JP4715985B2 - Switching power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention belongs to a switching power supply, and more particularly to a switching power supply capable of improving an input power factor with a small number of components.
[0002]
[Prior art]
FIG. 5 shows a flyback switching power supply device that has been widely used in the past. The switching power supply device shown in FIG. 5 has a rectifier bridge circuit (2) as a rectifier circuit that converts the _AC voltage VAC of the AC power supply (1) into a DC voltage _VDC , and an input connected to the rectifier bridge circuit (2). A smoothing capacitor (3), a transformer (4) having a primary winding (4a) and a secondary winding (4b), a MOS-FET (MOS field effect transistor) (5) as a main switching element, A rectifying / smoothing circuit (8) having a rectifying diode (6) and a smoothing capacitor (7), a voltage detecting circuit (9) for detecting an output voltage V _O of the rectifying / smoothing circuit (8), and a voltage detecting circuit (9) And a control circuit (10) for controlling on / off of the MOS-FET (5) by a detection signal. The primary winding (4a) of the transformer (4) and the MOS-FET (5) are connected in series with the input smoothing capacitor (3). The rectifying / smoothing circuit (8) is connected to the secondary winding (4b) of the transformer (4) and generates DC power of voltage V _O. Control circuit (10), defines the target value of the voltage level output voltage V _O of the detection signal of the MOS-FET (5) is in the ON state after the end of the reset period, the voltage detection circuit (9) of the transformer (4) The level of the DC output voltage V _O output from the rectifying and smoothing circuit (8) is kept constant by turning off the MOS-FET (5) when the level of the reference voltage to be exceeded is exceeded.
[0003]
The operation of the switching power supply device shown in FIG. 5 is as follows. When the AC voltage V _AC shown from the AC power source (1) in FIG. 6 (A) is applied to the rectifier bridge circuit (2), all the output terminals of the rectifier bridge circuit (2) shown by the broken line shown in FIG. 6 (B) A wave rectified voltage V _DC is generated. The full-wave rectified voltage V _DC of the rectifier bridge circuit (2) is smoothed by the input smoothing capacitor (3), and the voltage V _{C1 at} both ends thereof is as shown by the solid line in FIG. Here, in the period t ₁ , the voltage V _{C1 of the} input smoothing capacitor (3) is lower than the full-wave rectified voltage V _DC output from the rectifying bridge circuit (2). The charging current I _C1 shown in FIG. Conversely, the voltage V _C1 of the period t ₂ in the input smoothing capacitor (3) is higher than the full-wave rectified voltage V _DC output from the rectifier bridge circuit (2), the input smoothing capacitor (3) charging current I _C1 does not flow, and a discharge current flows from the input smoothing capacitor (3) to the primary winding (4a) of the transformer (4) and the MOS-FET (5). Therefore, the AC current I _AC flowing between the AC power source (1) and the rectifying bridge circuit (2) flows only in the vicinity of the maximum value of the _AC voltage V _AC as shown in FIG. 6 (D).
[0004]
As shown in FIG. 7 (E), a high voltage (H) level control pulse signal V _G is applied from the control circuit (10) to the gate terminal of the MOS-FET (5), and the MOS-FET (5) is turned on. In this state, current flows from the input smoothing capacitor (3) through the primary winding (4a) of the transformer (4) and the MOS-FET (5), and energy is stored in the transformer (4). As a result, as shown in FIG. 7C, the voltage V _Q1 between the drain and source terminals of the MOS-FET 5 drops rapidly to 0 [V], and the drain current I _Q1 is changed to FIG. It rises linearly as shown. At this time, since a reverse voltage is applied to the rectifying diode (6) constituting the rectifying / smoothing circuit (8) and the rectifying diode (6) becomes non-conductive, energy is transferred to the secondary winding (4b) of the transformer (4). Is not done.
[0005]
Next, the control pulse signal V _{G applied} from the control circuit (10) to the gate terminal of the MOS-FET (5) is changed from a high voltage (H) level to a low voltage (L) level as shown in FIG. When the MOS-FET (5) changes from the on state to the off state, the voltage V _Q1 between the drain and source terminals of the MOS-FET (5) is applied to the input smoothing capacitor (3) as shown in FIG. As the voltage V _C1 rises rapidly to the maximum value, the drain current I _Q1 becomes zero as shown in FIG. As a result, a forward voltage is applied from the secondary winding (4b) of the transformer (4) to the rectifying diode (6) of the rectifying / smoothing circuit (8) and becomes conductive. The supplied energy is supplied from the secondary winding (4b) to the rectifying / smoothing circuit (8), and the transformer (4) is reset. At this time, a flyback voltage is generated by the back electromotive force generated in the primary winding (4a) of the transformer (4). When the reset period of the transformer (4) ends, a high voltage (H) level control pulse signal V _G is applied from the control circuit (10) to the gate terminal of the MOS-FET (5), and the MOS-FET (3 ) Is turned on again. 7A and 7B show the _AC voltage V _AC and the AC current I _{AC of the AC} power source (1), respectively.
[0006]
[Problems to be solved by the invention]
In the conventional switching power supply shown in FIG. 5, the voltage V _C1 of the input smoothing capacitor (3) is lower than the full-wave rectified voltage V _DC output from the rectifier bridge circuit (2) as shown in FIG. 6 (C). The charging current I _C1 flows to the input smoothing capacitor (3) only during the period t ₁ . Therefore, the AC current I _AC flows only near the maximum value of the _AC voltage V _AC as shown in FIG. 6D with respect to the AC voltage V _AC of the AC power source (1) shown in FIG. Since the angle is narrow, the input power factor has a low drawback of about 0.5 to 0.6. In order to eliminate this drawback, a PFC converter or the like has been proposed in which a boost chopper circuit or the like is inserted between the rectifier bridge circuit (2) and the input smoothing capacitor (3) to improve the input power factor to 1.0. However, it is necessary to separately provide a circuit for performing switching control of the boost chopper circuit, and there is a problem that the number of parts increases and the circuit configuration becomes complicated.
[0007]
Accordingly, an object of the present invention is to provide a switching power supply apparatus that can improve the input power factor with a small number of parts.
[0008]
[Means for Solving the Problems]
A switching power supply according to the present invention includes a rectifier circuit (2) that converts AC power of an AC power supply (1) into DC power, an input smoothing capacitor (3) connected to the rectifier circuit (2), and an input smoothing capacitor ( 3) The primary winding (4a) and main switching element (5) of the transformer (4) connected in series to the secondary winding (4b) of the transformer (4) and the DC output ( A rectifying / smoothing circuit (8) for generating V _O ) and a control circuit (10) for controlling on / off of the main switching element (5) are provided. The control circuit (10) turns on the main switching element (5) after the reset period of the transformer (4) ends, and the level of the output voltage (V _O ) of the rectifying / smoothing circuit (8) exceeds the level of the reference voltage. The main switching element (5) is turned off. In the switching power supply device of the present invention, the reactor (first energy storage means) (11) connected between the rectifier circuit (2) and the input smoothing capacitor (3), and the primary winding of the transformer (4) A feedback capacitor (second energy storage means) (12) connected in parallel with (4a), and an auxiliary switching element (13) connected in series with the feedback capacitor (12). ) Is turned off, the feedback capacitor (12) is charged by the back electromotive force generated in the primary winding (4a) of the transformer (4), and the auxiliary switching element (13) is turned on after the main switching element (5) is turned on. ) Is turned on, and a closed circuit of the reactor (11), the feedback capacitor (12), and the rectifier circuit (2) is formed. The control circuit (10) gives an ON signal to the auxiliary switching element (13) after a predetermined delay time (t _D ) after the main switching element (5) is turned on, and the main switching element (5) While turning off, the auxiliary switching element (13) is also turned off. The on-period of the auxiliary switching element (13) is shorter than the on-period of the main switching element (5), and the on-period of the main switching element (5) is shorter than the delay time (t _D ) during overcurrent or light load. Then, the auxiliary switching element (13) does not turn on.
[0009]
During the OFF period of the main switching element (5), the second energy storage means (12) is charged by the back electromotive force generated in the primary winding (4a) of the transformer (4). Subsequently, when the auxiliary switching element (13) is turned on after the main switching element (5) is turned on, the first energy storage means (11), the second energy storage means (12), and the rectifier circuit (2) Therefore, the sum voltage of the charging voltage of the second energy storage means (12) and the output voltage of the rectifier circuit (2) is applied to the first energy storage means (11), Is accumulated. Next, when the main switching element (5) is turned off, the energy stored in the first energy storage means (11) is released, and a current for charging the input smoothing capacitor (3) flows. As a result, even when the input voltage is smaller than the voltage of the input smoothing capacitor (3), the input current flows and the conduction angle is widened. Therefore, the input force can be reduced with a small number of components that requires the addition of two energy storage means and one switching element. The rate can be improved.
[0010]
In the present invention, the first energy storage means is the reactor (11), and the second energy storage means is the capacitor (12). A rectifying element (14) is connected between the reactor (11) and the input smoothing capacitor (3). Further, by turning on the auxiliary switching element (13) after the delay time (t _D ) has elapsed since the main switching element (5) was turned on, the on period of the auxiliary switching element (13) is changed to the main switching element (13). Since it is shorter than the ON period of (5), the auxiliary switching element (13) will not turn ON if the ON period of the main switching element (5) becomes shorter than the delay time (t _D ) due to overcurrent or light load. Therefore, the boosting operation is not performed, and an abnormal increase in the voltage of the input smoothing capacitor (3) can be prevented. Further, a rectifying element (13a) may be connected between both main terminals of the auxiliary switching element (13).
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a switching power supply according to the present invention will be described with reference to FIGS. However, in these drawings, substantially the same parts as in FIGS. 5 to 7 are denoted by the same reference numerals, and description thereof is omitted.
As shown in FIG. 1, the switching power supply according to the present embodiment includes a boost reactor (11) as a first energy storage means connected between a rectifier bridge circuit (2) and an input smoothing capacitor (3). A feedback capacitor (12) as a second energy storage means connected in parallel with the primary winding (4a) of the transformer (4), and an auxiliary switching element connected in series with the feedback capacitor (12). And a step-up MOS-FET (13) and a diode (14) as a rectifier connected between the step-up reactor (11) and the input smoothing capacitor (3). A parasitic diode (13a) indicated by a broken line is formed between the drain and source in the boosting MOS-FET (13). After the delay time t _D has elapsed since the high voltage (H) level control pulse signal V _G1 has been applied to the gate terminal of the MOS-FET (5), the control circuit (10) boosts the MOS-FET (13 ) Is applied with a high voltage (H) level control pulse signal V _G2 . Therefore, the ON period of the boosting MOS-FET (13) is shorter than the ON period of the MOS-FET (5). Other configurations are substantially the same as those of the conventional switching power supply device shown in FIG.
[0012]
In the configuration shown in FIG. 1, the AC voltage V _AC shown in FIG. 2 (A) is applied from the AC power supply (1) to the rectifier bridge circuit (2), FIG from the output terminal of the rectifier bridge circuit (2) 2 ( C) and the full-wave rectified voltage V _DC shown in FIG. As shown in FIGS. 4E and 4D, control pulse signals V _G1 , V _{G provided} to the gate terminals of the MOS-FET 5 and the boosting MOS-FET 13 from the control circuit 10. _When both _G2 are in the off state at a low voltage (L) level, the energy stored in the boost reactor (11) is released during the ON period of the MOS-FET (5) and the boost MOS-FET (13), A charging current flows to the input smoothing capacitor (3) through the diode (14). Therefore, as shown in FIGS. 4B and 4A, the currents I _L1 and I _D1 of the boost reactor (11) and the diode (14) decrease linearly, and the boost reactor (11) and The voltage V _{1 at} the connection point with the diode 14 is fixed to a value substantially equal to the voltage V _C1 of the input smoothing capacitor 3 as shown in FIG. Therefore, the voltage V _L1 across the boost reactor (11) is the difference voltage between the voltage V ₁ and the full-wave rectified voltage V _DC as shown in FIG. Also, the feedback capacitor (12) through the diode (14) and the parasitic diode (13a) is generated by the flyback voltage generated in the primary winding (4a) of the transformer (4) when the MOS-FET (5) is turned off. As shown in FIG. 3 (D), the voltage V _{2 at} the connection point between the feedback capacitor (12) and the drain terminal of the boosting MOS-FET (13) is the boosting reactor shown in FIG. 3 (C). It becomes higher than the voltage V _{1 at} the connection point between (11) and the diode (14). At this time, the voltage V _Q1 between the drain and source terminals of the MOS-FET (5) holds a value substantially equal to the maximum value of the voltage V _C1 of the input smoothing capacitor (3) as shown in FIG. Since the drain current I _Q1 is zero as shown in FIG. 4C, a forward voltage is applied from the secondary winding (4b) of the transformer (4) to the rectifying diode (6) of the rectifying and smoothing circuit (8). When applied, the conductive state is established, and the energy stored in the transformer (4) during the ON period of the MOS-FET (5) is supplied from the secondary winding (4b) to the rectifying and smoothing circuit (8).
[0013]
As shown in FIG. 4 (E), a high voltage (H) level control pulse signal V _G1 is applied from the control circuit (10) to the gate terminal of the MOS-FET (5), and the MOS-FET (5) is turned on. In this state, current flows from the input smoothing capacitor (3) through the primary winding (4a) of the transformer (4) and the MOS-FET (5), and energy is stored in the transformer (4). As a result, as shown in FIG. 3 (E), the voltage V _Q1 between the drain and source terminals of the MOS-FET (5) rapidly drops to 0 [V] and the source terminal of the boosting MOS-FET (13). with voltage drops to ground potential, the drain current I _Q1 of the MOS-FET (5) rises linearly as shown in FIG. 4 (C). At this time, since a reverse voltage is applied to the rectifying diode (6) constituting the rectifying / smoothing circuit (8) and the rectifying diode (6) becomes non-conductive, energy is transferred to the secondary winding (4b) of the transformer (4). Is not done. When the delay time t _D elapses after the MOS-FET (5) is turned on, a high voltage (H) is applied from the control circuit (10) to the gate terminal of the boosting MOS-FET (13) as shown in FIG. ) Level control pulse signal V _G2 is applied, and the boosting MOS-FET 13 is turned on. At this time, a closed circuit of the boost reactor (11), the feedback capacitor (12), and the rectifier bridge circuit (2) is formed, so that the charging voltage V _{C2 of the} feedback capacitor (12) and all of the rectifier bridge circuit (2) are formed. The sum voltage with the wave rectified voltage V _DC is applied to the boost reactor (11) to accumulate energy, and the current I _L1 flowing through the boost reactor (11) rises linearly as shown in FIG. 4 (B).
[0014]
Next, as shown in FIGS. 4E and 4D, a low voltage (L) level is controlled from the control circuit (10) to the gate terminals of the MOS-FET (5) and the boosting MOS-FET (13). When the pulse signals V _G1 and V _G2 are applied and both are turned off, the energy accumulated in the boost reactor (11) is released, and a charging current flows to the input smoothing capacitor (3) via the diode (14). Therefore, as shown in FIGS. 4B and 4A, the currents I _L1 and I _D1 of the boost reactor (11) and the diode (14) decrease linearly, and the boost reactor (11) and The voltage V _{1 at} the connection point with the diode 14 is fixed to a value substantially equal to the voltage V _C1 of the input smoothing capacitor 3 as shown in FIG. In addition, the feedback capacitor (12) is charged through the diode (14) and the parasitic diode (13a) by the flyback voltage generated in the primary winding (4a) of the transformer (4), as shown in FIG. Thus, the voltage V _{2 at} the connection point between the feedback capacitor (12) and the drain terminal of the boosting MOS-FET (13) is equal to the connection point between the boosting reactor (11) and the diode (14) shown in FIG. It becomes higher than the voltage V ₁ . At this time, the voltage V _Q1 between the drain and source terminals of the MOS-FET (5) is substantially equal to the maximum value of the voltage V _C1 of the input smoothing capacitor (3) from 0 [V] as shown in FIG. rapidly rises to a value, since the drain current I _Q1 flowing through the MOS-FET (5) becomes zero as shown in FIG. 4 (C), the rectification smoothing circuit from the secondary winding of the transformer (4) (4b) A forward voltage is applied to the rectifier diode (6) in (8) to turn on, and the energy stored in the transformer (4) is supplied from the secondary winding (4b) to the rectifying and smoothing circuit (8). . By repeating the above operation, the average value of the current flowing from the rectifier bridge circuit (2) to the input smoothing capacitor (3) becomes a sine wave shape. Therefore, as shown in FIG. The alternating current I _AC flowing between the rectifying bridge circuit (2) becomes a sine wave having the same phase as the alternating voltage V _AC shown in FIG.
[0015]
In this embodiment, during the off-period of the MOS-FET (5), feedback is performed via the diode (14) and the parasitic diode (13a) by the flyback voltage generated in the primary winding (4a) of the transformer (4). The capacitor (12) is charged. Subsequently, when the boosting MOS-FET (13) on state after MOS-FET (5) delay time from the on-t _D has elapsed, the step-up reactor (11) and the feedback capacitor (12) rectifier bridge Since a closed circuit with the circuit (2) is formed, the sum voltage of the charging voltage V _C2 of the feedback capacitor (12) and the full-wave rectified voltage V _DC of the rectifier bridge circuit (2) is applied to the boost reactor (11). And energy is stored. Next, when the MOS-FET (5) is turned off, the energy stored in the boost reactor (11) is released, and a current for charging the input smoothing capacitor (3) flows. As a result, even when the full-wave rectified voltage V _DC of the rectifier bridge circuit (2) is smaller than the voltage V _{C1 of the} input smoothing capacitor (3), the input current flows and becomes a sine wave, and the conduction angle of the input current is widened. The input power factor can be improved to 1.0 with a small number of components such as the addition of the two energy storage means of the reactor (11) and the feedback capacitor (12) and the boosting MOS-FET (13). Further, by turning on state boosting MOS-FET (13) after the MOS-FET (5) has passed the delay time t _D from ON, the ON period of the boosting MOS-FET (13) is MOS since shorter than the on period of -FET (5), is the oN period of the MOS-FET (5) with overcurrent or light load or the like is shorter than the delay time t _D, boosting MOS-FET (13) Since it is not turned on, the boosting operation is not performed, and an abnormal increase in the voltage of the input smoothing capacitor (3) can be prevented.
[0016]
Embodiments of the present invention are not limited to the above-described embodiments, and various modifications can be made. For example, the connection order of the feedback capacitor (12) and the boosting MOS-FET (13) in the above embodiment may be switched. In the above-described embodiment, the reactor and the capacitor are used as the first energy storage unit and the second energy storage unit, respectively. However, an inductive element other than the reactor and a capacitive element other than the capacitor are used. May be. Further, in the above embodiment, a mode in which a MOS-FET is used as a switching element has been shown. However, a bipolar transistor, IGBT (insulated gate bipolar transistor), J-FET (junction field effect transistor) or thyristor can also be used as a switching element. It can be used as In particular, when a bipolar transistor that does not incorporate a parasitic diode is used as the auxiliary switching element, a rectifying element such as a diode may be connected between the collector and emitter terminals.
[0017]
【The invention's effect】
According to the present invention, there is no need to separately provide a circuit for performing switching control of the boost chopper circuit as in the conventional PFC converter system, and the number of components is small enough to add two energy storage means and one switching element. The input power factor can be improved. In addition, since the switching frequency of the main switching element and the auxiliary switching element is the same, mutual interference due to the difference in switching frequency between the main switching element and the boost chopper circuit does not occur as in the conventional case, and beats and beat sounds are prevented. Is possible. Furthermore, when the ON period of the auxiliary switching element is made shorter than the ON period of the main switching element, it is possible to prevent an abnormal increase in the voltage of the input smoothing capacitor at the time of overcurrent or light load.
[Brief description of the drawings]
FIG. 1 is an electric circuit diagram showing an embodiment of a switching power supply device according to the present invention. FIG. 2 is a waveform diagram showing the voltage and current of the AC power source of FIG. 1 and the output voltage of a rectifier bridge circuit. FIG. 4 is a waveform diagram showing the current of each part of FIG. 1 and the control signal of each switching element. FIG. 5 is an electric circuit diagram showing a conventional switching power supply apparatus. Waveform diagram showing voltage and current of AC power supply and rectifier bridge circuit [FIG. 7] Waveform diagram showing voltage and current of each part of FIG.
(1) ・ ・ AC power supply, (2) ・ Rectifier bridge circuit (rectifier circuit), (3) ・ Input smoothing capacitor, (4) ・ Transformer, (4a) ・ ・ Primary winding, (4b)・ ・ Secondary winding, (5) ・ ・ MOS-FET (main switching element), (6) ・ ・ Rectifier diode, (7) ・ ・ Smoothing capacitor, (8) ・ ・ Rectifying and smoothing circuit, (9) ・· Voltage detection circuit, (10) · · Control circuit, (11) · · Boost reactor (first energy storage means), (12) · · Feedback capacitor (second energy storage means), (13) · · MOS-FET for boosting (auxiliary switching element), (13a) ... Parasitic diode (rectifier), (14) Diode (rectifier)

Claims (1)

A rectifier circuit that converts AC power of an AC power source into DC power; an input smoothing capacitor connected to the rectifier circuit; a primary winding of a transformer and a main switching element connected in series to the input smoothing capacitor; A rectifying / smoothing circuit connected to the secondary winding of the transformer and generating a DC output; and a control circuit for controlling on / off of the main switching element, the control circuit ending the reset period of the transformer In the switching power supply apparatus that turns on the main switching element later and turns off the main switching element when the output voltage level of the rectifying and smoothing circuit exceeds the reference voltage level,
A reactor connected between the rectifier circuit and the input smoothing capacitor; a feedback capacitor connected in parallel with the primary winding of the transformer; and an auxiliary switching element connected in series with the feedback capacitor. ,
When the main switching element is in an off state, the feedback capacitor is charged by the back electromotive force generated in the primary winding of the transformer,
The auxiliary switching element is turned on after the main switching element is turned on, and a closed circuit of the reactor, the feedback capacitor, and the rectifier circuit is formed,
The control circuit gives an on signal to the auxiliary switching element after a delay time after the main switching element is turned on, and turns off the main switching element, and also turns off the auxiliary switching element,
The on-period of the auxiliary switching element is shorter than the on-period of the main switching element,
The switching power supply device, wherein the auxiliary switching element is not turned on when an on period of the main switching element becomes shorter than the delay time at the time of overcurrent or light load.

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