JPH0365053A - Switching power supply - Google Patents

Abstract

PURPOSE:To obtain a switching power supply of high efficiency and low noise by dividing primary and secondary windings of a transformer respectively into almost equal windings and connecting a main switch and a diode between these divided windings. CONSTITUTION:Primary and secondary windings of a transformer 2 are division- constituted respectively into almost equal windings N11, N12 and N21, N22 to respectively connect a main switching element Q between the windings N11, N12 while a diode D6 between the windings N21, N22. When the switching element Q is conducted, voltage V1, applied to the winding N11, is -1/2EIN, and voltage V2, applied to the winding N12, is 1/2EIN. When the switching element Q is turned off, counter electromotive force is generated in the windings N11 and N12, and forward voltage is applied to the diode D6 with a flow of current generated. Thus because each winding of the transformer 2 has the winding for generating a complementary voltage waveform, by action of mutually negating noise for the ground, a power supply of low noise can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a switching power supply used in OA equipment and the like.

[Conventional technology]

DCDC converters, which are the main part of conventional switching power supplies, include flyback and forward types. Electronic technology 1989. Although it is described in detail in the March issue, we will use the flyback type as an example to explain its operation.

Figure 7 shows the converter circuit and waveforms. When the main switch is ON, energy determined by the power supply voltage and ON time is accumulated in a part of the inductance of the transformer T. During the OFF period of the main switch, the diode is forward biased and becomes conductive, so the secondary Energy is transferred through the windings.

(Problems to be Solved by the Invention) However, switching power supplies are required to have lower noise and higher efficiency.

In the flybank converter, there is usually leakage magnetic flux in the transformer, resulting in energy that cannot be transmitted to the secondary side. This not only reduces efficiency, but also means that an excessive voltage is applied to the main switch during the transition from ON to OFF, requiring elements with high withstand voltage, and furthermore, this energy converts into heat. Until the stray capacitance disappears, unnecessary electrical vibrations are caused by resonance with the cage inductance. This vibration returns to the input power supply through the secondary side through the windings of the transformer and the stray capacitance to ground, causing noise.

In this way, the leakage magnetic flux of the transformer, that is, the leakage inductance, has an adverse effect on both noise and efficiency.

An object of the present invention is to provide a switching power supply with high efficiency and low noise.

[Means for solving problems]

The present invention provides a switching power supply comprising a transformer having a primary winding and a secondary winding, a main switching made of a semiconductor element connected to the primary winding, and a rectifying diode connected to the secondary winding. This switching power supply is characterized in that a primary winding and a secondary winding are divided into substantially identical windings, and a main switch and a diode are connected between the divided windings.

The present invention reduces the noise by making the potential fluctuations inside the DC-DC converter complementary by dividing a part of the transformer and the secondary winding into approximately two halves, and also reduces the leakage inductance of the transformer. This was done with the aim of efficiently transmitting the accumulated energy to the secondary side using complementary connected capacitors.

Here, "complementary" means that each winding of the divided transformer is configured to generate a complementary voltage waveform.
This means that even if there is a stray capacitance to the ground such as I□, they each have the effect of canceling out the noise to the ground.

〔Example〕

Embodiments of the present invention will be described below with reference to FIG.

FIG. 1 is a circuit diagram when the present invention is applied to a flyback converter. EIN is the power supply voltage, T is the transformer,
6 is the output smoothing capacitor + RL is the load, N, ~N2
□ is the winding of T, C, and C5 are the capacitors. Further, FIG. 2 shows waveforms of various parts of FIG. 1.

When switching element Q is conductive, N1. The voltage V applied to -'A E+, 4. The voltage V2 applied to NI2 is %EIN. In this case, since a reverse voltage is applied to the diode D6, (2). does not flow. When switching element Q is turned off, N1. A back electromotive force is generated at D6 and N2, a forward voltage is applied to D6, and In flows. At this time,
N, has a voltage according to the turns ratio of N I and N1□ -■
, and ■ are applied.

