Language
Country/Area
No result found
Why is there mysterious energy stored inside the transformer when the switch is turned off?
In the field of power electronics, the flyback converter is a widely used device, especially playing an important role in AC/DC and DC/DC conversion. What makes this converter special is its ability to provide electrical isolation between input and output. The flyback converter is actually a buck-boost converter that doubles the voltage ratio by dividing the inductor into a transformer, further introducing the advantage of isolation.
Structure and principle
The basic structure of a flyback converter can be viewed as a buck-boost converter, except that it splits the inductor into a transformer. When the switch is closed, the primary winding of the transformer is directly connected to the input voltage source. At this time, the primary current and magnetic flux increase, and energy is stored inside the transformer. ”
When the switch is closed, the primary current of the transformer causes energy to be stored inside it, forming a temporary "mysterious energy".
When the switch is turned on, the primary current and magnetic flux decrease, the voltage in the secondary winding is positive, and the diode conducts forward, which allows the energy in the transformer to be released and supplied to the load. This operation allows the flyback converter to easily generate multiple outputs, providing flexibility in design. But to ensure that these output voltages match, you need to rely on the winding ratio of the transformer.
Principle of operation
The control schemes of flyback converters mainly include voltage mode control and current mode control. Both methods require signals corresponding to the output voltage. The first technique involves using an optocoupler to transmit the signal, while the second utilizes additional windings or sampling the output voltage on the primary side for control. Especially in more cost-sensitive applications, the development of a second technology can bring good results.
First technology utilizing optocouplers enables tight voltage and current regulation, which is particularly effective in demanding applications.
However, in some applications, optocouplers may have a negative impact on the mean time between failures (MTBF) of the system. In addition, by using primary-side sensing technology, good accuracy can be achieved while ensuring sufficient load. This design method is not only economical and affordable, but also can further improve the accuracy of voltage and current regulation.
Limiting factors
Although the flyback converter performs well in many aspects, it still has some limitations that affect the stability of the control. For example, in continuous mode, the bandwidth of the voltage feedback loop must be lower due to the right half-plane zero in the converter response. In addition, in current mode control, slope compensation is required when the duty cycle exceeds 50%.
High RMS and peak currents and high flux changes in the inductor can affect the efficiency of the converter. Therefore, it is particularly important to reduce the energy loss of switching elements.
Application fields
Flyback converters are commonly used in low-power switch-mode power supplies, such as mobile phone chargers and computer standby power supplies; they are also commonly used in low-cost multi-output power supply systems, and the power range is usually between 50 and 100W. In addition to these applications, flyback converters can also be used in high-voltage power supplies for televisions and monitors.
In addition, it can be used to generate high voltages in devices such as xenon flash lamps, lasers, and photocopiers, and is also commonly used in isolated gate driver designs.
Such a flyback converter is a device that is mysterious in both structure and application. What more innovative changes and applications will be developed in future power supply technology?
