JP2010045971A - Switching power supply unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power supply unit which further reduces power consumption. <P>SOLUTION: A switching power supply unit 1 includes a rectifier circuit B1 to rectify an alternating current from an alternating current power supply into a direct current, a switching circuit to switch the current rectified by the rectifier circuit B1 via a switching element Q1, a pulse oscillator circuit IC 71 to output a switching signal to the switching element Q1, a transformer circuit T1 to step up or down the voltage using the current switched by the switching circuit IC 71, and a feedback circuit 80 to transmit a feedback signal to the pulse oscillator circuit IC 71 so that a conduction angle of the switching signal may become 0.35 or less in a rated mode. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a switching power supply apparatus that performs control using a switching element.

  Conventionally, an RCC (Ringing Choke Converter) method exists as one type of switching power supply device. This RCC switching power supply is configured such that the switching element self-oscillates without requiring an external clock or the like, and is also called a self-excited flyback converter.

  As a feature of this RCC type switching power supply device, the circuit configuration becomes very simple and can be produced at low cost. In addition, since it is self-excited, it has a feature that the output can be stabilized by changing the switching frequency according to the internal current / voltage conditions. Generally, an RCC switching power supply device shifts to a low frequency when the load is large, and stabilizes the output by shifting to a high frequency when the load is small.

  However, this RCC switching power supply device has a problem that power consumption due to a switching operation increases because a switching frequency increases in a low load state. In particular, in a situation where the load is extremely low as in the standby mode, an increase in power consumption on the power supply device side becomes apparent.

  In order to reduce power consumption at low load, there is a switching power supply that forcibly switches the frequency to low frequency at low load, which is shown in FIG. This switching power supply device includes an AC power supply CN1, a first rectification bridge D1 connected to the AC power supply CN1, a main switching element Q1, a primary winding and a secondary winding, and a transformer T1 functioning as a transformer circuit, A pulse oscillation circuit IC1 for outputting a switching signal to the main switching element Q1 is provided.

  The drain of the switching element Q1 is connected in series to one end of the primary winding of the transformer T1. The other end of the primary winding is connected to the positive DC pole of the first rectification bridge D1. Further, the negative DC pole of the first rectification bridge D1 is connected to the source of the switching element Q1. A smoothing capacitor C8 is connected between the positive DC pole and the negative DC pole of the first rectifying bridge D1, and serves as a DC power source by a rectifying action.

  A second rectification bridge D2 is further connected to the AC power supply CN1 side, and a pulse oscillation circuit IC1 is connected between the DC poles of the second rectification bridge D2. As a result, the voltage at the time of activation of the pulse oscillation circuit IC1 is supplied from the second rectification bridge D2.

  The output terminal OUT of the pulse oscillation circuit IC1 is connected to the gate of the switching element Q1, and the current detection terminal ISNF of the pulse oscillation circuit IC1 is connected to the source of the switching element Q1.

  The switching power supply device further includes an internal detection circuit 11 that detects a pulse signal supplied from the pulse oscillation circuit IC1. The internal detection circuit 11 controls the frequency of the switching signal of the switching circuit IC1. The internal detection circuit 11 includes a pulse detection circuit 12 that detects a switching signal (pulse output) supplied from the pulse oscillation circuit IC1, and here, resistors R16, R17, and R18 and a capacitor C7 exhibit their functions. To do. The pulse detection circuit 12 is connected between the gate of the switching element Q1 and the output terminal OUT of the pulse oscillation circuit IC1, and outputs a detected switching signal to the base of the switching element Q4.

  Further, the internal detection circuit 11 includes a DC signal level conversion circuit 13. The DC signal level conversion circuit 13 is connected between the collector and emitter of the switching element Q4. The DC signal level conversion circuit 13 includes a plurality of negation circuits IC4A to IC4D, a diode D7, a capacitor C16, and resistors R23 and R27. With these configurations, the pulse signal detected by the pulse detection circuit 12 is converted into a DC signal. Convert to level. When the on-time of the pulse oscillation circuit IC1 is relatively long, the capacitor C16 is sufficiently charged, and the DC signal level is in a high level during that time. On the other hand, when the on-time of the pulse oscillation circuit IC1 is relatively short, the capacitor C16 is not sufficiently charged and the DC signal level is in a low level state. When a low DC signal level is input to the negative circuit IC4B in the DC signal level conversion circuit 13, it is changed to a low frequency instruction signal (here, an ON signal), and on the contrary a high DC signal level is input. Then, it is converted into a high frequency instruction signal (here, an OFF signal).

  The internal detection circuit 11 includes a frequency switching circuit 14. The frequency switching circuit 14 includes a switching element Q3. The control terminal of the switching element Q3 is connected to the negation circuit IC4B of the DC signal level conversion circuit 13, and the low frequency instruction signal (ON signal) or the high frequency instruction signal (OFF signal) output from the negation circuit IC4B is This is input to the switching element Q3. The input terminal of the switching element Q3 is connected in series with the first capacitor C2. A second capacitor C17 is connected so as to be parallel to the series circuit of the switching element Q3 and the first capacitor C2.

  Therefore, when the low frequency instruction signal (ON signal) is transmitted to the frequency switching circuit 14, the switching element Q3 is turned on. When the switching element Q3 is turned on, the capacitor C2 is charged, and the switching frequency of the pulse oscillation circuit IC1 is lowered. On the other hand, when a high frequency instruction signal (OFF signal) is transmitted to the frequency switching circuit 14, the switching element Q3 is turned off. When the switching element Q3 is turned off, the capacitor C2 is discharged, the switching frequency of the pulse oscillation circuit IC2 is increased, and the power is increased.

JP 2004-187479 A

  The required level of power saving tends to increase with the recent lack of energy resources. Therefore, the conventional switching power supply device has a problem that it cannot sufficiently meet the demand.

