Why does the primary coil of a single-ended flyback transformer need to be connected to a diode?

The single-ended flyback transformer is a common circuit design that is widely used in many electronic devices. In this circuit, the primary coil needs to be connected to a diode to ensure the normal operation of the circuit. Next, we will introduce the single-ended flyback transformer in detail and why the primary coil needs a diode.

1. Working principle of single-ended flyback transformer

Single-ended flyback transformer is a basic circuit structure that can convert high voltage into low voltage. Its main components are a transformer, capacitor and switching tube. When the switch is turned on, the inductor stores energy, causing the transformer to generate high voltage. When the switch is turned off, the capacitor releases the stored energy, causing the current to reverse.

2. Why does the primary coil need to be connected to a diode

In a single-ended flyback transformer, the primary coil needs to be connected to a diode, mainly to prevent the high-voltage kickback voltage from damaging the switching tube. . In this kind of circuit, when the switch tube is turned off, the electrical energy stored in the primary inductor will be quickly released, thus generating a high-voltage kickback voltage. This kickback voltage can reach 2 times the input voltage or even higher. If there is no diode protection, the reverse voltage will generate very high voltage pulses and burn out the switching tube. Therefore, in a single-ended flyback transformer, a diode is used to limit the size of the kickback voltage to protect the switching tube and the entire circuit.

3. The role of diode

A diode is an electronic device that can limit current in one direction. In a single-ended flyback transformer, the function of the diode is to limit the kickback voltage within a reasonable range. The characteristic of a diode is that it only allows current to flow in one direction, and in this direction, its resistance is very small, almost zero. However, if the reverse voltage exceeds the rated reverse voltage of the diode, the resistance of the diode increases dramatically, limiting the kickback voltage to a safe range.

4. Diode selection

In the design of single-ended flyback transformer, it is very important to select the appropriate diode, and different diodes have different characteristics and parameters. Factors that should be considered when selecting include the maximum operating voltage, reverse voltage and current capacity of the diode. In addition, the reverse recovery time of the diode is also very important. A diode with a short reverse recovery time can improve the efficiency and response speed of the entire circuit.

5. Summary

Single-ended flyback transformer is a common circuit design. The primary coil needs to be connected to a diode to protect the switch tube and the entire circuit. The function of the diode is to limit the kickback voltage within a reasonable range to avoid burning the switch tube. When selecting a diode, factors such as its parameters and reverse recovery time should be considered. In practical applications, reasonable selection of diodes can improve the efficiency and stability of the entire circuit.