JP3628637B2 - Switching power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a switching power supply device that supplies a stabilized DC voltage to industrial and consumer electronic devices.
[0002]
[Prior art]
In recent years, as electronic devices have been reduced in price, size, performance, and energy saving, there is a strong demand for switching power supplies that are smaller, have higher output stability, and are more efficient.
In a bridge-type or push-pull type switching power supply, if the ON period balance between switching elements is lost, an exciting current is gradually accumulated in the transformer, and eventually the transformer core is saturated and an excessive current flows. There is a fear. Therefore, a highly safe switching power supply is required.
[0003]
A conventional switching power supply device will be described below. FIG. 5 shows a circuit configuration of a full bridge type switching power supply. In FIG. 5, 1 is an input DC power supply, 51 is a switching power supply, and 14 is a load. The input DC power source 1 is configured by means or a battery that inputs a commercial power source, rectifies and smoothes it, and outputs it.
Hereinafter, the switching power supply device 51 will be described. Reference numerals 2a-2b denote input terminals of the switching power supply 51, to which both ends of the input DC power supply 1 are connected. 3a is a primary winding of the current transformer, and 3b is a secondary winding of the current transformer. One end of the primary winding 3a of the current transformer is connected to the input terminal 2a, and the other end is connected to one end of switching means (having four switching elements 4, 5, 6, and 7). The other end of the switching means is connected to the input terminal 2b.
[0004]
The switching means includes a first switching element 4, a second switching element 5, a third switching element 6, and a fourth switching element 7 that are bridge-connected.
The first switching element 4 and the second switching element 5 are connected in series. Both ends of the first switching element 4 and the second switching element 5 connected in series are connected to the other end of the primary winding 3a of the current transformer and the negative terminal 2b of the input terminal, respectively.
Similarly, the third switching element 6 and the fourth switching element 7 are connected in series. Both ends of the third switching element 6 and the fourth switching element 7 connected in series are connected to the other end of the primary winding 3a of the current transformer and the negative terminal 2b of the input terminal, respectively.
The switching means alternately repeats the state in which the first switching element 4 and the fourth switching element 7 are in conduction and the state in which the second switching element 5 and the third switching element 6 are in conduction, A current is passed in both directions through the winding 8a.
[0005]
In the transformer having the primary winding 8a, the first secondary winding 8b, and the second secondary winding 8c, one end of the primary winding 8a is connected to the first switching element 4 and the second switching element 5. And the other end is connected to a connection point between the third switching element 6 and the fourth switching element 7. The first secondary winding 8b and the second secondary winding 8c are connected in series. A connection point between the first secondary winding 8b and the second secondary winding 8c is connected to the negative output terminal 13b.
Reference numeral 9 denotes a first rectifier diode, and reference numeral 10 denotes a second rectifier diode. The anode of the first rectifier diode 9 is connected to the first secondary winding 8b, and the anode of the second rectifier diode 10 is connected to the second secondary winding 8c. The cathode of the first rectifier diode 9 and the cathode of the second rectifier diode 10 are connected to each other.
[0006]
The inductance element 11 and the smoothing capacitor 12 form a series circuit and constitute a smoothing circuit. Both ends of the smoothing circuits 11 and 12 are connected to the cathodes of the rectifier diodes 9 and 10 and the connection points of the secondary windings 8b and 8c of the transformer, respectively. Reference numerals 13a to 13b denote output terminals of the switching power supply device 51, which output DC power. The output terminals 13a-13b are connected to both ends of the smoothing capacitor 12.
The load 14 is connected to the output terminals 13a-13b of the switching power supply device 51 and consumes power.
[0007]
A first resistor 15 is connected to the secondary winding 3b of the current transformer. When no current flows through the primary winding 3a of the current transformer, the first resistor 15 consumes the excitation energy of the current transformers 3a and 3b and resets the magnetic flux. 16 is a diode, and 17 is a second resistor. Both ends of the series circuit composed of the diode 16 and the second resistor 17 are connected to both ends of the secondary winding 3b of the current transformer. When a switching current flows through the primary winding 3a of the current transformer, a current corresponding to the turn ratio of the current transformer flows through the secondary winding 3b. The diode 16 rectifies the current output from both ends of the secondary winding of the current transformer, and generates a voltage across the second resistor 17 in proportion to the current flowing through the primary winding 3a of the current transformer.
[0008]
Reference numeral 18 denotes a reference voltage, and 19 denotes an OCL comparator (over current limit comparator overcurrent limiting comparator). When the voltage generated across the second resistor 17 exceeds the reference voltage 18, the output signal of the OCL comparator 19 becomes high level. Thereby, it is possible to detect that the current flowing through the primary winding 3a of the current transformer exceeds a certain value (overcurrent).
