JP2010136513A - Switching power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power supply which can prevent a switching element from being driven by a drive signal of a frequency which is different from a desired frequency. <P>SOLUTION: The switching power supply 1 includes a signal output circuit 45 which outputs a drive signal of a frequency corresponding to a cycle of the charging/discharging of a capacitor 47, a transistor 41 which is driven on the basis of the drive signal, and a current variable circuit 58 which makes variable a current flowing to a resistor 46 according to the charging/discharging of a capacitor 59. In the switching power supply, a time for charging the capacitor 59 is set longer than a time for charging the capacitor 47, and when the capacitor 59 is charged so that a voltage applied to the capacitor 59 becomes not lower than a voltage V4, the frequency of the drive signal is brought into a range of the desired frequency. The transistor 41 is turned off until the voltage applied to the capacitor 59 becomes not lower than the voltage V4. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a switching power supply including a switching element driven by a drive signal whose frequency is variable.

FIG. 4 is a diagram showing a conventional switching power supply.
A switching power supply 40 shown in FIG. 4 includes a transistor 41 (switching element), a coil 42, an electrolytic capacitor 43, a diode 44, a signal output circuit 45, a resistor 46, a capacitor 47 (first capacitor), A variable voltage source 48 and a signal source 49 are provided. That is, the drain terminal of the transistor 41 is connected to the input terminal 50, and the source terminal of the transistor 41 is connected to the output terminal 51 through the coil 42. The positive terminal of the electrolytic capacitor 43 is connected to the connection point between the transistor 41 and the output terminal 51, and the negative terminal of the electrolytic capacitor 43 is connected to the ground. The cathode terminal of the diode 44 is connected to the connection point between the transistor 41 and the coil 42, and the anode terminal of the diode 44 is connected to the ground. One end of the resistor 46 is connected to the ground via the variable voltage source 48, and one end of the capacitor 47 is connected to the ground.

  In the switching power supply 40 shown in FIG. 4, when the transistor 41 is turned on by the drive signal output from the signal output circuit 45, a DC voltage applied to the input terminal 50 is applied to the coil 42 via the transistor 41 and energy is applied to the coil 42. Accumulates. When the transistor 41 is turned off by the drive signal output from the signal output circuit 45, the electrolytic capacitor 43 is charged by the energy released from the coil 42 and a predetermined voltage is applied to the output terminal 51. To make this predetermined voltage constant, for example, the signal output circuit 45 controls the duty of the drive signal so that the predetermined voltage becomes constant.

The signal output circuit 45 includes an oscillation circuit 52 and a drive circuit 53.
The oscillation circuit 52 includes a current mirror circuit 54, a power supply 55, a switch 56, and a voltage monitoring circuit 57.

  The current mirror circuit 54 causes a current B flowing through the resistor 46 and a current B having a predetermined ratio to flow through the capacitor 47. At the initial start-up of the switching power supply 40, the switch 56 is off, the capacitor 47 is charged by the current B, and the voltage applied to the capacitor 47 increases from zero.

  When the capacitor 47 is charged by the current B and the voltage between the terminals of the capacitor 47 rises to the voltage V1 (first predetermined voltage), the voltage monitoring circuit 57 turns on the switch 56 and discharges the capacitor 47 so that the capacitor 47 is connected between the terminals. Reduce the voltage. Further, when the voltage between the terminals of the capacitor 47 drops to a voltage V2 (second predetermined voltage) smaller than the voltage V2, the voltage monitoring circuit 57 turns on the switch 56 and charges the capacitor 47 again with the current B, thereby causing the capacitor 47 to be charged. Increase the voltage between terminals. As described above, the voltage monitoring circuit 57 charges and discharges the capacitor 47 by turning on and off the switch 56 based on the voltage between the terminals of the capacitor 47, the voltage V1, and the voltage V2.

  The oscillation circuit 52 generates an oscillation signal having a frequency corresponding to the charge / discharge cycle of the capacitor 47 and outputs the oscillation signal to the drive circuit 53. For example, the oscillation circuit 52 generates an oscillation signal that becomes high level when the voltage applied to the capacitor 47 becomes the voltage V1 and becomes low level when the voltage applied to the capacitor 47 becomes the voltage V2.

