JPH11206116A - Constant voltage constant current power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress overvoltage of output voltage at sudden change of load condition. SOLUTION: A constant voltage and constant current power unit is equipped with switching means 5 and 6 which generate DC power on the secondary winding side, by switching the input DC through the primary winding 2a of the transformer 2 having auxiliary winding 2c, a first constant voltage control means 33 which feedback-controls the switching means so as to stabilize the DC voltage of the DC power to a first voltage value, when the output current based on the DC power voltage is under a specified current value, and a constant current control means 34 which feedback-controls the switching means so as to limit the output current to the specified current value when it is over the specified current value. Then, this power unit is equipped with a second constant voltage control means 9 which feedback-controls the switching means so as to limit the DC voltage of DC power to the second voltage value or under at higher voltage than the first voltage value, based on the induced voltage of the auxiliary winding 2c, and the auxiliary winding 2c is made in the same phase as the secondary winding 2b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant-voltage / constant-current power supply device for converting an input direct current into a direct-current power of a predetermined voltage and for limiting an output current output outside the device to a predetermined current value or less.

[0002]

2. Description of the Related Art A flyback type constant-voltage / constant-current power supply device 51 (hereinafter, also referred to as a "power supply device 51") shown in FIG. The power supply device 51 includes a switching transformer 2 having a primary winding 2a, a secondary winding 2b, and an auxiliary winding 2c. , A capacitor 4 for smoothing the input DC, an FET 5 for switching the input DC via the primary winding 2a,
Switching controller 6 for controlling the switching of ET5
A photocoupler 7 having a photodiode 7a and a phototransistor 7b, insulating the primary winding 2a side and the secondary winding 2b side from each other, and transmitting a control signal of a constant voltage control unit 33 described later to the switching control unit 6; , Resistance 8
And an auxiliary power supply unit 10 for rectifying and smoothing the induced voltage of the auxiliary winding 2c to supply a DC auxiliary power to the switching control unit 6. Here, the switching control unit 6 includes a reference voltage generation circuit 11 that generates the voltage VR1.
And a resistor 1 for dividing the voltage VR1 to generate a reference voltage V1.
2, 13; an error amplifier 14 for amplifying an error voltage between the reference voltage V1 and the control voltage VFB; and a switching signal generating circuit 15 for controlling the switching duty ratio of the FET 5 based on the output voltage VC of the error amplifier 14. Have. In addition, the auxiliary power supply unit 10 includes a diode 21 and a capacitor 22 for rectifying and smoothing the induced voltage of the auxiliary winding 2c, respectively.

On the other hand, on the secondary winding 2b side of the transformer 2,
A diode 31 for rectifying an induced voltage of the secondary winding 2b;
A capacitor 32 for smoothing the voltage rectified by the diode 31 and a switching control unit 6 for detecting the voltage value of the smoothed output voltage VO and for stabilizing the output voltage VO to a predetermined voltage based on the detected voltage. And the output current I output to the outside of the device.
A constant current control unit 34 for controlling the switching control unit 6 to detect the current value of O 2 and to limit the output current IO to a predetermined current value based on the detected current value, and a resistor for conducting the current to the photodiode 7a. 35 are provided. The constant voltage control unit 33 includes resistors 41 and 42 for dividing the output voltage VO and a shunt regulator 43 for flowing a sink current IS having a current value corresponding to the voltage value of the divided voltage VOD input to the control terminal. And a capacitor 44 for compensating the phase of the shunt regulator 43. On the other hand, the constant current control unit 34 includes a resistor 45 for detecting the output current IO, a reference voltage generating circuit 46 for generating the reference voltage V2, and an error between the reference voltage V2 and the voltage VIO generated across the resistor 45. Amplifier 47 for amplifying voltage
, A diode 48, and a current limiting resistor 49.

In the power supply device 51, when the switch 3 is turned on and DC is input from the DC power supply U, the switching control unit 6 is activated and outputs a switching signal to the FET 5. As a result, when the FET 5 starts switching, an induced voltage is induced in the secondary winding 2b of the transformer 2. Next, the diode 31 and the capacitor 3
2 generates DC power by rectifying and smoothing the induced voltage of secondary winding 2b.

