An Active Clamp Flyback Switching Power Supply Circuit

Abstract

An active clamp flyback switching power supply circuit, based on the LCL flyback converter, keeps the N in the transformer B P1 The power supply is terminated with the same name, the second primary winding N P2 The terminal of the same name is grounded, N P1 and N P2 For bifilar parallel winding, one end of capacitor C1 is connected to N P1 The opposite end is connected, and the other end is connected to N P2 Homo-ends connected, N P2 The end of the same name is connected to the power supply through the clamping network 400 connected in series with the field effect transistor Q2 and C3, which realizes: when Q1 is saturated and turned on, N P1 and N P2 are excited, when Q1 is turned off, the secondary side N S To output energy, the primary side is a voltage source connected in series with the leakage inductance, Q2 is turned on, and C3 resonates with the leakage inductance, so that Q1 can be turned on at zero voltage; under light load, Q2 is turned on every few cycles, during which the voltage of C3 will show a Step-like growth, when Q2 is turned on, C3 and the leakage inductance resonate, so that Q1 can be turned on with zero voltage, and at the same time further reduce the power consumption of driving Q2 at light load, and realize the energy recovery of the demagnetization circuit with a duty cycle greater than 0.5. Especially at light load, the conversion efficiency is improved.

Description

technical field [0001] The invention relates to the field of switching power supplies, in particular to a flyback switching power supply using active clamping. Background technique [0002] Switching power supplies are widely used. For occasions where the input power is below 75W and the power factor (PF, Power Factor, also known as power factor) is not required, the flyback switching power supply has attractive advantages: the circuit topology is simple , wide input voltage range. Due to the small number of components, the reliability is relatively high, so it is widely used. For convenience, many documents are also called flyback switching power supply, flyback power supply, and flyback converter. Japan and Taiwan are also called flyback converters, flyback switching power supplies, and flyback power supplies. Common topologies for AC / DC converters such as Picture 1-1 , the prototype of the figure comes from page 60 of "Switching Power Converter Topology and Design" wri...

AI Technical Summary

Problems solved by technology

[0004] The inductance of the primary winding is also low, and it often happens that the calculated number of turns cannot be tiled from the left to the right of the wire slot that is full of the skeleton. When the working voltage is high, the sandwich series winding method can be used. At low working voltage Downside, it is forced to adopt the sandwich parallel winding method. Since the two primary windings are not on the same layer, there is a leakage inductance between the two primary windings. This leakage inductance will cause losses, thereby reducing the efficiency of the switching power supply. , the loss problem caused by the leakage inductance between the two parallel primary windings: this will exist during excitation and demagnetization; Which of the side windings is wound in parallel, only two tertiary windings can be used, which are respectively wound in parallel with the two parallel primary windings, and then connected in parallel to form a "third winding". The process is complicated, and the third winding composed of two parallel windings Windings also induce unequal voltages, causing losses and greater electromagnetic interference

[0005] In fact, for the common demagnetization of the third winding, the advantage is lossless demagnetization and high efficiency, but the selection of the wire diameter of the third winding is also a problem: the selection is relatively thin, and it is troublesome to wind in parallel with the primary winding, and it is easy to The thin wire is broken; if the wire diameter is selected to be the same as that of the primary winding, the cost will be high

But in these two schemes, Figure 1-2 This demagnetization method has strict requirements on the leakage inductance, otherwise, the excitation energy may be directly returned to the DC power supply U by D1 DC , does not appear in the secondary winding N S In the middle, there is no current in the secondary side D2, so that the output voltage is low or there is no output; and it is required that the reflected voltage generated when D2 is turned on cannot be greater than the DC power supply U DC , and if the duty cycle cannot be greater than 0.5, the power density cannot be further improved

for Figure 1-3 , the degaussing circuit itself is a more classic topology, the duty cycle can be greater than 0.5, and the energy of the leakage inductance has not been recycled

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