JPH11150946A - Dc-dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily increase the capacity of a DC-DC converter which has an insulating means between an input and an output. SOLUTION: Input DC voltage Ein is supplied to a reactor L through a pair of semiconductor switches Q1, Q2. Both ends of a winding of the reactor L are connected to a capacitor C1 through a pair of diodes D1, D2. While the semiconductor switches Q1, Q2 are in an ON state, voltage of such a polarity as shown in the Fig. is applied to the reactor L, thereby increasing current and accumulating more electromagnetic energy in the reactor L. During this period, voltage which is the sum of the voltages of the reactor L and the capacitor C1 of such polarities as shown in the figure is applied to the diodes D1, D2. When the semiconductor switches Q1, Q2 becomes an OFF state, voltage having a polarity opposite to that shown in the Fig. is induced in the winding of the reactor L according to the energy conservation law, thereby conducting the diodes D1, D2 conduct and then discharging the electromagnetic energy accumulated in the reactor L toward the side of the capacitor C1 and a load. A section S surrounded by a broken line is a snubber circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC-DC converter having an input / output insulation function.

[0002]

2. Description of the Related Art In many cases, a DC-DC converter requires insulation between its input and output. For example, one end of an electrode may be grounded on a power supply on an input side and a load side on an output.
If there is a potential difference between both ground points (a DC or AC potential difference occurs in the process of power conversion inside the DC-DC converter), a leakage current occurs in a loop through the ground, and a leakage relay for security is used. It may cause malfunction, noise malfunction of the equipment of the load, or inconvenience in human safety.

FIG. 4 is a diagram illustrating the necessity of an insulating function in a DC-DC converter in an example where the DC-DC converter is grounded. 10 is a DC-DC converter, E is a DC power supply, R is a load, and C is a capacitor. Telephone office DC power supply 48V
Has a positive electrode grounded. DC-DC with this as input
The converter 10 may be grounded on the load R side. Most of the loads R have a capacitor C connected between the ground and one of the electrodes to suppress electromagnetic noise, thereby forming a noise bypass circuit. In this case, the AC is grounded, and an AC leakage current is generated.
As a countermeasure, an insulating transformer is inserted inside the DC-DC converter 10.

FIG. 5 is a circuit diagram of a conventional DC-DC converter having a high-frequency insulating transformer. The operation of the circuit will be described. Hinv is the semiconductor switch Qx1
ＸQx4, which converts the DC input voltage Ein into a high-frequency AC voltage and supplies it to the primary winding n1 of the transformer T. A diode rectifier circuit Hre configured by a diode D using the AC voltage induced in the secondary winding n2.
The output DC voltage Eout is obtained by converting the output DC voltage into a DC voltage and smoothing the DC voltage with the filter of the reactor Lx and the capacitor C at c. In this converter circuit, the transformer T to be inserted is reduced in size and weight by interposing a high-frequency alternating current. The converter also controls the voltage level of the output DC voltage Eout (by providing a control signal from a control device not shown) by controlling the semiconductor switches Qx1 to Qx4.

The series circuits S1 to S8 of capacitors and resistors provided in parallel with the semiconductor switches Qx1 to Qx4 and the diode D are snubber circuits.
x1 to Qx4, and a surge voltage applied to the diode D is recovered to suppress overvoltage stress. When the high-frequency transformer T used in this conventional example is used for a large current (large capacity), the winding diameter becomes large, so that it is difficult to make the magnetic coupling between the primary and secondary windings dense. . The reason why the coupling is not dense is that the leakage inductance increases. Since it is a high-frequency circuit, the voltage drop due to the leakage inductance becomes so large that it cannot be ignored, making voltage control difficult.
In addition, the power conversion efficiency is reduced. Generally, it is used for a device having a small capacity of 1 kW or less.

FIG. 6 is a circuit diagram of a conventional DC-DC converter using a chopper. A chopper is used instead of the circuit using the high frequency inverter Hinv in FIG. Upon receiving the DC voltage Ein, the semiconductor switch Qx is turned on to cause the reactor L to store electromagnetic energy. While the semiconductor switch Qx is off, the electromagnetic energy stored in the reactor L is discharged to the capacitor C side by the circuit of the secondary winding n2 and the diode Dx. The voltage Eout of the capacitor C becomes a DC output. The reactor L serves as an insulating transformer at the same time as storing energy, and insulates between input and output.

Next, voltage adjustment will be described. When the semiconductor switch Qx is turned on, the current flowing through the primary winding n1 of the reactor L increases. The magnitude of the electromagnetic energy stored in the reactor L is ×× (inductance) ×
(Current) ² . During the ON period of the semiconductor switch Qx, a voltage of the illustrated polarity is induced in each winding. During this period, the capacitor C is blocked by the diode Dx.
No current flows on the side. When the semiconductor switch Qx is turned off, a voltage having a polarity opposite to that shown in the figure is induced in the reactor secondary winding n2, the diode Dx is energized, and the electromagnetic energy stored in the reactor L is discharged to the capacitor C side.
Switching duty ratio X of semiconductor switch Qx =
When the ON period / (ON period + OFF period) is changed, the output voltage Eout changes from zero to the input voltage Ein as follows.
Can be changed to higher levels. Eout = x / (1−x) · n1 / n2 · Ein (0 ≦ x <1) (1) For example, when X = 0.5, n1 / n2 = 1, Eout
= Ein. The relationship in equation (1) is not affected by the magnitude of the flowing current. S9 and S10 are snubber circuits.

In this chopper converter, the switching frequency can be arbitrarily increased to, for example, 20 kHz, so that the insulating reactor itself is small and lightweight. However, when the power capacity of the reactor increases, the winding diameter increases, and the electromagnetic coupling between the input winding n1 and the output winding n2 becomes coarse. This is to increase the leakage inductance of the reactor, which causes a voltage drop and lowers controllability. It also reduces efficiency. In addition, electromagnetic radiation or conducted noise is increased, and it is necessary to take strong suppression measures, resulting in an increase in cost. Generally, it is used for a device of 100 W or less.

These DC-DC converter circuits become a DC-DC converter device by adding a control device for a semiconductor switch, and can be used alone, or can be inserted into a rectifier or a DC portion of a UPS for input / output. Also used for insulation between outputs. The semiconductor switches shown in FIGS. 5 and 6 include power MOSFETs in addition to the illustrated bipolar transistors.
And IGBTs are also used.

[0010]

However, conventionally, there has been a problem that it is difficult to increase the capacity of a DC-DC converter provided with an insulating means between input and output.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has a small and light-weight DC-DC converter having a large-capacity and practical insulation means between input and output.
An object is to provide a DC converter.

[0012]

In order to solve the problem of the loose coupling between the input and output of the transformer which is hindering the increase in the capacity of the DC-DC converter, a common winding is used for the input and output. The problem of insulation between input and output, which is lost by using a reactor and a common winding, is solved by inserting a semiconductor element in series and making it nonconductive.

[0013]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a DC input voltage Ein.
With the semiconductor switch Q on the positive side and the negative side, respectively.
1 and Q2 are received by a reactor L connected in series, and a circuit in which a positive electrode and a negative electrode of a capacitor C1 are connected in series with diodes D1 and D2, respectively, is connected in parallel with the reactor L. The DC voltage of the capacitor C1 is And a second winding n2 is provided in the reactor L, and the second winding n
2 in parallel with a third diode D3 and a second capacitor C
A DC-DC converter characterized by connecting two series circuits and outputting a DC voltage of the second capacitor C2. The reactor L is provided with a second winding n2. A third diode D in parallel with the second winding n2.
3 is connected to a series circuit of a second capacitor C2, and the DC voltage of the second capacitor C2 is added to produce an output.
A DC-DC converter is characterized in that a snubber circuit S is provided in parallel with the winding of each of the reactors L.

