JP2010273501A - Buck-boost switching power supply circuit - Google Patents

Abstract

A step-up / step-down switching power supply circuit is provided which is reduced in the number of switch elements, is highly efficient, is inexpensive, and is downsized.
A buck-boost switching power supply circuit 1, N-channel MOS transistor Q ₁ is a diode D _I to flow current from the inductor L _I in the off are connected. Further, the other end of the inductor _{L 2} is connected a capacitor _{C 2,} the connection point of the connection point between the other ends of the diode _{D 2} of the capacitor _{C 2,} an inductor _{L 1} and the N-channel MOS transistor _{Q 1} between, N-channel MOS transistor Q ₁ is the a diode D ₃ flow a current when on is connected. Then, by changing the ratio of on and off N-channel MOS transistors Q _1, so that changing the voltage generated across the capacitor C _2.
[Selection] Figure 1

Description

  The present invention relates to a switching power supply circuit, and more particularly to a step-up / down switching power supply circuit.

As a step-up / step-down switching power supply circuit that boosts and lowers a voltage from a power supply, a circuit in which a step-up switching power supply and a step-down switching power supply are connected in cascade is known as a well-known technique. FIG. 7 shows an example of such a step-up / step-down switching power supply circuit. Figure 7 The buck-boost switching power supply circuit 100 shown in the well-known step-up switching power supply circuit 101 and a known step-down switching power supply circuit 102 and the cascaded to load of the voltage across E ₂ inputs the magnitude of the voltage E It can be made larger or smaller than ₁ .

Step-up switching power supply circuit 101 is formed with an inductor _{L 101} and the switch element _{S 101} and the diode _{D 101} and the capacitor _{C 101,} the step-down switching power supply circuit 102 is an inductor _{L 102} and the switch element _{S 102} and the diode D ₁₀₂ and a capacitor _C102 . The boost ratio is changed by changing the time ratio (T _S / T _OFF1 ) of the switch element S ₁₀₁ . Here, T _S is a switching period, and T _OFF1 is a time when the switch element S ₁₀₁ is off. Further, the step-down ratio is changed by changing the time ratio (T _ON2 / T _S ) of the switch element S ₁₀₂ . Here, T _ON2 is the _{ON time} of the switch element _S102 . Here, between the input voltage E ₁ and the load voltage E ₂ , a relational expression of E ₂ / E ₁ = (T _S / T _OFF1 ) × (T _ON2 / T _S ) = T _ON2 / T _OFF Is established. In this way, also possible to obtain high voltage E ₂ than the voltage E ₁ of the input across the load, and a low voltage E ₂ than the voltage E ₁ of the input adapted can also be obtained across the load . Here, the switching element S ₁ and switching element S ₂ in which each is independently controlled.

A Cuk converter is known as another step-up / step-down switching power supply circuit. FIG. 8 shows the Chuuk converter 103. The Chuuk converter 103 includes an inductor L ₁₀₃ , an inductor L ₁₀₄ , a switch element S ₁₀₃ , a diode D ₁₀₃ , a capacitor C _103, and a capacitor C ₁₀₄ . Then, by changing the duty ratio of the switching element S _103, changing the buck-boost ratio. A relational expression of E ₂ / E ₁ = T _ON3 / T _OFF3 can be obtained. _{Here, T ON3} the time on the switching element _{S 103, T OFF3} is the time off of the switching element _{S 103.}

  A power factor correction circuit using a boost converter is also known as a well-known technique (see, for example, Patent Document 1 and Patent Document 2).

JP 2006-67730 A Japanese Patent Laying-Open No. 2005-229757

30 pages of basics of switching converter, Kosuke Harada, Keibun Ken Ninomiya, Corona Co., Ltd. February 25, 1992

In the step-up / step-down switching power supply circuit in which the step-up type switching power supply and the step-down type switching power supply shown in FIG. 7 are connected in series, two switch elements are required, and the price of the device becomes expensive. Further, since the loss in the switch element is also generated by two, the efficiency is low. The Cuk converter shown in FIG. 8, since the high frequency power to interpose a capacitor to pass (the capacitor C ₁₀₃₎ to the power transmission path, occurs loss in the capacitor. In addition, when the power supplied to the load is increased, the capacity of the capacitor must be increased, the shape of the switching power supply circuit is increased, and it is not very suitable as a power supply that handles large power. .

  The present invention has been made in view of the above-described problems, and provides a step-up / down switching power supply circuit that is highly efficient, inexpensive, and downsized with an extremely simple configuration.

