JP3466448B2 - DC-DC converter - Google Patents

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 insulation function between input and output.

[0002]

2. Description of the Related Art A DC-DC converter is often required to have insulation between its input and output. For example, one end of an electrode may be grounded on the input power source and the output load side.
If there is a potential difference between the two ground points (in the DC-DC converter, there is a potential difference in terms of direct current or alternating current in the process of power conversion), a leakage current will be generated in the loop through the ground, and a leakage relay for safety will be installed. It may cause malfunction, noise malfunction of load equipment, or inconvenience to human body safety.

FIG. 4 is a diagram for explaining the necessity of an insulation function in a DC-DC converter in an example of grounding. 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 load R side of the converter 10 may be grounded. In addition, most of the loads R connect the ground and one of the electrodes with a capacitor C in order to suppress electromagnetic noise to form a noise bypass circuit. In this case, the AC current is grounded, and an AC leakage current is generated.
As a countermeasure, an insulation transformer is inserted inside the DC-DC converter 10.

FIG. 5 is a circuit configuration diagram of a DC-DC converter having a high frequency insulating transformer in a conventional example. The operation of the circuit will be described. Hinv is a semiconductor switch Qx1
To Qx4, which is a bridge inverter, converts the DC input voltage Ein into a high-frequency AC voltage and applies it to the primary winding n1 of the transformer T. A diode rectifier circuit Hre in which an AC voltage induced in the secondary winding n2 is composed of a diode D.
It is converted to direct current by c and smoothed by the filter of the reactor Lx and the capacitor C to obtain the output direct current voltage Eout. In this converter circuit, the transformer T inserted by interposing a high-frequency alternating current is made smaller and lighter. This 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 semiconductor switches Qx1 to Qx4 and the series circuits S1 to S8 of capacitors and resistors provided in parallel with the diode D are snubber circuits.
x1 to Qx4 and surge voltage applied to the diode D are recovered to suppress overvoltage stress. The high-frequency transformer T used in this conventional example has a large winding diameter when used for a large current (large capacity), so that it is difficult to close the magnetic coupling between the primary and secondary windings. . The reason why the coupling does not become dense is that the leakage inductance becomes large. Since it is a high-frequency circuit, the voltage drop due to the leakage inductance becomes too large to be ignored, which makes voltage control difficult.
Moreover, the power conversion efficiency is reduced. Generally used for small capacity devices of 1 kW or less.

FIG. 6 is a circuit configuration diagram of a DC-DC converter using a chopper in a conventional example. 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. 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 while the semiconductor switch Qx is off. The voltage Eout of the capacitor C becomes a DC output. The reactor L accumulates energy and at the same time plays a role of an insulating transformer to insulate 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 this reactor L is 1/2 × (inductance) ×
(Current) ² . A voltage having the illustrated polarity is induced in each winding during the ON period of the semiconductor switch Qx. 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 drawing is induced in the secondary winding n2 of the reactor, the diode Dx is energized, and the electromagnetic energy stored in the reactor L is discharged to the capacitor C side.
Switching duty ratio of semiconductor switch Qx X =
When the ON period / (ON period + OFF period) is changed, the output voltage Eout changes from zero voltage to the input voltage Ein as follows.
Can be changed to a higher level. Eout = x / (1-x) · n1 / n2 · Ein (0 ≦ x <1) (1) For example, when X = 0.5 and n1 / n2 = 1, Eout
= Ein. The relationship of equation (1) is not affected by the magnitude of the flowing current. S9 and S10 are snubber circuits.

In this chopper converter, since the switching frequency can be arbitrarily increased to, for example, 20 kHz, the insulating reactor itself is small and lightweight. However, as 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 rough. This is because the leakage inductance of the reactor increases, which causes a voltage drop and lowers controllability. It also reduces efficiency. Furthermore, electromagnetic radiation or conduction noise is increased, and it is necessary to take strong suppression measures, resulting in cost increase. It is generally used in devices of 100 W or less.

These DC-DC converter circuits become a DC-DC converter device by adding a control device for semiconductor switches, and can be used alone, or can be inserted into a DC part of a rectifier device or a UPS. Also used for isolation between outputs. The semiconductor switches shown in FIGS. 5 and 6 include power MOSFETs in addition to the bipolar transistors shown in the figures.
And IGBT 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.

The present invention has been made in view of the above-mentioned problems, and is a DC-comprising a small and lightweight insulating means which is practical and has a large capacity without deterioration of controllability.
An object is to provide a DC converter.

