Stabilized power regulator. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Power regulators, thermometers, heat stabilizers

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Sometimes there are situations when it is necessary to stabilize the power in the load, the resistance of which varies over time over a wide range. In such cases, the proposed power regulator will help, which simultaneously performs the functions of a stabilizer.

Most of the power regulators described in amateur radio literature work either with a purely active (incandescent lamp, electric stove, electric furnace), or with an active-inductive load (electric motors). However, this load is either constant (electric furnace) or changes during a relatively short transient process and then tends to a steady value (incandescent lamp, electric motor). In both cases, the power of such loads is regulated by changing the flowing average current. Since the load power Рн, the current through it Iн and its resistance Rн are related by the dependence Pн=Iн2·Rн. with a constant resistance, power regulation is uniquely achieved by current regulation.

There are also such types of loads, the resistance of which depends on various factors and, therefore, changes in time according to a law unknown in advance. An example of such a load is an electrode water-heating boiler, in which the working medium and the electrically conductive body is water. The resistance of water depends on the type and amount of salts contained in it, temperature, flow rate through the boiler and other factors. The resistance of such a load can vary tenfold. In this case, controlling the current through the load does not solve the problem of power regulation, since its resistance is a variable. Here, the current through the load depends not only on the voltage on it, but also on its resistance. This does not allow power to be controlled in the usual way (by setting a specific current value). Even current stabilization will not be a way out.

Since, at a voltage at the load Un, its power Pn = Un·In, in order to stabilize the power in the load, the product Un·In should be stabilized, i.e., ensure its constancy. The controlled parameter (independent variable) can be voltage, since both the current and the load power depend on its value.

Therefore, it is necessary to regulate the voltage on the load so that when the resistance changes, a constant average power in the load is provided. In this case, to determine the instantaneous power, it is necessary to multiply the instantaneous values ​​of voltage and current in the load. This follows from the classical definition of power in electrical engineering.

The block diagram of the device that implements the control algorithm described above is shown in fig. 1.

The inputs of the multiplier are electrical signals proportional to the instantaneous values ​​of voltage and current in the load. From the output of the multiplier, a signal proportional to their product (i.e., power), after averaging it over time, enters the first input of the differential amplifier, the second input of which is supplied with a reference voltage. In the differential amplifier, the voltages are compared and the difference signal (error signal) is amplified, which is then fed to the comparator. The second input of the comparator receives sawtooth pulses, following with twice the mains frequency. At the output of the comparator, rectangular pulses are formed, the duty cycle of which determines the voltage from the output of the differential amplifier. Pulses from the output of the comparator control the triac switch, which, in turn, controls the load. If the power in the load deviates from the value specified by the voltage Uset, the error signal from the output of the differential amplifier will affect the comparator so that a change in the duty cycle of the pulses will lead to power stabilization.

Consider the operation of a stabilized power controller according to its circuit diagram (Fig. 2) and timing diagrams (Fig. 3).

(click to enlarge)

The X and Y inputs of the DA3 chip (integral signal multiplier) receive signals proportional, respectively, to the instantaneous values ​​of the voltage at the load and the current through it. A signal proportional to the instantaneous voltage value is taken from the trimmer resistor R4. Resistor R1 - load current sensor. The voltage from this resistor is supplied to the primary winding of the step-up transformer T2 (the transformation ratio is about 40). The need to use a transformer is due to two factors. Firstly, it increases the voltage applied to the input of the multiplier, and secondly, it provides galvanic isolation. Signals proportional to current and voltage are variable, but there is no need to rectify them, since the K525PS2 (DA3) chip allows AC voltage with an amplitude of up to 10,5 V to be applied to the X and Y inputs.

Note that the voltage and current signals applied to the multiplier must be in phase, which is achieved by appropriately connecting the windings of the transformer T2.

The integrated voltage multiplier K525PS2 is designed to implement a number of typical functional dependencies (multiplication, division, squaring, square root extraction). To perform these functions with analog signals, an exponential dependence of the transistor collector current on its base-emitter voltage is used. Multiplication error - no more than 1%. More detailed information about the structure and application of integral multipliers can be found in [1].

When the integral multiplier is turned on in accordance with the one shown in fig. 2, the voltage Uz≈0,15UxUy acts on its output Z, where Ux, Uy are the voltages applied to the X and Y inputs of the DA3 chip, respectively.

The control pulses of the triac VS1 come from the output of the voltage comparator DA4. The integral comparator K554SAZ used in the power controller has an open collector output designed for a load current of up to 50 mA. The output transistor is open (i.e., at the output when the load is connected, the voltage is low) if the voltage at the inverting input (pin 4) of the DA4 chip is greater than at the non-inverting one (pin 3). With the opposite ratio of voltages, the output of the comparator will have a high level voltage.

