JP5549159B2 - Power supply - Google Patents

Description

  The present invention relates to a power supply device including a DC / DC converter and the like.

  In general, there is an insulated DC / DC converter as a power source for external devices. Such a power supply device such as an insulation type DC / DC converter supplies a switching voltage turned on / off by a MOS-FET or the like to the transformer, the transformer transforms the input DC voltage, and a rectifier circuit outputs the transformer. A stable DC voltage is obtained by rectifying the voltage. And there exists a power supply provided with the short circuit current limiting function supposing when the load connected to a power supply short-circuits (for example, refer to patent documents 1).

  The power supply described in Patent Document 1 is configured to pass a current through a simulated resistor different from the load, compare the voltage generated in the simulated resistor with the output voltage, and limit the output current.

JP 2009-123244 A

Conventionally, a power supply device has been provided with a protection circuit that prevents damage to an output unit caused by a short circuit of a load.
The characteristics of the power supply device provided with such a protection circuit will be described with reference to FIGS.

  FIG. 4 is an internal block diagram of a conventional power supply apparatus. FIG. 5 is a characteristic diagram showing the relationship among the external load, the current IL flowing through the external load, the internal drive voltage V1A of the power supply, and the output voltage V2 to the external load in the conventional power supply.

In FIG. 4, 6 is a transformer and 2A is a protection circuit.
In FIG. 5, a section P1 is a section in which the power supply device outputs a current without the current suppressing action by the protection circuit 2A. That is, in section P1, it is shown that the impedance of the external load is within the range of the output current capacity of the power supply device (within an allowable value).

  The section P2 and the section P3 are sections in which the power supply device outputs current in a state where the current suppression action by the protection circuit 2A is activated. That is, it is shown that the impedance of the external load is outside the range of the output current capacity of the power supply device (outside the allowable value) in the sections P2 and P3.

  Here, a description will be given focusing on the internal drive voltage V1A and the output voltage V2 of the power supply device. The internal drive voltage V1A is a constant value in the sections P1 to P3. The output voltage V2 drops from the boundary between the section P1 and the section P2 where the current suppressing action by the protection circuit 2A starts to work. That is, in the section P2 and the section P3, the protection circuit 2A acts so that an excessive current does not flow to the load by decreasing the output voltage V2.

  As described above, the relationship between the internal drive voltage V1A and the output voltage V2 is a characteristic in which the difference widens as the impedance of the external load becomes smaller. Therefore, in the conventional power supply device, when the impedance of the external load decreases the allowable value. There is a problem that wasteful energy corresponding to the arrow A of the voltage difference between the internal drive voltage V1A and the output voltage V2 is consumed.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a power supply device that suppresses wasteful energy consumption when an external load is short-circuited.

In order to achieve the above-described problem, a power supply apparatus according to claim 1 of the present invention generates a second DC voltage from a first DC voltage using switching means, and supplies a predetermined current to an external load via an output unit. The power supply device for output includes a feedback control unit that compares the output voltage of the output unit and the second DC voltage, and the output unit responds to an increase in current due to a decrease in impedance of the external load below an allowable value. And a load adjusting means for supplementing the impedance of the external load so as to maintain the allowable value, and the feedback control unit follows the second output voltage drop due to the current flowing through the load adjusting means. A feedback signal for adjusting the DC voltage is generated, and this feedback signal is supplied to the switching means.

A power supply apparatus according to a second aspect is the power supply apparatus according to the first aspect, wherein the output unit outputs a first reference voltage source that outputs a predetermined voltage and an output voltage of the first reference voltage source. A constant current circuit that inputs and flows a current according to the output voltage; and a first voltage drop means that is connected to the constant current circuit and drops a voltage from a second DC voltage by the current passed by the constant current circuit; A second voltage drop means for dropping the voltage from the second DC voltage in accordance with a load current applied to the external load; a voltage generated in the second voltage drop means; and a voltage generated in the first voltage drop means And a differential amplifier that amplifies and outputs the difference between the two input voltages, and inputs the output voltage of the differential amplifier and maintains the allowable value according to the output voltage . be constituted by the amplification means to supplement the impedance And features.

