JP2009171752A - Power supply circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve drooping characteristics of an output voltage of a power supply circuit when executing constant-current control on the basis of a current flowing in the primary side of the power supply circuit. <P>SOLUTION: The power supply circuit 31 includes a transformer 37, in which a voltage converted from a DC current into an AC current by MOSFETs 32-35 is applied to a primary-side coil 37-1, diodes 39, 40 for rectifying output of the transformer 37, and a coil 41 and a capacitor 42 for smoothing the rectified voltage. A control circuit 1 controls each operation of the MOSFETs 32-35 so that an output voltage Vout of the power supply circuit becomes constant. When an output current Iout converted from a current flowing in the primary side exceeds a prescribed current Ir, the control circuit controls each operation of the MOSFETs 32-35 such that the output voltage Vout is reduced in response to an increase of an addition result between the output current Iout and a correction value based on the output voltage Vout. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a power supply circuit that performs constant current control in which when the output current of a power supply circuit exceeds a predetermined current, the output voltage of the power supply circuit is lowered in accordance with an increase in the output current.

FIG. 3 is a diagram showing a power supply circuit including a conventional control circuit.
A power supply circuit 31 shown in FIG. 3 includes a rectifier circuit including n-channel MOSFETs 32 to 35, a DC power supply 36, transformers 37 and 38, and diodes 39 and 40, and a smoothing circuit including a coil 41 and a capacitor 42. The circuit includes a full-wave rectifier circuit composed of diodes 57-60. That is, the source terminal of the MOSFET 32 is connected to the drain terminal of the MOSFET 33 and one end of the primary side coil 37-1 of the transformer 37 via the primary side coil 38-1 of the transformer 38, and the source terminal of the MOSFET 34 is the drain terminal of the MOSFET 35. The terminal and the other end of the primary coil 37-1 are connected. The drain terminals of the MOSFETs 32 and 34 are connected to the plus terminal of the DC power supply 36, and the source terminals of the MOSFETs 33 and 35 are connected to the minus terminal of the DC power supply 36. The cathode terminal of the diode 40 is connected to one end of the secondary side coil 37-2 of the transformer 37, and the cathode terminal of the diode 39 is connected to the other end of the secondary side coil 37-2 of the transformer 37. The center tap of the secondary coil 37-2 of the transformer 37 is connected to one end of the capacitor 42 and one output terminal of the power supply circuit 31 via the coil 41. The anode terminal of the diode 39 is the anode terminal of the diode 40 and the capacitor. The other end of 42 and the other output terminal of the power supply circuit 31 are connected. One end of the secondary coil 38-2 of the transformer 38 is connected to the anode terminal of the diode 57 and the cathode terminal of the diode 58, and the other end of the secondary coil 38-2 of the transformer 38 is the anode terminal of the diode 59. And the cathode terminal of the diode 60. The cathode terminal of the diode 57 and the cathode terminal of the diode 59 are connected to each other, and the anode terminal of the diode 58 and the anode terminal of the diode 60 are connected to the ground.

  The control circuit 43 shown in FIG. 3 includes an IC circuit 44, resistors 45 to 47, a diode 48, and a capacitor 49. That is, one end of the resistor 45 is connected to the cathode terminal of the diode 59 and the anode terminal of the diode 48, and the other end of the resistor 45 is connected to the anode terminal of the diode 60 and one end of the capacitor 49. The cathode terminal of the diode 48 is connected to the ground via the other end of the capacitor 49 and resistors 46 and 47 connected in series with each other.

  The IC circuit 44 includes an error amplifier 50, a constant voltage source 51, comparators 52 and 53, a triangular wave generation circuit 54, an AND circuit 55, and a drive circuit 56. That is, the resistors 46 and 47 divide the voltage V1 applied to the capacitor 49 into the voltage V2. The error amplifier 50 amplifies the difference between the voltage V2 input to the non-inverting input terminal and the voltage V3 of the constant voltage source 51 input to the inverting input terminal, and outputs the voltage V4. The comparator 52 compares the triangular wave of the triangular wave generation circuit 54 input to the positive input terminal with the output voltage Vout of the power supply circuit 31 input to the negative input terminal, and outputs the pulse signal S1. The comparator 53 compares the triangular wave of the triangular wave generation circuit 54 input to the positive input terminal with the voltage V4 input to the negative input terminal, and outputs the pulse signal S2. The AND circuit 55 calculates the logical product of the pulse signal S1 input to one input terminal and the pulse signal S2 input to the other input terminal, and outputs the pulse signal S3. The drive circuit 56 outputs a drive signal S4 based on the pulse signal S3 output from the AND circuit 55 to the gate terminals of the MOSFETs 32 and 35, and outputs a drive signal S5 that is an inverted signal of the drive signal S4 to the MOSFETs 33 and 34. Output to each gate terminal.

