JPH07274500A - Power circuit - Google Patents

Abstract

PURPOSE:To prevent the occurrence of noise by needless radiation by arranging a inductance in series to the diode, in a power circuit which forms a snubber circuit. CONSTITUTION:An inductance 22 is arranged between a diode 9, which forms the snubber circuit of a power circuit 21, and the primary low-voltage terminal of a switching transformer 5. Hereby, needless radiation can be reduced by suppressing the sudden ripple of the current flowing to a snubber circuit, and repressing high frequency ingredients, and also the damage, etc., of a diode 9 can be avoided effectively by reducing the peak value of a surge current, too.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit, and more particularly to a flyback type switching power supply circuit.

[0002]

2. Description of the Related Art Conventionally, in a flyback type switching power supply circuit, a snubber circuit is connected between the primary windings of a converter transformer also called a switching transformer. This snubber circuit has the function of reducing the surge voltage applied to the switching transistor and reducing the generation of noise.

In the conventional power supply circuit 1 shown in FIG. 6, a commercial power supply 2 is supplied to a diode bridge 3 forming a full wave rectification circuit, and the diode bridge 3 rectifies the commercial power supply. The output voltage of the diode bridge 3 is supplied to the smoothing capacitor 4 and smoothed by this smoothing capacitor 4.

The primary side of the converter transformer 5 of the power supply circuit 1 forms a series circuit with the field effect transistor 6, and this series circuit is connected in parallel with the smoothing capacitor 4. The field effect transistor 6 forms a switch circuit and repeats on / off operation in response to a predetermined drive signal applied to the gate from the control IC.

The converter transformer 5 is formed by winding a magnet wire or the like around a predetermined core material, and a gearup is formed on this core material so as to have a required inductance value (L value). The high voltage side terminal of the primary winding of the converter transformer 5 is connected to one end of the resistor 7 and the capacitor 8,
The other ends of the resistor 7 and the capacitor 8 are connected to the cathode of the diode 9. Further, the low voltage side terminal of the primary winding of the switching transformer 5 is connected to the anode of the diode 9.

As a result, in the conventional power supply circuit 1, the field effect transistor 6 is turned on and off, and the converter transformer 5 is driven by the flyback pulse determined by the inductance of the converter transformer 5 and the capacitance of the capacitor 8. At this time, in the converter transformer 5, since there is a gap in the core material as described above, energy due to leakage inductance not directly related to power transmission between the primary and secondary is generated, and this energy causes a large surge voltage or noise. Occurs.

For this reason, the energy generated by this leakage inductance is connected to the diode 9 so that the diode 9 is turned on during the period in which this energy is generated, and this energy is temporarily stored in the capacitor 8 and then stored in the resistor 7. Consume at. The output voltage on the secondary side of the converter transformer 5 is rectified by the diode 10 and then smoothed by the smoothing capacitor 11 for output, whereby a desired DC output voltage can be efficiently generated.

[0008]

However, in the snubber circuit of the power supply circuit 1 of this type, as shown in FIG. 3, the current I flowing through the diode 9 has a large peak value and contains many high frequency components. That is, the current I flowing through the diode 9
Has a large peak value and a large current change rate di / dt. Therefore, in this type of power supply circuit 1,
Even if the snubber circuit is provided, there is a problem that the generation of noise due to unnecessary radiation cannot be avoided.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a power supply circuit capable of reducing unnecessary radiation as compared with the conventional one.

[0010]

According to the present invention, a snubber circuit is formed by connecting a parallel circuit of a capacitor and a resistor and a diode in series between the primary windings of a converter transformer. This is achieved by a power supply circuit in which an inductance is arranged in series with the diode.

In the present invention, preferably, the inductance is a bead inductor in which a jumper wire is passed through a bead.

[0012]

According to the above-described structure, the peak current value can be reduced by suppressing the rapid current change of the current flowing through the snubber circuit and suppressing the high frequency component of the current.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings. The examples described below are
Since it is a preferred specific example of the present invention, various technically preferable limitations are attached, but the scope of the present invention is, unless otherwise stated to limit the present invention, in the following description.
These aspects are not limited.

FIG. 1 is a connection diagram showing a preferred embodiment of the power supply circuit of the present invention. In FIG. 1, this power supply circuit 2
In the structure of No. 1, the parts denoted by the same reference numerals as those of the above-mentioned conventional example have the same structure as this, and thus the duplicated description will be omitted.

In the power supply circuit 21 of FIG. 1, an inductance 22 is inserted or arranged between the diode 9 forming the snubber circuit described in the above-mentioned conventional example and the primary side low voltage side terminal of the switching transformer 5. The inductance 22 is preferably formed by forming a ferrite core into a bead shape and inserting a lead wire such as a jumper wire through the ferrite core. When the ferrite core is formed in this way, the
The material is selected so that good frequency characteristics can be secured up to frequencies of [Hz].

