401030 lipo battery.A design based on a simple battery automatic constant current charging circuit

0 Introduction With the explosive growth of the digital industry, more and more high-tech digital products have appeared on the market, all of which are inseparable from rechargeable batteries, especially nickel-metal hydride rechargeable batteries, which are currently the main variety of large-capacity batteries. It is widely used in communication, transportation, electric power and other departments, and it is also used in other smart meters...

0 Preface


With the explosive rise of the digital industry, more and more high-tech digital products have appeared on the market, all of which are inseparable from rechargeable batteries. In particular, nickel-metal hydride rechargeable batteries are currently an important variety of large-capacity batteries and have been used in communications, It is widely used in transportation, electric power and other departments. It is also the most commonly used backup battery in other smart instruments, and the battery is inseparable from the charger. This article introduces a battery automatic constant current charging circuit based on discrete components. It focuses on the composition, structural characteristics, working principle and circuit adjustment of the circuit.


1 Overall circuit design idea


The overall block diagram of a simple battery automatic constant current charging circuit is shown in Figure 1. It is composed of 5 parts: transformer rectifier circuit, constant current occurrence circuit, automatic power-off circuit, display circuit and power supply circuit.
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The function of the transformer rectifier circuit is to convert the 220V AC power in the public power grid into appropriate current and voltage signals to supply signals for subsequent circuits. The function of the constant current generating circuit is to use a transistor current source to generate a constant charging current for the circuit. The function of the automatic power-off circuit is to use the voltage characteristics of the transistor when it is saturated and conductive, so that the circuit can automatically cut off the power supply when the battery is fully charged. The function of the display circuit is to use light-emitting diodes to display the state of the circuit starting and ending charging. The function of the regulated power supply circuit is to supply DC voltage to all the above circuits.


1.1 Design of transformer rectifier circuit and power supply circuit


The transformer rectifier circuit and stabilized power supply circuit (shown on the left side of the dotted line in Figure 2) are mainly composed of a transformer, a diode bridge circuit, and a capacitor. The transformer adopts a conventional core transformer and converts the 220V AC power in the public power grid into 12V AC power, which is then rectified and filtered by capacitor C1 through a diode bridge circuit. The rectified signal is derived from VC1. On this basis, connect the three-terminal voltage regulator CW7812 and capacitors C3 and C4 (shown on the right side of the dotted line in Figure 2), so that the entire circuit forms a regulated power supply circuit. The DC voltage of +12V is supplied from point B.


1.2 Design of constant current circuit


As shown in Figure 3, the transistor current source composed of the voltage regulator VZ1, the transistor VT1, the resistor R1, and the capacitor C2 supplies a constant current. The voltage of the voltage regulator is 5V and R1 is 51Ω. At this time, IC≈1OOmA. As the circuit recharging current.
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1.3 Design of automatic charging detection circuit and indication circuit


As shown in the circuit of Figure 4, the automatic power-off circuit is composed of transistor VT2, voltage follower A1, voltage comparator A2, resistors R4, R5, R6, R7, R8, R11 and variable resistor Rp1. When charging starts, the voltage comparator outputs a high level, VT2 is turned on, VT1 is also turned on, and the indicator light-emitting diode lights up to charge the battery. You can first set the transfer switch to 1 to charge one battery, and set the transfer switch to 2 to charge two batteries, and so on, to charge 1-4 batteries. When the battery is fully charged, the voltage comparator outputs low level, VT2 is cut off, VT1 is not conductive, the light-emitting diode goes out, and charging is completed.


2 Simple charger general circuit schematic diagram and component list


2.1 Simple charger general circuit schematic diagram


The overall circuit diagram of a simple battery automatic constant current charging circuit is shown in Figure 5. It is composed of 5 parts: transformer rectifier circuit, constant current occurrence circuit, charging detection circuit, display circuit and power supply circuit. What should be noted in the general circuit diagram is that the connections between each unit circuit must be accurate, and the layout of each part must be reasonable.


2.2 Components list


The component list used in this design is shown in Table 1.


3Conclusion


The simple battery automatic constant current charging circuit introduced in this article has the characteristics of simple circuit, complete functions, and convenient adjustment. It is suitable for self-production by radio enthusiasts and electronic training for higher vocational students.