JPH03178569A - Switching power supply - Google Patents

Abstract

PURPOSE:To reduce energy loss due to surge voltage absorption by providing energy discharging tertiary winding in a transformer, and effectively discharging the energy of a surge absorbing capacitor through the winding. CONSTITUTION:One end of a series circuit of a tertiary winding 29, a reactor 27 and a diode 28 is connected to the emitter of a transistor 15, and the other end is connected to the connecting point of a capacitor 26 and a diode 25 in a DC/DC converter. The polarity of the winding 29 is so set that the lower end of the winding 29 becomes positive when the upper end of a primary winding 14 is positive. The diode 28 is turned ON during a period in which the transistor 15 is turned from OFF to ON, and the energy of the capacitor 26 is discharged by a closed circuit of the capacitor 26, the transistor 15, the winding 29, the reactor 27 and the diode 28. This energy is discharged to a load side through a transformer 13 to be effectively used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to switching power supplies such as DC-DC converters and DC-AC converters, and more particularly to low-loss switching power supplies.

[Prior Art] A switching regulator, that is, a DC, is configured to intermittent direct current and rectify the output of a transformer by turning on and off a switching element connected in series to an output transformer.
-DC converters are widely used. FIG. 4 shows an example of a conventional DC-DC converter. In this DC-DC converter, a transformer 13 is connected between the first and second power terminals 11 and 12 connected to the DC power supply 10.
A series circuit of a primary winding 14 and a transistor 15 as a switching element is connected. The secondary winding 16 of the transformer 13 has diodes 17 and 18 and a reactor 1.
9 and a capacitor 20. A control circuit 24 for controlling on/off of the switching transistor 15 is connected to the base of the switching transistor 15. A surge absorbing capacitor 26 is connected between the −# (upper end) and the other end (lower @) of the primary winding 14 via a first backflow blocking diode 25 . Further, a discharge resistor R is connected in parallel to the capacitor 26.

In this DC-DC converter, transistor 15
During the period when the power supply 1 is controlled to be turned on by the control circuit 24, the power supply 1
A voltage of zero is applied to the primary winding 14. This results in 2
The voltage induced in the next winding 16 is supplied via the output rectifying and smoothing circuit 21 to a load (not shown) connected between the output terminals 22 and 23. When the transistor 15 switches from on to off, a flyback voltage (surge voltage) is generated in the primary winding 14, but this is absorbed by the capacitor 26 connected in parallel to the primary winding 14.

[Problem to be Solved by the Invention 1] By the way, at least a portion of the charge in the capacitor 26 must be discharged before the next surge voltage occurs. For this purpose, a discharging resistor R is connected in parallel to the capacitor 26. However, power loss occurs here and efficiency decreases.

Therefore, an object of the present invention is to provide a switching power supply device that can lower surge voltage and reduce energy loss due to surge voltage absorption.6 [Means for Solving the Problems] The above-mentioned To achieve the object, the present invention includes a pair of power supply terminals for supplying DC voltage, a primary winding of a transformer having one end connected to one of the pair of power supply terminals, and a primary winding having one end connected to the primary winding. a switching element connected to the other end of the wire, the other end of which is connected to the other of the pair of power supply terminals; an output circuit coupled to the primary winding; and a switching element for controlling on/off of the switching element. a control circuit; a capacitor having one end connected to the other end of the primary winding; A switching power supply device comprising a backflow blocking diode connected between one end of the winding and a reverse current blocking diode connected between the other end of the switching element and the other end of the capacitor, and the primary an energy emitting winding electromagnetically coupled to the winding; and a second backflow blocking diode connected in series to the tertiary winding and having a directionality that turns on when the switching element is turned on. The present invention relates to a switching power supply device characterized by comprising: The output circuit is composed of a secondary winding of a transformer or a combination of a secondary winding and a rectifying and smoothing circuit.

