AC to DC voltage stabilizer

Stabilizers alternating current, are much less commonly used by radio amateurs than voltage stabilizers and power regulators. This is largely due to the more complex circuitry of traditional current sources. However, objective analysis shows that in some cases it is preferable to use current sources. The main advantage of the current source is its insensitivity to load short circuits.

Quite often there are cases when it is necessary to maintain a constant value of alternating current, for example, when turning on powerful incandescent lamps. This measure extends their service life several times. Adjustable stabilizer can provide invaluable assistance when checking and adjusting current protection devices.

Readers are offered a simple circuit of an alternating current stabilizer, with the ability to smoothly adjust its value. The current can be adjusted from a few milliamps to 8 Amps. With appropriate selection of circuit elements, the maximum stabilized current can be increased to 70-80 A.

The circuit is based on a current-stabilizing two-terminal network; this circuit solution has been known for quite a long time, but for a long time it was purely theoretical (remember what MOS transistors were 10-15 years ago). The situation changed with the advent of power MOSFETs on sale. Their use makes it possible to create current sources with good characteristics and extremely simple ones.

The current stabilizer itself is assembled on operational amplifier(O-Amp) DA1, transistor VT1 and resistors R1, R2, R4. The R1-R2 divider is a current “setter”. In this case, the current in amperes is numerically equal to the voltage on the motor R2 multiplied by 10. This allows you to select the voltage of the current sensor R4 very small. To work with alternating current, a diode bridge is introduced into the circuit, in one of the diagonals of which a current-stabilizing two-terminal network is included. This connection is equivalent to connecting the load and the two-terminal network in series, and, therefore, provides the same current through them.

Let us consider the process of current stabilization in more detail. Since the rectified voltage is not filtered, the voltage at the drain of transistor VT1 is unipolar, pulsating. When the drain voltage (Figure 2A) is zero, no current flows through VT1, and the voltage drop across sensor resistor R4 is also zero. Transistor VT1 is completely open. As the voltage in the network increases, the voltage taken from the sensor also increases (in proportion to the flowing current), approaching the “setter” voltage. Transistor VT1 begins to close. When the voltages on the sensor R4 and the “setter” R1-R2 coincide, further growth of the current is limited. Op-amp DA1 maintains the same voltage at its inputs by changing the resistance of channel VT1. This ensures current stabilization. The shape of the current through VT1 coincides with the voltage at the “setter” and has a trapezoidal shape (Figure 2B). The same shape, only alternating, current flows through the load (Figure 2B). Elements VD1, R3, C1, C2 form a parametric stabilizer for powering the op-amp.

If you need to change the range of stabilized currents, you should appropriately select the type of transistor VT1 and diodes VD2-VD5, and also adjust the current “setter” voltage or the resistance of sensor R4.

The stabilization current is determined by the formula:
I Art. =U back. /R4

Setting up the circuit comes down to monitoring the voltage of the “setter” (so that the current does not go beyond 7...8 A) and calibrating the control (resistor R2). For visual control, an ammeter can be connected to the current circuit.

The DA1 op-amp is suitable for any wide application (K140UD6, K140UD7, mA741, etc.). It is better to refrain from using high-speed op-amps with field-effect transistors, since with them the stabilizer can self-excite, which will inevitably damage the op-amp, transistor VT1 and bridge diodes (this is exactly how the author’s circuit reacted to the installation of K544UD2). Transistor VT1 should be selected based on the maximum permissible drain current and drain-source voltage. Zener diode VD1 is any precision one, with a stabilization voltage of 9...15 V. The stability of the “setter” voltage and, as a consequence, the stabilized current depends on its stability.

Transistor VT1 should be mounted on a massive radiator. There are no special requirements for other parts. It is convenient to make resistor R4 from an industrial shunt for measuring instruments. This will ensure the required accuracy and thermal stability. When installing it, special attention should be paid to the reliability of the connection between the inverse output of the op-amp and R4. A break in this connection causes the stabilizer to fail.

AC Voltage Stabilizers- these are devices that automatically convert the current elevated or undervoltage at a stable voltage of 220V (or 380V).

Voltage stabilizers are used to protect electrical equipment from increases and decreases in voltage in the electrical network, surges and surges, electromagnetic interference, and short circuits, thereby increasing the service life of the equipment.

We offer AC voltage stabilizers of two types: with step voltage regulation (or relay) and electromechanical (or servomotor).

Relay stabilizers are distinguished by their relatively low price, speed of regulation, high noise immunity, especially to surge voltages, low weight and dimensions. They are used for long intervals of reduced or increased voltage, but are not recommended for use to protect electrical equipment with AC motors and devices with high inrush currents. The disadvantage of relay stabilizers is the stepwise regulation of the output voltage, which limits the accuracy of stabilization.

Electromechanical stabilizers are suitable for protecting any load, are characterized by high accuracy of holding the output voltage, good load capacity, no interference during operation, and provide smooth regulation of the output voltage without distortion of the sinusoidal shape. The disadvantages of electromechanical stabilizers are low performance, noise, and the presence of an open sliding contact.

When choosing a voltage stabilizer, you should take into account the total power and nature of the load, the number of phases, and the characteristics of the supply network. Pay attention to the operating range of the stabilizer, the number and quality of sockets, whether they are grounded, and the accuracy of stabilization. We offer a wide range of AC voltage stabilizers ranging from 100 to 10,000 W. The main suppliers are Krauler, Calm, Era.

