JP4352451B2 - Multi-output switching power supply - Google Patents

Description

  The present invention relates to a multi-output switching power supply apparatus that individually supplies different output voltages from each output circuit.

  As a multi-output switching power supply that individually supplies different output voltages from each output circuit, for example, in Patent Document 1, the fluctuation of one output voltage is fed back to the first control circuit and is on the primary side of the transformer. While controlling the main switching element, in order to stabilize the other output voltage, while detecting the fluctuation of each output voltage, in synchronization with the control timing of the first control circuit, One having a second control circuit for controlling a switching element incorporated in an output circuit has been proposed.

  FIG. 6 shows an example of such a multi-output switching power supply device. In the figure, 1 and 2 are input terminals to which an input voltage Vin is applied, and 3 is an input smoothing capacitor connected between the input terminals 1 and 2. A transformer 4 insulates the primary side from the secondary side, and a series circuit of a primary winding 4a and an NPN transistor 5 as a main switching element is connected between the input terminals 1 and 2. The base of the transistor 5 is supplied with a pulse drive signal from a control circuit (not shown) and is PWM controlled.

  On the other hand, the transformer 4 includes a plurality of secondary windings 4b, 4c, and 4d. Each of the secondary windings 4b, 4c, and 4d includes, for example, a rectifying diode 13 and a commutation diode as shown in FIG. Step-down rectifier circuits 6a, 6b, 6c (step-down rectifier circuits 6b, 6c are not shown in the figure because of the same configuration) are connected as a step-down output circuit composed of a diode 14, a choke coil 15, and an output smoothing capacitor 18, respectively. . More specifically, the dot side of the secondary winding 4 b is connected to the anode of the rectifying diode 13, and the cathode of the rectifying diode 13 is connected to one end of the choke coil 15 that is an inductance and the cathode of the commutation diode 14. Is done. The non-dot side of the secondary winding 4 b is connected to the anode of the commutation diode 14, the other end of the output smoothing capacitor 18 that is a capacitive element, and the output terminal 9. The other end of the choke coil 15 is connected to one end of the output smoothing capacitor 18 and the output terminal 8. The output voltage V1 rectified and smoothed by the step-down rectifier circuit 6a is output between the output terminals 8 and 9, the output voltage V2 rectified and smoothed by the step-down rectifier circuit 6b is output between the output terminals 10 and 11, and the step-down rectifier circuit. An output voltage V3 rectified and smoothed in 6c is generated between the output terminals 12 and 13, respectively.

  Although not shown in FIG. 7, in order to stabilize the output voltages 4b, 4c, and 4d, the step-down rectifier circuits 6a, 6b, and 6c are provided with mag-amps as magnetic amplifiers. Since the control of the output voltages 4b, 4c and 4d by the magamp is well known, detailed description thereof is omitted here.

  Next, the operation of the above configuration will be described. When a pulse drive signal from a control circuit (not shown) is input to the base of the transistor 5 and the transistor 5 starts a switching operation, the input voltage Vin is changed to the primary winding 4a of the transformer 4. Is intermittently applied. Since the input voltage Vin is applied to the primary winding 4a of the transformer 4 when the transistor 5 is on, a voltage having a positive polarity on the dot side is induced in the secondary windings 4b, 4c, and 4d. Here, in the step-down rectifier circuit 6a, the rectifying diode 13 as a rectifying element is forward-biased to be conductive, while the commutating diode 14 as a commutating element is reverse-biased and becomes non-conductive, and energy is supplied to the choke coil 15. The output voltage V 1 smoothed by the output smoothing capacitor 18 is output between the output terminals 8 and 9. The same applies to the other step-down rectifier circuits 6b and 6c, and the respective output voltages V2 and V3 are respectively output between the output terminals 10 and 11 and between the output terminals 12 and 13.

On the other hand, when the transistor 5 is turned off, the supply of the input voltage Vin to the primary winding 4a of the transformer 4 is interrupted, so that a positive voltage is generated at the non-dot side terminal of the secondary winding 4b. Then, in the step-down rectifier circuit 6a described above, the rectifying diode 13 is reverse-biased and becomes non-conductive, the commutation diode 14 becomes conductive, and the energy previously stored in the choke coil 15 is released, and the output terminal continues. Between 8 and 9, the output voltage V1 smoothed by the output smoothing capacitor 18 is output. This also applies to the other step-down rectifier circuits 6b and 6c, and the respective unique output voltages V2 and V3 are continuously output from between the output terminals 10 and 11 and between the output terminals 12 and 13, respectively.
JP 2001-169550 A

  In the step-down rectifier circuit 6a shown in FIG. 6 and FIG. 7, when the rectifying diode 13 is turned on, a difference voltage between the induced voltage of the secondary winding 4b and the output voltage V1 is applied between both ends of the choke coil 15, When the diode 14 is turned on, the voltage across the choke coil 15 is output as the output voltage V1, which is a so-called step-down circuit. Therefore, if the voltage generated between both ends of the commutation diode 14 when the transistor 5 is turned on is Vp, the output voltage V1 after rectified and smoothed by the step-down rectifier circuit 6a is converted to the voltage Vp by the duty ratio of the transistor 5 (one cycle). The ratio of ON time to D) is substantially equal to Vp × D multiplied by D, and a voltage higher than at least the induced voltage of the secondary winding 4b cannot be extracted.

  This is because the output voltages V1, V2, and V3 correspond to the two output voltages V1, V2, and V3 in the multi-output switching power supply device in which the step-down rectifier circuits 6a, 6b, and 6c are connected to the plurality of secondary windings 4b, 4c, and 4d, respectively. There is a restriction that it is determined by the number of turns of the next windings 4b, 4c, 4d. That is, the number of turns of the secondary windings 4b, 4c, and 4d must be determined depending on the output voltages V1, V2, and V3, so that the output voltages V1, V2, and V3 and the secondary windings 4b, 4c, 4d naturally has a one-to-one relationship, and standardization of the transformer 4 using the common secondary windings 4b, 4c, and 4d cannot be achieved.

  In view of the above problems, the present invention provides a multi-output switching power supply apparatus that can extract an arbitrary output voltage from a secondary winding having the same number of turns without changing the number of turns of the secondary winding of the transformer even at different output voltages. The purpose is to do.

The multi-output switching power supply device according to the present invention is connected to a main switching element that intermittently applies an input voltage to a primary winding of a transformer, and to each secondary winding of the transformer, and is induced from the secondary winding. and a step-down output circuit for rectifying smoothing the voltage, the multiple-output switching power supply unit for taking out individual lower output voltage than the induced voltage of the secondary winding from each of the step-down output circuit, the secondary of the respective The number of turns of the windings is the same, and a step-up output circuit capable of extracting an output voltage higher than the induced voltage of the secondary winding is provided instead of the step-down output circuit, and the step-up output circuit is connected to the step-down output circuit. The step-down output circuit includes a rectifier element, a commutation element, and a choke coil, and the rectifier is turned on when the main switching element is turned on. And a commutator is connected to store energy in the choke coil, and the commutation element is turned on when the main switching element is turned off to send the energy stored in the choke coil to the output side. The boost output circuit has an ON period in which a series circuit of the secondary winding and the choke coil is short-circuited at least while the rectifying element is in conduction, and the energy of the choke coil is in the OFF period. And a unidirectional conducting element that prevents a current from flowing from the output side to the switch element during an on period of the switch element, and further, the rectifying element And a PWM control circuit for conducting the commutation element .

In this case, by mixing the step-down output circuit and the step-up output circuit on the secondary side of the transformer, not only the output voltage lower than the induced voltage of the secondary winding but also higher than the induced voltage of the secondary winding. The output voltage can be freely taken out, and various output voltages can be generated by sharing the number of turns of the secondary winding. Further, the output voltage can be made higher or lower than the induced voltage of the secondary winding depending on whether the turn-off timing of the switch element is during the conduction period of the rectifying element or during the conduction period of the commutation element. . Therefore, it is possible to extract an arbitrary output voltage simply by incorporating a buck-boost chopper circuit on the secondary side of the transformer and appropriately setting the on / off timing of the switch element.

  According to the multi-output switching power supply device of the present invention, an arbitrary DC voltage can be extracted from the secondary winding having the same number of turns without changing the number of turns of the secondary winding of the transformer even at different output voltages. It becomes possible to standardize a transformer having a secondary winding of the number of turns.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS. In addition, about the thing which a structure overlaps with FIG. 6, FIG. 7 of a prior art example, the same code | symbol is attached | subjected and the description is abbreviate | omitted as much as possible.

  In FIG. 1 showing the overall configuration of the multi-output switching power supply device, in this embodiment, a plurality of secondary windings 4b, 4c, 4d are provided on the secondary side of the transformer 4, and these secondary windings 4b, 4c are provided. , 4d (secondary windings 4c, 4d in this embodiment) are connected to step-up rectifier circuits 7a, 7b, which are step-up output circuits, instead of the step-down rectifier circuit 6. The step-up rectifier circuits 7a and 7b are incorporated in the output channels CH2 and CH3 of the power supply unit that generate output voltages V2 and V3 higher than the induced voltages of the secondary windings 4c and 4d. The circuit configuration of the step-down rectifier circuit 6 is as shown in FIG. 6 and is incorporated in the output channel CH1 of the power supply unit that generates the output voltage V1 lower than the induced voltage of the secondary winding 4b. However, the number of turns of the secondary windings 4b, 4c, and 4d is the same for all the output channels CH1, CH2, and CH3, and has the same component configuration.

  FIG. 2 shows a circuit configuration of the boost rectifier circuit 7a (the boost rectifier circuit 7b is not shown because it has the same configuration). The step-up rectifier circuit 7a in this embodiment is a step-up rectifier circuit 6 shown in FIG. 6 that can raise or lower the induced voltage of the secondary winding 4c between the choke coil 15 and the output smoothing capacitor 18. A pressure chopper circuit 31 is provided. This step-up / down chopper circuit 31 is a switching element in which a drain (one end) is connected to the other end of the choke coil 15 and a source (the other end) is connected to a connection point between the secondary winding 4 c and the commutation diode 14. The MOSFET 32 includes a diode 33 that is a backflow prevention element that prevents the charge from the output smoothing capacitor 18 from flowing into the choke coil 15 and the MOSFET 32, and a resistor 34 that is connected to the gate of the MOSFET 32. The choke coil 7 is caused to function as a boosting or step-down inductance by changing the on / off timing of the MOSFET 32 in accordance with the pulse control signal given to. Reference numeral 36 denotes a load connected between the output terminals 10 and 11.

  On the other hand, in order to determine the on / off timing of the MOSFET 32, a PWM control circuit 41 for supplying a pulse control signal having an arbitrary pulse width to the gate of the MOSFET 32 is provided. The step-up PWM control circuit 41 shown in FIG. 2 is for extracting the output voltage V2 higher than the induced voltage of the secondary winding 4c. The step-down PWM control circuit 71 will be described later.

  The PWM control circuit 41 includes a pulse shaping circuit 42 that generates an H (high) level rectangular wave a in synchronization with a voltage induced in the secondary winding 4c when the transistor 5 is turned on, When the rectangular wave a rises, the voltage level decreases, and when this rectangular wave falls, the voltage level rises, and an inverted sawtooth wave generating circuit 43 that generates an inverted sawtooth waveform c, and a voltage dividing resistor 44 between the output terminals 10 and 11. , 45 are connected in series, and a detection voltage d obtained by dividing the output voltage V2t is output from a connection point of the voltage dividing resistors 44, 45, and a detection voltage d from the output voltage detection circuit 46 Is compared with the inverted sawtooth wave c from the inverted sawtooth wave generation circuit 43, and a comparator 47 for generating a rectangular wave b of H level or L (low) level according to the comparison result, and from the pulse shaping circuit 42 Square wave a is at H level Only when the rectangular wave b from the comparator 47 is at the L level, the subtractor 48 that outputs the rectangular wave (ab) at the H level, and the rectangular wave (ab) from the subtractor 48 is switched to the switching element. And a buffer 49 as drive means for supplying a pulse control signal (gate drive pulse) to the gate of the MOSFET 32. The circuit configurations other than the step-up / step-down chopper circuit 31 and the PWM control circuit 41 are all the same as those shown in FIG.

  Next, the operation of the above configuration will be described with reference to the waveform diagram of FIG. In FIG. 3, the upper stage is the secondary tap voltage of the transformer 4 generated on the dot side of the secondary winding 4c. Hereinafter, the rectangular wave a from the pulse shaping circuit 42 and the inverted sawtooth wave generating circuit 43 are shown. Inverted sawtooth wave c and detection voltage d from output voltage detection circuit 46, rectangular wave b from comparator 47, rectangular wave (ab) from subtractor 48, and drain-source voltage of MOSFET 32 Each is shown.

