JPH08214545A - Switching power converter - Google Patents

Abstract

PURPOSE: To improve the efficiency by effectively utilizing the energy stored in the floating inductance of a circuit. CONSTITUTION: In a switching power converter which uses the switching of an input voltage by controlling ON, OFF a switch element 1 by a drive signal 3 obtained from a driving circuit 2, a capacitor 32 and a diode 33 are inserted in series between both the end terminals of the element 2, a capacitor 34 and a diode 35 are further connected in series between the connecting point C of the capacitor 32 and the diode 33 and the ground point of the element 1, and charge stored in the capacitor 34 is used as a voltage source. Accordingly, the energy stored in the floating inductance 12 of a circuit can be effectively utilized while obtaining its energy absorbing effect. The damage of the element and the adverse influence to other circuit due to noise can be reduced. As the utilizing destination of the absorbed energy, a charge pulling power source at the time of turning OFF the element can be realized by a simple circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power converter for switching DC input power by a switching element and converting the power to the output side to obtain output power in a form different from the input.

[0002]

2. Description of the Related Art A general switching power converter is a DC-DC power converter, which converts an input DC voltage into an output DC voltage having a desired value. Figure 5
FIG. 4 is a block diagram conceptually showing an example of a DC-DC power converter as a conventional switching power converter.
In FIG. 5, the switch element 1 is switched on and off by the drive signal 3 obtained from the switch element drive circuit 2 to switch the DC voltage of the DC power source 4. The rectangular wave voltage 5 obtained by the switching is converted into a DC voltage by the rectifying / smoothing circuit 6 and output from the output terminals 7 and 8. A part of this output voltage is fed back to the drive circuit 2 and the drive circuit 2 outputs a drive signal 3 according to the output voltage.

Since such a switching power converter has characteristics of small size and high efficiency, it has been widely used in recent years as a power supply circuit of various electronic equipment such as an information processing apparatus. As the switch element 1, an FET (field effect transistor), a bipolar transistor, other semiconductor switch element, or the like is used.

FIG. 6 shows a concrete example of the configuration of the circuit of FIG. 5, and the parts having the same functions as those of FIG. 5 are designated by the same reference numerals. Moreover, the case where FET is used as the switch element 1 is shown. In FIG. 6, the drive signal 3 output from the drive circuit 2 is applied to the control terminal (gate terminal of the FET) of the switch element 1 via the speed-up capacitor 9, the resistor 10 and the resistor 11. Switch element 1
Is on when the drive signal 3 is a positive voltage, and is off when the drive signal 3 is a zero voltage.

By the on / off operation of the switch element 1, the current from the DC power supply 4 is switched through the stray inductance 12 of the circuit and the primary winding of the transformer 13, thereby generating a rectangular wave voltage on the secondary side. The rectangular wave voltage is converted into a DC voltage by the rectifying / smoothing circuit 6 including the diode 14 and the capacitor 15, and then output from the output terminals 7 and 8.

It is generally known that the switching power converter can reduce the size of its components by increasing the switching frequency. However, when the switching frequency is increased, the power loss due to the power conversion operation tends to increase, and the power loss due to the high frequency is a non-negligible amount with respect to the volume of the device. Therefore, there is an upper limit to the switching frequency that can be set.

Such power loss includes not only the loss due to the capacitor and the reactor constituting the rectifying / smoothing circuit 6 but also the finite amount and time generated at the time of the state transition of the switch element 1 from ON to OFF and from OFF to ON. Occupies a large loss due to duplication of voltage and current and charging / discharging of the capacitive portion of the switch element 1. Therefore, in order to reduce the loss at the time of switching, it is necessary to make the transition time of the switch element 1 as short as possible, and various circuits have been conventionally proposed.

FIG. 7 shows an example of the proposed circuit, which is disclosed in Japanese Examined Patent Publication No. 53-132732. In FIG. 7, the transformer 13 is provided with a tertiary winding 16 and one end thereof is connected to the control terminal of the switch element 1 via a resistor 17 and a capacitor 18.

According to the above configuration, a flyback pulse, which is a negative voltage generated in the transformer 13 at the same time when the switch element 1 is turned off, is supplied from the tertiary winding 16 to the resistor 17 and the capacitor 1.
By adding to the control terminal of the switch element 1 via 8, it is possible to quickly extract the electric charge accumulated in the capacitance portion of the switch element 1. As a result, it is possible to make a fast transition from on to off.