An RS flip-flop 20 is set by the oscillator 21 and is reset by an output signal (high level output) of the OCL comparator 19. An output signal of the RS flip-flop 20 is input to the AND circuit 22. The output signal of the RS flip-flop 20 limits the ON period of the switching elements 4-7. This limits the overcurrent.
[0009]
The error amplifier 24 amplifies an error between the output voltage of the switching power supply device 51 (voltage between the output terminals 13a and 13b) and the reference voltage (target voltage) 23, and outputs an error amplification voltage. The error amplification voltage is input to the PWM comparator 25.
The oscillator 21 sends a set pulse to the RS flip-flop 20 and simultaneously generates a triangular wave signal synchronized with the output signal.
The PWM comparator 25 receives and compares the triangular wave signal output from the oscillator 21 and the error amplification voltage, and generates a PWM signal.
The AND circuit 22 inputs the output signal of the RS flip-flop 20 and the PWM signal, and outputs a logical product signal (drive signal of the switching element) of both. The output signal of the AND circuit 22 corresponds to the narrower one of the output signal of the RS flip-flop 20 and the PWM signal.
[0010]
The drive signal distribution circuit 26 receives the drive signal output from the AND circuit 22 and distributes the drive signal alternately to create A-phase and B-phase voltages. The A-phase voltage and the B-phase voltage alternately become high level. The drive circuit 27 inputs the A-phase voltage and causes the first switching element 4 and the fourth switching element 7 to conduct simultaneously. The drive circuit 28 inputs a B-phase voltage, and causes the second switching element 5 and the third switching element 6 to conduct simultaneously.
[0011]
When the first switching element 4 and the fourth switching element 7 are simultaneously turned on in the A phase, the input voltage is applied to the primary winding 8a of the transformer through the current transformer 3a. A voltage is generated in the secondary windings 8 b and 8 c of the transformer, and the voltage is applied to the smoothing circuits 11 and 12 through the first rectifier diode 9. When the PWM signal becomes low level and the first switching element 4 and the fourth switching element 7 are turned off, the primary winding current of the transformer becomes zero. The current that flows by discharging the magnetic energy accumulated in the inductance element 11 flows dividedly into the first secondary winding 8b and the second secondary winding 8c of the transformer, so that the first rectifier diode 9 and the second The rectifier diode 10 is turned on. The induced voltage of the secondary windings 8b and 8c of the transformer becomes zero, and the voltage applied to the smoothing circuit by the secondary windings 8b and 8c of the transformer also becomes zero, so the current flowing through the inductance element 11 decreases.
[0012]
Next, when the second switching element 5 and the third switching element 6 are turned on in the B phase, the input voltage is applied to the primary winding 8a of the transformer in the opposite direction to that in the A phase. A voltage is induced in the secondary windings 8 b and 8 c of the transformer, and a voltage is applied to the smoothing circuits 11 and 12 through the second rectifier diode 10. When the second switching element 5 and the third switching element 6 are turned off, the primary winding current of the transformer becomes zero. The current that flows by discharging the magnetic energy accumulated in the inductance element 11 flows dividedly into the first secondary winding 8b and the second secondary winding 8c of the transformer, so that the first rectifier diode 9 and the second The rectifier diode 10 is turned on. The induced voltage of the secondary windings 8b and 8c of the transformer becomes zero, and the voltage applied to the smoothing circuits 11 and 12 by the secondary windings 8b and 8c of the transformer becomes 0V. The current flowing through the inductance element 11 decreases.
[0013]
By repeating this operation, the switching power supply device supplies power to the load. The error amplifier 24 compares the output voltage of the switching power supply device with the reference voltage 23, amplifies the error, and outputs an error amplified voltage. The error amplification voltage is compared with the triangular wave signal output from the oscillator 21 and modulated. The switching power supply device is PWM controlled so that its output voltage is constant during normal operation. In the event of an abnormality such as an extremely small load resistance, the switching current increases abnormally. A voltage proportional to the switching current is generated in the secondary winding 3 b of the current transformer, and a voltage exceeding the reference voltage 18 is generated across the second resistor 17. As a result, the RS flip-flop 20 is reset, so that the drive signal is narrowed and the output is reduced.
