JPH03178570A - 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:In a DC/DC converter, a diode 26 is connected in series with a capacitor 25. A series circuit of the tertiary winding 27 of a transformer 13, a diode 28 and a reactor 29 is connected in parallel with the diode 26. The polarity of the winding 29 is so set that the lower end of the tertiary winding becomes positive when the upper end of a primary winding 14 is positive. When a transistor 15 is turned from OFF to ON, the energy of the capacitor 25 is started to be discharged by a closed circuit having the capacitor 25, the transistor 15, the winding 27, the diode 28, the transistor 30 and the reactor 29. When a current flows to the winding 27, the energy of the capacitor 25 is discharged to a load side through the 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 configured to intermittent direct current by turning on and off a switching element connected in series with an output transformer, and to obtain a controlled direct current output by rectifying the output of a transformer. That is, D.C.
-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 secondary winding 16 of a 6-transformer 13 to which a series circuit of a primary winding 14 and a switching transistor 15 is connected.
are connected to output terminals 22 and 23 via an output rectifying and smoothing circuit 21 that includes diodes 17 and 18, a reactor 19, and a capacitor 20. A control circuit 24 for controlling on/off of the switching transistor 15, which serves as a DC switching element, is connected to the base of the switching transistor 15. A capacitor 25 is connected in parallel to the switching transistor 15 for the purpose of absorbing surge voltage and reducing switching loss.

In this DC-DC converter, the voltage of the power supply 10 is applied to the primary winding 14 while the switching transistor 15 is controlled to be turned on by the control circuit 24 . The voltage thus induced in the secondary 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. The capacitor 25 has the function of absorbing the surge voltage generated when the transistor 15 switches from on to off and suppressing the increase in the voltage between the collector and emitter of the switching transistor 15. It has the function of slowing down the rise and reducing switching loss.

FIG. 5 shows the collector-emitter voltage V of the transistor 15 to explain this function. Indicates E.

It is practically impossible to reduce the time required to turn the transistor 15 from on to off and conversely from off to on to zero. During the turn-off time, the collector current of the transistor 15 decreases, and conversely, the collector-emitter voltage increases. At this time, if the collector-emitter voltage suddenly increases while current is flowing through the collector 1, power loss (switching loss) will inevitably increase. In the circuit shown in Figure 4, since the surge voltage is absorbed by the capacitor 25, the collector
The emitter voltage rises slowly and switching losses are reduced. If the capacitance of the capacitor 25 is set appropriately, the voltage of the capacitor 25 will become approximately equal to the voltage VS of the power supply 10 by the time the transistor 15 is turned on next time.

[Problems to be Solved by the Invention] In the circuit shown in FIG. 4, when the transistor 15 is turned on, the energy of the capacitor 25 is released through the transistor 15, resulting in a loss.

Therefore, the purpose of the present invention is 1. The purpose of the present invention is to improve the efficiency of a switching power supply device by effectively using the energy of a capacitor for absorbing surges and reducing switching loss.

[Means for Solving the Problems] To achieve the above object, the present invention includes a pair of power supply terminals for supplying DC voltage, and a primary transformer having one end connected to one of the pair of power supply terminals. a switching element having one end connected to the other end of the primary winding and the other end connected to the other of the pair of power supply terminals; an output circuit coupled to the primary winding; In a switching power supply device comprising a control circuit for controlling on/off of a switching element and a capacitor connected in parallel to the switching element, a first backflow blocking diode connected in series to the capacitor; an energy emitting winding connected in parallel to the reverse current blocking diode and electromagnetically coupled to the primary winding; and a directionality that is forward biased by the voltage of the capacitor when the switching element is turned on. The present invention relates to a switching power supply device characterized in that the present invention further comprises a second backflow blocking diode connected in series to the energy emitting winding. Note that the output circuit is connected to the secondary winding of the transformer or the secondary winding of the transformer.
It consists of a combination of a secondary winding and a rectifying and smoothing circuit.

Moreover, as shown in claim 2, it is desirable to connect a reactor in series with the energy release winding.

[Function] In the above invention, when the switching element is switched from on to off, the sum of the power supply voltage and the voltage (surge voltage) of the primary winding of the transformer is applied across the switching element. However, since a capacitor is connected in parallel to the switching element, the voltage across the switching element gradually increases as the capacitor is charged. This protects the switching element from surge voltage and reduces switching loss during turn-off. When the switching element turns from off to on, the energy in the capacitor is released to the output side (load side) via the energy release winding.As a result, the energy in the capacitor is used effectively, increasing the efficiency of the switching power supply. The amount of energy released by the energy release winding depends on the turn ratio between the primary winding and the energy release winding.If the number of turns of the energy release winding is reduced, the energy release effect will be increased. If the number of windings is increased, the energy of the capacitor will be released more quickly.Conversely, if the number of turns of the energy release winding is increased, the energy of the capacitor will be released more slowly.

According to claim 2, by providing a reactor, the energy release rate of the capacitor can be appropriately set.

First Embodiment] Next, a DC-DC converter according to a first embodiment of the present invention will be described with reference to FIG. However, in FIG. 1, the parts indicated by reference numerals 10 to 25 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, a first backflow blocking diode 26 is connected in series with a capacitor 25, and a tertiary winding 27 of a transformer 13 and a second reverse current blocking diode 26 are connected in parallel to the capacitor 25.
A series circuit including a reverse current blocking diode 28, an energy release control transistor 30, and a reactor 29 is connected. The tertiary winding a27 for energy release is electromagnetically coupled to the primary and secondary windings 14.16, and the polarity is such that when the upper end of the primary winding 14 is positive, the lower end of the tertiary winding 27 is positive. It has been determined that

The transistor 30 is a switch for selectively connecting the tertiary winding 27, and has a base connected to the emitter of the switching transistor 15 via a resistor 31, and an emitter connected to the lower end of the capacitor 25 via a reactor 29. , the collector is connected to the tertiary winding 2 via the diode 28.
It is connected to the upper end of 7.

[Operation] The main circuit of this DC-DC converter is the same as that shown in FIG. 4, and DC voltage control and level conversion are performed by turning on and off the switching transistor 15 as a conversion switching element.

When the switching transistor 15 switches from on to off, a surge voltage (flyback voltage) is generated in the primary winding 14, but this is absorbed by the capacitor 25, so that the collector-emitter voltage VC of the switching transistor 15 increases. The rapid rise in [was suppressed, and the fifth
It becomes slow as shown in the figure. As a result, the switching transistor 15 is protected from overvoltage and switching loss is reduced. The voltage on capacitor 25 is charged higher than the power supply voltage due to the flyback voltage, but then discharges and becomes approximately equal to the power supply voltage at the end of the off period if the capacitance of capacitor 25 is set appropriately. Note that during this off period, the upper terminal of the capacitor 25 is charged so that it becomes positive.

Further, the transistor 30 is in an off state.

Next, when the transistor 15 turns from off to on,
The energy of the capacitor 25 begins to be released in a closed circuit consisting of the capacitor 25, the transistor 15, the tertiary winding 27, the diode 28, the transistor 30, and the reactor 29. Since the inductance of the reactor 27 and the tertiary winding 27 exists in the closed circuit, the discharge current of the capacitor 26 does not flow suddenly. When current flows through the tertiary winding 27, the energy of the capacitor 25 is released to the load mark via the transformer 13 and is effectively utilized. The amount of energy released through the transformer 13 is divided into the primary winding 14 and the tertiary winding 2
It depends on the turns ratio with 7. When the number of turns of the tertiary winding 27 is large, energy is released slowly, and when the number of turns is small, energy is released quickly.

Note that the energy release control transistor 31, which functions as a switch, has an emitter potential lower than the base potential during the period when the transistor 15 is on, so that a base current flows and turns the energy release control transistor 31 on. Since the diode 26 is forward biased, the emitter and base are substantially shorted, and no base current flows. Therefore, the transistor 1
5, even if a voltage is generated in the tertiary winding 27 that forward biases the diode 28, the energy release control transistor 30 is kept off, and the tertiary winding 27, the diode 28, and the transistor 3 No current substantially flows through the closed circuit between the reactor 29 and the diode 26.

This embodiment has the following advantages.