On the DA4 comparator, the sawtooth voltage is compared (Fig. 3, diagram 3) and the voltage taken from the output of the op-amp DA5 (diagram 4).

The sawtooth voltage generator is made on transistors VT1, VT2. It generates pulses with a frequency of 100 Hz, synchronized with the mains voltage. The voltage from the rectifier bridge VD2 (Fig. 3, diagram 1) is supplied to the base of the transistor VT1. Most of the time, the transistor is open, and at the moments when the rectified voltage approaches zero, it closes. Short rectangular pulses are formed on its collector (Fig. 3, diagram 2), which are fed to the base of the transistor VT2. While the base voltage is zero, an increasing voltage is formed on the collector of the transistor (capacitor C6 is charged through resistor R13). At the moment a positive pulse appears on the base, transistor VT2 opens and the voltage on its collector decreases to almost zero (Fig. 3, diagram 3).

At the output of the comparator, rectangular pulses are formed (Fig. 3, diagram 5). Comparator load - resistor R16 and optocoupler LED U1. When current flows through the LED of the optocoupler, its triac opens, providing the opening of the triac VS1 - the current begins to flow through the load connected to the sockets of the XS1 connector. A change in the duty cycle of the pulses at the output of the comparator leads to a change in the voltage and, consequently, the power in the load. From the timing diagrams, it is easy to determine that an increase in the voltage at the output of the op-amp DA5 leads to a decrease in the power in the load.

Now - about the purpose and operation of the DA5 microcircuit, which performs the functions of a differential amplifier or an error signal amplifier (see Fig. 1). The setting voltage Uzad is removed from the engine of the variable resistor R18 and fed to the inverting input of the op-amp, the non-inverting input of which receives the average output voltage of the multiplier DA3. The averaging of the output signal of the multiplier provides an integrating circuit R20C8.

Op-amp DA5 amplifies the signals applied to its inputs, ensuring the equality of the voltage values ​​​​on them. This means that a decrease in the setting voltage Uset will lead to a decrease in the voltage at the output of the op-amp. Obviously, the lower position of the variable resistor R18 engine according to the diagram will correspond to the zero value of the power in the load. Capacitor C7 ensures stable operation of the op-amp when exposed to interference.

The power supply of the power regulator elements is made on two integrated voltage stabilizers DA1 and DA2. The use of two different types of microcircuits is due to the desire to get by with a network transformer with one secondary winding (albeit with a tap from the middle) and one rectifier bridge.

Diode VD1 eliminates the influence of the filter capacitor C1 on the shape of the rectified voltage supplied to the input of the sawtooth voltage generator.

The power regulator is assembled on a printed circuit board made of double-sided foil fiberglass. The PCB drawing is shown in fig. 4.

Insert pieces of tinned wire into the holes of the square pads and solder them on both sides of the board. Microcircuits DA1, DA2 are installed on small duralumin heat sinks with an area of ​​20 ... 30 cm² each; triac VS1 is mounted on a standard cooler (cast heat sink made of aluminum alloy) brand 0231. Resistor R1 is made of nichrome wire with a diameter of 3 mm.

In place of the DA4 comparator, in addition to that indicated in the diagram, you can also use K521CAZ, K521CA5, K521CA6 (the last microcircuit contains two comparators in one package), however, you will have to adjust the printed circuit board drawing. We will replace the KR140UD708 OU with K140UD7, K140UD8, K153UD2 and any similar microcircuits. Analog voltage multiplier K525PS2 can be replaced by K525PS3 with any letter index, but also with PCB correction. Transistors VT1, VT2 - any of the KT315, KT342, KT503, KT630, KT3I02 or KT3117A series. The imported optocoupler MOC3052 can be replaced by the domestic AOU160A-AOU160V with PCB correction. The VS1 triac can be used from the TS112, TS122, TS132, TS142 series with a permissible closed-state pulse voltage of at least 400 V and an open-state current corresponding to the maximum load current. Diode KD106A (VD1) can be replaced by any of the series KD105, KD221, KD226.

Rectifier bridge (VD2) - any of the KTs402, KTs405 series, with PCB correction. Oxide capacitors C1 - C3, C8 can be K50-16, K50-35, K50-24, K50-29; C4, C5, C7 - KM-6, K10-17, K73-17; C6 - K73-17, K73-24, K76-P2 (this capacitor should have a small TKE). Trimmer resistors R4, R5, R8-R10 - SP5-2, SPZ-19, SPZ-38, variable resistor R18 - SP-0,4, SPZ-4M, SPZ-16, SPZ-30, the rest - MLT, S2- 23. Transformer T1 - TPP232. It can be replaced by any other, in which the secondary winding with a tap from the middle provides a voltage of 33 ... 40 V and is rated for a current of at least 150 mA. Transformer T2 can be any other with a transformation ratio of 30...50. Power switch SA1 - circuit breaker A3161, AE2050 or AP50. In addition, it performs the function of a fuse.