  As the main switch element 5 is switched, the input voltage Vin is intermittently applied to the primary windings 4b, 4c, and 4d of the transformer 4. In this series of operations, when the transistor 5 is in the on state, a voltage Vtap having a positive polarity on the dot side of the secondary winding 4c is induced, and the rectifying diode 13 is forward-biased and conducted, while the commutation diode 14 is turned on. Is reverse biased and becomes non-conductive. Here, in synchronization with the generation of the induced voltage Vtap in the secondary winding 4c, the pulse wave forming circuit 42 of the PWM control circuit 41 generates a rectangular wave a of H level slightly earlier than the induced voltage Vtap rises. appear. Here, an H-level rectangular wave a may be generated from the pulse shaping circuit 42 simultaneously with the rise of the induced voltage Vtap. In response to the switching of the rectangular wave a from the pulse shaping circuit 42 to the H level, the inverted sawtooth wave generating circuit 43 outputs an inverted sawtooth wave c whose voltage level is decreased to the comparator 47. The comparator 47 compares the inverted sawtooth wave c and the detected voltage d from the output voltage detection circuit 46. Immediately after the induced voltage Vtap is generated, the voltage level of the inverted sawtooth wave c is higher than the detected voltage d. Outputs an L level rectangular wave b, and the subtractor 48 outputs an H level rectangular wave (ab).

  Thus, during the period in which the induced voltage Vtap is generated in the secondary winding 4c, an H level pulse control signal is supplied to the gate of the MOSFET 32 via the buffer 49 until the voltage level of the inverted sawtooth wave c becomes lower than the detection voltage d. Is applied, and the MOSFET 32 is turned on. Therefore, a closed loop composed of the secondary winding 4c, the choke coil 15, the MOSFET 32, and the secondary winding 4c is formed, and the current flowing through the choke coil 15 increases to store more energy.

  Eventually, when the voltage level of the inverted sawtooth wave c becomes lower than the detection voltage d from the output voltage detection circuit 46 during the period in which the induced voltage Vtap is generated on the dot side of the secondary winding 4c, The rectangular wave (ab) turns to the L level, and the MOSFET 32 is turned off. As a result, a counter electromotive force is generated between the both ends of the choke coil 15 due to the energy stored so far, and the flyback of the choke coil 7 is caused between the drain and source of the MOSFET 32 to the induced voltage Vtap of the secondary winding 4c. A boosted voltage is generated by adding the voltage Vflybuck. Therefore, the output voltage V2 generated between the output terminals 10 and 11 is substantially the same level as the boosted voltage Vtap + Vflybuck.

  Thereafter, when the transistor 5 as the main switch element is turned off, a voltage having a positive polarity on the non-dot side of the secondary winding 4c is generated, and the rectifying diode 13 is reverse-biased and becomes non-conductive, Diode 14 is forward biased and conductive. At this time, the pulse shaping circuit 42 of the PWM control circuit 41 generates an L-level rectangular wave a slightly later than the induced voltage Vtap rises. Here, an L-level rectangular wave a may be generated from the pulse shaping circuit 42 simultaneously with the fall of the induced voltage Vtap. In response to the switching of the rectangular wave a from the pulse shaping circuit 42 to the L level, the inverted sawtooth wave generating circuit 43 outputs the inverted sawtooth wave c whose voltage level increases in slope to the comparator 47. The comparator 47 compares the inverted sawtooth wave c with the detection voltage d from the output voltage detection circuit 46. The voltage level of the inverted sawtooth wave c is lower than the detection voltage d, and the comparator 47 outputs an H level rectangular wave b. Since the rectangular wave a from the pulse shaping circuit 42 is at the L level, the rectangular wave (ab) from the subtractor 48 remains at the L level, and the MOSFET 32 continues to be in the OFF state. At this time, no voltage is generated between the drain and source of the MOSFET 32.

  Eventually, when the period in which the induced voltage Vtap is generated in the secondary winding 4c approaches and the H-level rectangular wave a is generated from the pulse shaping circuit 42, the MOSFET 32 is turned on and the above operation is repeated. While the MOSFET 32 is on, energy transfer from the output smoothing capacitor 18 side to the choke coil 15 and the MOSFET 32 is blocked by the diode 33.