In this case, as shown in FIG.
When O is equal to or less than the preset current value I01, the output voltage VO is stabilized at the voltage value VO1 which is the rated voltage.
Specifically, the voltage V divided by the resistors 41 and 42
OD is input to the control terminal of the shunt regulator 43. In this case, the shunt regulator 43 supplies the resistor 35 with the sink current IS corresponding to the error voltage between the output voltage (for example, 2.5 V) of the built-in reference power supply and the voltage VOD.
And flows in through the photodiode 7a. As a result, the phototransistor 7b causes the collector voltage IC to flow through the resistor 8 to generate a control voltage VFB corresponding to the output voltage VO at the collector. Then
The error amplifier 14 amplifies the error voltage between the reference voltage V1 and the control voltage VFB, and outputs the amplified control voltage VC to the switching signal generation circuit 15. As a result, the switching signal generation circuit 15 controls the switching of the FET 5 by outputting a switching signal having a duty ratio corresponding to the control voltage VC, thereby changing the output voltage VO to the voltage value V
Stabilizes to O1.

On the other hand, when the output current IO is going to exceed the current value IO1 at the time of overload or short-circuit of the load, as shown in FIG.
Limited to O1. More specifically, the amplifier 47 amplifies the error voltage between the voltage VIO corresponding to the output current IO and the reference voltage V2, and outputs the amplified voltage to the control terminal of the shunt regulator 43. Here, when the output current IO is going to exceed the current value IO1, a current flows from the amplifier 47 to the control terminal of the shunt regulator 43 via the diode 48. As a result, the sink current IS of the shunt regulator 43 increases, so that the collector current I S of the phototransistor 7b is increased.
C increases. As a result, the control voltage VFB, which is the collector voltage of the phototransistor 7b, decreases, and the error amplifier 14
However, by lowering the control voltage VC to reduce the on-duty ratio of the FET 5, the output current IO decreases and is limited to the current value IO1. In this state, the output voltage VO is maintained at a predetermined voltage between 0 V and the voltage value VO1, as shown in FIG.

The shunt regulator 43 instructs the switching control unit 6 to perform a constant current control operation in a constant current control region between the points B and C shown in FIG. In the case where the constant current control operation in the constant voltage control area is controlled by alternately switching the operation,
The voltage VOD divided by the resistors 41 and 42 and the control voltage output from the amplifier 47 are alternately input to the control terminal of the shunt regulator 43. Therefore, when the loop gain of each of the feedback loops of the constant voltage control and the constant current control is large, an oscillation phenomenon may be caused. Therefore, in this power supply device 51,
By lowering the loop gain of both feedback loops by the capacitor 44 connected between the output terminal and the control terminal of the shunt regulator 43, the constant voltage control operation is changed to the constant current control operation, and the constant current control operation is changed to the constant voltage control. It can be switched smoothly to each operation.

As described above, in the power supply device 51, when the output current IO is equal to or less than the current value IO1, the constant voltage control operation for stabilizing the output voltage VO to the voltage value VO1 is performed.
When the output current IO is going to exceed the current value IO1,
A constant current control operation for limiting the output current IO to the current value IO1 is performed.

[0009]

However, the conventional power supply device 51 has the following problems. That is, when the load changes from the short-circuit state to the open state, when the load changes from the open state to the short-circuit state, and when the load resistance changes suddenly (hereinafter, these states are collectively referred to as “when the load state suddenly changes”). Problem). So, for example,
In the overload state, the power supply device 51 operates as shown in FIG.
A constant current control operation is performed near the point. In this case, the output voltage VO is the voltage value VO3 and the output current IO is the current value IO1. Therefore, when the state suddenly changes to the load release state, it is necessary to immediately shift to the constant voltage control operation near point A shown in FIG. However, in the power supply device 51, since the loop gain of the feedback loop for the constant voltage control operation by the constant voltage control unit 33 is set to be small,
It is difficult to quickly perform the feedback control for the switching control unit 6 to narrow the duty ratio of the switching control signal. In addition, the sink current IS of the shunt regulator 43 is
, There is a delay time until the photodiode 7a completely rises, so that it is more difficult to instantaneously perform feedback control of the switching control unit 6. For this reason, the output voltage VO cannot be instantaneously stabilized to the voltage value VO1, and as shown by the output voltage characteristic CR2 in FIG. 2, the output voltage VO is output exceeding the voltage value VO1, which is a so-called overvoltage. Shooting phenomenon occurs. As a result, there is a problem that an overvoltage is applied to components and loads of each part.

On the other hand, when the loop gain of the constant voltage control loop and the feedback loop for the constant current control operation is increased by reducing the capacitance value of the capacitor 44, the oscillation phenomenon occurs as described above, As a result, the ripple voltage of the output voltage VO increases in the steady state constant voltage control state, and the output current stability of the output current IO decreases in the steady state constant current control state. I will.

FIG. 4 shows an output terminal of the power supply device 51.
As shown by the broken line, it is possible to absorb the overshoot voltage of the output voltage VO by connecting a zener diode 52 having a zener voltage slightly higher than the voltage value VO1. However, in such a case, when configuring a high-output power supply device, the instantaneous power consumption of the Zener diode 52 becomes large, and the Zener diode 52 may cause power destruction. Is reduced.

The present invention has been made in view of such a problem, and has as its main object to provide a constant-voltage / constant-current power supply device capable of suppressing an overvoltage of an output voltage when a load state changes suddenly.

[0013]

According to a first aspect of the present invention, there is provided a constant-voltage / constant-current power supply device for switching an input direct current through a primary winding in a switching transformer having an auxiliary winding. A switching means for generating DC power of a predetermined voltage on the secondary winding side of the transformer, and when the output current output to the outside of the device based on the generated DC power is equal to or less than a predetermined current value, First constant voltage control means for feedback-controlling the switching means for stabilizing the DC voltage to the first voltage value, and for limiting the output current to the predetermined current value when the output current exceeds the predetermined current value A constant-current constant-current power supply device having constant-current control means for feedback-controlling the switching means; A second constant voltage control unit that controls the switching unit in a feedback manner to limit a DC voltage of the DC power to a second voltage value higher than the first voltage value, wherein the auxiliary winding is a secondary winding; It is characterized in that it is formed in phase with the line.

In this constant-voltage / constant-current power supply device, in the constant-voltage control state, the first constant-voltage control means performs feedback control of the switching means, so that the output voltage is stabilized at the first voltage value. . On the other hand, when the load condition changes suddenly, the auxiliary winding of the switching transformer is formed in the same phase as the secondary winding, so that the auxiliary winding has an induced voltage that is almost proportional to the induced voltage of the secondary winding. Voltage is generated. Therefore, when the DC voltage of the DC power increases, the induced voltage of the auxiliary winding also increases. In this case, the second
The constant voltage control means, when the DC voltage of the DC power is going to rise above the second voltage value, based on the induced voltage of the auxiliary winding, limits the DC voltage to the second voltage value or less. Then, the switching means is feedback-controlled. At this time, unlike the first constant voltage control means, the second constant voltage control means operates only when the load suddenly changes in a transient state. Therefore, there is no need to perform feedback control on the ripple voltage superimposed on the output voltage in the steady state, so that the switching means can be controlled with an emphasis on high-speed response rather than stability of the feedback loop. Further, since the auxiliary winding and the secondary winding are electrically insulated from each other, the switching means and the second
There is no need to provide an insulating means between the constant voltage control means. Therefore, the second constant voltage control means can instantaneously control the switching means without causing a response delay due to the insulating means such as a photocoupler. Thereby, even when the constant voltage control by the first constant voltage control unit is delayed, it is possible to instantaneously limit the output voltage to the second voltage value or less.

