JPH03183358A - Switching power supply - Google Patents

Abstract

PURPOSE:To absorb surge voltage and to reduce switching loss by arranging surge absorbing capacitor and diode and a resonance reactor around a switching element in a step-down switching power supply. CONSTITUTION:In a step-down switching power supply, surge absorbing capaci tor 21 and diode 22, a resonance reactor 23, and a reverse current block diode 24 are arranged around a switching element, i.e., a transistor 15. Surge voltage is produced from a smoothing reactor 17 upon OFF control of the transistor 15. Since current flows through a closed circuit comprising the reactor 17, the diode 22 and the capacitor 21, the surge voltage is absorbed by the capacitor 21. Furthermore, switching loss is reduced because collector-emitter voltage of the transistor 15 rises slowly at the time of turn OFF.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a switching power supply device generally referred to as a step-down switching regulator.

[Prior Art] As shown in FIG. 4, a conventional step-down switching regulator includes a DC power supply 10 consisting of a rectifying and smoothing circuit having first and second terminals 11 and 12, an output terminal 13, and a second terminal. a ground output terminal 14 connected to the first power supply terminal 12; a transistor 15 as a switching element whose -@ (collector) is connected to the first power supply terminal 11; A smoothing reactor 17 is connected between the connected control circuit 16 , the other end (emitter) of the transistor 15 and the output terminal 13 , and the input end of the smoothing reactor 17 and the ground output terminal 14 . The smoothing diode 18, the output end of the smoothing reactor 17, and the ground output terminal 1
4 and a smoothing capacitor 19 connected between the smoothing capacitor 19 and the smoothing capacitor 19. By controlling the transistor 15 on and off using this circuit, the DC voltage is intermittent, smoothed, and supplied to the load 20.

[Problems to be Solved by the Invention] Incidentally, a surge voltage is generated when the transistor 15 is switched from on to off. This surge voltage is absorbed by a single smoothing capacitor. However, the smoothing capacitor 19 absorbs only the surge voltage higher than this charging voltage. While the transistor 15 is off, the sum of the voltage of the power supply 10 and the voltage of the smoothing reactor 17 is applied between the collector and emitter of the transistor 15 . In order to reduce the power loss when the transistor 15 is turned off, it is necessary to prevent a sudden high voltage from being applied to the transistor 15 when the transistor 15 is turned off. Fourth
The conventional step-down switching regulator shown in the figure does not have a circuit for reducing the loss at turn-off of the transistor 15, so the efficiency is correspondingly low.This type of problem is caused by the smoothing reactor 17 being This also occurs in regulators that transfer energy from the reactor to the load side using a winding.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a switching power supply device that can satisfactorily absorb surge voltages and reduce switching losses by slowing the voltage rise of a switching element.

[Means for Solving the Problems] The present invention for achieving the above objects includes a DC power supply for supplying DC voltage, an output terminal for outputting the DC voltage, and one end of which is connected to one end of the DC power supply. A switching element connected to a terminal, a smoothing reactor connected between the other end of the switching element and the output terminal, and fl! of the switching element. ! a smoothing diode connected between the end and the other terminal of the DC power supply or a ground output terminal; and a smoothing capacitor connected between the output terminal and the other terminal of the DC power supply or the ground output terminal. a step-down switching power supply device comprising: a surge absorbing capacitor having one end connected to the other end of the switching element; and a surge absorbing capacitor having a directionality that turns on when the switching element is turned off. a surge absorbing diode connected between the output end of the surge absorbing capacitor and the other end of the surge absorbing capacitor; and a reverse current blocking diode connected between the other end of the surge absorbing capacitor and one end of the switching element. The present invention relates to a step-down switching power supply device characterized by comprising a series circuit of a diode and a resonant reactor.

Further, as shown in claim 2, the smoothing reactor is placed closer to the power source than the switching element, and the energy release winding is electromagnetically coupled to the smoothing reactor, so that the winding releases energy to the load side. be able to.

[Function] In the inventions of claims 1 and 2, the capacitor connected in parallel to the smoothing reactor is charged in the opposite direction due to resonance when the switching element is turned on. Therefore, the surge voltage at turn-off can be quickly absorbed. Furthermore, the rise of the voltage applied to the switching element at the time of turn-off can be made smoother.

[First Embodiment] Next, a step-down switching regulator according to a first embodiment of the present invention will be explained with reference to FIGS. 1 and 2. However, since the parts indicated by reference numerals 1 to 20 in FIG. 1 are substantially the same as those shown in FIG. 4, their explanation will be omitted.

The switching regulator shown in Figure 1 has a surge absorbing capacitor 21 and a surge absorbing diode 2 in the circuit shown in Figure 4.
2, resonance reactor 23, and backflow blocking diode 24
It is constructed by adding . -S of the surge absorbing capacitor 21 is connected to the output terminal of the transistor 15 as a switching element, that is, to the input terminal of the reactor 17. A surge absorbing diode 22 is connected between the output end of the reactor 17 and the other end of the capacitor 21 . A series circuit of the diode 24 and the resonant reactor 23 is connected to the a terminal of the capacitor 21 and the transistor 15.
is connected between the collector and the collector.

