Thermally compensated voltage regulator. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Regulators of current, voltage, power

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One of the important elements of the electrical equipment of the car is the battery (hereinafter referred to as the battery). Unlike other electrical equipment, the battery has a limited service life, and therefore (given its considerable cost), increasing its resource to the maximum value is an urgent task for motorists.

Since the battery is installed on the car almost all the time, to solve this problem, it is necessary to maintain the optimal charging voltage generated by the standard voltage regulator (hereinafter referred to as the regulator), which is part of the car's electrical equipment. The disadvantage of traditional regulators is their maintenance of a fixed voltage (usually 14,1 ± 0,2 V), although it is known ([1]) that this voltage should change in accordance with the expression: Ut=U0(1+KeT), where Ut is the voltage , which must be applied to the battery terminals to ensure the optimal charge current, at an electrolyte temperature of T ° C; U0 = 14,56 V - voltage that must be applied to the battery terminals to ensure the optimal charge current, at an electrolyte temperature of 0 ° C; Ke = -1,65x10-3 1/°С - temperature coefficient of electrolyte resistance; T is the temperature of the electrolyte, °C.

It follows from this expression that the optimal voltage generated by the regulator when the electrolyte temperature changes from -10 to +40 °C should change from 14,8 to 13,6 V, respectively. Since the deviation of the vehicle network voltage from the optimum by 0,4 V reduces the battery life by 25%, i.e. for approximately 1 year (according to other sources [2] a deviation of the charging voltage by 10 ... 12% from the optimal one reduces the battery life by 2 ... 2,5 times), the need for temperature correction of the regulator is indisputable. For this purpose, a regulator was developed that has the function of controlling the voltage maintained in the car's electrical network. From the previously published voltage regulators containing a similar function [2], the proposed one differs in the simplicity of the circuit, unification (installed instead of the standard regulator) and the absence of any adjustments, since the selection of circuit elements is determined by calculation.

The regulator circuit (see figure) does not have any features. A voltage comparator is connected to the diagonal of the measuring bridge. An exemplary voltage source is connected to one of the arms of the measuring bridge, and a thermal sensor having thermal contact with the electrolyte is connected to the other. From the output of the comparator, the signal, through an open emitter, is fed to a powerful output switch, switching the current through the excitation winding of the generator.

Elements of the measuring bridge - R1, R2, Rd, R3, VD1. Resistor R3 and Zener diode VD1 form a reference voltage source. Resistor R4 provides feedback to obtain the effect of electrical hysteresis in the operation of comparator DA1. Capacitor C1 is designed to suppress interference induced on the wire leading to the temperature sensor Rd. Comparator DA1, depending on the signal received at its direct input, controls the operation of the transistor VT1. Resistors R5, R6 limit the output current of the open emitter of the comparator, and also provide a bias to the base of the transistor VT1, which is necessary for its reliable opening and closing. Transistor VT1 switches the current through the excitation winding. Diodes VD2, VD3 protect the transistor VT1 from self-induction voltage surges that occur on the excitation winding at the time of its locking.

The voltage from the battery terminals is supplied to the voltage divider R1, R2, Rd. The signal taken from the temperature sensor Rd and changing in proportion to its resistance is fed to the direct input of the comparator DA1 and compared with the reference voltage generated by the zener diode VD1 and supplied to the inverse input of the comparator. If the signal at the direct input is less than the reference voltage, the comparator DA1 outputs a signal to the transistor VT1, which opens and turns on the excitation winding of the generator. When the signal at the direct input of the comparator exceeds the reference voltage, the transistor VT1 is locked and the excitation winding of the generator is turned off. Due to feedback through the resistor R4, the difference between the signal levels at the direct input of the comparator, at which it gives a signal to turn on and turn off the transistor VT1, is approximately 0,05 V.

Adjustment of the device is reduced to the calculation and selection of the values ​​of the elements of the measuring bridge. This requires a thermometer with a division value of 0,1 °C and a combined measuring instrument capable of measuring voltage to an accuracy of 10 mV and resistance to an accuracy of 1 Ω.

Example.