[0012]

In order to solve the problem of coarse coupling between the input and output of a transformer, which has hindered the increase in capacity of a DC-DC converter, a common winding is provided for 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 non-conductive.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is directed to a DC input voltage Ein.
To the semiconductor switch Q on the positive side and the negative side, respectively.
Received by the reactor L of the winding n1 in which 1 and Q2 are connected in series,
This reactor L is connected in parallel with a circuit in which the positive and negative electrodes of a capacitor C1 are connected in series with diodes D1 and D2, and the DC voltage of this capacitor C1 is used as an output to turn on the semiconductor switches Q1 and Q2 at the same time. Electromagnetic energy is accumulated in the reactor L, and after the required electromagnetic energy is accumulated, the semiconductor switch Q1,
DC-DC characterized in that an insulating function is provided between the input and the output by simultaneously turning off Q2 and discharging the capacitor C1 via the diodes D1 and D2.
A converter, the reactor L is provided with a second winding n2, and a series circuit of a third diode D3 and a second capacitor C2 is connected in parallel with the second winding n2,
A DC-DC converter characterized in that the DC voltage of the second capacitor C2 is also output, and the reactor L is provided with a second winding n2.
In parallel with 2, a third diode D3 and a second capacitor C
A DC-DC converter in which two series circuits are connected and the DC voltage of the second capacitor C2 and the DC voltage of the first capacitor C1 are added to produce an output. The purpose of the DC-DC converter is to provide a snubber circuit S in parallel with the L winding.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a first embodiment of the present invention. A reactor L with one winding n1 is used in place of the reactor L with two windings in FIG. The input DC voltage Ein is applied to the reactor L via the semiconductor switch pair Q1 and Q2.
The winding of the reactor L also has a diode pair D1, D
2 is connected to the capacitor C1. While the semiconductor switch pair Q1, Q2 is on, the voltage of the illustrated polarity is applied to the reactor L and the current increases. Along with this, the amount of accumulated electromagnetic energy in the reactor L increases. During this time, the voltage of the sum of the polarities of the reactor L and the capacitor C1 shown in the figure is applied to the diode pair D1 and D2. The polarity of this voltage is opposite to that of the diode pair D1 and D2, and no current flows. When the semiconductor switch pair Q1 and Q2 is turned off, a voltage having a polarity opposite to that shown in the drawing is induced in the winding of the reactor L according to the energy conservation law, and the diode pair D1 and D2
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 connecting and disconnecting the semiconductor switch pair Q1 and Q2. The output voltage Eout increases when the ON / OFF duty ratio X of the semiconductor switch pair Q1, Q2 is increased. This follows the equation (1) similarly to the control of the chopper circuit of the conventional example of FIG.
While the semiconductor switch pair Q1, Q2 is on, the input and output are separated by the diode pair D1, D2. That is, it is insulated. On the other hand, the semiconductor switch pair Q1, Q2 is off during the period when the diode pair D1, D2 is energized, and the input side and the output side are also disconnected during this period. That is, it is insulated. Since the semiconductor switch pair Q1 and Q2 and the diode pair D1 and D2 are not energized at the same time, the input and output sides are always insulated.

Reference numeral S in the broken line is a snubber circuit. The snubber capacitor C is rectified by rectifying the spike-shaped surge voltage generated by the intermittent current of the semiconductor switch and the diode.
let s absorb. 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 it. In addition, the snubber circuit S
It is also effective to provide a series circuit of a resistor and a capacitor in parallel with the reactor L instead of. In the case of the snubber circuit S shown in the drawing, an electrolytic capacitor having a large capacity can be used as the capacitor, so that a sufficient effect can be obtained. Even if the snubber is provided between the terminals of the semiconductor element as in the conventional example (FIGS. 5 and 6), it has the effect of suppressing the surge voltage. Leakage current flows into the device, weakening the effect of insulating between input and output.

FIG. 2 shows a second embodiment of the present invention in which the reactor of the first embodiment of 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 to each other, and the winding ratio n1 / n2 Is larger, the output voltage is higher. However, in the embodiment of FIG. 1, since the reactor L has one winding, the output voltage is equal when n2 = n1 is set in the equation (1), and in order to increase the voltage, it depends on only the duty ratio X. Become. Since this is also related to controllability, it is not practical to raise the output voltage Eout to more than twice the input voltage Ein. Therefore, in order to obtain higher output voltage,
This embodiment is modified.

