JP5417898B2 - Switching power supply - Google Patents

Description

  The present invention relates to a switching power supply device including a switching circuit and a rectifier circuit.

  Conventionally, various DC-DC converters have been proposed as switching power supply devices and put into practical use. Most of them use a switching circuit connected to the primary winding of the power conversion transformer (transformer element) to switch the DC input voltage and extract the switching output to the secondary winding of the power conversion transformer. is there. With the switching operation of the switching circuit, the voltage appearing in the secondary winding is rectified by the rectifier circuit, then converted to direct current by the smoothing circuit and output.

  In this type of switching power supply device, in general, so-called synchronous rectification operation is performed in the rectifier circuit in order to reduce efficiency reduction due to conduction loss of the rectifier circuit. This synchronous rectification operation is an operation for controlling the FET to be in an ON state during the rectification operation in the rectification element made of FET (Field Effect Transistor).

  Further, for example, Patent Document 1 proposes a switching power supply device that switches between a rectifying operation using only a rectifying element and the synchronous rectifying operation (switching a rectifying mode) according to the size of a load on the output side. Has been.

JP 2002-252971 A

  Here, in Patent Document 1, an input current or an output current in the power supply device is detected, and the rectification mode is switched using the detection signal. However, when the input voltage varies, the peak value and duty of the current waveform in the input current and output current to be detected also vary. For this reason, these current detection values greatly fluctuate with respect to the reference potential (constant) of the comparator that determines whether to switch the rectifying mode, and the switching point of the rectifying mode also fluctuates greatly.

  That is, in the conventional switching power supply device, when the input voltage fluctuates, the switching point of the rectification mode fluctuates greatly. Therefore, the switching point should be set sufficiently on the light load side in the fluctuation range of the input voltage. I could not. This is because when synchronous rectification operation is performed at light load, power loss may occur when the output current flows backward to the rectifier circuit side, resulting in reduced efficiency. This is because the synchronous rectification operation cannot be used up to the light load side. Therefore, in the past, the synchronous rectification operation, which is more efficient than the rectification operation using only the rectifier element, could not be used sufficiently to the light load side, so further improvement in the efficiency at the light load is desired. It was.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a switching power supply device capable of improving the efficiency particularly at a light load as compared with the conventional art.

The first switching power supply device of the present invention generates an output voltage by performing voltage conversion based on an input voltage input from the input terminal pair, outputs the output voltage from the output terminal pair , and the output voltage is higher than the input voltage. A step-down switching power supply device that is set to be low, a switching circuit disposed on the input terminal pair side, and disposed between the switching circuit and the output terminal pair, and a plurality of rectifying elements A rectifier circuit having a switching element connected in parallel to each of the plurality of rectifier elements, a transformer disposed between the switching circuit and the rectifier circuit, and an input current corresponding to the high voltage side flowing through the input terminal pair side. a current detection unit that detects a voltage detection unit for detecting an input voltage corresponding to the high pressure side, at the time of light load the output terminal pair side is small load, only the rectifying elements And the first rectification mode for performing the rectification operation, and the second rectification mode for performing the synchronous rectification operation using the rectification element and the switching element at the time of heavy load where the load is larger than that at the time of light load. And a switching unit that switches a rectification mode in the rectifier circuit. Further, the switching unit, by controlling the on and off states of the switching elements on the basis of the composite signal with the voltage detection signal detected by the current detection signal and the voltage detection unit detected by the current detection unit, the input voltage The switching of the rectification mode is performed while suppressing the fluctuation of the switching point of the rectification mode due to the fluctuation of the current.

In the first switching power supply device of the present invention, the input voltage input from the input terminal pair is switched in the switching circuit, and an alternating voltage is generated. Further, this AC voltage (input AC voltage) is transformed by a transformer to generate an output AC voltage. The output AC voltage is rectified by a rectifier circuit, and an output voltage is output from the output terminal pair. At this time, an input current corresponding to the high voltage side is detected to obtain a current detection signal, and an input voltage corresponding to the high voltage side is detected to obtain a voltage detection signal. In the light load, the first rectification mode in which the rectification operation is performed using only the rectification element is set, and in the heavy load, the second rectification mode in which the synchronous rectification operation is performed using the rectification element and the switching element. Thus, the rectification mode in the rectifier circuit is switched. Here, the ON / OFF state of the switching element in the rectifier circuit is controlled based on the combined signal of the current detection signal and the voltage detection signal, so that the switching point of the rectification mode due to the fluctuation of the input voltage is controlled . Switching of the rectification mode is performed while the fluctuation is suppressed . For this reason, when the input voltage fluctuates, fluctuation of the switching point of the rectification mode is suppressed more than before (preferably, the switching point is always constant). Therefore, the switching point can be set on the light load side as compared with the conventional case, and the second rectification mode having higher efficiency than the first rectification mode can be used up to the light load side. It becomes like this. Further, since the input current and the input voltage are detected on the high voltage side, the power loss is suppressed as compared with the case of detecting on the low voltage side, and the efficiency is further improved.

  In the first switching power supply device of the present invention, it is preferable that the switching unit includes a resistor for adjusting the weighting of the current detection signal and the voltage detection signal when generating the composite signal. In such a configuration, adjustment of the switching point of the rectification mode is facilitated by such weighting adjustment. Accordingly, the design is facilitated, and the degree of freedom in design is improved.

  In the first switching power supply device of the present invention, the switching unit includes a smoothing circuit that smoothes the pulsating current included in the current detection signal and the voltage detection signal, and the smoothing circuit includes a rectifier diode and a smoothing capacitor. It is preferable to use a peak hold circuit including this. When configured in this way, fluctuations in the composite signal according to fluctuations in the load are reduced, so that fluctuations in the switching point of the rectification mode can be further suppressed, and the switching point can be set to the light load side.

  In the first switching power supply device of the present invention, it is preferable that the threshold value at the time of switching the rectification mode is a value different between when the load tends to increase and when the load tends to decrease. When configured in this way, frequent switching of the rectification mode in the vicinity of the switching point is avoided, and the occurrence of switching noise due to the switching is suppressed.

  The first switching power supply device of the present invention can be configured to function as a DC / DC converter that generates a DC output voltage based on a DC input voltage.

  The second switching power supply of the present invention generates an output voltage by performing voltage conversion based on an input voltage input from one of the first and second input / output terminal pairs. Output from the other input / output terminal pair, arranged on the first input / output terminal pair side, and connected in parallel to the plurality of first rectifier elements and the plurality of first rectifier elements, respectively. A first circuit having a first switching element formed between the first circuit and the second input / output terminal pair, and a plurality of second rectifying elements and the plurality of second switching elements. A second circuit having a second switching element connected in parallel to each of the two rectifier elements, and an input current flowing through one input / output terminal pair side or an output current flowing through the other input / output terminal pair side is detected. Current detector and input voltage or output When the load on the other input / output terminal pair side is light and the load is small, the first rectification mode in which the rectification operation is performed using only the first or second rectifier element is set, and the light detection is performed. In a heavy load where the load is larger than the load, the first or second rectification mode is performed using the first or second rectifying element and the first or second switching element, so that the first or second rectification mode is performed. And a switching unit that switches the rectification mode in the second circuit. The switching unit controls the on / off state of the first or second switching element based on a combined signal of the current detection signal detected by the current detection unit and the voltage detection signal detected by the voltage detection unit. By doing so, the rectification mode is switched. In this case, the switching unit operates when the output voltage is output from the second input / output terminal pair based on the input voltage input from the first input / output terminal pair, and the second input / output terminal. The rectification mode may be switched only during the operation of outputting the output voltage from the first input / output terminal pair based on the input voltage input from the pair and during one of the operations.

  In the second switching power supply device of the present invention, during forward operation, an input voltage is input from the first input / output terminal pair, and the first switching element in the first circuit functioning as an inverter circuit causes an AC voltage to be input. Is generated. Then, the AC voltage based on the AC voltage is rectified in the second circuit functioning as a rectifier circuit, and an output voltage is output from the second input / output terminal pair. On the other hand, during reverse operation, an input voltage is input from the second input / output terminal pair, and an alternating voltage is generated by the second switching element in the second circuit that functions as an inverter circuit. Then, the AC voltage based on the AC voltage is rectified in the first circuit functioning as a rectifier circuit, and an output voltage is output from the first input / output terminal pair. At this time, the input current or the output current is detected to obtain a current detection signal, and the input voltage or the output voltage is detected to obtain a voltage detection signal. At the time of the light load, the first rectification mode in which the rectification operation is performed using only the first or second rectification element is set, and at the time of the heavy load, the first or second rectification element and the first or second rectification element are set. The rectification mode in the first or second circuit functioning as a rectifier circuit is switched so that the second rectification mode in which the synchronous rectification operation is performed using the two switching elements. Here, since the on / off state of the first or second switching element is controlled based on the combined signal of the current detection signal and the voltage detection signal, the rectification mode is switched. When the voltage or the output voltage fluctuates, the fluctuation of the switching point of the rectification mode is suppressed as compared with the conventional case (preferably, the switching point is always constant). Therefore, the switching point can be set on the light load side as compared with the conventional case, and the second rectification mode having higher efficiency than the first rectification mode can be used up to the light load side. It becomes like this.

  According to the switching power supply device of the present invention, by controlling the on / off state of the switching element in the rectifier circuit (first or second circuit) based on the combined signal of the current detection signal and the voltage detection signal, Since switching of the rectification mode is performed, the switching point of the rectification mode can be set on the light load side as compared with the conventional case. Therefore, the second rectification mode having high efficiency can be used up to the light load side, and the efficiency at the time of light load can be improved as compared with the conventional case.

It is a circuit diagram showing the structure of the switching power supply device which concerns on one embodiment of this invention. FIG. 2 is a circuit diagram for explaining a basic operation at a light load in the switching power supply device shown in FIG. 1. FIG. 2 is a circuit diagram for explaining a basic operation at a light load in the switching power supply device shown in FIG. 1. FIG. 2 is a circuit diagram for explaining a basic operation at a heavy load in the switching power supply device shown in FIG. 1. FIG. 2 is a circuit diagram for explaining a basic operation at a heavy load in the switching power supply device shown in FIG. 1. It is a circuit diagram showing the structure of the switching power supply device which concerns on a comparative example. FIG. 7 is a characteristic diagram illustrating an example of a relationship between output current and efficiency in the switching power supply device illustrated in FIG. 6. It is a characteristic view for demonstrating an example of the synthetic | combination process of the detection signal of the input current and input voltage by the switching part shown in FIG. It is a characteristic view showing an example of the relationship between the output current and efficiency in the switching power supply device shown in FIG. It is a characteristic view which compares and shows an example of the efficiency at the time of the light load which concerns on a comparative example and embodiment. It is a circuit diagram showing the structure of the smoothing circuit which concerns on the modification 1 of this invention. FIG. 12 is a characteristic diagram for explaining an example of a synthesis process of detection signals of input current and input voltage when the smoothing circuit shown in FIG. 11 is used. It is a characteristic view for demonstrating switching operation | movement of the rectification mode which concerns on the modification 2 of this invention. It is a circuit diagram showing the structural example of the switching part which performs the switching operation | movement shown in FIG. It is a circuit diagram showing the structure of the switching power supply device which concerns on the modification 3 of this invention. FIG. 16 is a circuit diagram for explaining a reverse operation in the switching power supply device shown in FIG. 15. FIG. 16 is a circuit diagram for explaining a reverse operation in the switching power supply device shown in FIG. 15. FIG. 16 is a circuit diagram for explaining a reverse operation in the switching power supply device shown in FIG. 15.

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

(Example of overall configuration of switching power supply)
FIG. 1 shows a circuit configuration of a switching power supply device (switching power supply device 1) according to an embodiment of the present invention. The switching power supply device 1 functions as a step-down DC / DC converter applied to, for example, an automobile, and converts the DC input voltage Vin input from the input terminals T1 and T2 on the high voltage battery 10 side. (Step-down) generates a DC output voltage Vout, and supplies the output voltage Vout to the low-voltage battery 90 via the output terminals T3 and T4. The switching power supply device 1 includes an input smoothing capacitor Cin, a voltage detection circuit 21, a current detection circuit 22, a switching circuit 3, a resonance inductor Lr, a transformer 4, a rectifier circuit 5, a smoothing circuit 6, A control unit 71, a transformer 72, a SW drive unit 73, and a switching unit 8 are provided.

