JP4898351B2 - Switching power supply - Google Patents

Description

  The present invention relates to a switching power supply device that supplies at least a first output and a second output from a secondary side of one transformer, and performs feedback control from the first output to the primary side of the transformer to control an output voltage. In particular, it relates to the reduction of the voltage fluctuation of the second output.

  There is a type of switching power supply in which a voltage of one output among a plurality of outputs from one transformer is fed back to control an output voltage and power is supplied to a plurality of loads. Some of these switching power supply devices have cross regulation characteristics in which other output voltages vary depending on the output current load.

  In such a switching power supply device, as in Patent Document 1, for example, a dummy load whose load size can be controlled is connected to an output with high accuracy of the output voltage to be fed back. In some cases, the control unit controls the size of the dummy load in accordance with the drive command of the load to which the switching power supply device is connected, thereby preventing a decrease in the output voltage that is not a feedback target.

Further, as in Patent Document 2, a dummy load is connected to an output that is not a feedback target in order to stabilize the output voltage. And it is controlled by the power supply external signal so as to control the current flowing in the dummy load at the timing of decreasing the output voltage, reducing unnecessary loss in the dummy load and reducing the fluctuation range of the output voltage There is.
JP 2004-357420 A Japanese Unexamined Patent Publication No. Sho 62-025872

  In the conventional example shown in the above-mentioned Patent Document 1, when the output load that is not subject to feedback increases and the output voltage decreases, the current of the dummy load connected to the output subject to feedback is increased to increase the output voltage that is not subject to feedback. I am letting. However, the output voltage rise when the load of the output that is not the feedback target is small has a problem that the output voltage cannot be controlled appropriately because a dummy resistor is not connected to the output. .

  Further, in the conventional example shown in Patent Document 2 described above, a dummy resistor is connected to an output that is not a feedback target in order to prevent a voltage increase of the output that is not a feedback target. When the voltage rise is not desirable, the voltage rise of the output not subject to feedback is reduced by energizing the dummy resistor. However, when a voltage drop occurs due to an increase in the load current of an output that is not a feedback target, there is a problem that the voltage cannot be raised.

  The present invention has been made under such circumstances, and it is an object of the present invention to realize output voltage increase limitation and voltage decrease limitation using the same dummy resistor in a switching power supply device having a plurality of outputs. Is.

In order to solve the above problems, in the present invention, the switching power supply device is configured as described in (1 ) below.

(1) a first output means for supplying the secondary side or we first output transformer to the first load, the second supplying a second output from the secondary side of the transformer to the second load and an output unit, by feeding back the first output to the primary side of the transformer, the switching power supply for controlling said first output according to the output of the feedback, the second output is the if it becomes more than a plant value, the voltage rise limiting means for limiting the voltage rise of the second output by flowing the second output to the first output means via the dummy load, the second of when the output is below the first plant value smaller than the first plant value, the first and the second output voltage by flowing an output to the dummy load voltage drop limiting means for limiting the decrease in the switching, characterized in that it comprises a and Power supply.

  According to the present invention, it is possible to realize output voltage rise restriction and voltage drop restriction using the same dummy resistor. Thereby, it is not necessary to install individual dummy resistors respectively corresponding to the voltage rise restriction and the voltage drop restriction, and the voltage rise restriction and the voltage drop restriction can be easily realized with an inexpensive configuration.

  In addition, wasteful power consumption can be prevented and power consumption can be reduced when there is no need to reduce the output voltage, for example, there is no load corresponding to the output.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to examples.

FIG. 1 is a diagram illustrating a connection relationship between a “switching power supply device” according to the first embodiment and a load device.
Reference numeral 100 denotes a block representing the entire switching power supply apparatus, which is a switching power supply that converts an alternating current (AC) supply source such as a commercial power supply into direct current (DC) within the switching power supply apparatus 100. The conversion from AC to DC is performed by a rectifier circuit and a switching method which will be described later.
Reference numeral 101 denotes a load 1 connected to the switching power supply apparatus 100, and the DC output 1 is connected to be supplied from the switching power supply apparatus 100. Further, the DC output 1 has a path 104 that feeds back the output in order to suppress the voltage fluctuation so as to be a predetermined output voltage and to suppress the voltage fluctuation due to the load current.

