JPH01177869A - Dc-dc converter - Google Patents

Abstract

PURPOSE:To reduce loss and noises by transferring energy to the load side through a choke coil connected in series with an energy transmission line during the conduction of a switching element. CONSTITUTION:A capacitor 10 in capacitance C connected in series with a diode 5 and an inductance 11 are mounted in a DC-DC converter. The time when currents i1 are brought to zero, a period when a switching element 2 is turned OFF, is set on the basis of a time scale by the capacitor 10 and the inductance 11. Consequently, when the element 2 is conducted by a signal from a control circuit 9, energy is transferred from a DC power 1, and load currents i0 are supplied while the capacitor 10 is charged. When an energy transfer cycle is completed, the switching element 2 is turned OFF, thus switching the element 2 under the state in which currents i1 are brought to zero, then reducing loss and noises.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a forward type DC-DC converter. By arranging a capacitor and connecting an inductor in series with the capacitor between energy transmission lines, the switching element can be switched with zero current to reduce loss and noise.

<Prior art> A conventional technology in which a switching element is switched with zero current in a forward type DC-DC converter to reduce loss and noise is described in Patent Application Publication No. 500585 of 1982. Something is publicly known. FIG. 6 shows an electrical circuit diagram of the forward type DC-DC converter disclosed in the above publication. In the figure, 1 is a DC power supply, 2 is a switching element, 3 is a transformer, 31 is a primary winding of the transformer 3, and 32 is a secondary winding. Transformer 3 has an effective secondary leakage inductance L2. It is configured to have a winding structure having.

4 is a forward rectifier diode, 5 is a flywheel rectifier diode, 6 is a chic coil, 7 is a load, 8 is a capacitor C connected in series with the diode 4 and the secondary winding 32.
9 is a control circuit.

In the above conventional technology, when the switching element 2 becomes conductive, the forward rectifier diode 4 becomes conductive, and the DC power supply 1
A secondary current 12 flows from the transformer 3 through the secondary leakage inductance L2e, and the flywheel rectifier diode 5
is supplied to the load along with the current flowing through it. When the secondary current 12 rises to the load current, the flywheel rectifier diode 5 is turned off and charging of the capacitor 8 is started. The charging current ir of the capacitor 8 has finite rise and fall times due to the secondary leakage inductance L0. The capacitor 8 starts discharging after its charging voltage reaches its peak. This discharge current -ir is the load current 1
When the voltage reaches 0, a reverse voltage is applied to the forward rectifier diode 4, and the forward rectifier diode 4 becomes non-conductive.
The energy transfer cycle ends. Here, the secondary leakage inductance L2. is the self-inductance L2, and L2. <<L2, so when the energy transfer cycle ends and the secondary current 12 disappears,
The primary current i+ also disappears. When the switching element 2 is turned off by the control circuit 9 in this state, the switching element 2 switches with the primary current 11 being zero, so that the loss and noise are reduced.

The time when the energy transfer cycle ends and the secondary current amount 2 disappears is the time when the secondary leakage, inductance and 2. and the capacitance C of the capacitor 8, the period 2πF is determined by the characteristic time scale at π. Therefore, by setting the off time of the switching element 2 based on the above characteristic time scale, the switching element T2 can be switched with zero current. can be done.

Next, switching element 2 is turned off, and capacitor 8
When the energy stored in is released, the flywheel %e-diode 5 becomes conductive and the choke coil 6C
The stored energy is released.

<Problems to be Solved by the Invention> However, in the above-mentioned conventional technology, since the secondary itt inductance L2s of the transformer 3 is utilized, there are the following problems.

(a) The secondary leakage inductance L2s of the transformer 3 is affected by the winding structure, etc., and usually differs from one transformer to another, and its drift is extremely difficult. Due to the error of this secondary leakage inductance Lza, the secondary current 1
2 and the primary current 11;
There is a problem in that the C converter has different currents, making it impossible to switch the switching element 2 with zero current.

(b) As a means for absorbing the error in the secondary leakage inductance L2a of the transformer 3, Patent Application Publication No. 50 of 1982
In Japanese Patent No. 0585, a compensating inductance is added in series to the secondary winding of the transformer 3.