  In particular, since the conventional switching power supply device is designed with an emphasis on labor saving in the rated mode, the power efficiency tends to decrease during the standby mode and during startup. For example, in the RCC switching power supply, as described above, the deterioration of efficiency at the time of low load becomes a problem. Further, as shown in FIG. 8, the conventional switching power supply device shown in FIG. 7 is in an early time constant state because the capacitor C2 and the like of the frequency switching circuit 14 are not charged at the time of startup, and the pulse oscillation circuit IC1 The switching signal always starts from the high frequency H. Due to the high frequency H, the voltage rise at the time of start-up is quick, but then an overcurrent (surge current) flows into the pulse oscillation circuit IC1 through the resistor R5, and the circuit IC1 forcibly reduces the output to suppress the output. Switch to. As a result, there is a problem that the power consumption increases because the start-up starts from the high frequency H. In addition, after the start-up, there is a problem in that switching from the high frequency H to the low frequency L occurs and the output drop X1 occurs at a light load stage.

  Furthermore, since the frequency switching circuit 14 is configured to switch the frequency using the capacitors C17 and C2, there is a problem that the responsiveness is poor due to the charge / discharge operation. Specifically, as shown in FIG. 8, even if the DC signal level rises when the switching signal is in the low frequency L state and the high frequency instruction signal is input to the frequency switching circuit 14, it takes time to discharge the charge in the capacitor C2. Therefore, the timing at which the frequency switching instruction is actually transmitted to the pulse oscillation circuit IC1 is delayed. As a result, since the switching frequency is switched from the low frequency L to the high frequency H after the output voltage has increased sufficiently, a large output capacity drop X2 occurs at the time of switching, and a smooth output characteristic cannot be obtained. was there.

  The present invention has been made in view of the above-mentioned problems, and can achieve labor saving as compared with the conventional case, and further, when the load is low while reducing a drop in output at the time of start-up or at the time of high-frequency transition. Another object of the present invention is to provide a switching power supply device in which the rising waveform is stable.

  To achieve the above object, the present invention provides a rectifier circuit that rectifies alternating current from an alternating current power source into direct current, a switching circuit that switches the voltage rectified by the rectifier circuit using a switching element, and the switching element. A pulse oscillation circuit for outputting a switching signal having a high frequency in the rated mode and a low frequency in the standby mode, a transformer circuit for stepping up or down the voltage by a current switched by the switching circuit, and a conduction angle of the switching signal. For the pulse oscillation circuit, the output voltage of the transformer circuit is detected and compared with a reference voltage so that the voltage is 0.35 or less in the rated mode and 0.11 or less in the standby mode. A feedback circuit that transmits a feedback signal based on a comparison circuit that comprises: The switching signal generated by the oscillation circuit is set so that the pulse width on the high frequency side is smaller than the pulse width on the low frequency side when comparing before and after shifting from the low frequency to the high frequency. And the peak value of the drain current supplied to the switching element based on the switching signal is set to be smaller in the standby mode than in the rated mode. It is.

  To achieve the above object, the present invention provides a rectifier circuit that rectifies alternating current from an alternating current power source into direct current, a switching circuit that switches the voltage rectified by the rectifier circuit using a switching element, and the switching element. A pulse oscillation circuit for outputting a switching signal having a high frequency in the rated mode and a low frequency in the standby mode, a transformer circuit for stepping up or down the voltage by a current switched by the switching circuit, and a conduction angle of the switching signal. For the pulse oscillation circuit, the output voltage of the transformer circuit is detected and compared with a reference voltage so that the voltage is 0.35 or less in the rated mode and 0.11 or less in the standby mode. A feedback circuit that transmits a feedback signal based on a comparison circuit that comprises: The switching signal generated by the oscillation circuit has an average pulse on the high frequency side compared with an average pulse width on the low frequency side when comparing before and after shifting from the low frequency to the high frequency. The width is set to be small, and the peak value of the drain current supplied to the switching element based on the switching signal is set to be smaller in the standby mode than in the rated mode. This is a switching power supply device.

  The pulse oscillation circuit of the switching power supply device of the present invention that achieves the above object oscillates the switching signal of 25 kHz to 500 kHz in the rated mode and 8 kHz to 25 kHz in the standby mode in the rated mode. It is characterized by that.

  In the switching power supply of the present invention that achieves the above object, in the above invention, the transformer circuit includes a transformer, and the number of secondary windings of the transformer is 8 turns or more in a 5V output circuit. Features.

  The switching power supply of the present invention that achieves the above object is characterized in that, in the above invention, the transformer circuit includes a transformer, and a winding ratio of the transformer is 0.08 or more.

  The switching power supply device of the present invention that achieves the above object is characterized in that, in the above-described invention, the switching power supply further includes frequency switching means for switching the frequency of the switching signal in the pulse oscillation circuit to a low frequency in the standby mode.

  In the switching power supply device of the present invention that achieves the above object, in the above invention, the frequency switching means detects a pulse output of the switching circuit, and changes a resistance value using a resistance based on the state of the pulse output. Thus, the frequency of the switching signal in the pulse oscillation circuit is switched.

  In the switching power supply device of the present invention that achieves the above object, in the above invention, the frequency switching means detects an output detection circuit that detects the pulse output of the switching circuit, and the pulse output detected by the output detection circuit. A DC signal level conversion circuit for converting to a DC signal level, a comparison circuit for comparing the DC signal level converted by the DC signal level conversion circuit with a reference voltage, and a resistance value of the resistor based on a comparison result of the comparison circuit And a resistance value changing circuit that changes the frequency of the switching signal in the pulse oscillation circuit.

  The switching power supply of the present invention that achieves the above object is the above-described invention, wherein when the DC signal level reaches the reference voltage, the resistance value changing circuit decreases the resistance value of the resistor, and the frequency of the switching signal is reduced. Is increased.