On the other hand, when the switching transition time is shortened as described above, the current flowing through the switch element 1 sharply decreases when the switch element 1 is turned off, so that the energy accumulated in the stray inductance 12 of the circuit is switched. Concentrate on the capacitance part of 1 and its anode terminal (F
A large surge voltage is suddenly generated between the ET drain terminal) and the cathode terminal (FET source terminal). Such a surge voltage causes noise, not only affects other circuits, but also exceeds the withstand voltage value of the switch element 1 depending on the amount of stored energy, and the switch element 1 may be destroyed. Furthermore, most of this accumulated energy is eventually consumed as a loss in the switch element, so that the temperature of the element rises, which may lead to destruction of the switch element. These problems are particularly remarkable when the switching power converter is used at a low voltage and a large current even if the capacity is the same.

In order to solve this problem, it has been conventionally proposed to provide a snubber circuit 19 or 20 as shown in FIG. In FIG. 8, a snubber circuit 19 including a diode 21, a capacitor 22, and a resistor 23 is provided in parallel with the primary winding of the transformer 13. Alternatively, the snubber circuit 20 including the diode 24, the capacitor 25, and the resistor 26 is provided in parallel with the switch element 1.

According to the above construction, the surge voltage generated when the snubber circuit 19 is turned off is absorbed by the capacitor 22 through the diode 21 and consumed by the resistor 23. Further, in the snubber circuit 20, the surge voltage generated on the anode side of the switch element 1 is absorbed by the diode 25 from the diode 24 and consumed by the resistor 26. Therefore, the surge voltage can be reduced, noise can be reduced, and the switch element 1 can be protected from damage.

[0013]

In the circuit of FIG. 7, it is necessary to provide the tertiary winding 16 as a power source for extracting the accumulated charge of the switch element 1. If the tertiary winding 16 is not provided, it is externally supplied. It is necessary to provide a dedicated power source, which causes problems such as power consumption, increase in component cost, and decrease in efficiency.

Further, as shown in FIG. 8, snubber circuits 19 and 20 are provided.
In the case of providing the device, although the energy absorption effect is large, the absorbed energy is consumed by the resistors 23 and 26, which causes problems such as a decrease in efficiency, an increase in capacity of the cooling device, and an increase in size.

The present invention has been made to solve the above problems, and an object thereof is to convert switching power capable of effectively using the absorbed energy while absorbing the stored energy due to the stray inductance of the circuit. To get the equipment.

Another object of the present invention is to obtain a switching power converter capable of realizing a power source for extracting accumulated charges of a switch element with a simple circuit.

[0017]

According to the present invention, in a switching power converter in which an input voltage is switched by controlling ON / OFF of a switch element, a switching power converter connected in series between both terminals of the switch element is provided. 1 diode and 1st capacitor, 2nd diode and 2nd diode connected in series between the connection point of said 1st diode and 1st capacitor, and the reference potential side terminal of said switch element. And a switching power converter including a capacitor.

[0018]

When the switching element makes a transition from on to off, electromotive force is generated due to the energy stored in the stray inductance of the circuit, and the cathode-anode voltage of the switching element tends to rise rapidly, but the first diode turns on. As a result, the energy is absorbed by the first capacitor, and a sharp increase in voltage is suppressed. Next, when the electromotive force decreases, the second
Is turned on, the accumulated charge of the first capacitor flows to the second capacitor, the terminal voltage rises,
This can be used as an auxiliary power source.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the first to fourth embodiments of the present invention will be described with reference to FIG.
4 will be described. 1 to 4, parts having substantially the same function in FIGS. 5 to 8 and in the other figures are denoted by the same reference numerals and overlapping description will be omitted.

FIG. 1 shows a first embodiment. In FIG. 1, the switching element 1 has an anode (point A) and a cathode (B).
The first capacitor 32 and the first diode 33 are provided in series with the connection point (point C) and B
The second diode 35 and the second capacitor 3 between the point
4 and 4 are provided in series. These capacitors 32, 3
4, the diodes 33 and 35 form an auxiliary power supply circuit 31. Incidentally, 36 is a load of this switching power converter. Although a resistive load is shown here, a capacitive load or the like may be used. The current direction of the diode 33 is the same as the current direction of the switch element 1, whereas the current direction of the diode 35 is opposite.