However, the secondary leakage inductance L0 of each transformer 3
Therefore, it is necessary to select and connect an inductor with a suitable inductance for each transformer 3, in other words, for each DC-DC converter. This significantly hinders the practical application of this type of DC-DC converter.

(c) Secondary leakage inductance L2 of transformer 3. Since it is essential to use the DC-
It cannot be applied to DC converters and its application range is narrow.

(d) The waveform of the voltage es seen at both ends of the secondary winding 32 of the transformer 3 has a large distortion, which is a source of noise.

<Means for Solving the Problems> In order to solve the above-mentioned conventional problems, the present invention provides a switching element for switching DC input, and a choke coil that is connected in series to an energy transmission line from the switching element to a load. and a diode that releases energy stored in the choke coil when the switching element is non-conductive, a capacitor connected in parallel to the diode, and a capacitor connected in series to the capacitor between the lines. The invention is characterized in that it includes an inductor.

Effect> While the switching element is conducting, energy is transferred from the DC power supply to the load side through the choke coil connected in series to the energy transmission line, and the capacitor is charged. The charging current of the capacitor has finite rise and fall times due to the inductor connected in series with the capacitor, and tends to oscillate with a period of 2πff. The capacitor starts discharging when the charging voltage reaches its peak. Then, when the discharge current reaches the load current, the current flowing through the switching element becomes zero, and the energy transfer cycle ends. Therefore, by turning off the switching element at the end of the energy transfer cycle,
By switching the switching element with zero current, it is possible to significantly reduce loss and reduce noise.

Next, when the switching element is turned off and the energy stored in the capacitor is released, the diode becomes conductive and the energy stored in the choke coil is released.

The DC-DC converter according to the present invention does not utilize the secondary leakage inductance of the transformer, but rather utilizes the inductance of the inductor, which is an independent component.

The inductance of this inductor, unlike the secondary leakage inductance, is easy to chemotactic. Therefore, a highly practical DC-DC converter that is easy to design can be obtained. Further, since a transformer is not necessarily required, the present invention is applicable not only to those equipped with a transformer but also to DC-DC converters not equipped with a transformer, such as chopper type converters.

<Example> FIG. 1 is an electrical circuit diagram of a DC-DC converter according to the present invention. In the figure, the same reference numerals as in FIG. 6 indicate the same components. This embodiment shows a DC-DC converter without a transformer. 10 is a capacitor with a capacity C which is connected in parallel with the diode 5, and 11 is an inductor with an inductance L which is connected in series with the capacitor 10 between lines (A) and (B). In the embodiment, a series circuit of a capacitor 10 and an inductor 11 is connected in parallel to a diode 5. Therefore, the capacitance C of the capacitor 10 and the inductance of the inductor 11 give a characteristic time scale with a period of 2πff, and based on this characteristic time scale, the current 1
The time when 1 becomes zero, that is, the time when the switching element 2 is turned off is set. The inductor 11 is the capacitor 1
0, it is composed of independent circuit components, and its inductance can be selected to a constant value.

Therefore, the characteristic time scale with a period of 2πff can be set to a constant time. 12 is a smoothing capacitor.

In the above embodiment, the switching element 2 is the control circuit 9
When conduction occurs due to a signal from the DC power source 1, energy is transferred from the DC power source 1, a load current of 50 is supplied, and the capacitor 1o is charged. At this time, diode 5 is non-conductive. The charging current ir of the capacitor 10 has a finite rise and fall time due to the inductor 11 connected in series with the capacitor 1o, and has a period of 2
It tries to vibrate at πff. The capacitor 10 starts discharging after the charging voltage reaches its peak.

Then, when the discharge current -1' reaches the load current 10,
The current 11 flowing through the switching element 2 becomes zero. By turning off the switching element 2 at the end of the energy transfer cycle, the switching element 2 switches with the current 11 being zero, significantly reducing loss and noise.

Next, switching element 2 is turned off, and capacitor 10
When the energy stored in the choke coil 6 is released, the diode 5 becomes conductive and the energy stored in the choke coil 6 is released.

