JP2008011587A - Power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an (auxiliary) power supply which can produce an output required for a load circuit stably without employing a voltage feedback circuit. <P>SOLUTION: The power supply comprises a transformer having a winding coupled with a main winding, a rectifier circuit connected with the winding of the transformer, and a series resonance circuit of the main winding of the transformer and a capacitor, and a resonance type power supply circuit generating output to the rectifier circuit by applying a square wave having a fixed frequency higher than the resonance frequency and a stabilized wave height to the series resonance circuit at a duty of 50%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a power supply device, and more particularly to a power supply device suitably used for an auxiliary power supply.

Conventionally, there is a converter circuit that converts a DC input voltage into a desired DC output voltage. Such a converter circuit is also used for a power supply device.
In recent years, DC-DC converter circuits including an AC stage in the middle have been used for various purposes. For example, when such a DC-DC converter circuit is used in an electronic device, it may be necessary to boost the DC voltage. At this time, the AC voltage is boosted and then converted to a high DC voltage by the rectifier circuit. The rectification is performed in two stages. The AC voltage is rectified and converted into a DC voltage, and then the DC voltage is converted into an AC voltage. Further, the AC voltage is rectified to obtain a desired DC voltage. be able to.

  In such a circuit, the conversion to the AC voltage is performed at a frequency higher than the commercial AC frequency, so that the transformer used for boosting and separating the voltage can be made smaller than the conventional transformer. In a DC-DC converter, a switching element and an energy conversion element are often used to obtain a predetermined output voltage. However, when such a switching element is used, a very high peak current often flows compared to a desired DC output current. In addition, electromagnetic interference has occurred with switching.

  In view of such a problem, a converter circuit including a tuning resonance circuit that generates an AC output waveform has been proposed (see, for example, Patent Document 1). According to this converter circuit, the switching means is held in a non-conductive state, and feedback is prevented during each cycle according to the output voltage. As a result, the frequency of the AC wave of the resonance circuit is changed somewhat according to the output level, and the output level is returned to a desired value by such frequency change.

  Since this converter circuit includes two switching elements and a series resonant circuit, the efficiency is improved. Since the current flowing through the transformer has a substantially sinusoidal shape close to the resonance frequency of the series resonance circuit, electromagnetic interference is reduced.

  However, the on / off timing setting of the switching element is delicate to improve the efficiency. If this setting is incomplete, it is difficult to improve the efficiency, and in some cases, it may be necessary to detect the circuit current or the like to determine the timing. In such a case, the circuit configuration is complicated. .

  In view of such a point, a power supply apparatus having a simple configuration and high efficiency has been proposed (see, for example, Patent Document 2).

  This power supply circuit includes a DC power supply and a switching element that can be controlled to be turned on / off, switching means for switching the DC power supply to convert it to AC, and outputting, and a full-wave rectification of the supplied AC input by a capacitor. DC output means for smoothing and taking out DC output, series resonance means formed in series between the output end of the switching means and the input end of the DC output means, and parallel to both ends of the switching element of the switching means The on-off control of the parallel resonance means formed on the switching means and the switching element of the switching means are periodically controlled, and after the switching means is turned on, the current flowing through the switching means is terminated by the end of the series resonance by the series resonance means. The switching means is turned off after becoming almost zero, and the switching means is turned off after the switching means is turned off. The voltage applied to the switching means and a control timing control means so as to turn on the switching means after reaching approximately zero changed by the parallel resonance by the parallel resonance means.

  According to this power supply circuit, since the entire switching operation of the switching element is performed at either zero voltage or zero current, the switching loss is very close to zero, and the efficiency of the entire circuit becomes extremely high. In addition, both the series resonance current and the parallel resonance voltage have a spectrum close to a single frequency, and the possibility of ringing or overshooting by buffering with the resonance dip of each part of the circuit is drastically reduced. Therefore, unnecessary radiation such as harmonics is extremely reduced.

  That is, the current and voltage waveforms are made closer to a sine wave by using resonance to reduce noise and to reduce switching loss. Further, the ON / OFF timing of the switching transistor may be fixed, the setting is easy, and the entire circuit can be designed simply.