Next, the operation of the above configuration will be described. In this circuit, the energy stored by the stray inductance 12 is absorbed by the auxiliary power supply circuit 31 and finally stored in the capacitor 4, and the charging voltage thereof is supplied to the load 36 for use. The switch element 1 repeats the on / off operation by the drive signal 3 from the drive circuit 2.
When turned on, the current flowing through the switch element 1 simultaneously stores energy in the stray inductance 12 of the circuit. The accumulated amount of energy E, the inductance of L _k in the stray inductance 12, the current and I, represented by _{E = 1/2 (L k} × I 2).

When the switching element 1 makes a transition from on to off, the current flowing through the circuit suddenly decreases, so that the energy stored in the stray inductance 12 cannot maintain the state represented by the above equation. Stray inductance 12
An electromotive force is generated in the circuit forming the. Due to this electromotive force, between the anode and cathode of the switch element 1 (A, B
Voltage) rises sharply. At this time, a current flows through the capacitor 32 and the diode 33, and the capacitor 32 absorbs the energy stored in the stray inductance 12. As a result, the voltage between the terminals of the capacitor 32 becomes
It rises with the voltage between the cathodes. At this time, the speed of the voltage increase becomes slow due to the energy absorption by the capacitor 32, and the rapid increase is suppressed.

This effect is the same as that of the snubber circuit in the prior art. The larger the capacitance of the capacitor 32, the larger the amount of energy absorption and the slower the voltage rise. As a result, it is possible to prevent the switch element 1 from being broken due to a voltage increase, and also to reduce the surge voltage that causes noise.

After that, when the emission of the energy of the stray inductance 12 ends and the electromotive force decreases, the voltage between the anode and the cathode of the switch element 1 decreases. At this time, the inter-terminal voltage of the capacitor 32 is maintained at the maximum voltage due to the non-linear characteristic of the diode 33 connected in series. However, since the anode potential of the switch element 1 and the anode potential of the capacitor 32 are equipotential, as the anode-cathode voltage of the switch element 1 decreases, the cathode potential of the capacitor 32 becomes higher than the cathode potential of the switch element 1. It becomes relatively low. This allows the capacitor 3
The cathode potential of the capacitor 32 becomes lower than the cathode potential of 4, the forward voltage is applied to the diode 35, and the diode 35 is turned on. And the capacitor 32,
A current flows from the capacitor 34 to the capacitor 32 until the cathode potentials of both capacitors 34 become equal, and the capacitor 34 is charged.

Next, when the switch element 1 is turned on again after the switch element 1 is turned off, the anode potentials of the switch element 1 and the capacitor 32 decrease and become substantially equal to the cathode potential of the switch element 1. Also at this time, the cathode potential of the capacitor 32 becomes relatively lower than the cathode potential of the switch element 1, and a current flows from the capacitor 34 toward the capacitor 32 in the same manner as described above, and the capacitor 34 is charged.

By repeating the series of operations described above together with the switching operation of this switching power converter, the energy stored in the stray inductance 12 is always converted into the charge stored in the capacitor 34 via the capacitor 32. The form of energy as the accumulated charge of the capacitor 34 is a DC voltage, which can be effectively used as an auxiliary power supply. In this circuit, the auxiliary power supply is supplied to the load 36, which can improve efficiency. Also, the use of the auxiliary power supply does not have any influence on the switching operation as the main operation.

According to the first embodiment described above, the auxiliary power supply circuit 31 is provided to absorb the stored energy of the stray inductance 12 and convert it into a DC voltage, which is conventionally wasted. It is possible to obtain an effect that the stored energy can be effectively used and efficiency can be improved, a surge voltage can be suppressed to prevent generation of noise, and the switch element 1 can be protected from heat generation and damage due to high voltage.

Next, a second embodiment will be described with reference to FIG. In FIG. 2, an inductor 37 is added in series between the diode C and the point C in the auxiliary power supply circuit 31. In the case of the first embodiment described above, when the capacitor 34 is charged, a large current flows between the capacitors 32 and 34 for a short time due to the voltage difference between the capacitor 32 and the capacitor 34. The power loss in the resistor is large.

In the present embodiment, the addition of the inductor 37 has the effect of absorbing the potential difference between the capacitors 32 and 34 and reducing the loss due to a large current. This effect is more remarkable as the inductance value of the inductor 37 is larger, and contributes to the improvement of the efficiency of the entire switching power converter.

Next, a third embodiment will be described with reference to FIG. In FIG. 3, the second transformer 38 is connected to the auxiliary power supply circuit 31, and the primary winding 39 is connected to the diode 35.
And the secondary winding 40 is provided with a rectifying and smoothing circuit 41 and output terminals 42 and 43. The rectifying / smoothing circuit 41 includes diodes 44, 45, an inductor 46,
It is composed of a capacitor 47.

According to the present embodiment, in the case of the first and second embodiments, the stored energy is converted into the DC voltage by the capacitor 34, while the electric power of the electric power is supplied via the second transformer 38. The effect that conversion and transmission are performed and the auxiliary power supply can be taken out from the outside and used. In this case, since the output is insulated from the switching power converter main body by the second transformer 38, it can be used for a load whose voltage fluctuates.
By selecting the turns ratio of the secondary windings 39 and 40, the effect that a desired output voltage can be obtained can be obtained.

Next, a fourth embodiment will be described with reference to FIG. In FIG. 4, the inductor 37 is connected in series to the diode 35 of the auxiliary power supply circuit 31, and the voltage converted by the capacitor 4 is applied to the control terminal of the switch element 1 via the resistor 11.

This embodiment corresponds to the above-mentioned conventional example shown in FIG. 7, and uses the auxiliary power supply of the auxiliary power supply circuit 31 as a voltage for extracting the accumulated charge of the switch element 1. Therefore, according to the present embodiment, it is not necessary to provide the tertiary winding 16 on the transformer 13 as in the conventional case shown in FIG. 7, and there is an effect that the stored energy can be effectively utilized as a voltage for extracting the stored charge.

The above-described second to fourth embodiments all have the effects of the first embodiment. Also, the first
The fourth embodiment is a flyback type switching power converter in which the rectifying / smoothing circuit 6 is composed of the diode 14 and the capacitor 15, but the rectifying / smoothing circuit 6 is composed of a diode, an inductor, a capacitor, etc. 5
It may be a feedforward type switching power converter as shown in FIG.

[0035]

As described above, according to the present invention, the first diode and the first capacitor are connected in series between both terminals of the switch element, and the connection point between them and the reference potential of the switch element. With the configuration in which the second diode and the second capacitor are connected in series between the side terminal and the side terminal, it is possible to effectively use the accumulated energy of the stray inductance of the circuit and improve the efficiency. Further, it is possible to suppress the surge voltage and reduce noise. Further, it is possible to obtain the effect that the destruction of the switch element 1 can be prevented.

Further, as in the second aspect of the invention, by connecting the inductor to the second diode and the second capacitor in series, it is possible to further improve the efficiency.

Further, as in the third aspect of the present invention, by connecting the primary winding of the transformer to the second diode and the second capacitor in series, the stored energy is passed through the transformer in the form of voltage. Can be taken out to the outside and used effectively for various purposes. In particular, since the voltage insulated by the transformer can be obtained, it is possible to obtain an effect that it can be used for a load having a large voltage fluctuation.

Furthermore, by applying the voltage of the second capacitor to the control terminal of the switch element as in the fourth aspect of the present invention, a power supply for extracting the accumulated charge of the switch element can be obtained by a simple circuit, An effect that can contribute to speeding up of the device is obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a third embodiment of the present invention.

FIG. 4 is a circuit diagram showing a fourth embodiment of the present invention.

FIG. 5 is a configuration diagram conceptually showing a conventional switching power converter.

FIG. 6 is a circuit diagram showing a configuration example of a conventional switching power converter.

FIG. 7 is a circuit diagram showing another configuration example of a conventional switching power converter.

FIG. 8 is a circuit diagram showing still another configuration example of the conventional switching power conversion device.

[Explanation of symbols]

 1 Switch element 2 Drive circuit 12 Stray inductance 31 Auxiliary power supply circuit 32 Capacitor 33 Diode 34 Capacitor 35 Diode 37 Inductor 38 Transformer

Claims (4)

[Claims] 1. A switching power converter in which an input voltage is switched by controlling ON / OFF of a switch element, comprising a first diode and a first capacitor connected in series between both terminals of the switch element. A switching power conversion device including a second diode and a second capacitor connected in series between a connection point between the first diode and the first capacitor and a reference potential side terminal of the switch element . 2. The switching power converter according to claim 1, further comprising an inductor connected in series to the second diode and the second capacitor. 3. The secondary winding of the transformer is further connected in series to the second diode and the second capacitor, and a voltage is taken out from the secondary winding of the transformer. 1. The switching power converter according to 1. 4. The switching power converter according to claim 1, wherein the voltage generated in the second capacitor is applied to the control terminal of the switch element.