(1) The energy of the capacitor 25 is transferred to the transistor 15
When it is turned on, it is not consumed here but is discharged to the load 4 via the tertiary winding 27. Therefore, power loss is reduced and efficiency is increased.

(2) When the transistor 15 turns on, the energy in the capacitor 25 is limited by the inductance of the reactor 29 and the tertiary winding 27 and is slowly released. No current flows, so the switching loss when the transistor 15 turns on is reduced.

[Second Embodiment] Next, the DC-DC converter of the second embodiment shown in FIG. 2 will be explained. However, parts in FIG. 2 that are common to those in FIGS. 1 and 4 are designated by the same reference numerals and their explanations will be omitted.

The DC-DC converter of this second embodiment has a diode 26 and the emitter of the transistor 15, that is, the power supply terminal 12.
It has an auxiliary power supply capacitor 32 connected between the two. One end of this auxiliary power supply capacitor 32 is connected to the control circuit 24.
It is connected to by line 33. Also, this DC-DC
The converter does not have the transistor 30 and resistor 31 shown in FIG.

When transistor 15 turns from on to off, current flows through the circuit consisting of capacitor 25, diode 26, and capacitor 32. As a result, as in the first embodiment, a surge voltage absorption operation and an operation of slowing down the rise of the collector-emitter voltage VCE of the transistor 15 occur. During this off period, a voltage is generated in the tertiary winding 27 that forward biases the diodes 28 and 26, but since the auxiliary power supply capacitor 32 is provided, no excessive current flows and the transistor 15 is turned off. When turned on, capacitor 25 and transistors 15 and 3
A current flows through the closed circuit consisting of the next winding 27, the diode 28, and the reactor 29, and the energy in the capacitor 25 is
The DC-DC converter of the second embodiment, which is then discharged to the load 4 through the winding 27, has the same advantages as the first embodiment, making it easy to obtain power for the control circuit 24. It has the advantage of being able to

[Third Embodiment] In the third embodiment shown in FIG. 3, a transistor 3o as an energy release control switch is connected between the first backflow blocking diode 26 and the lower end of the tertiary winding 27 has been done. The base of this transistor 30 is connected to the control circuit 24. Transistor 30 is turned on at the same time as transistor 15. Thereby, the energy of the capacitor 25 is released in substantially the same operation as in the first embodiment. Note that the time point at which the transistor 3o starts to turn on can be delayed slightly from the time point at which the transistor 15 starts to turn on.

C Modification] The present invention is not limited to the above-mentioned embodiment, and, for example, the following modification is possible.

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

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

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

Furthermore, the present invention can be applied to both self-excited and separately excited 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 power source 10 is generally composed of a rectifier circuit, a smoothing capacitor, etc., but may also be a storage battery, etc.

[Effects of the Invention] According to the present invention, the energy of the capacitor for absorbing surge voltage and reducing switching loss is not wasted.
A switching power supply device with less loss can be provided.

[Brief explanation of drawings]

1 is a circuit diagram showing a DC-DC converter according to a first embodiment of the present invention, FIG. 2 is a circuit diagram showing a DC-DC converter according to a second embodiment of the present invention, and FIG. 3 is a circuit diagram showing a DC-DC converter according to a second embodiment of the present invention. FIG. 2 is a circuit diagram showing a DC-DC converter according to an embodiment of the present invention. FIG. 4 is a circuit diagram showing a conventional DC-DC converter, and FIG. 5 is a waveform diagram showing the collector-emitter voltage of a switching transistor. 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 rectification and smoothing circuit, 24...Control circuit, 25...Capacitor, 26...First reverse current Blocking diode, 27...Third winding, 28...Second backflow blocking diode, 29...Reactor.

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 switching power supply device comprising a circuit and a capacitor connected in parallel to the switching element, comprising: a first reverse current blocking diode connected in series to the capacitor; and a first reverse current blocking diode connected in parallel to the reverse current blocking diode. an energy discharging winding which is electromagnetically coupled to the primary winding; and an energy discharging winding connected in series to the energy discharging winding so as to be forward biased by the voltage of the capacitor when the switching element is turned on. A switching power supply device comprising a second backflow blocking diode. [2] The switching power supply device according to claim 1, further comprising a reactor connected in series to the energy emitting winding.