JP2003153539A - Current balance circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify a circuit structure, and to avoid the malfunctioning of normal power supply apparatuses, even if some apparatuses among a plurality of power supply apparatuses connected in parallel with each other stop. SOLUTION: A ground side of one transistor TR3 of a second current mirror circuit 16 is connected to a transistor TR2 of a first current mirror circuit 15 and branched and connected to a current balance terminal CB and the ground side of the other transistor TR4 of the second current mirror circuit 16 is connected to an output voltage control resistor R8. A voltage, obtained by adding an output current detecting voltage V1 to a bias voltage VB, is applied to the transistor TR3 and a current balance current IC, corresponding to the difference of output currents of respective switching power supplies is applied to the current balance terminal CB. Using such a constitution, the output voltage is controlled, so as to keep the current balance by applying a current (IR and IC) using the other transistor TR4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current balance circuit for a switching power supply device which, when the outputs of a plurality of switching power supply devices are connected in parallel and used, makes the output current values of the switching power supply devices approximately equal.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 7, when two switching power supply devices 1A and 1B, which are known as switching regulators having a current balance circuit, are connected in parallel to a load 19, they are output. The terminals + V and -V are connected in parallel and the current balance terminals CB are connected, and the output voltage is controlled by the current balance circuit so that the output current values of the switching power supply devices 1A and 1B are substantially equalized. There is.

FIG. 8 shows a circuit of a conventional switching power supply device. The AC input voltage Vin is rectified and smoothed by the input rectification smoothing circuit 3, and then switched by an inverter circuit including an output transformer 4, an inverter element 5 using a MOS-FET, a drive control circuit 6, and a rectification smoothing circuit 7. A constant output voltage Vout is supplied to the load from the output terminals + V and -V.

Output terminals + V and -V are sensing terminals +
S, -S connected to the output voltage Vou of the error detection circuit 8.
You are entering t. The error detection circuit 8 includes resistors R6 and R
An output current corresponding to the difference between the input voltage of the series circuit of 7 and R8 and the reference voltage VR is supplied to the photocoupler light emitting element 13a connected in series with the resistor R9 by the differential amplifier 11 to drive light emission.

The light from the photocoupler light emitting element 13a is received by the photocoupler light receiving element 13b built in the drive control circuit 6, and the inverter element 5 is switching-controlled so as to keep the output voltage at a constant voltage.

The current balance circuit 9 includes resistors R3 and R
4. A current mirror circuit 20 including transistors TR3 and TR4 is provided. The current detection resistor R0 and the current detection voltage V1 of the output current detected by the output current detection circuit 21 are input to the current mirror circuit 20.

Since all the circuit operations of the current mirror circuit 20 operate on the basis of the ground potential, it is necessary to provide a negative potential and flow a constant current to the negative potential side, and a negative voltage circuit is provided. ing.
This minus voltage circuit is composed of, for example, the auxiliary winding 10c of the output transformer 4, the diode D3, and the capacitor C2.

A junction type FE which operates as a constant current source by applying a negative voltage by a negative voltage circuit to the collector of one transistor TR3 of the current mirror circuit 20.
The constant current element 22 using T is connected, and further the current balance terminal CB is connected. Other transistor TR
Reference numeral 4 connects the collector to the resistor R8 of the error detection circuit 8.

FIG. 9 shows the current balance circuit 9 of FIG. 8 taken out, and its operation is as follows. A constant current IR flows through the transistor TR3 of the current mirror circuit 20 by the constant current element 22. Further, a current balance voltage lower than the current detection voltage V1 proportional to the output current by a voltage drop of the resistor R3 and the transistor TR3 due to the constant current IR is applied to the current balance terminal CB.

If the voltage of the current balance terminal of another switching regulator power supply device connected to the current balance terminal CB is low, the current balance current Ic corresponding to the difference between the two flows out, and therefore the collector of the transistor TR3. The current is (IR + Ic). Therefore, the collector current of the other transistor TR4 also becomes (IR + Ic), and the voltage generated in the resistor R8 increases in accordance with the current balance current Ic.

As a result, the output of the differential amplifier 11 also increases, the drive control circuit 6 controls the switching of the inverter element 5 so as to reduce the output voltage Vout, the output current Iout decreases, and the current balance is achieved. .

