JPH0740786B2 - Switching power supply - Google Patents

Description

The present invention relates to a switching power supply device, and more particularly to a device in which input feedback noise that affects noise generated during switching to the outside through an input line is reduced. In a conventional power supply device such as a switching regulator, there is a drawback that switching noise propagates to other devices through an input line and adversely affects it, and noise from the outside adversely affects internal devices through the input line. Therefore, in each country, when implementing this measure (so-called EMI measure), the noise standard for the entire device (FCC, FTZ, etc.) is obligatory, and the input feedback noise standard for the power supply is strongly requested by the user accordingly. In view of this point, the present invention has a particularly strict FTZ standard (West Germany)
The present invention provides a device that can satisfy the above. A description will be given below with reference to the drawings. Fig. 5 is a circuit diagram of a conventional device of this type. In the figure, AC is an input AC power supply (100V system or 200V system), REC is a rectifier, SW is an input selector switch, C ₁ and C ₂ are input smoothing capacitors, and T is Main transformer for conversion, N ₁ , N ₂ , N _f is the 1
Winding, said primary winding N ₁ in the secondary (output) windings and regenerative winding
A switching element Q ₁ (eg FET, transistor) is connected in series to the secondary winding N ₂ and output rectification diodes D ₁ and D ₂ are connected to the secondary winding N _2.
And a smoothing coil L ₀ and a capacitor C ₀ are connected. D _f is a flywheel diode. The circuit operation is intermittent at a high frequency (20KHz~300KHz) a rectified DC input voltage by the switching element Q _1, and converts the arbitrary voltage through the transformer T, supplied to a load DC output V ₀ by rectifying and smoothing To do. The regenerative winding N _f and the diode D _f release the residual energy accumulated in the transformer T when the main switch element Q ₁ is off. In such a conventional device, switching noise propagates and adversely affects other devices connected to the AC input power source AC side through the input lines (a) and (b) as described above. FIG. 1 is a circuit diagram of an embodiment of the present invention, and the same reference numerals as those in the conventional example show the same parts. As is clear from the conventional example, the present invention uses a shield type transformer T ₀ as a main transformer and connects the shield terminal to the primary winding of the main transformer T ₀ via a through core L _B. It is characterized by doing so. Incidentally, the main transformer T ₀ is formed by concentrically winding a primary coil n ₁ and a secondary coil n ₂ on a bobbin 1 via an insulating tape 2 as shown in the sectional view of FIG. In Fig. 1, a shield plate (shield plate) 3 such as copper is wound between the primary coil and the secondary coil, and a terminal (not shown) electrically connected to the shield plate 3 is led out. . In addition, in FIG. 2, reference numeral 4 is an insulation material for securing a relief distance, and 5 is an iron core. Also, as the transmembrane core L _B illustrates an example of using the conductive allowed the so-called bead core (trade name BLOZN-R62) core F _1, F ₂ on lead 6 that penetrates as shown in Figure 3. FIG. 4 is a characteristic diagram comparing the switching noise intensities of the conventional device and the device of the present invention. The horizontal axis represents the noise frequency (MHz), the vertical axis represents the feedback noise electric field strength (db / μv), and in FIG. B shows the ranges of Class A and Class B of the West German Standard (FTZ) regarding the input feedback noise, and curve (i) shows the characteristic of the embodiment of the present invention and (ii) shows the characteristic of the conventional example. That is, in the conventional example, the frequency is 0.1MHz, 0.2MHz
Noise source (in this case, normal switching frequency band)
On the other hand, the standard A cannot be satisfied, and there is no margin in the standard with a noise source of 1 to 3 MHz. On the other hand, according to the present invention, it was confirmed that the standard A can be satisfied with a margin in the entire frequency band of 0.1 MHz to 30 MHz as shown by the curve (i). As is apparent from the above description, according to the present invention, noise generated from the power supply device is effectively shielded, so that malfunction of external electronic equipment such as an electronic calculator or an electronic exchange can be prevented, which is a great practical effect.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIGS. 2 and 3 are structural diagrams of a transformer and a through core, which are applied to an embodiment of the present invention, and FIG. 4 is an embodiment of the present invention. FIG. 5 is a characteristic diagram comparing the example and the conventional example, and FIG. 5 is a conventional circuit diagram. In FIG, AC is an input AC supply, REC rectifier, T _1, T ₀ is the main transformer, Q ₁ is the main switching element, L _B feedthrough core, 1 bobbin 2 insulating tape, 3 shielding plate, 5, F ₁ and F ₂ are iron cores, and 6 is a conductor.

Claims (1)

[Claims] 1. An AC input power supply AC is rectified to supply power to a main transformer T0 via an input smoothing capacitor C1, and a main switch element Q ₁ is connected to the primary winding N ₁ side of the main transformer T0. the switching power supply apparatus for supplying a DC output through the rectifying diode D ₁ provided to the secondary winding N ₂ side of the main transformer by the switching operation of the main switching element Q _1, the main transformer T ₀ 1 A shield type transformer provided with an electromagnetic shield between the secondary winding N ₁ and the secondary winding N ₂ is used, and the main transformer T _{0 is} passed through the shield terminal through a through core L _8.
A switching power supply device characterized in that it is connected between one end of the primary winding N ₁ side of the above and a connection point of the input smoothing capacitor C _{1 on} the (+) side.