  In the step-up / step-down switching power supply circuit according to the present invention, a first inductor and a switch element are connected in series to an input power supply, and when the switch element is off at a connection point between the first inductor and the switch element. A first diode is connected to flow a current from the first inductor, the other end of the first diode is connected to a first capacitor, and the other end of the diode and the first capacitor are connected to each other. A second diode and the second inductor are connected to the connection point so that a current flows through the second inductor when the switch element is off, and the other end of the second inductor is connected to the second inductor. Between the other end of the second capacitor and the other end of the second diode, and the connection point between the first inductor and the switch element. Switching element is connected to the third diode to flow current when on, the by changing the ratio of the switching element on and off, changing the voltage generated at both ends of the second capacitor.

  In the step-up / step-down switching power supply circuit according to the present invention, the first inductor and the switch element are connected in series to the input power supply. The first diode is connected so that the current from the inductor flows, and the other end of the first diode is connected to the first capacitor, so that the voltage can be boosted. The second diode and the second inductor are connected to a connection point between the other end of the diode and the first capacitor so that a current flows through the second inductor when the switch element is off. Since the second capacitor is connected to the other end of the inductor, the voltage can be stepped down. In addition, a current is allowed to flow between the connection point between the other end of the second capacitor and the other end of the second diode and the connection point between the first inductor and the switch element when the switch element is on. Is connected to a third diode. With such a configuration, the voltage generated at both ends of the second capacitor can be changed by changing the ON / OFF ratio of the switch element.

  In another step-up / step-down switching power supply circuit according to the present invention, a first switch element is connected to an AC power supply, and the first switch element is turned off at a connection point between the AC power supply and the first switch element. A first diode is connected to cause a current to flow through the first inductor via the first capacitor and the first rectifier diode, and the other end of the first diode, the first capacitor, The second diode and the second inductor are connected to the connection point so that a current flows through the second inductor when the first switch element is off, and the other end of the second inductor is connected to Is connected to a second capacitor, between a connection point between the other end of the second capacitor and the other end of the second diode, and a connection point between the AC power supply and the first switch element. , The first switch element A third diode is connected so as to pass a current when it is on, a second switch element is connected to a connection point between the first rectifier diode and the first inductor, and the first inductor and the A fourth diode is connected to the first diode and the second switch element so that a current flows through the second inductor when the second switch element is off. And a connection point between the other end of the second capacitor and the other end of the second diode, the first rectifier diode, and the first inductor. A fifth diode is connected between a connection point with the second switch element so that a current flows when the second switch element is on, and the other end of the first switch element and the second switch element Second switch The other end of the child is connected to the other end of the first rectifier diode and the other end of the second rectifier diode having the same polarity as the other end of the first rectifier diode, In addition, the ratio of ON and OFF of the second switch element is changed to change the voltage generated at both ends of the second capacitor, and the power factor is brought close to 1.

  In another step-up / step-down switching power supply circuit according to the present invention, when the first switch element is connected to the AC power supply and the first switch element is turned off at the connection point between the AC power supply and the first switch element. A first diode is connected to flow a current to the first inductor via the first capacitor and the first rectifier diode, and at the connection point between the other end of the first diode and the first capacitor, The second diode and the second inductor are connected so that a current flows through the second inductor when the first switch element is off, and a second capacitor is connected to the other end of the second inductor. And when the first switch element is on between the connection point between the other end of the second capacitor and the other end of the second diode and the connection point between the AC power source and the first switch element. A third diode to pass current De the first buck converter so as to be connected is formed.

  The second switch element is connected to the connection point between the first rectifier diode and the first inductor, and the second switch element is connected to the connection point between the first inductor, the first rectifier diode, and the second switch element. A fourth diode is connected to a connection point between the second diode and the second inductor so that a current flows through the second inductor when the switch element is off, and the other end of the second capacitor and the second Current flows between the connection point with the other end of the diode and the connection point between the first rectifier diode, the first inductor, and the second switch element when the second switch element is on. The other end of the first switch element and the other end of the second switch element have the same polarity as the other end of the first rectifier diode and the other end of the first rectifier diode. Other than the second rectifier diode The second buck converter is formed so as to be connected to and.

  Then, by changing the ON / OFF ratio of the first switch element and the second switch element, the voltage generated at both ends of the second capacitor can be changed, and the power factor can be made close to 1.

  According to the step-up / step-down switching power supply circuit of the present invention, it is possible to perform step-up / step-down by reducing the number of switch elements, and since there is no capacitor through which a large amount of AC power passes, it is highly efficient, inexpensive, and compact. Thus, a step-up / step-down switching power supply circuit can be provided.