  The switching power supply device of the present invention that achieves the above object is characterized in that, in the above invention, the resistance value changing circuit is capable of changing the resistance value in a plurality of stages.

  In the switching power supply device of the present invention that achieves the above object, in the above invention, the resistance value changing circuit includes a first resistor and a second resistor that can be selectively connected in parallel to the first resistor. When the DC signal level does not reach the reference voltage, the first resistor is set to an independent state to set the switching signal to a low frequency, and when the DC signal level reaches the reference voltage, The switching signal is set to a high frequency by setting the first resistor and the second resistor in parallel.

  The switching power supply device of the present invention that achieves the above object is characterized in that, in the above invention, the output detection circuit outputs, as the pulse output, a pulse voltage applied to the switching circuit or a pulse current for overcurrent detection of the switching circuit. Any one of them is detected.

  The switching power supply device of the present invention that achieves the above object is characterized in that, in the above invention, the comparison circuit includes a bias circuit that applies a bias voltage to the DC signal level according to a comparison result.

  The switching power supply device of the present invention that achieves the above object is characterized in that, in the above invention, the switching power supply device further comprises an external control circuit capable of forcibly changing the resistance value of the frequency switching means in response to an external signal.

  According to the present invention, it is possible to reduce power consumption particularly in the standby mode. In addition, since the frequency switching means changes the resistance value by the resistance, the responsiveness of the frequency switching timing is improved, and it is possible to smoothly shift to the high frequency particularly at the time of startup. Moreover, since the frequency switching means uses a resistor, the switching signal can be started from a low frequency. As a result, it is possible to improve the stability at the time of startup and to reduce power consumption.

1 is a circuit diagram showing a switching power supply device according to an embodiment of the present invention. A graph showing the state of the DC signal level of the switching power supply device Timing chart showing conduction control of main switching element of the switching power supply device Graph showing voltage rise and frequency state at startup of the switching power supply Graph showing the efficiency of the switching power supply The graph which shows the power consumption state of the Example of the switching power supply device and a comparative example Circuit diagram of conventional switching power supply The graph which shows the voltage rise and frequency state at the time of starting of the conventional switching power supply device

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a circuit diagram of a switching power supply device 1 according to an embodiment of the present invention. This switching power supply device 1 is rectified by an AC power supply CN1, a first full-wave rectification bridge B1, a second half-wave rectification circuit B2, and a first full-wave rectification bridge B1 that are connected to the AC power supply CN1 and rectify AC to DC. Switching circuit 10 for switching the current, transformer T1 for stepping up or down the voltage by the DC current switched by switching circuit 10, pulse oscillation circuit IC71 for outputting a switching signal to switching circuit 10, and switching of pulse oscillation circuit IC71 Frequency switching means 15 that switches the frequency of the signal, and a feedback circuit 80 that transmits a feedback signal to the pulse oscillation circuit IC71 are provided so that the conduction angle of the switching signal is 0.35 or less in the rated mode. In the symbols in the figure, PC is a photocoupler, C is a capacitor, D is a diode, and R is a resistor.

  The switching circuit 10 includes a main switching element Q1 serving as an EFT, and the main switching element Q1 switches the direct current of the first full-wave rectification bridge B1. The output terminal OUT of the pulse oscillation circuit IC71 is connected to the gate of the main switching element Q1. Further, the current detection terminal IS of the pulse oscillation circuit IC71 is connected to the source of the main switching element Q1.

  The transformer T1 includes a primary winding, a secondary winding, and an auxiliary winding, and the first winding and the second winding are insulated. One end of the primary winding of the transformer T1 is connected to the drain of the main switching element Q1, and the source of the switching element Q1 is connected to the negative DC pole MT of the first full-wave rectification bridge B1. The other end of the primary winding of the transformer T1 is connected to the plus DC pole PT of the first full-wave rectification bridge B1.

  The two AC poles K1, K2 of the first full-wave rectification bridge B1 are connected to the AC poles 1, 3 of the AC power supply CN1, respectively. A smoothing capacitor C5 is connected between the DC poles PT-MT of the first full-wave rectification bridge B1. As a result, the current of the AC power supply CN1 is rectified by the first full-wave rectification bridge B1, and further smoothed to function as a DC power supply.

  A rectifier diode D21 and a reactance L21 for smoothing the ripple are connected in series to the positive pole on the secondary winding side of the transformer T1. Further, a capacitor C21 or the like is disposed between the positive pole and the negative pole of the secondary winding so that current accumulation / discharge is repeated. As a result, the switching power supply device 1 functions as a flyback converter. Specifically, the primary current of the transformer T1 flows along a series circuit of the primary winding, the main switching element Q1, and the primary current detection resistor R8, and the secondary current of the transformer T1 is generated by the primary current. Is induced. Then, the induced secondary winding accumulates electric charge in the capacitor C21 and the like by releasing energy, and further, the capacitor C21 releases electric charge, thereby applying a DC power source to the load CN2 side. A feedback circuit 80 is connected to the positive pole side of the secondary winding of the transformer T1.

  The feedback circuit 80 includes a resistor R22 connected to the positive pole side of the secondary winding, a photocoupler PC22B connected in series with the resistor R22, and a reference voltage connected in series with the photocoupler PC22B for stabilization. And a constant voltage element IC21 such as a Zener diode for generating Therefore, when the output voltage of the transformer T1 is larger than the reference voltage of the constant voltage element IC21, a current flows through the photocoupler PC22B, and a feedback signal is output by light. The optical output of the feedback signal is input to the voltage feedback terminal FB of the pulse oscillation circuit IC71 via the photocoupler PC22A. As a result, the conduction angle of the switching signal is controlled to stabilize the voltage.

