JPS6149911B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching regulator that reduces noise generated from semiconductor elements such as switching elements and flywheel diodes.

A typical conventional constant voltage switching regulator circuit is shown in FIG. An input AC voltage from an AC power source 1 is passed through a line filter consisting of a coil 4 and a capacitor group 5, and then rectified by a rectifier 2, and the output is smoothed by a smoothing capacitor 3 to obtain a DC voltage, which is then passed through a switching transistor 20, and then an inverter transistor 21, 22, 23, and 24 to obtain a square wave, an AC voltage is obtained on the secondary side via an output transformer 43, and is smoothed by a rectifier 12 and capacitors 13 and 14 to obtain a predetermined DC voltage 15.
get.

In addition, 31, 32, 33, 34, 35, 36 are drive coils of the inverter circuit, 40, 41,
42 is an output transformer coil.

By converting alternating current to direct current and switching at high speeds of around 20 kHz, the output transformer can be made smaller, making it possible to create a compact and lightweight power source. However, since the DC voltage is switched in a square waveform at high speed, noise is generated in a wide band, and the noise leaks directly to the outside from the space of the input AC power supply and electrical components, causing problems. For this reason, in transformers and the like, devices have been invented in which the primary winding and the secondary winding are insulated and provided with a shield layer, but this is difficult to apply to semiconductor devices and has little heat dissipation effect, and the shield layer is It requires winding or covering, which causes problems such as a complicated and expensive structure.

The present invention seeks to eliminate the aforementioned drawbacks and to reduce to a minimum the noise generated by switching regulators.

Below, the present invention will be explained with reference to the circuit examples shown in FIGS. 2 and 3. The electrical components that mainly become noise sources are the switching transistor 20, the flywheel diode 8, the choke coil 10,
Inverter transistors 21, 22, 23, 2
4 and an output transformer 43. Noise generated from these electrical components is rectified and smoothed from the AC power source 1, and is propagated to positive and negative potentials 16 and 16' through a line filter consisting of a coil 4 and a capacitor group 5, and is transmitted to the power line in normal mode. This occurs as common mode noise to the external case of the switching regulator, which is grounded. The electrical components of each of the noise sources mentioned above generate a large amount of heat, so it is necessary to dissipate the heat through an insulator.
A noise source exists between the AC power line 1 and the ground, and common mode noise creates a loop between the AC power line and the ground, propagating the noise to the outside.

The present invention connects each of the above-mentioned noise sources to the sub-chassis 50, and the sub-chassis 50
The sub-chassis 50 is brought into contact with the chassis or exterior case 52 via an insulating sheet 51 to radiate heat to equalize the potential and form a closed loop against common mode noise. It is connected to the positive potential 16 or negative potential 16' after the line filter after the input AC voltage is rectified by the rectifier 2 as shown, or after the line filter before the input AC voltage is rectified as shown in FIG. Thereby, common mode noise generated from semiconductor elements such as the switching transistor 20, the flywheel diode 8, and the inverter transistors 21 to 24 can be reduced. Further, as mentioned above, the sub-chassis 50 also needs to play the role of heat dissipation, so the sub-chassis 50 with a positive or negative potential is fixed to a chassis or an exterior case 52 with an earth potential via an insulating sheet 51 to conduct heat and dissipate heat.

By doing this, the potential of the sub-chassis 50 becomes cool and the output side of the switching transistor 20 is hot in the normal mode, so it is necessary to insert the inductor 6 of the filter composed of the electrolytic capacitor 7 and the inductor 6 on the hot side. This makes it possible to reduce noise in normal mode. Whether the sub-chassis is connected to the positive potential side or the negative potential side may be determined depending on the type of switching transistor. In this example, we have described the NPN type polarity, but it goes without saying that even in the case of PNP, the connection is reversed, but the content is the same as the NPN type.

Further, in FIG. 2, the collector of the switching transistor 20 is directly connected to the sub-chassis 50, and other electrical components (diode 8, inverter transistors 21-24) are connected to the sub-chassis 50 via an insulator 53 as shown by dotted lines. In FIG. 3, the switching transistor 20 and the other electrical components mentioned above are brought into contact with the negative potential of the sub-chassis 50 via an insulator 53. The former has a greater heat dissipation effect from the transistor. The latter has a double insulation structure and is extremely effective in terms of safety.

As a result of measuring the induced voltage generated at the positive potential 16 or negative potential 16' with respect to the ground potential for the switching regulator of the present invention and the conventional switching regulator, the conventional switching regulator was 830 mV _PP.
In contrast, the present invention was able to reduce the induced voltage by approximately 28 dB to 33 mV _PP .

As described above, the present invention is an epoch-making invention that can significantly reduce the noise of switching regulators, and has extremely high industrial and practical value.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a typical conventional switching regulator circuit, FIGS. 2 and 3 are schematic diagrams of an example of the switching regulator circuit of the present invention, and FIG. transistor 20
The collector of is directly connected to the positive potential of the sub-chassis 50, and the other semiconductor elements are connected to the sub-chassis 50 through an insulator 53. In FIG. It was brought into contact. 1: AC power supply, 2: Rectifier, 3: Smoothing capacitor, 4: Coil, 5: Capacitor group, 6: Inductor, 7: Electrolytic capacitor, 8: Flywheel diode, 9: Capacitor, 10: Chiyoke coil, 11: Feedback Resistor, 12: Rectifier, 13,1
4: Capacitor, 20: Switching transistor, 21 to 24: Inverter transistor,
50: Sub chassis, 51: Insulating sheet, 52:
Chassis or outer case, 53: Insulator.

Claims (1)

[Claims] 1 Rectify and smooth the input AC voltage to obtain DC voltage,
In a switching regulator that intermittently supplies AC voltage to the input coil of a transformer using a switching element, and obtains an AC voltage to the output coil of the transformer and rectifies it to obtain a predetermined DC voltage, the input AC voltage is in front of the circuit that rectifies and smoothes the input AC voltage. Alternatively, a line filter is connected later, and a semiconductor element such as a switching element or a flyhole diode that generates noise is directly connected to the sub-chassis or brought into contact with the sub-chassis through an insulator, and the sub-chassis is connected to the line filter. A switching regulator connected to a positive potential or a negative potential, provided with a closed loop circuit for each noise source, and configured to radiate heat by bringing the sub-chassis into contact with a chassis or a case via an insulating sheet.