JPH05236738A - Control method for switching power source - Google Patents

Abstract

PURPOSE:To effective by use the leakage energy occurring when-a switch element is off by adding a capacitor and a pulse transformer to the primary side of a switching power source thereby making a simple power circuit, and reduce the loss as a switching power source and lower noise by suppressing surge voltage. CONSTITUTION:When a switch element 7 is turned off, leakage energy is generated on the primary winding of a converting transformer 4. This leakage energy is charged into a capacitor 2 and is discharged through a pulse capacitor 8, and is rectified and smoothed and made into DC power by a diode 9 and a capacitor 10. Moreover, as the effect appendant to the capacitor 2, the charge and the discharge to the capacitor 2 are completed each time the main switch element 7 is turned on or turned off, the surge voltage occurring at sudden change of load can be suppressed. Hereby the leakage energy consumed as heat in a snubber circuit in the past can be effectively used, and high efficiency and low noise can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for absorbing and utilizing leakage energy generated when a switching element is turned off in a switching power supply.

[0002]

2. Description of the Related Art In a conventional switching power supply, the leakage energy generated when a switch element is turned off.
Was absorbed by the snubber circuit as shown in FIGS. 1a and 1b. 1a and 1b, 1 diode, 2 capacitors, 3 resistors, 4 conversion transformers, 5 rectifying diodes, 6 smoothing capacitors, and 7 switch elements.

[0003]

2. Description of the Related Art Leakage energy generated when a switch element is turned off has been conventionally absorbed by a snubber circuit and released as heat. Therefore, the efficiency of the switching power supply is reduced, and heat generation hinders miniaturization of the switching power supply.

[0004]

In a flyback type switching power supply which is one type of switching power supply, the leakage energy generated when the switch element is turned off is charged in a capacitor connected to the primary side of the switching power supply, and at the same time. By supplying the pulse transformer prepared on the primary side with a simple power supply circuit on the secondary side of the pulse transformer, the leakage energy is effectively utilized and the efficiency is improved. On the other hand, by increasing the capacitance of the capacitor 2, the surge voltage applied to the switch element 7 when the switch element 7 is turned off is suppressed and dv / dt is reduced.
As a switching power supply, loss reduction and noise reduction can be achieved.

[0005]

FIG. 2 shows an embodiment of the present invention. Figure 2
In FIG. 1, the same reference numerals are given to those described in FIGS. 1a and 1b. Other than that, there are 8 pulse transformers, 9 diodes, 10 capacitors, and 11 control circuits. Next, the outline of the operation will be described with reference to FIG. When the switch element 7 is turned off, 1 / 2LI @ 2 of leakage energy is generated in the primary winding of the conversion transformer 4.
Here, L is the inductance of the primary winding, and I is the current flowing in the primary winding at the moment when the switch element is turned off.
This leakage energy is charged in the capacitor 2,
It is discharged through the pulse transformer 8 and rectified and smoothed by the diode 9 and the capacitor 10 to become a DC power source. As an additional effect that the capacitor 2 has, even if there is a sudden load change (for example, a change from the maximum load to the minimum load) because the charging / discharging of the capacitor 2 is completed every time the main switch element 7 is turned on / off, It is possible to suppress the surge voltage generated by this. 3a, 3b and 3c are modified circuit examples of FIG. 2 and have the same effect as FIG. FIG. 4 shows operation waveforms (VCE, IC) of the switch element 7 and current waveforms flowing through the pulse transformer 8 through the capacitor 2. In FIG. 4, the shaded portion is the leakage energy supplied to the pulse transformer.

[0006]

As described above, according to the present invention, the leakage energy, which was conventionally consumed as heat in the snubber circuit, is effectively utilized by adding several parts, and Low loss, low noise and high efficiency are achieved.
Further, as a ripple effect thereof, a switch element having a small current / voltage rating can be used, which contributes to cost reduction of the switching power supply.

[Brief description of drawings]

Fig. 1a Example of snubber circuit Fig. 1b Example of snubber circuit Fig. 2 One embodiment according to the present invention Fig. 3a Modification of the embodiment according to the present invention Fig. 3b Modification of the embodiment according to the present invention 3c Modification of Embodiment Based on the Present Invention Voltage / Current Applied to Switch Element Corresponding to FIGS. 3a, 3b, and 3c

[Explanation of symbols]

 1 diode 2 capacitor 3 resistance 4 conversion transformer 5 rectification diode 6 smoothing capacitor 7 switch element 8 pulse transformer 9 diode 10 capacitor 11 control circuit 12 diode

Claims (1)

[Claims] 1. A DC input power source is supplied to a primary winding of a conversion transformer, and intermittent energy generated in the primary winding by turning on / off a switching element connected in series to the primary winding.
In the switching power supply for taking out through the secondary winding of the conversion transformer, a diode and a capacitor connected in series are connected in parallel with the primary winding, and the positive side of the diode is connected to the primary winding. Connect the negative side to the capacitor to the wire. Further, a pulse transformer is connected between the midpoint of the diode and the capacitor and the output side of the switching element, and the leakage energy generated in the primary winding of the conversion transformer when the switching element is off is generated. A method of controlling a switching power supply, comprising: a circuit for charging the capacitor and supplying the pulse transformer to generate a small power source by utilizing leakage energy.