Further, as shown in claim 2, it is desirable to connect a reactor in series with the energy release winding [Function] In the above invention, the surge absorbing capacitor is configured to emit energy through the switching element during the ON period of the switching element. Connected to the winding. As a result, the energy of the capacitor is released to the load side via the energy release winding. The amount of energy released by the energy release winding is determined by the turn ratio between the primary winding and the energy release winding.

If the number of turns of the energy release winding is made small, the energy of the capacitor will be released quickly. Conversely, if the number of turns of the energy release winding is made large, the energy of the capacitor will be released slowly. Since no resistance is connected to the energy release circuit, power loss is small.

Note that by connecting the reactor according to claim 2, it becomes possible to reliably achieve slow release of energy from the capacitor.

[First Embodiment] Next, a DC-DC converter according to a first embodiment of the present invention will be described with reference to FIGS. 1 and 2. However, in FIG. 1, the parts indicated by reference numerals 10 to 26 are substantially the same as those shown by the same reference numerals in FIG. 4, so their explanation will be omitted.

In the DC-DC converter shown in FIG. 1, two tertiary windings are provided as energy release windings of the capacitor 26. This tertiary winding 29 is connected in series to the reactor 27 and the second diode 28, and is electromagnetically coupled to the primary and secondary windings 14,16. The polarity of the tertiary winding 29 is determined such that when the upper end of the primary winding 14 is positive, the lower end of the tertiary winding 29 is positive. One end of the series circuit consisting of the tertiary winding 29, the reactor 27, and the diode 28 is connected to the emitter of the transistor 15,
The other end is connected to the connection point between the capacitor 26 and the diode 25. Note that one end of the capacitor 26 is connected to the lower end of the primary winding 14 , and the other end is connected to the upper end of the primary winding 14 via a diode 25 .

The main operation of the DC-DC converter in Figure 1 is the DC-DC converter in Figure 4.
- It is substantially the same as a DC converter, and sends a controlled DC voltage to the output terminal 22, 23 by controlling the transistor 15 on and off.

As shown in FIG. 2, during the period t1 to t2 when the transistor 15 is switched from on to off, the diode 25 is turned on and the current 11 flows there as shown in FIG. The surge voltage generated on line 14 is transferred to capacitor 26.
The voltage Vc of the capacitor 26 increases. As a result, the collector-emitter voltage V of the transistor 15. This prevents E from becoming excessive. Note that during this off period, the capacitor 26 is charged so that the lower terminal of the capacitor 26 becomes positive.

Next, at t3, the transistor 15 turns from off to on.
~t4 period, as shown in FIG. 2(D), diode 28 is turned on and current I2 flows through it, connecting capacitor 26, transistor 15, tertiary winding 29, and reactor 2.
A closed circuit consisting of a capacitor 26 and a diode 28
energy is released, and the voltage VC across the capacitor 26 drops. Since the inductance of the reactor 27 and the tertiary winding 29 exists in the closed circuit, the discharge current of the capacitor 26 does not flow suddenly. When current flows through the two tertiary windings, the energy of the capacitor 26 is released to the load side via the transformer 13 and is effectively utilized.

The amount of energy released through transformer 13 depends on the turns ratio between primary winding 14 and tertiary winding 29. When the number of tertiary windings 29 is large, energy is released slowly,
When the number of turns is small, it is released quickly.

This embodiment has the following advantages.

(1) Since the energy of the surge absorbing capacitor 26 is released to the load side by the tertiary winding 29, loss is reduced and efficiency can be increased.

(2) When the transistor 15 turns on, the energy in the capacitor 26 is limited by the inductance of the reactor 27 and the tertiary winding 29 and is slowly released. Collector current does not flow. Therefore,
Switching loss when the transistor 15 turns on is reduced.

[Second Example] Next, a DC-DC converter according to a second example shown in FIG. 3 will be described. However, in FIG. 3, parts common to those in FIG. 1 and the fourth country are designated by the same reference numerals, and their explanations will be omitted.