1. Measure the resistance of the temperature sensor at a known temperature, for example, at T=21 °C Rd=1883 Ohm.

2. According to the formula Rt \u0d R1 (0 + KmT), where Rt, R0 are the resistance of the copper conductor at a temperature of T ° C and 4,26 ° C, respectively; Km=10x3-1 0/°С - temperature coefficient of copper resistance; T - temperature of the temperature sensor (electrolyte), ° C, find R1728 = XNUMX Ohm.

3. Using the obtained value of R0, the same formula calculates the values ​​of Rt for temperatures of -10 and +40 °C; R-10=1655 Ohm; R+40=2023 Ohm.

4. By connecting the +14 V power supply to terminal "B", measure the reference voltage Uop = 8,84 V.

5. Consistently for a temperature of -10 and +40 ° C, find the total resistance of the resistors R1, R2 (R1 + R2) t \uXNUMXd (UtRt / Uop) - Rt,

where Ut is the voltage that must be applied to the battery terminals to ensure the optimal charge current, at an electrolyte temperature of T ° C (U-10 \u14,8d 40 V; U + 13,6 \u1d 2 V) (R10 + R1116) -1 \u2d 40 ohm; (R1089+RXNUMX)+XNUMX=XNUMX Ohm.

6. The average value of these two values: (R1 + R2) cp \u1102,5d XNUMX Ohm.

7. Taking into account that R2~2R1, the closest resistance values ​​of the specified resistors R1=360 Ohm, R2=750 Ohm are chosen according to the nominal resistance range.

With this calculation, the relative error in the selection of the resistances of resistors R1, R2 does not exceed 1%.

The regulator is placed in the body of a regular, failed "chocolate" type regulator, for example Ya112-V. To do this, open the glued cover, remove the old "stuffing" and clean the metal base. The transistor VT1 is pressed tightly against the metal base, having previously placed a mica gasket lubricated on both sides with LITOL-24 grease and soldered the collector mounting plate to the inside of the "Sh" contact pad, and the emitter output to the base of the case. Comparator DA1, capacitor and resistors are located on a separate circuit board.

Using the base of the housing and the standard contact pads "Sh", "B", "C", the rest of the elements and in-circuit connections are mounted by surface mounting. To connect the temperature sensor, use a free contact pad (indicated by the symbol "A" in the diagram), located on the same diagonal with the contact pad "B". The temperature sensor itself is crimped with a copper plate, to which one of its leads is soldered, and filled with epoxy. The second output of the winding is connected by a separate wire to the contact pad "A". Since this circuit is low current, there are no special requirements for the wire. The copper plate is chosen in such a size that a mounting hole is drilled in it for installation under the mounting screw of the "collar" of the negative battery terminal.

The terminal itself with the part of the "negative" bus extending from it is thermally insulated from the environment. Given the relatively high thermal conductivity of the lead plates of the battery, with this method of fastening the temperature sensor, the minimum temperature difference between the electrolyte and the sensor is obtained. All elements of the regulator are varnished, the cover is glued and installed in its original place.

The regulator uses the following resistors: R5 - type MLT-0,25; the rest of the MLT-0,125 type, capacitor C1 of the KM type

5. As a zener diode VD1, you can use any zener diode with a stabilization voltage from 6 to 9 V, but given that the regulator is installed on the body of the generator, which changes its temperature over a wide range during engine operation, the zener diode is selected with the smallest possible temperature coefficient of voltage change, for example KS191F, D818E. It is desirable to determine its thermally stable point by the method described in [3]. As a DA1 comparator, you can use a K554CA3 type comparator, but it should be borne in mind that this microcircuit has a different pin numbering and somewhat larger overall dimensions than indicated in the diagram. The KT829B transistor can be used as an output key, but in any case, the current transfer coefficient of the transistor VT1 must be at least 50. As diodes VD2, VD3, you can use KD209A, and as a temperature sensor, a winding with a resistance of 1 ... 2 kOhm of a small-sized relay, for example , RES-60, made with copper wire.

References:

1. Handbook of circuitry for a radio amateur / Ed. V.P. Borovsky - K .: Technique, 1987.
2. Lomanovich V. Thermally compensated voltage regulator // Radio.-1985.- No. 5.- P.24-27.
3. Inozemtsev V. Determination of the thermostable point of zener diodes // Radio.- 1983.-№8.- P.31.

Author: V.G. Petik

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