  The drive circuit 53 compares the oscillation signal output from the oscillation circuit 52 with the voltage value applied to the output terminal 51 to generate a pulse, and outputs the pulse to the gate terminal of the transistor 41 as a drive signal. 41 is turned on and off.

The variable voltage source 48 varies the potential at one end of the resistor 46 based on the control signal output from the signal source 49.
For example, when the potential at one end of the resistor 46 increases, the voltage applied to the resistor 46 decreases and the current flowing through the resistor 46 decreases. Then, the current flowing through the capacitor 47 is also reduced, and the time for charging the capacitor 47 is increased, so that the frequency of the oscillation signal is lowered. Further, when the potential at the other end of the resistor 46 decreases, the voltage applied to the resistor 46 increases and the current flowing through the resistor 46 increases. Then, the current flowing through the capacitor 47 also increases and the time for charging the capacitor 47 is shortened, so that the frequency of the oscillation signal is increased.

  Thus, the frequency of the drive signal can be changed by varying the current flowing through the resistor 46. Therefore, for example, the frequency of the drive signal can be changed so that the transistor 41 is driven without being affected by external noise (see, for example, Patent Document 1).

FIG. 5 is a diagram illustrating a configuration example for changing the current flowing through the resistor 46. In addition, the same code | symbol is attached | subjected to the same structure as the structure shown in FIG.
The switching power supply 40 shown in FIG. 5 includes a current variable circuit 58 for changing the current flowing through the resistor 46.

  The variable current circuit 58 includes a capacitor 59 (second capacitor), a power source 60, current sources 61 and 62, a switch 63, and a voltage monitoring circuit 64. That is, the power source 60 is connected to one end of the switch 63 via the current source 61, and the other end of the switch 63 is connected to the ground via the current source 62. The capacitor 59 is provided between the other end of the switch 63 and the ground.

FIG. 6 is a diagram showing the voltage monitoring circuit 64.
The voltage monitoring circuit 64 shown in FIG. 6 includes comparators 65 and 66 and NAND circuits 67 and 68.

  A voltage V3 (third predetermined voltage) is input to the positive input terminal of the comparator 65, and a voltage V4 (fourth predetermined voltage) smaller than the voltage V3 is input to the negative input terminal of the comparator 66. . Further, the voltage between terminals of the capacitor 59 is input to the negative input terminal of the comparator 65 and the positive input terminal of the comparator 66, respectively. In addition, at the initial start of the switching power supply 40, the control signal output from the NAND circuit 67 is at a low level and the switch 63 is turned on. The capacitor 59 is charged by the current from the current source 61 and the voltage between the terminals of the capacitor 59 is increased. It rises from zero.

  The upper and lower limits of the target voltage of the capacitor 59 are determined so that the frequency of the drive signal falls within a desired frequency range. The upper limit of the target voltage of the capacitor 59 is the voltage V3, and the lower limit of the target voltage of the capacitor 59 is the voltage. V4.

  After the switching power supply 40 shown in FIG. 5 is started, as shown in FIG. 7, when the voltage across the capacitor 59 becomes higher than the voltage V3, the output of the comparator 65 changes from the high level to the low level and is output from the NAND circuit 67. The control signal to be changed from the low level to the high level, and the switch 63 is turned off. Then, the capacitor 59 is discharged, and the voltage between the terminals of the capacitor 59 decreases. Further, as shown in FIG. 7, when the voltage between the terminals of the capacitor 59 becomes smaller than the voltage V4, the output of the comparator 66 changes from low level to high level, and the output of the NAND circuit 68 changes from low level to high level. The control signal output from the NAND circuit 67 changes from the high level to the low level, and the switch 63 is turned on. Then, the capacitor 59 is charged again, and the voltage between the terminals of the capacitor 59 increases. In this way, the voltage monitoring circuit 64 charges and discharges the capacitor 59 by turning on and off the switch 63 based on the voltage across the capacitor 59, the voltage V3, and the voltage V4. Here, the charging / discharging cycle of the capacitor 59 is longer than the charging / discharging cycle of the capacitor 47 so that the switching frequency of the switch 63 in the current variable circuit 58 does not adversely affect the operation of the oscillation circuit 52. Assume that the capacitances of the capacitors 47 and 59, the current of the current source 61, and the like are set.