In this second embodiment, a noise prevention capacitor Cf is connected in parallel to the primary winding 14, and a noise prevention inductance element Lf is connected in series. Also, the first volume it! A capacitor 31 is connected in parallel to 14 and the inductance element Lf via a third diode 30. In addition, the capacitor 31 and the transistor 15
A reactor 32 is connected via a diode 33 in parallel to the series circuit.

When a capacitor Cf and an inductance element Lf are provided,
Generation of high frequency noise is suppressed. When an inductance element Lf is connected in series with the primary winding 14, a high surge voltage is generated based on both of them. However, in this embodiment, the capacitance value of the capacitor 26 is set to delay the rise of the voltage of the transistor 15, and the capacitance value of the capacitor 31 is set to cut the overshoot of the voltage of the transistor 15 when it is off. Therefore, both the absorption of surge voltage and the reduction of switching loss when the transistor 15 is turned off can be well related. Note that unless the voltage of the transistor 15 rises suddenly when it is off,
It is well known that switching loss is reduced.

The energy of the capacitor 31 is transferred to the reactor 32 when the transistor 15 is turned on, and then returned to the power supply via the diode 30. Therefore, the energy loss of the capacitor 31 is extremely small.

The DC-DC converter of this second embodiment also has the same effects as the first embodiment.

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

(1) The reactor 27 can be omitted by increasing the inductance value of the tertiary winding 29.

(2) The output rectifying and smoothing circuit 21 can be omitted to form a DC-AC converter.

(3) The present invention is not limited to on-on type switching regulators, but can also be applied to on-off type switching regulators.

Further, the present invention can be applied to both automatic type and separately excited type switching regulators.

(4) In order to take out the output, the transformer 13 can be configured as a single-turn transformer.

(5) Instead of transistor 15, other switching elements such as field effect transistors can be used.

(6) The DC power supply 10 generally consists of a rectifier circuit, a smoothing capacitor, etc., but it may also include a power supply such as a storage battery.

[Effects of the Invention] According to the present invention, it is possible to provide a switching power supply device that can satisfactorily absorb surge voltage and has less energy loss in the surge voltage absorption circuit.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a DC-DC converter according to a first embodiment of the present invention, Fig. 2 is a waveform diagram showing the states of each part in Fig. 1, and Fig. 3 is a circuit diagram showing a DC-DC converter according to a first embodiment of the present invention. FIG. 4 is a circuit diagram showing a conventional DC-DC converter. 10... DC power supply, 11... First power supply terminal, 12
...Second power supply terminal, 13...Transformer, 14...
・Primary winding, 15...Transistor, 16...Secondary winding, 21...Output rectifying and smoothing circuit, 24...Control circuit, 25...First reverse current blocking diode, 26・・・
・Capacitor, 27...Reactor, 28...Second
backflow blocking diode, 29...tertiary winding. Agent Nori Takano 1 diagram

Claims (1)

[Scope of Claims] [1] A pair of power supply terminals for supplying DC voltage; a primary winding of a transformer having one end connected to one of the pair of power supply terminals; and one end connected to the primary winding. a switching element connected to the other end and whose other end is connected to the other of the pair of power supply terminals; an output circuit coupled to the primary winding; and a control for controlling on/off the switching element. a circuit, a capacitor having one end connected to the other end of the primary winding, and a capacitor having a directionality that is turned on by a surge voltage generated in the primary winding, and connecting the other end of the capacitor and the primary winding. a first reverse-blocking diode connected between one end of the line, and a first backflow blocking diode connected between the other end of the switching element and the other end of the capacitor, and connected between the other end of the switching element and the other end of the capacitor, and an energy emitting winding electromagnetically coupled to the winding; and a second backflow blocking diode connected in series to the tertiary winding and having a directionality that turns on when the switching element is turned on. A switching power supply device comprising: [2] A switching power supply device further comprising a reactor connected in series to the energy emitting winding.