(1) Battery charger with UCG3906 as a dedicated chip
UC3906, as a dedicated chip for sealed lead-acid battery charging, has all the control and detection functions required to achieve the best charging of sealed lead-acid batteries. More importantly, it can make the charger’s various conversion voltages change with the change of the battery voltage temperature coefficient, so that the sealed lead-acid battery can reach the best state of charge in a wide temperature range.
1) The structure and characteristics of UC3906. The internal block diagram of UC3906 is shown as in Fig. 1. The chip contains an independent voltage control circuit and a current-limiting amplifier, which can control the driver in the chip. The output current provided by the driver is up to 25mA, which can directly drive an external series regulator tube to adjust the output voltage and current of the charger. The voltage sampling and current sampling detection comparator detects the state of charge of the battery and controls the input signal of the state of charge logic circuit. When the battery voltage or temperature is too low, the charge start comparator controls the charger to enter the trickle charge state. When the driver is cut off, the comparator can also output a 25mA trickle charging current. In this way, when the battery is short-circuited or reversely connected, the charger can only charge with a small current, avoiding damage to the battery due to excessive charging current.
2) The actual circuit is shown in Figure 2. The rated voltage of the battery is 12V, the capacity is 7A·h, VIN=18V, the battery float voltage VF=13.8V, the battery overcharge voltage Voc=15V, the maximum charging current Imax=500mA, The termination charging current IOCT=50mA, because the charger is always connected to the battery, in order to prevent the battery current from flowing back into the charger, a diode is connected in series between the series regulator tube and the output terminal. At the same time, in order to prevent the battery from discharging through the voltage divider resistors R1, R2 and R3 after the input power is interrupted, the R3 is grounded through the power indicator light-emitting diode (pin 7). After the 18V input voltage is added, VT1 is turned on and constant current charging starts. The charging current is 500mA, and the battery voltage gradually increases. When the battery voltage reaches 95% of the overcharge voltage Voc (that is, 14.25V), the battery enters the overcharge state, the charging voltage remains at the overcharge voltage, and the charging current begins to drop. When the charging current drops to the termination charging current (IOCT), the pin 10 of UC3906 outputs a high level, and the comparator LM339 outputs a low level, and the battery automatically switches to a floating charge state. At the same time, the full charge indicator LED lights up, indicating that the battery is fully charged. Electricity.
Among them, the floating charge voltage VF, overcharge voltage Voc, maximum charge current Imax and termination charge current IOCT and the relationship between R1, R2, R3 and R4, RS can be obtained from the following formula
Voc =VREF[1+(R1+R2)/R3+(R1+ R2)/R4]
Imax = 0.25V/RS
VF, Voc and VREF are proportional. The temperature coefficient of VREF is -3.9mV/℃, and when VREF (reference voltage) is at 25℃, it is 2.3V. Imax, IOCT, Voc and VF can be set independently.
(2) Solar lawn lamp controller
The solar lawn lamp is an independent photovoltaic power generation system, so the lawn lamp controller is the same as other controllers. In addition to controlling the normal operation of the lamp, it should also have protection functions such as anti-overcharge, anti-overdischarge and anti-reverse charging.
There are many controller circuits for solar lawn light, ranging from discrete components to integrated components, but because of its simple control process, it is not complicated for the entire circuit. Here are several control chips, such as ANA6601 F, YX80 Series, QX5252, 5253 and B18530, etc., these chips have few peripheral components and are relatively easy to manufacture, as shown in Figure 3. YX8182 is a solar LED drive controller, mainly used in applications where lithium batteries and 3 1.2V rechargeable batteries are connected in series. Its working principle is to use the energy of solar cells to work; sunlight shines on the solar cells during the day and converts the light energy into electrical energy for storage in the storage battery. The electrical energy of the storage battery at night provides power to the LED through the controller. Its advantages are safety, energy saving, convenience, environmental protection and adjustable output current.
The lithium battery overcharge protection voltage is 4.15-4.35V, and the lithium battery overdischarge protection voltage is 2.5-2.8V. The actual circuit of YX8182 is shown in Figure 4 and Figure 5.