JP2002159170A - Switching power source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching power source capable of reducing a switching noise and a switching loss and facilitating an increase in a frequency. SOLUTION: One end of a first switching element SW11 is connected to one of output terminals of a DC power source 12, and an LC circuit 20 having a reactor LS and a first capacitor CS connected in series is connected in parallel between another end to which no power source 12 of the element SW11 is connected and another output terminal to which no first element SW1 of the power source 12 is connected. One end of a second switching element SW12 is connected to another end to which no power source 11 of the element SW11 is connected, a smoothing second capacitor C11 is connected in parallel between one end to which no element SW11 of the element SW12 is connected and one of the output terminals of the power source 12, and a load 16 is connected in parallel with the second capacitor C11. The elements SW11 and SW12 are connected to a control circuit 14, and alternately repeated to be ON and OFF.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply for converting a DC voltage to a desired voltage and supplying the converted voltage to an electronic device.

[0002]

2. Description of the Related Art In order to maximize the characteristics of recent electronic devices, a plurality of voltages set for each circuit device are used instead of a single voltage inside the electronic device. In this case, it is inefficient to provide a plurality of power supply voltages to the electronic device or supply a plurality of voltages from the outside. A method of converting the voltage into an appropriate voltage for each circuit is used. A switching power supply is often used as a voltage conversion device in this case.

Conventionally, for example, a step-down chopper type switching power supply shown in FIG. 7 has been widely used as a voltage converter. Hereinafter, the operation of the step-down chopper type switching power supply will be described.

A step-down chopper type switching power supply is shown in FIG.
, A switching element SW1 having one end connected to one of the output terminals of the DC power supply 2, a reactor L1 connected to the other end of the switching element SW1, and the other end of the switching element SW1 and the DC power supply. A diode D1 connected to the other output terminal of the
And a smoothing capacitor C1 connected between the other end of the DC power supply 2 and the other output terminal of the DC power supply 2. Further, the control circuit 4 detects the output voltage of the smoothing capacitor C1 and sends a control signal to the switching element SW1. The load 6 is connected to the smoothing capacitor C1.

The operation of the control circuit 4 is as follows. When the ON signal of the switching element SW1 is output from the control circuit 4, and when the switching element SW1 is turned on, the DC power supply 2 passes through the switching element SW1 and the reactor L1 to the smoothing capacitor C1 and the load. Current flows through 6. At this time, current I _L flowing through the reactor L1 increases with time.
When not considering the voltage drop or the like due to a voltage drop or a printed circuit board of the pattern wiring by the switching element SW1, the amount of increase in I _L [Delta] I L _(ON), as shown in equation (1),
Voltage V _{L (ON) of} reactor L1 and reactor L
It is determined by the reactance L of 1 and the time T _(ON) during which the switching element SW1 is ON. Here, the voltage of the reactor L1 V _{L (ON)} is, _{V in} a DC power supply voltage
_{Minus Vout} which is the voltage of the capacitor C1 (the voltage applied to the load).

[0006] ΔI_{L (ON)}= V_{L (ON)}・ T_(ON)/ L (1) V_{L (ON)}= V_in-V_out (2) Next, the switching element SW1 is turned off from the control circuit 4.
A signal is issued to the user. At this time, switch from DC power supply 2
The current passing through the switching element SW1 is cut off.
However, the reactor L1 has a switch
The current immediately before the switching element SW1 turns off
Try to. Therefore, the capacitor C1 is connected to the reactor L1.
And the current passing through the load 6 passes through the diode D1.
Flow along the path returning to the reactor L1. This and
The current I flowing through the reactor L1 _LDecreases over time
Less. Does not consider voltage drop due to diode D1
Then I_LReduction amount ΔI_{L (OFF)}Is shown in equation (3)
As described above, the voltage V of the reactor L1_{L (OFF)}and
Reactance L of reactor L1, switching element S
Time T when W1 is OFF_(OFF)Is determined.
Here, the voltage V of the reactor L1_{L (OFF)}Is a conde
V which is the voltage of the sensor C1 (the voltage applied to the load)_out
Becomes

ΔI _{L (OFF)} = V _{L (OFF)} · T _(OFF) / L (3) V _{L (OFF)} = V _out (4) where, the total time of T _(ON) and T _{(OFF) Has} a fixed value equal to the reciprocal of the switching frequency f _SW of the step-down chopper type switching power supply.

[0008] f_SW= 1 / (T_(ON)+ T_(OFF)(5) And the current required by the load and the step-down chopper type switch
If the average value of the current output from the
The voltage output from the voltage chopper type switching power supply is
It becomes equal to the voltage value set by the control circuit 4. Therefore,
The control circuit 4 is T _(ON)And T_(OFF)Is the relationship of equation (6)
ON time of switching element SW1 is controlled so that
I will. At this time, ΔI_{L (ON)}And ΔI_{L (OFF)}Equal
It's getting worse.

