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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Refinement of the automotive voltage regulator 59.3702-01. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Automobile. Electronic devices The proposed improvements in the regulator provide increased stability of the output voltage of the automobile generator when the current of its load and the engine operating mode change. Modern cars have complex and multifunctional electrical equipment, the reliable operation of which ensures the operability of the vehicle and the safety of its operation. The reliability of electrical equipment largely depends on the stability of the voltage in the on-board network. Ensuring the stability of this voltage is a difficult task, especially in transient conditions, when the generator speed and its load current change dramatically. Together with the voltage regulator, which maintains its constancy, the generator forms an automatic control system. Under certain conditions, such a system may lose stability, which manifests itself in the form of sharp fluctuations in the output voltage of the generator and the charging current of the battery. Therefore, it is very important to ensure the stability of the control system under all operating conditions. The most widely used today are electronic controllers operating in a relay self-oscillating mode. Such a regulator, when the generator output voltage exceeds a given upper threshold, disconnects its excitation winding from the onboard network. The current in the winding begins to decrease, which leads to a decrease in the generated voltage. As soon as it becomes less than the lower threshold, the excitation winding is reconnected to the onboard network and the current in it, and with it the output voltage of the generator, increase. Thus, the generator voltage fluctuates all the time, but its average value is kept stable. Regulators with "forced" PWM are more perfect. Due to the increased switching frequency of the excitation winding, the voltage of the generator in the steady state is practically unchanged, although oscillations can still occur in transient modes. Such regulators (one of them is described in the article by E. Tyshkevich "SHI voltage regulator". - Radio, 1984, No. 6, pp. 27, 28) are not widely used, probably due to the fact that their parameters are not much better than conventional self-oscillating. Although they are mass-produced, they are difficult to find in stores. Sellers either do not know anything about such regulators, or claim that they are not in demand. When operating a car, an important role is played by such a parameter as the load capacity of the generator at low engine speeds. It determines the minimum engine speed at which the battery is charged. Electronic voltage regulators most often lose stability precisely in situations where the rotational speed is low and the load current is high. This feature is well known to motorists, some of whom are replacing electronic regulators with obsolete contact-vibration ones, which are more reliable in this respect. But along with increased stability, they get the disadvantages inherent in this type of regulators. Many motorists replace the standard battery with another one with an increased capacity, as they believe that this improves the stability of the electronic regulators. Unfortunately, fluctuations in the output voltage of the generator are not taken to be eliminated in car services. At the same time, their employees claim that there is no malfunction, since the battery is still charging, although both the charging current and the generator voltage pulsate. Given all of the above, the author tried to increase the stability of the standard electronic voltage regulator 59.3702-01. On fig. 1 shows its circuit after the first version of refinement, which was reduced to installing an additional circuit from the resistor R8 and the capacitor C2, highlighted in the figure in color. The imported S1M diode can be replaced with a domestic one from the KD202 or KD209 series.
The principle of operation of the regulator remains the same. As the voltage in the on-board network, applied to the output "15" of the regulator, increases, the base potential of the transistor VT1 relative to its emitter becomes more negative, and at a certain value of this voltage (set by jumpers S1-S3), the transistor opens. As a result, transistors VT2 and VT3 are closed, breaking the power supply circuit of the excitation winding of the generator connected between the terminal "67" of the regulator and the common wire. But the current in a winding with a significant inductance cannot stop instantly. It continues to flow through the opened VD2 diode, gradually decreasing. Together with the excitation current, the voltage supplied by the generator to the onboard network also decreases. After some time, the transistor VT1 closes, and VT2 and VT3 open, which leads to an increase in current in the excitation winding of the generator and an increase in voltage. The described process is periodically repeated, and the average value of the generator voltage is maintained unchanged. The R7C3 circuit speeds up the process of switching transistors VT1 -VT3. With an increase in the voltage in the on-board network, caused, for example, by turning off a powerful load or increasing the engine speed, the newly installed capacitor C2 is charged, and the charging current, part of which flows through the base circuit of the transistor VT1, is proportional to the rate of voltage rise. As a result, VT1 opens, and transistors VT2 and VT3 close earlier than it was without a capacitor. The current decay in the excitation winding also starts earlier, which greatly slows down or completely eliminates the increase in voltage caused by an external factor. A similar process occurs with a rapid decrease in voltage. The resulting oscillations are damped, and their amplitude is significantly reduced. With slow voltage changes, the current through the capacitor C2 is small and practically does not affect the operation of the regulator in the steady state, as well as the accuracy of stabilizing the