JPH0783588B2 - Switching power supply - Google Patents

Description

TECHNICAL FIELD The present invention relates to a switching power supply device generally called a step-down type switching regulator.

[Prior Art] As shown in FIG. 4, a conventional step-down switching regulator has a DC power source 10 including a rectifying and smoothing circuit having first and second terminals 11 and 12, an output terminal 13, and a second terminal 13. The ground output terminal 14 connected to the power supply terminal 12, the transistor 15 as a switching element whose one end (collector) is connected to the first power supply terminal 11, and the transistor 15 turned on.
A control circuit 16 connected to the base for off control,
A smoothing reactor 17 connected between the other end (emitter) of the transistor 15 and the output terminal 13, and a smoothing reactor 17.
A smoothing diode 18 connected between the input terminal of 17 and the ground output terminal 14, and a smoothing capacitor connected between the output terminal of the smoothing reactor 17 and the ground output terminal 14.
It consists of 19 and. When the transistor 15 is controlled to be turned on / off by this circuit, the DC voltage is interrupted, smoothed and supplied to the load 20.

[Problems to be Solved by the Invention] By the way, a surge voltage is generated when the transistor 15 is turned on. This surge voltage is absorbed by the smoothing capacitor 19. However, the smoothing capacitor 19
Absorbs only surge voltages 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 the emitter of the transistor 15. In order to reduce the power loss at the time of turning off the transistor 15, it is necessary to prevent the sudden application of a high voltage to the transistor 15 at the time of turning off. The conventional step-down switching regulator shown in FIG. 4 does not include a circuit for reducing the loss when the transistor 15 is turned off, and therefore the efficiency is correspondingly low. This kind of problem also occurs in a regulator in which the smoothing reactor 17 is moved between the transistor 15 and the power supply 10 and the energy of this reactor is discharged to the load side by using a winding.

Therefore, an object of the present invention is to provide a switching power supply device that can absorb a surge voltage satisfactorily and can moderate the rise of the voltage of a switching element to reduce switching loss.

[Means for Solving the Problems] The present invention for achieving the above object provides a DC power supply for supplying a DC voltage, an output terminal for outputting the DC voltage, and one end of one of the DC power supplies. A switching element connected to a terminal, a smoothing reactor connected between the other end of the switching element and the output terminal, the other end of the switching element and the other terminal of the DC power supply or a ground output terminal. In a step-down switching power supply device including a smoothing diode connected between the output terminals and a smoothing capacitor connected between the output terminal and the other terminal of the DC power supply or the ground output terminal, one end The surge absorbing capacitor connected to the other end of the switching element, and the smoothing element having a direction to turn on when the switching element turns off. Absorption diode connected between the output end of the power reactor and the other end of the surge absorption capacitor, and backflow prevention connected between the other end of the surge absorption capacitor and one end of the switching element. The present invention relates to a step-down type switching power supply device characterized by comprising a series circuit of a diode for resonance and a resonance reactor.

Further, as described in claim 2, the smoothing reactor is arranged on the power source side of the switching element, and the energy emitting winding is electromagnetically coupled to the smoothing reactor, and the energy is emitted to the load side by this winding. be able to.

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

[First Embodiment] Next, a step-down switching regulator according to a first embodiment of the present invention will be described with reference to FIGS. 1 and 2. However, the reference numerals 1 to 20 in FIG. 1 are substantially the same as those shown in FIG. 4, and thus the description thereof will be omitted.

The switching regulator of FIG. 1 is configured by adding a surge absorbing capacitor 21, a surge absorbing diode 22, a resonance reactor 23, and a reverse current blocking diode 24 to the circuit of FIG. One end of the surge absorbing capacitor 21 is a transistor as a switching element.
It is connected to the output end of 15 or the input end of the reactor 17. The surge absorbing diode 22 is connected between the output end of the reactor 17 and the other end of the capacitor 21. The series circuit of the tire 24 and the resonance reactor 23 is a capacitor.
It is connected between the other end of 21 and the collector of the transistor 15.