Thereafter, after the power stored in the transformer T is released by 1, V,=V2=O until the switching element Q is turned on again. However, in this case, it is well known that vibrations as shown by the dotted line in FIG. 2 may occur due to glue, C, etc. in the circuit.

Further, voltage waveforms similar to N, , N, are generated in the secondary windings Nz and Nz□, respectively, depending on the turns ratio.

Since each winding of the transformer has a winding that generates a complementary voltage waveform, even if there is a stray capacitance to the ground such as C++ or C1□, they work to cancel out the noise to the ground. Therefore, a low-noise power supply can be realized.

Now, when considering only N11 and N1□, the transformer T
The equivalent circuit of is shown in Figure 3. Here, Lll and L
The leakage inductance represented by + is the cause of the loss and noise mentioned above.

The energy accumulated during the ON time of switch Q in Figure 1 is transferred to this leakage inductance by 2 during the OFF time of Q.
Another key point of the present invention is to provide capacitors Ca and Cs for efficient transmission to the next side. Considering that the capacitor of the present invention is added to the conventional flyback converter shown in FIG. 7, the energy accumulated in the leakage inductance is transmitted to the secondary side, but the noise generated by the primary winding 7 is also It will be transmitted to the secondary side.

On the other hand, in the switching power supply configured according to the present invention, if capacitors C4 and C3 shown in FIG. It is possible to transmit energy without

In addition, capacitors C4 and C5 are stray capacitances inside the transformer,
Stray capacitance of printed wiring board, capacitance with case.

Various capacitances such as capacitors can be used as components.

FIGS. 4(a) to 4(d) show an embodiment in which the present invention is applied to a flyback converter.

Further, FIGS. 5 and 6 show an embodiment in which the present invention is applied to a forward converter.

Although the embodiment used in the explanation shows a single-stone flyback type switching power supply circuit, it goes without saying that the present invention can be applied to other types or multi-type switching power supply circuits.

The point is that the transformer winding is divided to obtain complementary potential changes on both the primary and secondary sides, and the power accumulated in the leakage inductance is transmitted to the secondary side via the capacitance. This is the main point.

〔Effect of the invention〕

As described above, by using the circuit according to the present invention, it is possible to realize a switching power supply that generates little noise and has high efficiency.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment in which the present invention is applied to a flyback converter. FIG. 2 is a diagram illustrating waveforms of various parts representing the operation of FIG. 1. Fig. 3 is an explanatory diagram of beam cage inductance, Fig. 4 is a circuit diagram showing another embodiment applied to a flyback converter, and Figs. 5 and 6 are another embodiment applied to a forward converter. FIG. 2 is a circuit diagram showing an example. FIG. 7 is a circuit diagram and an operating waveform diagram of a conventional flyback converter. 1: Input power supply, 2: T transformer, 3: Semiconductor switch,
4: Capacitor, 5: Capacitor, 6: Rectifier diode, 7: Capacitor, 8: Load. Figure 1 Figure 4 Flyback 4 Figure 5

Claims (1)

[Claims] 1) A transformer having a primary winding and a secondary winding, and a main switching made of a semiconductor element connected to the primary winding,
In a switching power supply in which a rectifying diode is connected to the secondary winding, the primary winding and the secondary winding of the transformer are each divided into substantially identical windings, and the main winding is connected between the divided windings. A switching power supply characterized by connecting a switch and a diode. 2) The switching power supply according to claim 1, which is comprised of a plurality of substantially identical transformers each having a set of primary windings and secondary windings. 3) The switching power supply according to claim 1 or 2, characterized in that a plurality of substantially identical capacitive elements are used to connect both terminals of the main switch and the diode. 4) The switching power supply according to claim 3, characterized in that the capacitance between the windings of a transformer is used as all or part of the capacitance of the capacitive element. 5) The switching power supply according to claim 3, characterized in that the stray capacitance of a wiring board is used as all or part of the capacitance of the capacitive element.