As a result, the snubber circuit in which the inductance 22 of the power supply circuit 21 is inserted suppresses an abrupt current change. Therefore, the high-frequency component of the current I1 flowing through the snubber circuit can be suppressed by the amount corresponding to the suppression of the abrupt current change, whereby unnecessary radiation can be reduced. Further, by suppressing the rapid current change in this way, the peak value of the surge current can be reduced, and damage to the diode 9 or the like can be effectively avoided by that amount.

FIG. 2 shows the result of observing the current I1 flowing in the snubber circuit with an oscilloscope for the embodiment of the power supply circuit of the present invention shown in FIG. According to this result, the peak value of the surge current can be reduced to about 2 [A], and the current change rate di / dt can also be reduced. As a result, the surge current stress of the diode 9 can be suppressed, and the noise due to the high frequency current can be reduced. On the other hand, FIG. 3 shows the result of observing the current I flowing through the snubber circuit of the conventional power supply circuit 1 of FIG. In the power supply circuit 1 of FIG. 6, the inductance 22 of FIG.
Therefore, the peak value of the surge current increases to about 3 [A], and the current change rate di / dt also increases.

FIG. 4 shows data of the unnecessary radiation electric field intensity measured with the power supply circuit 21 of the present invention of FIG. 1 incorporated in a set (for example, OA equipment). Further, data of the unnecessary radiation electric field intensity measured in a state where the conventional power supply circuit 1 of FIG. 6 is incorporated in a set (for example, OA equipment) is shown in comparison with FIG. As is clear from comparison between FIG. 4 and FIG. 5, the electric field strength (radiation noise) of unnecessary radiation in the frequency band of 110 to 120 MHz is reduced by about 4 dB.

In the power supply circuit 21 of the present invention, the unnecessary radiation noise can be remarkably reduced and the diode 9 of the snubber circuit can be significantly reduced with a simple structure in which the inductance is inserted at one end of the diode forming the snubber circuit. The peak value of the surge current can also be reduced and the surge current stress can be reduced. As described above, in the power supply circuit 21 of the present invention, the high frequency flowing in the snubber circuit is obtained by inserting the inductance (L) in series with the diode of the snubber circuit in the snubber circuit that absorbs energy generated by the leakage inductance. The power supply radiation noise can be reduced by improving the current.

In the above embodiment, the case where the lead wire such as a jumper wire is inserted into the bead-shaped ferrite core to form the inductance has been described, but the present invention is not limited to this, and the bead-shaped ferrite core may be used. An inductance may be formed by inserting the lead of the diode 9 into the core.

Further, in the above-mentioned embodiment, the case where the inductance is arranged on the anode side of the diode 9 has been described, but the present invention is not limited to this, and may be arranged on the cathode side.

Further, in the above-mentioned embodiments, the case where the switch circuit is formed by the field effect transistor has been described, but the present invention is not limited to this, and can be widely applied to the case where it is formed by the bipolar transistor.

[0023]

As described above, according to the power supply circuit of the present invention, unnecessary radiation can be reduced as compared with the conventional one.

[Brief description of drawings]

FIG. 1 is a connection diagram showing a preferred embodiment of a power supply circuit of the present invention.

2 is a signal waveform diagram showing a current flowing through a diode of the snubber circuit of the power supply circuit of FIG. 1 having an inductance.

3 is a signal waveform diagram showing a current flowing through a diode of the snubber circuit of the conventional power supply circuit of FIG. 6 having no inductance.

4 is a characteristic curve diagram showing the electric field strength of unnecessary radiation in the snubber circuit of the power supply circuit of FIG. 1 having an inductance.

5 is a characteristic curve diagram showing the electric field strength of unnecessary radiation in the snubber circuit of the conventional power supply circuit of FIG. 6 having no inductance.

FIG. 6 is a connection diagram showing a conventional power supply circuit.

[Explanation of symbols]

 1, 21 Power supply circuit 2 Commercial power supply 3 Diode bridge 4, 8, 11 Capacitor 5 Converter transformer 6 Field effect transistor 7 Resistor 9, 10 Diode 22 Inductance

Claims (2)

[Claims] 1. Between the primary winding of the converter transformer,
A power supply circuit in which a parallel circuit of a capacitor and a resistor and a diode are connected in series to form a snubber circuit, wherein an inductance is arranged in series with the diode. 2. The power supply circuit according to claim 1, wherein the inductance is a bead inductor in which a jumper wire is passed through a bead.