  In recent years, liquid crystal displays (LCDs) have become widespread, and there is a demand for more efficient power supply devices used for the backlights.

  From this point of view, for example, a dual boost power factor calibration (Dual Boost PFC) circuit converts a power frequency AC voltage directly input into a DC bus voltage of several hundred volts, and an input current power factor calibration function. An realized power supply device has been proposed (see, for example, Patent Document 3).

  In this power supply, since one power frequency rectifier is saved, this PFC can obtain higher efficiency. Also, unlike the traditional + 24V input voltage, the input voltage of the backlight inverter in the power supply system is several hundred volts DC voltage, which is directly derived from the output voltage of the backlight inverter circuit of the pre-class PFC circuit It is.

  Because it is a direct current / direct current (DC / DC) converter via a previous class PFC circuit and a backlight inverter, it has a simpler structure and lower material cost. Therefore, higher transmission efficiency can be obtained, which is suitable for thermal structure design under natural cooling work conditions.

  In addition to this, an input voltage generating means for generating a DC input voltage by inputting a commercial AC power supply, and a primary side that is a commercial AC power supply side by inputting the DC input voltage and performing DC-DC power conversion. And a first power conversion means for generating a DC power supply voltage to be supplied to a predetermined load on the secondary side that is DC-insulated (see, for example, Patent Document 4).

  In this power supply device, a DC input voltage is inputted and power conversion is performed by DC-AC conversion, so that the secondary side of the commercial AC power supply side that is galvanically isolated from the primary side is connected to the display device. Second power conversion means for generating a power supply voltage to be supplied to the backlight unit is provided.

According to this power supply apparatus, the second power conversion unit directly inputs the DC voltage generated by the input voltage generation unit, not the DC output voltage output from the first power conversion unit. Will work. That is, this power supply device is configured not to employ a circuit configuration in which power conversion is performed a plurality of times.
Japanese Patent Publication No.54-43168 Japanese Patent No. 2722869 JP 2005-316429 A JP 2005-20992 A

  However, in the conventional power supply device described in Japanese Patent Publication No. 54-43168, a large area is required to form a feedback circuit for voltage stabilization on the substrate (particularly in the case of a power supply having a primary and a secondary). In short, there is a problem that it is difficult to reduce the size.

  Further, in the power supply device described in Japanese Patent No. 2722869, the on / off timing of the switching transistor is fixed and the circuit is simplified, but at least a circuit for timing control means is required, so it is difficult to reduce the size. It had the problem that.

  Furthermore, in the power supply devices described in JP-A-2005-316429 and JP-A-2005-20992, since both the main power supply circuit and the inverter circuit are independent, both require a feedback circuit or a control circuit. There was a problem that it was difficult to downsize. FIG. 6 is a diagram showing an example of such a conventional power supply device for lighting a cold cathode tube.

  The present invention solves the above-mentioned conventional problems, and provides an (auxiliary) power supply device configured to obtain a substantially stable output required by a load circuit without using a voltage feedback circuit. Objective.

  In order to solve the conventional problem, a power supply device of the present invention is connected to a series resonance circuit in which a main winding and a capacitor of a transformer are connected in series, and to a sub winding of the transformer, and A rectifier circuit that rectifies the output of the sub-winding and supplies a DC voltage to the load, and the transformer converts the square wave voltage having a constant frequency higher than the resonance frequency of the series resonance circuit and a constant peak value to the transformer. It is applied to the main winding and operates.

  Further, according to the present invention, the impedance of the main winding of the transformer is constant in the fluctuation range of the load.

  Furthermore, according to the present invention, at the time of start-up, the frequency of the square wave voltage is set higher than the frequency in the steady operation state.

  Further, the present invention includes a square wave voltage generating means for generating a square wave voltage and supplying the square wave voltage to a plurality of portions, one of the plurality of portions being a main winding of the transformer.

  Furthermore, the present invention provides a power supply device comprising a low-voltage power supply and a backlight power supply for supplying power to a cold cathode tube, wherein the backlight power supply generates two signals of square wave voltage, A transformer for turning on the cold cathode tube with the two signals as input, and adjusting the output of the transformer by changing the phase of the two signals to supply power to the cold cathode tube; The square wave is supplied to the main winding of the low-voltage power source.

