JP2008172979A - Switching power supply device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power supply device in which a transformer structure is simplified so as to suppress the increase in the circuit constituent components. <P>SOLUTION: The switching power supply device includes a transformer 10 having three secondary windings 12a, 12b, and 12c. The device also includes an average-voltage calculating part 20, which calculates the average value of output voltages Vo1, Vo2, and Vo3, respectively generated by each of the secondary windings 12a, 12b, and 12c; and a voltage feedback control part 30 that performs PWM-control or PFM-control of conduction of a primary winding 11 in the transformer 10 so as to make the error between a target setting voltage and the average value calculated by the average-voltage calculation part 20 zero. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a switching power supply device having a transformer structure.

  Conventionally, the primary winding on the primary DC power source side having the voltage control circuit and the secondary winding on the secondary DC power source side having the voltage signal generating circuit are transformer-coupled to generate a voltage signal from the secondary DC power source side. There is known a switching power supply device that feeds back to a voltage control circuit and controls the switching element on the primary DC power supply side to be turned on and off to stabilize the voltage of the secondary DC power supply (see, for example, Patent Document 1). This switching power supply device has another primary winding separately from the primary winding connected to the switching element on the primary DC power supply side, and the primary winding serves as a control power source for the voltage control circuit. Is to be generated.

Also, in order to perform voltage feedback and abnormality detection to stabilize the output voltage, a primary winding is provided for generation of a control power source for the voltage control circuit. There is also known a switching power supply device in which a winding for monitoring a voltage or an output voltage on the secondary winding side is provided in a transformer. For example, the switching power supply shown in FIG. 2 has a voltage monitoring dedicated coil on the primary side of the transformer, and is detected by the voltage monitoring dedicated coil in order to ensure the accuracy of the transformer output voltages Vo1, Vo2, and Vo3. The voltage feedback control is performed based on the voltage.
JP-A-5-236743

  However, the above-described prior art requires a configuration dedicated to voltage detection such as a winding provided in the transformer, which complicates the transformer structure and increases the number of circuit components.

  Accordingly, an object of the present invention is to provide a switching power supply device that can simplify the structure of a transformer and suppress an increase in circuit components.

In order to achieve the above object, the first invention provides:
A switching power supply device comprising a transformer having a plurality of secondary windings,
Average value calculating means for calculating an average value of output voltages generated by each of the plurality of secondary windings;
Control means for controlling the duty ratio of the energization frequency of the primary winding of the transformer so that the difference between the average value calculated by the average value calculation means and a predetermined set value becomes zero. Yes.

In order to achieve the above object, the second invention provides:
A switching power supply device comprising a transformer having a plurality of secondary windings,
Average value calculating means for calculating an average value of output voltages generated by each of the plurality of secondary windings;
Control means for controlling the energization frequency of the primary winding of the transformer so that the difference between the average value calculated by the average value calculation means and a predetermined set value becomes zero.

  Here, the control means may output a control signal for driving a switching element connected to the primary winding.

  According to the present invention, the structure of a transformer can be simplified and an increase in circuit components can be suppressed.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an embodiment of a switching power supply device according to the present invention. The switching power supply device of this embodiment is a power supply device that converts the power of the input voltage Vi according to the transformation ratio of the transformer 10 and generates three independent power supply voltages (output voltages) Vo1, Vo2, and Vo3. . Each power of the power supply voltages Vo1, Vo2, and Vo3 is supplied to an electric load (not shown). The switching power supply according to the present embodiment performs constant power supply voltages Vo1, Vo2, and Vo3 by performing voltage feedback to be described later even when the voltage fluctuation of the input voltage Vi and the fluctuation of the consumption current (load current) of the electric load occur. Is output to each electric load.

  The switching power supply according to the present embodiment converts an input voltage (primary voltage) Vi by a transformer 10 (steps up or down) and generates three systems of output voltages (secondary voltages) Vo1, Vo2, and Vo3. The transformation ratio between the input voltage Vi and the output voltage Vo1 is equal to the winding ratio between the primary winding 11 and the secondary winding 12a of the transformer 10, and the transformation ratio between the input voltage Vi and the output voltage Vo2 is the primary winding of the transformer 10. 11 and the secondary winding 12b, and the transformation ratio between the input voltage Vi and the output voltage Vo3 is equal to the winding ratio between the primary winding 11 and the secondary winding 12c of the transformer 10. That is, the output voltages Vo1, Vo2, and Vo3 are determined according to the respective winding ratios. Therefore, if each winding ratio is set to be the same, each output voltage Vo1, Vo2, Vo3 can be set to the same voltage value, and if each winding ratio is set to be different from each other, the output voltages Vo1, Vo2 are set. , Vo3 can have different voltage values. The voltage values of the output voltages Vo1, Vo2, and Vo3 may be determined according to specifications required for the power supply voltage.

  The secondary winding 12a is connected to a rectifying / smoothing circuit constituting a diode 13a and a smoothing capacitor 14a, and the secondary winding 12b is connected to a rectifying / smoothing circuit constituting a diode 13b and a smoothing capacitor 14b. A rectifying / smoothing circuit constituting a diode 13c and a smoothing capacitor 14c is connected to 12c. The voltages rectified and smoothed by these rectifying and smoothing circuits are applied to the electric loads as output voltages Vo1, Vo2, and Vo3.

  When the switching power supply device according to the present embodiment is mounted on a vehicle, for example, the input voltage Vi is supplied by an in-vehicle battery or a power circuit connected to the in-vehicle battery, and the output voltages Vo1, Vo2, Vo3 are Applied to electrical load. Further, when the switching power supply device of the present embodiment is mounted on a so-called hybrid vehicle, for example, the output voltage Vo1 is supplied as the power supply voltage of the booster circuit that boosts the low voltage system voltage to the high voltage system voltage, and the output voltage Vo2 is used for running The output voltage Vo3 is supplied as the power supply voltage of the electronic circuit of the regeneration generator. Since three independent output voltages Vo1, Vo2, and Vo3 are generated by dividing the secondary winding, even if an abnormality such as a failure occurs in the electrical load connected to one of the output voltages. Therefore, it is possible to prevent the abnormality from affecting the electric load of the other system (for example, even if an abnormality occurs in the booster circuit of the system of the output voltage Vo1, the influence on the running of the vehicle is minimized. be able to). Further, when the switching power supply device of this embodiment is mounted on a so-called hybrid vehicle, for example, the output voltage Vo1 is supplied as the power supply voltage of the U-phase drive circuit of the traveling motor, and the output voltage Vo2 is the V-phase of the traveling motor. The output voltage Vo3 is supplied as a power supply voltage for the W-phase drive circuit of the traveling motor. Since the three independent output voltages Vo1, Vo2, and Vo3 are generated by dividing the secondary winding, each system can be prevented from affecting each other (for example, the output voltage Vo1 is an inductance). Even if it fluctuates due to the voltage surge of the load, the influence on the output voltages Vo2 and Vo3 can be suppressed).

  The output voltages Vo1, Vo2, and Vo3 are input to the average voltage calculation unit 20. The average voltage calculation unit 20 includes a voltage detection circuit including an A / D converter and a calculation circuit that calculates an average value. The average voltage calculation unit 20 calculates an average voltage that is an average value of the output voltages Vo1, Vo2, and Vo3 detected by the voltage detection circuit.

  The voltage feedback unit 30 compares the average voltage fed back by the average voltage calculation unit 20 with a predetermined target setting voltage, and the switching frequency of the switching element 40 (that is, the primary winding of the transformer 10 so that the difference becomes zero). The duty ratio of the switching frequency is varied while keeping the energization frequency of the line 11 constant. The voltage feedback unit 30 outputs a control signal that drives the switching element 40 at the switching frequency and the duty ratio. In other words, the voltage feedback unit 30 in this case executes pulse width modulation (PWM) control for changing the pulse width of the switching pulse while keeping the frequency of the switching pulse for driving the switching element 40 constant.

  Further, the voltage feedback unit 30 compares the average voltage fed back by the average voltage calculation unit 20 with a predetermined target set voltage, and the switching on time of the switching element 40 is kept constant so that the difference becomes zero. The switching frequency of the switching element 40 (that is, the energization frequency of the primary winding 11 of the transformer 10) may be varied. The voltage feedback unit 30 outputs a control signal that drives the switching element 40 at its switching frequency and on-time. In other words, the voltage feedback unit 30 in this case performs pulse frequency modulation (PFM) control that varies the frequency of the switching pulse while keeping the pulse width of the switching pulse that drives the switching element 40 constant.

FIG. 3 is a diagram showing the relationship between the energization current I _OUT of the primary winding 11 and PWM control or PFM control. In the case of PWM control that varies the pulse width T _ON of the switching pulse while keeping the frequency (period T) of the switching pulse constant, as shown in the figure, the energization current I of the primary winding 11 increases as the pulse width T _ON increases. _OUT increases. In the case of PFM control in which the frequency (period T) of the switching pulse is varied while keeping the pulse width T _ON of the switching pulse constant, as shown in the figure, the energization current I of the primary winding 11 decreases as the period T decreases. _OUT increases. As the energization current I _OUT of the primary winding 11 increases, the energy of the primary winding 11 increases. As a result, the output voltages Vo1, Vo2, and Vo3 can be adjusted according to the transformation ratio of the transformer 10.

  FIG. 4 is a table showing differences in performance between PWM control and PFM control. Compared with PFM control, PWM control has a more complicated circuit configuration, consumes a large amount of current, has a small ripple current, and has good follow-up to variations in load voltage and current.

  The control signal output from the voltage feedback unit 30 is input to a gate driving unit (not shown). The gate driving unit is a drive circuit that generates a driving voltage for driving the switching element 40 at a switching frequency and a duty ratio or a switching frequency and an on time related to the control signal output from the voltage feedback unit 30. When the switching element 40 performs a switching operation by the gate drive unit, the energization of the primary winding 11 of the transformer 10 is controlled, and the input voltage Vi is transformed.

  The switching element 40 is a switching element composed of a semiconductor such as an IGBT, MOSFET, or bipolar transistor. The switching element 40 has one end connected to a terminal on the downstream side of the primary winding 11 and the other end grounded.

  The average voltage calculation unit 20 and the voltage feedback unit 30 include a ROM that stores an average voltage calculation program and a voltage feedback control program, a CPU that processes these programs, and a RAM that temporarily stores processing results of the programs. You may have. The average voltage calculation unit 20 and the voltage feedback unit 30 may be integrated or separated.

  Next, the transformation operation of the switching power supply device of this embodiment will be described. When an operation of an electric load connected to the output side of the switching power supply device is required, power is supplied to each electric load via the transformer 10 or the like. Thereby, the operation of the electric load on the output side becomes possible.

  The voltage feedback control unit 30 receiving the operation request for the electric load drives the switching element 40 with the initial setting switching frequency and duty ratio or switching frequency and on-time required for generating the output voltages Vo1, Vo2, and Vo3 by the transformer 10. The output of the control signal to start is started. Each of the output voltages Vo1, Vo2, and Vo3 is generated according to the transformation ratio of the transformer 10. The voltage feedback control unit 30 feeds back the average voltage of the output voltages Vo1, Vo2, and Vo3 calculated by the average voltage calculation unit 20, compares the average voltage with a predetermined target set voltage, and the difference becomes zero. Thus, PWM control or PFM control is executed.

  The predetermined target set voltage corresponds to a value obtained by averaging design values of output voltages Vo1, Vo2, and Vo3 that can be calculated from the energization frequency of the primary winding 11, the input voltage Vi, and the transformation ratio of the transformer 10. That is, when there is a difference between the average voltage calculated by the average voltage calculation unit 20 and the target set voltage for the output voltages Vo1, Vo2, and Vo3 actually generated by the transformer 10, each output voltage Vo1, Vo2, and Vo3. It can be considered that an error has occurred in any of the above. Therefore, by performing PWM control or PFM control so that the difference between the average voltage and the target set voltage becomes zero, the average values (design values) of the output voltages Vo1, Vo2, and Vo3 can be brought close to each other. The output voltage can be stabilized.

For example, when the target set voltage is larger than the average voltage calculated by the average voltage detector 30, it is assumed that the output voltages Vo1, Vo2, and Vo3 are shifted to the larger side as a whole. In the case of PWM control, the primary winding 11 is adjusted so as to reduce the on-duty ratio of the current frequency (i.e., primary winding 11 energized time (corresponding to the pulse width T _oN of FIG. 3) is adjusted so that shorter), in the case of PFM control Is adjusted to lower the energization frequency of the primary winding 11 (that is, adjusted so that the switching cycle of the primary winding 11 (corresponding to the cycle T in FIG. 3) becomes longer).

  Correspondence relationship (in the case of PWM control) between the difference between the average voltage calculated by the average voltage calculation unit 20 and the target set voltage and the on-duty ratio of the energization frequency of the primary winding 11 that makes the difference zero, the average voltage The correspondence between the difference between the average voltage calculated by the calculation unit 20 and the target set voltage and the energization frequency of the primary winding 11 that makes the difference zero (in the case of PFM control) is determined by a voltage feedback unit in advance by simulation or the like. 30 is stored in the memory. Therefore, the voltage feedback control unit 30 can obtain the on-duty ratio and the energization frequency that can correct the error in the average voltage of the output voltages Vo1, Vo2, and Vo3 according to the correspondence relationship in the memory.

  Therefore, the switching power supply device according to the present embodiment includes three secondary windings 12a, 12b, and 12c of the transformer 10, and the output voltages Vo1, Vo2, and 2 generated by the secondary windings 12a, 12b, and 12c, respectively. An average voltage calculation unit 20 that calculates an average value of Vo3, and PWM control of energization of the primary winding 11 of the transformer 10 so that an error between the average value calculated by the average voltage calculation unit 20 and the target set voltage is zero. Alternatively, the voltage feedback control unit 30 that performs PFM control is provided, so that voltage feedback control is performed based on the average value of the output voltages Vo1, Vo2, and Vo3, so that a voltage such as a coil dedicated to voltage detection is taken out of the transformer 10 There is no need to provide a configuration. As a result, the structure of the transformer 10 can be simplified and an increase in circuit components such as a voltage detection dedicated winding can be suppressed.

  In addition, since the switching power supply device of the present embodiment performs simple voltage feedback based on calculating the average value of the output voltages Vo1, Vo2, and Vo3, the allowable voltage range of the output voltages Vo1, Vo2, and Vo3 is This is particularly effective when it is wide or when demands such as simplification of structure and cost reduction are stronger than demands for accuracy of output voltages Vo1, Vo2, and Vo3.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention. Can be added.

  For example, in the above-described embodiment, the case where the number of secondary windings is three has been described as an example, but the same effect can be obtained with the same configuration even when the number is two or four or more.

  Further, although the average value of the output voltages Vo1, Vo2, and Vo3 is voltage-feedback, when the design values of the output voltages Vo1, Vo2, and Vo3 are different from each other, the output voltage Vo1, Vo2, and Vo3 that are actually detected are intermediate. The energization frequency and duty ratio or energization frequency and on-time of the primary winding 11 of the transformer 10 are controlled so that the difference between the voltage value of the output voltage Vo1 and the voltage value in the middle of the design values of the output voltages Vo1, Vo2 and Vo3 becomes zero. May be.

It is the figure which showed one Embodiment of the switching power supply device which concerns on this invention. It is the figure which showed one Embodiment of the conventional switching power supply device. It is the figure which showed the relationship between the energization current Iout of the primary winding 11, and PWM control or PFM control. It is the table | surface which showed the difference of the performance of PWM control and PFM control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Transformer 11 Primary winding 12 Secondary winding 13 Diode 14 Smoothing capacitor 20 Average voltage calculation part 30 Voltage feedback control part 40 Switching element

Claims (3)

A switching power supply device comprising a transformer having a plurality of secondary windings,
Average value calculating means for calculating an average value of output voltages generated by each of the plurality of secondary windings;
Control means for controlling the duty ratio of the energization frequency of the primary winding of the transformer so that the difference between the average value calculated by the average value calculation means and a predetermined set value becomes zero. Switching power supply. A switching power supply device comprising a transformer having a plurality of secondary windings,
Average value calculating means for calculating an average value of output voltages generated by each of the plurality of secondary windings;
And a control means for controlling the energization frequency of the primary winding of the transformer so that the difference between the average value calculated by the average value calculation means and a predetermined set value becomes zero. apparatus.   The switching power supply device according to claim 1, wherein the control unit outputs a control signal for driving a switching element connected to the primary winding.

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