1 is a circuit diagram of a step-up / down switching power supply circuit according to an embodiment. FIG. It is an equivalent circuit for demonstrating operation | movement of the buck-boost switching power supply circuit of embodiment. It is a figure which shows the buck-boost switching power supply circuit of embodiment for obtaining a constant voltage. It is a figure which shows the voltage waveform of each part, and shows the operation | movement of the step-up / step-down switching power supply circuit of embodiment. In the step-up / step-down switching power supply circuit of the embodiment, each of a capacitor voltage, an output voltage, and a voltage conversion rate with respect to a pulse duty is shown. 1 shows a step-up / step-down switching power supply circuit that functions as an AC-DC converter. An example of a conventional step-up / step-down switching power supply circuit is shown. 1 shows a conventional Chuuk converter.

  The step-up / step-down switching power supply circuit according to the embodiment will be described below with reference to the drawings.

FIG. 1 is a circuit diagram of a step-up / step-down switching power supply circuit according to an embodiment. The step-up / down switching power supply circuit 1 according to the embodiment includes an inductor L ₁ (first inductor), an N-channel MOS transistor Q ₁ (switch element), a diode D ₁ (first diode), and a capacitor C ₁ (first capacitor). ), A diode D ₂ (second diode), an inductor L ₂ (second inductor), a capacitor C ₂ (second capacitor), and a diode D ₃ (third diode). .

In the step-up / step-down switching power supply circuit 1, an inductor L ₁ and an N-channel MOS transistor Q ₁ are connected in series to an input power supply E _I having a voltage E _I. The inductor _{L 1} is connected to the positive electrode of the input power supply _{E I,} the source of N-channel MOS transistor _{Q 1} is connected to the negative electrode of the input power source _{E I,} is connected to the drain of the inductor _{L 1} and the N-channel MOS transistor _{Q 1} is . The anode of the inductor _{L 1} and the N-channel MOS transistor diode _{D 1} to the connection point of the drain of _{Q 1} is connected. Further, the cathode of the diode D _1, the capacitor C ₁ is connected, the other end of the capacitor C ₁ is connected to the negative pole of the source and the input power supply E _I of N-channel MOS transistor Q _1. The inductor L ₁ and the N-channel MOS transistor Q _1, a diode D ₁ and capacitor C _1, is adapted to constitute a major portion of the switching power supply step-up.

In the step-up / step-down switching power supply circuit 1, the inductor L ₂ and the cathode of the diode D ₂ are connected to the connection point between the cathode of the diode D ₁ and the capacitor C ₁ . The other end of the inductor L ₂ is connected to the capacitor C _2, the other end of the capacitor C ₂ cathode of the diode D ₂ is connected. At both ends of the capacitor C ₂ load R _L is connected. Then, the anode of the other end and the diode D ₂ of the capacitor C ₂ is connected, the anode of the diode D ₃ is connected to the connection point. The cathode of the diode D ₃ is connected to the drain of the inductor L ₁ and the switching element S _1. The inductor L ₂ and the diode D ₂ and the capacitor C _2, is adapted to constitute a major portion of the switching power supply of buck type.

In the step-up / down switching power supply circuit 1 described above, the polarity of the output voltage _EO is positive. However, the polarity of the output voltage E _O is made negative by changing the N channel MOS transistor Q ₁ to a P channel MOS transistor, changing the polarity of the diodes D ₁ to D ₃ , and changing the polarity of the input power supply E _I. be able to.

  The step-up / step-down switching power supply circuit 1 shown in FIG. 1 is a novel circuit that does not exist conventionally. Therefore, it is difficult to understand the circuit operation. Therefore, in order to facilitate understanding of the circuit operation, how the inventor described in the application of the present application invented such a circuit as a result of repeated experiments and thoughts will be described in order. This method of explanation is intended to help the understanding of the step-up / step-down switching power supply circuit 1 shown in FIG. 1 by a third party, and the step-up / step-down switching power supply circuit 1 can easily invent the invention. It's not that you can.

The circuit shown in FIG. 2 is an equivalent circuit of the step-up / step-down switching power supply circuit 1 shown in FIG. The broken line labeled 2 is a step-up switching power supply, and the broken line labeled 3 is a step-down switching power supply. Here, in order to guide the circuit of Figure 1, for the switching power supply of the step-down type, it connects the N-channel MOS transistors Q ₂ to the negative polarity side. This equivalent circuit operates in the same manner as the step-up / step-down switching power supply circuit 100 shown in FIG. 7 as the background art. Then, a relational expression of E _O / E _I = (T _S / T _OFF1 ) × (T _ON2 / T _S ) = T _ON2 / T _OFF1 can be obtained. Here, T _S is a switching period, T _OFF1 is an OFF time of the N-channel MOS transistor Q ₁ , and T _ON2 is an _ON time of the N-channel MOS transistor Q ₂ .

The inventors have thought reached and the equivalent circuit for the first shown in FIG. 2, and the source of N-channel MOS transistors Q _1, since the source of the N-channel MOS transistor Q _2, is considered trying to have a common connection point It is. Further, the inventors of the N-channel MOS transistors Q _1, N-channel MOS transistors Q _2, it one the other also turned on in the case of on, which one of the operations other also such that off If off This is because of the idea that the circuit can be simplified.

The inventor conducted the following thought experiment on the assumption that the forward voltage of the diode is 0 V (volt) and the ON voltage of the N-channel MOS transistor is 0 V. When N-channel MOS transistor _{Q 1} is turned on, if so it is also on the N-channel MOS transistors _{Q 2,} in principle, the drain of N-channel MOS transistor to _{Q 1} source and N-channel MOS transistor _{Q 1} and the drain of the N-channel MOS transistor Q ₂ of the source and the N-channel MOS transistor Q ₂ has reached thought to be equivalent to that the is connected to one point. Also, N-channel MOS transistor _{Q 1} is when it is off, the potential of the drain of the N-channel MOS transistor _{Q 2} are noticed to be lower by the voltage _{E O} than the drain potential of the N-channel MOS transistor _{Q 1} . Then, it was led think that it is possible to use a diode D ₃ in place of the N-channel MOS transistor Q _2.

That is, when a diode is used D ₃ as shown in FIG. 1, when N-channel MOS transistor Q ₁ is turned on, regarded the source and the drain of N-channel MOS transistor Q ₁ is short-circuited, the potential of the power supply a negative side potential of the E _I. The diode D ₁ connected to the source and drain of N-channel MOS transistor Q ₁ is in an off the reverse voltage is applied by the capacitor C _2. The current flowing through the load R _L passes through the diode D ₃ flows back to the negative side of the power source E _I. That is, the diode D ₃ is to the effect of the equivalent when N-channel MOS transistor Q ₂ in FIG. 2 is on. At this time, it is equal to the negative potential and the negative potential of the capacitor C ₂ of the capacitor C _1.

Then, when the N-channel MOS transistor _{Q 1} is off, it can be regarded as open source and the drain of the N-channel MOS transistor _{Q 1.} The diode _{D 1} connected to the drain of N-channel MOS transistor _{Q 1} is turned on. At this time, the potential of the cathode of the diode D ₃ is equal to the potential of the positive electrode of the capacitor C _1, the potential of the cathode of the diode D ₃ is a negative electrode potential of the capacitor C _2, i.e., the potential of the negative electrode of the capacitor C ₁ since equal to, the diode D ₃ is turned off. That is, the diode D ₃ is, N-channel MOS transistor Q ₂ in FIG. 2 is to the effect equivalent When it is turned off.

The above is an easy-to-understand description of the operation of the conventional circuit shown in FIG. 1, but a more detailed description of the operation will be described later. The relationship between the input voltage E _I and the output voltage E _{O at} this time is obtained by the following (Equation 1). Here, T _ON is a time when the N-channel MOS transistor Q ₁ is turned on, and T _OFF is a time when the N-channel MOS transistor Q ₁ is turned off.

E _O / E _I = T _ON / T _OFF (Formula 1)

In summary, in the step-up / step-down switching power supply circuit 1 shown in FIG. 1, an inductor L _I and an N-channel MOS transistor Q ₁ are connected in series to an input power supply E _I , and the connection between the inductor L _I and the N-channel MOS transistor Q ₁ is connected. At a point, a diode D _I is connected so that a current from the inductor L _I flows when the N-channel MOS transistor Q ₁ is off. The other end of the diode _{D I} is connected to the capacitor _{C I,} the connection point between the other end and the capacitor _{C I} of the diode _{D I,} N-channel MOS transistor _{Q 1} is current flow in the inductor _{L 2} in the off diode D ₂ and the inductor L ₂ is connected to. Further, the other end of the inductor _{L 2} is connected a capacitor _{C 2,} the connection point of the connection point between the other ends of the diode _{D 2} of the capacitor _{C 2,} an inductor _{L 1} and the N-channel MOS transistor _{Q 1} between, N-channel MOS transistor Q ₁ is the a diode D ₃ flow a current when on is connected. Then, by changing the ratio of on and off N-channel MOS transistors Q _1, it is possible to change the voltage generated across the capacitor C _2.

FIG. 3 is a diagram showing a step-up / step-down switching power supply circuit 11 according to an embodiment for obtaining a constant voltage by adding a control unit to the step-up / step-down switching power supply circuit 1 shown in FIG. In the step-up / step-down switching power supply circuit 11, the differential amplifier AMP outputs a difference between the output voltage E _O and the reference voltage E _REF . The difference voltage (error voltage) output from the differential amplifier AMP is input to the PWM modulator (pulse width modulator) PWM, and the output voltage E _O is less than the reference voltage E _REF . The time T _ON when the N-channel MOS transistor Q ₁ is turned on is increased. In this way, feedback control is performed, and control is performed such that the output voltage E _O matches the reference voltage E _REF .

In summary, the step-up / step-down switching power supply circuit 11 shown in FIG. 3 adds a control unit to the step-up / step-down switching power supply circuit 1, and the control unit outputs the difference between the output voltage E _O and the reference voltage E _REF. a differential amplifier AMP that, and a pulse width modulator PWM the output from the differential amplifier AMP is input, the pulse width signal from the pulse width modulator PWM, to control the N-channel MOS transistor Q ₁ The output voltage E _O is controlled to a predetermined voltage that matches the reference voltage E _REF .

FIG. 4 is a diagram showing the operation of the step-up / step-down switching power supply circuit 11 shown in FIG. 3 by showing the voltage waveform and current waveform of each part. From top in order below the figure 4, the diode _{D 1} of the current _{I D1,} current _{I D3} of the diode _{D 3,} the current _{I D2} of the diode _{D 2,} current _{I L1} of inductor _{L 1,} the inductor _{L 2} of the current _{I L2,} N-channel MOS transistor to _{Q 1} drain voltage _{V Q1} between the source and shows respectively.

The following can be seen from FIG. A current _{I D1} and the diode _{D 2} of the current _{I D2} of the diode _{D 1} does not flow when the N-channel MOS transistor _{Q 1} is on (when the voltage _{V Q1} is near 0V), the N-channel MOS transistor _{Q 1} It flows when it is off (when voltage _VQ1 is not near 0V). Current _{I D3} of the diode _{D 3} is, N-channel MOS transistor _{Q 1} is the flow when the on, N-channel MOS transistor _{Q 1} is not flow at the time of off. The current _{I L1} and the current _{I L2} in the inductor _{L 2} of the inductor _{L 1} is increased when the N-channel MOS transistor _{Q 1} is ON, the N-channel MOS transistor _{Q 1} is reduced when off.

FIG. 5 is a diagram illustrating a case where the feedback control loop of the step-up / step-down switching power supply circuit 11 of the embodiment is turned off (the operation of the feedback control loop is stopped), and the capacitor with respect to the pulse duty (Duty), that is, (T _ON / T _S ) It shows the respective voltage and the output voltage _{E O} voltage conversion ratio of the _{C 1 (T ON / T OFF} ). According to FIG. 5, by changing the pulse duty (T _ON / T _S ) or by changing the voltage conversion rate (T _ON / T _OFF ) from where T _S = T _ON + T _OFF It shows that the output voltage E _O can be changed.

  According to the step-up / step-down switching power supply circuit of the embodiment, step-up / step-down can be performed using only one switch element. In the combination of the conventional step-up type and step-down type shown in FIG. 7 of the background art, it is difficult to increase the power supply efficiency because the step-up / step-down is performed using two switch elements. In the step-up / step-down switching power supply circuit, the efficiency can be improved. Moreover, according to the step-up / step-down switching power supply circuit of the embodiment, since the step-up / step-down can be performed using only one switch element, an inexpensive power supply circuit can be provided.

  In addition, according to the step-up / step-down switching power supply circuit of the embodiment, since a capacitor in which a large amount of high-frequency current flows like the Chuk converter shown in FIG. Can be improved. Further, since a special capacitor having such a large capacity and particularly good high frequency characteristics is not used, an inexpensive power supply circuit can be provided.

  An embodiment in which the step-up / step-down switching power supply circuit 11 of the embodiment is used for an AC-DC converter instead of a DC-DC converter will be described below.

  FIG. 6 shows the step-up / step-down switching power supply circuit 12 that functions as the AC-DC converter of the embodiment.

The portion of the step-up / step-down switching power supply circuit 12 that is enclosed by a broken line and has the reference numeral 13 has the same configuration as the step-up / step-down switching power supply circuit 1 described above. It differs only that the position of the inductor L ₁ is moving to the AC power supply AC side. Others are the same and operate in the same manner, and detailed description thereof is omitted. Here, the inductor is connected L ₁ on the side of the AC power source AC is not only to function inductor L ₁ as an inductor L ₁ during the temperature step-down switching power supply circuit 1 described above, direct PFC circuit (Direct power factor correction circuit ) To function as a part of.

  A power factor improving circuit that rectifies AC power with a bridge rectifier circuit and then connects a step-up inverter and improves the power factor by supplying a current proportional to the AC voltage as the input current of the step-up inverter. This is a well-known technique. In addition, a direct PFC circuit that simultaneously performs full-wave rectification and power factor improvement by replacing two diodes in the bridge rectification circuit with MOS transistors is also a well-known circuit.

  In the well-known direct PFC circuit, the control of the MOS transistor in the power factor correction circuit configured as a step-up switching power supply is performed by a single control system. The control of the MOS transistor for controlling the output voltage in the step-down switching power supply circuit connected to the power factor correction circuit is performed by a separate control system. As described above, it has been a well-known technique to perform power factor improvement control and constant voltage control using independent and independent control systems.

  Further, in a special case where the output voltage is set higher than the peak value of the input AC power supply, the MOS transistor of the direct PFC circuit is controlled to improve the power factor and the boosting ratio as the boosting switching power supply circuit Some also controlled at the same time. In this case, the control is performed based on the following control law.

First, power factor improvement will be explained. That the power factor is 1, the relationship between the voltage _{V AC} and the current _{I AC} power supply AC is a case where a current _{I AC} = K × voltage _{V AC.} Here, K is a constant. Thus, for example, when the voltage _VAC is a sine wave, a power factor of 1 is a case where the current I _AC is also a sine wave and the phase difference between the two is zero. Further, a sinusoidal voltage waveform of the AC power source AC is a square wave, an AC power supply generally including a triangular wave, etc., are cases where the voltage V _AC and a current I _AC becomes similar waveform is when the power factor is 1.

In order to control the power factor to be 1, that is, the current I _AC = K × voltage V _AC , the voltage V _AC is detected, and the voltage is boosted so that the relation of current I _AC = K × voltage V _AC is obtained. The switching power supply circuit was controlled. Here, upon detection of the voltage V _AC of the AC detects aim insulation from a commercial AC power source AC by using a photocoupler, an insulating from the commercial AC power source AC with the current I _AC current transformer CT AC It was a conventional technique to detect it.

Next, boost ratio control, that is, constant voltage control will be described. Even if the above-mentioned constant K is not a perfect constant, the power factor can be regarded as 1 when it fluctuates with a sufficiently large period compared with the period of the AC power supply AC. Therefore, when the cycle of fluctuation of the power supplied to the load has a sufficiently large cycle compared to the cycle of the AC power supply AC, the voltage supplied to the load is kept constant at the same time while keeping the power factor at 1. Can do. That is, when the load is heavy, the value of the current I _AC AC is increased while the voltage V _AC and similar relationships, when the load becomes lighter, the voltage V a value of current I _AC AC The voltage value of the output from the step-up switching power supply circuit can be made constant by reducing the voltage while maintaining a similar relationship to _AC .

Here, in order to perform constant voltage control, the value of the constant K may be changed as follows. Error voltage _{V ERR} = reference voltage _{E REF} - the relation of voltage _{E O} of the output, obtaining an error voltage _{V ERR.} Then, by constructing a feedback loop that increases the value of the constant K when the value of the error voltage V _ERR is large, the power supplied to the load is increased so that the error voltage V _ERR approaches 0V. Can be done. In other words, the feedback loop automatically obtains the most appropriate value of the constant K to maintain the constant voltage and performs the constant voltage control.

In such a technique, while achieving power factor correction, the range of the output voltage can be obtained a constant voltage characteristic, as described above, if the value of the output voltage is greater than the peak value of the voltage V _AC limited. Therefore, in order than the peak value of the voltage V _AC obtain a voltage of a small output is conventionally generally, a further addition of the step-down switching power supply circuit in the subsequent stage of the step-up switching power supply circuit as described above It was.

In buck-boost switching power supply circuit 12 of the embodiment shown in FIG. 6, the aim of power factor correction, while closer the power factor to 1, without depending on the peak voltage value of the AC power source AC, the voltage E _O of any output It can be obtained.

In the step-up / step-down switching power supply circuit 12 of the embodiment, a direct PFC circuit is composed of two N-channel MOS transistors Q ₁ and N ₂ , a diode D ₁ and a diode D ₄ , a diode D ₃ and a diode D _5. And realized. And, originally changing the place should be used N-channel MOS transistor in the diode _{D 3} and the diode _{D 5,} the buck-boost converter of the N-channel MOS transistor _{Q 1,} the buck converter N-channel MOS transistor _{Q 2} and the same It is driven by a pulse width signal (PWM signal).

When the load is constant, the output voltage _EO is controlled to increase as the PWM signal ON time becomes longer, that is, as the PWM signal OFF time becomes shorter. The Further, the waveform of the alternating current I _AC is changed by the pulse width signal that changes the ON / OFF ratio of the N channel MOS transistor Q ₁ and the N channel MOS transistor Q _{2 in} a cycle shorter than the AC power source cycle. It may be similar in shape to the voltage V _AC waveform.

Pulse width signal for controlling the N-channel MOS transistors _{Q 1,} N-channel MOS transistor _{Q 2} are generated in the control unit. In the control unit, and input voltage E _O of the output AC voltage V _AC and the AC current I _Ac, in the same manner as described above, was used in the buck-boost switching power supply circuit 11 of the embodiment technique, the constant K The N-channel MOS transistor Q is controlled by a pulse width signal from the control unit in combination with a control technique for improving the power factor of the direct PFC circuit, which is a well-known technique, while stabilizing the output voltage _EO by substantially controlling the value. and by controlling the ₁ and the N-channel MOS transistor _{Q 2.}

That is, the control unit, while stabilizing such that the voltage E _O a constant voltage to the input output voltage E _O of the output, type and voltage V _AC of the AC and the AC current I _Ac power factor the like to improve, and supplies the pulse width signal to the N-channel MOS transistors _{Q 1,} N-channel MOS transistor _{Q 2.}

More particularly, the circuit shown in FIG. 6, in the circuit shown in FIG. 1, the circuit portion consisting of N-channel MOS transistor Q _1, a diode D ₁ and a diode D ₃ Metropolitan (first buck-boost switching unit), A circuit part (second step-up / step-down switching part) composed of an N-channel MOS transistor Q ₂ , a diode D _4, and a diode D ₅ and having the same connection is provided. Then, the output side of the diode D ₃ of the first buck-boost switching unit and the output side of the diode D ₅ of the second buck-boost switching unit are connected to each other. The input side of the first step-up / step-down switching unit is connected to the diode D _A1, and the input side of the second step-up / step-down switching unit is connected to the rectifier diode D _A2 .

By adopting such a configuration, the first step-up / step-down switching unit operates in the half cycle of AC power, and the second step-up / step-down switching unit operates in the other half cycle of AC power. That is, when the anode side of the rectifier diode _DA2 is positive, the first step-up / step-down switching unit operates. Here, to form a buck-boost switching power supply circuit (first buck switching power supply circuit) between the N-channel MOS transistor _{Q 1,} a diode _{D 1} and the diode _{D 3} and a diode _{D 2} and the inductor _{L 2} and capacitor _{C 2.}

In addition, when the anode side of the diode _DA1 is positive, the second step-up / step-down switching unit operates. Then, a buck-boost switching power supply circuit (second buck switching power supply circuit) between the N-channel MOS transistor _{Q 2} and the diode _{D 4} and a diode _{D 5} and the diode _{D 2} and the inductor _{L 2} and capacitor _{C 2.}

As described above, the circuit shown in FIG. 6 operates the first step-up / step-down switching power supply circuit and the second step-up / step-down switching power supply circuit alternately every half cycle, thereby improving the power factor and increasing / decreasing the voltage. Can be considered as a switching power supply circuit. Here, varied in a cycle slow compared to the AC power source AC cycle a constant K as described above, to the power factor correction characteristics and favorable, and the capacitance value of the capacitor C ₂ and the appropriate .

Buck-boost switching power supply circuit 12 of the embodiment, the AC power source AC N-channel MOS transistor _{Q 1} is connected to, the connection point of the alternating current power source AC and N-channel MOS transistors _{Q 1,} N-channel MOS transistor _{Q 1} is off diode D ₁ is connected to flow a current to the inductor L ₁ through the capacitor C ₁ and the rectifier diode D _A1 when. Further, the connection point between the other end and the capacitor C ₁ of the diode D _1, N-channel MOS transistor Q ₁ is connected and a diode D ₂ and the inductor L ₂ so as to flow a current to the inductor L ₂ in the off Yes. The capacitor C ₂ is connected to the other end of the inductor L _2. Further, a connection point between the other ends of the diode _{D 2} of the capacitor _{C 2,} between the connection point of the alternating current power source AC and N-channel MOS transistors _{Q 1,} when N-channel MOS transistor _{Q 1} is ON diode D ₃ is connected to flow a current to.

Further, the N-channel MOS transistor _{Q 2} is connected to the connection point of the rectifier diode _{D A1} and the inductor _{L 1,} the connection point of the rectifier diode _{D A1} and the inductor _{L 1} and the N-channel MOS transistors _{Q 2,} N-channel MOS transistor Q ₂ is connected to the connection point of the diode D ₄ to flow a current to the inductor L ₂ is a diode D ₂ and the inductor L ₂ in the off. An N channel MOS transistor Q is connected between a connection point between the other end of the capacitor C _{2 and} the other end of the diode D ₂ and a connection point between the rectifier diode D _A1 , the inductor L ₁ and the N channel MOS transistor Q _{2. 2} is a diode D ₅ to pass an electric current when on is connected. Further, the other end of the N-channel MOS transistor to _{Q 1} and the other end and N-channel MOS transistor _{Q 2,} the other end of the rectifier diode _{D A2} of the other end of the same polarity as the other end and the rectifier diode _{D A1} of the rectifier diode _{D A1} And connected to. Then, by changing the ratio of on and off N-channel MOS transistors Q ₁ and N-channel MOS transistors Q _2, together with changing the voltage generated across the capacitor C _2, buck-boost switching to approximate the power factor to 1 It is a power supply circuit.

Since the step-up / step-down switching power supply circuit 12 of the embodiment uses a direct PFC circuit, an AC-DC converter having a good power factor can be provided. Further, since in place of the N-channel MOS transistor is to use a diode (diode D ₃ and diode D _5), can simplify the circuit. Also, constant voltage characteristics can be obtained by substantially changing the constant K by feedback control. Further, the step-up / step-down switching power supply circuit 12 is provided with two systems of step-up / step-down switching power supply circuits equivalent to the step-up / step-down switching power supply circuit 1, thereby outputting an arbitrary constant voltage regardless of the peak value of the _AC voltage VAC. Can be obtained.

1, 11, 12 buck-boost switching power supply circuit, _C 1, _{C 2 capacitors, D 1, D 2, D} 3, D 4, D 5 _{diodes, D} A1, _{D A2} rectifier diode, _L 1, _{L 2} inductor, Q ₁ , Q ₂ MOS transistor

Claims (3)

A first inductor and a switch element are connected in series to the input power source,
A first diode is connected to a connection point between the first inductor and the switch element so that a current from the first inductor flows when the switch element is off,
The other end of the first diode is connected to a first capacitor;
A second diode and the second inductor are connected to a connection point between the other end of the diode and the first capacitor so that a current flows through the second inductor when the switch element is off. ,
A second capacitor is connected to the other end of the second inductor,
A current is applied between the connection point between the other end of the second capacitor and the other end of the second diode and the connection point between the first inductor and the switch element when the switch element is on. A third diode is connected so that
A step-up / step-down switching power supply circuit that changes a voltage generated at both ends of the second capacitor by changing a ratio between ON and OFF of the switch element. With a control unit,
The control unit includes a differential amplifier that outputs a difference between an output voltage and a reference voltage;
A pulse width modulator to which an output from the differential amplifier is input,
The step-up / step-down switching power supply circuit according to claim 1, wherein the switching element is controlled by a pulse width signal from the pulse width modulator to control an output voltage to a predetermined voltage. A first switch element is connected to the AC power source;
A current is passed through the first inductor via a first capacitor and a first rectifier diode at a connection point between the AC power supply and the first switch element when the first switch element is off. A first diode is connected to
The second diode and the second diode are connected to a connection point between the other end of the first diode and the first capacitor so that a current flows through the second inductor when the first switch element is off. The inductor is connected,
A second capacitor is connected to the other end of the second inductor,
The first switch element is turned on between a connection point between the other end of the second capacitor and the other end of the second diode and a connection point between the AC power supply and the first switch element. A third diode is connected so that current flows when
A second switch element is connected to a connection point between the first rectifier diode and the first inductor;
The fourth inductor is connected to the first inductor, the first rectifier diode, and the second switch element so that a current flows through the second inductor when the second switch element is off. A diode is connected to a connection point between the second diode and the second inductor;
Between a connection point between the other end of the second capacitor and the other end of the second diode, and a connection point between the first rectifier diode, the first inductor, and the second switch element. A fifth diode is connected to pass a current when the second switch element is on;
The other end of the first switch element and the other end of the second switch element are the second rectifier having the same polarity as the other end of the first rectifier diode and the other end of the first rectifier diode. Connected to the other end of the diode,
Step-up / step-down switching that changes the on / off ratio of the first switch element and the second switch element to change the voltage generated at both ends of the second capacitor and to bring the power factor close to 1. Power supply circuit.

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