JP2002223566A - Direct current converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily stabilize both a first output voltage Vo1 and a second output voltage Vo2, when both output voltages are obtained from a common output transformer 2. SOLUTION: A first rectifying smoothing circuit 4 and a second rectifying smoothing circuit 5a are connected to the transformer 2, and a switching element 3 on the secondary side of the transformer 2 is on/off-controlled, so as to make the output voltage of the first circuit 4 constant. Between the transformer 2 and the second circuit 5a, a magnetic amplifier 6 is connected. The magnetic amplifier 6 is controlled, so as to make the output voltage Vo2 of the circuit 5a constant. First and second smoothing reactors L1, L2 respectively of the first and second circuits 4, 5a are coupled electromagnetically to each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a DC converter capable of obtaining a plurality of DC output voltages.

[0002]

2. Description of the Related Art A conventional DC converter for obtaining a plurality of DC output voltages includes a DC power supply 1 having first and second power supply terminals 1a and 1b for supplying DC power as shown in FIG. , Transformer 2, switching element 3, first
And a second rectifying / smoothing circuit 4, 5, a magnetic amplifier (mag amplifier) 6, first and second control circuits 7, 8, and a backflow preventing diode 9. The transformer 2 has a primary winding N1, a secondary winding N2, and a tertiary winding N3. The switching element 3 converts the DC voltage to a high frequency (for example,
150 kHz), and the first and second power supply terminals 1 through the primary winding N1 of the transformer 2.
a and 1b. The first rectifying / smoothing circuit 4 is connected to the secondary winding N2 of the transformer 2 to obtain a first DC output voltage, and includes a first rectifying diode D1, a first commutating diode Dc1, and a first Smoothing reactor L1
And a first smoothing capacitor C1. First rectifying diode D1 and first smoothing reactor L1
Are connected in series to the line between the secondary winding N2 and the first pair of output terminals 10a, 10b. The first smoothing capacitor C1 is connected between the pair of output terminals 10a and 10b. The first commutation diode Dc1 is connected in parallel to the first smoothing capacitor C1 via the first smoothing reactor L1. A pair of first DC output terminals 10
The first load 10 is connected between a and 10b. Second
The rectifying / smoothing circuit 5 is connected to the tertiary winding N3 of the transformer 2 via a magnetic amplifier 6 to obtain a second DC output voltage, and the second rectifying diode D2, the second commutating diode Dc2 and A second smoothing reactor L2 and a second smoothing capacitor C2. The second rectifying diode D2 and the second smoothing reactor L2 are connected in series to a line between the tertiary winding N3 and the second pair of output terminals 11a and 11b. The second smoothing capacitor C2 is connected between the pair of second output terminals 11a and 11b.
The second commutating diode Dc2 is connected in parallel to the second smoothing capacitor C2 via the second smoothing reactor L2. The second load 11 is connected between the pair of second DC output terminals 11a and 11b. The magnetic amplifier 6 is 3
It is connected in series to a path through which current flows from the secondary winding N3 to the second rectifying / smoothing circuit 5. As is well known, the magnetic amplifier 6 is formed of a saturable reactor, and can control the time until reaching saturation by a control current.
The first control circuit 7 forms a means for detecting the first output voltage Vo1 obtained from the first rectifying and smoothing circuit 4 and a pulse width modulation signal for setting the first output voltage Vo1 to a predetermined value. Pulse forming means for controlling the on / off of the switching element 3. The second control circuit 8 includes a means for detecting the second output voltage Vo2 obtained from the second rectifying / smoothing circuit 5 and a control current Ic for setting the second output voltage Vo2 to a predetermined value. Means for supplying According to the conventional DC converter shown in FIG. 1, the first output voltage Vo1 stabilized by the first control circuit 7 can be obtained, and the second output voltage stabilized by the second control circuit 8 can be obtained. The voltage Vo2 can be obtained.