[0012]

However, in such a conventional current balance circuit, all the circuit operations are performed with reference to the ground potential, so that a negative potential is provided and a constant current is applied. Since it is necessary to supply it to the negative potential side and a negative power source must be prepared, there is a problem that the number of parts is large.

When the current balance terminals are connected in parallel to operate in parallel, for example, even if one switching power supply device fails for some reason and the main fuse is blown and the negative potential is stopped, a constant current is maintained. As the circuit continues to operate, current flows from another normal power supply through the current balance terminal, and the other normal power supply lowers the output voltage in order to balance the current, causing abnormal operation. There was a problem that would end up.

The present invention provides a current balance circuit for a switching power supply, which has a simple circuit configuration and does not malfunction a normal power supply even if some power supplies connected in parallel stop. With the goal.

[0015]

In order to achieve this object, the present invention is constructed as follows.

The present invention is a switching power supply device in which outputs of two or more switching power supply devices are connected in parallel and a current balance terminal is connected between the switching power supply devices so that output current values of the respective switching power supply devices are made substantially equal. The current balance circuit of is targeted.

As the current balance circuit, the present invention has a bias voltage source for generating a predetermined bias voltage VB with reference to the ground potential, and a pair of transistors.
By applying the bias voltage VB to one transistor, the other transistor is operated at a constant current I
It has a first current mirror circuit for flowing R and a pair of transistors. The ground side of one transistor is connected to the other transistor of the first current mirror circuit and is branched and connected to the current balance terminal. The ground side is added and connected to the output voltage input to the output voltage control circuit, and the bias voltage VB is applied to one transistor.
(VB + V1) which is the output current detection voltage V1 added to
The current (IR + IC) obtained by adding the current balance current IC flowing through the current balance terminal to the constant current IR of the first current mirror circuit is applied to apply a current (IR + IC), and thereby the same constant current and the current balance current are added to the other transistor. A second current mirror circuit for controlling the output voltage control circuit so that the current balance current IC becomes zero by flowing (IR + IC).

Therefore, according to the present invention, by forming the constant current circuit by the first current mirror circuit with the bias voltage as a reference, the negative potential is not required, and the circuit structure is simplified and the size can be reduced. Is.

Also, one of the power supplies is destroyed during parallel operation,
When the main fuse is blown, the sub-power supply inside the power supply also stops, so the bias voltage also becomes zero. The present invention is
Since the constant current circuit is built based on the bias voltage, the current value of the constant current circuit also becomes zero, avoiding the problem that current flows from other power supply through the current balance terminal and causes other power supply to malfunction. it can.

Here, the primary side inverter current is detected by the current transformer as the output current detection voltage. When the output current is detected by the current transformer in this way, a voltage exceeding the sub power supply voltage can be generated, and the voltage applied to the current balance terminals can be set to a large value.
Can be strong against disturbances.

Further, as the output current detection voltage, the primary side inverter current is detected by the current detection resistor, and then the bias voltage is differentially amplified and detected as the ground potential. Also in this case, it is possible to generate a current detection voltage exceeding the sub power supply voltage by the differential amplification, and it is possible to set the voltage applied to the current balance terminal to be large and to be strong against disturbance.

[0022]

FIG. 1 is a circuit diagram of an embodiment of a switching power supply device having a current balance circuit according to the present invention.

In FIG. 1, a switching power supply unit 1A
Is the other switching power supply device 1B as shown in FIG.
It is used by connecting in parallel to the load between the output terminal and the output terminal, and in order to balance the current in this case, a current balance circuit is provided.

The switching power supply 1A has an input voltage V
An input rectifying / smoothing circuit 3 is provided following the input terminals 2a and 2b to which in is applied, and the DC input voltage from the input rectifying / smoothing circuit 3 is applied to the inverter circuit.

The inverter circuit includes the output transformer 4 and MO.
It is composed of an inverter element 5 using an S-FET, a drive control circuit 6, a rectifying / smoothing circuit 7 on the secondary side, and an error detection circuit 8.

The error detection circuit 8 has sensing terminals + S,-
It has S, and the output terminals + V and -V are connected here.
Output terminal Vou applied to sensing terminals + S, -S
The voltage t is divided by the series circuit of the resistors R6, R7 and R8 and input to the differential amplifier 11.

The differential amplifier 11 is provided with a reference voltage VR and a negative feedback circuit 12, and the output current corresponding to the difference between the output detection voltage according to the output voltage from the sensing terminals + S and -S and the reference voltage VR is resistance. Photocoupler light-emitting element 1 via R9
3a, and the photocoupler light emitting element 13a is driven to emit light.

The light from the photocoupler light emitting element 13a is input to the photocoupler light receiving element 13b using a phototransistor or the like built in the drive control circuit 6, so that the drive control circuit 6 receives the error voltage from the error detection circuit 8. Accordingly, the switching control of the inverter element 5 is performed so that the output voltage Vout is maintained at a constant voltage.

The current balance circuit 9 of the present invention comprises a bias voltage source 14 for generating a bias voltage VB, a first current mirror circuit 15 and a second current mirror circuit 16. The bias voltage source 14 is created by using an inverter primary current or the like, and receives a power supply from a sub power supply to stably generate a constant bias voltage VB.

The first current mirror circuit 15 is composed of a pair of transistors TR1 and TR2 and resistors R1, R2 and R5. The bases of the transistors TR1 and TR2 are connected to each other, and the transistor TR1 is connected to this base.
One collector is connected.

A resistor R5 is connected to the collector side of the transistor TR1. Furthermore, transistors TR1 and T
Resistors R1 and R2 are connected to the emitter of R2. Here, the transistor circuits TR1 and TR2 are NPN transistors.

The second current mirror circuit 16 is composed of transistors TR3 and TR4 and resistors R3 and R4. The bases of the transistors TR3 and TR4 are connected to each other,
The base connection portion is connected to the collector of the transistor TR3. Resistors R3 and R4 are connected to the emitter sides of the transistors TR3 and TR4.

The first current mirror circuit 15 receives a constant bias voltage VB from the bias voltage source 14. In addition, the bias voltage VB is applied to the second current mirror circuit 16.
The output current detection voltage V proportional to the output current Vout detected from the inverter primary current by the current transformer 10
A voltage (VB + V1) obtained by adding 1 is applied.

In the current transformer 10, the primary winding is connected to the primary side of the inverter, and the output of the secondary winding is a diode D.
1, D2, resistor R10 and capacitor C1 for current detection
The output current detection voltage V1 is extracted after being rectified and smoothed by.

The first current mirror circuit 15 applies a constant current I to the transistor TR1 by applying the bias voltage VB.
R flows, so that a constant current IR also flows through the other transistor TR2, and the transistor TR2 side is connected to the transistor TR3 side of the second current mirror circuit 16 and operates as a constant current source.

One of the transistors TR3 of the second current mirror circuit 16 is connected to the side of the transistor TR2 which operates as a constant current source of the first current mirror circuit 15 and at the same time is branched and connected to the current balance terminal CB.

Therefore, the transistor TR3 has a constant current IR of the transistor TR2 and a current balance terminal CB.
Current balance current IC and the added current (IR + I
C) flows. Here, the current balance current IC will flow according to the difference of the current balance voltage VC of each switching power supply device.

The collector of the other transistor TR4 of the second current mirror circuit 16 is connected to the resistor R of the error detection circuit 8.
8 is connected to the positive side of the transistor TR3, the same current as the current (IR + IC) flowing through the transistor TR3 is passed through the resistor R8, and the output voltage to the differential amplifier 11 is changed in proportion to the output current Iout.

FIG. 2 shows the operation of the current balance circuit 9 of FIG. 1 taken out together with the error detection circuit 8 depending on the voltage / current of each part.

In FIG. 2, the transistor TR2 is driven by a constant current by the operation of the first current mirror circuit 15 by stabilizing the bias voltage VB, and a constant current IR flows through its collector. This constant current IR is given by IR = (VB-VBE1) / (R1 + R5). However, VBE1 is a base-emitter voltage of the transistor TR1.

A voltage (VB + V1) obtained by superimposing the output current detection voltage V1 detected by the current transformer 10 on the bias voltage VB is applied to the second current mirror circuit 16. Therefore, the current balance voltage VC generated at the current balance terminal CB becomes VC = VB + V1- (R3 · 1R + VBE3). However, VBE3 is the base-emitter voltage of the transistor TR3.

At this time, even when the output current Iout = 0 and V1 = 0 due to this, the voltage VC0 of the current balance terminal CB becomes VC0 = VB- (R3 · 1R + VBE3) and a constant voltage is applied. Become.

FIG. 3 shows the relationship between the output current detection voltage V1 and the current balance voltage VC in the present invention.