  A power supply device according to claim 3 is the power supply device according to claim 1, wherein the feedback control unit inputs the output voltage of the output unit and the second DC voltage, and the second DC voltage and the output unit. And a second reference voltage source that inputs a voltage divided by the voltage dividing circuit and outputs a predetermined voltage. The second reference voltage source The output voltage is used as a feedback signal.

  A power supply apparatus according to a fourth aspect is the power supply apparatus according to any one of the first to third aspects, wherein the output unit is driven by a second DC voltage.

  Since the present invention is configured to decrease the drive voltage of the output unit following the decrease of the voltage of the external output terminal that is output via the load adjusting means, when the impedance of the external load decreases below the allowable value , Wasteful energy consumption can be suppressed. In addition, since useless energy is not consumed, heat generation of the protection unit can be suppressed, and the power supply device can be downsized.

It is a block diagram of the power supply which concerns on the Example of this invention. It is a circuit diagram of the output part and feedback control part which concern on the Example of this invention. FIG. 6 is a characteristic diagram showing a relationship between current and voltage with respect to external load impedance according to an embodiment of the present invention. It is an internal block diagram of the conventional power supply device. FIG. 10 is a characteristic diagram of a power supply device showing a relationship of a current and a voltage with respect to an external load impedance in a conventional power supply device.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings of FIGS. These drawings are for explaining an embodiment of the present invention, and the present invention is not limited by these drawings. Further, the same components are denoted by the same reference numerals.

  FIG. 1 is a block diagram showing an embodiment of a power supply device of the present invention. The power supply 1 controls the input predetermined DC voltage by switching means such as a MOS-FET (not shown) and rectifies the voltage generated on the secondary side of the transformer 6 by a rectifier circuit (DC voltage (internal drive voltage)). V1) is output.

  Similarly, in FIG. 1, reference numeral 5 denotes a photocoupler that transmits a feedback signal output from a feedback control unit 3 described later to the switching means 4. Reference numeral 4 denotes switching means for receiving the control signal output from the photocoupler 5 and controlling the frequency and pulse width of the switching voltage (signal) to the transformer 6.

  Reference numeral 2 denotes an output unit that receives the DC voltage V1 and outputs a predetermined current to an external load. When the impedance of the external load connected to the outside of the power supply apparatus is reduced from a predetermined allowable value, the output unit 2 supplements the impedance corresponding to the reduced amount with the impedance of the external load to supply current (IL) to the external load. Has the function of flowing. In other words, the output unit has a function of adjusting the output voltage in accordance with the current IL (adjusting means), and the current IL flows to the external load via the adjusting means.

  Subsequently, 3 is a feedback control unit that inputs the output voltage V2 output from the output unit to the outside via the adjusting unit, and outputs a feedback signal to the switching unit 4 following the output voltage V2. The feedback control unit 3 outputs a feedback signal to the switching unit 4 so that the pulse width of the switching voltage (signal) to the transformer 6 is reduced following the decrease, for example, when the output voltage V2 is decreased.

FIG. 2 is a circuit diagram of the output unit 2 and the feedback control unit 3 according to the embodiment of the present invention.
In FIG. 2, a circuit constituted by an operational amplifier 22, an FET 24, and a resistor 25 is a constant current circuit that converts a reference voltage output from the reference voltage IC 20 into a predetermined current. The current output from the constant current circuit always flows through the resistor 23, and a voltage corresponding to the current is generated in the resistor 23.

A resistor 27 generates a voltage according to the current IL.
Reference numeral 26 denotes an operational amplifier. A resistor 23 is connected to one input terminal of the operational amplifier 26, and the voltage of the resistor 23 is applied. A resistor 27 is connected to the other input terminal of the operational amplifier 26, and the voltage of the resistor 27 is applied. The gate of the FET 28 is connected to the output terminal of the operational amplifier 26.

  Subsequently, a circuit constituted by the operational amplifier 30, the resistor 31, the resistor 32, and the reference voltage IC 33 is a feedback control circuit. Since the operational amplifier 30 is a voltage follower, its output voltage is the same voltage as the output voltage V2. The resistors 31 and 32 are voltage dividing circuits that divide the internal drive voltage V1 and the output voltage V2, and this voltage dividing circuit is a circuit for determining the output voltage of the reference voltage IC33. The reference voltage IC 33 is a control IC that inputs a voltage divided by the resistors 31 and 32 and outputs a predetermined voltage (feedback signal). Note that the multipliers are determined so that the voltages divided by the resistors 31 and 32 fall slightly when the difference between the internal drive voltage V1 and the output voltage V2 increases.

