How to use diodes in communication switch power supply design?

The main functions and applications of diodes in communication switching power supplies
(1) Rectification function
Application principle: Rectification is one of the most basic applications of diodes in communication switching power supplies. After the input of AC power, the rectifier circuit composed of diodes converts AC power into DC power. Common rectification circuits include half wave rectification, full wave rectification, and bridge rectification. Bridge rectifier circuit is widely used in communication switching power supplies due to its ability to fully utilize the positive and negative half cycles of AC power, output high DC voltage with small pulsation.
Selection points: In rectification applications, parameters such as reverse withstand voltage, forward average current, and forward voltage drop of diodes need to be considered. The reverse withstand voltage should be greater than the peak value of the input AC voltage to ensure that the diode will not be broken down when reverse biased; The forward average current should meet the output current requirements of the power supply; The smaller the forward voltage drop, the higher the rectification efficiency, and the smaller the heat generation of the power supply.
Attention: The heat dissipation problem of diodes cannot be ignored. Long term high current operation can cause serious heating of diodes, affecting their performance and lifespan. Therefore, in the design process, the circuit should be laid out reasonably to ensure that the diodes have good heat dissipation conditions, and heat sinks can be added if necessary.
(2) Continuation function
Application principle: In the inductive load circuit of a switching power supply, when the switching tube is turned off, the inductance will generate a reverse electromotive force, which may damage the switching tube. The freewheeling diode is connected in parallel at both ends of the inductor. When the switching transistor is turned off, the inductor forms a loop through the freewheeling diode, releasing the energy stored in the inductor and protecting the switching transistor.
Selection key points: The freewheeling diode needs to have fast recovery characteristics to reduce the turn off loss of the switching tube. At the same time, its reverse withstand voltage should be greater than the reverse electromotive force generated by the inductor, and the forward average current should be able to withstand the magnitude of the inductor current.
Attention: The shorter the reverse recovery time of the freewheeling diode, the less impact it has on the performance of the switching power supply. Therefore, when choosing a freewheeling diode, priority should be given to models with short reverse recovery time.
(3) Anti reverse connection function
Application principle: In order to prevent users from accidentally reversing the polarity of the power input and causing damage to communication equipment, a diode can be connected in series at the power input end to achieve anti reverse protection. When the polarity of the power supply is correct, the diode conducts and the power supply provides normal power; When the polarity of the power supply is reversed, the diode is turned off and the power supply cannot output.
Selection points: The forward voltage drop of the anti reverse diode should be minimized as much as possible to reduce the input loss of the power supply. At the same time, its reverse withstand voltage should be greater than the maximum input voltage of the power supply, and the forward average current should meet the output current requirements of the power supply.
Attention: Due to the fact that the anti reverse diode is always in a conducting state, it will generate a certain amount of power consumption. Therefore, a diode with lower power consumption, such as a Schottky diode, should be selected.
(4) Clamp protection function
Application principle: In communication switch power supplies, transient overvoltages such as lightning strikes and electrostatic discharge may affect the power supply, which may damage the electronic components inside the power supply. Clamp diodes can clamp overvoltage to a safe level, protecting subsequent circuits from damage. Common clamp diodes include voltage regulator diodes and transient voltage suppression diodes (TVS).
Selection points: The breakdown voltage of the voltage regulator diode should be selected based on the operating voltage of the protected circuit and the amplitude of the overvoltage; The reverse breakdown voltage and clamping voltage of TVS diodes should be appropriate to ensure timely action and voltage clamping within a safe range when overvoltage occurs.
Attention: The response speed of the clamp diode should be fast and able to quickly respond to overvoltage. At the same time, its power capacity should be large enough to absorb the energy generated by overvoltage.
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