You can view and buy the product in our stores in the cities: Moscow, St. Petersburg, Volgograd, Voronezh, Yekaterinburg, Kazan, Kaluga, Krasnodar, Minsk, Nizhny Novgorod, Novosibirsk, Omsk, Perm, Rostov-on-Don, Ryazan, Samara , Tver, Tula, Ufa, Chelyabinsk. Delivery of the order by mail or through Euroset showrooms to the following cities: Rostov-on-Don, Krasnoyarsk, Saratov, Izhevsk, Ulyanovsk, Tyumen, Irkutsk, Yaroslavl, Khabarovsk, Vladivostok, etc.

You can buy products from the “AC Voltage Stabilizers” group wholesale and retail.

Current stabilizers are used much less frequently by radio amateurs than Surge Protectors and power regulators. This is largely due to the more complex circuitry of traditional current sources. However, objective analysis shows that in some cases it is preferable to use current sources. The main advantage of the current source is its insensitivity to load short circuits.

Quite often there are cases when it is necessary to maintain a constant value of alternating current, for example, when turning on powerful incandescent lamps. This measure extends their service life several times. An adjustable stabilizer can provide invaluable assistance when checking and adjusting current protection devices.

Readers are offered a simple AC stabilizer circuit with smooth adjustment of its value. The current is regulated from several milliamps to 8 A. With appropriate selection of circuit elements, the maximum stabilized current can be increased to 70...80 A.

The stabilizer circuit is shown in Fig. 1. It is based on a current-stabilizing two-terminal network, described in detail in. This circuit solution has been known for quite a long time, but for a long time it was purely theoretical (remember what MOS transistors were 10... 15 years ago). The situation changed with the advent of powerful MOSFET transistors (MOSFET; from Intersil and International Rectifiei. Their use makes it possible to create current sources with good characteristics and extremely simple circuits(and the coincidence of calculations with practice pleasantly surprised the author).

The current stabilizer itself is assembled on op-amp DA1, transistor VT1 and resistors R1, R2, R4. The R1-R2 divider is a current controller. In this case, the current in amperes is numerically equal to the voltage on the motor R2 multiplied by 10. This allows you to select the voltage of the current sensor R4 very small. To work with alternating current, a diode bridge is introduced into the circuit, in one of the diagonals of which a current-stabilizing two-terminal network is included. This connection is equivalent to connecting the load and the two-terminal network in series, and, therefore, provides the same current through them.

Fig. 1 AC stabilizer circuit

Let us consider the process of current stabilization in more detail. Since the rectified voltage is not filtered, the voltage at the drain of VT1 is unipolar, pulsating. When the voltage at the drain (Fig. 2a)is zero, no current flows through VT1, and the voltage drop across the sensor resistor R4 is also 0. Transistor VT1 is completely open. As the voltage in the network increases, the voltage taken from the sensor also increases (in proportion to the flowing current), approaching the voltage of the set pointer. Transistor VT1 begins to close.
When the voltages on the sensor R4 and the set point R1-R2 coincide, further growth of the current is limited. Op-amp DA1 maintains the same voltage at its inputs by changing the resistance of channel VT1. This ensures current stabilization. The shape of the current through VT1 coincides with the voltage at the setpoint and has a trapezoidal shape (Fig. 2b).The same shape, only alternating, current flows through the load (Fig. 2c).Elements VD1, R3, C1, C2 form a parametric stabilizer for powering the op-amp.

If you need to change the range of stabilized currents, you should appropriately select the type of transistor VT1 and diodes VD2...VD5, and also adjust the voltage of the current setter (U set) or the resistance of sensor R4.

The stabilization current is determined by the formula:

This circuit can also be converted into an active AC load, how to do this is described in detail in.

Rice. 2 Signal diagram

Setting up the circuit comes down to monitoring the voltage of the set pointer (so that the current does not go beyond 7...8 A) and calibrating the control element (resistor R2). For visual control, an ammeter can be connected to the current circuit.

The DA1 op-amp is suitable for any wide application (K140UD6, K140UD7, mA741, etc.). It is better to refrain from using high-speed op-amps with field-effect transistors, since with them the stabilizer can self-excite, which will inevitably damage the op-amp, transistor VT1 and bridge diodes (this is exactly how the author’s circuit reacted to the installation of K544UD2). Transistor VT1 should be selected from the range of the above companies, focusing on the maximum permissible drain current and drain-source voltage. Zener diode VD1 - any precision one, with a stabilization voltage of 9... 15 V. The stability of the setpoint voltage and, as a consequence, the stabilized current depends on its stability.

Transistor VT1 should be mounted on a massive radiator. There are no special requirements for other parts. It is convenient to make resistor R4 from an industrial shunt for measuring instruments. This will ensure the required accuracy and thermal stability. When installing it, special attention should be paid to the reliability of the connection between the inverse output of the op-amp and R4. A break in this connection causes the stabilizer to fail.

A. Uvarov

Literature

1. Uvarov A.S. Resistive load is a current source. - Radio Amateur, 2001, N1, P.14.

2. Ivanov P., Semushkin S. Stable current sources and their use in radio equipment. - To help the radio amateur. Vol. 104. - M.: DOSAAF, 1989.

3. http://www.intersil.com

4. Powerful field-effect switching transistors from International Rectifier. - Radio, 2001, N5, P.45.