average voltage value. To check the stability of the voltage stabilization system, when the engine and generator are running, turn on and off a powerful consumer, such as headlights, by monitoring the battery current with an ammeter. In this case, the ammeter needle after the initial maximum deviation from the steady state (it is associated with the inertia of the generator and is inevitable even with an ideal regulator) should return to the old one or come to a new steady state monotonously, without any fluctuations. It is possible to regulate the dynamic characteristics of the system within certain limits by selecting the capacitance of the capacitor C2 and the resistance of the resistor R8 connected in series with it. The minimum duration of the transient is usually achieved with a capacitance of the capacitor C2 slightly larger than that at which oscillations occur. A further increase in capacity leads to a strong slowdown in the response of the system to changing external conditions. It should be noted that for the regulator with the described modification, the moment of its initial connection to the on-board network is very dangerous. Capacitor C2 is completely discharged at this time. Its charging current may well reach a dangerous value for transistors and disable it. Therefore, you should not significantly reduce the value of the resistor R8 or completely eliminate it. Although in the practice of the author of the failures of the modified regulator for the described reason did not happen, it is recommended to take measures to limit the current flowing through the base of the transistor VT1, for example, to include an additional resistor in the open circuit connecting the base to the connection point of resistors R6-R8, capacitor C1 and zener diode VD1 . Its value should be chosen as maximum, which does not noticeably worsen the operation of the regulator without capacitor C2. It is known that in order to increase the service life of the battery, the voltage in the on-board network must increase with decreasing temperature. Therefore, in practice, seasonal voltage adjustment is performed. In the regulator 59.3702-01, jumpers S1-S3, closing the resistors R1-R3, the average voltage of the generator can be changed within 13,8 ... 14,6 V. When the jumpers are removed, it decreases. Resistors R1-R3 can be replaced with one trimmer, which will allow you to smoothly adjust the generator voltage. The purpose of the LEDs HL1 and HL2 has not changed after the revision. They allow you to evaluate the performance of the control system. With the ignition on and the engine off, only the HL2 LED should light up, indicating that voltage is applied to the excitation winding of the generator. The glow of the HL1 LED when the engine is not running means that the regulator is faulty. When the engine is running, both LEDs light up. Reducing the frequency of its rotation or increasing the load on the on-board network leads to the fact that the brightness of the HL2 LED increases, and HL1 decreases. With an increase in speed or a decrease in load, the brightness changes in the opposite direction. The regulator before and after the described refinement was tested on an old car with an old battery. It was noticed that on this car, due to the oxidation of the contacts, the resistance of the electrical wiring increased noticeably, and the internal resistance of the battery increased. Both of these factors lead to a decrease in the stability of the voltage regulation system. With an unfinished regulator 59.3702-01, the ammeter needle, included in the break in the wire connecting the positive terminal of the battery to the car's on-board network, usually fluctuated with a swing of 5.10 A. Immediately after starting the engine, the swing often exceeded 10 A, headlights began to flash. When driving for a long time at high speed, the swing sometimes became less than 5 A, but this happened infrequently. After the refinement of the regulator discussed above, the ammeter needle never fluctuated with a swing of more than 0,5.1 A. After starting the engine, the headlights on never blinked. When driving for a long time at high speed, the range of oscillation of the arrow usually decreased so much that it was difficult to notice them. With further refinement, resistor R7 and capacitor C3 were removed from the controller under consideration, and a node was inserted between the base of transistor VT2 and the connection point of the collector of transistor VT1 with capacitor C1 and resistor R9, the circuit of which is shown in Fig. 2. In the diagram shown in fig. 1, the locations of circuit breaks are shown as crosses. Numbering of elements in fig. 2 continues what was started in Fig. 1.
An exponential pulse generator on logic elements DD1.1 and DD1.3 and a threshold device on element DD1.2 with a pulse amplifier on a transistor VT4 are added to the controller. Chip DD1 is powered by a voltage of 5 V from the integral stabilizer DA1. After completion, the transistor VT1 serves as an amplifier of the mismatch signal. The voltage on its load - resistor R9 - linearly depends on the difference between the current and nominal voltage values in the on-board network. This voltage with the help of resistors R13 and R14 is added to the pulses of the generator. The amount is fed to the input of the threshold device. As a result, pulses are formed at its output, the duration of which depends on the deviation of the voltage in the on-board network from the nominal value, and the repetition rate is constant (about 2 kHz). Through the amplifier on the transistor VT4, they enter the base of the transistor VT2 and control the voltage on the excitation winding of the generator.
The view of the modified regulator with the cover removed is shown in fig. 3. Additional parts are added to it by surface mounting. After installing this regulator on the car, the ammeter needle never fluctuated with a swing of more than 0,5 A. It can be assumed that with a low transient resistance of the electrical wiring contacts and with a new battery, the current fluctuations will be even less. Author: A. Sergeev
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