  Furthermore, the present invention is configured such that a square wave voltage is supplied from both ends of the main winding of the transformer, the low-voltage power source is connected to one end of the main winding, and a coil and a capacitor are connected to the other end of the main winding. Are connected in series.

  According to the power supply device of the present invention, a small (auxiliary) power supply with low noise can be realized.

  Embodiments of a power supply apparatus according to the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is a circuit diagram of a power supply device according to a first embodiment showing an example of the present invention.

  In the first embodiment, the transformer 2 has a winding ratio of 1: N, where N is a positive number. The transformer 2 has two main windings and two sub-windings having the same number of turns, and a capacitor 1 and the main winding of the transformer 2 form a series resonance circuit, and outputs according to the turn ratio. Output to the secondary winding. The output of the transformer 2 is converted into direct current by the rectifier circuit 3 and supplies a direct current voltage to the load 4.

  In the power supply device of the first embodiment configured as described above, the applied square wave voltage has a constant frequency, a duty of 50%, and a constant wave height. The inductance of the main winding is set to be sufficiently small in order to maintain the resonance point in the fluctuation range of the load 4. Here, assuming that the capacitance of the capacitor 1 becomes a constant value within the fluctuation range of the load 4, the square wave voltage that is the input signal, the inductance that determines the resonance frequency, and the capacitance value are constant, and the output voltage is constant. Thus, a power supply device that does not require a feedback circuit can be configured. The square wave voltage is converted by the transformer 2 into two sine wave voltages having a phase difference of 180 degrees.

  In the rectifier circuit 3, one sine wave voltage is converted into a half wave having only a positive half cycle by the rectifier, and the other sine wave is output by the other rectifier as a half wave having a phase different from that of the half wave by 180 degrees. Then, the combined signal is charged in the capacitor, and a DC voltage is supplied to the load (full wave rectification).

  As described above, in the first embodiment, the voltage (square wave) applied to the resonance circuit constituted by the main winding of the transformer 2 and the capacitor 1 is constant in frequency, the duty is 50%, the wave height is constant, and By making the inductance of the main winding stable with respect to load fluctuations, it is possible to obtain a stable output without requiring a feedback circuit for voltage control, and to reduce the size.

  In the first embodiment, the voltage (square wave) applied to the resonance circuit composed of the main winding of the transformer 2 and the capacitor 1 at the time of start-up is higher than that during normal operation. In addition, it is possible to limit the current flowing through each element, and it is also possible to use a component with a small rated current.

  FIG. 2 is a circuit diagram of the power supply device according to the second embodiment of the present invention. In FIG. 2, the drive circuit 5 includes a transformer 6, a switching element 7 and a switching element 8 having a main winding having a turns ratio of 1: N and a sub-winding having the same number of turns. , A transformer 10 having a main winding having a turns ratio of 1: N, a sub-winding having an equal number of turns, a switching element 11 and a switching element 12, and the transformer 13 is a cold cathode tube. 14.

  The difference from the power supply device described in the first embodiment is that the method for supplying the voltage (square wave) applied to the resonance circuit composed of the main winding of the transformer 16 and the capacitor 15 is more specifically shown. .

  In FIG. 2, the drive circuit 5 outputs a square wave synchronized with the voltage waveform VA supplied from the oscillation circuit, and the drive circuit 9 outputs a square wave synchronized with the voltage waveform VB supplied from the oscillation circuit. The transformer 13 is supplied with a voltage waveform VC-VD, which is an output from the drive circuit 5 and the drive circuit 9, to the main winding, and outputs an output proportional to the phase difference between the voltage waveform VA and the voltage waveform VB. To supply.

  FIG. 3 shows a voltage waveform VA, a voltage waveform VB, and a voltage waveform VC-VD, and the output of the cold cathode tube 14 is adjusted by controlling the voltage waveform at a timing according to this principle diagram.

  In the power supply device according to the second embodiment configured as described above, the drive circuit 5 is configured such that the switching element 7 is turned on in the positive half cycle of the voltage waveform VA, outputs “H” to the VC point, and the voltage waveform VA is In the negative half cycle, the switching element 8 is turned on, outputs “L” to the point VC, and outputs a voltage waveform VC synchronized with the voltage waveform VA.

