JPH0974754A - Switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching type power supply device wherein switching noises of a main switching element can be emitted at a similar level without providing a shield winding between primary and secondary windings of a switching transformer. SOLUTION: A bias winding 22, whose wire diameter is changed for dense winding according to the number of windings or wherein several wires are parallelly wound in the case of less number of windings, is provided between a primary winding 21 and a secondary winding 23 of a switching transformer 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching type power supply device using a switching transformer used as a power supply for various electronic devices.

[0002]

2. Description of the Related Art In recent years, there has been a demand for miniaturization and cost reduction of various electronic devices, and a switching type power supply device using a switching transformer used in these electronic devices is also required to be miniaturized and cost-effective, and further safe. The requirements for protection of equipment such as surfaces and radio interference are becoming more severe.

A conventional switching power supply device will be described below. FIG. 3 shows the configuration of a conventional switching type power supply device. In FIG. 3, 1 is a rectifying / smoothing circuit, which receives an AC input voltage and converts it into a DC input voltage. A switching transformer 2 has a primary winding 21, a bias winding 25, a secondary winding 23, and a shield winding 24. The structure of the switching transformer 2 has a structure in which a shield winding 24 is sandwiched between a primary winding 21 and a secondary winding 23 as shown in FIG. Primary winding 21
Has one end connected to the positive electrode of the rectifying and smoothing circuit 1,
The other end is connected to the negative electrode of the rectifying / smoothing circuit 1 via the main switching element 3. The main switching element 3 is controlled by the control circuit 4 so as to stabilize the DC output voltage. The resistor 5 is connected to the positive electrode of the rectifying / smoothing circuit 1, the positive electrode of the control circuit 4, the cathode of the diode 6, and the positive electrode of the capacitor 7. The anode of the diode 6 is connected to one end of the bias winding 25, and the other end is connected to the negative electrode of the control circuit 4. One end of the shield winding 24 is connected to the negative electrode of the rectifying / smoothing circuit 1. The AC voltage generated in the secondary winding 23 is rectified and smoothed by the output smoothing circuit 8 for its forward voltage or flyback voltage, and is supplied to the output terminal as a DC output voltage.

The operation of the switching type power supply device configured as described above will be described below. First, when an AC input is received, the rectifying / smoothing circuit 1 converts the AC input into a DC voltage. When a DC input voltage is generated, the resistance 5
The capacitor 7 is charged via and is applied to the control circuit 4. The control circuit 4 starts operating from the voltage thus applied (hereinafter referred to as a bias voltage) and outputs an output pulse. The output pulse turns on and off the main switching element 3 to convert the DC input voltage into an AC voltage, which is input to the primary winding 21. As a result, an AC voltage proportional to the winding ratio of the switching transformer is generated in the bias winding 25 and the secondary winding 23.

The flyback voltage of the AC voltage induced in the bias winding 25 is rectified and smoothed by the diode 6 and the capacitor 7, and supplied as the bias voltage of the control circuit 4. On the other hand, the flyback voltage of the AC voltage induced in the secondary winding 23 is rectified and smoothed by the output smoothing circuit 8 and supplied to the DC output.

When such a DC output is supplied, switching noise caused by turning on and off the main switching element 3 is a cause, which adversely affects other electronic equipment. The main one is that the switching noise of the main switching element 3 is caused by the primary winding 2 of the switching transformer 2.
Stray capacitor 2 formed between the primary winding 1 and the secondary winding 23
There is noise leaking from the output terminal through 6.

Therefore, as a method of reducing the noise, by inserting a shield winding 24 between the primary winding 21 and the secondary winding 23, it is possible to prevent the switching noise from being transmitted to the secondary winding 23. Main switching element 3
The noise generated in the primary winding 21, the shield winding 24,
By making a closed loop of the main switching element 3 to prevent switching noise from leaking to the outside of the power supply, on the other hand, the shield winding 24 is required only for noise countermeasures due to the structure of the switching transformer 2. Therefore, it is difficult to reduce the size of the switching transformer 2 itself, and it is also a factor that makes it difficult to reduce the size and cost of the switching power supply device.

[0008]

However, in the above-mentioned conventional configuration, by using the shield winding 24,
There is a problem in that it is difficult to reduce the size of the switching transformer 2 itself, and it is difficult to reduce the size and cost of the switching power supply device.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a switching type power supply device which is small in size and easy in cost reduction.

[0010]

To achieve this object, a switching type power supply device of the present invention uses a DC input voltage obtained by rectifying and smoothing a DC voltage or an AC voltage, and an AC by a switching main switching element. A primary winding of a switching transformer that is converted into a voltage and applied, an output terminal that extracts a DC output voltage obtained by rectifying and smoothing an AC voltage generated in the secondary winding of the switching transformer, and a switching transformer. In a switching power supply device that has a bias voltage obtained by rectifying and smoothing an AC voltage generated in a bias winding provided in the switching winding, and a control circuit that operates by supplying the bias voltage, a primary winding and a secondary winding of a switching transformer. Change the wire diameter according to the number of turns so that it can be wound tightly between the windings. Or, if the number of turns is small has a configuration in which a bias winding wound those in parallel several lines.