[0014]
FIG. 6 shows the structure of a transformer (8a, 8b, 8c in FIG. 5) of a conventional switching power supply device. The transformer of the bridge type or push-pull type converter is designed to increase the inductance during normal operation in order to reduce the exciting current, and the core has no gap as shown in FIG. And the cross-sectional area in the magnetic path is designed to be uniform in both the middle leg 61 and the outer legs 62 and 63. Since the magnetic flux flows in the middle leg 61 and flows in half in the outer legs 62 and 63, the fact that the cross-sectional area is uniform means that the following equation is established. Cross section of middle leg 61 = cross section of outer leg 62 + cross section of outer leg 63
[Problems to be solved by the invention]
However, in the conventional configuration, if there is a difference in the ON period of the two sets of switching elements due to slight variations, the voltage time product applied to the primary winding of the transformer is not balanced between the A phase and the B phase. Excitation current is accumulated (referred to as biased magnetism). When the exciting current gradually increases, there is a problem that the transformer is saturated rapidly and an excessive current flows.
[0016]
In a conventional switching power supply device using a transformer having a gap length of 0 or as small as possible and having a uniform cross-sectional area in the magnetic path, all parts of the magnetic path are saturated at the same time when a bias occurs. The transformer inductance decreases rapidly.
FIG. 7 shows a current waveform of the primary winding 8a of the transformer when the magnetic field is biased in the conventional switching power supply apparatus using the transformer of FIG. As shown in FIG. 7, when the biased state is reached, the primary winding current rises sharply when the transformer core is saturated (part 71).
In the switching power supply device, an overcurrent limiting circuit is provided as shown in FIG. However, there is a certain delay time from when the primary winding current rises sharply until the overcurrent limiting circuit operates. The conventional switching power supply device has a problem that the overcurrent limiting circuit cannot sufficiently prevent the overcurrent because the rise of the primary winding current is too steep when the transformer core is saturated and the transformer core is saturated. .
[0017]
An object of the present invention is to provide a switching power supply device in which a primary winding current of a transformer does not increase sharply even in a biased state, and an overcurrent protection circuit functions effectively. Accordingly, it is an object of the present invention to provide a stable and safe switching power supply device that prevents the proceeding of the demagnetization and prevents a sudden saturation current from flowing.
[0018]
[Means for Solving the Problems]
The switching power supply device of the present invention has the following configuration in order to solve the above problems.
The first invention is
Switching means having a bridge-type or push-pull type configuration and alternately applying positive and negative voltages to the outside ,
A primary winding in which a current flows in both directions when a positive / negative voltage is applied, a secondary winding in which a voltage is induced when the positive / negative voltage is applied to the primary winding, and a gap length A core having a non-uniform gap formed thereon, and a transformer ,
Including an inductance element, which releases the magnetic energy when the magnetic energy accumulated, the current flowing through the primary winding of the transformer is zero when the voltage induced in the secondary winding of the transformer is applied, Smoothing means for converting the voltage induced in the secondary winding of the transformer into a smoothed DC voltage and outputting the same ; and
Overcurrent limiting means for detecting a current flowing in the primary winding of the transformer and limiting a peak value of the current by changing a turn-off timing of the switching means ;
It is a switching power supply device characterized by having.
[0019]
A second aspect of the invention is seen in wedge from perpendicular first direction gap of the transformer core for a gap length direction, a switching power supply apparatus of the first invention.
[0020]
The third invention is
Switching means having a bridge-type or push-pull type configuration and alternately applying positive and negative voltages to the outside ,
A primary winding in which a current flows bidirectionally when the positive and negative voltages are applied; a secondary winding in which a voltage is induced when the positive and negative voltages are applied to the primary winding; and a magnetic path A core having a non-uniform cross-sectional area, and a transformer ,
Including an inductance element, which releases the magnetic energy when the magnetic energy accumulated, the current flowing through the primary winding of the transformer is zero when the voltage induced in the secondary winding of the transformer is applied, Smoothing means for converting the voltage induced in the secondary winding of the transformer into a smoothed DC voltage and outputting the same ; and
Overcurrent limiting means for detecting a current flowing in the primary winding of the transformer and limiting a peak value of the current by changing a turn-off timing of the switching means ;
It is a switching power supply device characterized by having.
[0021]
According to a fourth aspect of the present invention, in the switching power supply device according to the third aspect of the present invention, the sum of the outer leg cross-sectional areas of the transformer core is different from the middle leg cross-sectional area.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, examples specifically showing the best mode for carrying out the present invention will be described with reference to the drawings.
[0023]
Example 1
A switching power supply apparatus according to Embodiment 1 of the present invention will be described with reference to FIGS. The switching power supply of Example 1 is the same as the switching power supply of the conventional example, except that the structure of the transformer (8a, 8b, 8c) used is different from the structure of the transformer used in the switching power supply of the conventional example. (FIG. 5). The description of the same configuration as that of the conventional switching power supply device is omitted.
[0024]
FIG. 1 is a diagram showing the structure of a transformer (8a, 8b, 8c) used in the switching power supply device according to the first embodiment of the present invention. Conventional transformers (FIG. 6) have no gaps or are uniform and have as narrow a gap as possible. As shown in FIG. 1, when viewed from a direction perpendicular to the gap length direction of the transformer, the transformer of the first embodiment has a wedge-shaped gap.
FIG. 3 compares the DC superimposition characteristic 31 of the transformer of Example 1 with the DC superposition characteristic 35 of the conventional transformer. The DC superimposition characteristic is a characteristic in which the horizontal axis represents the DC excitation current of the primary winding and the vertical axis represents the inductance of the transformer.
In the conventional transformer, as indicated by reference numeral 36, when the core is saturated, the inductance sharply decreases. In the transformer of the first embodiment, as indicated by the part 32, when the core is saturated, the inductance gradually decreases.
[0025]
In the transformer of the first embodiment, when the exciting current increases and the core is saturated, the inductance gradually decreases. When the primary winding current gradually increases, the core gradually increases from the portion closer to the narrow gap portion. Is saturated.
When the excitation current of the transformer is small, the magnetic flux concentrates through the narrowest part of the core gap (having a wedge shape as viewed from the side as shown in FIG. 1). In the narrow gap portion, the magnetoresistance is sufficiently small. The inductance of the transformer of Example 1 when the exciting current is small (from the current 0 to before the inductance starts to decrease) is smaller than the inductance of the conventional transformer, and therefore the degree of the decrease is small (FIG. 3). 31 and 35).
[0026]
FIG. 4 shows a current waveform of the primary winding of the transformer when the switching power supply device according to the first embodiment is in a biased state. As shown in FIG. 4, when the transformer core becomes saturated, the rise of the primary winding current when the transformer core is saturated is much more gradual than that of the conventional example (the portion 71 in FIG. 7) (41). portion).
In the switching power supply device, an overcurrent limiting circuit is provided as shown in FIG. Since the primary winding current rises gently, the delay until the overcurrent limiting circuit operates is not a problem. In the switching power supply device according to the first embodiment, since the rise of the primary winding current when the transformer core is saturated and the transformer core is saturated, the overcurrent limiting circuit can reliably prevent the overcurrent.
Although the full bridge type switching power supply is shown in the first embodiment, it goes without saying that the same effect can be obtained by applying the transformer shown in the first embodiment to the push-pull type switching power supply.
[0027]
Example 2
A switching power supply apparatus according to Embodiment 2 of the present invention will be described with reference to FIGS. The switching power supply of the second embodiment is the same as the switching power supply of the conventional example, except that the structure of the transformer (8a, 8b, 8c) used is different from the structure of the transformer used in the conventional switching power supply. (FIG. 5). The description of the same configuration as that of the conventional switching power supply device is omitted.
[0028]
FIG. 2 is a diagram showing the structure of a transformer (8a, 8b, 8c) used in the switching power supply device according to the second embodiment of the present invention.
In the conventional transformer (FIG. 6), the core cross-sectional area of the transformer is uniform. Therefore, the sum of the cross-sectional areas of the two outer legs of the transformer and the cross-sectional area of the midfoot were the same. As shown in FIG. 2, in the transformer of Example 2, the outer foot cross-sectional area (SA2 + SA3) and the middle foot cross-sectional area SA1 are different.
SA1 ≠ SA2 + SA3
FIG. 3 is a comparison of the DC superposition characteristics 33 of the transformer of Example 2 and the DC superposition characteristics 35 of the conventional transformer.
In the conventional transformer, as indicated by reference numeral 36, when the core is saturated, the inductance sharply decreases. In the transformer of the second embodiment, as indicated by a portion 34, when the core is saturated, the inductance is gradually decreased.
[0029]
In the transformer of the second embodiment, when the exciting current increases and the core is saturated, the inductance gradually decreases because when the primary winding current gradually increases, the core gradually saturates from a portion having a small cross-sectional area. It is.
When the transformer excitation current is small, the core does not saturate even in a portion with a small cross-sectional area. When the exciting current is small (from the current 0 to before the inductance starts to decrease), the inductance of the transformer of Example 2 is smaller than the inductance of the conventional transformer. Therefore, the degree of the decrease is small (FIG. 3). 33 and 35).
[0030]
FIG. 4 shows a current waveform of the primary winding of the transformer when the switching power supply device according to the second embodiment is demagnetized. As shown in FIG. 4, when the transformer core is saturated, the rise of the primary winding current when the transformer core is saturated is much more gradual than that of the conventional example (the portion 71 in FIG. 7). portion).
In the switching power supply device, an overcurrent limiting circuit is provided as shown in FIG. Since the primary winding current rises gently, the delay until the overcurrent limiting circuit operates is not a problem. In the switching power supply device according to the second embodiment, since the rising of the primary winding current when the transformer core is saturated and the transformer core is saturated, the overcurrent limiting circuit can reliably prevent the overcurrent.
Although the full bridge type switching power supply is shown in the second embodiment, it goes without saying that the same effect can be obtained by applying the transformer shown in the second embodiment to the push-pull type switching power supply.
[0031]
【The invention's effect】
As described above, according to the present invention, an advantageous effect that a switching power supply device in which an overcurrent protection circuit works effectively can be realized by adopting a transformer whose inductance gradually decreases even when the core is saturated. It is done. As a result, it is possible to prevent a sudden saturation current from flowing due to the progress of the demagnetization, and to realize a stable and safe switching power supply device.
[Brief description of the drawings]
FIG. 1 is a structural diagram of a transformer of a switching power supply apparatus according to a first embodiment of the present invention. FIG. 2 is a structural diagram of a transformer of a switching power supply apparatus according to a second embodiment of the present invention. Fig. 4 is a diagram showing the DC superposition characteristics of the transformer. Fig. 4 is a diagram showing the current waveform of the primary winding of the transformer when the switching power supply device of the present invention is biased. Fig. 5 is a circuit configuration of a full bridge converter. FIG. 6 is a diagram showing a structure of a transformer of a conventional switching power supply device. FIG. 7 is a diagram showing a current waveform of a primary winding of the transformer when the conventional switching power supply device is biased. Explanation of]
1 Input DC power supply 2a-2b Input terminals 3a, 3b Primary winding and secondary winding of current transformer 4 First switching element 5 Second switching element 6 Third switching element 7 Fourth switching element 8a, 8b, 8c Transformer primary and secondary windings 9 First rectifier diode 10 Second rectifier diode 11 Inductance element 12 Smoothing capacitor 13a-13b Output terminal 14 Load 15 First resistor 16 Diode 17 Second Resistor 18 Reference voltage 19 OCL comparator 20 RS flip-flop 21 Oscillator 22 AND circuit 23 Reference voltage 24 Error amplifier 25 PWM comparator 26 Distribution circuit 27, 28 Drive circuit 51 Switching power supply device

Claims (4)

Switching means having a bridge-type or push-pull type configuration and alternately applying positive and negative voltages to the outside ,
A primary winding in which a current flows in both directions when a positive and negative voltage is applied; a secondary winding in which a voltage is induced when the positive and negative voltages are applied to the primary winding; and a gap length A core formed with a non-uniform gap of a transformer ,
Including an inductance element, which releases the magnetic energy when the magnetic energy accumulated, the current flowing through the primary winding of the transformer is zero when the voltage induced in the secondary winding of the transformer is applied, Smoothing means for converting the voltage induced in the secondary winding of the transformer into a smoothed DC voltage and outputting it , and
Overcurrent limiting means for detecting a current flowing in the primary winding of the transformer and limiting a peak value of the current by changing a turn-off timing of the switching means ;
A switching power supply device comprising: The gap of the transformer core, the switching power supply device according to claim 1, characterized in that visible wedges from perpendicular one direction to the gap length direction. Switching means having a bridge-type or push-pull type configuration and alternately applying positive and negative voltages to the outside ,
A primary winding in which a current flows bidirectionally when the positive and negative voltages are applied, a secondary winding in which a voltage is induced when the positive and negative voltages are applied to the primary winding, and a magnetic path A core having a non-uniform cross-sectional area, and a transformer ,
Including an inductance element, which releases the magnetic energy when the magnetic energy accumulated, the current flowing through the primary winding of the transformer is zero when the voltage induced in the secondary winding of the transformer is applied, Smoothing means for converting the voltage induced in the secondary winding of the transformer into a smoothed DC voltage and outputting it , and
Overcurrent limiting means for detecting a current flowing in the primary winding of the transformer and limiting a peak value of the current by changing a turn-off timing of the switching means ;
A switching power supply device comprising: 4. The switching power supply device according to claim 3, wherein the sum of the cross-sectional areas of the outer legs is different from the cross-sectional area of the middle legs in the core of the transformer.

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