JP4356110B2 - Switching power supply - Google Patents

Description

  The present invention relates to a switching power supply apparatus that reduces noise generated by a switching operation with a simple configuration.

  In recent years, interest in electromagnetic compatibility (EMC: Electro-Magnetic Compatibility) between devices has increased due to the rapid increase in control frequency in electronic devices and the spread of wireless communication such as mobile phones. In fact, there is a noise standard such as CE marking as an EMC-compliant standard, and various countermeasures are taken to suppress noise generated from electronic equipment. In particular, switching power supplies that are widely used as power supplies for electronic devices generate strong noises associated with switching operations, which may cause adverse effects such as malfunctions or malfunctions of other devices as noise sources, and noise suppression is strong. Requested.

As a conventional switching power supply device, there is one disclosed in Patent Document 1. This is achieved by full-wave rectifying commercial AC power with a diode bridge, suppressing harmonic currents with a PFC circuit (Power Factor Collect), and improving DC power by improving the power factor, and switching elements are turned on and off. The output voltage is extracted from the DC power. In such a switching power supply, since commercial AC power is used for the input power supply, a large amount of energy is generated during the switching operation, and strong switching noise accompanying the switching operation occurs. As a known technique for suppressing such switching noise, a snubber circuit, a tank circuit (resonance circuit), and various filters are known.
Japanese Patent Laid-Open No. 09-296036

  However, in the above conventional switching power supply device, there is a problem that switching noise occurs due to the switching operation of the switching element, and even if the noise countermeasure circuit as described above is provided, the noise is not effectively suppressed. For this reason, if measures are taken with a filter or the like, a large one is required, and an area and labor are consumed.

  SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a switching power supply apparatus that can effectively reduce noise including a fundamental wave component generated in association with a switching operation with a simple configuration.

The switching power supply device according to a further aspect of the present invention, the AC switching power supply device for taking out an output voltage from the voltage, rectified voltage obtained by rectifying the AC voltage is marked pressurized by dividing by on-off operation of the switching element Thus, the control frequency for controlling the on / off operation of the switching element is changed so as to fluctuate according to the amplitude of the AC voltage, and the switching element of the switching element is concentrated in a frequency band corresponding to the control frequency. the noise generated by, and configured to include a switching control means for Ru dispersed in the bandwidth in which the control frequency is fluctuating.

  In this case, the control frequency for controlling the on / off operation of the switching element increases / decreases in accordance with the amplitude of the AC voltage, so that the control frequency fluctuates. When the control frequency fluctuates, the switching frequency does not become constant, and noise that is concentrated in each band corresponding to the n-th harmonic of the switching frequency is dispersed in the bandwidth where the switching frequency fluctuates. The Rukoto. Therefore, the peak of the noise intensity within the measurement band can be averaged and reduced by the frequency fluctuation width. Further, since it is only necessary to change the control frequency in accordance with the amplitude of the alternating voltage originally having fluctuations, noise can be suppressed with a simple configuration.

  According to the first aspect of the present invention, it is possible to provide a switching power supply capable of averaging and reducing the noise intensity peak accompanying the switching operation by the frequency amplitude with a simple configuration.

  Hereinafter, preferred embodiments of a switching power supply according to the present invention will be described with reference to the accompanying drawings. Note that, in each of these embodiments, the same portions as those in the conventional example are denoted by the same reference numerals, and the description of the common parts will be omitted as much as possible.

  FIG. 1 shows a circuit diagram of a switching power supply device according to this embodiment. In the figure, reference numeral 2 denotes an AC input power source such as a commercial power source, which is connected to a pair of input terminals 3 and 4 of the switching power supply device 1. A diode bridge 5 is connected to the PFC circuit 6. The AC voltage supplied from the AC input power supply 2 via the pair of input terminals 3 and 4 is converted into a DC voltage by full-wave rectification by the diode bridge 5 and power factor improvement by the PFC circuit 6. A transformer 7 insulates the input side from the output side. The PFC circuit 6 is connected to one end of the primary winding 7a, and the drain of the switching element 10 made of a MOS FET is connected to the other end. The source of the switching element 10 is connected to the diode bridge 5, and the gate is connected to a PWM control IC 11 that controls the on / off operation (switching operation) of the switching element 10. In the PWM control IC 11, one end of the resistor 12 is connected to the resistor connection terminal 11 a, and one end of the capacitor 13 is connected to the capacitor connection terminal 11 b, and the other end of the resistor 12 and the capacitor 13 is connected to the source of the switching element 10 and the diode bridge 5. Connected to the line connecting The switching frequency of the switching element 10, that is, the control frequency of the PWM control IC 11 is determined by the time constant of the resistor 12 and the capacitor 13, and by changing the time constant, the control frequency also changes. In a generally used PWM control IC, when the value of the capacitor 13 is fixed, increasing the resistance value of the resistor 12 lowers the control frequency, and conversely, decreasing the resistance value of the resistor 12 increases the control frequency. Become. Reference numeral 14 denotes a resistor having one end connected to a connection point between the diode bridge 5 and the PFC circuit 6 and the other end connected to a connection point (resistance connection terminal 11a) between the PWM control IC 11 and the resistor 12.

  Further, the secondary winding 7 b which is the secondary side of the transformer 7 is provided with a rectifying / smoothing circuit 15 and a pair of output terminals 16 and 17, and an output voltage is taken out from the pair of output terminals 16 and 17. In addition, an output voltage detection circuit 18 is provided as a feedback loop for stabilizing the output voltage, and an output voltage feedback signal is sent from the output voltage detection circuit 18 to the PWM control IC 11. The PWM control IC 11 stabilizes the output voltage by performing well-known PWM control (pulse width control) on the pulse input to the gate of the switching element 10 based on the feedback signal.