According to a second aspect of the present invention, there is provided a constant-voltage / constant-current power supply device.
2. The constant-voltage / constant-current power supply device according to claim 1, wherein the switching unit switches the input DC through the primary winding, a switching control unit that controls switching of the switching element, and an induced voltage of the auxiliary winding. And an auxiliary power supply for supplying an auxiliary power generated based on the above to the switching control unit.

Auxiliary windings for detecting a voltage when the switching means are controlled to a constant voltage by the second constant voltage control means can be formed separately and independently. On the other hand, in this constant voltage / constant current power supply device, an auxiliary winding for detecting the voltage,
An auxiliary winding for generating an auxiliary power supply for the switching control unit is commonly used. For this reason, it is possible to reduce the manufacturing cost of the second constant voltage control means.

According to a third aspect of the present invention, there is provided a constant-voltage / constant-current power supply device.
3. The constant-voltage / constant-current power supply device according to claim 2, wherein the second constant-voltage control means includes a Zener diode that conducts when the auxiliary power supply exceeds a predetermined voltage value. The switching means is operated based on the switching means to control the switching means.

In this constant-voltage / constant-current power supply device, the DC voltage of the generated DC power is higher than the second voltage.
When the voltage value of the auxiliary winding reaches the predetermined voltage value, the induced voltage of the auxiliary winding also reaches a predetermined voltage value. Only when this state is reached, the Zener diode becomes conductive. In this state, the second constant voltage control means operates based on the conduction current of the Zener diode to feedback-control the switching means. On the other hand, in a state where the DC voltage of the DC power is stabilized at the first voltage value, the Zener diode maintains a non-conductive state. In this state, since no power is consumed by the Zener diode and the second constant voltage control means, it is possible to prevent a decrease in the conversion efficiency of the constant voltage / constant current power supply device.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a constant-voltage / constant-current power supply according to the present invention will be described below with reference to the accompanying drawings. Note that the same components as those of the conventional power supply device 51 are denoted by the same reference numerals, and redundant description will be omitted.

First, a constant-voltage / constant-current power supply device 1 (hereinafter, referred to as a
The configuration of the “power supply device 1” will be described.

As shown in FIG. 1, the power supply device 1 is composed of a flyback type DC / DC converter. The power supply device 1 includes a switching transformer 2 having a primary winding 2a, and a secondary winding 2b and an auxiliary winding 2c formed in the same phase with each other. , Switch 3, capacitor 4, FET 5 corresponding to a switching element in the present invention, switching controller 6, photocoupler 7, resistor 8, which constitute switching means in the present invention together with FET 5, and correspond to a second constant voltage control means in the present invention. Further, the present invention includes a voltage limiting section 9 for limiting the output voltage VO to a voltage value VO2 which is a second voltage value or less, and an auxiliary power supply section 10. Here, the voltage limiter 9 includes a transistor 16 for lowering the control voltage VFB when the output voltage VO exceeds the voltage value VO2, and a bias circuit 17 for the transistor 16. The bias circuit 17 includes a Zener diode 18 that conducts a Zener current when the power supply voltage VA of the auxiliary power supply unit 10 reaches a voltage value VA1, and resistors 19 and 20. In the power supply device 1, when the output voltage VO reaches the voltage value VO2, the power supply voltage VA of the auxiliary power supply 10 reaches the voltage value VA1,
In this state, the Zener voltage is predetermined so that the Zener diode 18 becomes conductive for the first time.

On the other hand, on the secondary winding 2b side of the transformer 2,
The diode 31, the capacitor 32, and the first
A constant voltage controller 33 corresponding to the constant voltage controller, a constant current controller 34 corresponding to the constant current controller in the present invention,
And a resistor 35 are provided.

Next, the overall operation of the power supply device 1 will be described. Note that the constant voltage control operation and the constant current control operation in the steady state operate in the same manner as the power supply device 51. A description will be given by taking as an example the case of a sudden change in the load state in which the constant voltage control operation has suddenly changed.

At the time of the constant current control operation, the amplifier 47 amplifies the error voltage between the voltage VIO corresponding to the output current IO and the reference voltage V2, and outputs the amplified voltage to the control terminal of the shunt regulator 43. In this case, when the output current IO is going to exceed the current value IO1, a larger current flows into the control terminal of the shunt regulator 43. As a result, the sink current IS of the shunt regulator 43 increases, so that the collector current IC of the phototransistor 7b increases. As a result, the control voltage VFB, which is the collector voltage of the phototransistor 7b, decreases, and the error amplifier 14 lowers the control voltage VC to reduce the on-duty ratio of the FET 5, so that the output current IO decreases and the current value decreases. Limited to IO1. In this state, as shown in FIG.
Is maintained at a predetermined voltage between 0 V and the voltage value VO1.

On the other hand, for example, from the constant current control operation at the point D shown in FIG. 3 in which the output voltage is the voltage value V03 and the output current IO is the current value IO1, the output voltage VO becomes the voltage value VO1 and the output current I0
In the case where the instantaneous transition is made to the constant voltage control operation near point A shown in the figure where O is near 0 ampere, the FET 5 changes the output current IO to the current value IO1 immediately before the load state suddenly changes.
Switching at a duty ratio limited to On the other hand, when the output current IO instantaneously enters a no-load state near 0 amps, the constant current control by the constant current control unit 34 is momentarily stopped, and in this state, the constant voltage control unit 3
3 cannot respond immediately.
Therefore, since the feedback control for the switching control unit 6 is not performed, the output voltage VO starts to rise instantaneously as shown by the output voltage characteristic CR1 in FIG.

At this time, since the induced voltage of the auxiliary winding 2c also starts to increase, the voltage VA of the auxiliary power supply generated by the auxiliary power supply 10 also starts to increase at the same time. Next, when the output voltage VO reaches the voltage value VO2, the voltage VA of the auxiliary power supply also reaches the voltage value VA2. In this state, the Zener diode 18 that has been in a non-conducting state conducts, whereby a current based on the auxiliary power supply conducts to the bias circuit 17. At this time, a current is supplied to the base terminal of the transistor 19 via the resistor 19 and the Zener diode 18. In this state, the transistor 16 causes the output current of the reference voltage generation circuit 11 to flow through the resistor 8 to the ground, so that the control voltage VFB, which is the voltage at the collector terminal of the transistor 16, is reduced. Next, the error amplifier 14
Lowers the control voltage VC, so that the switching signal generation circuit 15 lowers the on-duty ratio of the control signal. Therefore, when the FET 5 switches according to the control signal, the output voltage VO is limited to the voltage value VO2 slightly exceeding the voltage value VO1 as shown by the output voltage characteristic CR1.

Next, after the output voltage VO is limited to the voltage value VO2 for a predetermined time, the constant voltage control by the constant voltage control section 33 functions, so that the switching signal generating circuit 15 operates in accordance with the voltage value of the output voltage VO. Constant voltage control is performed. Therefore, the output voltage VO is stabilized at the voltage value VO1.

As described above, according to the power supply device 1, the voltage limiter 9 controls the switching controller 6 so as to suppress the rise of the output voltage VO based on the induced voltage of the auxiliary winding 2c.
, The operation delay of the feedback control of the constant voltage control unit 33 and the constant current control unit 34 by the phase compensation capacitor 44 and the excessive overshoot with respect to the output voltage VO due to the response delay until the rise of the photocoupler 7 The phenomenon can be effectively prevented. When the output voltage VO is stabilized at the voltage value VO1, no power is consumed by the transistor 16, the Zener diode 18, and the resistors 19 and 20, so that
A decrease in the conversion efficiency of the power supply device 1 can be prevented.

The present invention is not limited to the embodiment of the present invention, and the configuration can be appropriately changed. For example, in the embodiment of the present invention, the primary winding 2a side and the secondary winding 2b side are insulated from each other by using the transformer 2 and the photocoupler 7, but the present invention is not limited to this.
The present invention can also be applied to a power supply device in which the primary winding 2a side and the secondary winding 2b side are not insulated. In the embodiment of the present invention, the bipolar transistor 16 is used as the second constant voltage control means in the present invention.
It can also be constituted by a field effect transistor.