Reference numeral 102 denotes another load 2 connected to the switching power supply apparatus 100, and the DC output 2 is connected to be supplied from the switching power supply apparatus 100. In this embodiment, the DC output 2 to the load 2 has a configuration without a feedback path.
Reference numeral 103 denotes an nth load n connected to the switching power supply apparatus 100.

  As described above, the switching power supply device 100 has a plurality of outputs, and is configured to stabilize the output by feeding back one of the outputs, and the other output is a power supply device configured not to feed back the voltage. It represents something.

FIG. 2 is a diagram illustrating a configuration and a dummy load of the switching power supply device according to the present embodiment.
A rectifier diode 200 in the switching power supply apparatus 100 is a diode bridge that converts an AC voltage from an AC supply source into a DC voltage. The rectified voltage is smoothed by the primary smoothing capacitor 201.
A power control IC 202 controls the switching element 203 in the switching power supply apparatus 100. In this embodiment, a flyback type switching power supply will be described.
Reference numeral 204 denotes a transformer for switching power supply, which generates a DC output 1 and a DC output 2 by insulating the primary side and the secondary side. The primary side includes a primary main winding 204a and a power supply winding 204b. The secondary side includes a secondary output 1 winding 204c and a secondary output 2 winding 204d.

205 is a rectifier diode connected to the secondary output 1 winding 204c, and half-wave rectifies the AC output 1 corresponding to the number of turns of the primary main winding 204a and the number of turns of the secondary output 1 winding 204c, The rectified output is smoothed by the secondary side smoothing capacitor 206.
207 is a rectifier diode connected to the secondary output 2 winding 204d, and half-wave rectifies the AC output 2 corresponding to the number of turns of the primary main winding 204a and the number of turns of the secondary output 2 winding 204d, The rectified output is smoothed by the secondary side smoothing capacitor 208.

  The switching element 203 is turned on by the control of the power supply control IC 202, the smoothed DC voltage is applied to the primary main winding 204a, and the current of the winding 204a rises with time. After a predetermined period, the switching element 203 is turned off by the power supply control IC 202, and the current output from the secondary output 1 winding 204c and the secondary output 2 winding 204d on the secondary side passes through the rectifier diodes 205 and 207 in the forward direction. Flowing. Then, the secondary smoothing capacitors 206 and 208 operate so that the output of each secondary winding is charged, and each voltage is smoothed.

  Reference numeral 209 denotes a photocoupler that insulates the primary side and secondary side circuits and feeds back the voltage output state of the DC output 1 to the power supply control IC 202.

  Reference numeral 210 denotes a reference voltage setting element (for example, a shunt regulator), which divides the voltage of the DC output 1 by resistors 211 and 212 and inputs it to the reference voltage control terminal. When the voltage of the resistor 212 becomes equal to or higher than a predetermined reference voltage, the reference voltage setting element 210 is turned on and the light emitting diode in the photocoupler 209 is turned on. If the voltage of the resistor 212 is lower than a predetermined reference voltage, the LED is turned off.

  The light receiving element changes the amount of current drawn from a predetermined terminal of the power supply control IC 202 corresponding to the light emitting diode in the photocoupler 209, and the power supply control IC 202 performs ON / OFF control of the switching element 203 by the change in the current value.

  Depending on the ON / OFF period and period change of the switching element 203, the voltage and current applied to the primary winding 204a on the primary side of the transformer 204 change, and the voltage output to the secondary output 1 winding 204c changes. . Further, the voltage output is fed back to operate so as to output the voltage of the DC output 1 within a predetermined range. At the same time, a predetermined voltage is output from the secondary output 2 winding 204d.

  The output voltage of the DC output 1 is fed back to the power supply control IC 202 as described above, and can be controlled with higher accuracy than the DC output 2. The DC output 2 outputs a voltage determined by the winding of the switching transformer 204. The DC output 2 has a characteristic that the output voltage increases when the load current is small, and the output voltage decreases when the load current of the DC output 2 increases. Further, it has a cross regulation characteristic that the voltage output of the DC output 2 increases as the load current of the DC output 1 increases.

  First, suppression of voltage increase when the output voltage is not fed back to the primary side power supply control IC 202 and the current load of the DC output 2 is small will be described. In order to suppress this voltage rise, a current is passed from the DC output 2 to the DC output 1 via the dummy resistor 217 as indicated by the broken line arrow in FIG.

In other words, a voltage dividing circuit including resistance elements 213 and 214 is connected to the output terminal of the DC output 2, and the voltage dividing point is connected to an input terminal of the reference voltage setting element 215. When the current load of the DC output 2 decreases, the voltage of the DC output 2 rises, and the voltage at the voltage dividing point exceeds the reference voltage of the reference voltage setting element 215, the reference voltage setting element 215 is turned on and the transistor 216 is turned on. Become. As a result, current flows from the DC output 2 to the DC output 1 through the path indicated by the broken-line arrow in FIG. As a result, the current of the DC output 2 increases and the output voltage decreases, so that it is possible to limit the voltage increase to prevent the voltage increase of the DC output 2.
When the current of the DC output 2 increases and the voltage of the DC output 2 decreases, the divided voltage of the resistance element 214 decreases, the reference voltage setting element 215 is turned off, the transistor 216 is turned off, and the dummy resistor Current flow to DC output 1 via 217 stops.
That is, it becomes possible to determine when the current load of the DC output 2 is small and large and to set the upper limit value of the output voltage.
However, in this embodiment, it is assumed that the DC output 1 is a voltage lower than the DC output 2.

Next, suppression of voltage drop when the output voltage is not fed back to the primary side power supply control IC 202 and the current load of the DC output 2 is large will be described. In order to suppress this voltage drop, a current is passed from the DC output 1 to the GND via the dummy resistor 217 as shown by the broken line arrow in FIG.
That is, the divided voltage 1 of the resistance elements 219 and 220 with respect to the DC output 1 where the voltage output is stable, and the divided voltage 2 of the resistance elements 221 and 222 with the end voltage of the resistance element 218 as a reference. Comparison is performed by the comparator 223. When the current load of the DC output 2 becomes larger than that during the above-described voltage rise suppression, the output voltage of the DC output 2 decreases, and the divided voltage 2 becomes lower than a predetermined value, the following operation is performed. The output of the comparator 223 drops from a voltage in the vicinity of the voltage of the DC output 2 to a voltage in the vicinity of GND, draws the base current of the transistor 224, and turns on the transistor 224.
When the transistor 224 is turned on, the transistor 225 is turned on, and a current flows in the direction of the broken arrow through the dummy resistor 217 in FIG.
As a result, the current of the DC output 1 increases, and the output voltage of the DC output 2 increases due to the cross regulation characteristics. In this way, even when the load current of the DC output 2 increases, the state of the load current can be detected to prevent the output voltage from being reduced, and the voltage drop can be limited to prevent the voltage drop.

FIG. 4 shows a graph in which the load current of DC output 1 and DC output 2 is on the horizontal axis and the output voltage is on the vertical axis.
The DC output 1 feeds back the state of the output voltage to the power supply control IC 202 on the primary side, so that the fluctuation of the output voltage is small with respect to the fluctuation of the load current.
DC output 2, since there is no feedback control to the primary side, when there is no control of the upper and lower limit limit the voltage output, an output characteristic as shown by the broken line.
In this embodiment, by selecting the combination of the resistance elements 213 and 214 and the resistance elements 218 to 222 and the reference voltage setting element 215 shown in FIGS. So that the voltage drop does not exceed the lower limit. This makes it possible to define the output voltage range.

As described above, according to the present embodiment, one dummy resistor 217 can be shared for limiting the increase and decrease of the output voltage of the DC output 2.
In addition, there is no voltage lower limit operation during the voltage upper limit operation, and conversely there is no voltage upper limit operation during the voltage lower limit operation. Therefore, it is possible to realize the limiting operation stably and inexpensively with a single dummy resistor.

  FIG. 5 is a diagram illustrating a configuration of a “switching power supply device” according to the second embodiment. The present embodiment is an example in which a configuration for stopping the DC output 2 is further added to the configuration of the first embodiment.

  The DC output 2 is configured to be switchable by selecting whether or not the output is performed by the switch element (MOSFET or the like) 300, and is selected by control by the load 1 (101) driven by the DC output 1 which is another output. . The switch element 300 is connected to the upstream side of the portion where the resistance element 213 is connected to the DC output 2 and to the winding 204d side of the transformer.

  When the load 2 (102) connected to the DC output 2 is a DC motor or other actuators, the output of the DC output 2 is not required when the load 2 (102) is not driven without supplying power to the load. In addition, the voltage output is stopped and there is no need to limit the upper voltage limit. In such a case, the DC output 2 is stopped by turning off the switch element 300.

  The switch element 300 is controlled by a control device (not shown) in the load 1 (101), and is controlled by, for example, a one-chip microcomputer. Similarly, when the load 2 (102) is a DC motor or other actuators, drive control is also performed by the control line 301.

When the upper limit of the voltage of the DC output 2 is not limited, the voltage is indicated by a broken line exceeding the predetermined upper limit voltage of the DC output 2 shown in FIG.
Voltage to resistance elements 213 and 214 and reference voltage setting element 215 for determining whether or not current flows into DC output 1 having a voltage lower than that of DC output 2 via dummy resistor 217 by stopping DC output 2 There is no application. Further, no current flows into the dummy resistor 217 via the transistor 216.

If an appropriate voltage output to the load 2 (102) is required, the switch element 300 can be turned on so that current can be supplied to the dummy resistor 217.
Further, when the current to the load 2 (102) increases and the output voltage of the DC output 2 becomes a predetermined value or less, the output of the comparator 223 is inverted and the transistors 224 and 225 are turned on. As a result, the current of the DC output 1 flows into the GND of the reference voltage lower than the voltage of the DC output 1 via the dummy resistor 217 and the transistor 225. The transformer 204 operates so that the output voltage of the DC output 2 rises due to the cross regulation characteristics of the transformer 204.

  As described above, according to the present embodiment, when the current of the DC output 2 is not necessary and the upper limit value of the voltage of the DC output 2 does not need to be limited, the current passing through the dummy resistor is cut. Can do. In addition, an appropriate output voltage can be set by flowing a current through a dummy resistor only when current output to the load is necessary, so that wasteful power consumption can be prevented and power consumption can be reduced.

The figure showing the connection structure of the switching power supply apparatus and load apparatus of Example 1. The figure showing the structure of the switching power supply apparatus of Example 1, and a dummy load (at the time of the voltage rise of output 2) The figure showing the structure of the switching power supply apparatus of Example 1, and a dummy load (at the time of the voltage drop of the output 2) The figure showing the relationship between the output voltage in the switching power supply apparatus of Example 1, and load current The figure showing the structure of the switching power supply device of Example 2.

Explanation of symbols

202 Power control IC
203 Primary side switching element 204 Transformer 209 DC output 1 feedback element 215 Reference voltage setting element (shunt regulator)
217 Dummy resistor 223 Comparator

Claims (3)

And a secondary or we first output of the transformer first first output means for supplying a load, a second output means for supplying a second output to the second load from the secondary side of the transformer in the provided, by feeding back the first output to the primary side of the transformer, the switching power supply device for controlling the first output according to the output of the feedback,
If the second output is equal to or greater than the first plant value, the voltage that limits the voltage rise of the second output by flowing the second output to the first output means via the dummy load A rise limiting means,
If the second output is below the first plant value smaller than the first plant value, the voltage to limit the decrease of the second output voltage by flowing the first output to the dummy load A switching power supply , comprising: a reduction limiting unit; Previous SL second output comprises a switch means for switching whether to output to the second load,
Said switching means, the switching power supply device according to claim 1, characterized in that said connected to the transformer side of the connection point between the voltage rise limiting means second output means. Before SL first load is a control means,
The switching power supply device according to claim 2 , wherein the switching means controls the switching operation of the switch means.

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