[0003]

By the way, when the first load 10 becomes smaller, the current flowing through the secondary winding N2, the first rectifying diode D1, and the first smoothing reactor L1 also decreases. Since the voltage drop here is small, the first output voltage Vo1 increases. In particular, when the load current I1 decreases so that the current flowing through the first smoothing reactor L1 is cut off, the voltage rise of the smoothing capacitor C1 increases. As a result, the duty ratio of the switching element 3 decreases in order to keep the first output voltage Vo1 at a constant value. As a result, the amount of power supplied from the secondary winding N2 decreases, and the first output voltage Vo1 becomes the target value. At this time, the amount of power that can be supplied from the tertiary winding N3 decreases. If the amount of power supplied from the tertiary winding N3 decreases in a state where conduction is not limited by the magnetic amplifier 6, that is, in a state where the control angle is zero, a predetermined voltage continues to supply the power required by the second load 11. 2 and the second output voltage Vo2 decreases as shown by the solid line in FIG.

An object of the present invention is to provide a DC converter capable of suppressing a decrease in the second output voltage Vo2 when the current of the first load decreases.

[0005]

SUMMARY OF THE INVENTION In order to solve the above problems and to achieve the above object, the present invention provides first and second power supply terminals for supplying DC power, a transformer, a switching element, A first rectifying / smoothing circuit, a magnetic amplifier, and first and second control circuits, wherein the switching element is connected between the first and second power supply terminals via the transformer; The first rectifying and smoothing circuit is connected to the transformer to obtain a first DC output voltage, and includes a first rectifying element, a first commutating element, a first smoothing reactor, and a first smoothing capacitor. The second rectifying and smoothing circuit is connected to the transformer to obtain a second DC output voltage, and includes a second rectifying element, a second commutating element, a second smoothing reactor, And a smoothing capacitor. Said amplifier from said transformer second
The first control circuit is connected to a path through which a current flows to the rectifying / smoothing circuit, and the first control circuit detects a first output voltage obtained from the first rectifying / smoothing circuit, and sets the first output voltage to a predetermined value. Pulse forming means for forming a pulse width modulation signal for turning on / off the switching element, wherein the second control circuit comprises a second rectifying / smoothing circuit obtained from the second rectifying / smoothing circuit. A control current supply unit for supplying a control current for setting the second output voltage to a predetermined value to the magnetic amplifier;
Wherein the smoothing reactor and the second smoothing reactor are electromagnetically coupled to each other.

It is desirable to provide an auxiliary smoothing reactor whose inductance value changes according to a current as described in claim 2.

[0007]

According to the present invention, when the output current of the first rectifying / smoothing circuit decreases, the voltage of the first smoothing reactor increases as a result of the constant voltage control. Since the second smoothing reactor is electromagnetically coupled to the first smoothing reactor, when the voltage of the second smoothing reactor increases, the voltage of the second smoothing reactor also increases, and
The output voltage of the rectifying / smoothing circuit is compensated, and the second output voltage can be kept constant. According to the invention of claim 2,
Since the inductance value of the auxiliary smoothing reactor changes in inverse proportion to the value of the current flowing therethrough, a voltage adjustment action occurs here, and the control range of the magnetic amplifier can be narrowed, and this size reduction can be achieved Can be.

[0008]

Next, an embodiment of the present invention will be described with reference to FIGS. The DC converter shown in FIG. 3 includes a DC power supply 1 having first and second power supply terminals 1a and 1b for supplying DC power, a transformer 2, and an FET, similarly to the DC converter of FIG. A switching element 3, first and second rectifying and smoothing circuits 4 and 5 a, a magnetic amplifier (mag amplifier) 6, first and second control circuits 7 and 8, and a backflow preventing diode 9. . The DC converter shown in FIG. 3 differs from the DC converter shown in FIG. 1 in that the first and second smoothing reactors L1 and L2 are electromagnetically coupled to each other via a magnetic core 12 and that an auxiliary smoothing reactor L3 is provided. Is different from the conventional DC converter.