  Up to this point, the boosting operation of the step-up / step-down chopper circuit 31 has been described. By turning on the switching control of the MOSFET 32 slightly later than the timing at which the induced voltage Vtap is generated, energy is stored in the choke coil 15 for a short period of time. When the MOSFET 5 is turned off after the transistor 5 is turned off and a voltage having a positive polarity on the non-dot side of the secondary winding 4c is generated, the energy stored in the choke coil 15 is released there, and the secondary winding An output voltage V2 lower than the voltage induced in the line 4c can be obtained.

  FIG. 4 shows a circuit configuration for realizing such a step-down operation. The PWM control circuit 71 here increases the voltage level when the rectangular wave a from the pulse shaping circuit 42 rises instead of the inverted sawtooth wave generation circuit 43 in FIG. 2, and the voltage level rises when the rectangular wave falls. A sawtooth wave generating circuit 73 for generating a descending sawtooth waveform c ′ is provided, and instead of the subtractor 48, the rectangular wave a from the pulse shaping circuit 42 and the rectangular wave b from the comparator 47 are both at the H level. Only in this case, an AND circuit 78 for outputting an H level rectangular wave (a & b) is provided. Other configurations are the same as those shown in FIG.

  The operation of the circuit configuration of FIG. 3 will be described with reference to the waveform diagram of FIG. 5. When the transistor 5 as the main switch element is turned on, a positive induced voltage Vtap is generated on the dot side of the secondary winding 4c. Then, a rectangular wave a of H level is generated from the pulse generating circuit 42, and the sawtooth wave generating circuit 73 has a voltage level in response to the switching of the rectangular wave a from the pulse forming circuit 42 to the H level. The sawtooth wave c ′ that rises in inclination is output to the comparator 47. The comparator 47 compares the sawtooth wave c 'with the detection voltage d from the output voltage detection circuit 46. Immediately after the induced voltage Vtap is generated, the voltage level of the sawtooth wave c' is lower than the detection voltage d. Outputs a rectangular wave b of L level, and the rectangular wave (a & b) from the AND circuit 78 becomes L level. As a result, a differential voltage between the induced voltage Vtap of the secondary winding 4c and the output voltage Vout is applied across the choke coil 15, and energy is stored in the choke coil 15. Here, an H-level rectangular wave a may be generated from the pulse shaping circuit 42 simultaneously with the rise of the induced voltage Vtap.

  Eventually, when the voltage level of the sawtooth wave c ′ becomes higher than the detection voltage d from the output voltage detection circuit 46 during the period in which the induced voltage Vtap is generated on the dot side of the secondary winding 4c, the rectangular shape from the AND circuit 78 The wave (a & b) turns to H level and the MOSFET 32 is turned on. As a result, a closed loop composed of the secondary winding 4c, the choke coil 15, the MOSFET 32, and the secondary winding 4c is formed, and the current flowing through the choke coil 15 is increased to store more energy.

  Thereafter, when the transistor 5 is turned off, a voltage having a positive polarity on the non-dot side of the secondary winding 4c is generated, and the rectifying diode 13 is reverse-biased and non-conductive, while the commutation diode 14 is forward-biased. Is conducted. At this time, the pulse shaping circuit 42 of the PWM control circuit 41 generates an L-level rectangular wave a slightly later than the induced voltage Vtap rises. Here, an L-level rectangular wave a may be generated from the pulse shaping circuit 42 simultaneously with the fall of the induced voltage Vtap. In response to the switching of the rectangular wave a from the pulse shaping circuit 42 to the L level, the sawtooth wave generating circuit 73 outputs a sawtooth wave c 'whose voltage level is decreased to the comparator 47. The comparator 47 compares the sawtooth wave c ′ with the detection voltage d from the output voltage detection circuit 46, and continues to output the rectangular wave b at the H level. However, since the rectangular wave a from the pulse shaping circuit 42 is at the L level, the AND circuit The square wave (a & b) from 78 goes low and MOSFET 32 is turned off there. As a result, only the flyback voltage Vflybuck of the choke coil 15 is generated between the drain and source of the MOSFET 32, and the output voltage V2 generated between the output terminals 10 and 11 is almost equal to the flyback voltage Vflybuck lower than the induced voltage Vtap. It becomes the same level.

  Eventually, the voltage level of the sawtooth wave c ′ becomes lower than the detection voltage d from the output voltage detection circuit 46, but the rectangular wave (a & b) from the AND circuit 78 remains at the L level, and the MOSFET 32 is turned off. maintain. Then, the transistor 5 is turned on again, and the above operation is repeated. While the MOSFET 32 is on, energy transfer from the output smoothing capacitor 14 side to the choke coil 15 or the MOSFET 32 is blocked by the diode 33. The same operation is performed for the other boost rectifier circuit 7b.

  As described above, the boost rectifier circuit 7a of the present embodiment has an on period of the transistor 5, that is, a period in which the MOSFET 32 is turned on and energy is stored in the choke coil 7 while the rectifier diode 13 is conducting. The output voltage V2 is made higher or lower than the induced voltage of the secondary winding 4b depending on whether the turn-off timing is during the conduction period of the rectifier diode 13 or otherwise during the conduction period of the commutation diode 14. Can do. Therefore, an arbitrary output voltage V2 can be extracted simply by incorporating the step-up / step-down chopper circuit 31 on the secondary side of the transformer 3 and appropriately setting the on / off timing of the MOSFET 32.

  Further, by mixing the step-down rectifier circuit 6 and the step-up rectifier circuits 7a and 7b, not only the output voltage V1 lower than the induced voltage of the secondary winding 4b but also the high output voltages V2 and V3 can be freely extracted. Thus, the output voltages V1, V2, and V3 are not restricted by the number of turns of the secondary windings 4b, 4c, and 4d. Therefore, standardization of the transformer 4 using the common secondary windings 4b, 4c, and 4d can be achieved. In the present embodiment, independent secondary windings 4b, 4c, 4d are provided corresponding to each step-down rectifier circuit 6 and step-up rectifier circuits 7a, 7b, but the ground lines of the respective channels CH1, CH2, CH3 are provided. If common, these step-down rectifier circuit 6 and step-up rectifier circuits 7a and 7b can be connected to a single secondary winding to further simplify the structure of the transformer 4.

In the present embodiment as described above, the transistor 5 as a main switching element for intermittently applying the input voltage Vin to the primary winding 4a of the transformer 4, each of the secondary winding 4b of the transformer 4, 4c, and 4d Step-down output circuits 6a, 6b, and 6c connected to each other and rectifying and smoothing the voltage induced from the secondary windings 4b, 4c, and 4d , and the step-down output circuits 6a, 6b, and 6c from the secondary winding 4b. , 4c, 4d, the output voltages V1, V2, V3 that are lower than the induced voltages are taken out individually, and the secondary windings 4b, 4c, 4d have the same number of turns . Boost output circuits 7a and 7b that can extract an output voltage higher than the induced voltage of 4c and 4d are provided instead of the step-down output circuits 6a, 6b, and 6c.

  In this case, by mixing the step-down rectifier circuit 6 and the step-up rectifier circuits 7a and 7b on the secondary side of the transformer 4, not only the output voltage V1 lower than the induced voltage of the secondary winding 4b but also a high output voltage. V2 and V3 can be freely taken out, and it is possible to generate various output voltages V1, V2, and V3 by using the same number of turns of the secondary windings 4b, 4c, and 4d. Therefore, any output voltage from the secondary windings 4b, 4c, 4d having the same number of turns can be obtained without changing the number of turns of the secondary windings 4b, 4c, 4d of the transformer 4 even if the output voltages V1, V2, V3 are different. V1, V2, and V3 can be taken out, and it becomes possible to standardize the transformer 4 using the common secondary windings 4b, 4c, and 4d.

Further, in this embodiment, a rectifying / smoothing circuit for rectifying and smoothing a voltage induced in the secondary winding 4c of the transformer 4 to obtain an output voltage V2 as the transistor 5 is switched is provided. When the transistor 5 is turned on, the rectifier diode 13 is turned on to store energy in the choke coil 15 which is an inductance. When the transistor 5 is turned off, the commutation diode 14 is turned on and stored in the choke coil 15 until then. The step-down rectifier circuit 6 configured to send energy to the output side has an ON period in which the series circuit of the secondary winding 4c and the choke coil 15 is short-circuited at least while the rectifier diode 13 is conductive. In the off period, the MOSFET 32 as a switch element for sending the energy of the choke coil 15 to the output side, and the MO Incorporate buck chopper circuit 31 and a diode 33 as a unidirectional conductive element to prevent flow from the output side to the ON period of SFET32 of current to MOSFET 32, constitutes booster rectifier circuit 7a, the 7b, further MOSFET 32 of the off timing, and a PWM control circuit 41, 71 which during the conduction period of the conduction period during or commutating diode 14 integer diverted diode 13.

In this case, when the MOSFET 32 constituting the step-up / step-down chopper circuit 31 is turned on during the conduction period of the rectifying diode 13, the voltage induced in the secondary winding 4 c is applied across the choke coil 15. Accumulate energy promptly. Thereafter, if the off timing of the MOSFET 32 is during the conduction period of the rectifying diode 13, the flyback voltage of the choke coil 15 is superimposed on the induced voltage of the secondary winding 4c, which is higher than the induced voltage of the secondary winding 4c. The output voltage V2 can be taken out. If the MOSFET 32 is turned off during the conduction period of the commutation diode 14, only the flyback voltage of the choke coil 15 is applied to the output side, and the output voltage V2 is lower than the induced voltage of the secondary winding 4c. Can be taken out. Therefore, if the step-up rectifier circuits 7a and 7b of the present embodiment are incorporated on the output side of the transformer 4, it is possible to take out arbitrary output voltages V2 and V3 only by appropriately setting the on / off timing of the MOSFET 32 .

  In addition, this invention is not limited to the said Example, The following various deformation | transformation are possible. For example, a MOSFET or the like can be used as the main switch element in addition to the transistor 5. Similarly, for example, a transistor may be used as the MOSFET 32 as the switch element. Further, a rectification / commutation switch element such as a MOSFET may be used as the rectification / commutation element of the rectification / smoothing circuit, and these rectification / commutation switch elements may be driven in synchronization with the switching of the main switch element. Thereby, the loss of the rectifying / smoothing circuit 21 can be reduced and the efficiency can be improved. Further, the circuit configuration of the rectifying / smoothing circuit may be a center tap type, and the rectifying diode 13 may be connected not to the dot side terminal side of the secondary windings 4b, 4c, 4d but to the non-dot side terminal side. Good. Further, the configuration of the step-down rectifier circuit or the step-up rectifier circuit shown as the embodiment is merely an example.

  According to the present invention, since an output voltage with a high degree of freedom can be taken out regardless of the turns ratio of the transformer, a multi-output switching power supply device can be easily configured with a common transformer.

It is a circuit diagram which shows an example of the multiple output switching power supply device in a present Example. It is a circuit diagram which shows an example of the boost rectifier circuit in a present Example. FIG. 4 is a waveform diagram showing voltages at various parts during the boosting operation. It is a circuit diagram which shows another modification same as the above. FIG. 4 is a waveform diagram showing voltages at various parts during the step-down operation. It is a circuit diagram which shows an example of the conventional multiple output switching power supply device. It is a circuit diagram which shows an example of the step-down rectifier circuit in a prior art example.

4 transformer 5 transistor (main switching element)
6, 6a, 6b, 6c Step-down rectifier circuit (Step-down output circuit)
7a, 7b step-up rectifier circuit (step-up output circuit)
13 Rectifier diode (rectifier element)
14 Commutation diode (commutation element)
15 Choke coil
31 Buck-boost chopper circuit
32 MOSFET (switch element)
33 Diode (unidirectional conducting element)
41, 71 PWM control circuit

Claims (1)

A main switching element that intermittently applies an input voltage to the primary winding of the transformer, and a step-down output circuit that is connected to each secondary winding of the transformer and rectifies and smoothes the voltage induced from the secondary winding In a multi-output switching power supply apparatus that individually extracts an output voltage lower than the induced voltage of the secondary winding from each of the step-down output circuits,
The number of turns of each secondary winding is the same,
A step-up output circuit capable of extracting an output voltage higher than the induced voltage of the secondary winding is provided instead of the step-down output circuit ;
The step-up output circuit is configured by incorporating a step-up / step-down chopper circuit into the step-down output circuit,
The step-down output circuit includes a rectifier element, a commutation element, and a choke coil. When the main switching element is turned on, the rectifier element conducts, stores energy in the choke coil, and the main switching element is turned off. Sometimes the commutation element is conducted, and the choke coil is configured to send the energy stored so far to the output side,
The step-up output circuit has an ON period in which a series circuit of the secondary winding and the choke coil is short-circuited at least while the rectifying element is in conduction, and the energy of the choke coil is reduced in the OFF period. A switching element for sending to the output side, and a one-way conduction element for preventing a current from flowing from the output side to the switching element during an on period of the switching element,
The multi-output switching power supply apparatus further comprising a PWM control circuit for setting the switch element OFF timing during a conduction period of the rectifying element or a conduction period of the commutation element .

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