  By the way, when the current IL flows to the external load, the resistor 27 generates a voltage according to the current IL. When the impedance of the external load decreases and the current IL increases and the voltage of the resistor 27 becomes lower than the voltage of the resistor 23, the operational amplifier 26 controls the FET 28 to increase its output voltage and suppress the current IL. As a result, the voltage of the resistor 27 starts to rise, and the current IL is adjusted so that the two input terminals of the operational amplifier 26 have the same voltage. That is, the operational amplifier 26 controls the FET 28 so that the voltage of the resistor 23 and the voltage of the resistor 27 become equal, and adjusts the current IL.

  As a result, the voltage of the resistor 27 is maintained approximately equal to the voltage of the resistor 23. The fact that the voltage of the resistor 27 is maintained at the voltage of the resistor 23 restricts the current flowing through the resistor 27, that is, the current IL from flowing beyond a predetermined current.

  Since the FET 28 increases the impedance between the source and the drain so as to satisfy the condition that the voltages at the two input terminals of the operational amplifier 26 become equal following the excess current when the current IL exceeds a predetermined value, The output voltage V2 to the load decreases following the excess current.

  That is, when the impedance of the external load falls below the allowable value, the load adjustment circuit (load adjustment means) constituted by the resistor 23, the resistor 27, the operational amplifier 26, and the FET 28 causes the current IL to be constant at a predetermined current value. The impedance between the source and drain of the FET 28 is adjusted. At this time, the FET 28 supplements the impedance between the source and the drain so as to supplement the impedance of the external load below the allowable value to the allowable value. For example, when the impedance of the external load is reduced to 15Ω when 20Ω is an allowable value, 5Ω is supplemented by the FET 28, and the total value of the impedance supplemented by the external load and the FET 28 becomes 20Ω so that the source-drain between the FET 28 Is controlled (this action is also referred to as a load adjustment function). Since a predetermined voltage is generated between the source and drain of the FET 28 controlled in this way as the current IL is output, the output voltage V2 is lowered as a result.

  As described above, when the output voltage V2 decreases due to overload of the external load, the difference between the internal drive voltage V1 and the output voltage V2 increases. As described above, when the voltage difference between the internal drive voltage V1 and the output voltage V2 increases, the voltage at the connection point between the resistor 31 and the resistor 32 slightly decreases. Then, the reference voltage IC33 acts to lower the output voltage and draw the current IB from the photocoupler 5. When the reference voltage IC 33 draws the current IB from the photocoupler 5, the photocoupler 5 gives a control signal (feedback signal) to the switching means 4, and the switching means 4 switches the switching voltage (signal) so as to lower the internal drive voltage V1. Control the pulse width.

  As described above, when the output voltage V2 decreases as described above due to an overload of the external load, the feedback control unit outputs a feedback signal corresponding to the voltage difference between the internal drive voltage V1 and the output voltage V2. The pulse width of the switching voltage (signal) to the transformer 6 is controlled by the switching means 4 that has received the feedback signal. As a result, the internal drive voltage V1 of the power supply device decreases following the output voltage V2.

That is, the feedback control unit 3 compares the output voltage V2 of the output unit with the internal drive voltage V1 that drives the output unit, and outputs a feedback signal according to the voltage difference.
FIG. 3 is a characteristic diagram showing the relationship among the external load impedance, current IL, internal drive voltage V1, and output voltage V2. For convenience, FIG. 3 also shows the characteristics of the internal drive voltage V1A of the conventional power supply apparatus.

  In FIG. 3, a section P1 is a section in which the power supply device outputs the current IL without the load adjustment function. That is, in section P1, it is shown that the impedance of the external load is within the range of the output current capacity of the power supply device (within an allowable value).

  The sections P2 and P3 are sections in which the power supply device outputs the current IL in a state where the load adjustment function is activated. That is, it is shown that the impedance of the external load is outside the range of the output current capacity of the power supply device (outside the allowable value) in the sections P2 and P3. The section P2 is a transition section until the output voltage V2 starts to decrease and the current IL becomes constant.