Here, if a difference occurs in the output currents of the other switching power supply devices to which the current balance terminal CB is connected, the voltage (VC + V1) applied to the second current mirror circuit 16 between the respective current balance circuits is generated. A voltage difference occurs. Therefore, a voltage difference is generated between the voltages VC of the respective current balance terminals CB, which causes a current balance current IC to flow between the switching power supply devices via the current balance terminals CB.

Here, as a specific example, the operation of the current balance circuit will be described taking the case where the output current Iout on the switching power supply side of FIG. 2 increases as an example.

As the output current Iout increases, the output current detection voltage V1 also increases. Therefore, the superimposed voltage (VB + V1) applied to the second current mirror circuit 16 becomes larger than that on the other switching power supply side, and the voltage VC at the current balance terminal CB is proportional to the output current detection voltage V1 as shown in FIG. To increase.

Therefore, the current balance terminal voltage VC becomes larger than that of the other connected power supply device side, and the current balance current IC flows out from the current balance terminal CB. This causes the collector current (IR + I) of the transistor TR3.
C), the collector current of the other transistor TR4 forming the current mirror also becomes (IR + IC).

The collector current (IR + IC) from the transistor TR4, which has increased with the increase of the output current detection voltage V1 as described above, flows into the resistor R8 of the error detection circuit 8 to increase the sensing voltage for the differential amplifier 11, As a result, the drive control circuit 6 of FIG. 1 is switched so as to lower the output voltage Vout of the inverter element 5, and lowers the output current Iout.

Here, in the current balance circuit 9 shown in FIGS. 1 and 2, the primary side inverter current is detected by the current transformer 10 as a method of obtaining the output current detection voltage V1 proportional to the output current Iout. As described above, by using the current transformer 10 to peak-hold the current value of the rectangular wave component, the output current detection voltage V1 having a sufficiently large voltage level can be obtained relatively easily.

Therefore, the detection of the output current detection voltage V1 by the current transformer 10 can generate a voltage exceeding the sub power supply, and the current balance voltage VC to which the current balance terminal CB is added can be set to a large value. It is possible to stabilize the operation of the current balance circuit 9 and realize a circuit resistant to disturbance.

Further, when the current transformer 10 is used, the power supply for obtaining the output current detection voltage V1 is not required, so that there is an advantage that the entire circuit can be simplified.

FIG. 4 shows another embodiment of the current balance circuit of the present invention, which can be applied to the case where the output current detection voltage is detected by a method other than the current transformer.

As a method of the output current detection voltage other than the current transformer, for example, the output current detection signal V1 can be obtained by using a current detection resistor. When this current detection resistor is used, the resistor itself uses a small value in order to prevent loss, and therefore the output current detection signal V1 obtained from the current detection resistor becomes small.

Therefore, in the embodiment of FIG. 4, the output current detection signal V1 obtained from the output current detection resistor is input to the differential amplifier 17 having the input resistor R1 and the negative feedback circuit 18 to set the bias voltage VB. It is applied to the second current mirror circuit 16 after being differentially amplified in a superimposed manner.

As a result, similarly to the case where the current transformer 10 is used, by obtaining a sufficiently large output current detection signal V1, the current balance voltage VC to the current balance terminal CB can be made sufficiently large, and the current balance circuit 9 that is strong against disturbances. Can be realized.

In addition to the current transformer, another method of obtaining the output current detection signal is to generate a resistance component of the output choke coil by averaging and amplifying a rectangular wave voltage generated across the output choke coil. There is a method of extracting only the voltage component and obtaining this as the output current detection signal V1.

In order to take out the output current detection signal using this output choke, it is not necessary to additionally provide a current detection resistor, so that the loss can be reduced and miniaturization can be achieved.

However, since the voltage proportional to the output current generated in the resistance component of the output choke coil is small with respect to the voltage of the rectangular wave component generated at both ends of the output choke coil, the detection voltage is small, and the amplification considering this point is performed. Is required.

FIGS. 5 and 6 are circuit diagrams showing another embodiment of the first current mirror circuit 15 which operates as a low current circuit by applying the bias voltage VB in the above embodiment.

FIG. 5A shows the transistor TR9 of the first current mirror circuit of the embodiment shown in FIG.
This is a circuit substituted by 1. FIG. 5B shows a current mirror circuit, which contains the input side transistor TR1.

