Fly-back type switching power supply

Abstract

The invention provides a fly-back type switching power supply. On the basis of a common three-winding absorption fly-back type switching power supply, an NP1 dotted terminal in a transformer B is connected with the power supply; an NP2 dotted terminal of a secondary primary edge winding is grounded; an NP1 and an NP2 are bifilar windings and a capacitor C1 is increased; one end of the C1 is connected with an NP1 heteronymous terminal and the other end of the C1 is connected with an NP2 heteronymous terminal; a secondary edge adopts a Q2 of an opposite connection method to the prior art and is controlled by PWM (Pulse-Width Modulation) signal controlled by the other path of output voltage, so that when Q1 is conducted, the NP1 and the NP2 are excited and energy is abundant; when the Q1 is switched off, a secondary edge NS realizes rectification output voltage through the Q2 according to requirements on an output load, and lossless absorption of leakage inductance and surplus energy is realized by the NP2 through a D1, so that the fly-back type switching power supply is suitable for working under low voltage, the utilization rate and current density of the primary edge winding are improved and the power density is great; the leakage inductance between the primary edge and the secondary edge is allowable to be relatively great and the conversion efficiency is high; EMI (Electromagnetic Interference) is great; the bandwidth of the power supply is very wide and loop response is good.

Description

technical field [0001] The invention relates to the field of switching power supplies, in particular to a flyback switching power supply. Background technique [0002] At present, switching power supplies are widely used. For occasions where the input power is below 75W and the power factor (PF, PowerFactor, also known as power factor) is not required, the flyback (Fly-back) switching power supply has attractive advantages: circuit topology Simple, wide input voltage range. Due to the small number of components, the reliability of the circuit 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. In Japan and Taiwan, they are also called flyback converter, flyback switching power supply, and flyback power supply. Common topologies for AC / DC converters such as figure 1 As shown, the prototype of the figure comes from page 60 of "Switching Power Converter Topology...

AI Technical Summary

Problems solved by technology

When the working voltage is high, the primary winding can be sandwiched in series. Under low operating voltage, the inductance is too large due to series connection, and the sandwich parallel scheme is forced to be used. Since the two primary windings are not on the same layer, this There is a leakage inductance between the two primary windings, which will cause losses, which will reduce the efficiency of the switching power supply and cause problems:

If the third winding is used to demagnetize, which of the two parallel primary windings is the third winding in parallel with? Only two tertiary windings can be used, which are respectively wound in parallel with the two primary windings connected in parallel, and then connected in parallel to form a "third winding". voltage, causing loss and large electromagnetic interference

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

[0005] There is another disadvantage of the flyback switching power supply: the bandwidth of the switching power supply is insufficient, that is, the loop response is poor. For a common switching power supply with a working frequency of 65KHz, its bandwidth is generally only a few hundred Hz, generally below 400Hz. 1KHz requires design engineers with superb design experience, superb circuit board design level, and superb debugging skills; for switching power supplies with a working frequency of 280-330KHz, the bandwidth is generally only 1-2KHz, and if you want to achieve 10KHz, the same It is very difficult, which is determined by the inherent working characteristics of the flyback switching power supply. The optocoupler detects the voltage change at the output terminal to determine the duty cycle of the primary side, in order to achieve: after considering the efficiency loss, within a unit time, the primary side The energy of the excitation is equal to the energy output by the secondary side in the same period

However, as the frequency of load jumps increases, the control loop of the system cannot keep up with it synchronously.

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