  When the switch 63 is turned on, the voltage between the terminals of the capacitor 59 increases, so that the voltage applied to the resistor 46 increases, and the current flowing through the resistor 46 increases. When the switch 63 is turned off, the voltage between the terminals of the capacitor 59 is lowered, so that the voltage applied to the resistor 46 is lowered and the current flowing through the resistor 46 is reduced.

As described above, the current variable circuit 58 varies the current flowing through the resistor 46 using the capacitor 59, the switch 63 that is turned on / off according to the voltage between the terminals of the capacitor 59, and the current sources 61 and 62. .
JP 2000-236660 A

  However, in the switching power supply 40 shown in FIG. 5, as described above, the charging / discharging cycle of the capacitor 59 is longer than the charging / discharging cycle of the capacitor 47, so the terminal voltage of the capacitor 59 is from zero to the target voltage of the capacitor 59. The time until the voltage V3 that is the upper limit value of the capacitor 47 reaches a voltage V1 that is the upper limit value of the target voltage of the capacitor 47 is longer than the time that the voltage between the terminals of the capacitor 47 reaches zero. Therefore, the voltage between the terminals of the capacitor 47 is at the initial stage of starting the switching power supply 40, that is, before the voltage V3 that is the upper limit of the target voltage of the capacitor 59 first after the voltage between the terminals of the capacitor 59 is started. When the capacitor 47 starts to discharge up to the voltage V1, which is the upper limit value of the target voltage 47, an oscillation signal having a frequency lower than the desired frequency is output from the oscillation circuit 52, and has a frequency different from the desired frequency. The transistor 41 is driven by the drive signal.

  Therefore, an object of the present invention is to provide a switching power supply capable of preventing a switching element from being driven by a drive signal having a frequency different from a desired frequency.

In order to solve the above problems, the present invention adopts the following configuration.
That is, the switching power supply according to the present invention charges and discharges the first capacitor charged by the current flowing through the resistor and the first capacitor, and drives the frequency according to the charging / discharging cycle of the first capacitor. A current variable circuit that includes a signal output circuit that outputs a signal, a switching element that is driven based on the drive signal, and a second capacitor that applies a terminal voltage to the resistor, and charges and discharges the second capacitor. When the time required for charging the second capacitor is longer than the time required for charging the first capacitor, and the voltage across the terminals of the second capacitor is equal to or higher than a predetermined voltage, A switching power supply in which the frequency of the drive signal falls within a desired frequency range until the voltage between the terminals of the second capacitor becomes equal to or higher than the predetermined voltage. Turn off the serial switching element.

  As a result, even when charging and discharging of the first capacitor starts in the initial stage of starting the switching power supply, the switching element can be turned off, so that the switching element is driven with a drive signal having a frequency different from the desired frequency. Can be prevented.

  The switching power supply according to the present invention includes a first capacitor that is charged by a current flowing through a resistor and a terminal of the first capacitor after the voltage between the terminals of the first capacitor rises to a first predetermined voltage. After the voltage between the terminals of the first capacitor decreases and the voltage between the terminals of the first capacitor decreases to a second predetermined voltage smaller than the first predetermined voltage, the voltage between the terminals of the first capacitor repeatedly increases. A signal output circuit that charges and discharges the first capacitor and outputs a drive signal having a frequency corresponding to a charge / discharge cycle of the first capacitor, and a switching element that is driven based on the drive signal And a second capacitor for applying a voltage to the resistor, and after the voltage across the terminals of the second capacitor rises to a third predetermined voltage, The voltage between the terminals decreases, and the voltage between the terminals of the second capacitor decreases to a fourth predetermined voltage that is smaller than the third predetermined voltage, and then the voltage between the terminals of the second capacitor increases. A current variable circuit that charges and discharges the second capacitor, and the time required for the voltage across the terminals of the second capacitor to reach the fourth predetermined voltage is zero. When the voltage between the terminals of the capacitor is longer than the time taken from zero to the second predetermined voltage and the voltage between the terminals of the second capacitor becomes equal to or higher than the fourth predetermined voltage, the driving is performed. A switching power supply in which a signal frequency falls within a desired frequency range, and the switching element is turned off until the voltage between the terminals of the second capacitor becomes equal to or higher than the fourth predetermined voltage.

  As a result, even when charging and discharging of the first capacitor starts in the initial stage of starting the switching power supply, the switching element can be turned off, so that the switching element is driven with a drive signal having a frequency different from the desired frequency. Can be prevented.

In the switching power supply, the switching element may be turned off until the voltage across the second capacitor reaches the third predetermined voltage.
As a result, it is sufficient to employ a configuration that detects the timing at which the voltage applied to the second capacitor first becomes the third predetermined voltage, so that the configuration can be realized by a flip-flop.

  According to the present invention, it is possible to prevent the switching element from being driven by a drive signal having a frequency different from a desired frequency in the initial stage of starting the switching power supply.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a switching power supply according to an embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the same structure as the structure shown in FIG.

  A characteristic feature of the switching power supply 1 shown in FIG. 1 is that the transistor 41 is turned off until the voltage between the terminals of the capacitor 59 first reaches the voltage V3 from the start. That is, as shown in FIG. 2, when the voltage between the terminals of the capacitor 59 first becomes higher than the voltage V3 from the start-up, the permission signal output from the voltage monitoring circuit 2 in the current variable circuit 58 becomes high level. When the permission signal becomes high level, a drive signal is output from the drive circuit 3 in the signal output circuit 45 to the gate terminal of the transistor 41.

  In this embodiment, the upper limit and lower limit of the target voltage of the capacitor 59 are determined so that the frequency of the drive signal falls within a desired frequency range. The upper limit of the target voltage of the capacitor 59 is V3, and the target voltage of the capacitor 59 is The lower limit is V4.

  According to the switching power supply 1 shown in FIG. 1, at the initial start of the switching power supply 40, even if the voltage between the terminals of the capacitor 47 rises to the voltage V <b> 1 that is the upper limit value of the target voltage of the capacitor 47, the discharge of the capacitor 47 starts. Therefore, even if an oscillation signal having a frequency lower than a desired frequency is output from the oscillation circuit 52, a drive signal based on the oscillation signal is not output from the drive circuit 3 to the transistor 41. It is possible to prevent the transistor 41 from being driven by a drive signal having a frequency different from the frequency.

FIG. 3 is a diagram illustrating the voltage monitoring circuit 2 of the present embodiment. In addition, the same code | symbol is attached | subjected to the same structure as the structure shown in FIG.
The voltage monitoring circuit 2 shown in FIG. 3 includes comparators 65 and 66, NAND circuits 67 and 68, and a latch circuit 4.

The operations of the components other than the latch circuit 4 are the same as those of the components in the voltage monitoring circuit 64 shown in FIG.
When the control signal output from the NAND circuit 67 first changes from the low level to the high level, the latch circuit 4 changes the permission signal from the low level to the high level, and thereafter, the control signal changes from the low level to the high level. Also, the permission signal is maintained at a high level.

  The latch circuit 4 may be configured by an RS flip-flop, for example. When the control signal input to the input terminal S first changes from the low level to the high level, the permission signal output from the output terminal Q changes from the low level to the high level, and the reset signal (switching power supply) input to the reset terminal R. When a signal indicating that 1 is stopped) changes from the low level to the high level, the permission signal output from the output terminal Q changes from the high level to the low level.

The drive circuit 3 may be configured by an AND circuit in which an oscillation signal is input to one input terminal and a permission signal is input to the other input terminal, for example.
In addition, the drive circuit 3, for example, an AND circuit in which an oscillation signal is input to one input terminal and a permission signal is input to the other input terminal, and an output of the AND circuit is amplified and output to the gate terminal of the transistor 41. You may comprise with an amplifier circuit.

  The drive circuit 3 is provided between, for example, an amplifier circuit that amplifies the oscillation signal and outputs the drive signal to the gate terminal of the transistor 41, and the input signal of the amplifier circuit and the ground. In this case, the transistor may be turned on.