  When the MOSFETs 32 and 35 and the MOSFETs 33 and 34 are alternately turned on and off by the drive signals S4 and S5 output from the drive circuit 56, an AC voltage is applied to the primary coil 37-1 of the transformer 37, and the voltage corresponds to the voltage. AC voltage is applied to the secondary coil 37-2. A current flows alternately to the diodes 39 and 40 by the AC voltage applied to the secondary coil 37-2, and the output voltage Vout is output through the coil 41 and the capacitor. That is, the power supply circuit 31 converts the voltage of the DC power supply 36 into alternating current using the MOSFETs 32 to 35, transforms the alternating voltage with the transformer 37, rectifies the alternating voltage after the transformation with the diodes 39 and 40, The output is smoothed by the coil 41 and the capacitor 42 and output as the output voltage Vout.

  Further, when a current flows to the primary side of the power supply circuit 31, a voltage corresponding to the voltage applied to the primary side coil 38-1 of the transformer 38 is applied to the secondary side coil 38-2 and a current flows to the diode 48. A voltage V1 is applied to the capacitor 49. This voltage V1 is a voltage corresponding to the current flowing through the primary side coil 37-1 of the transformer 37.

  The ratio of the output current Iout of the power supply circuit 31 and the current flowing to the primary side of the power supply circuit 31 is the same as the ratio of the number of windings of the primary side coil and the number of windings of the secondary side coil of the transformer 38. For example, if the number of windings of the primary side coil: the number of windings of the secondary side coil = 1: 2, the current flowing through the primary side of the power supply circuit 31: the output current Iout of the power supply circuit 31 = 2: 1 Become.

FIG. 4A is a diagram showing the relationship between the output current Iout of the power supply circuit 31 and the output voltage Vout.
As shown in FIG. 4A, the power supply circuit 31 controls the output voltage Vout to be constant when the output current Iout is lower than the predetermined current Ir, and when the output current Iout is higher than the predetermined current Ir. The MOSFETs 32 to 35 are controlled so that the output voltage Vout decreases as the output current Iout increases.

  In the power supply circuit 31 shown in FIG. 4A, since the output current Iout is a current converted from the current flowing in the primary side, the current flowing in the primary coil 37-1 is used instead of the output current Iout. Then, the control method is switched based on the comparison result between the voltage corresponding to the current flowing through the primary coil 37-1 and the predetermined voltage.

  For example, when the voltage corresponding to the current flowing through the primary coil 37-1 of the transformer 37 is lower than a predetermined voltage, that is, when the voltage V2 is lower than the voltage V3, the voltage V4 output from the error amplifier 50 is The pulse signal S2 output from the comparator 53 becomes high level. At this time, since the comparator 52 outputs the pulse signal S1 that makes the output voltage Vout constant, the pulse signal S3 output from the AND circuit 55 becomes a pulse signal that makes the output voltage Vout constant. . That is, the MOSFETs 32 to 35 are controlled so that the output voltage Vout is constant (constant voltage control).

  Further, when the voltage corresponding to the current flowing through the primary side coil 37-1 of the transformer 37 is higher than a predetermined voltage, that is, when the voltage V2 is higher than the voltage V3, the comparator 53 responds to the increase in the voltage V2. Thus, the duty of the pulse signal S2 is reduced. At this time, since the pulse width of the pulse signal S2 output from the comparator 53 is smaller than the pulse width of the pulse signal S1 output from the comparator 52, the pulse signal S3 output from the AND circuit 55 is output from the comparator 53. It becomes the same pulse signal as the pulse signal S2 to be performed. That is, the MOSFETs 32 to 35 are controlled so that the output voltage Vout decreases as the current flowing through the primary coil 37-1 of the transformer 37 increases (constant current control).