Transistor 15 of the switching regulator in Figure 1
The output voltage control operation by turning on and off is the same as the circuit shown in FIG. 4, but the surge voltage absorption operation is different. During the ON period of the transistor 15, the capacitor 21 is charged to a negative polarity as shown in FIG. 2(B). That is, the capacitor 21 is charged so that the lower terminal becomes positive and the upper terminal becomes negative. When the transistor 15 is turned off in this state, a surge voltage is generated from the smoothing reactor 17, but a surge voltage is generated from t1 to t in FIG.
As shown in 2, the surge voltage is absorbed by the capacitor 21 so that the current 1 flows. As a result, transistor 15
The collector-emitter voltage VCE of the transistor 15 also rises relatively smoothly as shown in FIG. is well known.

Next, when the transistor 15 is turned on at t3 in FIG. 2, the closed circuit consisting of the capacitor 21, the diode 24, the resonant reactor 23, and the transistor 15 receives a current of 2 as shown in FIG. 2(D). flows, and the capacitor 21 is charged in the opposite direction. This makes it possible to absorb the next surge voltage. In addition,
When the voltage generated based on the energy release reactor 23 is higher than the voltage of the power supply 10, the reactor 23
A portion of the energy is returned to the smoothing capacitor included in the power supply 10.

As described above, according to this embodiment, absorption of surge voltage and reduction of switching loss can be achieved satisfactorily.

[Second Embodiment] Next, a switching regulator according to a second embodiment of the present invention will be described with reference to FIG.

However, in FIG. 3, parts that are substantially the same as those in FIGS. 1 and 4 are designated by the same reference numerals, and their explanations will be omitted.

In the circuit shown in FIG. 3, a smoothing reactor 17 is connected between the power supply 10 and the transistor 15. And this smoothing reactor 17 has a winding for energy release! 125 are electromagnetically coupled. The energy emitting winding 25 is connected in series to the smoothing diode 18. In FIG. 3, a series circuit of a capacitor 21 and a diode 22 is connected in parallel to a smoothing reactor 17, and a resonance reactor 23 is connected to a transistor 15.
As in FIG. 1, the series circuit of diode 24 and capacitor 21 is connected in parallel. Therefore,
The effects of surge absorption and switching loss reduction are substantially the same as in FIG. The smoothing effect of the smoothing reactor 17 is performed via the energy emitting winding. That is, the energy stored in the smoothing reactor 17 while the transistor 15 is on is released to the capacitor 19 and the load 20 via the energy release winding 25 while the transistor 15 is off.

[Modifications] The present invention is not limited to the above-described embodiments, and, for example, the following modifications are possible.

(1) The transistor 15 can be replaced with another switching element such as a field effect transistor.

(2) The on/off control of the transistor 15 as a switching element may be of a self-excitation type or of an @-operation type.

[Effects of the Invention] According to the present invention, it is possible to provide a switching power supply device that can absorb surge voltage and reduce switching loss.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a switching regulator according to an embodiment of the present invention, Fig. 2 is a waveform diagram showing the state of each part in Fig. 1 in principle, and Fig. 3 is a circuit diagram showing a switching regulator according to a second embodiment. FIG. 4 is a circuit diagram showing a conventional switching regulator. 10... DC power supply, 13... Output terminal, 14 - Ground output terminal, 15... Transistor, 16...
Control circuit, 17... Smoothing reactor, 18... Smoothing diode, 19... Smoothing capacitor, 20.
...Load, 21...Surge absorption capacitor, 23.
... Resonant reactor.

Claims (1)

[Scope of Claims] [1] A DC power supply for supplying DC voltage, an output terminal for outputting DC voltage, a switching element having one end connected to one terminal of the DC power supply, and the switching device. a smoothing reactor connected between the other end of the element and the output terminal; a smoothing diode connected between the other end of the switching element and the other terminal of the DC power supply or the ground output terminal; In a step-down switching power supply device comprising a smoothing capacitor connected between the output terminal and the other terminal of the DC power source or the Gundo output terminal, the surge voltage converter has one end connected to the other end of the switching element. an absorption capacitor; and a surge absorption diode connected between the output end of the smoothing reactor and the other end of the surge absorption capacitor and having a directionality of turning on when the switching element is turned off. and a series circuit of a backflow blocking diode and a resonant reactor connected between the other end of the surge absorbing capacitor and one end of the switching element. Device. [2] A DC power supply for supplying DC voltage, an output terminal for outputting DC voltage, a smoothing reactor having one end connected to one terminal of the DC power supply, and the other end of the smoothing reactor. and one of the pair of output terminals, and a switching element connected between the other end of the switching element and the other terminal of the DC power supply or the ground output terminal, and an electromagnetic element connected to the smoothing reactor. a smoothing diode connected in series to the energy emitting winding; and a smoothing diode connected between the output terminal and the other terminal of the DC power supply or the ground output terminal. A step-down switching power supply device comprising a surge absorbing capacitor, one end of which is connected to the other end of the smoothing reactor, and a surge absorbing capacitor having a directionality that is turned on when the switching element is turned off. a surge absorbing diode connected between the input end of the smoothing reactor and the other end of the surge absorbing capacitor; and a surge absorbing diode connected between the other end of the surge absorbing capacitor and the output end of the switching element. A step-down switching power supply device comprising a series circuit of a reverse current blocking diode and a resonant reactor.