  That is, in the case where the frequency is fixed in the rated mode or the standby mode as in this embodiment, the feedback signal from the photocoupler PC22B in the feedback circuit 80 is the reference voltage in the constant voltage element IC21 and the second voltage of the transformer T1. It is determined by the difference in the secondary voltage. By the way, the secondary side output voltage in the transformer T1 is proportional to the winding ratio of the primary winding and the secondary winding. Therefore, when the winding ratio of the transformer T1 is small, the secondary output voltage of the transformer T1 is small, so that the feedback signal is output so as to increase the conduction angle compared with the reference voltage. On the other hand, when the winding ratio is large, the secondary output voltage of the transformer T1 increases, so that a feedback signal that stabilizes the voltage by narrowing the conduction angle is output.

  In general, the conduction angle is designed to be in the range of 0.4 to 0.5. However, the feedback circuit 80 of the present embodiment increases the secondary winding of the transformer T1 so that the 5V output circuit has 8 turns or more. Alternatively, the winding ratio is increased to 0.08 or more so that the conduction angle in the rated mode is 0.35 or less. In a standby mode, which will be described later, the winding ratio in the rated mode is determined so that the conduction angle is 0.11 or less while performing low frequency control. Although details will be described later, it is possible to reduce power consumption.

  The second half-wave rectifier circuit B2 is arranged in parallel with the first full-wave rectifier bridge B1 with respect to the AC power supply CN1, but is not a bridge configuration with four diodes but a configuration with two diodes D71 and D72. Has been. The single AC pole K1 of the second half-wave rectifier circuit B2 is connected to one AC pole 1 side of the AC power supply CN1 via a capacitor C6 connected in series so as to perform half-wave rectification. Capacitor C6 has a function of introducing an AC current from AC power supply CN1 to the second half-wave rectifier circuit B2 side at the time of startup.

  One diode D71 is further connected in series to the AC pole K1 of the second half-wave rectifier circuit B2 so that only the AC current from the capacitor C6 flows. Therefore, the opposite end of the AC pole K1 in the diode D71 is a plus DC pole PT. The other diode D72 is disposed between the AC pole K1 and the negative DC pole MT of the second half-wave rectifier circuit, and allows a current to flow from the negative DC pole MT toward the AC pole K1. Due to the presence of the diode D72, the residual charge of the capacitor C6 can be discharged to the AC power supply CN1 side. In this way, by discharging the residual charge of the capacitor C6 for each half-wave rectification, it is possible to prepare for the next half-wave rectification charging, so that the output can be increased. Furthermore, the negative DC pole MT of the second half-wave rectifier circuit B2 is connected to the negative DC pole MT of the first full-wave rectifier bridge B1.

  A smoothing capacitor C71 is connected between both DC poles PT-MT of the second half-wave rectifier circuit B2, and serves as a DC power source by the rectifying action of the second half-wave rectifier circuit B2. A pulse oscillation circuit IC71 is further connected between both DC poles PT-MT of the second half-wave rectifier circuit B2. Specifically, the positive DC pole PT of the second half-wave rectifier circuit B2 is connected to the power input terminal VCC of the pulse oscillation circuit IC71, and the negative DC pole MT of the second half-wave rectifier circuit B2 is connected to the RT terminal of the pulse oscillation circuit IC71. , Each connected. Accordingly, a DC voltage is applied to the pulse oscillation circuit IC71 via the capacitor C6 and the second half-wave rectifier circuit B2 without using a resistor or the like. Since the second half-wave rectifier circuit B2 includes a capacitor and a diode, the second half-wave rectifier circuit B2 is configured so that almost no power is consumed, and the rise of the power can be made quick. Since the number of parts is small compared with the bridge configuration, the manufacturing cost can be reduced.

  The frequency switching means 15 detects the pulse output of the switching circuit 10, changes the resistance value based on the state of the pulse output, and switches and controls the switching signal frequency of the pulse oscillation circuit IC71. Specifically, the frequency switching unit 15 includes an output detection circuit 20, a DC signal level conversion circuit 30, a comparison circuit 40, a resistance value change circuit 50, and an external control circuit 60.

  The output detection circuit 20 includes a resistor R83, and the input side is connected to the output terminal OUT of the pulse oscillation circuit IC71. Therefore, the output detection circuit 20 can detect the switching signal (pulse output) supplied from the pulse oscillation circuit IC71. On the other hand, the output side of the output detection circuit 20 is connected to the DC signal level conversion circuit 30.

  The DC signal level conversion circuit 30 is configured by connecting a resistor R82 and a capacitor C76 in parallel. As already described, since the pulse output detected by the output detection circuit 20 is input to the DC signal level conversion circuit 30, the pulse output is converted to a DC signal level by the capacitor C76 and the resistor R82. Actually, a DC signal level having a sawtooth waveform as shown in FIG. 2A is generated by charging and discharging the capacitor C76 based on the pulse signal. The detection value of the DC signal level can be arbitrarily set by arbitrarily setting the circuit arrangement of the resistor R82 and the capacitor C76, the resistance value of each element, and the capacitance. This DC signal level is output to the comparison circuit 40 described later.

  The comparison circuit 40 includes a comparator IC72, a reference resistor R81, and a bias resistor R79 that functions as a bias circuit. The comparator IC72 compares the DC signal level input from the DC signal level conversion circuit 30 with the reference voltage generated by the reference resistor R81, and outputs an ON signal when the DC signal level is higher than the reference voltage. . Since the output side of the comparison circuit 40 is connected to the resistance value changing circuit 50 (specifically, the base of the switching element Q71) via the diode D73, the ON signal is output to the switching element Q71. On the other hand, when the DC signal level is smaller than the reference voltage, an OFF signal (no output) is generated, and a predetermined base current does not flow through the switching element Q50 of the resistance value changing circuit 50.