The establishment of a power regulator begins with checking the output voltage of the DA1 chip (+ 15 V) and setting the output voltage of the DA2 chip (-15 V) with resistor R6. After that, the voltage multiplier DA3 is adjusted. For this, inputs X, Y, output Z and output 1 are disconnected from other elements. The engines of the tuning resistors R8-R10 are set to the middle position. A voltage of +5 V is applied to the X input, and a voltage of +9 V to the Y input. The output voltage of the multiplier O V is set with resistor R5. Then, a voltage of O V is applied to the X input, and +8 V to the Y input. B. Then, + 5 V is applied to both inputs of the multiplier and the output voltage is measured. Then, at one of the inputs, the polarity of the input signal is changed (i.e., -5 V is applied) and the output voltage is again measured. With the help of resistor R10, it is ensured that the last two values ​​of the output voltage are equal in absolute value (they must be opposite in sign). If necessary, repeat the adjustment. After that, the inputs and output of the voltage multiplier are connected to the elements of the regulator. The engines of the tuned resistors R4 and R5 are set to the middle position, and the variable resistor R18 is set to the lower position according to the diagram.

A load is connected to connector XS1 and power is supplied to the power regulator. By smoothly rotating the axis of the variable resistor R18, we are convinced of an increase in the voltage across the load. If the voltage at the load is maximum at any position of the variable resistor R18 slider, the reason for this may be incorrect phasing of the windings of the transformer T2, leading to the supply of anti-phase voltages to the X and Y inputs of the DA3 microcircuit and a negative voltage at its output Z. In this case, the conclusions should be swapped any of the windings of the transformer T2.

Trimmer resistors R4 and R5 ensure that the maximum (amplitude) voltage values ​​​​at the inputs of the multiplier do not exceed 10 V. This is conveniently controlled using an oscilloscope. In extreme cases, you can use an AC voltmeter. With a sinusoidal voltage on the load (this takes place if the triac VS1 opens at the beginning of each half-cycle, and the voltage on the load is practically equal to the mains voltage), the effective voltage at the inputs of the multiplier should not exceed 7 V. Power control should be smoothly carried out throughout the entire turn interval axis of the variable resistor R18. If in the upper position of the variable resistor R18 engine according to the diagram with the maximum connected load, the voltage on it does not reach the mains value, you should reduce the resistance of the resistor R17 to no more than 2,2 kOhm or reduce the current and voltage transfer coefficients by moving the trimming resistor engines down the circuit R4 and R5.

To test the power stabilization function, it is necessary to have a load with a variable resistance (it is convenient to use a two-section household heater) and a laboratory autotransformer of the appropriate power. The load must necessarily be active (i.e., not have an inductive or capacitive component).

The power regulator is connected to the network through an autotransformer and one section of the domestic heater is connected to the output of the regulator. A voltage of 220 V is set with an autotransformer. By connecting an AC voltmeter measuring effective values ​​​​(a quadratic voltmeter) in parallel with the load, a voltage of 18 ... It should decrease by 150 times [200]. With a different law of change in load resistance, in any case, the equality Un² / Rn = const will be fulfilled. If the load resistance increases so much that the voltage must exceed its maximum value to maintain the set power, the regulator will exit the power stabilization mode.

The power regulator has stabilizing properties not only under conditions of changes in load resistance, but also in relation to fluctuations in the mains voltage. This can be verified by changing the supply voltage of the regulator using an autotransformer in the range from 190 to 240 V (of course, with the load connected). The voltage at the load with such a change in the supply should be stable. Only the opening angle of the triac VS1 will vary, which can be verified using an oscilloscope. The signal can be taken either from the load or from the output of the comparator DA4.

If the radio amateur does not have at his disposal a voltmeter that measures the effective value (for example, an electromagnetic system device), then an induction electric energy meter is used to measure power: the number of revolutions of the meter disk must be constant when the load resistance changes and the position of the variable resistor R18 slider remains unchanged. It is impossible to use a voltmeter of the average rectified voltage value for these purposes.

To increase reliability, we recommend connecting a resistor with a resistance of about 150 ohms in series with the opto-triac.

Literature

1. Putnikov VS Integrated electronics in measuring devices. - 2nd ed., revised. and additional - L.: Energoatomizdat. Leningrad. department, 1988.
2. Biryukov S. Amplitude, average, effective. - Radio, 1999, No. 6, p. 58, 59.

Author: A. Evseev, Tula

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