FIG. 5C shows a current mirror circuit having no resistors R1 and R2, which is used in an IC or the like. Figure 5
(D) is a current mirror circuit in which, in addition to the transistors TR1 and TR2, the transistor TR5 is quickly added to the transistor TR2 side.

FIG. 6 (E) is a modification of FIG. 5 (D).
The transistor TR2 is replaced with the diode D12. FIG. 6F is a modified example of FIG. 6E, and the diodes D1 and D2 are removed.

FIG. 6 (G) is also a modification of FIG. 6 (E), which is a current mirror circuit used in an IC or the like excluding the resistors R1 and R2. Of course, other current mirror circuits may be used.

It should be noted that the present invention is not limited to the above-described embodiment, but includes appropriate modifications that do not impair the advantages of the object. The present invention is not limited by the numerical values shown in the above embodiment.

[0065]

As described above, according to the present invention, the negative voltage for operating the constant current circuit in the current balance circuit is not required, and the circuit configuration is simplified accordingly and the size of the device can be reduced. You can

Further, when one power supply device is broken during parallel operation and the main fuse is broken, for example, the sub-power supply inside the power supply device is also stopped, so that the bias voltage in the current balance circuit becomes zero. Since the first current mirror circuit that operates as a constant current circuit is provided in the current balance terminal, the current flows into the current balance terminal of the power supply apparatus whose constant current operation has stopped via the current balance terminal of another normal power supply apparatus, It is possible to reliably prevent the normal power supply device from malfunctioning.

Further, by generating the output current detection voltage proportional to the output current by using the current transformer, it becomes possible to generate the output current detection voltage exceeding the sub power supply, and the voltage applied to the current balance terminal can be set large. Therefore, it is possible to realize a current balance circuit with few malfunctions due to disturbance.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a switching power supply device showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing the operating voltage and current by extracting the current balance circuit of FIG.

FIG. 3 is a characteristic diagram of a current balance voltage VC with respect to an output current detection voltage V1.

FIG. 4 is a circuit diagram of another embodiment of the current balance circuit of the present invention.

FIG. 5 is a circuit diagram of another embodiment of the current mirror circuit used in the present invention.

FIG. 6 is a circuit diagram of another embodiment of the current mirror circuit used in the present invention.

FIG. 7 is a circuit block diagram in which outputs of a plurality of switching power supply devices are connected in parallel and used.

FIG. 8 is a circuit diagram of a conventional switching power supply device.

FIG. 9 is a circuit diagram showing the operating voltage and current by extracting the conventional current balance circuit of FIG.

[Explanation of symbols]

1A, 1B: Switching power supply device 2a, 2b: input terminals 3: Input rectification smoothing circuit 4: Output transformer 5: Inverter element 6: Drive control circuit 7: Rectifying and smoothing circuit 8: Error detection circuit 9: Current balance circuit 10: Current transformer 11, 17: Differential amplifier 12, 18: Negative feedback circuit 13a: Photocoupler light emitting element 13b: Photocoupler light receiving element 14: Bias voltage source 15: First current mirror circuit 16: Second current mirror circuit

Claims (3)

[Claims] 1. A current of a switching power supply device in which outputs of two or more switching power supply devices are connected in parallel and a current balance terminal is connected between the switching power supply devices so that output current values of the respective switching power supply devices are made substantially equal. The balance circuit has a bias voltage source that generates a predetermined bias voltage with reference to the ground potential, and a pair of transistors. By applying the bias voltage to one transistor, the other transistor operates at a constant current. A first current mirror circuit for flowing a constant current and a pair of transistors, and the ground side of one transistor is connected to the other transistor of the first current mirror circuit and is branched and connected to the current balance terminal, Input the ground side of the other transistor to the output voltage control circuit. A current balance current flowing through the current balance terminal is added to the constant current of the first current mirror circuit by applying a voltage obtained by adding the output current detection voltage to the bias voltage to the one transistor. A second current mirror circuit that controls the output voltage control circuit so that the current balance current becomes zero by causing a current to flow and thereby causing the same addition current of the constant current and the current balance current to flow through the other transistor; Current balance circuit characterized by having. 2. The current balance circuit according to claim 1, wherein a primary side inverter current is detected by a current transformer as the output current detection voltage. 3. The current balance circuit according to claim 1, wherein as the output current detection voltage, a primary side inverter current is detected by a current detection resistor, and then the bias voltage is differentially amplified as ground potential for detection. A current balance circuit characterized by: