JP6553578B2 - Switching power supply device and control method thereof - Google Patents

Description

  The present invention relates to a switching power supply device in which a double-ended isolated (half bridge, full bridge, or push-pull) non-stable converter is connected downstream of a step-down chopper stable converter and a control method thereof.

  Conventionally, as disclosed in Patent Document 1, switching provided with a step-down chopper type transformer circuit that converts an input voltage into an intermediate voltage and a double-end insulation type half-bridge circuit that converts an intermediate voltage into an output voltage There was a power supply. The transformer circuit in the front stage is a stable converter in which the on / off ratio of the switching element is variably controlled, and the half bridge circuit in the rear stage is an unstable that the on / off ratio of the two switching elements is set to about 50%. Type converter. This switching power supply device is characterized in that a drive circuit is provided for controlling the difference in on / off time ratio between the two switching elements so that the transformer of the half-bridge circuit is not biased.

  Further, as disclosed in FIG. 2B of Patent Document 2, a non-insulated DC-DC converter that converts an input voltage into an intermediate voltage, and an unstable stable DC-DC that converts an intermediate voltage into an output voltage. There has been a power supply device provided with a DC converter (half bridge method). The front-stage non-stable insulated DC-DC converter is variably controlled with the switching element ON / OFF time ratio, and the rear-stage non-stable DC-DC converter has the ON time ratio of two switches set to about 50%. ing. This power supply apparatus is characterized in that a protective circuit is provided to reduce the on / off ratio of the two switching elements when an abnormality occurs in the non-stable insulation type DC-DC converter, thereby suppressing an overcurrent.

JP 2003-88113 A JP 2008-54475 A

  The switching power supply device of Patent Document 1 does not include means for limiting the current flowing to the half bridge circuit in the subsequent stage, so, for example, when an instantaneous power failure or the like occurs, an overcurrent may flow in the half bridge circuit. In other words, if the input power is turned on again (when the power failure recovers) with the intermediate voltage high and the output voltage low shortly after the input power is shut off (after a power failure occurs), the half bridge circuit There is a possibility that current flows and internal circuit elements are damaged.

  In the case of the power supply device of Patent Document 2, since the protection circuit is provided, the above overcurrent does not flow. However, since it is necessary to change the ON / OFF time ratio of the two switching elements, the configuration of the circuit for generating the drive pulse becomes very complicated. In addition, the double-ended isolation method such as a half bridge has a merit that the output smoothing inductor can be miniaturized (or omitted) by fixing the on / off ratio of the switching element to about 50%. However, when the protection circuit operates, the on / off ratio decreases, so that a large-scaled output smoothing inductor is essential for the astable-insulated DC-DC converter to operate properly, resulting in an increase in size or cost of the device. There is a problem that.

  The present invention has been made in view of the above background art, and provides a switching power supply device capable of easily preventing an overcurrent from flowing to a non-stable converter at a later stage when an instantaneous power failure or the like occurs, and a control method thereof. The purpose is to provide.

The present invention provides a first converter which is a step-down chopper type stable converter that converts an input voltage into an intermediate voltage by a switching operation of a first switching element whose ON / OFF time ratio is variably controlled, and an ON / OFF time ratio is A second converter which is a non-stable converter of double-end isolation system that converts the intermediate voltage to an output voltage by switching operation of a second switching element set to approximately 50%; and the first and second switching elements Control circuit to control the on / off operation of the
The control circuit issues a command to the switching control unit that outputs a driving pulse for the first and second switching elements to perform a switching operation, and when the input power is turned on and off, and A sequence control unit for controlling the sequence of start and stop of the switching operation of the first and second switching elements;
The sequence control unit stops the switching operation of the first switching element when the input power is shut off, and then the switching operation of the second switching element when the intermediate voltage falls below a predetermined reference value. The switching power supply apparatus starts the switching operation of the second switching element when the input power is turned on and the input voltage is established, and then starts the switching operation of the first switching element.

The control circuit is provided with an intermediate voltage detection unit for detecting the intermediate voltage, and the sequence control unit turns on the input power to establish an input voltage, and further, based on the detection result of the intermediate voltage detection unit, the intermediate voltage May be configured to start the switching operation of the second switching element and then start the switching operation of the first switching element.

When the output rectification element of the second converter is a synchronous rectification FET, the switching control unit outputs a drive pulse for turning on and off the synchronous rectification FET together with a drive pulse for turning on and off the first and second switching elements. The sequence control unit issues a command to the switching control unit when the input power is turned on and off, and controls a start and stop sequence of the switching operation of the first switching element, the second switching element, and the synchronous rectification FET. Is what
When the input power is cut off, the sequence control unit stops the switching operation of the first switching element, and then stops the switching operation of the synchronous rectification FET, and then the intermediate voltage is equal to or lower than a predetermined reference value. When the input power is turned on and the input voltage is established, the switching operation of the second switching element is started, and then the switching operation of the first switching element is started. The switching operation is started, and thereafter, the switching operation of the synchronous rectification FET is started.

In this case, the control circuit is provided with an intermediate voltage detection unit for detecting the intermediate voltage, and the sequence control unit turns on the input power to establish an input voltage, and further, based on the detection result of the intermediate voltage detection unit. When the intermediate voltage is detected to be equal to or lower than a predetermined reference value, the switching operation of the second switching element is started, and then the switching operation of the first switching element is started, and then the switching of the synchronous rectification FET is performed. It may be configured to start the operation.

Further, the control circuit is provided with a regenerative operation detection unit that detects a regenerative operation in which the second converter regenerates output-side power to the input side, and the regenerative operation detection unit is configured so that the second converter Upon detecting that there is a possibility to do the or the regenerative operation is performed regenerative operation, issues a command to the sequence controller, the switching operation of the synchronous rectification FET may be configured so as to stop. The regenerative operation detection unit, for example, observes the output current of the first converter, and when the output current is below a predetermined value and when the back flow from the second converter to the first converter, it can be the second converter is configured to determine that there is a possibility to perform in that or the regeneration operation carried out the regenerative operation.

The present invention also provides a first converter that is a step-down chopper-type stable converter that converts an input voltage into an intermediate voltage by a switching operation of a first switching element whose ON / OFF time ratio is variably controlled. A switching power supply device comprising: a second converter which is a non-stabilizing converter of a double end isolation system which converts the intermediate voltage to an output voltage by switching operation of a second switching element whose ratio is set to approximately 50%. Control method, and
When the input power is cut off, the switching operation of the first switching element is stopped, and then the switching operation of the second switching element is stopped when the intermediate voltage drops below a predetermined reference value. It is a control method of a switching power supply device which starts switching operation of the second switching element when power is turned on and input voltage is established, and then starts switching operation of the first switching element.

  When the input power is turned on and the input voltage is established, after confirming that the intermediate voltage is less than a predetermined reference value, the switching operation of the second switching element is started, and then the switching of the first switching element is performed. It may be configured to start the operation.

  When the output rectification element of the second converter is configured by a synchronous rectification FET, when the input power is cut off, the switching operation of the first switching element is stopped, and then the switching operation of the synchronous rectification FET is performed. When the intermediate voltage drops below a predetermined reference value, the switching operation of the second switching element is stopped, and when the input power is turned on and the input voltage is established, the second switching element A switching operation is started, and then the switching operation of the first switching element is started, and then the switching operation of the synchronous rectification FET is started.

  In this case, when the input power is turned on and the input voltage is established, after confirming that the intermediate voltage is less than a predetermined reference value, the switching operation of the second switching element is started, and then the first switching is performed. The switching operation of the element may be started, and then the switching operation of the synchronous rectification FET may be started.

Further, when it is determined that the second converter is performing a regenerative operation for regenerating output power to the input side or that there is a possibility of performing the regenerative operation, the switching operation of the synchronous rectification FET is stopped. It may be configured to For example, when the output current of the first converter is observed and it is detected that the output current is less than a predetermined value or is flowing back from the second converter to the first converter, the second converter The converter can be configured to determine that the regeneration operation is being performed.

  According to the switching power supply device and the control method thereof of the present invention, when the input power is turned on and off, each switching of the first converter (stable converter) in the front stage and the second converter (unstable converter) in the rear stage By appropriately controlling the operation start and stop sequences, it is possible to reliably prevent an overcurrent from occurring in the second converter even when an instantaneous power failure or the like occurs. Moreover, since the second converter does not change the on / off ratio of the switching element from about 50%, the second converter can be used even if a small output smoothing inductor is used (or even if the output smoothing inductor is omitted). The converter can operate normally.

  Further, this control method can be easily realized, for example, by configuring the function of the control circuit by a digital processor, and a switching power supply device with high intelligence and a simple structure can be easily obtained.

It is a circuit diagram showing a first embodiment of a switching power supply device of the present invention. It is a flowchart which shows the control method at the time of interruption | blocking of the input power supply of the switching power supply device of 1st embodiment. It is a flowchart which shows the control method at the time of input of an input power supply of the switching power supply device of 1st embodiment. It is a time chart which shows operation | movement until it recovers from the momentary power failure of the switching power supply device of 1st embodiment (at the time of load). It is a time chart which shows the operation | movement until it recovers from the momentary power failure of the switching power supply device of 1st embodiment (at the time of no load). It is a circuit diagram showing a second embodiment of a switching power supply device of the present invention. It is a flowchart which shows the control method at the time of interruption | blocking of the input power supply of the switching power supply device of 2nd embodiment. It is a flowchart which shows the control method at the time of supply of input power of the switching power supply device of 2nd embodiment. It is a time chart which shows the operation | movement until it recovers from the momentary power failure of the switching power supply device of 2nd embodiment (at the time of load). It is a time chart which shows the operation | movement until it recovers from the momentary power failure of the switching power supply device of 2nd embodiment (at the time of no load).

  Hereinafter, a first embodiment of a switching power supply device and a control method thereof according to the present invention will be described based on FIGS. 1 to 5. As shown in FIG. 1, the switching power supply device 10 of this embodiment includes first and second converters 12 and 14 and a control circuit 16.

  The first converter 12 is a step-down chopper type stable converter, and the first switching element 18 performs switching operation to convert the input voltage Vi supplied from the input power source Ei into the intermediate voltage Vo1. The first switching element 18 is driven by the drive pulse Vg18 output from the control circuit 16, and the ON / OFF time ratio is variably controlled. The output smoothing capacitor 20 generates an intermediate voltage Vo1 at its both ends, and outputs it to the second converter 14.

