Flyback transformers, advantages and disadvantages of flyback transformers
Flyback transformers are also known as single-ended flyback or "Buck-Boost" converters. Its output is named after its primary winding obtains energy when it is disconnected from the power source. The flyback converter is favored by many development engineers for its simple circuit structure and low cost.
Flyback transformers are suitable for low power power supplies as well as various power adapters. However, the difficulty in the design of the flyback converter is the design of the transformer because of the wide input voltage range, especially at low input voltage and full load conditions. The transformer will operate in continuous current mode and at high input voltage and light load conditions. Will work in discontinuous current mode again.
advantage:
The advantages of the flyback transformer are:
1. The circuit is simple and can provide multiple DC outputs efficiently, so it is suitable for multiple groups of output requirements.
2. High conversion efficiency and low loss.
3. The transformer turns ratio is small.
4. When the input voltage fluctuates within a large range, it can still have a more stable output. At present, it is possible to realize the requirement that the AC input be in the range of 85~265V without switching to achieve stable output.
Disadvantages:
The disadvantages of the flyback transformer are:
1. There is a large ripple in the output voltage, and the load adjustment accuracy is not high, so the output power is limited, and it is usually applied below 150W.
2. When the converter transformer operates in the continuous current (CCM) mode, it has a large DC component, which easily leads to saturation of the magnetic core. Therefore, an air gap must be added to the magnetic circuit to cause the transformer to become bulky.
3. The transformer has a DC current component and will work in both CCM / DCM modes at the same time, so the transformer is more difficult to design, the number of repeated adjustments is more than the forward type, and the iterative process is more complicated.
When the switching transistor Tr ton is switched, the transformer primary Np has a current Ip and stores energy therein. Since Np has an opposite polarity to Ns, the diode D is reversed biased and turned off, and no energy is transmitted to the load. When the switch Tr off is switched off, it can be seen from Lenz's law that the primary winding of the transformer will generate a reverse potential. At this time, the diode D is conducting forward, and the load has current IL flowing.
Flyback transformers generally work in two ways:
1. Discontinuous Inductor Current Mode (DCM) or Full Energy Conversion: All energy stored in the transformer is transferred to the output during the flyback period (toff).
2. Inductor CCM (Continuous Inductor Current Mode) or "Incomplete Energy Conversion": Part of the energy stored in the transformer is retained at the beginning of the next ton period at the end of toff.
The electrolyte material inside the electrolytic capacitor, which has charge storage, is divided into positive and negative polarity, similar to the battery, and cannot be connected backwards.A metal substrate having an oxide film attached to a positive electrode and a negative electrode connected to an electrolyte (solid and non-solid) through a metal plate.
Nonpolar (dual polarity) electrolytic capacitor adopts double oxide film structure, similar to the two polar electrolytic capacitor after two connected to the cathode, the two electrodes of two metal plates respectively (both with oxide film), two groups of oxide film as the electrolyte in the middle.Polar electrolytic capacitors usually play the role of power filter, decoupling (like u), signal coupling, time constant setting and dc isolation in power circuit, medium frequency and low frequency circuit.Non-polar electrolytic capacitors are usually used in audio frequency divider circuit, television S correction circuit and starting circuit of single-phase motor.
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