Constant current and voltage-limited high-power battery charger solution

This machine can quickly and fully automatically charge batteries below 48 volts, with a maximum charging power of 600 watts. STK702-015 is a powerful large-scale thick-film switching power supply circuit, which contains auxiliary power supply, PWM control, output drive circuit, power field effect tube output circuit, etc. It forms a reliable switching voltage regulator circuit together with simple and dedicated peripheral circuits. After passing through the power filter, the AC power is divided into two paths: one path is supplied to the 31st and 32nd pins of the PWM pulse width control drive module STK702-015 after rectification and filtering, and the internal PWM starts to work, generating a 70KHZ switching signal and driving the power field effect tube for strong D-class amplification and output from the 25th and 26th pins. After a special LC circuit, the high-frequency transformer is driven to work, and after the secondary voltage is stepped down, it is output after half-wave rectification by the fast recovery diode MOR3040PT. There is no filter capacitor here, which is somewhat different from the ordinary switching power supply. Theory and practice tell us that pulsating DC has a better charging effect on the battery than smooth DC, and the charging pulse frequency of this machine is as high as 70KHZ, so the charging effect is better and the charging speed is faster. The other 300V DC path supplies power to the auxiliary switching power supply. The DC voltage output by the auxiliary power supply provides DC working voltage to the PWM pulse width control drive module after passing through a switching circuit.

When charging starts, the battery voltage is low, the voltage difference with the charger is large, and the initial charging current is very large. If it is not limited, it may damage the battery and the charger. Therefore, an LM358 op amp and a current sampling resistor form an automatic current limiting circuit in this machine. When the charging current exceeds the set value (for example, 10 amperes), the voltage drop on the current sampling resistor causes an LM358 op amp to output a low level, which controls the pulse width output by the PWM pulse width control driver module STK702-015 to become narrower, thereby reducing the output voltage and the charging current. When the battery is fully charged (generally, the battery voltage after full charge is 1.3 times the nominal voltage), the voltage comparator composed of another LM358 op amp outputs a low level, and the green light-emitting diode lights up, and the DC working voltage of the PWM pulse width control driver module is cut off at the same time. It means that charging is completed. At this time, the charger is only powered by the auxiliary power supply, and the power consumption is very small.