JPH0353776A - Switching power supply device - Google Patents

Abstract

PURPOSE:To prevent a switching noise from appearing on a monitor screen by constituting a switching power supply device with a comparator comparing an output voltage with a reference voltage, a phase comparator and an oscillator and setting a switching element to be operated at a blank period of a drive signal. CONSTITUTION:An output voltage Vo is compared with a reference voltage Vr at a comparator 9, and when the output voltage Vo is, e.g. decreased, an inverting voltage is inputted to an oscillator 11 and the oscillating frequency of the oscillator 11 is increased. The frequency signal is applied to a switching element 1, the switching frequency of the element 1 gets higher and the output voltage Vo is increased. When a switching phase is, e.g. retarded, an error signal being an output of a phase comparator 10 is increased and a voltage fed to the oscillator 11 is also increased. As a result, the phase of the output of the oscillator 11 is advanced and the switching phase is also advanced. Thus, no switching noise appears on the monitor screen by applying the switching for an idle period of the drive signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a switching power supply device used in video equipment such as televisions and video cameras.

<Prior Art> In video equipment such as televisions and videos, switching power supplies are used to obtain stable output voltages. There are various types of conventional switching power supplies, and FIG. 2 shows a circuit of a switching power supply using a pulse width control method as a typical example.

This switching power supply device includes a switching element 1 consisting of a transistor that intermittently oscillates an input voltage Vi at a high frequency and converts it into an AC voltage, a transformer 2 that transforms the AC voltage and outputs it to the secondary side, and a transformer 2 that transforms the AC voltage and outputs it to the secondary side. a smoothing circuit 3 that rectifies and smoothes the AC output of
A control circuit 4 that performs feedback control so that
It is equipped with

The control circuit 4 includes a differential amplifier 5 that compares the output voltage Vo with a reference voltage Vr and outputs an error signal E, and compares this error signal E with a sawtooth wave generated from a sawtooth wave generator 6. a comparator 7 that converts the increase or decrease in the error signal E into a pulse width and outputs it as a pulse width control signal P; and the comparator 7
The isolator 8 inputs the pulse width control signal P from the switching element 1 to the switching element 1.

Next, the operating principle will be explained. As shown in FIG. 3, in order to obtain a stable output voltage, the output voltage is controlled by keeping the frequency constant and changing the pulse width. The following relationship exists between the output voltage and the pulse width.

However, Vo2 output voltage Vin: Input voltage Ton: Switching transistor on period T: Switching frequency Period The error signal E between the output voltage and the reference voltage is compared with the sawtooth wave by the comparator 7, and the increase or decrease of the error signal E is determined. Convert to pulse width.

When the output voltage decreases, the pulse width of the pulse width control signal P becomes wider, and as a result, the output voltage increases and the output voltage is kept constant.

<Problems to be Solved by the Invention> Generally, switching power supply devices are used in a wide range of areas to meet the demands for smaller size and energy saving of electrical products.
Since switching noise is large, countermeasures against this noise are required.

Especially in video equipment, the switching power supply operates independently of the video signal of the video equipment, and this switching noise is superimposed on the video signal, causing a cathode built in the video equipment or connected externally.・This is periodic noise that appears on a certain monitor screen from an image display element such as a ray tube (CRT) or liquid crystal display element, so it becomes a very noticeable noise on the monitor screen, and it is a few mVrms with respect to the video signal IVp-p. It needs to be at a very small level below.

Therefore, countermeasures such as component arrangement, printed circuit boards, shields, noise filters, etc. are required, and these countermeasures require a large amount of labor and cost.

SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to provide a switching power supply device that can easily take measures against noise by performing switching so that switching noise does not appear on a monitor screen of a video device or the like.

Means for Solving the Problems> The means for solving the problems according to the present invention, as shown in FIG. A transformer 2 that outputs to the secondary side, a smoothing circuit 3 that rectifies and smoothes the alternating current output from the transformer 2 and outputs it, and a control circuit 4 that performs feedback control so that the output voltage vO is constant. The circuit 4 includes a comparator 9 that compares the output voltage VO with a reference voltage Vr, and a phase comparator 10 that compares the phase of the AC output from the transformer 2 with a drive signal D such as a video signal.
and an oscillator II that changes the oscillation frequency and phase of the switching element l according to the output signals of the comparator 9 and the phase comparator IO, so that the switching element l operates during the blank period of the drive signal D. It has been set.

Effect> In the above problem solving means, a DC input voltage Vi obtained by rectifying and smoothing a commercial power source is oscillated at high frequency by a switching element 1, transformed by a transformer 2, and outputted as an AC output to the secondary side. Then, it is rectified and smoothed by the smoothing circuit 3, and a DC output voltage Vo is output.

To control the output voltage Vo, the output voltage Vo is compared with the reference voltage Vr by the comparator 9. For example, when the output voltage VO decreases, the inverted voltage output high by the comparator 9 is input to the oscillator it, and the output voltage of the oscillator l1 is inputted to the oscillator it. The oscillation frequency becomes higher. This frequency is applied to the switching element 1, and the switching frequency of the switching element 1 increases, resulting in an increase in the output voltage VO.

On the other hand, the phase of the switching is compared with the drive signal D obtained by synchronously separating the phase of the AC output from the transformer 2 from the video signal in the phase comparator 10, and the error signal is added to the oscillator 1l.

For example, if the switching phase is delayed, the phase comparator lO
The error signal, which is the output of , rises, and the voltage applied to oscillator ll also rises. As a result, the phase of the output of the oscillator 11 advances, and the phase of the switching also advances. Here, since the switching phase is set to correspond to the blank period of the horizontal drive signal D, switching noise does not appear on the monitor screen.

Therefore, by synchronizing the switching frequency and phase with the drive signal of the video signal and performing switching during the blank period of the drive signal, it is possible to prevent switching noise from appearing on the monitor screen. It is no longer necessary to thoroughly consider the arrangement of PCBs, printed circuit boards, shields, noise filters, etc., and the labor and costs for these countermeasures can be significantly reduced.

<Example> Hereinafter, one embodiment of the present invention will be described based on FIG.

FIG. 1 is a circuit diagram of a switching power supply device showing one embodiment of the present invention. It should be noted that the same reference numerals are given to the same components as before.

As shown in the figure, the switching power supply device of this embodiment includes a switching element 1 consisting of a transistor that intermittently oscillates an input voltage Vi at high frequency and converts it into an AC voltage, and a transformer that transforms the AC voltage and outputs it to the secondary side. 2, and a smoothing circuit 3 consisting of a diode, a capacitor, a choke coil, etc., which rectifies and smoothes the AC output from the transformer 2 and outputs the same.
and a control circuit 4 that performs feedback control so that the output voltage Vo is constant.

The control circuit 4 includes a comparator 9 that compares the output voltage Vo with a reference voltage Vr, a phase comparator 1O that compares the phase of the AC output from the transformer 2 with a drive signal 4o such as a video signal, and the comparator 9 and It consists of an oscillator 2 that changes the oscillation frequency and phase of the switching element 1 according to the output signal of the phase comparator 10, and the switching element 1 changes the drive signal to prevent switching noise from appearing on the monitor screen of the video equipment. It is set to operate during the blank period of D.

The comparator 9 is composed of an inverting differential amplifier, and its negative input terminal is connected to a DC power supply that outputs a reference voltage Vr,
The positive input terminal is connected to one side of the output terminal O.

The phase comparator 1O is composed of a phase detector (PSD), and the horizontal drive signal D obtained by synchronously separating the video signal is input as a reference signal.

The oscillator 11 is composed of a voltage controlled oscillator (VCO), and usually oscillates at a horizontal frequency, and the oscillation frequency changes depending on the input amplitude.

One side of the input terminal I is connected to the collector terminal of the transistor of the switching element l, and the other side is connected to the collector terminal of the transistor of the switching element l.
It is connected to the emitter terminal of the transistor through the primary winding of the transistor. The base terminal of the transistor is connected to the control circuit 4 via an isolator 8. Further, the output terminal O is connected to the secondary winding of the transformer 2 via the smoothing circuit 3.