  The second converter 14 is a full-bridge non-stable converter, and the four second switching elements 22 perform a switching operation to convert the intermediate voltage Vo1 into the output voltage Vo2. Each of the second switching elements 22 is driven by a drive pulse Vg22 output from the control circuit 16, and the on / off time ratio is fixed to approximately 50%. The output rectifying element that rectifies the voltage of the output winding of the transformer 24 is two diodes 26. The smoothing circuit that smoothes the voltage rectified by the diode 26 is the output smoothing capacitor 28, and the output smoothing inductor is omitted. The output smoothing capacitor 28 generates an output voltage Vo2 at both ends, and outputs it toward the load Lo.

  The control circuit 16 is a circuit that controls the switching operation of the first and second switching elements 18 and 22, and includes a switching control unit 30, an input voltage detection unit 32, an intermediate voltage detection unit 34, and a sequence control unit 36. .

  The switching control unit 30 generates drive pulses Vg18 and Vg22 for the first and second switching elements 18 and 22 to perform a switching operation. The switching control unit 30 changes the on / off ratio of the first switching element 18 so that the intermediate voltage Vo1 or the output voltage Vo2 approaches the target value by changing the high level / low level time ratio of the drive pulse Vg18. Variable control. The high / low time ratio of the drive pulse Vg22 is fixed so that the on / off time ratio of the second switching element 22 is about 50%.

  The input voltage detection unit 32 detects the input voltage Vi, and outputs the detection result to the sequence control unit 36. The intermediate voltage detection unit 34 detects the intermediate voltage Vo1 and outputs the detection result to the sequence control unit 36.

  The sequence control unit 36 is composed of, for example, a digital processor, and issues a command to the switching control unit 30 based on the detection results of the input voltage detection unit 32 and the output voltage detection unit 34 when turning on and off the input power supply Ei. A process of controlling the sequence of start and stop of the switching operation of the first and second switching elements 18 and 22 is performed. Specific processing contents will be described in detail later in the operation description.

  Although not shown in FIG. 1, a power supply circuit is provided that generates a DC voltage by stepping down the input voltage Vi. The power supply circuit serves to supply a power supply voltage for operation to the control circuit 16.

  Next, the operation of the switching power supply device 10 will be described. Here, it is assumed that the input power source Ei is shut off while the power is on and is turned on again in a very short time (that is, a situation where an instantaneous power failure has occurred). Since the behaviors of the intermediate voltage Vo1 and the output voltage Vo2 are slightly different, the operation will be described separately when there is a load and when there is no load. The control method executed by the control circuit 16 has the contents shown in the flowcharts of FIGS. 2 and 3, and is the same when there is a load and when there is no load.

  First, the operation under load will be described based on FIG. 2, FIG. 3, and FIG. When the input power source Ei is shut off during energization, the input voltage Vi gradually decreases. The sequence control unit 36 detects that the input power source Ei is cut off from the detection result of the input voltage detection unit 32 (step S11), and stops the on / off of the first switching element 18 toward the switching control unit 30. A command is issued (step S12). As a result, the switching control unit 30 stops outputting the drive pulse Vg18, the first switching element 18 stops the switching operation, and the first converter 12 does not supply power to the second converter 14.

  When step S12 is performed, since the second switching element 22 continues the switching operation, the energy of the smoothing capacitor 20 in which the intermediate voltage Vo1 is generated at both ends is sent out toward the load Lo, and the intermediate voltage Vo1 Decreases rapidly. Further, the energy of the output smoothing capacitor 28 in which the output voltage Vo2 is generated at both ends is consumed by the load Lo, and the output voltage Vo2 also decreases rapidly.

  When the sequence control unit 36 detects from the detection result of the intermediate voltage detection unit 34 that the intermediate voltage Vo1 has dropped below the reference value Vr1 (very low voltage) (step S13), the sequence control unit 36 is directed to the switching control unit 30. Command to stop the on / off of the second switching element 22 (step S14). As a result, the switching control unit 30 stops outputting the drive pulse Vg22, and the second switching element 22 also stops the switching operation. Thereafter, the input voltage Vi further decreases, the power supply circuit cannot supply a sufficient power supply voltage to the control circuit 16, and the control circuit 16 goes down (step S15).

  Soon, when the input power supply Ei is turned on and the input voltage Vi increases, the power supply voltage of the control circuit 16 increases and the control circuit 16 stands by (step S21). Then, the sequence control unit 36 detects that the input voltage Vi has been established from the detection result of the input voltage detection unit 32 (step S22), and further determines that the intermediate voltage Vo1 is the reference value Vr from the detection result of the intermediate voltage detection unit 34. When the following is detected (step S23), a command is issued to the switching control unit 30 to start on / off of the second switching element 22 (step S24). As a result, the switching control unit 30 starts to output the drive pulse Vg22, and the second switching element 22 starts the switching operation.

  Here, when step S24 is carried out, it becomes a problem whether the overcurrent occurs in the second converter 14. Both the intermediate voltage Vo1 and the output voltage Vo2 have dropped to almost zero volts after step S12 is performed and before step S13 is performed. Therefore, even if the second switching element 22 starts the switching operation in this state, neither the overcurrent flowing from the input side to the output side nor the overcurrent flowing from the output side to the input side is generated in the second converter 14. .

  Note that step S23 is a step for preventing step S24 from being performed when the intermediate voltage Vo1 does not drop below the reference value Vr for some reason. Although step S23 may be omitted, by providing step S23, it is possible to prevent the occurrence of overcurrent in the second converter 14 with more certainty, thereby further improving safety.

  Thereafter, the sequence control unit 36 issues a command to the switching control unit 30 to start on / off of the first switching element 18 (step S25). As a result, the switching control unit 30 starts to output the drive pulse Vg18, the first switching element 18 starts the switching operation, and the first converter 12 starts to supply power to the second converter 14. Then, the intermediate voltage Vo1 and the output voltage Vo2 rise while maintaining the relationship Vo1≈ (Np / Ns) · Vo2, respectively, and return to the original state. Here, Np is the number of turns of the input winding of the transformer 24, and Ns is the number of turns of the output winding of the transformer 24.

  Next, the operation at no load will be described with reference to FIGS. When the input power source Ei is shut off due to the power failure, the input voltage Vi gradually decreases. The sequence control unit 36 detects from the detection result of the input voltage detection unit 32 that the input power source Ei is cut off (step S11), and stops turning on and off the first switching element 18 toward the switching control unit 30. A command is issued (step S12). As a result, the switching control unit 30 stops outputting the drive pulse Vg18, the first switching element 18 stops the switching operation, and the first converter 12 does not supply power to the second converter 14.

  When step S12 is performed, since the second switching element 22 continues the switching operation, the energy of the smoothing capacitor 20 in which the intermediate voltage Vo1 is generated at both ends is consumed as the iron loss of the transformer 24, and the intermediate voltage Vo1 decreases. On the other hand, the energy of the output smoothing capacitor 28 in which the output voltage Vo2 is generated at both ends is not consumed by the load Lo (no load condition) and is only slightly consumed by an additional circuit (not shown). Drops very slowly.

  When the sequence control unit 36 detects that the intermediate voltage Vo1 has dropped below the reference value Vr1 (very low voltage) from the detection result of the intermediate voltage detection unit 34 (step S13), the sequence control unit 36 directs the switching control unit 30. Command to stop the on / off of the second switching element 22 (step S14). As a result, the switching control unit 30 stops outputting the drive pulse Vg22, and the second switching element 22 also stops switching operation. Thereafter, the input voltage Vi further decreases, the power supply circuit cannot supply a sufficient power supply voltage to the control circuit 16, and the control circuit 16 goes down (step S15).

  Soon, when the input power supply Ei is turned on and the input voltage Vi increases, the power supply voltage of the control circuit 16 increases and the control circuit 16 stands by (step S21). Then, the sequence control unit 36 detects that the input voltage Vi has been established from the detection result of the input voltage detection unit 32 (step S22), and further determines that the intermediate voltage Vo1 is the reference value Vr from the detection result of the intermediate voltage detection unit 34. When the following is detected (step S23), a command is issued to the switching control unit 30 to start on / off of the second switching element 22 (step S24). As a result, the switching control unit 30 starts to output the drive pulse Vg22, and the second switching element 22 starts the switching operation.

  Here, when step S24 is carried out, it becomes a problem whether the overcurrent occurs in the second converter 14. The intermediate voltage Vo1 drops to approximately zero volts after step S12 is performed and before step S13 is performed. On the other hand, the output voltage Vo2 is held at a predetermined high voltage. Therefore, since the second switching element 22 starts the switching operation in the state of Vo1 <(Np / Ns) · Vo2, the overcurrent flowing from the input side to the output side does not occur in the second converter 14. Further, the direction from the output side to the input side is also blocked by the diode 26 which is an output rectifying element, so that no overcurrent is generated.

  Thereafter, the sequence control unit 36 issues a command to the switching control unit 30 to start on / off of the first switching element 18 (step S25). As a result, the switching control unit 30 starts to output the drive pulse Vg18, the first switching element 18 starts the switching operation, and the intermediate voltage Vo1 increases. Then, after the intermediate voltage Vo1 reaches (Np / Ns) · Vo2, the intermediate voltage Vo1 and the output voltage Vo2 rise while maintaining the relationship of Vo1 ((Np / Ns) · Vo2, and the original state Return to.

  As described above, according to the switching power supply device 10 and its control method, when the input power supply Ei is turned on and off, the switching operation start and stop sequences of the first converter 12 and the second converter 14 are performed. Since the second converter 14 starts switching operation in a state of Vo1 ≦ (Np / Ns) · Vo2 at all times when the input power source Ei is turned on, even when an instantaneous power failure occurs, the second converter is properly controlled. It is possible to reliably prevent the occurrence of an overcurrent in the circuit 14. In addition, since the on / off time ratio of the second switching element 22 does not change from about 50%, the second converter 14 can operate normally even if the output smoothing inductor is omitted.

  Further, this control method can be easily realized by configuring the sequence control unit 36 with a digital processor, and the switching power supply device 10 having high intelligence and a simple structure can be easily obtained.

  Next, a second embodiment of the switching power supply device and the control method thereof according to the present invention will be described based on FIGS. Here, the same components as those in the above embodiment are denoted by the same reference numerals and description thereof is omitted. As shown in FIG. 6, the switching power supply device 38 of this embodiment includes first and second converters 12 and 14 and a control circuit 16.

  The configuration of the first converter 12 is the same as that of the switching power supply device 10 described above. The second converter 14 is different in that a synchronous rectification FET 40 which is an N-channel MOS type FET is used as an output rectification element, and the other configuration is the same as that of the switching power supply device 10.

  When the output rectification element is the synchronous rectification FET 40, when the synchronous rectification FET 40 performs switching operation in the state of Vo1 <(Np / Ns) · Vo2, the regenerative operation is performed to regenerate the power on the output side to the input side. Become. Therefore, in the case of the switching power supply 38, it is necessary to prevent the regenerative operation from being performed in order to prevent an overcurrent from occurring in the second converter 14.

  The control circuit 16 is a circuit that controls the on / off operation of the first and second switching elements 18 and 22 and the synchronous rectification FET 40, and includes a switching control unit 30, an input voltage detection unit 32, an intermediate voltage detection unit 34, and a regenerative operation detection unit 42. And a sequence control unit 44.

  As described above, the switching control unit 30 generates the drive pulses Vg18 and Vg22 for the first and second switching elements 18 and 22 to perform the switching operation, and the synchronous rectification FET 40 is synchronized with the second switching element 22. Then, the drive pulse Vg 40 for performing the switching operation is generated.

  The input voltage detection unit 32 detects the input voltage Vi, and outputs the detection result to the sequence control unit 44. The intermediate voltage detection unit 34 detects the intermediate voltage Vo1 and outputs the detection result to the sequence control unit 44.

Regenerative operation detecting unit 42 detects that the second converter 14 is likely to do the or regenerative operation is performed regenerative operation, issues a command to the sequence controller 44, the switching operation of the synchronous rectification FET40 It is a block that performs control to make it stop. Here, the output current Io1 of the first converter 12 is observed, and when the output current Io1 is not more than a predetermined value and when the second converter 14 is flowing backward to the first converter 12 (the output current Io1 is When it is flowing in the opposite direction to the arrow shown in FIG. 6), it is configured to determine that the second converter 14 is performing the regeneration operation or may perform the regeneration operation.

  The sequence control unit 44 is formed of, for example, a digital processor, and the switching control unit 30 is based on the detection results of the input voltage detection unit 32, the output voltage detection unit 34 and the regeneration operation detection unit 42 when turning on and off the input power source Vi. The first and second switching elements 18 and 22 and the synchronous rectification FET 40 are controlled to start and stop the switching operation. Specific processing contents will be described in detail later in the operation description.

  Next, the operation of the switching power supply device 38 will be described. Again, assuming the situation where the input power source Ei was shut off during energization and turned on again in a very short time (that is, a situation where an instantaneous power failure occurred), it was divided into a load time and a no load time. The operation will be described. The control method executed by the control circuit 16 has the contents shown in the flowcharts of FIGS. 7 and 8, and is the same when there is a load and when there is no load.

  First, the operation under load will be described based on FIG. 7, FIG. 8, and FIG. When the input power source Ei is shut off during energization, the input voltage Vi gradually decreases. The sequence control unit 44 detects that the input power source Ei is cut off from the detection result of the input voltage detection unit 32 (step S31), and stops the on / off of the first switching element 18 toward the switching control unit 30. A command is issued (step S32). As a result, the switching control unit 30 stops outputting the drive pulse Vg18, the first switching element 18 stops the switching operation, and the first converter 12 does not supply power to the second converter 14.

  When step S32 is performed, since the second switching element 22 and the synchronous rectification FET 40 continue the switching operation, the energy of the smoothing capacitor 20 in which the intermediate voltage Vo1 is generated at both ends is sent out toward the load Lo. , And the intermediate voltage Vo1 drops quickly. Further, the energy of the output smoothing capacitor 28 in which the output voltage Vo2 is generated is consumed by the load Lo, and the output voltage Vo2 also decreases rapidly.

  While the intermediate voltage Vo1 and the output voltage Vo2 are decreasing, the sequence control unit 44 instructs the switching control unit 30 to stop on / off of the synchronous rectification FET 40 (step S33). As a result, the switching control unit 30 stops outputting the driving pulse Vg40, and the synchronous rectification FET 40 stops the switching operation. However, since the parasitic diode of the synchronous rectification FET 40 acts as an output rectifying element, step S33 is performed. Even so, no significant change appears in the movement of the intermediate voltage Vo1.

  Then, when the sequence controller 44 detects from the detection result of the intermediate voltage detector 34 that the intermediate voltage Vo1 has dropped below the reference value Vr1 (very low voltage) (step S34), the sequence controller 44 goes to the switching controller 30. Command to stop the on / off of the second switching element 22 (step S35). As a result, the switching control unit 30 stops outputting the drive pulse Vg22, and the second switching element 22 also stops the switching operation. Thereafter, the input voltage Vi further decreases, the power supply circuit cannot supply a sufficient power supply voltage to the control circuit 16, and the control circuit 16 goes down (step S36).

  Soon, when the input power supply Ei is turned on and the input voltage Vi increases, the power supply voltage of the control circuit 16 increases and the control circuit 16 stands by (step S41). Then, the sequence control unit 44 detects that the input voltage Vi is established from the detection result of the input voltage detection unit 32 (step S42), and further, the intermediate voltage Vo1 is detected from the detection result of the intermediate voltage detection unit 34 as the reference value Vr. When the following is detected (step S43), a command is issued to the switching control unit 30 to start on / off of the second switching element 22 (step S44). As a result, the switching control unit 30 starts to output the drive pulse Vg22, and the second switching element 22 starts the switching operation.

  Here, when step S44 is performed, it becomes a problem whether the overcurrent occurs in the second converter 14. Both the intermediate voltage Vo1 and the output voltage Vo2 have dropped to almost zero volts after step S32 and before step S34. Therefore, even if the second switching element 22 starts the switching operation in this state, neither the overcurrent flowing from the input side to the output side nor the overcurrent flowing from the output side to the input side is generated in the second converter 14. .

  Note that step S43 is a step for preventing step S44 from being performed when the intermediate voltage Vo1 does not drop below the reference value Vr for some reason. Although step S43 may be omitted, by providing step S43, it is possible to prevent overcurrent from occurring in the second converter 14 with more certainty, thereby further improving safety.

  Thereafter, the sequence control unit 44 issues a command to the switching control unit 30 to start on / off of the first switching element 18 (step S45). As a result, the switching control unit 30 starts to output the drive pulse Vg18, the first switching element 18 starts the switching operation, and the first converter 12 starts to supply power to the second converter 14. The intermediate voltage Vo1 and the output voltage Vo2 rise while maintaining the relationship of Vo1≈ (Np / Ns) · Vo2. The reason that the output voltage Vo2 rises is because the output current Io1 starts to flow in the direction of the arrow in FIG. 6, but synchronization is made by the command of the regenerative operation detection unit 42 until the output current Io1 reaches a predetermined value. The rectification FET 40 is in a state in which the switching operation is stopped. Therefore, for a while after the output voltage Vo2 starts to rise, the parasitic diode of the synchronous rectification FET 40 functions as an output rectification element.

  After that, when the output current Io1 exceeds a predetermined value, the regenerative operation detection unit 42 issues a command to release the stop of the synchronous rectification FET 40 to the sequence control unit 44, and the sequence control unit 44 sends to the switching control unit 30. Then, a command is issued to start on / off of the synchronous rectification FET 40 (step S46). As a result, the switching control unit 30 starts to output the drive pulse Vg40, and the synchronous rectification FET 40 starts the switching operation. Then, the intermediate voltage Vo1 and the output voltage Vo2 further increase and return to the original state.

  As can be seen from the operation waveform of FIG. 9, there is no period of Vo1 <(Np / Ns) · Vo2 when there is a load, so there is no concern about the regenerative operation being performed. Therefore, the overcurrent due to the regenerative operation (the overcurrent flowing from the output side to the input side) does not flow to the second converter 14.

  Next, the operation at the time of no load will be described based on FIG. 7, FIG. 8, and FIG. When the input power source Ei is shut off due to the power failure, the input voltage Vi gradually decreases. The sequence control unit 44 detects that the input power source Ei is cut off from the detection result of the input voltage detection unit 32 (step S31), and stops the on / off of the first switching element 18 toward the switching control unit 30. A command is issued (step S32). As a result, the switching control unit 30 stops outputting the drive pulse Vg18, the first switching element 18 stops the switching operation, and the first converter 12 does not supply power to the second converter 14.

  When step S32 is performed, since the second switching element 22 continues the switching operation, the energy of the smoothing capacitor 20 in which the intermediate voltage Vo1 is generated at both ends is consumed as the iron loss of the transformer 24, and the intermediate voltage Vo1 decreases. On the other hand, the energy of the output smoothing capacitor 28 in which the output voltage Vo2 is generated at both ends is not consumed by the load Lo (no load condition) and is only slightly consumed by an additional circuit (not shown). Drops very slowly.

  While the intermediate voltage Vo1 and the output voltage Vo2 are decreasing, the sequence control unit 44 instructs the switching control unit 30 to stop on / off of the synchronous rectification FET 40 (step S33). As a result, the switching control unit 30 stops outputting the drive pulse Vg40, and the synchronous rectification FET 40 stops the switching operation. However, almost no current flows in the synchronous rectification FET 40 in no load state, so step S33 is performed. Even so, no significant change appears in the movement of the intermediate voltage Vo1.

  When the sequence control unit 44 detects that the intermediate voltage Vo1 has dropped below the reference value Vr1 (very low voltage) from the detection result of the intermediate voltage detection unit 34 (step S34), the sequence control unit 44 proceeds to the switching control unit 30. Command to stop the on / off of the second switching element 22 (step S35). As a result, the switching control unit 30 stops outputting the drive pulse Vg22, and the second switching element 22 also stops switching operation. Thereafter, the input voltage Vi further decreases, the power supply circuit cannot supply a sufficient power supply voltage to the control circuit 16, and the control circuit 16 goes down (step S36).

  Soon, when the input power supply Ei is turned on and the input voltage Vi increases, the power supply voltage of the control circuit 16 increases and the control circuit 16 stands by (step S41). Then, the sequence control unit 44 detects that the input voltage Vi is established from the detection result of the input voltage detection unit 32 (step S42), and further, the intermediate voltage Vo1 is detected from the detection result of the intermediate voltage detection unit 34 as the reference value Vr. When the following is detected (step S43), a command is issued to the switching control unit 30 to start on / off of the second switching element 22 (step S44). As a result, the switching control unit 30 starts to output the drive pulse Vg22, and the second switching element 22 starts the switching operation.

  Here, when step S44 is performed, it becomes a problem whether the overcurrent occurs in the second converter 14. The intermediate voltage Vo1 is reduced to approximately zero volts after step S32 is performed and before step S34 is performed. On the other hand, the output voltage Vo2 is held at a predetermined high voltage. Therefore, since the second switching element 22 starts the switching operation in the state of Vo1 <(Np / Ns) · Vo2, the overcurrent flowing from the input side to the output side does not occur in the second converter 14. Further, with respect to the direction from the output side to the input side, the synchronous rectification FET 40 stops the switching operation and is blocked by the parasitic diode between the drain and source, so that no overcurrent is generated.

