JP3365139B2 - Switching power supply control method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a switching power supply device which outputs a constant voltage while intermittently switching a switching means at a cycle designated by a synchronizing signal.
The present invention relates to a control method particularly suitable for a so-called current mode control type switching power supply.

[0002]

2. Description of the Related Art As is well known, in a switching power supply device, it is customary to maintain a constant output voltage taken from the secondary side of a transformer while intermittently connecting the primary side current of the transformer by switching means. In addition to controlling the intermittent operation of the switching means according to the output voltage value,
The above-mentioned current mode control type, which can improve the constant voltage performance by controlling according to the primary side current value, has been widely adopted. Hereinafter, with reference to a typical circuit example of the current mode control type switching power supply device shown in FIG. 4 and an operation waveform example thereof shown in FIG. The outline of the control method will be described.

The main circuit of the switching power supply device is shown in the upper right portion of FIG. 4, and in the primary coil 2a which receives the power supply voltage V of the flyback type transformer 2 in the illustrated example by the switching transistor 1 as usual. While interrupting the flowing current, the AC voltage induced in the secondary coil 2b is converted into a DC voltage by the rectifier diode 3, and in the example of the figure, it is boosted to a predetermined voltage value by the freewheeling diode 4 and the reactor 5, and The voltage value is the capacitor 6
Is stabilized as much as possible and then taken out as the output voltage Vo.

The control system of the switching power supply device shown in the lower left portion of FIG. 4 receives the actual value Va of the output voltage Vo and outputs a voltage error signal Vc which amplifies the difference from the reference value Vr and outputs a voltage error amplifier 21.
And a comparator 30 which receives the detection signal Vb of the current of the switching transistor 1 and compares it with the voltage error signal Vc. The voltage error amplifier 21 receives the actual value Va of the output voltage Vo through an insulating path indicated by a broken line in the example of the drawing for convenience of illustration such as a photocoupler, and receives the voltage error signal Vc under the integration operation by the input resistor 21a and the feedback capacitor 21b. It emits as a nearly complete DC signal. The comparator 30 outputs this voltage error signal Vc
And the current of the switching transistor 1 to the current detection resistor 1a
And outputs a comparison result signal Sd obtained by comparing a detection signal Vb having a sawtooth waveform, which will be described later, with the detection signal Vb.

A flip-flop 40 is provided for turning on / off the switching transistor 1 on the basis of the comparison result signal Sd and the synchronization signal SP. The flip-flop 40 is set by the synchronization signal SP and reset by the comparison result signal Sd, and its Q output is set. It is output as an on / off command Se for the switching transistor 1. The synchronizing signal SP is advantageously a pulse waveform signal as shown in FIG. 5 (a), and the flip-flop 40 is set according to the rising edge of the synchronizing signal SP and the on / off command Se is shown in FIG.
Since it becomes high as shown in (d), the switching transistor 1 is turned on and a current flows through the primary coil 2a of the transformer 2. Since the primary coil 2a is inductive, this current rises from 0 with a slope determined by its inductance, and the detection signal Vb by the current detection resistor 1a has a substantially constant slope from 0 in synchronization with the synchronization signal SP as shown in FIG. 5 (b). The waveform rises with.

The voltage error signal Vc, which is the aforementioned DC signal, is compared with the waveform of the current detection signal Vb by the comparator 30 as shown in FIG. 5 (b).
Vc is usually created by the voltage error amplifier 21 so that the level of the signal value is inversely related to the actual value Va of the output voltage Vo, and when this signal value is exceeded by the rising waveform of the current detection signal Vb, FIG. ), The comparison result signal Sd becomes high.
In response to this, the flip-flop 40 is reset and FIG.
Since the ON / OFF command Se of (d) becomes low and the switching transistor 1 is turned OFF to cut off the current, the current detection signal Vb returns to 0 as shown in FIG. 5 (b) and returns to the sawtooth shape as described above. It becomes a waveform. The comparison result signal Sd in FIG. 5C also returns to low after having been high for a very short time, and the same operation as before is repeated after the next rising of the synchronizing signal SP.

As described above, in the conventional control system of FIG.
While the switching transistor 1 is turned on in synchronization with the synchronization signal SP and turned off at the timing at which the voltage error signal Vc intersects the rising waveform of the current detection signal Vb with a predetermined slope, the output voltage Vo is low and the voltage error signal Vc Value is Figure 5
When it is high as in the left part of (b), the high time of the on / off command Se in FIG.
Of the voltage error signal
When the value of Vc is low as shown on the right side of FIG. 5 (b), the output voltage Vo is held at a predetermined value by shortening the high time of the on / off command Se, that is, the on time of the switching transistor 1.

[0008]

Although the above-mentioned conventional technique can provide the switching power supply device with good constant voltage performance, in principle, the generation and control of the output voltage Vo depends on the switching operation. Output voltage Vo
Although it is very slight, it is inevitable that pulsating voltage will be applied, and depending on the application, it is necessary to take measures against noise due to this pulsating component.
In the current mode control type as described above, there is a problem that it is actually very difficult to take measures against this noise.

It is necessary to take measures against noise, for example, when power is supplied to the drive circuit of the display panel by the switching power supply device, and if the pulsating voltage is added to the output voltage Vo, it tends to appear as noise on the display screen. As for the above, it is most effective to scan the display screen except at the time of noise occurrence, but it is very difficult to take this measure because the timing of noise occurrence is undefined in the conventional control method of FIG.

That is, the pulsating component of the output voltage Vo is of course caused by the ON / OFF operation of the switching transistor 1. However, the waveform change of the pulsating voltage is large during the OFF operation, which is apt to cause noise on the display screen. However, in the conventional control method of FIG. 4, the timing of this off operation is determined by the timing at which the voltage value of the voltage error signal Vc cuts off the sawtooth waveform of the current detection signal Vb as described above. As shown in FIG. 5, the off-operation timing varies widely within the period of the synchronizing signal SP, usually within the latter half of the period, as shown in FIG. In principle, it is impossible to reduce the fluctuation range of the noise generation timing unless the constant voltage performance of the output voltage Vo is significantly reduced.

SUMMARY OF THE INVENTION An object of the present invention is to provide a control system for a switching power supply device, which solves the above-mentioned problems by performing an off operation of a switching means which causes a trouble such as noise on a display screen at a constant timing. Especially.

[0012]

According to the control system of the present invention, this object is to provide a reference wave signal generating means for generating a reference wave signal having a constant waveform in a cycle synchronized with a synchronizing signal, and a switch.
The actual value of the output voltage of the power supply and the specified reference voltage value
Error amplifier that amplifies the difference between
And the signal value of the detection signal of the current flowing through the switching means
Current error amplifier that amplifies the difference between
Using a control means composed of and a comparison means for mutually comparing the signal values of the reference wave signal and the control signal, the switching means is turned on in accordance with the comparison result of the comparison means and synchronized with the synchronization signal. This is achieved by turning it off.

The reference wave signal generating means generates a reference wave signal having a waveform rising at a predetermined gradient in accordance with the synchronizing signal, and the comparison result signal of the comparison result signal of the signal values of the reference wave signal and the control signal is generated. The switching means may be turned on at the timing when the logic state changes during the rising of the former waveform. The simplest way to determine the timing of the OFF operation of the switching means is to give the reference wave signal a sawtooth waveform and turn off the switching means at the timing when the logical state of the comparison result signal by the comparing means changes in accordance with the fall of this waveform. It suffices to operate it. In this embodiment, the timing of the ON operation and the OFF operation of the switching means can be directly designated by the change of the logic state of the comparison result signal of the comparison means.

However, when the sawtooth waveform is disturbed, there is a possibility that the timing of the OFF operation of the switching means designated by the fall of the waveform may be misaligned. Therefore, a flip-flop is provided and the comparison result signal is supplied to the input thereof. If the synchronizing signal is applied and the flip-flops are alternately set or reset according to the change in the logical state of both signals to control the switching means by using the output signal as an ON / OFF command, the OFF operation is synchronized with the synchronizing signal. The timing fluctuation can be completely eliminated.
In this embodiment, the waveform of the reference wave signal generated by the reference wave signal generating means is not limited to the sawtooth waveform but may be a triangular wave such as an isosceles triangle or an isosceles triangle, so that the constant voltage performance of the switching power supply device is maximized. In the above, it is desirable that the waveform has an isosceles triangular shape similar to a sawtooth waveform.

Further, the take out in the form of a DC signal which does not include the ripple component of the control signal using the differential amplifier of the integration operation type as voltage and current error amplifier desirable in enhancing the constant voltage performance of the switching power supply device.

[0016]

In the conventional control method, as described with reference to FIGS. 4 and 5, the timing at which the switching means is turned off by utilizing the waveform in which the current rises after the switching means is turned on in synchronization with the synchronizing signal. Although it has been decided, in the method of the present invention, conversely, the ON operation is decided by using the rising waveform, so that the OFF operation is synchronized with the synchronizing signal to solve the problem. However, since the rising waveform of the current that should be used to determine the timing of the off operation in the conventional method cannot occur unless the switching means is first turned on before that, the on and off operations of the switching means remain unchanged. Cannot simply be replaced.

Therefore, in the method of the present invention, a reference wave signal generating means is provided to generate a reference wave signal having a constant rising waveform at a cycle synchronized with the synchronizing signal, and the waveform of this reference wave signal and the control signal by the control means are generated. The timing at which the switching means is turned on is determined from the result of comparing the signal values by the comparison means, and the off operation is always synchronized with the synchronization signal. Thus, in the method of the present invention, the timing of the ON operation of the switching means is adjusted so as to keep the output voltage of the switching power supply device constant,
It is possible to make the timing of the OFF operation always coincide with the synchronization signal so that it does not vary according to the signal value of the control signal.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 are circuit diagrams showing different embodiments of the present invention, and FIG. 3 is a waveform diagram showing the operation of the embodiment of FIG. 1, corresponding to FIGS. 4 and 5 explained before these figures. Since the same reference numerals are given to the portions to be performed, the description of the overlapping portions will be omitted as appropriate.

The main circuit of the switching power supply device shown in the upper right portion of FIG. 1 is the same as that of FIG. 4, and in this embodiment, in order to control ON / OFF of the switching means 1 so as to keep the value of the output voltage Vo constant, a block is used in this embodiment. Reference wave signal generating means shown
10, control means 20 surrounded by a chain line, and comparison means 30
And are used. The reference wave signal generating means 10 used in the method of the present invention receives a synchronizing signal SP having a repetitive pulse waveform as shown in FIG. 3 (a), and generates a reference wave signal Sr having a waveform rising at a predetermined gradient in synchronization with it. However, in the embodiment of FIG. 1, this reference wave signal generating means is sufficient.
A reference wave signal Sr is generated at 10 with a sawtooth waveform as shown in the frame. For this purpose, the reference wave signal generating means 10 is composed of, for example, a capacitor and a charging / discharging circuit, and when the pulse of the synchronization signal SP is received, the capacitor is discharged and then the charging is started while the reference voltage signal Sr is applied. You can take it out as.

The control means 20 issues a control signal Sc for controlling the output voltage Vo to a constant value with a signal value that changes according to the load state of the switching power supply device. For example, as shown in FIG. A voltage error amplifier 21 that receives the actual value Va of Vo and amplifies the difference from the value of the reference voltage Vr, and the voltage error signal Vc and the value of the current detection signal Vb detected by the resistor 1a for the current of the switching means 1 It is preferable to be configured with a current error amplifier 22 that amplifies the difference between the above and outputs as a control signal Sc. In the example of the figure, in order to stabilize the operation of the switching power supply device as much as possible, these amplifiers 21 and 22 are integrated operation type including the input resistors 21a and 21b and the feedback resistors 22b and 22b, respectively, and the control signal Sc is wasted. It is designed to be extracted in the form of a direct current signal that does not contain pulsating components.

The comparison means 30 may be a single comparator as shown in the figure, and the control signal Sc and the reference wave signal described above may be used.
Sr is compared with each other and the logic state of the comparison result signal Sd is normally changed to high when the signal value of the former intersects with the rising waveform of the latter to determine the timing of the ON operation of the switching means 1. In the embodiment shown in FIG. 1, the reference wave signal Sr is generated by the reference wave signal generating means 10 in a sawtooth waveform, so that the logic state of the comparison result signal Sd is changed to low in accordance with the fall of the waveform and the switching means. The timing of the OFF operation of 1 is also determined. Therefore, in the embodiment of FIG. 1, the comparison result signal Sd of the comparison means 30 is used as it is as an on / off command for the switching means 1.

FIG. 3 shows the operation of the embodiment of FIG. 1 constructed as described above by a waveform diagram of main signals. Depending on the repetition pulse of the sync signal SP shown in FIG.
The reference wave signal Sr shown in (b) is generated by the reference wave signal generating means 10 in a sawtooth waveform. The voltage error amplifier 21 in the control means 20 receives the actual value Va of the output voltage Vo and amplifies the difference from the reference voltage value Vr to output a voltage error signal Vc as a DC signal as shown in FIG. The signal value is the actual value Va as usual.
The lower the value, the higher the value, and the higher the actual value Va, the lower the value. Current detection signal Vb obtained by detecting the current of the switching means 1 with the resistor 1a
Has a waveform that rises diagonally during the ON time of the switching means 1 and falls simultaneously with the OFF operation as shown in FIG. 3 (d). The current error amplifier 22 and this waveform and the voltage error signal
The difference from the value of Vc is amplified and the control signal Sc is output with a refraction waveform as shown in FIG. 3 (b).

The comparison means 30 uses this control signal shown in FIG. 3 (b).
By comparing Sc with the waveform of the reference wave signal Sr, the comparison result signal Sd shown in FIG. 3 (c) is output in a waveform in which the logic states of high and low alternate according to the magnitude of the signal values of both signals Sc and Sr. At this time, when the control signal Sc crosses the rising waveform of the reference wave signal Sr, the logic state of the comparison result signal Sd changes from low to high, and the switching means 1 is designated as the ON operation timing.
Further, in this embodiment, the logic state of the comparison result signal Sd changes from high to low in response to the fall of the sawtooth reference wave signal Sr, and the switching means 1 is designated the timing of the off operation. Incidentally, the current detection signal Vb has a waveform as shown in FIG. 3 (d) as described above with the ON / OFF operation of the switching means 1 by such designation.

As can be seen from the above operation, the output voltage Vo
Is lower than a predetermined value and the value of the voltage error signal Vc is high as shown on the left side of FIG. 3 (d), the level of the control signal Sc is
As shown on the left side of (b), the reference wave signal Sr
The timing of the ON operation of the switching means 1, which is determined by the intersection with the rising waveform of, becomes faster, so that the ON operation time becomes longer and the level of the output voltage Vo is raised. On the contrary, when the output voltage Vo is high and the voltage error signal Vc is low, the level of the control signal Sc becomes high as shown on the right side of FIG. 3 (b), so the switching means determined at the intersection with the rising waveform of the reference wave signal Sr. The ON operation timing of No. 1 is delayed, so that the ON operation time is shortened and the level of the output voltage Vo is pushed down. In the embodiment of FIG. 1, the output voltage Vo of the switching power supply device is always maintained at a constant value by such control operation.

In the embodiment of FIG. 1 described above, the comparison means 30
The comparison result signal Sd is used as an ON / OFF command to directly specify not only the ON operation timing but also the OFF operation timing with respect to the switching means 1 by the change of its logic state. However, when the sawtooth waveform of the reference wave signal Sr is disturbed, There is a possibility that the timing of the OFF operation of the switching means 1 designated by the fall of the waveform may fluctuate slightly. The following embodiment shown in FIG. 2 is for solving this point. For simplification of the drawing, FIG. 2 shows only the part excluding the output circuit part of the switching power supply device.

The embodiment of FIG. 2 is the same as the previous embodiment in that the reference wave signal generating means 10, the control means 20 and the comparing means 30 are used, but the switching means 1 is switched by the comparison result signal Sd of the comparing means 30. 40 flip-flops instead of direct drive
Is provided and the comparison result signal Sd and the synchronizing signal SP are given to its input, and its Q output is given to the switching means 1 as an on / off command Se. In the illustrated example, the flip-flop 40 is set when the logic state of the comparison result signal Sd changes from low to high designating the on-operation timing, and the switching means 1 is turned on by the high on-off command Se.
Is turned on, and the switching means 1 is turned off by being reset in response to the rising of the synchronizing signal SP to set the on / off command Se to low.

As described above, in the embodiment shown in FIG. 2, by synchronizing the OFF operation of the switching means 1 with the synchronizing signal SP, it is possible to substantially eliminate the fluctuation of the timing. Further, in this embodiment, the waveform of the reference wave signal Sr generated by the reference wave signal generating means 10 does not have to be a sawtooth wave as easily understood, and may be a triangular wave as shown in the frame. Note that this triangular wave may be an isosceles triangle, but in order to facilitate the control of the output voltage Vo of the switching power supply device, as shown in the figure, it is an isosceles triangle in which the rising portion is longer than the falling portion. Is good. This Figure 2
The configuration and operation of the other parts of the embodiment of FIG. 3 are the same as those of the embodiment of FIG.

Both the embodiments shown in FIGS. 1 and 2 described above are suitable for the current mode control type switching power supply device. That is, the current error amplifier 22 in the control means 20 plays a role of this current mode control, and when the load of the switching power supply device is heavy and the current flowing through the switching means 1 is large, the ON operation time is lengthened and the output voltage is increased. To keep Vo at a desired value, raise it.

As can be seen from these embodiments, in the control system of the present invention, the reference wave signal having the constant rising waveform synchronized with the synchronizing signal SP by the reference wave signal generating means 10 is used.
Sr is generated and the timing of the ON operation of the switching means 1 is determined from the result of comparison of the value of the control signal Sc for holding the output voltage Vo constant with respect to the waveform thereof. On the contrary, the timing of the off operation can be made to always coincide with the synchronization signal SP so that it does not vary depending on the signal value of the control signal Sc. The switching power supply device to which the method of the present invention is applied is suitable for applications such as supplying power to a drive circuit of a display device, and prevents noise generation on a display screen by relating a screen scanning clock signal given to the drive circuit to a synchronization signal. be able to

[0030]

As described above, in the control system of the switching power supply device according to the present invention, the reference wave signal generating means for generating the reference wave signal having a constant waveform in the cycle synchronized with the synchronizing signal, and the output voltage of the switching power supply device Actual value and predetermined
Voltage error amplifier that amplifies the difference in reference voltage value and its voltage
Detection signal of error signal value and current flowing through switching means
Current that amplifies the difference from the signal value of and outputs as a control signal
Using a control means composed of an error amplifier and a comparison means for mutually comparing the signal values of the reference wave signal and the control signal,
By deciding the ON operation timing of the switching means in accordance with the comparison result signal from the comparison means, the OFF operation timing is always matched with the synchronization signal so that there is no fear of being affected by the control signal value and the like, and the switching power supply is eliminated. It is possible to prevent an adverse effect of noise on a circuit device such as a drive circuit of a display device which is supplied with power from the device and which repeats operation at a constant cycle.

The reference wave signal generating means generates the reference wave signal with a waveform rising at a predetermined slope in synchronization with the synchronizing signal, and the comparison means compares the signal values of the reference wave signal and the control signal with the comparison result signal. In the embodiment of the present invention in which the switching means is turned on at the timing when the logic state changes during the rising of the waveform of the reference wave signal, the switching operation is performed by accurately determining the on operation timing according to the signal value of the control signal. It has the effect of enhancing the constant voltage performance of the output voltage. Further, an embodiment in which the reference wave signal is generated in the reference wave signal generating means by a sawtooth wave and the switching means is turned off at the timing of the fall of the waveform, and the comparison result signal by the comparing means is directly turned on / off to the switching means. Each of the embodiments used as a command has the effect of simplifying the circuit configuration of the switching power supply device.

A flip-flop for inputting a comparison result signal by the comparison means and a synchronizing signal is used, and the switching means is turned on and off by its output signal while alternately setting or resetting the flip-flop according to the change in the logic state of both signals. The aspect has an effect that there is almost no possibility that the OFF operation timing of the switching means may be disturbed due to the disturbance of the waveform of the reference wave signal.

In addition, the aspect in which the integral operation type differential amplifier is used as the voltage and current error amplifier has an effect of making the constant voltage operation of the switching power supply device accurate by using the control signal as a direct current signal containing no pulsating component.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a switching power supply device showing an embodiment of a control system of the present invention.

FIG. 2 is a circuit diagram of a switching power supply device showing another embodiment of the system of the present invention.

3 shows waveforms of main signals in the switching power supply device of FIG. 1 to show an operation example of the method of the present invention. FIG. 3 (a) is a waveform diagram of a synchronization signal, and FIG. 3 (b) is a reference wave. The waveform diagram of the signal and the control signal, FIG. 6C is the waveform diagram of the comparison result signal, and FIG. 7D is the waveform diagram of the current error signal and the current detection signal of the switching means.

FIG. 4 is a circuit diagram of a switching power supply device showing a conventional control method.

5A and 5B show waveforms of main signals in the switching power supply device of FIG. 4 to show the operation of the conventional control method. FIG. 5A is a waveform diagram of a synchronization signal, and FIG. 5B is a current error signal. And (a) is a waveform diagram of a current detection signal of the switching means, (c) is a waveform diagram of a comparison result signal of both signals, and (d) is a waveform diagram of an on / off command to the switching means.

[Explanation of symbols]

1 Switching means 1a Current detection resistor 10 Reference wave signal generation means 20 Control means 21 Voltage error amplifier 22 Current error amplifier 30 means of comparison Sc control signal Comparison result signal by Sd comparison means ON / OFF command for Se switching means SP sync signal V Power supply voltage of switching power supply Actual value of Va output voltage Vb switching means current detection signal Vc voltage error signal Vo Switching power supply output voltage Reference value for the actual value of Vr output voltage

Claims (6)

(57) [Claims] 1. A method of controlling a switching power supply device for extracting a constant controlled output voltage while intermittently switching a switching device at a period designated by a synchronizing signal, the reference wave having a constant waveform at a period synchronized with the synchronizing signal. A reference wave signal generating means for generating a signal and a switching power supply device.
Amplifies the difference between the actual value of the output voltage and the specified reference voltage value.
Pressure error amplifier, its voltage error signal value and switching
Amplifies the difference between the detection current of the stage and the signal value of the detection signal to control
A control means composed of a current error amplifier which outputs as a control signal and a comparison means for mutually comparing the signal values of the reference wave signal and the control signal are used, and the switching means is used as a comparison result of the comparison means. A control system for a switching power supply device characterized in that it is turned on in response to it and turned off in synchronization with a synchronization signal. 2. The method according to claim 1, wherein the reference wave signal has a waveform rising in synchronization with the synchronizing signal with a predetermined gradient, and the signal values of the reference wave signal and the control signal are mutually compared by a comparison means. A control system for a switching power supply device, characterized in that the switching means is turned on at the timing when the logical state of the result signal changes during the rising of the former waveform. 3. The system according to claim 1, wherein the reference wave signal has a sawtooth waveform rising at a predetermined gradient in synchronization with the synchronizing signal, and the switching means is turned off at the falling timing of the waveform. A switching power supply control method characterized by the above. 4. The method according to claim 1, wherein the comparison means compares the signal values of the reference wave signal and the control signal with each other to directly turn on / off the switching means in response to a change in its logic state. A control method of a switching power supply device characterized in that 5. The method according to claim 1, wherein a flip-flop for inputting a comparison result signal and a synchronizing signal by the comparing means is used, and the flip-flop is alternately set or reset according to a change in the logical state of both signals. However, the control method of the switching power supply device is characterized in that the switching means is turned on and off by the output signal thereof. 6. The method according to claim 1, wherein the voltage and
And an integral operation type differential amplifier is used as the current error amplifier.
Control method of a switching power supply device is characterized in that the so that.