The transformer 2 has a primary winding N1, a secondary winding N2 and a tertiary winding N3 which are electromagnetically coupled to each other. FE
The switching element 3 made of T turns on and off a DC voltage at a high frequency (for example, 20 to 150 kHz).
Are connected between the power supply terminals 1a and 1b. The first rectifying / smoothing circuit 4 is connected to the secondary winding N2 of the transformer 2 to obtain a first DC output voltage, and includes a first rectifying diode D1, a first commutating diode Dc1, and a first smoothing diode. Reactor L1, a first smoothing capacitor, and C1. The first rectifying diode D1 and the first smoothing reactor L1 are composed of the secondary winding N2 and the first output terminals 10a, 1a.
0b in series. The first smoothing capacitor C1 is connected between the pair of output terminals 10a and 10b. The first commutation diode Dc1 is the first
Is connected in parallel to the first smoothing capacitor C1 via the smoothing reactor L1. The first load 10 is connected between the pair of first DC output terminals 10a and 10b.

A second rectifying / smoothing circuit 5a is connected to a tertiary winding N3 of the transformer 2 via a magnetic amplifier 6 in order to obtain a second DC output voltage. Diversion diode Dc2 and second smoothing reactor L
2 and an auxiliary smoothing reactor L3 and a second smoothing capacitor C2. The second smoothing reactor L2 is electromagnetically coupled to the first smoothing reactor L1 as described above. That is, they are electromagnetically coupled to each other such that the voltage VL2 of the second smoothing reactor L2 changes proportionally to the voltage VL1 of the first smoothing reactor L1.

The auxiliary smoothing reactor L3 connected in series to the second smoothing reactor L2 is formed such that the current IL3 flowing therethrough and the inductance value L have the relationship shown in FIG. In other words, the auxiliary reactor L3 has a large inductance value L in a region where the current IL3 is small as Ia or less, and decreases in a region where the current IL3 is large as Ib or more. The inductance gradually decreases between the currents Ia and Ib. Has characteristics.

The second rectifying diode D2, the second smoothing reactor L2, and the auxiliary smoothing reactor L3 are 3
It is connected in series to the line between the next winding N3 and the second pair of output terminals 11a, 11b. The second smoothing capacitor C2 is connected between the pair of second output terminals 11a and 11b. The second commutating diode Dc2 is connected in parallel to the second smoothing capacitor C2 via the second smoothing reactor L2 and the auxiliary reactor. The second of the pair
The second load 11 is connected between the DC output terminals 11a and 11b. The magnetic amplifier 6 is connected in series to a path through which a current flows from the tertiary winding N3 to the second rectifying / smoothing circuit 5a. As is well known, the magnetic amplifier 6 is formed of a saturable reactor, and can control the time until reaching saturation by a control current.

The first control circuit 7 is for controlling the first output voltage Vo1 obtained from the first rectifying / smoothing circuit 4 to a predetermined value, and as shown in FIG. It comprises a feedback control signal forming circuit 20, a sawtooth wave generator 21, and a comparator 22 for forming a pulse width modulation (PWM) signal. Voltage detection resistors R1 and R2 of the voltage feedback control signal forming circuit 20
Is connected between the pair of first output terminals 10a and 10b. One input terminal of the error amplifier 23 is connected to resistors R1 and R2.
And the other input terminal is connected to a reference voltage source 24.
It is connected to the. A light emitting diode 25 is connected between the output terminal 10a and the output terminal of the error amplifier 23 via a resistor R3. The phototransistor 26 optically coupled to the light emitting diode 25 is connected between the power supply terminal 27 and the ground via a resistor R4. One input terminal of the PWM signal forming comparator 22 is connected to the sawtooth wave generating circuit 21, and the other input terminal is a phototransistor 26 and a resistor R.
4 and connected to the partial pressure point. An output terminal 28 of the comparator 22 is connected to a control terminal (gate) of the switching element 3 in FIG. 3 via a well-known drive circuit (not shown). The sawtooth wave generating circuit 21 generates a high sawtooth wave or a triangular wave such as 20 to 150 kHz. The comparator 22 compares the sawtooth wave with the signal obtained from the voltage feedback control signal forming circuit 20 to form a PWM control signal.