  Thereafter, the sequence control unit 44 issues a command to the switching control unit 30 to start on / off of the first switching element 18 (step S45). As a result, the switching control unit 30 starts to output the drive pulse Vg18, and the first switching element 18 starts the switching operation, so that the intermediate voltage Vo1 increases. Then, after the intermediate voltage Vo1 reaches (Np / Ns) · Vo2, the intermediate voltage Vo1 and the output voltage Vo2 rise while maintaining the relationship of Vo1 ≒ (Np / Ns) · Vo2. The reason that the output voltage Vo2 rises is because the output current Io1 starts to flow in the direction of the arrow in FIG. 6, but synchronization is made by the command of the regenerative operation detection unit 42 until the output current Io1 reaches a predetermined value. The rectification FET 40 is in a state in which the switching operation is stopped. Therefore, for a while after the output voltage Vo2 starts to rise, the parasitic diode of the synchronous rectification FET 40 functions as an output rectification element.

  After that, when the output current Io1 exceeds a predetermined value, the regenerative operation detection unit 42 issues a command to release the stop of the synchronous rectification FET 40 to the sequence control unit 44, and the sequence control unit 44 sends to the switching control unit 30. Then, a command is issued to start on / off of the synchronous rectification FET 40 (step S46). As a result, the switching control unit 30 starts to output the drive pulse Vg40, and the synchronous rectification FET 40 starts the switching operation. Then, the intermediate voltage Vo1 and the output voltage Vo2 further increase and return to the original state.

  As can be seen from the operation waveform in FIG. 10, since there is a period of Vo1 <(Np / Ns) · Vo2 when there is no load, the regenerative operation may be performed. However, as the regenerative operation detection unit 42 operates, the synchronous rectification FET 40 reliably stops in the period Vo1 <(Np / Ns) · Vo2 at least, so the second converter 14 causes the overcurrent due to the regenerative operation. (Overcurrent flowing from the output side to the input side) never flows.

  As described above, according to the switching power supply device 38 and its control method, the same effect as the switching power supply device 10 can be obtained. Moreover, although the output rectification element of the second converter 14 is the synchronous rectification FET 40 in which the regenerative operation may occur, the overcurrent due to the regenerative operation of the second converter 14 is also obtained by the unique configuration and control method, It can be easily prevented.

  The switching power supply device and the control method thereof according to the present invention are not limited to the above embodiment. As shown in FIG. 2, after step S12 is performed, the switching power supply 10 compares the detection result of the intermediate voltage detection unit 34 with the reference value Vr as to whether the intermediate voltage Vo1 has dropped below the reference value Vr. This is determined (step S13), and the timing for executing step S14 is determined, but the timing for executing step S14 may be determined by other methods. For example, the time required for the intermediate voltage Vo1 to reliably fall below the reference value Vr is checked in advance, and after step S12 is performed, step S14 may be performed at the timing when the required time has elapsed. Good. This makes it possible to omit the intermediate voltage detection unit 34. Similarly, as shown in FIG. 7, the switching power supply 38 performs steps S32 and S33 and then determines whether the intermediate voltage Vo1 has dropped below the reference value Vr, based on the detection result of the intermediate voltage detector 34 and the reference. Although the determination is made by comparing with the value Vr (step S34) and the timing for performing step S35 is determined, for example, the time required for the intermediate voltage Vo1 to reliably fall below the reference value Vr is checked in advance In addition, after step S32 is performed, step S35 may be performed when the required time has elapsed. This makes it possible to omit the intermediate voltage detection unit 34.

  The control method performed by the regenerative operation detection unit and the regenerative operation detection unit is not limited to the configuration of the switching power supply device 38. Since the regenerative operation is performed only when Vo1 <(Np / Ns) · Vo2, for example, whether or not “the regenerative operation is performed or there is a possibility of performing the regenerative operation” is output as the intermediate voltage Vo1. The voltage Vo2 may be observed and the determination may be made according to whether the relationship Vo1 <(Np / Ns) · Vo2 is satisfied.

  Further, the control performed by the regenerative operation detection unit and the regenerative operation detection unit can be omitted. In this case, after the sequence control unit 44 issues a command to start on / off of the first switching element 18 at the time of turning on the input power, a command to start on / off of the synchronous rectification FET 40 is issued when a predetermined time elapses. By setting it as "to put out", possibility that regeneration operation is performed can be made low. However, by performing the control to prevent the regenerative operation by detecting the regenerative operation, it is possible to reliably prevent the overcurrent from occurring in the second converter 14 and further improve the safety of the power supply device.

  The second converter 14 is a full-bridge type, but may be changed to a half-bridge type or a push-pull type, which is another double-end insulation type, and the same effect can be obtained.