Further, in the embodiment of the present invention, the auxiliary winding 2c is formed by an auxiliary power generation winding by the auxiliary power supply unit 10,
Although the example in which the voltage limiting unit 9 also serves as the winding for detecting the output voltage has been described, the present invention is not limited to this.
Both windings may be configured separately and independently. However,
If both windings are used, the cost of the device can be reduced.

[0031]

As described above, according to the constant-voltage / constant-current power supply device of the first aspect, the second constant-voltage control means applies the DC voltage of the DC power to the auxiliary winding to the switching means. By performing the feedback control so as to limit the output voltage to the second voltage value or less based on the induced voltage, the output voltage can be instantaneously limited to the second voltage value or less at the time of a sudden change in the load state. An excessive rise in voltage can be suppressed. As a result, it is possible to effectively prevent application of an overvoltage to components in the constant voltage / constant current power supply device, so that the reliability of the device can be improved and the load can be reliably protected from the overvoltage.

According to the constant voltage and constant current power supply device of the second aspect, the auxiliary winding for detecting the output voltage and the auxiliary winding for generating the auxiliary power supply are commonly used by the second constant voltage control means. By using this, the manufacturing cost of the second constant voltage control means can be reduced.

Furthermore, according to the constant voltage / constant current power supply device of the third aspect, when the output voltage is maintained at the first voltage value, power is consumed by the Zener diode and the second constant voltage control means. Therefore, the conversion efficiency of the constant-voltage / constant-current power supply device can be prevented from lowering.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a constant-voltage / constant-current power supply device according to an embodiment of the present invention.

FIG. 2 shows an output voltage characteristic CR1 of the constant-voltage / constant-current power supply according to the embodiment of the present invention at the time of a sudden change in the load state and an output voltage characteristic CR2 of the conventional constant-voltage / constant-current power supply at the time of a sudden change in the load state. FIG.

FIG. 3 is a characteristic diagram of an output voltage with respect to an output current for explaining an operation region of the constant-voltage / constant-current power supply device.

FIG. 4 is a circuit diagram of a conventional constant-voltage / constant-current power supply device.

[Explanation of symbols]

 Reference Signs List 1 constant voltage constant current power supply device 2 transformer 2a primary winding 2b secondary winding 2c auxiliary winding 5 FET 6 switching control unit 9 voltage limiting unit 10 auxiliary power supply unit 18 Zener diode 33 constant voltage control unit 34 constant current control unit

Claims (3)

[Claims] 1. A switching means for switching a direct current input through a primary winding in a switching transformer having an auxiliary winding to generate a DC power of a predetermined voltage on a secondary winding side of the transformer. A feedback control of the switching means for stabilizing the DC voltage of the DC power to a first voltage value when an output current output to the outside of the device based on the generated DC power is equal to or less than a predetermined current value; A first constant voltage control means,
A constant-current constant-current power supply device comprising: a constant-current control unit that performs feedback control on the switching unit to limit the output current to the predetermined current value when the output current exceeds the predetermined current value. A second feedback control of the switching means for limiting a DC voltage of the DC power to a second voltage value higher than the first voltage value based on an induced voltage of an auxiliary winding in the transformer; A constant-voltage / constant-current power supply device, comprising: constant-voltage control means, wherein the auxiliary winding is formed in the same phase as the secondary winding. 2. The switching device according to claim 1, wherein the switching unit switches the input DC through the primary winding, a switching control unit that controls switching of the switching device, and an induced voltage of the auxiliary winding. The constant-voltage / constant-current power supply device according to claim 1, further comprising: an auxiliary power supply unit that supplies the generated auxiliary power supply to the switching control unit. 3. The second constant voltage control means includes a Zener diode that conducts when the auxiliary power supply exceeds a predetermined voltage value, and operates based on the conduction current when the Zener diode conducts. 3. The constant-voltage / constant-current power supply according to claim 2, wherein said switching means is controlled.