The operation of controlling the output voltage by turning on / off the transistor 15 of the switching regulator of FIG. 1 is the same as that of the circuit of FIG. 4, but the surge voltage absorbing 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 is positive and the upper terminal is negative. When the transistor 15 is turned off in this state, a surge voltage is generated from the smoothing reactor 17, but a closed circuit composed of the reactor 17, the diode 22 and the capacitor 21 is shown at t1 to t2 in FIG. 2 (C). So the current I1
The surge voltage is absorbed by the capacitor 21 as the current flows.
As a result, the collector-emitter voltage VCE of the transistor 15 rises relatively gently as shown in FIG. It is well known that the switching loss is reduced by the rise of the collector-emitter voltage of the transistor 15 at the time of turn-off.

Next, when the transistor 15 is turned on at t3 in FIG. 2, the capacitor 21, the diode 24 and the resonance reactor 23 are turned on.
As shown in FIG. 2 (D), a current I2 flows through the closed circuit composed of the transistor 15 and the transistor 15, and the capacitor 21 is charged in the opposite direction. This makes it possible to absorb the surge voltage that occurs next. When the voltage generated by the energy emitting reactor 23 is higher than the voltage of the power source 10, a part of the energy of the reactor 23 is returned to the smoothing capacitor included in the power source 10.

As described above, according to this embodiment, it is possible to favorably achieve the absorption of the surge voltage and the reduction of the switching loss.

[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 given the same reference numerals, and descriptions thereof will be omitted.

In the circuit of FIG. 3, a smoothing reactor 17 is connected between the power source 10 and the transistor 15. The energy discharge winding 25 is electromagnetically coupled to the smoothing reactor 17. The energy emitting winding 25 is connected to the smoothing diode 18 in series. 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, a diode 24 and a capacitor are connected to the transistor 15.
It is the same as FIG. 1 that the series circuit with 21 is connected in parallel. Therefore, the effects of surge absorption and switching loss reduction are substantially the same as in FIG. The smoothing action by 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 stored in the capacitor via the energy discharge winding 25 while the transistor 15 is off.
Released to 19 and load 20.

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

(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 a self-excited type or a separately excited type.

EFFECTS OF THE INVENTION According to the present invention, it is possible to provide a switching power supply device capable of absorbing surge voltage and reducing switching loss.

[Brief description 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 of FIG. 1 in principle, and FIG. 3 is a switching regulator of the 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 …… resonance reactor.

Claims (2)

[Claims] 1. A DC power supply for supplying a DC voltage, an output terminal for outputting a DC voltage, a switching element having one end connected to one terminal of the DC power supply, and the other end of the switching element. And a smoothing reactor connected between the output terminal, and a smoothing diode connected between the other end of the switching element and the other terminal of the DC power supply or a ground output terminal, and the output terminal. In a step-down switching power supply device comprising a smoothing capacitor connected between the other terminal of the DC power supply or a ground output terminal, a surge absorbing capacitor having one end connected to the other end of the switching element, The output terminal of the smoothing reactor and the surge absorbing capacitor have a directivity to be turned on when the switching element is turned off. A surge absorbing diode connected between the other end of the surge absorbing capacitor, a series circuit of a reverse current blocking diode connected between the other end of the surge absorbing capacitor and one end of the switching element, and a resonance reactor. A step-down switching power supply device comprising: 2. A DC power supply for supplying a DC voltage, an output terminal for outputting a DC voltage, a smoothing reactor having one end connected to one terminal of the DC power supply, and a smoothing reactor. A switching element connected between the other end and one of the pair of output terminals, and a smoothing reactor connected between the other end of the switching element and the other terminal of the DC power supply or a ground output terminal. Is connected between the output terminal and the other terminal of the DC power supply or the ground output terminal, and the smoothing diode serially connected to the energy discharging winding. A step-down switching power supply device including a smoothing capacitor, a surge absorbing capacitor having one end connected to the other end of the smoothing reactor, A surge absorbing diode connected between the input end of the smoothing reactor and the other end of the surge absorbing capacitor so as to be turned on when the switching element is turned off; and A step-down switching power supply device comprising: a series circuit of a reverse current blocking diode and a resonance reactor connected between the other end of the capacitor and the output end of the switching element.