  A bias resistor R79 serving as a bias circuit is connected at both ends to the output side of the comparator IC72 and the DC signal level input side. When the comparator IC72 outputs an ON signal, the bias voltage is set to the DC signal level on the input side at the same time. To increase the voltage level. As a result, when the ON signal is output at one end, the DC signal level increases as shown in FIG. As a result, the bias circuit can avoid chattering (situation in which ON and OFF are frequently repeated) of the comparator IC72 due to the sawtooth-shaped DC signal level.

  The resistance value changing circuit 50 includes a switching element Q71 and two resistors R74 and R76. The ON / OFF signal of the comparison circuit 40 is input to the base of the switching element Q71. The resistor R76 and the switching element Q71 (collector / emitter) are connected in series, and another resistor R74 is connected in parallel to the series circuit of the resistor R76 and the switching element Q1.

  Accordingly, when an OFF signal is input to the base of the switching element Q71 and no current flows between the collector and the emitter, the resistor R76 connected in parallel does not function, so that the resistor R74 acts as an independent unit. On the other hand, when an ON signal is input to the base of the switching element Q71 and a current flows between the collector and the emitter, the resistor R76 functions, the resistor R74 and the resistor R76 are in parallel, and the combined resistance value decreases. Therefore, the voltage level applied to the RT terminal can be switched by changing the resistance value of the resistance value changing circuit 50 according to the resistance in accordance with the switching state of the switching element Q71. In the pulse oscillation circuit IC71, since the frequency of the switching signal is uniquely determined by the voltage level of the RT terminal, the frequency can be controlled in two steps here.

  The external control circuit 60 is connected in parallel to the DC signal level conversion circuit 30, receives an external signal, and shorts the capacitor C76 of the DC signal level conversion circuit 30. Specifically, the external control circuit 60 includes a switching element Q90, and a capacitor C76 is connected between its collector and emitter, and an external signal is input to the gate. When a signal is input to the gate, the collector and the emitter are brought into conduction to short-circuit the capacitor C76. As a result, the DC signal level is forcibly reduced to zero, so that the pulse oscillation circuit IC71 can shift to the low frequency state and shift to the power saving mode or standby mode as will be described later.

  In the present embodiment, when the output of the comparison circuit 40 is an OFF signal and no current flows through the switching element Q71 of the resistance value changing circuit 50, the switching signal of the pulse oscillation circuit IC71 is set to a low frequency. Is set to a frequency of 17 kHz or more and 25 kHz or less. When the output of the comparison circuit 40 becomes an ON signal and a current flows through the switching element Q71 of the resistance value changing circuit 50, the switching signal of the pulse oscillation circuit IC71 is set to a high frequency, specifically set to 70 kHz or more and 100 kHz or less. The As described above, according to the frequency switching means 15, two types of frequencies can be fixedly used by changing resistance values in two stages.

  Further, since the resistance value changing circuit 50 uses the change in resistance value due to the combination of the resistors R74 and R76, the switching signal of the pulse oscillation circuit IC71 can be started from a low frequency when the switching power supply device 1 is started. it can. Further, when the DC signal level is increased due to the increase in power on the load side, the resistance value can be switched at substantially the same timing as the output of the comparison circuit 40, and the high frequency can be quickly shifted.

  The switching power supply device 1 configured as described above operates as follows.

  The alternating current generated at each pole of the alternating current power supply CN1 is rectified by the first full-wave rectification bridge B1. By this rectification action, the smoothing capacitor C5 is charged and becomes a DC power source. The alternating current also flows to the series capacitor C6 side, and is rectified by the second half-wave rectifier circuit B2. Since the second half-wave rectifier circuit B2 has only one AC pole K1, only the half-wave current is rectified in the second half-wave rectifier circuit B2. By this rectification action, the smoothing capacitor C71 is charged to become a DC power source, and the pulse oscillation circuit IC71 is activated. In the second half-wave rectifier circuit B2, the DC power supply can be started up by adjusting the time constant by the capacitor C6, so that the rise of the pulse oscillation circuit IC71 can be optimized. The second half-wave rectifier circuit B2 is mainly responsible for starting up the pulse oscillation circuit IC71. On the other hand, after startup, current is supplied from the auxiliary winding side of the transformer T1 to the pulse oscillation circuit IC71 via the diode D3.

  The DC power charged in the smoothing capacitor C5 through the first full-wave rectification bridge B1 becomes a primary current that is intermittently turned on and off by the main switching element Q1 that repeatedly turns on and off. The on / off operation of the main switching element Q1 depends on a switching signal (driving pulse) output from the output terminal OUT of the pulse oscillation circuit IC71. The switching frequency of the main switching element Q1 starts at a low frequency (8 kHz to 25 kHz or less) at the same time as the standby mode, and is automatically switched to a high frequency (25 kHz to 500 kHz or less) when the load increases. It becomes. In the present embodiment, specifically, control is performed so that the frequency is 18 kHz in the low load region including the standby mode and 70 kHz in the high load region including the rated mode.

  The primary current flows along the series circuit of the primary winding of the transformer T1, the main switching element Q1, and the primary current detection resistor R8, and the secondary winding of the transformer T1 is induced by this primary current. . Here, since the number of turns of the secondary winding of the transformer T1 is set to 8 times or more in the case of the 5V output circuit, the induced voltage tends to increase. Then, the induced secondary winding accumulates electric charge in the capacitor C21 and the like by releasing energy, and further, the capacitor C21 releases electric charge, thereby applying a DC power source to the load CN2 side. On the positive pole side of the secondary winding of the transformer T1, the feedback circuit 80 detects the induced voltage on the secondary winding side. The feedback signal in the feedback circuit 80 is input to the voltage feedback terminal FB of the pulse oscillation circuit IC71 via the photocoupler PC22A to control the conduction angle. Since the primary current flowing through the primary winding of the transformer T1 is controlled by the conduction control of the switching signal, the voltage can be stabilized as a result.

