The simplest example analysis of charger

　　In recent years, as the market for portable devices such as mobile phones, tablet computers, digital cameras, MP3 players, and personal digital assistants (PDAs) has continued to develop rapidly, various battery chargers have also developed rapidly. There are many types of chargers, mainly constant-voltage current-limiting chargers, constant-voltage/constant-current chargers, pulse chargers, fast chargers and trickle chargers, as well as multi-purpose chargers with lighting and other functions .

　　The charger shown in the figure only uses three components, so it is called the simplest charger. This circuit is a capacitive current-limiting constant-current charging circuit. The size of the charging current is determined by the current-limiting capacitor C. Whether charging a battery alone or charging several or more than a dozen batteries in series, the charging current does not change. D1 and D2 are rectifier diodes. The current-limiting capacitor should be a non-polar capacitor with a withstand voltage greater than 400V. The maximum charging current should not exceed 100mA. If you are charging a AA Ni-Cd battery with a capacity of 500mAh, the charging time is about 6 hours.

　　Simple nickel-cadmium battery charger

　　Nickel-cadmium battery is a kind of DC-powered battery. The nickel-cadmium battery can be charged and discharged more than 500 times, which is economical and durable. Its internal resistance is small, not only the internal resistance is small, it can be quickly charged, but also can provide a large current for the load, and the voltage change is small when discharging, it is a very ideal DC power supply battery.

　　The simple nickel-cadmium battery charger not only has the characteristics of constant current charging, but also prevents the battery from overcharging. The charger circuit is shown in the figure. The charger is to charge four nickel-cadmium batteries in series. 220V AC voltage is stepped down by capacitor C1, D1~D4 are rectified, R is true, D. After voltage stabilization, it flows into the nickel-cadmium battery through LED1 and LED2 to realize low-current constant-current charging. If the components are selected according to the parameters shown in the figure, the charging current is approximately 60mA.

　　At the beginning of charging, the voltage value of the four nickel-cadmium batteries in series is less than 5.4V, and the voltage regulator tube D is cut off at this time. As the charging continues, the terminal voltage of the nickel-cadmium battery gradually rises. When the voltage rises above 5. 4V, D is reversely broken down, and the true voltage across D is clamped at 7.5V. The nickel-cadmium battery The voltage will not rise continuously. If it continues to rise, LED1 and LED2 will turn from on to off, thus preventing the battery from overcharging and protecting the battery's service life.

　　Nickel-cadmium batteries can be charged and discharged more than 500 times and are economical and durable. Its internal resistance is small, not only the internal resistance is small, it can be quickly charged, but also can provide a large current for the load, and the voltage change is small when discharging, it is a very ideal DC power supply battery. Compared with other types of batteries, nickel-cadmium batteries can withstand overcharge or overdischarge.

　　The charger shown in the figure is simple and practical, and adopts international standards to ensure safe and reliable use. It uses half-wave rectification to charge the battery in two ways, each of which can charge two 5s. Nickel-cadmium batteries. The charging current is 50mA. Charging time is 14 hours.

　　The 220V city power is stepped down by transformer B to 9V. When the true terminal of D is a positive half cycle, D: on, D: off, the current is truly rectified by D, and R. Limit current to charge the battery. Similarly, when D: terminal is positive for half a cycle, D is cut off, D: on, current flows through D. Rectify, charge the other two batteries after R+ current limit. LED:, LED2 are charging indicator lights, R true, R: are the protective resistance of the light-emitting diode.

　　Self-made AA battery charger

　　With the current development trend of mobile phones with multiple functions, the power consumption of mobile phones has gradually increased, which has increased the requirements for batteries, but on the other hand, batteries have become smaller and smaller as the size of mobile phones gradually shrink. The power supply technology has not been improved accordingly, which has brought about the problem of reduced standby time and brought a lot of trouble to people who often go out to use mobile phones.

　　In order to solve this problem, this article introduces a mobile phone emergency charger, which uses two AA alkaline batteries or rechargeable batteries. After the circuit is boosted, it uses direct charging to charge the mobile phone without affecting the normal use of the mobile phone. .

　　The charger shown in the figure is simple, easy to make, and practical. Its working principle is roughly the same as the previous example. Four batteries can be charged at the four positions A, B, C, and D at the same time. Of course, it can also be charged at any position. One battery is charged, which overcomes the shortcomings of the above example that the Xijie battery must be charged at the same time.

　　After 220V alternating current is stepped down by double 6V transformer B, after full-wave rectification. Slowly charge each battery. R:, R. , R true, R: are current-limiting resistors, and D5, D6, D7, and D8 light-emitting diodes are charging indicators respectively.

　　Multifunctional constant current charger for nickel-cadmium batteries

　　In addition to being a constant current charger, the charging device can also be used as a current limiter and variable power load. The circuit is shown in Figure 4-7. The principle is: when the electrical current is less than the set value, BG: working in a saturated state, the voltage drop across ce is very small, when it exceeds the set value, BG enters a constant current state and acts as a current limiter. Because the current of BG: is adjustable, it can also be used as a variable power load. It can be seen that the load can be connected to the A and B terminals to limit the current. When it is only used as a charger, connect 2-4 sections to AB, and adjust W1 to adjust the charging current.

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