  The drive circuit 9 outputs a voltage waveform VD synchronized with the voltage waveform VB in the same manner as the operation of the drive circuit 5. The transformer 13 receives a voltage waveform VC-VD, which changes depending on the phase difference between the voltage waveform VC and the voltage waveform VD, in the main winding (FIG. 3). A wave is supplied to the cold cathode tube 14, and the cold cathode tube is turned on.

  In addition, the power supply device including the capacitor 15, the transformer 16, and the rectifier circuit 17 having the same configuration as that of the power supply device according to the first embodiment receives the voltage waveform VC or the voltage waveform VD as an input, so A voltage can be supplied.

  As described above, the resonance circuit, the drive circuit, and the switching element that generate the voltage waveform VC originally required for the power supply device of the first embodiment by connecting the power supply device of the first embodiment to the drive circuit 5 of the second embodiment. Can be omitted.

  FIG. 5 is a schematic diagram of the power supply device. As shown in FIG. 5, the power supply device shown in the second embodiment does not require the control circuit 27 as compared with the conventional power supply device shown in FIG. For this reason, size reduction of an apparatus can be achieved.

  Further, since the power supply device of the first embodiment is a resonance type power supply, the noise is smaller than that of a non-resonance type power supply, and the noise is reduced by not requiring a means for generating the voltage waveform VC. (Auxiliary) power supply can be built.

  Further, by connecting a series circuit including a capacitor 19 and a coil 20 to the other drive circuit 9 of the second embodiment, heat generation of the power supply circuit of the second embodiment can be suppressed to a lower level (FIG. 4).

  The power supply apparatus according to the present invention has a low noise and a small (auxiliary) power supply, and is useful as a power supply apparatus for a liquid crystal television.

1 is a circuit diagram of a power supply device according to a first embodiment of the present invention. Circuit diagram of the power supply device in Embodiment 2 of the present invention Principle diagram of a power supply device in Embodiment 2 of the present invention Circuit diagram of the power supply device in Embodiment 2 of the present invention The block diagram of the power supply device in Example 2 of this invention Block diagram of a conventional power supply

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Capacitor 2 Transformer 3 Rectifier circuit 4 Load 5, 9 Drive circuit 6, 10 Transformer 7, 8, 11, 12 Switching element 13 Transformer 14 Cold cathode tube 15 Capacitor 16 Transformer 17 Rectifier circuit 18 Load 19 Capacitor 20 Coil 21 Commercial Power Supply 22 PFC Circuit 23 Low Voltage Power Supply Circuit 24 Backlight Power Supply Circuit 25 DC Load 26 Cold Cathode Tube 27 Control Circuit 28 Low Voltage Power Supply Circuit

Claims (6)

A series resonance circuit in which a main winding of a transformer and a capacitor are connected in series, and a rectification circuit that is connected to the sub winding of the transformer and rectifies the output of the sub winding and supplies a DC voltage to a load. And a square wave voltage having a constant frequency higher than the resonance frequency of the series resonance circuit and a constant peak value is applied to the main winding of the transformer to operate. The power supply device according to claim 1, wherein an impedance of a main winding of the transformer is constant in a fluctuation range of the load. 3. The power supply device according to claim 1, wherein at the time of startup, the frequency of the square wave voltage is set to a frequency higher than a frequency in a steady operation state. The square wave voltage generating means for generating a square wave voltage and supplying the square wave voltage to a plurality of parts, wherein one of the plurality of parts comprises a main winding of the transformer. The power supply apparatus in any one. 5. A power supply device comprising: a low-voltage power supply comprising the power supply device according to claim 1; and a backlight power supply for supplying power to a cold cathode tube, wherein the backlight power supply is a square wave voltage. A two-signal generating means for generating two signals, and a transformer for turning on the cold-cathode tube using the two signals as input, and adjusting the output of the transformer by changing the phase of the two signals. A power supply device that supplies power to the cold cathode tube and supplies the square wave to a main winding of the low-voltage power supply. A square wave voltage is supplied from both ends of the main winding of the transformer, the low-voltage power source is connected to one end of the main winding, and a coil and a capacitor are connected in series to the other end of the main winding. The power supply device according to claim 5.