FIG. 3 schematically shows a time chart of the conduction control of the main switching element Q1 in the present embodiment. 3A is a time chart of conduction control in the rated mode, and FIG. 3B is a time chart in the standby mode. As described above, the number of turns of the secondary winding of the transformer T1 is set to 8 turns or more in the 5V output circuit, or the winding ratio thereof is set to 0.08 or more so that the secondary side output of the transformer T1 is increased. Designed to. As a result, in the rated mode, the feedback circuit 80 generates a feedback signal that narrows the conduction angle so that the conduction angle of the gate voltage (switching signal) of the main switching element Q1 is 0.35 or less. . Accordingly, the pulse waveform of the primary current (drain current) _ID flowing through the main switching element Q1 has a sawtooth shape with a conduction angle of 0.35 or less. Voltage V _CD is applied between the source and drain of the main switching element Q1 rises and at the same time the drain current I _D is turned off, is applied to the next drain current I _D is turned on.

In the standby mode, the switching frequency is significantly suppressed by the frequency control to be 8 kHz to 25 kHz, and the interval between the switching pulses is widened. Since the load is low in the standby mode, the feedback circuit 80 is controlled so as to further narrow the conduction angle so that the conduction angle of the gate voltage of the main switching element Q1 is 0.11 or less. However, even a conduction angle of the gate voltage is reduced, as shown in the gate voltage V _G of FIG. 3 (B), the switching signal by the low-frequency shift, the unit pulse becomes longer. In addition, since the conduction angle becomes 0.11 or less and the low frequency state is set, a long switching pulse OFF time can be secured, so that power consumption is reduced. Further, the switching loss (power loss) in the main switching element Q1 is a region where the drain current _{ID at the} moment of turn-off and the applied voltage V _CD between the source and the drain rising simultaneously with the turn-off, that is, I _D × V _CD The switching loss (I _D × V _CD ) can be reduced by reducing the peak current value Ip and the rise delay of the source-drain voltage V _{CD due to} this. Furthermore, this decrease in the peak current value Ip can also reduce the amount of heat generated by the main switching element Q1, suppress the variation width of the magnetic flux density in the transformer T1, and reduce the loss in the transformer T1.

For example, the change width ΔB of the magnetic flux density of the transformer T1 can be expressed by the following equation.
ΔB = (V _IN × T _ON ) / (Np × Ae) × 10 ⁸
V _IN : Input voltage, T _ON : Conduction time (ON time), Np: Number of windings, Ae: Core cross-sectional area

Therefore, it can be seen that by reducing this T _ON : conduction angle, the change width ΔB of the magnetic flux density can be suppressed, and the loss of the transformer T1 is reduced.

Further, the energy storage amount P of the transformer T1 is expressed by the following equation.
P = Lp × I _1P ² × f / 2 = V _IN ² × T _ON ² × f / 2 Lp = I ₀ (V ₀ + V _F )
P: energy storage amount of transformer T1, Lp: inductance of primary winding, I _1P : primary winding current, f: frequency, V _IN : input voltage, T _ON : conduction time (ON time), I ₀ : Output current, V ₀ : Output voltage, V _F : Diode forward voltage

Here, since V _{IN is an} input voltage, f is a frequency, and Lp is an inductance of a primary winding, there are certain restrictions. To suppress this energy storage amount P, T _ON ² is a value of a conduction time. It can be seen that it is important to suppress this. In particular, the energy storage amount P is affected by the square of the conduction time. Therefore, for example, when the conduction angle in the standby mode is halved compared to the conventional case, the energy accumulation amount can be reduced to about ¼. . Therefore, in this embodiment, the conduction angle is set to 0.11 in the standby mode in order to make T _ON close to 1 (μ second).

In addition, the on-resistance loss I _D × V _{CDS of the} main switch element (FET) Q1 in which the drain current _ID equivalent to I _1P (primary winding current) flows is simultaneously suppressed and the energy storage amount of the transformer T1 is suppressed. since it is also possible to reduce loss I ₀ × V _F side of the diode, efficiency can be further improved.

  As described above, when a conduction angle of 0.35 or less, which is different from the general range (0.4 to 0.5), is adopted in the rated mode, the switching pulse is turned off particularly in the standby mode in which the frequency shifts. Since power saving elements such as longer time, reduction of switching loss at turn-off, and iron loss of the transformer T1 act in a superimposed manner, the power consumption of the switching power supply device 1 can be reduced. Further, if the conduction angle is suppressed in the rated mode, the time during which current flows through the transformer T1 can be shortened. As a result, since the heat generation of the transformer T1 is suppressed, the winding can be made thinner, so that the power loss of the transformer T1 can be reduced even if the number of turns of the secondary winding is increased. Further, by making the winding thin, the transformer T1 itself can be made compact. As a result, labor saving can be achieved even in the rated mode.

  Note that the photocoupler PC21A connected to the positive pole side of the secondary winding detects an overvoltage, and transmits an overcurrent signal to the pulse oscillation circuit IC71 to be input to the overvoltage control terminal CS.

  The pulse output (switching signal) output from the output terminal OUT of the pulse oscillation circuit IC71 is detected by the output detection circuit 20 in the frequency switching means 15, and passes through the resistor R83 of the circuit 20 to the DC signal level conversion circuit 30 side. Is output. The DC signal level conversion circuit 39 converts the transmitted pulse output to a DC signal level. Specifically, the capacitor C76 is charged with a charge of a rectangular wave signal serving as a switching signal. At this time, if the on-time of the pulse oscillation circuit IC71 is relatively long (in the case of a high duty ratio), the capacitor C76 is sufficiently charged, and the DC signal level becomes high. On the other hand, when the on-time of the pulse oscillation circuit IC71 is relatively short (in the case of a low duty ratio), the capacitor C76 is not sufficiently charged, so that the DC signal level becomes low. The signal converted to the DC signal level is output to the comparison circuit 40.

