The application principle of diodes in chargers

1, Working principle of diode
A diode is composed of a PN structure formed by a P-type semiconductor and an N-type semiconductor. Space charge layers are formed on both sides of the PN junction interface, and a self built electric field is established. When there is no external voltage, the diffusion current caused by the difference in carrier concentration on both sides of the PN junction is equal to the drift current caused by the self built electric field, and the diode is in an electrical equilibrium state.
When there is a forward voltage bias from the outside, the external electric field and the self built electric field cancel each other out, causing an increase in the diffusion current of carriers and leading to forward current. At this point, the diode is in a conducting state. When there is a reverse voltage bias from the outside, the external electric field and self built electric field are further strengthened, forming a reverse saturation current (or leakage current) that is independent of the reverse bias voltage value within a certain range of reverse voltage. At this point, the diode is in the off state.
2, Application of diodes in chargers
Prevent reverse current
During the charging process, if the cable is accidentally short circuited or reversed, the AC power source may attempt to supply power in reverse to the battery. At this point, the diode quickly conducts, allowing current to flow along the normal path and preventing the battery from being damaged by reverse voltage. This feature is crucial in protecting batteries and circuit boards.
Rectification effect
Chargers typically need to convert AC power to DC power for battery use. The diode plays the role of a rectifier in this process. For example, after being rectified by diodes, 220 volt AC power will become a full upper half cycle DC power. This rectification effect ensures a stable supply of current and provides the required DC energy for the battery.
Filtering effect
In the design of charging stations, diodes can also help filter out high-frequency pulsating components in the AC power supply, providing smoother DC input to the battery management system. This is particularly important for situations such as electric vehicles that require stable DC input.
Isolation circuit
Diodes can also be used as part of circuits to isolate different parts of the power supply, ensuring the safety and stability of the circuit. This isolation effect helps prevent the spread of faults in the circuit and improve the reliability of the entire system.
3, Selection and wiring of diodes
The selection of diodes is crucial in chargers. Usually, it is necessary to choose diodes with appropriate rectification characteristics, fast response, and high voltage resistance, such as Schottky diodes or fast recovery diodes. These diodes can meet the strict requirements of chargers for current and voltage, while providing stable performance.
In terms of wiring, it is necessary to ensure the correct connection of diodes. Usually, the positive electrode (anode) of a diode is connected to the input terminal, and the negative electrode (cathode) is connected to the output terminal. This connection method ensures that the diode conducts under forward voltage and shuts off under reverse voltage, thereby protecting the circuit.
4, Practical application cases of diodes in chargers
In practical applications, chargers may use multiple diodes for rectification. For example, some chargers use four diodes to form a full wave rectification circuit to more effectively convert AC power to DC power. This circuit structure can fully utilize each half cycle of AC power and improve rectification efficiency.
In addition, some chargers also adopt additional protective measures, such as using inductor mode and installing fuses, to further enhance the safety performance and stability of the charger. These measures are used in conjunction with diodes to ensure that the charger operates efficiently while also ensuring the long-term safe use of the battery and circuit board.
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