A second winding n2 is provided in the reactor L and combined with a diode D3 and a capacitor C2 to obtain a second output voltage. The output voltages Eout are obtained by adding the voltages of the capacitors C1 and C2. The ratio of the voltages of C1 and C2 depends on the ratio of the windings of the reactor L, n2 / n1. Since the voltage of C1 is the same as that in the first embodiment of FIG. 1, the output voltage Eout is increased by the voltage of C2. Also, 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. Since the sum of the input voltage Ein and the voltage of the capacitor C1 is applied to the semiconductor switches Q1 and Q2 while they are off, the withstand voltage of the semiconductor switch used in the embodiment of FIG. 2 is lower than that in the case of FIG. It will be good.

FIG. 3 shows a third embodiment of the present invention. Figure 2
In this embodiment, the DC voltage of the capacitors C1 and C2 is used as the output of the DC-DC converter to feed the two loads. A high-voltage or multi-output DC-DC converter can be obtained by increasing the number of windings wound around the reactor L and configuring it in the same manner as the circuit of the winding n2.

2 and 3, the snubber circuit S in the embodiment of FIG. 1 is connected to each winding n of the reactor L.
It goes without saying that the addition of 1 and n2 is effective in 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, Q2 is increased, for example, 20 kHz, the reactor L becomes smaller and lighter.

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

[0022]

As described above, according to the present invention, since the input and output can be insulated by the semiconductor element, the reactor L does not need a plurality of windings as shown in FIGS. The defects caused by the coarse 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 multi-output DC-DC converter can be easily constructed. These greatly contribute to improving the controllability, downsizing, and weight saving of the DC-DC converter. In particular, a large capacity device has a remarkable effect. Also,
The same effect can be obtained by applying the present invention as a DC voltage control or an insulating unit of a rectifier or UPS (uninterruptible power supply). By providing the snubber circuit S independent of the input / output, the voltage stress applied to the semiconductor can be relaxed without impairing the insulation between the input / output, so that the life and reliability of the power conversion device can be improved.

[Brief description of 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 in 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 is a DC-DC using a chopper in a conventional example.
It is a circuit block diagram of a converter.

[Explanation of symbols]

10 DC-DC converter C, C1, C2, Cs capacitors D, D1, D2, D3, Dx diodes Ds Zener diode E power supply L, Lx reactor R, Rs resistance Q1, Q2, Qx, Qx1 to Qx4 semiconductor switches S, S1-10 Snubber circuit T transformer

   ─────────────────────────────────────────────────── ─── Continued front page       (56) References JP-A-61-191263 (JP, A)                 JP-A-3-49556 (JP, A)                 JP-A-60-51458 (JP, A)                 Actual Kaihei 7-11892 (JP, U)                 Actual Development Sho 61-22148 (JP, U)

Claims (4)

(57) [Claims] 1. A direct current input voltage (Ein) is received by a reactor (L) of a winding (n1) in which semiconductor switches (Q1, Q2) are connected in series on the positive electrode side and the negative electrode side, respectively. A circuit in which the positive electrode and the negative electrode of the capacitor (C1) are respectively connected in series with the diodes (D1, D2) in parallel is connected, and the direct current voltage of the capacitor (C1) is output, and the semiconductor switch (Q1, Q2) is turned on. The semiconductor switches (Q) are turned on at the same time to accumulate electromagnetic energy in the reactor (L), and after the required electromagnetic energy is accumulated.
1, Q2) are turned off at the same time and the diode (D1,
A DC-DC converter characterized in that an insulating function is provided between the input and the output by discharging the capacitor (C1) via D2). 2. A second winding (n) is attached to the reactor (L).
2) is provided, a series circuit of a third diode (D3) and a second capacitor (C2) is connected in parallel with the second winding (n2), and a DC voltage of the second capacitor (C2) is connected. The DC- according to claim 1, characterized in that
DC converter. 3. A second winding (n) is attached to the reactor (L).
2) is provided, a series circuit of a third diode (D3) and a second capacitor (C2) is connected in parallel with the second winding (n2), and a DC voltage of the second capacitor (C2) is connected. The DC-DC converter according to any one of claims 1 and 2, wherein the DC voltage of the capacitor (C1) according to claim 1 is added to produce an output. 4. The snubber circuit (S) is provided in parallel with the winding of the reactor (L).
The DC-DC converter according to any one of 1.