  The comparator IC 72 of the comparison circuit 40 compares the DC signal level with a reference voltage, and generates an ON signal when the DC signal level is higher. On the other hand, when the DC signal level is smaller than the reference voltage, an OFF signal is issued. When the switching power supply device 1 is started up, it always starts from a state where the DC signal level is low, so that the comparison circuit 40 also starts from the OFF signal.

  The ON / OFF signal output from the comparison circuit 40 is input to the base of the switching element Q71 of the resistance value changing circuit 50. In the case of the ON signal, the collector-emitter of the switching element Q71 is made conductive, so that the two resistors R74 and R76 are in parallel and the resistance value is lowered. On the other hand, in the case of the OFF signal, the collector and the emitter of the switching element Q71 are in a non-conductive state, so that only the resistor R74 is provided and the resistance value is increased. As described above, in this switching power supply device 1, the resistance value changing circuit 50 always starts from a state in which the resistance value is large, and the resistance value is changed by switching to the ON signal. Get smaller.

  The frequency of the switching signal of the pulse oscillation circuit IC71 is set according to the input voltage of the frequency change terminal RT. However, when the resistance value of the resistance value change circuit 50 is high, the frequency is low, and when the resistance value is low, the frequency is high. It becomes. Therefore, at startup, the switching signal starts from a low frequency and switches to a high frequency as the power increases. That is, as shown in FIG. 4, in this switching power supply device 1, the switching signal at the start always starts from the low frequency L, and when the load increases, it shifts to the high frequency H to increase the power. As a result, the output voltage can be increased smoothly. Furthermore, since the frequency switching is performed by a resistor, the time delay of the switching timing is reduced, and when the set voltage reaches the midway of rising, it can be quickly switched to a high frequency. As a result, frequency switching in a high voltage state such as a rated voltage is avoided, and a drop in the rated voltage can be suppressed. On the other hand, if the load subsequently decreases, the power is automatically shifted to a low frequency to reduce the power.

  The graph of FIG. 5 shows the relationship between the output of the switching power supply device 1 and the efficiency. At the time of low output, since it is always maintained at a constant low frequency L, for example, a frequency L of 20 kHz, high efficiency can be maintained. In addition, even at high output, a constant high frequency H, for example, a frequency H of 80 kHz, is always maintained, so that high efficiency can always be maintained. In this way, the low frequency L side is set within a predetermined range of 17 kHz or more and 25 kHz or less, and the high frequency is set within a predetermined range of 70 kHz or more and 100 kHz or less, as shown by a dotted line. In comparison with the case where the frequency is controlled steplessly from several kHz to about 100 kHz according to the output, the efficiency can be increased as a result. In particular, the efficiency of the second half-wave rectifier circuit B2 is also synergistic because the efficiency including the switching loss is greatly increased in the start-up and power saving mode (standby mode). However, the power consumption of the entire apparatus can be reduced.

  When the frequency is controlled steplessly according to the output, the low frequency is shifted to less than 17 kHz and noise noise is generated. In this embodiment, the low frequency side is divided into two steps (or multiple steps). Can be fixed at a desired frequency, so that generation of noise sound can be avoided.

  <Examples and Comparative Examples>

  In FIG. 6, the switching power supply device according to this embodiment of Examples 1 to 4 set to outputs 5 W, 10 W, 15 W, and 30 W is prepared, and the input power and the rated mode in the standby mode (load factor 10%). The result of measuring the input power (W) at (load factor 100%) is shown. As Comparative Examples 1 to 5, conventional switching power supply devices with outputs of 5 W, 10 W, 15 W, and 30 W were prepared, and similarly, the input power and the rated mode (load factor 100%) in the standby mode (load factor 10%). The input power (W) at was measured.

  In the switching power supply device of the present embodiment, as shown in FIG. 6, the conduction angle in the rated mode is 0 by adjusting the winding ratio of the transformer to 0.08 or more and the secondary winding to 8 turns or more. .35 or less, and the conduction angle in the standby mode is set to satisfy 0.11 or less.

  As can be seen from FIG. 6, the switching power supply of the first embodiment with an output of 5 W is about 10% in the rated mode and about 50% in the standby mode, compared with Comparative Examples 1 and 2 with 5 W. It can be seen that is reduced. In addition, it can be seen that the switching power supply of Example 2 with an output of 10 W reduces power consumption by about 10% in the rated mode and about 50% in the standby mode compared to Comparative Example 3 with 10 W. . It can be seen that the power consumption of the switching power supply of Example 3 with an output of 15 W is about 8% lower in the rated mode and about 40% lower in the standby mode than the comparative example 4 of 15 W. It can be seen that the power consumption of the switching power supply of Example 4 with an output of 30 W is about 5% lower in the rated mode and about 25% lower in the standby mode than Comparative Example 5 with 30 W. Therefore, it can be seen that the reduction rate increases especially in the switching power supply device that has a large reduction amount of power consumption in the standby mode and a small output.

  In this embodiment, both the low-frequency side frequency and the high-frequency side frequency can be easily changed by appropriately selecting the resistance of the resistance value changing circuit 50. The frequency at the time of output can be determined flexibly. In addition, the switching timing can be set flexibly by changing the setting of the reference resistor R81 of the comparison circuit 40, the resistor R82 of the DC signal level conversion circuit 30, and the capacitor C76. Therefore, in this switching power supply device 1, it is very easy to change the design corresponding to the required specifications on the load side.

