JPH03251076A - Switching power supply - Google Patents

Abstract

PURPOSE:To suppress noise and to prevent erroneous function of an overcurrent detecting circuit by connecting resonance inductance and capacitor, respectively in series and parallel, with the rectifying diode in a rectifying circuit. CONSTITUTION:DC power from an input power supply 6 is inverted through a switching transistor 1 into an AC power which is transformed through a pulse transformer 2 and rectified through a rectifying diode 3 and outputted through a smoothing capacitor 4. Resonance inductance 7 and capacitors 8 are connected, respectively in series and parallel, with the rectifying diode 3. When the half period of a resonance circuit comprising the resonance inductance 7 and capacitor 8 is set equal to the pulse width, short circuit current is eliminated from the pulse transformer 2 upon turn ON of the switching transistor 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a switching power supply circuit, and more particularly to a switching power supply circuit that suppresses current flowing during a rectifier diode recovery time.

[Conventional technology]

Conventionally, in a switching power supply circuit composed of this type of flyback converter, as shown in FIG. , a rectifier diode 3 and a smoothing capacitor 4 constitute a capacitor input type rectifier circuit, and the base of the switching transistor was controlled from the output of the switching power supply circuit through a control circuit 5.

[Problem that the invention seeks to solve]

In the conventional switching power supply circuit configured with the flyback type converter described above, the rectifier circuit does not have a current limiting element, so the pulse is generated during the recovery time of the rectifier diode 2 after the switching transistor 1 is turned on. A short circuit current flows through each of the primary and secondary lines of the transformer 2. Therefore, as shown in FIG. 2(a), the short-circuit current IC5, which is represented by the collector current of the switching transistor 1, flows rapidly and may be radiated to the outside as noise, causing malfunctions or peaks of the normal collector current. If it becomes larger than the value (Icp in FIG. 2(b)), there is a drawback that the overcurrent detection circuit may malfunction.

[Means for solving problems]

The switching power supply circuit of the present invention is a flyback type switching power supply circuit in which voltage is transformed by a pulse 1 to a lance, and the output thereof is rectified and smoothed. and a capacitor connected in parallel to the rectifier diode.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1(a) is a circuit diagram showing the configuration of an embodiment of the present invention,
FIG. 1(b) shows the collector current waveform of the switching transistor of this example.

The switching transistor 1 is connected to the input power supply 6 via the primary winding of the pulse transformer 2.
The secondary winding is connected in reverse polarity and connected to a series circuit of a rectifier diode 3, a resonant inductance 7, and a smoothing capacitor 4, and a resonant capacitor 8 is connected in parallel to the rectifier diode 3. The control circuit 5 is a control circuit that detects the output voltage and controls the pulse width of the switching transistor 1.

Here, let us assume that the half period of the resonant circuit consisting of the resonant inductance 7 and the resonant capacitor 8 is equal to the pulse width. In this way, the collector current Ic of the switching transistor 1 becomes a resonant current I which is composed of the DC weight current IDC flowing through the pulse 1 to the lance 2, the excitation current IL of the pulse 1 lance 2, the resonant inductance 7, and the resonant capacitor 8. The short circuit current shown in the conventional example does not flow because the resonant inductance 7 is in series in the rectifier circuit.

In addition, by increasing the period of the resonant circuit of the resonant inductance 7 and the resonant capacitor 8, the inflection point W shown in FIG. 1(b) can be brought to the maximum value of the collector Ic, and the above-mentioned Reduce the period of the resonant circuit and set the inflection point W to 0
It is also possible to take it to

〔Effect of the invention〕

As explained above, the present invention connects a resonant inductance in series with a rectifier diode of a rectifier circuit, and a resonant capacitor in parallel to create a flyback type DC-D.
It is possible to eliminate the short-circuit current generated by the rectifier diode recovery characteristic of the C converter, and as a result, the noise generated from the converter can be reduced, and the malfunction of the overcurrent detection circuit can be prevented.

[Brief explanation of drawings]

FIG. 1(a) is a circuit diagram showing the configuration of an embodiment of the present invention,
FIG. 1(b) is the collector current waveform of the switching transistor in FIG. 1(a), FIG. 2(a) is a circuit diagram showing an example of the configuration of a switching power supply circuit according to the conventional technology, and FIG. 2(b) is the collector current waveform of the switching transistor in FIG. 2<a). DESCRIPTION OF SYMBOLS 1... Switching transistor, 2... Pulse transformer, 3... Rectifier diode, 4... Smoothing capacitor, 5... Control circuit, 6... Input power supply, 7...
・Resonance inductance, 8... Resonance capacitor.

Claims (1)

[Claims] In a flyback switching power supply circuit that transforms voltage with a pulse transformer and rectifies and smoothes its output, an inductance is connected in series to a rectifier diode on the secondary side of the pulse transformer, and an inductance is connected in parallel to the rectifier diode. A switching power supply circuit comprising a capacitor and a capacitor.