  The high voltage battery 10 is a battery that stores a voltage of about 100V to 500V. On the other hand, the low voltage battery 90 is a battery that stores a voltage of about 12V.

  The input smoothing capacitor Cin is for smoothing the DC input voltage Vin input from the input terminals T1 and T2.

  The voltage detection circuit 21 is disposed between the primary high-voltage line L1H and the primary low-voltage line L1L connected to the input terminals T1 and T2, and detects the input voltage Vin between both ends and detects this. The detection signal S (Vin1) corresponding to the input voltage Vin is output to the switching unit 8. As a specific circuit configuration of such a voltage detection circuit 21, for example, a voltage is detected by a voltage dividing resistor (not shown) disposed between the primary high-voltage line L1H and the primary low-voltage line L1L. In addition, a device that generates a voltage corresponding to this can be used.

  The current detection circuit 22 is disposed between the voltage detection circuit 21 and the switching circuit 3 on the primary side high voltage line L1H, and detects the input current Iin flowing on the primary side high voltage line L1H. A detection signal S (Iin1) corresponding to the detected input current Iin is output into the switching unit 8. A specific circuit configuration of such a current detection circuit 22 includes, for example, a circuit including a current transformer.

  The switching circuit 3 includes switching elements SW1 to SW4 and constitutes a full bridge type inverter circuit. Each of the switching elements SW1 to SW4 is configured by, for example, a field effect transistor (MOS-FET), a bipolar transistor, an IGBT (Insulated Gate Bipolar Transistor), or the like. Here, each of the switching elements SW1 to SW4 is configured by an N-channel MOS-FET. Here, the gate of the switching element SW1 is connected to the signal line of the SW control signal S1, the source is connected to the drain of the switching element SW2, and the drain is connected to the primary high voltage line L1H. The gate of the switching element SW2 is connected to the signal line of the SW control signal S2, the source is connected to the primary side low-voltage line L1L, and the drain is connected to the source of the switching element SW1. The gate of the switching element SW3 is connected to the signal line of the SW control signal S3, the source is connected to the drain of the switching element SW4, and the drain is connected to the primary high-voltage line L1H. The gate of the switching element SW4 is connected to the signal line of the SW control signal S4, the source is connected to the primary side low-voltage line L1L, and the drain is connected to the source of the switching element SW3. The source of the switching element SW3 is connected to one end of a primary winding 41 in the transformer 4 described later via a resonance inductor Lr described later. The source of the switching element SW1 is connected to the other end of the primary winding 41. With such a configuration, the switching circuit 3 converts the DC input voltage Vin into an input AC voltage in accordance with SW control signals S1 to S4 supplied from the SW drive unit 73 described later. Each of the SW control signals S1 to S4 is a control signal for performing switching driving by pulse width modulation (PWM).

  The resonance inductor Lr is disposed between the source of the switching element SW1 and the primary winding 41 described above, and constitutes a predetermined LC resonance circuit together with the parasitic capacitance elements in the switching elements SW1 to SW4. Is.

  The transformer 4 has a magnetic core 40, and a primary side winding 41 and secondary side windings 421 and 422 that are insulated from each other. Among these, one ends of the pair of secondary windings 421 and 422 are connected to each other by a center tap CT, and wiring from the center tap CT is led to the output line LO. The transformer 4 transforms an input AC voltage generated by the switching circuit 3 and is 180 degrees from each end (end opposite to the center tap CT) of the pair of secondary windings 421 and 422. Output AC voltages with different phases are output. Note that the degree of transformation in this case is determined by the turn ratio between the primary winding 41 and the secondary windings 421 and 422.

  The rectifier circuit 5 includes a pair of rectifier diodes D51 and D52 (for example, parasitic diodes of the switching elements S51 and S52) and switching elements SW51 and SW52 connected in parallel to the rectifier diodes D51 and D52. belongs to. Each of the switching elements SW51 and SW52 is configured by, for example, a MOS-FET, a bipolar transistor, an IGBT, or the like. Here, each of the switching elements SW51 and SW52 is configured by an N-channel MOS-FET. The gate of the switching element SW51 is connected to the signal line of the SW control signal S51, the source is connected to the ground line LG, and the drain is connected to the other end of the secondary winding 421. The gate of the switching element SW52 is connected to the signal line of the SW control signal S52, the source is connected to the ground line LG, and the drain is connected to the other end of the secondary winding 422. The SW control signals S51 and S52 are control signals for performing switching driving by PWM. On the other hand, the cathode of the rectifier diode D51 is connected to the other end of the secondary winding 421, and the cathode of the rectifier diode D52 is connected to the other end of the secondary winding 422. The anodes of the rectifier diodes D51 and D52 are connected to each other and led to the ground line LG. In other words, the rectifier circuit 5 has a center tap type anode common connection configuration, and each half-wave period of the output AC voltage from the transformer 4 is individually rectified by the rectifier diodes D51 and D52 to generate a DC voltage. To get.

  The smoothing circuit 6 has a choke coil 61 and an output smoothing capacitor 62. The choke coil 61 is inserted into the output line LO, one end is connected to the center tap CT, and the other end is connected to the output terminal T3 of the output line LO. The output smoothing capacitor 62 is connected between the output line LO and the ground line LG. An output terminal T4 is provided at the end of the ground line LG. With such a configuration, the smoothing circuit 6 smoothes the DC voltage rectified by the rectifier circuit 5 to generate a DC output voltage Vout, and supplies this to the low voltage battery 90 from the output terminals T3 and T4. Yes.

  Based on the detection signal S (Vout) corresponding to the output voltage Vout, the controller 71 controls the SW control signal S0 that is the basis of the SW control signals S1 to S4 so that the output voltage Vout maintains a constant value. Is supplied to the SW drive unit 73 via the transformer 72, and the SW control signal S50 that is the basis of the SW control signals S51 and S52 is supplied to the SW drive unit 86 in the switching unit 8 described later.

  The SW drive unit 73 generates the aforementioned SW control signals S1 to S4 based on the SW control signal S0 input via the transformer 72, and supplies the generated SW control signals S1 to S4 to the switching elements SW1 to SW4.

  The switching unit 8 includes transformers 811 and 812, smoothing circuits 821 and 822, buffers 831 and 832, resistors R81 and R82, a reference power supply 84, a comparator (comparator) 85, and a SW drive unit 86. Have. The switching unit 8 switches the rectification mode in the rectifier circuit 5 based on the detection signal S (Iin1) detected by the current detection circuit 22 and the detection signal S (Vin1) detected by the voltage detection circuit 21. Is to do. Specifically, when the load (not shown) of the output terminals T3 and T4 is small, the first rectification mode in which the rectification operation is performed using only the rectification diodes D51 and D52 is set, and the above-described light load is achieved. When the load is heavy and heavy, the rectification mode in the rectifier circuit 5 is switched so that the second rectification mode in which the synchronous rectification operation is performed using the rectifier diodes D51 and D52 and the switching elements SW51 and SW52. Yes. Details of the switching operation of the rectification mode will be described later.

  The transformer 811 transforms the current detection signal S (Iin1) supplied from the current detection circuit 22 into a low-voltage signal and outputs it to the smoothing circuit 821. The transformer 812 transforms the voltage detection signal S (Vin1) supplied from the voltage detection circuit 21 into a low-voltage signal and outputs it to the smoothing circuit 822.

  The smoothing circuit 821 is a circuit for smoothing the pulsating flow included in the detection signal S (Iin1) supplied via the transformer 811. The smoothing circuit 822 is a circuit for smoothing the pulsating flow included in the detection signal S (Vin1) supplied via the transformer 812. These smoothing circuits 821 and 822 are configured by, for example, an LPF (low-pass filter) including resistors and capacitors.

  The buffer 831 outputs the current detection signal S (Iin2) by performing impedance conversion on the detection signal S (Iin1) output from the smoothing circuit 821. The buffer 832 outputs a voltage detection signal S (Vin2) by performing impedance conversion on the detection signal S (Vin1) output from the smoothing circuit 822.

  Resistors R81 and R82 synthesize (add) the current detection signal S (Iin2) output from the buffer 831 and the voltage detection signal S (Vin2) output from the buffer 832 to thereby detect these detection signals. A synthesized signal (summed signal) S (Iin + Vin) of S (Iin2) and detection signal S (Vin2) is generated. Further, the weighting when generating such a combined signal S (Iin + Vin) can be adjusted according to the resistance values of the resistors R81 and R82. That is, the resistance value of the resistor R81 constitutes a weighting coefficient of the detection signal S (Iin2), and the resistance value of the resistor R82 constitutes a weighting coefficient of the detection signal S (Vin2).

  In the comparator 85, the combined signal S (Iin + Vin) is input to the inverting input terminal, and the reference voltage (reference voltage) Vref supplied from the reference power supply (reference power supply) 84 to the non-inverting input terminal. Is supplied. As a result, the comparator 85 compares the potentials of the reference voltage Vref and the combined signal S (Iin + Vin), and an output signal Sout indicating a value corresponding to the comparison result is output from the output terminal. .

  The SW drive unit 86 generates SW control signals S51 and S52 based on the SW control signal S50 supplied from the control unit 71 and the output signal Sout supplied from the comparator 85, and the switching elements SW51 and SW52. To supply.

  Here, the rectifier diodes D51 and D52 correspond to a specific example of “a plurality of rectifier elements” in the present invention, and the switching elements SW51 and SW52 correspond to a specific example of the “switching element” in the present invention. Further, the current detection circuit 22 corresponds to a specific example of “current detection unit” in the present invention, and the voltage detection circuit 21 corresponds to a specific example of “voltage detection unit” in the present invention. The resistors R81 and R82 correspond to a specific example of “resistor” in the present invention, and the smoothing circuits 821 and 822 correspond to a specific example of “smoothing circuit” in the present invention.

  Next, the operation and effect of the switching power supply device 1 of the present embodiment will be described.

(Example of basic operation of switching power supply)
First, the basic operation of the switching power supply device 1 will be described with reference to FIGS. 2 to 5 show the state of the basic operation of the switching power supply device 1 using circuit diagrams. Of these, FIGS. 2 and 3 show the operation at a light load, and FIGS. 4 and 5 show the operation at a heavy load, respectively. In these FIGS. 2 to 5, the switching elements SW1 to SW4, SW51, and SW52 are shown in the form of switches for easy explanation.

  In this switching power supply device, in the switching circuit 3, a DC input voltage Vin supplied from the high voltage battery 10 via the input terminals T1 and T2 is switched to generate an input AC voltage. 4 to the primary side winding 41. The transformer 4 transforms the input AC voltage, and the transformed output AC voltage is output from the secondary windings 421 and 422.

  In the rectifier circuit 5, the output AC voltage output from the transformer 4 is rectified by the rectifier diodes D51 and D52, or the rectifier diodes D51 and D52 and the switching elements SW51 and SW52. As a result, a rectified output is generated between the center tap CT and the connection point (anode side) between the rectifier diodes D51 and D52.

  In the smoothing circuit 6, the rectified output generated in the rectifying circuit 5 is smoothed by the choke coil 61 and the output smoothing capacitor 62, and is output from the output terminals T3 and T4 as a DC output voltage Vout. The output voltage Vout is supplied to the low voltage battery 90 for charging, and a load (not shown) is driven.

  At this time, at the time of the light load shown in FIGS. 2 and 3, the operation state shown in FIG. 2 and the operation state shown in FIG. 3 are alternately repeated.

  Specifically, first, as shown in FIG. 2, when the switching elements SW1 and SW4 of the switching circuit 3 are turned on, the primary loop current Ia1 flows in the direction from the switching element SW1 to the switching element SW4. . Then, the voltages appearing in the secondary windings 421 and 422 of the transformer 4 are in the reverse direction with respect to the rectifier diode D52, while in the forward direction with respect to the rectifier diode D51. For this reason, a secondary loop current Ia2 that flows from the rectifier diode D51 through the secondary winding 421, the choke coil 61, and the output smoothing capacitor 62 in this order flows. The secondary loop current Ia2 feeds the DC output voltage Vout to the low voltage battery 90 and drives a load (not shown).

  On the other hand, as shown in FIG. 3, when the switching elements SW1 and SW4 of the switching circuit 3 are turned off and the switching elements SW2 and SW3 of the switching circuit 3 are turned on, the switching elements SW3 to SW2 are switched. The primary loop current Ib1 flows in the direction of. Then, the voltages appearing on the secondary windings 421 and 422 of the transformer 4 are in the reverse direction with respect to the rectifier diode D51, while in the forward direction with respect to the rectifier diode D52. For this reason, the secondary loop current Ib2 that flows from the rectifier diode D52 through the secondary winding 422, the choke coil 61, and the output smoothing capacitor 62 in this order flows. The secondary loop current Ib2 feeds the DC output voltage Vout to the low voltage battery 90 and drives a load (not shown).

  Thus, at the time of the light load shown in FIGS. 2 and 3, the SW control signals S51 and S52 are supplied from the SW drive unit 86 in the switching unit 8 so that both the switching elements SW51 and SW52 are turned off. Thus, the rectification mode in the rectifier circuit 5 becomes the first rectification mode in which the rectification operation is performed using only the rectification diodes D51 and D52.

  4 and FIG. 5, the operation state shown in FIG. 4 and the operation state shown in FIG. 5 are alternately repeated. Specifically, in the operation states shown in FIGS. 4 and 5, the switching elements SW51 and SW52 perform the synchronous rectification operation in addition to the operation at the light load shown in FIGS. That is, the switching unit 8 is set so that the switching element SW51 is turned on during the rectification operation of the diode D51 (FIG. 4) and the switching element SW52 is turned on during the rectification operation of the diode D52 (FIG. 5). SW control signals S51 and S52 are supplied from the SW drive unit 86. Thereby, at the time of this heavy load, the second rectification mode in which the synchronous rectification operation is performed using the rectification diodes D51 and D52 and the switching elements SW51 and SW52, and the secondary loop currents Ia3 and Ib3 shown in the figure flow. It will be.

  Here, in both the light load and the heavy load, the control unit 71 maintains the output voltage Vout at a constant value based on the detection signal S (Vout) corresponding to the output voltage Vout. As described above, the SW control signal S0 is supplied to the SW drive unit 73 via the transformer 72, and the SW control signal S50 is supplied to the SW drive unit 86. The current detection circuit 22 detects a current detection signal S (Iin1) corresponding to the input current Iin, and the voltage detection circuit 21 detects a voltage detection signal S (Vin1) corresponding to the input voltage Vin. And input to the switching unit 8.

(Example of switching operation in rectification mode by switching unit)
Next, referring to FIGS. 6 to 10 in addition to FIG. 1, the switching operation of the rectification mode of the rectifier circuit 5 by the switching unit 8 which is one of the characteristic parts of the present invention is compared with the comparative example. The details will be described. Here, FIG. 6 shows a circuit configuration of a conventional switching power supply device (switching power supply device 101) according to a comparative example, and FIG. 7 shows an output current Iout (with respect to a rated current) in the switching power supply device 101. This shows an example of the relationship between the overall load factor) and the efficiency of the entire apparatus.

  First, in the switching power supply device 101 according to the comparative example shown in FIG. 6, the voltage detection circuit 21 in the present embodiment is not provided, and the switching unit 108 is provided instead of the switching unit 8 in the present embodiment. ing. Specifically, the switching unit 108 generates the SW control signals S51 and S52 based only on the current detection signal S (Iin1) corresponding to the input current Iin, thereby switching the rectification mode in the rectifier circuit 5. To do. That is, based on the current detection signal S (Iin1), the transformer 811, the smoothing circuit 821, and the buffer 831 generate the current detection signal S (Iin2), and the comparator 85 uses the detection signal S (Iin2) and the reference. An output signal Sout corresponding to the comparison result with the voltage Vref is output, and the SW drive unit 86 generates SW control signals S51 and S52 based on the output signal Sout.

  However, when the input voltage Vin changes, the peak value and duty of the current waveform in the input current Iin to be detected also change. For this reason, the current detection signal S (Iin2) largely fluctuates with respect to the reference voltage Vref (constant) of the comparator 85 that determines whether to switch the rectification mode. Thereby, in this comparative example, as indicated by reference numerals P101 and P102 in FIG. 7, for example, the switching point of the rectification mode between the diode rectification (first rectification mode) and the synchronous rectification (second rectification mode) is also provided. The input voltage Vin varies greatly according to the magnitude of the input voltage Vin (here, the rated input voltage is 260 V and the input voltage range is 100 V to 420 V) (the fluctuation range in the output current Iout corresponding to the size of the load). Is great). Note that the efficiency characteristic lines shown in FIG. 7 are arranged in the order of the input voltage Vin = 100V to 420V from the upper side in the drawing.

  That is, in the switching power supply device 101 according to this comparative example, when the input voltage Vin fluctuates, the switching point of the rectification mode fluctuates greatly, and as the input voltage Vin increases, the switching point is also displaced toward the high load side. Therefore, the switching point cannot be set to the light load side sufficiently in the fluctuation range of the input voltage Vin (for example, the switching point is set within the target output current range ΔIout shown in FIG. 7). Can not). This is due to the following reason. That is, first, when performing a synchronous rectification operation at a light load, a power loss occurs when the output current flows backward from the low voltage battery 90 to the rectifier circuit 5 side as in the current I101 shown in FIG. May fall. Further, based on the energy stored in the choke coil 61 by the backflow current I101, a surge voltage is generated when both of the switching elements SW51 and SW52 are turned off, whereby the switching elements SW51 and SW52 are destroyed. There is a risk of being. Therefore, in consideration of these matters, when the switching point fluctuates greatly, the synchronous rectification operation cannot be used up to the light load side. From the above, in this comparative example, synchronous rectification (second rectification mode), which is more efficient than diode rectification (first rectification mode), cannot be used sufficiently to the light load side, Efficiency at light load will be low.

  In contrast, in the present embodiment, as shown in FIG. 1, the switching unit 8 detects the current detection signal S (Iin1) detected by the current detection circuit 22 and the voltage detection circuit 21. The rectification mode is switched by controlling the on / off state of the switching elements SW51 and SW52 in the rectifier circuit 5 based on the combined signal S (Iin + Vin) based on the voltage detection signal S (Vin1). . Specifically, in the comparator 85, for example, when the combined signal S (Iin + Vin) is smaller than a predetermined reference voltage Vref, diode rectification (first rectification mode) is performed, that is, the switching element SW51. , SW52 are controlled to turn on / off the switching elements SW51, SW52. On the other hand, for example, when the composite signal S (Iin + Vin) is larger than the predetermined reference voltage Vref, the synchronous rectification (second rectification mode) is performed, that is, the switching elements SW51 and SW52 are turned on during rectification. Thus, the on / off states of the switching elements SW51 and SW52 are controlled.

  Here, for example, as shown in FIG. 8, under the same output voltage Vout and output current Iout, the detection signal S (Iin1) of the input current Iin has a higher detection value and a lower input voltage Vin. The higher the voltage Vin, the lower the detected value (here, the detected value is inversely proportional to the input voltage Vin). Further, since the smoothing circuits 821 and 822 are configured by LPF or the like, unlike the peak detection by the diode, the smoothing circuits 821 and 822 are hardly affected by temperature. On the other hand, the detection value of the detection signal S (Vin1) of the input voltage Vin is proportional to the input voltage Vin. Therefore, in the combined signal S (Iin + Vin) based on the detection signal S (Iin1) and the detection signal S (Vin1), even if the input voltage Vin fluctuates at a certain output current Iout, as shown in FIG. It will be kept constant.

  Thus, for example, as shown in FIG. 9, when the input voltage Vin fluctuates, the switching point (output current) of the rectification mode between the diode rectification (first rectification mode) and the synchronous rectification (second rectification mode). The fluctuation of the threshold current Ith of Iout is suppressed as compared with the comparative example (preferably, the switching point is always constant). Therefore, the switching point (threshold current Ith) can be set to a lighter load side compared to the conventional case (for example, the threshold current Ith can be set within the target output current range ΔIout shown in FIG. 9). As a result, synchronous rectification (second rectification mode), which is more efficient than diode rectification (first rectification mode), can be used up to a lighter load side. Note that the efficiency characteristic lines shown in FIG. 9 are also arranged in the order of the input voltage Vin = 100V to 420V from the upper side in the figure.

  As described above, in the present embodiment, the switching unit 8 uses the current detection signal S (Iin1) detected by the current detection circuit 22 and the voltage detection signal S (Vin1) detected by the voltage detection circuit 21. Since the switching of the rectification mode is performed by controlling the on / off state of the switching elements SW51 and SW52 in the rectifier circuit 5 based on the combined signal S (Iin + Vin) based on the rectification mode, The switching point (threshold current Ith) can be set to a lighter load side in the fluctuation range of the input voltage Vin. Therefore, high efficiency synchronous rectification (second rectification mode) can be used up to the light load side, and it becomes possible to improve the efficiency especially at the light load as compared with the conventional case.

  Here, FIG. 10 is a comparison between the comparative example and an example of the efficiency at light load according to the present embodiment, and the characteristic indicated by reference sign G101 in the drawing is that of the comparative example. The characteristics indicated by reference numeral G1 in the figure represent those of the present embodiment. As indicated by the arrow P1 in the figure, it can be seen that the efficiency at light load is improved in the present embodiment (G1) as compared with the comparative example (G101).

  The switching unit 8 includes resistors R81 and R82 for adjusting the weighting of the current detection signal S (Iin2) and the voltage detection signal S (Vin2) when the composite signal S (Iin + Vin) is generated. Since it is provided, adjustment of the switching point (threshold current Ith) of the rectification mode is facilitated by such weighting adjustment. Therefore, the design is facilitated, and the degree of freedom in design can be improved. Further, since the current detection signal S (Iin2) and the voltage detection signal S (Vin2) are synthesized by the resistors R81 and R82, for example, an inexpensive configuration compared with an adder using an operational amplifier. It becomes possible to do.

  Furthermore, in the step-down switching power supply device 1, the current detection circuit 22 and the voltage detection circuit 21 detect the input current Iin and the input voltage Vin corresponding to the high voltage side, so that the output current Iout corresponding to the low voltage side. Compared with the case where the output current Vout is detected and the switching operation of the rectification mode is performed, the power loss can be suppressed and the efficiency can be further improved.

  As described above, when performing a synchronous rectification operation at a light load, a surge voltage may be generated based on the energy stored in the choke coil 61 due to the reverse current I101. Considering this, it can be said that the switching operation of the rectification mode described in the present embodiment is particularly effective in the switching power supply device in which the choke coil is provided on the output side.

[Modification]
Next, some modifications of the present invention will be described. In addition, the same code | symbol is attached | subjected about the component similar to the said embodiment, and description is abbreviate | omitted suitably.

(Modification 1)
FIG. 11 shows a circuit configuration of a smoothing circuit (smoothing circuits 821A and 822A) according to Modification 1 of the present invention. These smoothing circuits 821A and 822A are configured using a peak hold circuit having a rectifier diode D82 and a smoothing capacitor C82. Specifically, the anode of the rectifier diode D82 is connected to the input signal line from the transformers 811 and 812, the cathode is connected to one end of the smoothing capacitor C82 and the output signal line, and the other end of the smoothing capacitor C82 is grounded. Yes. That is, although the smoothing circuits 821 and 822 of the above embodiment have been described with reference to the configuration using the LPF, the smoothing circuits 821A and 822A of the present modification have a configuration using the peak hold circuit.

  In the smoothing circuits 821 and 822 having such a configuration, for example, as indicated by arrows P2 and P3 in FIG. 12, the fluctuation of the combined signal S (Iin + Vin) corresponding to the fluctuation of the load (output current Iout) is reduced. Therefore, the fluctuation of the switching point (threshold current Ith) in the rectification mode can be further suppressed, and the switching point can be set to the light load side.

(Modification 2)
FIG. 13A shows a rectification mode switching operation according to the second modification of the present invention. In this modification, the threshold value (threshold current) of the output current when switching the rectification mode is a different value (threshold current IthL, IthH) when the output current Iout is increasing or decreasing. Yes. That is, in the above embodiment, as shown in FIG. 13B, the threshold current Ith is the same when the output current Iout is increasing and decreasing, whereas in this modification, Hysteresis is shown.

  Specifically, in this modification, as shown in FIG. 13A, when the output current Iout is increasing, the rectification mode is switched at the threshold current IthH (> IthL). On the other hand, when the output current Iout is decreasing, the connection state is switched at the threshold current IthL (<IthH).

  Further, in order to realize such a switching operation, the switching unit (switching unit 8A) of this modification is provided with a hysteresis comparator as shown in FIG. 14, for example. That is, in the comparator 85 described in the above embodiment, the resistor R85 is provided between the output terminal and the non-inverting input terminal. Thus, based on the combined signal S (Iin + Vin), the output signal Sout corresponding to the comparison result with the different reference voltages Vref is output when the output current Iout is increasing and decreasing. The values of the threshold currents IthL and IthH can be arbitrarily adjusted according to the resistance value of the resistor R85.

  With such a configuration, in this modification, it is possible to avoid frequent switching of the rectification mode in the vicinity of the threshold current, and thus it is possible to suppress the occurrence of switching noise caused by the switching.

(Modification 3)
FIG. 15 illustrates a circuit configuration of a switching power supply device (switching power supply device 1A) according to Modification 3 of the present invention. The switching power supply device 1A of the present modification functions as a bidirectional switching power supply device (DC / DC converter). Specifically, in the switching circuit 1A, rectifier diodes D31 to D32 (for example, parasitic diodes of the switching elements S1 to S4) are connected in parallel to the switching elements S1 to S4 in the switching circuit (rectifier circuit) 3A. . Thus, in addition to the step-down operation of stepping down the DC input voltage Vin input from the input terminals T1 and T2 and outputting the DC output voltage Vout from the output terminals T3 and T4 as described in the above embodiment, As will be described below, it is also possible to perform a boosting operation of boosting the DC input voltage Vin input from the output terminals T3 and T4 and outputting the DC output voltage Vout from the input terminals T1 and T2 (bidirectional). Operation is possible). In that case, during the step-down operation (forward operation), the switching circuit 3A functions as an inverter circuit and the switching circuit (rectifier circuit) 5 functions as a rectifier circuit, and during the step-up operation (reverse operation). The switching circuit 5 functions as an inverter circuit and the switching circuit 3A functions as a rectifier circuit.

  In the switching power supply apparatus 1A, the output signal Sout based on the combined signal S (Iin + Vin) output from the comparator 85 in the switching unit 8 is input to the SW drive unit 73 in addition to the SW drive unit 86. It is like that. Thus, during the reverse operation, the on / off states of the switching elements SW1 to SW4 in the switching circuit 3A functioning as a rectifier circuit are controlled, and the rectification mode is switched in the switching circuit 3A.

  In this case, the input terminals T1 and T2 correspond to a specific example of “first input / output terminal” in the present invention, and the output terminals T3 and T4 correspond to one specific example of “second input / output terminal” in the present invention. Corresponds to the example. Further, the switching circuit (rectifier circuit) 3A corresponds to a specific example of “first circuit” in the present invention, and the switching circuit (rectifier circuit) 5 corresponds to a specific example of “second circuit” in the present invention. To do. The switching elements SW1 to SW4 correspond to a specific example of “first switching element” in the present invention, and the rectifier diodes D31 to D34 correspond to a specific example of “a plurality of first rectifying elements” in the present invention. To do. Further, the switching elements SW51 and SW52 correspond to a specific example of “second switching element” in the present invention, and the rectifier diodes D51 and D52 correspond to a specific example of “a plurality of second rectifying elements” in the present invention. To do.

  In the switching power supply device 1A, during the forward operation, the same basic operation and rectification mode switching operation as in the above embodiment are performed, and thus the same effect as in the above embodiment can be obtained.

  On the other hand, during reverse operation, the operation states shown in FIGS. 16 to 18 are repeated alternately. In FIGS. 17 and 18, the current loop at the time of light load is indicated by a solid line, and the current loop at the time of heavy load is indicated by a solid line and a broken line.

  First, as shown in FIG. 16, the switching elements SW51 and SW52 are both turned on. Therefore, on the low voltage side including the switching circuit 5, loop currents Ic11 and Ic12 as shown in the figure flow from the low voltage battery 70, and the inductor 61 is excited. In addition, since the windings 421 and 422 of the transformer 4 have the opposite winding directions and the same number of turns, the magnetic fluxes generated by the currents flowing through these windings 421 and 422 cancel each other, and the windings 421 and 422 The voltage between both ends is 0V. Therefore, power transmission from the low voltage side to the high voltage side is not performed during this period. However, on the high voltage side, an output current Iout as shown in the figure flows from the input smoothing capacitor Cin to the high voltage battery 10L.

  Next, as shown in FIG. 17, the switching element SW52 is turned off. Therefore, only the loop current Ic11 as shown in the figure flows on the low voltage side, and electric power is transmitted from the low voltage side to the high voltage side based on the energy accumulated in the inductor 61. On the high voltage side including the switching circuit 3A, the secondary loop current Ic21 and the output current Iout as shown in the figure flow. Note that after the period of the operation state shown in FIG. 17, the operation state shown in FIG. 16 is obtained again.

  Next, after the state shown in FIG. 16 again, the switching element SW51 is turned off as shown in FIG. Therefore, only the loop current Ic12 as shown in the figure flows on the low voltage side, and electric power is transmitted from the low voltage side to the high voltage side based on the energy accumulated in the inductor 61. On the high voltage side including the switching circuit 3A, the secondary loop current Ic22 and the output current Iout as shown in the drawing flow.

  Here, during such reverse operation, the switching unit 8 supplies the output signal Sout based on the combined signal S (Iin + Vin) to the SW drive unit 73, thereby switching the switching circuit 3A functioning as a rectifier circuit. The on / off states of the elements SW1 to SW4 are controlled to switch the rectification mode in the switching circuit 3A. Thereby, it becomes possible to improve the efficiency especially at the time of light load compared with the past by the effect | action similar to the time of the forward operation demonstrated in the said embodiment. However, in the bidirectional switching power supply device (DC / DC converter) as in this modification, such a switching operation of the rectification mode may be performed only in one of the forward operation and the forward operation. Alternatively, as described above, it may be performed in both the forward operation and the reverse operation.

  Note that the rectifying mode switching operation described above is also particularly effective in a switching power supply device in which a choke coil is provided on the output side even in a bidirectional switching power supply device as in this modification. That is, for example, the switching power supply device 1A shown in FIG. 15 is particularly effective during forward operation in which a choke coil is provided on the output side.

  Although the present invention has been described with reference to the embodiment and the modification examples, the present invention is not limited to the embodiment and the like, and various modifications can be made.

  For example, the configurations of the switching circuit, the transformer, the rectifier circuit, the smoothing circuit, the control unit, and the like described in the above embodiments are not limited to these, and may be other configurations. Specifically, for example, in the above-described embodiment and the like, the case where the switching circuit is a full bridge type circuit has been described, but a switching circuit having another circuit configuration such as a half bridge type may be used. Further, for example, the function (configuration by hardware) of the comparator 85 described in the above embodiment may be configured by software.

  In the above-described embodiment and the like, the case where the current detection circuit 22 and the voltage detection circuit 21 detect a current or voltage corresponding to the high voltage side has been described. However, in some cases, the current or voltage corresponding to the low voltage side is detected. You may make it detect.

  Further, although an example has been described so far with an insulating switching power supply device using a transformer as an example, the present invention is applicable to a switching power supply device that does not have a transformer, such as a non-isolated chopper type switching power supply device. Can also be applied.

  In addition, the case where the switching power supply device functions as a DC / DC converter has been described so far, but the switching power supply device of the present invention can be applied to, for example, an AC / DC converter or a DC / AC inverter. It is possible to apply.

  In addition, the case where the switching power supply device is a step-down switching power supply device (DC / DC converter) has been described so far. However, the switching power supply device of the present invention can be applied to, for example, a step-up switching power supply device. It is possible to apply.

  In addition, the case where the entire switching power supply device is used as a charging / discharging device for a battery or the like has been described so far. However, the switching power supply device according to the present invention is not limited to such a charging / discharging device. It can be applied to other uses such as a power supply device.

  DESCRIPTION OF SYMBOLS 1,1A ... Switching power supply device, 10 ... High voltage battery, 21 ... Voltage detection circuit, 22 ... Current detection circuit, 3, 3A ... Switching circuit (rectifier circuit), 4 ... Transformer, 40 ... Magnetic core, 41 ... Primary side Winding (high voltage side winding), 421, 422 ... Secondary side winding (low voltage side winding), 5 ... Rectifier circuit (switching circuit), 6 ... Smoothing circuit, 61 ... Choke coil, 62 ... Output smoothing capacitor, 71 ... Control unit, 72 ... Transformer, 73 ... SW drive unit, 8,8A ... Switching unit, 811,812 ... Transformer, 821,822,821A, 822A ... Smoothing circuit, 831,832 ... Buffer, 84 ... Reference power supply, 85 ... Comparator, 86 ... SW drive unit, 90 ... Low voltage battery, T1, T2 ... Input terminal (input / output terminal), T3, T4 ... Output terminal (input / output terminal), Vin ... Input voltage, Iin ... Input power Current, Vout ... Output voltage, Iout ... Output current, L1H ... Primary side high voltage line, L1L ... Primary side low voltage line, LO ... Output line, LG ... Ground line, Cin ... Input smoothing capacitor, SW1 to SW4, SW51, SW52... Switching element (FET), S0, S1 to S4, S50, S51, S52... SW control signal, S (Vin1), S (Vin2), S (Iin1), S (Iin2), S (Vout). Signal, S (Iin + Vin) ... Composite signal (summation signal), Sout ... Output signal, Lr ... Resonance inductor, CT ... Center tap, D51, D52 ... Rectifier diode, R81, R82 ... Resistor, Vref ... Reference voltage, D82 ... Rectifier diode, C82 ... Smoothing capacitor, R85 ... Resistor, Ia1, Ib1, Ic11, Ic12 ... Current (primary current loop), Ia2, Ia3, Ib2 Ib3, Ic21, Ic22 ... current (secondary current loop), ΔIout ... output current range, Ith, IthL, IthH ... threshold current.

Claims (5)

The output voltage is generated by performing voltage conversion based on the input voltage input from the input terminal pair, output from the output terminal pair, and the step-down type set so that the output voltage is lower than the input voltage a switching power supply unit,
A switching circuit disposed on the input terminal pair side;
A rectifier circuit disposed between the switching circuit and the output terminal pair, and having a plurality of rectifier elements and switching elements respectively connected in parallel to the plurality of rectifier elements;
A transformer disposed between the switching circuit and the rectifier circuit;
A current detection unit for detecting an input current corresponding to the high voltage side flowing through the input terminal pair side;
A voltage detector for detecting the input voltage corresponding to the high voltage side ;
When the load on the output terminal pair side is small and light load, the first rectification mode for performing rectification operation using only the rectifier element is set, and at the time of heavy load where the load is larger than that at the light load, the rectifier element and A switching unit that switches a rectification mode in the rectifier circuit so as to be in a second rectification mode in which a synchronous rectification operation is performed using the switching element,
The switching unit controls the on / off state of the switching element based on a combined signal of the current detection signal detected by the current detection unit and the voltage detection signal detected by the voltage detection unit, The switching power supply device is characterized in that the switching of the rectification mode is performed while suppressing the fluctuation of the switching point of the rectification mode due to the fluctuation of the input voltage . The switching power supply according to claim 1, wherein the switching unit includes a resistor for adjusting a weight of the current detection signal and the voltage detection signal when the combined signal is generated. The switching unit includes a smoothing circuit that smoothes a pulsating current included in the current detection signal and the voltage detection signal,
The switching power supply according to claim 1 or 2, wherein the smoothing circuit is configured using a peak hold circuit including a rectifier diode and a smoothing capacitor. Threshold during switching of the rectifier mode, in a time of decreasing the time of increase of the load, according to any one of claims 1 to 3, characterized in that has a value different from each other Switching power supply. The switching power supply device according to any one of claims 1 to 4 , wherein the switching power supply device functions as a DC / DC converter that generates a DC output voltage based on a DC input voltage.

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