  In this embodiment, the transformer T1 in which the primary winding and the secondary winding are insulated is used as the transformer circuit. However, the transformer T1 is not necessarily an insulated switching power supply circuit. It can be applied to a non-insulated switching power supply circuit employing a chopper method or the like.

  In the present embodiment, the switching power supply device 1 is shown only when it functions as a flyback converter. However, the present invention is not limited to this, and can be applied to a forward converter. In this case, a rectifying diode D21 and a reactance L21 for storing energy are connected in series with the positive pole on the secondary winding side of the transformer T1, and the reactance L21 is sandwiched between the secondary windings. It is preferable to arrange a diode for conducting a flywheel current and a capacitor for accumulating current between the plus and minus poles of the line.

  It should be noted that the switching power supply device of the present invention is not limited to the above-described embodiment, and it is needless to say that various changes can be made without departing from the gist of the present invention.

  The switching power supply device of the present invention can be applied to electronic devices and the like that are required to save power.

Q1 main switching element T1 transformer IC71 pulse oscillation circuit B1 first full-wave rectification bridge B2 second half-wave rectification circuit 15 frequency switching means 20 output detection circuit 30 DC signal level conversion circuit 40 comparison circuit 50 resistance value change circuit 60 external control circuit 80 Feedback circuit

Claims (14)

A rectifier circuit that rectifies alternating current from an alternating current power source into direct current;
A switching circuit that switches the voltage rectified by the rectifier circuit using a switching element;
For the switching element, a pulse oscillation circuit that outputs a switching signal having a high frequency in the rated mode and a low frequency in the standby mode;
A voltage transformer circuit for stepping up or stepping down the voltage according to the current switched by the switching circuit;
The output voltage of the transformer circuit is detected with respect to the pulse oscillation circuit so that the conduction angle of the switching signal is 0.35 or less in the rated mode and 0.11 or less in the standby mode. And a feedback circuit that transmits a feedback signal based on a comparison circuit that compares with a reference voltage.
The switching signal generated by the pulse oscillation circuit has a pulse width on the high frequency side that is smaller than the pulse width on the low frequency side when comparing before and after shifting from the low frequency to the high frequency. Set to
The switching power supply apparatus according to claim 1, wherein a peak value of a drain current supplied to the switching element based on the switching signal is set to be smaller in the standby mode than in the rated mode. A rectifier circuit that rectifies alternating current from an alternating current power source into direct current;
A switching circuit that switches the voltage rectified by the rectifier circuit using a switching element;
For the switching element, a pulse oscillation circuit that outputs a switching signal having a high frequency in the rated mode and a low frequency in the standby mode;
A voltage transformer circuit for stepping up or stepping down the voltage according to the current switched by the switching circuit;
The output voltage of the transformer circuit is detected with respect to the pulse oscillation circuit so that the conduction angle of the switching signal is 0.35 or less in the rated mode and 0.11 or less in the standby mode. And a feedback circuit that transmits a feedback signal based on a comparison circuit that compares with a reference voltage.
The switching signal generated by the pulse oscillation circuit is compared with the average pulse width on the low frequency side when comparing before and after shifting from the low frequency to the high frequency. The pulse width is set to be small,
The switching power supply apparatus according to claim 1, wherein a peak value of a drain current supplied to the switching element based on the switching signal is set to be smaller in the standby mode than in the rated mode.   3. The switching power supply device according to claim 1, wherein the pulse oscillation circuit oscillates the switching signal of 25 kHz or more and 500 kHz or less in the rated mode and 8 kHz or more and 25 kHz or less in the standby mode. The transformer circuit includes a transformer;
4. The switching power supply device according to claim 1, wherein the number of secondary windings of the transformer is 8 turns or more in a 5V output circuit. 5. The transformer circuit includes a transformer;
The switching power supply according to any one of claims 1 to 4, wherein a winding ratio of the transformer is 0.08 or more.   6. The switching power supply device according to claim 1, further comprising frequency switching means for switching a frequency of the switching signal in the pulse oscillation circuit to a low frequency in the standby mode.   The frequency switching means detects a pulse output of the switching circuit, changes a resistance value using a resistor based on a state of the pulse output, and switches a frequency of the switching signal in the pulse oscillation circuit. The switching power supply device according to claim 6. The frequency switching means is
An output detection circuit for detecting the pulse output of the switching circuit;
A DC signal level conversion circuit that converts the pulse output detected by the output detection circuit into a DC signal level;
A comparison circuit that compares the DC signal level converted by the DC signal level conversion circuit with a reference voltage;
A resistance value changing circuit that changes a resistance value of a resistor based on a comparison result of the comparison circuit, and switches a frequency of the switching signal in the pulse oscillation circuit;
The switching power supply according to claim 6 or 7, further comprising:   9. The switching power supply device according to claim 8, wherein when the DC signal level reaches the reference voltage, the resistance value changing circuit decreases the resistance value of the resistor and increases the frequency of the switching signal.   10. The switching power supply device according to claim 8, wherein the resistance value changing circuit is capable of changing the resistance value in a plurality of stages.   The resistance value changing circuit includes a first resistor and a second resistor that can be selectively connected in parallel to the first resistor, and when the DC signal level does not reach the reference voltage, The switching signal is set to a low frequency by setting one resistor to an independent state, and when the DC signal level reaches the reference voltage, the first resistor and the second resistor are put in parallel to set the switching signal. The switching power supply according to claim 8, wherein the switching power supply is set to a high frequency.   The output detection circuit detects either a pulse voltage applied to the switching circuit or a pulse current for overcurrent detection of the switching circuit as the pulse output. Or a switching power supply.   The switching power supply device according to claim 8, wherein the comparison circuit includes a bias circuit that applies a bias voltage to the DC signal level according to a comparison result.   14. The switching power supply device according to claim 8, further comprising an external control circuit that can receive an external signal and forcibly change the resistance value of the frequency switching means.