FIG. 2 shows an electrical circuit diagram of another embodiment of the DC-DC converter according to the present invention. In this example,
Capacitor 10 is connected in parallel to diode 5,
The inductor 11 is connected in series with the parallel circuit of the capacitor 10 and the diode 5. The operation of this embodiment is the same as that of FIG. 1, except that when the energy stored in the choke coil 6 is released through the diode 5, it is released through the inductor 11. Details are omitted.

FIG. 3 shows an electrical circuit diagram of yet another embodiment of the DC-DC converter according to the present invention. In this embodiment, a transformer 3 is provided, a switching element 2 is connected in series to its primary winding 31, and a forward rectifier diode 4 is connected in series to its secondary winding 32, as shown in FIG. The circuit configuration corresponds to the conventional circuit. However, instead of using the leakage inductance value of the transformer 3, a series circuit of a capacitor 10 and an inductor 11 is connected in parallel to the diode 5, and the inductance L of the inductor 11 is used. As will be described later, an increase in leakage inductance of the transformer 3 tends to increase noise, so the winding structure is designed so that the leakage inductance is as small as possible.

Next, the operation of the embodiment shown in FIG. 3 will be explained with reference to the waveform diagram shown in FIG. In FIG. 5, (a) shows the waveform of the voltage as appearing across the secondary winding 32, (b) shows the waveform of the secondary current 12 flowing through the forward rectifier diode 4, and (C) shows the terminal voltage ej2 of the inductor 11. waveform diagram,
(d) is a waveform diagram of the terminal voltage ec of the capacitor 10, (e
) is a waveform diagram of the primary current 1, (f) is a waveform diagram of the voltage e1 applied to the switching element 2, and (g) is a waveform diagram of the capacitor 10.
FIG. 2 is a waveform diagram of current ir.

First, the switching element 2 is activated by a signal from the control circuit 9. When conductive at the same time, the fifth
A voltage es as shown in Figure (a) is generated. This voltage e
The forward rectifier diode 4 is made conductive by s, the secondary current 12 flows, a load current amount 〇 is supplied to the load 7, and a charging current i'' flows into the capacitor 10 to start charging.Charging of the capacitor 10 Since the current ir flows through the inductor 11 connected in series with the capacitor 10, 1. At times, almost no current flows, and most of the voltage es is applied across the inductor 11, and its terminal voltage ef
L becomes the voltage ed across the diode 5, which is transmitted to the load side.

After time t1, the charging current ir to the capacitor 10 that starts flowing from zero reaches a positive peak and then decreases to zero.

Meanwhile, the charging voltage ec of the capacitor 10 is
The period 2π determined by the inductance L and capacitance C of 1
increases according to the characteristic time scale at ff,
The terminal voltage eL of the inductor 11 decreases. After the charging voltage ec of the capacitor 10 reaches its peak, the capacitor 10 starts discharging and supplies a discharge current -ir to the load. The secondary current 12 decreases due to this discharge current -ir.

Then, at time t2, the discharge current -ir of the capacitor 10 is 2
When the next current i exceeds, a reverse voltage is applied to the forward rectifier diode 4, the forward rectifier diode 4 becomes non-conductive, and the energy transfer cycle ends. here,
When the energy transfer cycle ends and the secondary current 12 disappears, the primary current i also becomes negligibly small.

Therefore, by turning off the switching element 2 at time t7, the switching element 2 switches in a state where the primary current iI is zero, and the loss and noise are significantly reduced.

Next, even after the switching element 2 is turned off at time t2, the energy stored in the capacitor 10 is released. The energy released by the capacitor 10 has the opposite polarity with respect to the forward rectifier diode 4, and most of it is transmitted to the load 7.
is efficiently supplied. The energy stored in the choke coil 6 causes the diode 5 to conduct from time t5, when the energy stored in the capacitor 10 becomes zero, to time t4, when the switching element 2 is next turned on.

One of the important advantages of this embodiment is that the two
The waveform distortion of the voltage as appearing in the next winding 32 is reduced. Next, this point will be explained with reference to measurement data. FIG. 7 is a secondary winding voltage waveform diagram of a conventional DC-DC converter, and FIG. 8 is a secondary winding voltage waveform diagram of a DC-DC converter according to the present invention. FIG. 7 shows the waveform of the voltage es generated between the secondary winding 32 when a transformer 3 having a structure having a secondary leakage inductance of 160 nH is used, as equivalently shown by the broken line in FIG. 9. . Fig. 8 shows a case where a transformer 3 with a normal structure having a small secondary leakage inductance of 80 nH is used, and an 80 nH inductor 11 is connected in series with a capacitor 10 to match the resonant frequency, as shown in Fig. 10. The waveform of the voltage es generated between the secondary windings 32 is shown. In FIGS. 7 and 8, the horizontal axis represents the time (μS) after the switching element 2 is turned on, and the vertical axis represents the voltage es (V).

As shown in FIG. 7, the conventional DC-DC converter using secondary leakage inductance has two switching elements.
After turning on, the voltage increases to 10 between 0.2 and 0.4 μs.
~25V, oscillating at a maximum of 15 (V).

On the other hand, in the DC-DC inverter according to the present invention, as is clear from FIG. , the maximum is about 7V, and the vibration width is halved compared to FIG. This means that noise can be reduced more than before.

FIG. 4 is an electric circuit diagram of still another embodiment of the DC-DC converter according to the present invention. In this embodiment, a transformer 3 is used, and a capacitor 10 is replaced by a diode 5.
Inductor 11 is connected in parallel to capacitor 1.
0 and a diode 5 in series. The operation of this embodiment is also substantially the same as that of FIG. 3, so the details will be omitted.

<Effects of the Invention> As described above, according to the present invention, the following effects can be obtained.

(a) DC-DC with reduced loss and noise by switching the switching element with zero current
We can provide converters.

(b) Unlike the secondary leakage inductance, the circuit configuration includes a capacitor connected in parallel to the flywheel rectifier diode and an inductor connected in series to the capacitor between the lines.

It is easy to stabilize the time when the current becomes zero. Therefore, a highly practical DC-DC converter that is easy to design can be obtained.

(C) Since a transformer is not necessarily required, the present invention is applicable not only to those equipped with a transformer but also to DC-DC converters not equipped with a transformer, such as chopper type converters.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram of a DC-DC converter according to the present invention, FIG. 2 is an electric circuit diagram of another embodiment, FIG. 3 is an electric circuit diagram of still another embodiment, and FIG.
The figure is an electric circuit diagram in yet another embodiment, FIG. 5(a)
~(g) is a waveform diagram of each part in the embodiment shown in FIG. 3, FIG. 6 is an electric circuit diagram of a conventional DC-DC converter,
FIG. 7 is a secondary winding voltage waveform diagram of a conventional DC-DC converter, and FIG. 8 is a secondary winding voltage waveform diagram of a DC-DC converter according to the present invention.
The next winding voltage waveform diagram, Figure 9 is an electric circuit diagram of a conventional DC-DC converter used to obtain the data in Figure 7, and Figure 10 is used to obtain the data in Figure 8. FIG. 2 is an electrical circuit diagram of a DC-DC converter according to the present invention. 1... DC power supply 2... Switching element 5... Diode 6... Choke coil 10... Capacitor 11... Inductor Figure 1 Figure 5 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Time ζμG)-

Claims (4)

[Claims] (1) A switching element that switches DC input, a choke coil that goes in series with the energy transmission line from the switching element to the load, and a diode that releases the energy stored in the choke coil when the switching element is non-conducting. DC-D comprising
The D converter includes a capacitor connected in parallel to the diode, and an inductor connected in series to the capacitor between the lines.
C-DC converter. (2) The DC-DC converter according to claim 1, wherein the series circuit of the capacitor and the inductor is connected in parallel with the diode. (3) The capacitor is connected in parallel to the diode, and the inductor is connected in series to a parallel circuit of the capacitor and the diode. DC-DC
converter. (4) The transformer includes a primary winding in which the switching element is connected in series, and a secondary winding in which a diode that conducts when the switching element is conductive is connected in series. The DC-DC converter according to item 1, 2 or 3.