On-board voltage stabilizer on the KR1171SP47 chip. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Automobile. Electronic devices

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The electronic on-board voltage stabilizer failed on the car. What is the owner doing? If he is not a radio amateur, he buys a new one and replaces the damaged one with it. The radio amateur, on the other hand, will independently manufacture the original device, and such that it will not yield to the old one in terms of characteristics (and often surpass it). The article below is another confirmation of what has been said.

In the event of a failure of an automobile voltage stabilizer (made in the form of a small-sized unit built directly into the generator housing), it is not always possible to purchase a serviceable one for replacement without problems. Deciding to make a self-made stabilizer instead of 17.3702 for the generator 37.3701 (VAZ 2104, 2105, 2107, 2108, 2109) based on publications in the Radio magazine, I immediately ran into the need to use only miniature parts in the device and minimize their number. This was dictated by the lack of free space for installing a stabilizer.

One of the solutions to this problem is the use of a KR1171SP47 microcircuit voltage drop detector (foreign analogue - PST529) in the stabilizer [1]. The detector according to the scheme (Fig. 1, a) is the best suited for the stabilizer as its first stage. The principle of operation of the detector is illustrated in fig. 1b.

When the increasing input voltage reaches the threshold level (4,7 V for KR1171SP47 and 4,8 V for PST529), the detector abruptly switches from the zero state to the unit state (the output voltage is removed from the load resistor connected between pins 1 and 3). The temperature coefficient of the detector switching voltage is within ±0,03%/°C. The device is produced in a plastic three-terminal housing KT - 26. Own current consumption does not exceed several tens of microamperes.

The automobile voltage stabilizer must control the current through the excitation winding of the generator so that the voltage on the battery is within 13,8 ... 14,1 V [2].

If the voltage drops out of this range, the battery will wear out prematurely.

The detector in the stabilizer can be powered from the output of a voltage divider consisting of a zener diode and a current-setting resistor. The zener diode must be such that the sum of the stabilization voltage and the detector operation voltage is within the specified limits, i.e. with a 9,2 V zener diode and a KR1171SP47 detector, the stabilizer will provide a battery voltage of 13,9 V (with PST529 - 14 V).

Since the current of the excitation winding during switching can reach several amperes, a powerful composite transistor will be required at the output of the stabilizer. The schematic diagram of the stabilizer is shown in fig. 2.

Diodes VD2 and VD3 protect the powerful transistor VT1 from high voltage surges. The operation of the stabilizer does not have any features. The width of the voltage "hysteresis" loop on the battery is entirely determined by the characteristics of the comparator in the voltage detector; it is close to 0,2 V.

Work on the manufacture of a new stabilizer begins with the disassembly of the failed one (17.3702). To do this, turn off the outputs of the stabilizer and remove it from the generator. Unscrew the M3 screw, which attaches the brass square to the body, and solder (remove the solder) two leads - the one closest to this screw and the one closest to the first - these are the leads from the graphite collector brushes located on the opposite side of the body and marked with the letters Ш and В. Desoldering is most convenient carry out using a soldering iron and a device for suctioning molten solder. Then the square with the parts is pulled out along the plastic guides of the case, the board is soldered from the three corner leads and the transistors are dismantled.

The connection diagram of the manufactured stabilizer to the generator 37.3701 is shown in fig. 3. The numbering of the stabilizer parts (it is circled with a dotted line) is the same as in fig. 2. In the generator (it is circled with a dash-dotted line) OB is the excitation winding of the generator.

All elements of the stabilizer (except the VD2 diode and the VT1 transistor) are mounted on a 33x24 mm printed circuit board made of foil fiberglass 1 mm thick. The drawing of the board is shown in fig. 4. The transistor is fixed in its place on the square and the leads are bent at a right angle so that when the board is installed (with the side with the parts inside), they each enter their hole.

Nearby, as in the factory version, you can mount the same second transistor and connect them in parallel. However, an increase in the reliability of the stabilizer can be expected only if both transistors are either carefully selected to be the same in terms of parameters, or their modes are equalized in terms of collector current (for which equalizing resistors of low resistance are included and selected in their emitter circuit).

It is really possible to increase the reliability of the operation of a node with one (and not two) transistors if KT973A is replaced with KT853A. To do this, however, you will have to slightly adjust the printed circuit board, taking into account the difference in their pinout. Thermally conductive paste should be placed under the transistors.

Diode VD2 is soldered to pins W and B on the stabilizer body.

During the final assembly of the stabilizer, the mounted board is installed in place of the old one, soldered to the elbow terminals and the transistor terminals are soldered. Do not forget to provide a reliable connection between the common (negative) conductor of the board and the elbow. To do this, a hole A is provided on the board - a wire jumper with a diameter of 0,8 mm is soldered into it, the second end of which is soldered to the square from the outside. The square with the board along the guides is pushed into its original place and fixed with an M3 screw. The final operation is the soldering of the conclusions W and B, soldered at the beginning of disassembly.

Before mounting the assembled stabilizer on the generator, you should make sure that it is working. This will require a constant voltage source, regulated within 2 ... 16 V, capable of delivering a current of 4,5 ... 5 A to the load (in extreme cases, a nine-ampere LATR with a powerful diode rectifier and an effective smoothing filter is suitable), a load resistor with a resistance of 5 ... 10 Ohms with a power of at least 50 W and a DC voltmeter with a scale of 16 V (or any avometer).

Conclusions C and B of the stabilizer are connected to the positive output of the source, and the case is connected to the negative. A load resistor is connected between the positive output of the source and the output Ш of the stabilizer (it can be temporarily soldered to the soldered output on the stabilizer elbow closest to the M3 screw), a voltmeter is connected between the output Ш and the stabilizer body.

The power supply is set to a minimum output voltage and connected to the network. When the supply voltage is increased to 9,2 V, the voltmeter should show the same increase. A further increase in the supply voltage will lead to the opening of the zener diode VD1, while the detector starts working and the transistor VT1 opens - the voltmeter readings should decrease to the saturation voltage of the collector-emitter of the transistor, i.e., to about 1,5 V.

If you continue to increase the supply voltage, then the voltmeter readings will remain unchanged. However, at around 14 V, the detector will switch and transistor VT1 will close - the voltmeter should show a voltage of 14 V.

After the described check, the stabilizer is installed in its place on the generator, all connections are restored and tested as a whole.

In conclusion, it should be noted that, along with KR1171SP47, other voltage detectors of this series can be used in the stabilizer with the same success. It is only necessary to select a zener diode VD1 (see Fig. 2) so that its stabilization voltage in total with the operation voltage of the detector used is within 13,8 ... 14,1 V. So, to work with the KR1171SP64 detector, a zener diode with a voltage of 7,6 .XNUMX V.

If it is required to ensure the minimum possible value of the stabilization voltage temperature coefficient, a 5,6 V zener diode and a KR1171SP87 detector should be used.

The zener diode VD1 in the voltage divider (Fig. 2 and 3) can be replaced with a resistor, choosing it so that the detector operates at a voltage of 13,8 ... 14,1 V between terminal B and the common wire. This will slightly increase the "hysteresis" of the stabilizer, but it will improve its thermal stability and get rid of the selection of the zener diode.

Literature

1. Integrated circuits. Microcircuits for linear power supplies and their application. Handbook (second ed., corrected and supplemented). - M.: DODEKA, 1998.
2. Zhiguli cars. VAZ 2104, 2105, 2107. Device. Repair. Handbook (Second ed.). - M.: Transport, 1991.

Author: Yu.Kitrar, Samara

See other articles Section Automobile. Electronic devices.

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