[0011]

With this configuration, the switching transformer 1
The wire diameter is changed according to the number of turns so that it can be tightly wound between the secondary winding and the secondary winding. If the number of turns is small, a bias winding is provided by winding several wires in parallel. With the simple and simple switching transformer, the switching noise of the main switching element can be prevented from being transmitted to the secondary winding, and a compact and low-priced switching power supply device can be realized.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of a switching power supply device according to an embodiment of the present invention. In FIG. 1, 1 is a rectifying / smoothing circuit, which receives an AC input voltage and converts it into a DC input voltage. A switching transformer 2 has a primary winding 21, a bias winding 22, and a secondary winding 23. The switching transformer 2 has a structure in which the wire diameter is changed according to the number of turns so that it can be tightly wound between the primary winding 21 and the secondary winding 23 as shown in FIG. It has a structure in which a bias winding 22 formed by winding a plurality of wires in parallel is sandwiched.

The primary winding 21 has one end connected to the positive electrode of the rectifying / smoothing circuit 1 and the other end connected to the negative electrode of the rectifying / smoothing circuit 1 via the main switching element 3. The main switching element 3 is controlled by the control circuit 4 so as to stabilize the DC output voltage. The resistor 5 is connected to the positive electrode of the rectifying / smoothing circuit 1, the positive electrode of the control circuit 4, the cathode of the diode 6, and the positive electrode of the capacitor 7. The anode of the diode 6 is connected to one end of the bias winding 22, and the other end of the bias winding 22 is connected to the control circuit 4. The output smoothing circuit 8 rectifies and smoothes the flyback voltage of the AC voltage generated in the secondary winding 23, and supplies it to the output terminal as a DC output voltage.

With respect to the switching type power supply device configured as described above, the basic operation is the same as in the prior art, and therefore the description thereof is omitted, and a method of reducing switching noise will be described. In order to prevent the switching noise of the main switching element 3 from transmitting the switching noise leaking to the output terminal through the stray capacitor 26 formed between the primary winding 21 and the secondary winding 23 of the switching transformer 2, the primary winding Instead of winding a new winding shield winding between the wire 21 and the secondary winding 23, the bias winding 22 that supplies the bias voltage to the control circuit 4 is used, and the winding number is adjusted so that the winding can be wound densely. The noise generated in the main switching element 3 can be reduced by changing the wire diameter or winding several wires in parallel when the number of turns is small. By making a closed loop of 3, it is possible to prevent switching noise from leaking to the outside of the power supply. That is, by using the bias winding 22 that supplies the bias voltage to the control circuit 4, the wire diameter is changed according to the number of turns so that the winding can be densely performed, or when the number of turns is small, several lines are arranged in parallel. By winding things, there is no need to add shield winding,
The switching type power supply device can be downsized and the price can be reduced accordingly.

[0015]

As described above, according to the present invention, instead of providing the shield winding between the primary winding and the secondary winding of the switching transformer, it is provided between the primary winding and the secondary winding of the switching transformer. Since the switching transformer has a simple structure in which the wire diameter is changed according to the number of turns so that it can be tightly wound, and when the number of turns is small, a bias winding formed by winding several wires in parallel is provided. Not only can the winding height be made smaller than that of the switching transformer with the shield winding of, but the noise emission of the switching noise of the main switching element can be made at the same level as before, which reduces noise control components. Therefore, it is possible to realize the downsizing and cost reduction of the switching power supply device.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of a switching power supply device of the present invention.

FIG. 2 is a configuration diagram of a switching transformer of the present invention.

FIG. 3 is a circuit configuration diagram of a conventional switching power supply device.

FIG. 4 is a configuration diagram of a conventional switching transformer.

[Explanation of symbols]

 1 Rectifying / Smoothing Circuit 2 Switching Transformer 3 Main Switching Element 4 Control Circuit 5 Resistor 6 Diode 7 Capacitor 8 Output Smoothing Circuit 21 Primary Winding 22 Bias Winding 23 Secondary Winding 26 Stray Capacitor

Claims (1)

[Claims] 1. A DC input voltage obtained by rectifying and smoothing a DC voltage or an AC voltage, a primary side circuit including at least a primary side control circuit and a main switching element, and a bias supplied to the primary side control circuit. Consisting of a switching transformer with a circuit and a secondary side rectifying and smoothing circuit,
The wire diameter is changed according to the number of turns so that it can be tightly wound between the primary winding and the secondary winding of the switching transformer, and when the number of turns is small, a bias winding is formed by winding several wires in parallel. Switching type power supply device with wires.