10, 38 Switching power supply 12 First converter 14 Second converter 16 Control circuit 18 First switching element 22 Second switching element 30 Switching control section 34 Intermediate voltage detection section 36, 44 Sequence control section 40 Synchronous rectification FET (output Rectifier element)
42 Regenerative operation detector
Ei input power
Io1 First converter output current
Vi input voltage
Vo1 intermediate voltage
Vo2 output voltage
Vr reference value
Vg18, Vg22, Vg40 drive pulse

Claims (12)

The first converter, which is a step-down chopper type stable converter that converts the input voltage to an intermediate voltage by the switching operation of the first switching element whose ON / OFF time ratio is variably controlled, and the ON / OFF time ratio is almost 50%. A second converter, which is a double-end insulation type unstable converter that converts the intermediate voltage into an output voltage by a switching operation of the set second switching element, and an on / off operation of the first and second switching elements. And a control circuit to control
The control circuit issues a command to the switching control unit that outputs a driving pulse for the first and second switching elements to perform a switching operation, and when the input power is turned on and off, and A sequence control unit for controlling the sequence of start and stop of the switching operation of the first and second switching elements;
The sequence control unit stops the switching operation of the first switching element when the input power is shut off, and then the switching operation of the second switching element when the intermediate voltage falls below a predetermined reference value. And switching operation of the second switching element is started when the input power is turned on and the input voltage is established, and then the switching operation of the first switching element is started. . The control circuit is provided with an intermediate voltage detection unit that detects the intermediate voltage;
The sequence control unit establishes an input voltage when an input power is turned on, and further detects that the intermediate voltage is equal to or lower than a predetermined reference value from a detection result of the intermediate voltage detection unit. The switching power supply device according to claim 1, wherein the switching operation is started and then the switching operation of the first switching element is started. In the second converter, the output rectification element is a synchronous rectification FET,
The switching control unit outputs a driving pulse for turning on and off the synchronous rectification FET together with a driving pulse for turning on and off the first and second switching elements,
The sequence control unit issues a command to the switching control unit when the input power is turned on and off, and controls a start and stop sequence of the switching operation of the first switching element, the second switching element, and the synchronous rectification FET. Is what
When the input power is cut off, the sequence control unit stops the switching operation of the first switching element, and then stops the switching operation of the synchronous rectification FET, and then the intermediate voltage is equal to or lower than a predetermined reference value. When the input power is turned on and the input voltage is established, the switching operation of the second switching element is started, and then the switching operation of the first switching element is started. The switching power supply device according to claim 1, wherein the switching operation is started and then the switching operation of the synchronous rectification FET is started. The control circuit is provided with an intermediate voltage detection unit that detects the intermediate voltage;
The sequence control unit establishes an input voltage when an input power is turned on, and further detects that the intermediate voltage is equal to or lower than a predetermined reference value from a detection result of the intermediate voltage detection unit. The switching power supply device according to claim 3, wherein the switching operation is started, then the switching operation of the first switching element is started, and then the switching operation of the synchronous rectification FET is started. The control circuit is provided with a regenerative operation detection unit that detects a regenerative operation in which the second converter regenerates output-side power to the input side, and the regenerative operation detection unit includes the regenerative operation of the second converter. Upon detecting that there is a possibility of performing are possible or the regenerative operation performed, the issues a command to the sequence controller, the switching power supply of the switching operation according to claim 3 or 4, wherein is in the stopped state of the synchronous rectification FET apparatus. The regenerative operation detection unit observes an output current of the first converter, and when the output current is equal to or less than a predetermined value and when the second converter is flowing backward from the second converter to the first converter, second converter switching power supply device according to claim 5, wherein being configured to determine that there is a possibility to perform in that or the regeneration operation carried out the regenerative operation. The first converter, which is a step-down chopper type stable converter that converts the input voltage to an intermediate voltage by the switching operation of the first switching element whose ON / OFF time ratio is variably controlled, and the ON / OFF time ratio is almost 50%. A control method of a switching power supply device comprising: a second converter which is a non-stable converter of a double end isolation system for converting the intermediate voltage to an output voltage by switching operation of a set second switching element,
When the input power is cut off, the switching operation of the first switching element is stopped, and then the switching operation of the second switching element is stopped when the intermediate voltage drops below a predetermined reference value. A control method of a switching power supply characterized in that when power is turned on and an input voltage is established, the switching operation of the second switching element is started and then the switching operation of the first switching element is started.   When the input power is turned on and the input voltage is established, after confirming that the intermediate voltage is less than a predetermined reference value, the switching operation of the second switching element is started, and then the switching of the first switching element is performed. The control method of the switching power supply device according to claim 7, wherein the operation is started. In the second converter, the output rectification element is configured by a synchronous rectification FET,
When the input power is cut off, the switching operation of the first switching element is stopped, and then the switching operation of the synchronous rectification FET is stopped.Then, when the intermediate voltage drops below a predetermined reference value, The switching operation of the second switching element is stopped, and when the input power is turned on and the input voltage is established, the switching operation of the second switching element is started, and then the switching operation of the first switching element is started. The control method of the switching power supply device according to claim 7, wherein the switching operation of the synchronous rectification FET is then started.   When the input power is turned on and the input voltage is established, after confirming that the intermediate voltage is less than a predetermined reference value, the switching operation of the second switching element is started, and then the switching of the first switching element is performed. The control method of the switching power supply device according to claim 9, wherein the operation is started, and then the switching operation of the synchronous rectification FET is started. When it is determined that the second converter is performing a regenerative operation for regenerating output power to the input side or that there is a possibility of performing the regenerative operation, the switching operation of the synchronous rectification FET is stopped. The control method of the switching power supply device according to claim 9 or 10. When the output current of the first converter is observed, and it is detected that the output current is equal to or less than a predetermined value or is flowing back from the second converter to the first converter, the second converter The control method of the switching power supply device according to claim 11, wherein it is determined that the regeneration operation is performed.

Images