[0014]

FIG. 1 shows a first embodiment of the present invention. The reactor L having one winding n1 is used instead of the reactor L having two windings in FIG. The input DC voltage Ein is applied to the reactor L via the semiconductor switch pair Q1, Q2.
The winding of the reactor L also connects both poles to the diode pair D1, D
2 is connected to the capacitor C1. While the semiconductor switch pair Q1 and Q2 are on, a voltage having the illustrated polarity is applied to the reactor L, and the current increases. Accordingly, the amount of stored electromagnetic energy in the reactor L increases. During this time, a voltage of the sum of the illustrated polarity of the reactor L and the capacitor C1 is applied to the diode pair D1 and D2. The polarity of this voltage is reversed for the diode pair D1 and D2, and no current flows. When the semiconductor switch pair Q1 and Q2 are turned off, a voltage having a polarity opposite to that shown in FIG.
2 is energized and the electromagnetic energy stored in the reactor L is discharged to the capacitor C1 and the load side.

As described above, the input DC power is converted to the output side by the intermittent connection of the semiconductor switch pair Q1 and Q2. The output voltage Eout increases as the duty ratio X of turning on and off the semiconductor switch pair Q1 and Q2 increases. This follows equation (1) as in the control of the conventional chopper circuit of FIG.
While the semiconductor switch pair Q1 and Q2 are on, the input and output are separated by the diode pair D1 and D2. That is, it is insulated. On the other hand, during the period when the diode pair D1 and D2 are energized, the semiconductor switch pair Q1 and Q2 are off, and the input and output sides are also disconnected during this period. That is, it is insulated. There is no simultaneous period during which the semiconductor switch pair Q1, Q2 and the diode pair D1, D2 are energized, so that the input and output sides are always kept insulated.

S in the broken line is a snubber circuit. Rectifies the spike-like surge voltage generated by the current interruption of the semiconductor switch and the diode to form the snubber capacitor C
s. The electric charge (energy) absorbed by the capacitor Cs is discharged to the resistor Rs provided in parallel to prevent the voltage of the capacitor Cs from excessively increasing. The same effect can be obtained by providing a Zener diode Ds instead of the resistor Rs and discharging the Zener diode Ds. Snubber circuit S
There is also an effect if a series circuit of a resistor and a capacitor is provided in parallel with the reactor L instead of. In the case of the illustrated snubber circuit S, a sufficient effect can be obtained because an electrolytic capacitor having a large capacity can be used as the capacitor. Although a snubber can be provided between the terminals of the semiconductor element as in the conventional example (FIGS. 5 and 6), the effect of suppressing the surge voltage can be obtained. Leakage current flows through the wire, and the effect of insulating between input and output is weakened.

FIG. 2 shows a second embodiment of the present invention. The reactor of the first embodiment shown in FIG. 1 is provided with a second winding. Equation (1) shows the relationship between the input voltage Ein and the output voltage Eout in the chopper DC-DC converter. Here, the windings n1 and n2 (FIG. 6) of the reactor are related, and the winding ratio n1 / n2 is used. Is larger, the output voltage is higher. However, in the embodiment of FIG. 1, the output voltage is equal to the case where n2 = n1 is set in the equation (1) because the winding of the reactor L is one. In order to increase the voltage, only the duty ratio X depends. Become. Since this is related to controllability, it is not practical to increase the output voltage Eout to twice or more the input voltage Ein. Therefore, in order to obtain a higher output voltage, FIG.
Is modified.

A second winding n2 is provided in the reactor L, and a second output voltage is obtained in combination with the diode D3 and the capacitor C2. An output voltage Eout is obtained by adding the voltages of the capacitors C1 and C2. The ratio between the voltages of C1 and C2 is determined by the ratio n2 / n1 of the winding of the reactor L. Since the voltage of C1 is the same as that of the first embodiment of FIG. 1, the output voltage Eout becomes higher by the voltage of C2. In addition, the added DC voltage Eou
When t is the same as Eout in FIG. 1, the voltage of the capacitor C1 is lower than the voltage of C1 in FIG. 1 corresponding to the divided voltage. During the period when the semiconductor switches Q1 and Q2 are off, the sum of the input voltage Ein and the voltage of the capacitor C1 is applied to them, so that the breakdown voltage of the semiconductor switch used in the embodiment of FIG. 2 is lower than that of FIG. Will be fine.