  As described above, the control circuit 43 shown in FIG. 3 controls the MOSFETs 32 to 35 so that the output voltage Vout becomes constant when the voltage corresponding to the current flowing through the primary coil 37-1 is lower than the predetermined voltage. When the voltage corresponding to the current flowing through the primary side coil 37-1 is higher than the predetermined voltage, the output voltage Vout is lowered as the voltage corresponding to the current flowing through the primary side coil 37-1 increases. The MOSFETs 32 to 35 are controlled.

  Some power supply circuits control the operation of the switching element provided on the primary side so that the current flowing through the transformer coil is constant based on the primary side detection current and the primary side detection voltage. (For example, refer to Patent Document 1).

By the way, when the power supply circuit 31 shown in FIG. 3 outputs a large current, the maximum value of the output current Iout of the power supply circuit 31 for the purpose of protecting a harness or a short-circuit protection fuse provided in the output section of the power supply circuit 31. Is defined in advance. Further, when the power supply circuit 31 is a step-down type, constant current control is often performed based on the current flowing to the primary side (high voltage side) as in the control circuit 43 shown in FIG.
JP-A-8-242578

  However, in the power supply circuit 31 as shown in FIG. 3, the current flowing in the primary side includes the ripple current and the exciting current of the transformer 37, so that the current flowing in the primary side as in the control circuit 43 shown in FIG. For example, as shown in FIG. 4B, if the ripple current or the excitation current is large, the primary current is controlled even if the output current Iout required from the load is doubled. The primary detection current does not increase linearly with respect to the output current Iout required from the load, for example, the side detection current does not double, and the output voltage Vout drops below the maximum value of the output current Iout defined in advance. There is a risk that it will not be possible.

  Therefore, the present invention provides a power supply circuit including a control circuit capable of improving the drooping characteristics of the output voltage of the power supply circuit when performing constant current control based on the current flowing on the primary side of the power supply circuit. For the purpose.

In order to solve the above problems, the present invention adopts the following configuration.
That is, the power supply circuit of the present invention includes a plurality of switching elements that convert a DC voltage into an AC, and a primary side coil and a secondary side coil to which a voltage converted into an AC by the plurality of switching elements is input. A power circuit having a transformer, a rectifier circuit that rectifies a voltage applied to a secondary coil, and a smoothing circuit that smoothes a voltage output from the rectifier circuit, the current flowing to the primary side of the power circuit A current detection unit for detecting the power supply, a correction circuit for outputting a correction value based on the output voltage of the power supply circuit, and an output current of the power supply circuit converted from a current flowing on the primary side of the power supply circuit is lower than a predetermined current In this case, the first control circuit that controls the plurality of switching elements so that the output voltage of the power supply circuit is constant, and the current converted to the primary side of the power supply circuit When the output current of the source circuit is higher than a predetermined current, the plurality of switching elements are controlled so that the output voltage decreases according to an increase in the addition result of the voltage corresponding to the current flowing on the primary side and the correction value. And a second control circuit.

  As a result, constant current control can be performed based on the result of adding the ripple current from the coil in the smoothing circuit and the excitation current of the transformer to the output current, so that the drooping characteristics of the output voltage during constant current control can be improved. Can do.

The correction circuit may be configured to amplify a difference between the output voltage and a predetermined voltage and output the correction value.
The correction circuit may be configured to divide the output voltage and output the correction value.

  According to the present invention, the drooping characteristic of the output voltage of the power supply circuit can be improved when the constant current control is performed based on the current flowing on the primary side of the power supply circuit.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating a power supply circuit including a control circuit according to an embodiment of the present invention. The same components as those shown in FIG. 3 are denoted by the same reference numerals, and description of the same components as those shown in FIG. 3 is omitted.

  The control circuit 1 shown in FIG. 1 includes an IC circuit 44, resistors 45 to 47, a diode 48, a capacitor 49, and a correction circuit 2. The current detection unit described in the claims is configured by the transformer 38 of the power supply circuit 31, and the first control circuit described in the claims includes the comparator 52 and the triangular wave generation circuit of the IC circuit 44. 54, and the second control circuit described in the claims includes the error amplifier 50, the constant voltage source 51, the comparator 53, and the triangular wave generation circuit 54 of the IC circuit 44.