  Next, the operation of the switching power supply device according to this embodiment will be described with reference to FIGS.

  FIG. 2 is a voltage waveform showing the switching operation of the switching element 10. In the figure, 20 is a DC voltage waveform after full-wave rectification by the diode bridge 5, and 21 is a pulse waveform input from the PWM control IC 11 to the gate of the switching element 10. The switching element 10 connected to the primary winding 7a of the transformer 7 performs a switching operation when the pulse waveform 21 is input from the PWM control IC 11 to the gate. That is, when the H level is input to the gate of the switching element 10, it is turned on, and when the L level is input, it is turned off. When the switching element 10 is turned on / off, a DC voltage is intermittently applied to the primary winding 7 a, a voltage is induced in the secondary winding 7 a of the transformer 7, and the output voltage is rectified and smoothed by the rectifying and smoothing 15. It becomes.

  At this time, the PWM control IC 11 outputs a pulse while performing PWM control based on the feedback signal sent from the output voltage detection circuit 18. That is, a pulse is output every cycle t0 while increasing or decreasing the conduction width t1 of the pulse waveform 21 input to the gate of the switching element 10 in order to stabilize the output voltage. The pulse period t0 representing the control frequency of the switching element 10 changes in magnitude according to the resistance value of the resistor 12 connected to the resistor connection terminal 11a of the PWM control IC 11 as described above. This means that the control frequency of the switching element 10 changes depending on the current value flowing out from the resistance connection terminal 11a as the input terminal of the oscillator (OSCILATOR) which is an oscillation circuit constituting the PWM control IC 11. Here, a voltage obtained by dividing the DC voltage waveform 20 by the resistor 14 and the resistor 12 is applied to the resistor connection terminal 11 a of the PWM control IC 11. Therefore, when the value of the DC voltage waveform 20 increases, the current flowing out from the resistance connection terminal 11a of the PWM control IC 11 decreases, and the control frequency of the switching element 10 also decreases. On the other hand, when the value of the DC voltage waveform 20 decreases, the current flowing out from the resistance connection terminal 11a of the PWM control IC 11 increases and the control frequency of the switching element 10 also increases. In this way, the control frequency of the switching element 10 and thus the switching frequency changes in a manner that fluctuates as the voltage waveform 20 changes.

  FIG. 3 exemplifies the measurement result of the noise generated in the switching power supply in this embodiment. 25 is an output frequency spectrum when the resistor 14 is not provided, and 26 is an output when the resistor 14 is provided. It is a frequency spectrum. When the resistor 14 is not provided, the control frequency of the PWM control IC 11 is fixed at a constant value, so that noise is concentrated in the frequency band corresponding to the switching frequency of the switching element 10, and the peak of the noise intensity greatly protrudes. It has become a form. On the other hand, when the resistor 14 is provided, since the control frequency of the PWM control IC 11 fluctuates, noise is dispersed in the bandwidth where the switching frequency of the switching element 10 changes, and the peak of the noise intensity does not protrude significantly. Recognize. Since such switching noise appears for each band corresponding to the n-th harmonic of the switching frequency, the noise intensity peaks in a certain bandwidth are averaged and reduced.

  As described above, in this embodiment, the switching element 10 is turned on / off in the switching power supply 1 that extracts the output voltage from the AC voltage supplied from the AC input power supply 2 by turning on / off the switching element 10. PWM control 11 is provided as switching control means for changing the control frequency for controlling the frequency according to the amplitude of the AC voltage.

  Further, the AC voltage supplied from the AC input power source 2 is full-wave rectified by the diode bridge 5, and the rectified voltage is divided by the resistors 14 and 12 to input an oscillator that constitutes the PWM control IC 11. By applying the voltage to the resistance connection terminal 11a as a terminal, the value of the current flowing out from the resistance connection terminal 11a is fluctuated.

  In this way, the control frequency for controlling the on / off operation of the switching element 10 increases or decreases according to the amplitude of the AC voltage supplied from the AC input power supply 2, so that the control frequency fluctuates. When the control frequency fluctuates, the switching frequency does not become constant, and noise that is concentrated in each band corresponding to the n-th harmonic of the switching frequency is dispersed in the bandwidth where the switching frequency fluctuates. The Rukoto. Accordingly, noise intensity peaks in a certain bandwidth can be averaged and reduced. In addition, since it is only necessary to change the control frequency in accordance with the amplitude of the AC power originally having fluctuations, noise can be suppressed with a simple configuration.

  In addition, this invention is not limited to the said Example, It can change in the range which does not deviate from the meaning of this invention. The switching power supply may be of various types such as forward type, flyback type, half bridge type, full bridge type, etc., and may be either a single stone type or a multi stone type.

1 is a circuit diagram of a switching power supply device according to a first embodiment of the present invention. It is a wave form diagram which shows switching operation of a switching power supply device same as the above. It is a wave form diagram which illustrated the measurement result of the noise which occurs in a switching power supply same as the above.

1 Switching power supply
10 Switching element
11 PWM control IC (switching control means)

Claims (1)

In the switching power supply device that extracts the output voltage from the AC voltage by turning on and off the switching element,
The rectified voltage an alternating voltage is rectified by is marked by dividing pressure, the control frequency for controlling the on-off operation of the switching element varied to fluctuate in accordance with the amplitude of the alternating voltage, the switching element with the switching operation, the control the noise generated by concentrating on a frequency band corresponding to the frequency, the switching power supply apparatus characterized by comprising a switching control means for Ru dispersed in the bandwidth in which the control frequency fluctuates with .

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