Note that 13 in the figure is an addition point that adds the output signals from the comparator 9 and the phase comparator IO and outputs the result to the oscillator 11. The other configurations are the same as the conventional configuration.

In the above configuration, the DC input voltage Vi obtained by rectifying and smoothing the commercial power supply is controlled by the switching element L at a frequency of several hundred KHz, for example.
oscillates intermittently at a high frequency and converts it into pulsed alternating current.

This pulse wave is transformed by a transformer 2 and output as an AC output to the secondary side. Then, the smoothing circuit 3 performs rectification and smoothing to output a DC output voltage vO.

To control the output voltage Vo, first, the comparator 9 compares the output voltage Vo with a reference voltage Vr. For example, when the output voltage Vo decreases, the inverted voltage output high by the comparator 9 is input to the oscillator l1, and the oscillation frequency of the oscillation Bit increases.

This frequency is applied to the switching element 1 via the isolator 8, and the switching frequency of the switching element 1 increases, resulting in an increase in the output voltage Vo. In this way, feedback is applied so that the output voltage Vo becomes constant.

On the other hand, the switching phase is compared with the horizontal drive signal D obtained by synchronously separating the phase of the AC output from the transformer 2 from the video signal in the phase comparator 10, and the error signal is output from the oscillator 1! added to. For example, if the switching phase is delayed, the error signal, which is the output of the phase comparator lO, will rise, and the voltage applied to the oscillator l1 will also rise. As a result, the phase of the output of the oscillator 1l advances, and the phase of the switching also advances. In this way, feedback is applied so that the switching phase is also constant.

Here, if the switching phase is set to correspond to the blank period of the horizontal drive signal D, switching noise will not appear on the monitor screen.

Therefore, by synchronizing the switching frequency and phase with the horizontal drive signal of the video signal and performing switching during the blank period of the drive signal, it is possible to prevent switching noise from appearing on the monitor screen. Therefore, it is no longer necessary to thoroughly consider the arrangement of components, printed circuit boards, shields, noise filters, etc. as noise countermeasures, and the labor and cost for these countermeasures can be significantly reduced.

It should be noted that the present invention is not limited to the above embodiments, and it goes without saying that many modifications and changes can be made to the above embodiments within the scope of the present invention.

<Effects of the Invention> As is clear from the above description, the present invention provides a comparator that compares the output voltage with a reference voltage, and a phase comparator that compares the phase of the AC output from the transformer with a drive signal such as a video signal. and an oscillator that changes the oscillation frequency and phase of the switching element according to the output signals of the comparator and the phase comparator.The switching element is set to operate during the blank period of the drive signal, so that the monitor screen It is possible to prevent switching noise from appearing on
It is no longer necessary to thoroughly consider shields, noise filters, etc., and there is an excellent effect that the labor and cost for these measures can be significantly reduced.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a switching power supply device showing an embodiment of the present invention, FIG. 2 is a circuit diagram of a conventional pulse width control type switching power supply device, and FIG. 3 is a time chart thereof. 1: switching element, 2: transformer, 3: smoothing circuit,
4: Control circuit, 9: Comparator, lO two-phase comparator, 1l:
Oscillator, D: Drive signal. Sharp Co., Ltd. Tsunehisa Nakamura Figure 2 Figure 3 Figure l: ZuA,,,Na) 7゛ Thread 2: Tofu Messenger: Le Soft Each A: Ieba 8l Futatsu Chihi each ll: Salary analysis: Y Raigui Yorau

Claims (1)

[Claims] A switching element that intermittently oscillates an input voltage at high frequency and converts it into an AC voltage, a transformer that transforms the AC voltage and outputs it to the secondary side, and a smoothing circuit that rectifies and smoothes the AC output from the transformer and outputs it. , a control circuit that performs feedback control so that the output voltage is constant, and the control circuit includes a comparator that compares the output voltage with a reference voltage, and a control circuit that compares the phase of the AC output from the transformer with a drive signal such as a video signal. Comprised of a phase comparator for comparison, and an oscillator that changes the oscillation frequency and phase of a switching element according to the output signals of the comparator and the phase comparator, and the switching element is set to operate during a blank period of the drive signal. A switching power supply device characterized by: