Abstract: Introduced one kind of novel seal lead-acid battery battery charger’s principle of design, has given the determination charge parameter method and the fundamental formula. Simultaneously gave one kind simply practical, the work to be stable, and perform reliably 12V seal lead-acid battery double level floating battery charger’s practical application electric circuit.
Key word: Seal lead-acid battery; Battery charger; Surcharge; Floats the charge
The seal exempts the maintenance lead-acid battery, because has seals, pollution merits and so on does not have divulging, not to have, in recent years in domestic and foreign obtained the widespread application. But because the charge technology cannot adapt exempts maintains battery’s special request and the charge method not correct causes it very inaccessibility stipulation the cycle life.
UC3906 seals the lead-acid battery charge special-purpose chip, it has the complete control which and the measuring ability the seal lead-acid battery best charge needs. 熕 can cause the battery charger each kind of transformation voltage more importantly to change along with the battery voltage temperature coefficient change, thus enables the seal lead-acid battery to achieve the best charge condition in the very wide temperature range.
1 UC3906 structure principle
1.1 UC3906 structural properties
UC3906 internal structure as shown in Figure 1. This chip content independent voltage control return route and the current limiting amplifier, it may control in the chip the driver. The driver provides the output current reaches 25mA, but the direct drive exterior series regulation tube, adjusts battery charger’s output voltage and the electric current. The voltage and the electric current examination comparator may use in examining accumulator cell’s charge condition, meanwhile may use for to control the charge state logic electric circuit’s input signal.
When the battery voltage or the temperature are excessively low, the charge enables the comparator to be possible to control the battery charger to enter the trickling charge condition. When the driver cuts off, this comparator can also output the 25mA trickling charge electric current. Thus, when the battery short-circuits or ties hands behind the back, the battery charger can only by the undercurrent charge, thus avoided damaging the battery oversized because of the charging current.
A UC3906 very important characteristic is its internal precision voltage reference is completely consistent along with the ambient temperature change rule with the lead-acid battery voltage temperature characteristic. At the same time, this chip only needs 1.7mA the input current to be possible to work, thus may reduce the chip the power loss, realizes to the working conditions temperature accurate examination, guarantees the battery both the sufficient electricity and not to be able the serious surcharge. In addition, the UC3906 chip interior also includes an input undervoltage examination electric circuit by to carry on the initialization to the charge cycle, and may actuate a logical output. After adding on inputs the power source, component’s 7 feet may also instruct the power source condition.
1.2 charge parameter determination
Uses UC3906 only to the very few exterior primary device be possible to realize for seals lead-acid battery’s fast precise charge. Shown in Figure 2 is a complete battery charger electric circuit. And by RA, RB and Rc is composed the resistance bleeder network may use for to examine rechargeable battery’s voltage. In addition, this electric circuit may also through (VREF) compare with the precise reference voltage determined that the floating voltage, the surcharge press with the trickling charge threshold voltage.
An accumulator cell’s charge cycle may divide into the big electric current rapid charge rate condition, the surcharge condition according to the time and floats the charge condition and so on three kinds, its charge parameter mainly has VF, Voc, IMAX, IOCT and so on. They with between RA, RB, Rc, the Rs relations may reflect from the following formula:
VOC=VREF 煟 guarantees RA/RB RA/RC
VF=VREF 煟 guarantees RA/RB
IMAX=0.25V/Rs
IOCT=0.025V/Rs
In the above formula, VF, Voc and VREF are proportional. The VREF temperature coefficient for - 3.9mV/℃, IMAX, IOCT, Voc, VF may establish independently. So long as the input power source permission or the power tube may withstand, the IMAX value may as far as possible big. Although certain factories called, if has had the sufficient protection circuit, the charging rate may achieve even surpasses 2C, but the battery manufacturer recommendation’s charging rate scope is C/20~C/3. The surcharge termination electric current IOCT choice should cause the battery close 100% charge as far as possible. The appropriate value is decided by Voc and when Voc battery charging current weaken characteristic. IMAX and IOCT separately examine amplifier’s bias voltage and the electric current examination resistance Rs decision by the current limitation amplifier and the electric current. VF, the Voc value the network which by materials for internal reference voltage VREF and non-essential resistance RA, RB, Rc is composed decided.
Figure 2 pair of level floating battery charger basic electric circuit
2 practical application electric circuits
Figure 3 is in an environment parameter reflectoscope reflector’s battery charger’s practical application electric circuit. And: Battery’s rated voltage is 12V, the capacity is 7Ah, VIN=18V, VF=13.8V, Voc=15V, IMAX=500mA, IOCT=50mA. Because the battery charger beginning terminates on the accumulator cell, to prevent accumulator cell’s output current inflow battery charger, should in connect between the regulation tube and the out-port the string enters a diode. After simultaneously to avoid inputs the power source interrupt, the accumulator cell through the voltage-division resistance R3 electric discharge, when design R3 through the power source instructed that the transistor (7 feet) connect.
After the 18V input voltage joins, the series power tube TIP42C breakover, starts the big electric current constant flow charge, the charging current is 500mA, by now the charging current maintained invariable, the battery voltage elevates gradually. When the battery voltage achieves the surcharge presses Voc 95% (i.e. 14.25V), the battery changes over to the surcharge condition, this time the charging voltage maintains at the surcharge voltage, the charging current starts to drop. When the charging current falls has been to the charge termination electric current (IOCT), the UC3906 10 feet output the high level, comparator LM339 output the low level, the accumulator cell automatically change over to the floating condition. Simultaneously is sufficient the electricity instruction photo tube illumination, instructs the accumulator cell already sufficient electricity.
Figure 3 12V seal lead-acid battery double level floating battery charger electric circuit
3 conclusions
Because only need the very few exterior part be possible to realize battery’s precise rapid charge rate in the very wide temperature range, therefore used UC3906 to simplify battery charger’s design process. This battery charger indicated in the practical application: It has simply practical, the work is stable, merits and so on perform reliably.
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