  In the voltage monitoring circuit 2 of the above embodiment, the transistor 41 is turned off until the voltage between the terminals of the capacitor 59 starts up and reaches the voltage V3 that is the upper limit value of the target voltage of the capacitor 59 first. The transistor 41 may be configured to be turned off until the voltage between the terminals 59 first becomes equal to or higher than the voltage V4, which is the lower limit value of the target voltage of the capacitor 59, and the frequency of the drive signal falls within a desired frequency range. .

  In the current variable circuit 58 of the above embodiment, the current flowing through the resistor 46 is varied using the capacitor 59, the power source 60, the current sources 61 and 62, the switch 63, and the voltage monitoring circuit 64. However, the configuration of the current variable circuit 58 is not particularly limited as long as it can be repeated that the current flowing through the resistor 46 gradually increases and then gradually decreases.

It is a figure which shows the switching power supply of embodiment of this invention. It is a figure which shows a capacitor voltage, voltage V1, voltage V2, and a permission signal. It is a figure which shows the voltage monitoring circuit in this embodiment. It is a figure which shows the conventional switching power supply. It is a figure which shows the structural example for changing the electric current which flows into resistance in the conventional switching power supply. It is a figure which shows the voltage monitoring circuit in the conventional switching power supply. It is a figure which shows a capacitor | condenser voltage, the voltage V1, and the voltage V2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Switching power supply 2 Voltage monitoring circuit 3 Drive circuit 4 Latch circuit 40 Switching power supply 41 Transistor 42 Coil 43 Electrolytic capacitor 44 Diode 45 Signal output circuit 46 Resistance 47 Capacitor 48 Variable voltage source 49 Signal source 50 Input terminal 51 Output terminal 52 Oscillation circuit 53 Drive circuit 54 Current mirror circuit 55 Power supply 56 Switch 57 Voltage monitoring circuit 58 Current variable circuit 59 Capacitor 60 Power supply 61, 62 Current source 63 Switch 64 Voltage monitoring circuit 65, 66 Comparator 67, 68 NAND circuit

Claims (3)

A first capacitor charged by a current flowing through a resistor;
A signal output circuit that charges and discharges the first capacitor and outputs a drive signal having a frequency corresponding to a charging and discharging period of the first capacitor;
A switching element that is driven based on the drive signal;
A second capacitor that applies a terminal voltage to the resistor, and a current variable circuit that charges and discharges the second capacitor,
When the time required for charging the second capacitor is longer than the time required for charging the first capacitor, and the voltage between the terminals of the second capacitor is equal to or higher than a predetermined voltage, the frequency of the drive signal Is a switching power supply that falls within the desired frequency range,
The switching power supply, wherein the switching element is turned off until the voltage between the terminals of the second capacitor becomes equal to or higher than the predetermined voltage. A first capacitor charged by a current flowing through a resistor;
After the inter-terminal voltage of the first capacitor rises to a first predetermined voltage, the inter-terminal voltage of the first capacitor decreases, and the inter-terminal voltage of the first capacitor is greater than the first predetermined voltage. The first capacitor is charged and discharged and the first capacitor is charged and discharged so that the voltage across the terminals of the first capacitor rises repeatedly after the voltage drops to the second predetermined voltage. A signal output circuit that outputs a drive signal having a frequency corresponding to the period of
A switching element that is driven based on the drive signal;
A second capacitor for applying a voltage to the resistor; and after the voltage across the second capacitor rises to a third predetermined voltage, the voltage across the second capacitor falls, The second capacitor is repeatedly increased after the voltage across the terminals of the second capacitor has dropped to a fourth predetermined voltage that is smaller than the third predetermined voltage. And a variable current circuit for charging and discharging the capacitor,
The time taken for the inter-terminal voltage of the second capacitor to become the fourth predetermined voltage from zero than the time taken for the inter-terminal voltage of the first capacitor to become the second predetermined voltage from zero A switching power supply in which when the voltage between the terminals of the second capacitor becomes equal to or higher than the fourth predetermined voltage, the frequency of the drive signal falls within a desired frequency range,
The switching power supply, wherein the switching element is turned off until a voltage between terminals of the second capacitor becomes equal to or higher than the fourth predetermined voltage. The switching power supply according to claim 2,
The switching power supply, wherein the switching element is turned off until the voltage between the terminals of the second capacitor reaches the third predetermined voltage.

Images