difference lies in the fact that the coil of a telephone capsule is used as an inductance, and the resonant frequency is in the range of sound vibrations due to the selection of capacitive circuit elements.

Another low-frequency LC-oscillator, made according to the cascode scheme, is shown in Fig. 11.17 [R 1/88-51]. As an inductance, you can use a universal or erasing heads from tape recorders, windings of chokes or transformers.

The RC generator (Fig. 11.18) is implemented on field-effect transistors [Рl 10/96-27]. A similar scheme is usually used in the construction of highly stable LC oscillators. Generation already occurs at a supply voltage exceeding 1 V. When the voltage changes from 2 to 10 6, the generation frequency decreases from 1.1 kHz to 660 Hz, and the current consumption increases, respectively, from 4 to 11 mA. Pulses with a frequency from units of Hz to 70 kHz and higher can be obtained by changing the capacitance of the capacitor C1 (from 150 pF to 10 μF) and the resistance of the resistor R2.

The sound generators presented above can be used as economical status indicators (on/off) of components and blocks of radio electronic equipment, in particular, light emitting diodes, for replacing or duplicating light indication, for emergency and alarm indication, etc.

Literature: Shustov M.A. Practical Circuitry (Book 1), 2003

A long stay without hot water turns a person's life into gray despondency. All people try to solve this problem, and everyone does it in their own way. Some install a large boiler, others prefer taps with a built-in water heater.

The device is almost no different from a conventional mixer. Instant taps are connected to a cold hose. Heating is carried out inside the equipment. Within 3-5 seconds the water will be up to 70°C. It is worth noting that the flowing electric water heater on the faucet is made of a special steel alloy that does not corrode and does not form scale.

The device has 3 operating modes:

• "Off" - the handle is in the "down" position. Water does not flow, electrical circuits are de-energized.
• "Cold" - the lever is in the "left" position. The power grid is off, and ordinary water at room temperature runs from the tap.
• "Hot" - the knob is turned to the right. The electrical system is turned on and within a few seconds hot water begins to flow from the tap.

There are models of mixers in which the temperature controller is located outside the structure. This is convenient - electronics controls all the necessary indicators.

Advantages and disadvantages

The advantages include:

• Fast water heating. Hot liquid will be dispensed within 5 seconds after switching on.
• Excellent technical characteristics of a cold water heater for a faucet in the bathroom or in the kitchen. Liquid temperature - up to 70 °C, good pressure, compact dimensions, local area of ​​use.
• Constant temperature. There will be no hesitation towards the appearance of boiling water or, conversely, the entry of too cold liquid.
• It will perfectly fit into any interior and will never spoil the appearance of the room.

The flow heater, which is put on the faucet, has almost no drawbacks. Only high power consumption can be noted - 3 kW per hour. Another drawback is the low throughput (up to 6 liters per minute). However, this indicator is quite enough to fill the bath or wash the dishes in the kitchen.

Overview of Chinese-made faucets with heating function

Model name	Peculiarities	Characteristics	t load, °С	Consumed energy, kW	Price, rubles
"Aquaterm"	Attractive design, quick installation, water filter.	High quality electric heating element, protection against overheating and electric shock.	60	3	3 900
"Delimano"	Fast supply of hot water, attractive design, possibility of regulation of temperature.	Material: plastic, metal. Working pressure: 0.4-0.6 MPa.	50-60	3	2 500
"Aquastream"	Compact size, energy saving.	The body is made of composite plastic.	60	2,5	3 500
RAPID™	Instantaneous water heating, saving resources compared to a boiler - 30%, simple installation.	High level overheating protection.	60	3	3 900
Corraveni	The valve is made of ceramic, the surface finish is of chromed steel.	There is a self-controlled water temperature system.	60	3	4 200

Before purchasing these devices, you need to pay attention to the power consumption. This indicator should be minimal, since the lower it is, the greater the savings in resources, and hence money.