  Similarly, in FIG. 3, the output voltage V2 is substantially the same voltage as the internal drive voltage V1 in the section P1. Then, the output voltage V2 starts to decrease at the boundary between the section P1 and the section P2. This increases the impedance between the source and the drain so that the FET 28 compensates for the decrease in the impedance of the external load at the boundary between the section P1 and the section P2, and the current IL flows between the source and the drain to generate a voltage. Because it does. The output voltage V <b> 2 also decreases in the period P <b> 3 following the period P <b> 2 as the impedance between the source and drain of the FET 28 increases.

  Subsequently, the current IL increases as the impedance of the external load decreases in the section P1, and the current IL increases to the boundary between the sections P2 and P3. In the section P3, the current IL is constant.

  Subsequently, the internal drive voltage V1 is constant in the sections P1 and P2. In the section P3, the internal drive voltage V1 decreases following the output voltage V2 by the action of the feedback control unit 3 and the switching means 4.

  The characteristics of the internal drive voltage V1A in the conventional power supply apparatus are the same as the characteristics of the internal drive voltage V1 of the power supply apparatus of the present invention in the sections P1 to P2. Also in the section P3, the internal drive voltage V1A is constant after the section P2. Therefore, in the section P3, the conventional power supply apparatus consumes useless energy corresponding to the arrow A that is the voltage difference between the internal drive voltage V1A and the output voltage V2 inside the power supply apparatus.

  On the other hand, in the power supply device of the present invention, the internal drive voltage V1 decreases following the output voltage V2 in the section P3, so that useless energy is not consumed. For this reason, since heat generation in the output section is suppressed, the power supply device of the present invention can reduce the circuit size.

  As described above, the present invention is provided with load adjusting means for supplementing the impedance of the external load in accordance with the increase in current accompanying the decrease in the impedance of the external load below the predetermined threshold, and the output unit is configured to adjust the load. The current is supplied to the external load through the means. Further, the feedback control unit is configured to decrease the drive voltage of the output unit following the voltage drop (that is, the voltage of the external output terminal decreases) due to the current flowing through the load adjusting unit.

By doing so, when the impedance of the external load falls below the allowable value, useless energy consumption of the output unit is suppressed. In addition, since useless energy is not consumed, heat generation of the protection unit can be suppressed, and the power supply device can be downsized. Needless to say, the present invention can be applied to various power sources.

DESCRIPTION OF SYMBOLS 1 Power supply device 2 Output part 3 Feedback control part 4 Switching means 5 Photocoupler 6 Transformer 20, 33 Reference voltage IC
21, 23, 25, 27, 31, 32 Resistor 22, 26, 30 Operational amplifier

Claims (4)

In a power supply device that generates a second DC voltage from a first DC voltage using a switching means and outputs a predetermined current to an external load via an output unit,
A feedback control unit for comparing the output voltage of the output unit and the second DC voltage;
The output unit has load adjustment means for supplementing the impedance of the external load so as to maintain the allowable value in accordance with an increase in current due to the impedance of the external load being lower than the allowable value .
The feedback control unit generates a feedback signal for adjusting the second DC voltage following the decrease in the output voltage due to the current flowing through the load adjusting unit , and provides the feedback signal to the switching unit. A featured power supply. The power supply device according to claim 1,
The output unit is
A first reference voltage source that outputs a predetermined voltage;
A constant current circuit for inputting an output voltage of the first reference voltage source and flowing a current corresponding to the output voltage;
A first voltage drop means connected to the constant current circuit to drop the voltage from the second DC voltage by a current passed by the constant current circuit;
Second voltage drop means for dropping the voltage from the second DC voltage in accordance with a load current passed through the external load;
A differential amplifier that inputs a voltage generated in the second voltage drop means and a voltage generated in the first voltage drop means, amplifies and outputs a difference between the two input voltages;
A power supply apparatus comprising: an amplification means for inputting an output voltage of the differential amplifier and supplementing the impedance of the external load so as to maintain the allowable value according to the output voltage. The power supply device according to claim 1,
The feedback control unit receives the output voltage of the output unit and the second DC voltage, and divides the second DC voltage and the output voltage of the output unit, and the voltage dividing circuit A power supply device comprising a second reference voltage source that inputs a divided voltage and outputs a predetermined voltage, and uses the output voltage of the second reference voltage source as the feedback signal. 4. The power supply device according to claim 1, wherein the output unit is driven by the second DC voltage. 5.

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