The second control circuit 8 has a second output voltage Vo2
Controls the magnetic amplifier 6 in order to stabilize the resistance, and as shown in FIG. 5, resistors 31 and 32 for voltage detection,
It comprises an error amplifier 33 and a reference voltage source. The voltage detection resistors 31 and 32 are connected to the second output terminals 11 a and 11
b. The negative input terminal of the error amplifier 33 operating as a subtractor is connected to the voltage dividing point of the resistors 31 and 32, the positive input terminal is connected to the reference voltage source 34, and the output terminal 35 is connected via the diode 9 of FIG. Connected to the magnetic amplifier 6. One power supply terminal 36 of the error amplifier 33
Is connected to a power supply terminal 38 to which a voltage indicated by + V is supplied, and the other power supply terminal 37 is connected to the output terminal 11b. Therefore, the control current Ic can flow through the path of the output terminal 35 of the error amplifier 33, the diode 9, the magnetic amplifier 6, the tertiary winding N3, and the power supply terminal 37.

Next, the operation of the DC converter shown in FIG. 3 will be described with reference to FIG. 7 showing the voltage of each part in FIG. The switching element 3 responds to the control signal Vg shown in FIG.
When it is turned on in the sections 1 to t3 and t4 to t5, the first and second winding voltages V1 and V2 corresponding to the turns ratio of the secondary winding N2 and the tertiary winding N3 are changed as shown in FIG. D). When the first output voltage Vo1 becomes higher than the target value, for example, an operation of narrowing the pulse width of the PWM control signal Vg occurs. Conversely, when the first output voltage Vo1 becomes lower than the target value, an operation of expanding the pulse width occurs. .

The time width of the positive direction section of the voltage V2 of the tertiary winding N3 is independent of the size of the second load 11, and is equal to the ON time width of the switching element 3. But,
Since the magnetic amplifier 6 is kept in a high inductance state from t1 to t2 indicated by hatching in FIG. 7D, the current is limited and the second output voltage Vo2 can be controlled.
That is, when the second output voltage Vo2 becomes higher than the target value,
The control current Ic decreases, the time width from t1 to t2 increases, and the second output voltage Vo2 returns to the target value. Conversely, the second
When the output voltage Vo2 becomes lower than the target value, the control current I
c increases, the saturable reactor 6 as a magnetic amplifier saturates quickly, the time width from t1 to t2, that is, the control width becomes narrow, and the second output voltage Vo2 is returned to the target value. In order to enable control of the output voltage Vo2 by the saturable reactor 6, the tertiary winding N3 is set so as to obtain a voltage higher than the target value of the second output voltage Vo2. The first and second voltage smoothing reactor _{L1, L2 V L1, V L2} , if the voltage of the auxiliary smoothing reactor L3 and V _L3, each part of the voltage relationship in saturation interval t2 -t3 saturable reactors 6 Can be expressed by the following equation. _{Vo1 = V1 + V L1 Vo2 =} V2 + V L2 + V L3

If a sufficiently large voltage V2 can be obtained from the tertiary winding N3 and the control width of the magnetic amplifier 6 is set to be large, the tertiary winding N3 is independent of the magnitude of the current I1 of the first load 10. The target second output voltage Vo2 can be supplied from N3. However, if the control range of the magnetic amplifier 6 is reduced and the size is reduced in the conventional device of FIG. 1, the target second output voltage Vo2 is obtained even when the control angle is zero, that is, the interval between t1 and t2 in FIG. Can not get.
On the other hand, in the DC converter according to the present invention shown in FIG. 3, since the first and second smoothing reactors L1 and L2 are electromagnetically coupled, the current I1 of the first load 10 decreases and the first When the voltage V _L1 of the smoothing reactor L1 increases, the voltage V _L2 of the second smoothing reactor L2 is also increased, it is compensated such that the second output voltage Vo2 is increased. Thereby, the second output voltage Vo2 indicated by the solid line can be compensated to the value indicated by the dotted line in the region below the current Ia in FIG.

As is apparent from the above, the second output voltage Vo2 can be stabilized over a wide range of the first load current I1. Since the auxiliary smoothing reactor L3 has the characteristics shown in FIG. 6, the second output voltage Vo2
Satisfactorily can be achieved.

[0019]

[Modifications] The present invention is not limited to the above-described embodiment, and for example, the following modifications are possible. (1) The auxiliary smoothing reactor L3 can be omitted. (2) The magnetic amplifier 6 is connected to the main winding 6a as shown in FIG.
In addition, a control winding 6b is provided, and a control current I is supplied to the control winding 6b.
c can be configured to flow. (3) The rectifier diodes D1 and D2 are used as other rectifiers such as synchronous switches, and commutation diodes Dc1 and D2.
Dc2 can be another rectifying element such as a synchronous switch. Here, the synchronous switch is a switch such as a transistor which is turned on only during a period of supplying power to the output side or a period of flowing commutation current. (4) It is possible to provide a circuit for supplying power to three or more loads by providing more windings in the transformer 2. (5) The transformer 2 has a single-turn transformer configuration, or one or more taps are provided in one secondary winding, and the first and second output voltages having different voltage levels from one secondary winding. Vo1 and Vo2 can be obtained. (6) The magnetic amplifier 6 can be arranged on the output side of the rectifier diode D2.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a conventional DC converter.

FIG. 2 shows a first load current I in the circuits of FIGS. 1 and 3;
FIG. 6 is a diagram showing a relationship between 1 and a second output voltage Vo2.

FIG. 3 is a circuit diagram showing a DC converter according to an embodiment of the present invention.

FIG. 4 is a circuit diagram showing a first control circuit of FIG. 3;

FIG. 5 is a circuit diagram showing a control circuit of FIG. 3;

FIG. 6 is a characteristic diagram showing a relationship between a current of the auxiliary smoothing reactor L3 and an inductance value.

FIG. 7 is a waveform chart showing a state of each unit in FIG. 3;

FIG. 8 is a circuit diagram showing a modified magnetic amplifier.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC power supply 2 Transformer 3 Switching element 4, 5, 5a Rectifying smoothing circuit 6 Magnetic amplifier 7, 8 First and second control circuit D1, D2 Rectifying diode L1, L2 First and second smoothing reactor L3 Auxiliary smoothing Reactor C1, C2 Smoothing capacitor

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H006 CA07 CA08 CB03 CC08 DA04 DC01 5H730 AA04 AS01 BB23 BB57 DD04 EE08 EE10 EE45 EE46 EE59 EE73 FD01 FG05

Claims (2)

[Claims] 1. A first and a second power supply for supplying DC power.
Power terminal, a transformer, a switching element, and a first
And a second rectifying / smoothing circuit, a magnetic amplifier, and first and second control circuits, wherein the switching element is connected to the first
And a second power supply terminal, wherein the first rectifying and smoothing circuit is connected to the transformer to obtain a first DC output voltage, and is connected to the first rectifying element and the first rectifying element.
, A first smoothing reactor, and a first smoothing capacitor, wherein the second rectifying and smoothing circuit is connected to the transformer to obtain a second DC output voltage, Rectifier and second
Wherein the magnetic amplifier is connected to a path through which current flows from the transformer to the second rectifying / smoothing circuit, and wherein the first amplifier includes a first smoothing reactor, a second smoothing reactor, and a second smoothing capacitor. The control circuit turns on the switching element by forming means for detecting a first output voltage obtained from the first rectifying / smoothing circuit and a pulse width modulation signal for setting the first output voltage to a predetermined value. A pulse forming means for performing off control, wherein the second control circuit detects a second output voltage obtained from the second rectifying and smoothing circuit, and sets the second output voltage to a predetermined value. Control current supply means for supplying a control current to the magnetic amplifier for performing the control, wherein the first smoothing reactor and the second smoothing reactor are electromagnetically coupled to each other. DC converter. 2. An auxiliary smoothing reactor connected in series with the second smoothing reactor, wherein the auxiliary smoothing reactor has an inductance value when a current flowing therethrough is small. 2. The DC converter according to claim 1, wherein the DC converter has a characteristic that becomes larger than an inductance value when a current is large.