  The correction circuit 2 includes an operational amplifier 3, resistors 4 and 5, and a constant voltage source 6. That is, the correction circuit 2 is a negative feedback amplifier circuit, and the voltage V5 of the constant voltage source 6 is input to the inverting input terminal of the operational amplifier 3, and the output voltage Vout and the resistor 4 are connected to the non-inverting input terminal of the operational amplifier 3. Output is input. The operational amplifier 3 amplifies the difference between the output voltage Vout and the voltage V5 of the constant voltage source 6, and outputs the voltage V6 through the resistor 5. The voltage V6 is applied to the connection point between the resistors 46 and 47, and a voltage V7 obtained by adding the voltage V6 to the voltage V2 is output to the plus input terminal of the error amplifier 50. It is assumed that the resistance value and voltage V5 of the resistor 4 are set such that the voltage output from the operational amplifier 3 increases as the output voltage Vout decreases.

Here, the operation of the power supply circuit 31 having the control circuit 1 configured as described above will be described.
When a current flows through the primary side of the power supply circuit 31, a voltage corresponding to the voltage applied to the primary side coil 38-1 of the transformer 38 is applied to the secondary side coil 38-2, and the secondary side coil 38-2 receives the voltage. This voltage is rectified by a full-wave rectifier circuit composed of diodes 57-60. Then, a current flows through the diode 48, the voltage V1 is applied to the capacitor 49, and the voltage V2 is applied to the connection point between the resistors 46 and 47. When a current flows to the primary side of the power supply circuit 31, an output current Iout flows to the secondary side of the power supply circuit 31 via the transformer 37, and the output voltage Vout is applied to the capacitor 42. Then, as described above, the operational amplifier 3 amplifies the difference between the output voltage Vout and the voltage V5 of the constant voltage source 6 and outputs the voltage V6 through the resistor 5. The voltage V6 is applied to the connection point between the resistors 46 and 47, and a voltage V7 obtained by adding the voltage V6 to the voltage V2 is output to the plus input terminal of the error amplifier 50. When the voltage V7 is lower than the voltage V3, the voltage V4 output from the error amplifier 50 becomes zero, and the pulse signal S2 output from the comparator 53 becomes high level. At this time, since the comparator 52 outputs the pulse signal S1 that makes the output voltage Vout constant, the pulse signal S3 output from the AND circuit 55 becomes a pulse signal that makes the output voltage Vout constant. . That is, the MOSFETs 32 to 35 are controlled so that the output voltage Vout is constant (constant voltage control). When the voltage V7 is higher than the voltage V3, the comparator 53 decreases the duty of the pulse signal S2 according to the increase of the voltage V7. At this time, since the pulse width of the pulse signal S2 output from the comparator 53 is smaller than the pulse width of the pulse signal S1 output from the comparator 52, the pulse signal S3 output from the AND circuit 55 is output from the comparator 53. It becomes the same pulse signal as the pulse signal S2 to be performed. That is, the MOSFETs 32 to 35 are controlled so that the output voltage Vout decreases as the current flowing through the primary coil 37-1 of the transformer 37 increases (constant current control).

  In the control circuit 1 shown in FIG. 1, the voltage output from the operational amplifier 3 increases as the output current Iout required from the load increases and the output voltage Vout decreases during the constant current control. Compared to 43, the voltage V4 output from the error amplifier 50 to the comparator 53 increases, the pulse width of the pulse signal S2 output from the comparator 53 decreases, and the pulse of the pulse signal S4 that controls the operation of the MOSFETs 32 and 35 The width becomes smaller. Therefore, the control circuit 1 shown in FIG. 1 can drop more the output voltage Vout at the time of constant current control compared with the control circuit 43 shown in FIG.

  Further, as shown in FIG. 2, the correction circuit 2 may be configured by resistors 7 and 8. The resistors 7 and 8 are connected in series with each other, the resistor 7 is connected to a connection point between the coil 41 and the capacitor 42 of the power supply circuit 31, and the resistor 8 is connected to the ground. The connection point between the resistors 7 and 8 is connected to the connection point between the resistors 46 and 47. The correction circuit 2 shown in FIG. 2 divides the output voltage Vout by the resistors 7 and 8, and outputs the voltage V6 like the correction circuit 2 shown in FIG. As a result, a voltage V7 obtained by adding the voltage V6 to the voltage V2 is output to the plus input terminal of the error amplifier 50.

  According to the control circuit 1 of the present embodiment shown in FIG. 1 and FIG. 2, when the output current Iout converted from the current flowing on the primary side of the power supply circuit 31 exceeds the predetermined current Ir, it is rippled to the output current Iout. The voltage V6 is added to the voltage V2 to obtain a voltage V7 so that a current corresponding to the current or the excitation current is added, and each of the MOSFETs 32 to 35 decreases so that the output voltage Vout decreases as the voltage V7 increases. Control the behavior. As a result, the voltage V7 can be increased linearly with respect to the output current Iout required from the load, so that the drooping characteristic of the output voltage Vout during constant current control can be improved.

