JP2003299356A - Dc-dc converter control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control method that attenuates the abnormal noise of a transformer without causing power consumption at a light load, because, if a DC power source voltage is higher than usual when switching elements are changed over in a DC-DC (direct current-direct current) converter, a rush current that flows into the transformer causes harsh grating noise. <P>SOLUTION: This DC-DC converter is the one that converts a DC power source voltage into a DC output of a constant voltage by on-off operations of switching elements, and that oscillates the switching elements intermittently by providing an oscillating period and a forced stop period at the time of a light load including no load. In this converter, by controlling the output of a comparator that compares the output of a function voltage generating circuit including a triangular-wave voltage with a command value according to the DC power source voltage, the on-range width of the switching elements is made to change so that the current that flows into the transformer does not increase as the DC power source voltage increases. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC / D for converting the output of a DC power supply into an arbitrary DC output via a transformer.
The present invention relates to an improvement of a control method of a C converter, particularly a control method at a light load including no load.

[0002]

2. Description of the Related Art FIG. 8 shows a circuit connection diagram of a conventional example. Figure 8
The circuit is an example of flyback converter, DC power supply 1,
A power circuit is composed of the switch element 2, the flyback transformer 3, the rectifier 4, and the capacitor 5. The output voltage Vo of the capacitor 5 is given to the differential amplifier 61, which is the input stage of the output voltage detection adjustment circuit 6, together with the set voltage Vref, and a signal corresponding to the deviation is output as the command value Vc via the photocoupler 62. It This command value Vc is compared with the output Vt of the function voltage generation circuit 8 in the comparator 7, and a PWM (pulse width modulation) signal Vm is generated. The function voltage generation circuit 8 has a triangular wave (including a sawtooth wave)
It produces an output voltage.

The PWM signal Vm and the output Vs of the rectangular wave signal generating circuit 10 having a fixed frequency and a fixed duty ratio are logically ANDed in the AND gate 11 and become a gate signal Vg via the gate drive circuit 9. Switch element 2 is turned on and off.

FIG. 9 shows the operation waveforms of the conventional circuit of FIG. 8. (1) shows the relationship between the output command value Vc and the output Vt of the function voltage generating circuit 8, and (2) shows the rectangular wave. The drawing is centered on the L level region of the output Vs of the signal generation circuit 10. As shown in (3), the PWM signal Vm output from the comparator 7 is the command value Vc in the waveform diagram of (1).
Is at the H level while the output voltage Vt of the function voltage generating circuit 8 is higher than the output voltage Vt, the PWM signal Vm can pass through the AND gate 11 only when the output Vs of the rectangular wave signal generating circuit 10 is at the H level. The output signal Vg of the AND gate 11 has a waveform as shown in (4).

As described above, in the conventional circuit shown in FIG. 9, when the output Vs of the rectangular wave signal generation circuit 10 is at the H level, the switching element 2 repeats switching, and the oscillation period is reached.
When the output Vs is at the L level, the switch element 2 is forced to stop switching, and the forced stop period is set.
The switch element 2 is intermittently oscillated through the gate drive circuit 9.

According to the above-mentioned conventional circuit, the number of times of switching per unit time can be reduced by providing the forced stop period, and the switching loss and the conduction loss can be reduced. However, since energy is not supplied to the output of the flyback converter during the forced stop period,
Since the output voltage pulsates a little, it is necessary to optimally set the oscillation period and the forced stop period so that the pulsation of the output voltage at the time of the maximum load, which is assumed at the time of light load, is suppressed within the allowable value.

[0007]

By the way, in the prior art example shown in FIG. 8, when the ON width of the switching element changes abruptly at the timing of switching between the forced stop period and the oscillation period and the voltage of the DC power supply 1 is high. Since a large current rapidly flows through the transformer and electrical stress is applied to the transformer, if the oscillation frequency of the rectangular wave signal generation circuit 10 is within the audible band,
There is a problem that an abnormal sound that is very offensive to the ear is generated from the transformer.

That is, in FIG. 9, paying attention to the time point to when the forced stop period is switched to the oscillation period, when the DC power supply voltage is low (A), the primary current Ip of the transformer is as shown in (5) of FIG. When the DC power supply voltage is high (B), the output voltage rises at a not so steep gradient and the output voltage repeats a gentle increase and decrease as shown in (6).
As shown in (7), the current suddenly flows in and the output voltage rises steeply, so intermittent strong electromagnetic force acts on the transformer windings and iron core, resulting in annoying noise. Will be done.

Therefore, an object of the present invention is to provide a DC / DC converter in which no abnormal sound is generated from the transformer for any input voltage in a converter which is designed to perform an intermittent oscillation operation at a light load to reduce power consumption. It is to provide a control method of.

[0010]

According to the present invention, the above object is to convert a DC power supply voltage into a DC output of a constant voltage by an ON / OFF operation of a switch element, and to oscillate at a light load including no load. In a DC / DC converter that intermittently oscillates a switch element by providing a period and a forced stop period, the crest value of a triangular wave voltage that is compared with an output command value for generating a PWM signal is controlled according to the level of a DC power supply voltage. This can be achieved by changing the ON width of the switch element.

In order to determine the peak value of the triangular wave voltage, it is easy to switch the capacity of the capacitor charged and discharged with a constant current (the invention according to claim 2).

Further, in order to determine the peak value of the triangular wave voltage, it is also an object to switch the charging current to the capacitor for generating the triangular wave voltage (the invention according to claim 3).

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit connection diagram showing an embodiment of the invention described in claim 1. The operation mode will be described with reference to FIG. 2 and FIG. 3 showing operation waveforms of this circuit. In this embodiment, a flyback converter is taken as an example, and the upper half of the figure has the same structure as that of FIG.
The same elements or circuits as those in FIG. 8 are designated by the same reference numerals. The difference from FIG. 8 lies in the configuration of the function voltage generation circuit.

In the function voltage generation circuit 18 shown in FIG. 1, the output voltage detection adjustment circuit 6 is provided in the comparator 7.
The output voltage Vt to be compared with the output command value Vc of is the terminal voltage of the parallel connection circuit of the capacitors 20 and 21. More precisely, the capacitor 20 is connected directly and the capacitor 21 is connected to ground potential via the switch circuit 22. These two capacitors are charged and discharged from the constant voltage Vcc by the switch circuits 24 and 25 and the constant current circuits 26 and 27 which are turned on and off by the output of the rectangular wave signal generation circuit 23. Therefore, the terminal voltages of the capacitors 20 and 21 change in a triangular waveform.

The switch circuit 22 connected in series with the capacitor 21 is turned on and off as follows. That is, the voltage Vd obtained by dividing the voltage of the DC power supply 1 by the resistors 28 and 29 is compared with the reference voltage Vb by the comparator 30, and if the divided voltage Vd is smaller than the reference voltage Vb, the output of the comparator 30 causes the capacitor The switch 22 connected in series with 21 is turned on. As a result, the capacitor for forming the triangular wave voltage is the capacitor 20 and the capacitor 21 connected in parallel, and the capacitance increases, so that the peak value of the triangular wave voltage decreases. Therefore, the ON time of the switch element 2 due to the output of the comparator 7 becomes long.

On the contrary, when the divided voltage Vd exceeds the reference voltage Vb, the switch 22 connected in series with the capacitor 21 is turned off by the output of the comparator 30, and only the capacitor 20 generates a triangular wave, and the triangular wave voltage is generated. Has a high peak value. As a result, the ON time of the switch element 2 due to the output of the comparator 7 becomes shorter. In addition,
It is preferable that the capacitors 20 and 21 have a capacitance of about 1: 2.

This will be described with reference to FIGS. 2 and 3. When the DC power supply voltage is low and therefore the divided voltage Vd shown in FIG. 1 does not exceed the reference voltage Vb, the triangular wave voltage Vt is also reduced. Correspondingly, as shown in (1) of FIG. 2, the crest value is low, and the time when the output command value Vc exceeds the triangular wave voltage Vt also becomes long, so that the PWM signal Vm shown in (3) of FIG. Since the gate signal Vg shown in (3) also has a certain width, the ON time of the switch element 2 also becomes long. The primary current Ip of the transformer also has a low waveform as shown in (5), and the output voltage Vo also changes gently.

On the other hand, when the DC power supply voltage is high and therefore the divided voltage Vd in FIG. 1 exceeds the reference voltage Vb, the triangular wave voltage Vt is also correspondingly shown in (1) of FIG. The peak value is high and the output command value Vc is the triangular wave voltage V.
Since the time over t is shortened, P shown in (3) of FIG.
WM signal Vm, and therefore gate signal Vg shown in (4)
Also has a relatively narrow width, and the ON time of the switch element 2 correspondingly shortens. As a result, the primary current Ip of the transformer does not have a large value as in the conventional case as shown in (5), and the output voltage Vp also shows a gradual change.

Thus, according to the embodiment of FIG. 1, even if the voltage of the DC power supply changes, the change in the current flowing into the transformer is reduced as compared with the conventional case, and therefore the abnormal noise of the transformer is reduced. Will or the level will be lower.

FIG. 4 shows a different embodiment of the present invention, and FIGS. 5 and 6 are operation waveform diagrams thereof. In FIG. 4, the circuit briefly indicated by block 18 is similar to the functional voltage generator 18 of FIG. The embodiment of FIG. 4 further includes a circuit including circuit elements 33 to 38 having the same circuit configuration as the constant current charge / discharge circuit of FIG. 1, an impedance conversion element 39 and a diode 40.

In the circuit of FIG. 4, the output Vs of the rectangular wave signal generating circuit 33 for controlling the oscillation period of the switching element 2 and the forced stop period is used, and the constant current circuit is used at the timing of switching from the forced stop period to the oscillation period. Switch circuit 34 so that capacitor 38 is charged with a constant current via 36
Is turned on so that the voltage of the capacitor 38 gradually increases. The capacitor 38 is charged to the power supply voltage Vcc connected to the switch circuit 34.

At the timing of switching from the oscillation period to the forced stop period, the switch circuit 35 is turned on so that the capacitor 38 is discharged with a constant current through the constant current circuit 37, and the voltage of the capacitor 38 is gradually decreased. To do. The voltage on capacitor 38 is discharged until it reaches zero.

Further, the signal obtained by impedance-converting the voltage Vcs of the capacitor 38 by the impedance conversion element 39 and the output signal Vc of the output voltage detection adjustment circuit 6 are compared, and the smaller value is used as the input signal of the comparator 7. Therefore, the diode 40 is connected. As a result, after the timing at which the forced stop period is switched to the oscillation period, the ON pulse width of the switch element 2 gradually increases at the charging speed of the capacitor 38, and the output Vc of the output voltage detection adjustment circuit 6 becomes higher than the voltage of the capacitor 38. When it becomes smaller, the on / off timing of the switch element 2 is PWM-controlled so that the output voltage becomes constant. Also,
After the timing of switching from the oscillation period to the forced stop period, the switching element 2 is driven at the discharge speed of the capacitor 38.
When the on-pulse width of is reduced to zero and the voltage of the capacitor 38 becomes zero, the switch element 2 is completely turned off.

At this time, similarly to the embodiment of FIG. 1, the peak value of the function voltage generating circuit 18 is switched according to the voltage of the DC power supply, and even if the voltage of the DC power supply 1 is changed, the current flowing into the transformer 3 is changed. Is reduced and the generation of abnormal noise of the transformer is reduced.

FIG. 5 shows operation waveforms when the DC power supply voltage is high, and FIG. 6 shows operation waveforms when the DC power supply voltage is low.
In both figures, (1) is the output signal Vs of the rectangular wave signal generation circuit Vs, (2) is the terminal voltage Vcs of the capacitor 38,
(3) is the relationship between the triangular wave voltage Vt and the output command value Vc,
(4) shows the output voltage Vo and the set voltage Vref, (5) shows the relationship between the triangular wave voltage Vt and the output command value, (6) shows the PWM signal Vm, and (7) shows the transformer primary current Ip.

As is clear from a comparison between FIG. 5 and FIG.
When the DC power supply voltage is low, the triangular wave voltage Vt is also low as shown in FIG. 5, so that the period during which the output command value Vc exceeds the triangular wave voltage Vt is relatively long, and therefore the width of the PWM signal Vm is small. Since it becomes longer, the ON time of the switch element 2 also becomes longer accordingly.

On the other hand, when the DC power supply voltage is high, the triangular wave voltage Vt is also high as shown in FIG. 6, so that the period during which the output command value Vc exceeds the triangular wave voltage Vt becomes relatively short, Therefore, since the width of the PWM signal Vm is shortened, the ON time of the switch element 2 is correspondingly shortened.

Thus, according to the embodiment shown in FIG. 4, even if the voltage of the DC power supply changes, the change in the current flowing into the transformer is reduced as compared with the prior art, as in the embodiment shown in FIG. The abnormal noise of the transformer is reduced or the level is lowered.

FIG. 7 shows a different embodiment of the function voltage generating circuit used when implementing the present invention. The voltage of the DC power supply 1 is divided by the resistors 41 and 42, the divided voltage Vd and the reference voltage Vb are compared by the comparator 43, and the result is applied to one input of the AND gate 44 via the inverter 43N. The output of the rectangular wave signal generation circuit 45 is given to the other input of the AND gate 44. The output of the rectangular wave signal generation circuit 45 is given to a switch circuit 46 or 47 connected in series with a constant current circuit 48 or 49, and these switch circuits are alternately turned on / off to charge the capacitor 52 with a predetermined constant current. Or discharge. The output of the aforementioned AND gate 44 is given to the switch circuit 50, and when the switch circuit 50 is turned on, the additional constant current circuit 51 participates in the charging of the capacitor 52. Constant current circuits 48 and 51
It is better to select the supply current ratio of about 1: 2.

When the apparatus is operated under such a structure, the capacitor 52 repeats constant current charging or constant current discharging by the output of the rectangular wave signal generating circuit 45, and the triangular wave voltage V
However, when the DC power supply voltage is low and the divided voltage Vd is lower than the reference voltage Vb, the switch 5 connected in series to the constant current circuit 51 is generated by the inverted output of the comparator 43.
0 does not turn on, and only the constant current circuit 48 contributes to the charging current to the capacitor that generates the triangular waveform.
The peak value of the triangular wave voltage becomes low. At this time, the ON time of the switch element 2 due to the output of the comparator 7 becomes long.

When the DC power supply voltage rises and the divided voltage Vd exceeds the reference voltage Vb, the switch 44 connected in series with the constant current circuit 45 is turned on by the inverted output of the comparator 43, and a new constant current circuit 51. Is charged for charging the capacitor 52, the peak value of the triangular wave voltage becomes high. At this time, the ON time of the switch element 2 due to the output of the comparator 7 becomes short.

Here, in the above embodiment, the capacitance ratio of the capacitor 20 and the capacitor 21 or the supply current ratio of the constant current circuit 48 and the constant current circuit 51 is set to 1: 2. This is an example of the case where the ratio of the assumed minimum value and the maximum value of the voltage is about 1: 3, and may be appropriately determined based on the ratio of the assumed minimum value and the maximum value of the voltage.

[0033]

As described above, according to the present invention, by detecting the DC power supply voltage and changing the peak value of the function voltage for PWM calculation, the abnormal noise of the transformer generated when the power supply voltage changes can be reduced. Therefore, in applications where it is necessary to reduce power consumption during light loads such as during standby, a special converter dedicated for standby can be omitted, and a low-cost power supply system can be provided.

[Brief description of drawings]

FIG. 1 is a circuit connection diagram in a first embodiment of the present invention.

FIG. 2 is an operation waveform diagram of the first embodiment (when the DC power supply voltage is low).

FIG. 3 is an operation waveform diagram of the first embodiment (when the DC power supply voltage is high).

FIG. 4 is a circuit connection diagram in the second embodiment of the present invention.

FIG. 5 is an operation waveform diagram of the second embodiment (when the DC power supply voltage is low).

FIG. 6 is an operation waveform diagram of the second embodiment (when the DC power supply voltage is high).

FIG. 7 is a circuit connection diagram of another embodiment of the function voltage generating circuit according to the present invention.

FIG. 8 is a circuit connection diagram of a conventional example.

FIG. 9 is an operation waveform diagram of a conventional circuit.

[Explanation of symbols]

1 DC power supply 2 switch elements 3 transformers 4 rectifier 5 capacitors 6 Voltage detection adjustment circuit 7 comparator 9 Gate drive circuit 10, 23, 33 rectangular wave signal generation circuit 11 AND GATE 18 Function voltage generation circuit 39 Impedance conversion circuit

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kiyoshi Moriya             153 Shimo-Kashiwanocho, Matsuto City, Ishikawa Prefecture Co., Ltd.             In Nanao (72) Inventor Kuwahara Konasa             1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa             Within Fuji Electric Co., Ltd. F-term (reference) 5H730 AA02 BB43 DD01 EE02 EE07                       EE59 FD01 FD11 FF03 FG03                       FG05

Claims (3)

[Claims] 1. A DC power supply voltage is converted into a DC output of a constant voltage by an ON / OFF operation of a switch element, and an intermittent oscillation operation of the switch element is provided by providing an oscillation period and a forced stop period at a light load including no load. In the DC / DC converter, the ON width of the switching element is changed by controlling the peak value of the triangular wave voltage that is compared with the output command value for generating the PWM signal according to the level of the DC power supply voltage. A characteristic method of controlling a DC / DC converter. 2. The method of controlling a DC / DC converter according to claim 1, wherein the capacity of a capacitor charged and discharged with a constant current is switched to determine the peak value of the triangular wave voltage. 3. The method of controlling a DC / DC converter according to claim 1, wherein the charging current to the capacitor for generating the triangular wave voltage is switched in order to determine the peak value of the triangular wave voltage.