FIG. 3 shows a third embodiment of the present invention. FIG.
In this embodiment, the DC voltages of the capacitors C1 and C2 are output from the DC-DC converter and supplied to two loads. If the number of windings wound around the reactor L is increased and the circuit is configured similarly to the winding n2, a high-voltage or multi-output DC-DC converter can be obtained.

In the embodiment shown in FIGS. 2 and 3, the snubber circuit S in the embodiment shown in FIG.
Needless to say, adding to 1, n2 is effective for alleviating the voltage stress applied to the semiconductor. In the first to third embodiments, if the intermittent repetition frequency of the semiconductor switch pair Q1 and Q2 is increased, for example, to 20 kHz, the reactor L becomes small and light.

The DC-DC converter circuit shown in FIGS. 1 to 3 is combined with a control device to form a DC-DC converter (device). Although the bipolar transistors are illustrated as the semiconductor switches Q1 and Q2, it is needless to say that the semiconductor switches Q1 and Q2 can also be used with power MOSFETs and IGBTs.

[0022]

As described above, according to the present invention, the input and output can be insulated by the semiconductor element, so that the reactor L does not require a plurality of windings as shown in FIGS. Defects caused by loose coupling between
Controllability is improved. Further, even a large-capacity reactor L can be put to practical use. Since the switching frequency of the semiconductor switch pair Q1 and Q2 can be easily increased, the reactor L
Can be miniaturized. A high voltage output or a multi-output DC-DC converter can be easily configured. These greatly contribute to improving controllability, downsizing, and weight reduction of the DC-DC converter. In particular, a large capacity device has a remarkable effect. Also,
A similar effect can be obtained by applying the present invention as a DC voltage control or insulation unit of a rectifier or a UPS (uninterruptible power supply). By providing the snubber circuit S independent of the input and output, the voltage stress applied to the semiconductor can be reduced without impairing the insulation between the input and output, so that the life and reliability of the power converter can be increased.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of a DC-DC converter according to a first embodiment of the present invention.

FIG. 2 is a circuit configuration diagram of a DC-DC converter according to a second embodiment of the present invention.

FIG. 3 is a circuit configuration diagram of a DC-DC converter according to a third embodiment of the present invention.

FIG. 4 is a diagram illustrating the necessity of an insulation function in a DC-DC converter.

FIG. 5 is a circuit configuration diagram of a DC-DC converter in a conventional example.

FIG. 6 shows a DC-DC using a chopper according to a conventional example.
FIG. 3 is a circuit configuration diagram of a converter.

[Explanation of symbols]

 10 DC-DC converter C, C1, C2, Cs Capacitor D, D1, D2, D3, Dx diode Ds Zener diode E Power supply L, Lx Reactor R, Rs Resistance Q1, Q2, Qx, Qx1 to Qx4 Semiconductor switch S, S1 -10 snubber circuit T transformer

Claims (4)

[Claims] 1. A DC input voltage (Ein) is received by a reactor (L) of a winding (n1) having semiconductor switches (Q1, Q2) connected in series on a positive electrode side and a negative electrode side, respectively. A DC-DC converter comprising a circuit in which a positive electrode and a negative electrode of a capacitor (C1) are connected in series with diodes (D1, D2), respectively, and a DC voltage of the capacitor (C1) is output. . 2. The reactor (L) according to claim 1, wherein
And a third diode (D3) and a second capacitor (C) in parallel with the second winding (n2).
2) and the second capacitor (C
DC-D characterized in that the DC voltage of 2) is also output.
C converter. 3. The reactor (L) according to claim 1, wherein
And a third diode (D3) and a second capacitor (C) in parallel with the second winding (n2).
2) and the second capacitor (C
2. A DC-DC, comprising adding the DC voltage of 2) and the DC voltage of the capacitor (C1) according to claim 1 to an output.
converter. 4. A snubber circuit (S) is provided in parallel with a winding of a reactor (L).
DC-DC converter.