  Further, according to the control circuit 1 of the present embodiment shown in FIGS. 1 and 2, it is not necessary to increase the size of the coil 41 in order to reduce the ripple current included in the current flowing on the secondary side of the power supply circuit 31. The increase in size and cost of the entire circuit can be suppressed.

In addition, this invention is not limited to the said embodiment, For example, you may actualize as follows.
In the embodiment shown in FIGS. 1 and 2, when the voltage V7 obtained by adding the voltage V2 and the voltage V6 exceeds the voltage V3 of the constant voltage source 51, the plurality of switching elements 32 to 35 are set so that the output voltage Iout decreases. However, the present invention is not limited to this. For example, when the voltage V2 is higher than the voltage V3, the voltage V6 may be added to the output from the comparator 50.
In the embodiment shown in FIG. 1, the value of the resistor 4 and the value of the voltage V5 are fixed values, but by increasing the value of the resistor 4 or the value of the voltage V5, the rate of increase from the reference of the output current Iout (Decrease rate) and the rate of increase (decrease rate) from the reference of the current flowing in the primary side coil 37-1 (current flowing in the primary side coil 37-1 when the reference output current Iout is output) May be matched. For example, when a current that is twice the reference output current Iout is output, the value of the resistor 4 or the voltage V5 is set so that the voltage V7 becomes a current that is twice the reference current flowing through the primary side coil 37-1. Make the value variable.
In the embodiment shown in FIG. 2, the value of the resistor 8 is a fixed value, but by making the value of the resistor 8 variable, the increase rate (decrease rate) from the reference of the output current Iout and the primary coil The increase rate (decrease rate) from the reference of the current flowing through 37-1 (the current flowing through the primary coil 37-1 when the reference output current Iout is output) may be matched.

It is a figure which shows a power supply circuit provided with the control circuit of embodiment of this invention. It is a figure which shows a power supply circuit provided with the control circuit of other embodiment of this invention. It is a figure which shows a power supply circuit provided with the conventional control circuit. (A) is a figure which shows the relationship between the output current of a power supply circuit, and an output voltage. (B) is a figure which shows the electric current which flows into the primary side of the output current converter of a power supply circuit, and the electric current which flows into a secondary side.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Control circuit 2 Correction circuit 3 Operational amplifier 4, 5 Resistance 6 Constant voltage source 7, 8 Resistance 31 Power supply circuit 32-35 MOSFET
36 DC power supply 37, 38 Transformer 39, 40 Diode 41 Coil 42 Capacitor 43 Control circuit 44 IC circuit 45 to 47 Resistor 48 Diode 49 Capacitor 50 Error amplifier 51 Constant voltage source 52, 53 Comparator 54 Triangle wave generation circuit 55 AND circuit 56 Drive circuit 57-60 diodes

Claims (3)

A plurality of switching elements for converting a DC voltage into an AC;
A transformer having a primary side coil and a secondary side coil to which a voltage converted into alternating current by the plurality of switching elements is input;
A rectifier circuit for rectifying the voltage applied to the secondary coil;
A smoothing circuit for smoothing a voltage output from the rectifier circuit;
A power supply circuit comprising:
A current detector for detecting a current flowing in the primary side of the power supply circuit;
A correction circuit that outputs a correction value based on the output voltage of the power supply circuit;
When the output current of the power supply circuit converted from the current flowing through the primary side of the power supply circuit is lower than a predetermined current, the first switching element controls the plurality of switching elements so that the output voltage of the power supply circuit is constant. A control circuit;
When the output current of the power supply circuit converted from the current flowing through the primary side of the power supply circuit is higher than a predetermined current, according to the increase in the addition result of the voltage corresponding to the current flowing through the primary side and the correction value A second control circuit that controls the plurality of switching elements so that the output voltage decreases;
A power supply circuit comprising: The power supply circuit according to claim 1,
The power supply circuit, wherein the correction circuit amplifies a difference between the output voltage and a predetermined voltage and outputs the correction value. The power supply circuit according to claim 1,
The power supply circuit, wherein the correction circuit divides the output voltage and outputs the correction value.