[0009] _{T (ON) / (T (} ON) + T (OFF)) = V out / V in (6) The conventional step-down chopper type switching power supply, a load 6
When the current output from the switching power supply is smaller than the current required by the control circuit 4, the voltage output from the switching power supply becomes a voltage lower than the voltage value set by the control circuit 4. Then, the control circuit 4 turns on the switching element SW1 so that the time of T _(ON) is longer than the time determined by the above equation (6). At this time, ΔI
_{L (ON)} > ΔI _{L (OFF)} , and the average value of the current output from the step-down chopper type switching power supply increases in each cycle of switching. With this operation, the output voltage of the step-down chopper type switching power supply rises and approaches the voltage value set by the control circuit 4.

On the other hand, when the current output from the step-down chopper type switching power supply is larger than the current required by the load 6, the voltage output from this switching power supply is higher than the voltage value set by the control circuit 4. Becomes
Then, the control circuit 4 turns on the switching element SW1 so that the time of T _(ON) is shorter than the time determined by the above equation (6). At this time, ΔI _{L (ON)} <Δ
The relationship is _{IL (OFF)} , and the average value of the current output from the step-down chopper type switching power supply decreases in each switching cycle. By this operation, the output voltage of the step-down chopper type switching power supply decreases, and approaches the voltage value set by the control circuit 4.

By the above operation, the output voltage of the conventional step-down chopper type switching power supply is maintained at a constant voltage value set by the control circuit.

[0012]

In the above conventional step-down chopper type switching power supply, when a large current is flowing through the switching element SW1, the switching element SW1 is turned off.
There is a disadvantage that switching noise occurs because of N and OFF.

In addition, during the ON conversion period and the OFF conversion period of the switching element SW1, a current waveform flowing through the switching element SW1 and a voltage waveform applied to the switching element SW1 overlap each other, resulting in a switching loss due to the overlap. There is.

The present invention has been made in view of the above-mentioned conventional technology, and has as its object to provide a switching power supply that can reduce switching noise and switching loss and can easily increase the frequency.

[0015]

According to the present invention, one end of a first switching element such as a transistor is connected to one of output terminals of a DC power supply, and the DC power supply of the first switching element is not connected. An LC circuit in which a reactor and a first capacitor are connected in series is connected in parallel between the other end and the other output terminal of the DC power supply to which the first switching element is not connected; A switching power supply in which one end of a second switching element such as a transistor is connected to the other end of the switching element to which the DC power supply is not connected. Then, a second capacitor for smoothing is connected in parallel between one end of the second switching element, to which the first switching element is not connected, and one of output terminals of the DC power supply, A load is connected in parallel with the second capacitor. The first and second switching elements are connected to a control circuit and alternately turn on and off alternately. Also, a diode may be provided in parallel with the first capacitor.

Further, according to the present invention, one end of a first switching element such as a transistor is connected to one of output terminals of the DC power supply, and the other end of the first switching element to which the DC power supply is not connected is connected to the other end. Connect one reactor,
Connect a second reactor to one end of the first reactor where the first switching element is not connected,
A first capacitor is connected in parallel between a connection point between the first reactor and the second reactor and the other output terminal of the DC power supply to which the first switching element is not connected, A switching power supply in which a second switching element is connected to one end of the second reactor to which the first reactor is not connected. The first and second switching elements are connected to a control circuit,
ON and OFF are alternately repeated. A second capacitor for smoothing between one end of the second switching element to which the second reactor is not connected and the other output terminal of the DC power supply to which the first switching element is not connected. Are connected in parallel, and a load is connected in parallel with the second capacitor.

[0017] Further, a diode may be provided in parallel with the first capacitor. The first reactor and the second reactor may have a magnetically coupled structure. Further, a third switching element connected in parallel with the diode may be provided. Further, a third switching element may be connected instead of the diode.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIGS. 1 and 2 show a first embodiment of a switching power supply according to the present invention. One output terminal of a DC power supply 12 is connected to one end of a first switching element SW11 such as a transistor. The other end of the switch SW11 to which the DC power supply 12 is not connected, and the first switching element SW11 of the DC power supply 12
The LC circuit 20 in which the reactor LS and the first capacitor CS are connected in series is connected in parallel with the other output terminal to which is not connected. One end of the first switching element SW11 to which the DC power supply 12 is not connected is connected to a second switching element SW12 such as a transistor.
Are connected at one end. The smoothing is performed between the other end of the second switching element SW12 to which the first switching element SW11 is not connected and the other output terminal of the DC power supply 12 to which the first switching element SW11 is not connected. The second capacitor C11 is connected in parallel, and the load 16 is connected in parallel with the second capacitor C11.

The first and second switching elements SW11,
The SW 12 is connected to the control circuit 14 so as to alternately repeat ON and OFF. The control circuit 14
Detecting the output voltage, the first and second switching elements SW1
1, ON / OFF of SW12 is controlled.

Next, the operation of the switching power supply of this embodiment will be described below with reference to FIGS.
First, the control circuit 14 turns on the switching element SW11.
(Point A in FIG. 2). Switching element SW11 is O
When N, the voltage Vin of the DC power supply is applied to the reactor LS and the capacitor CS. The reactor LS is in a state where the dot side in the figure is applied with a positive voltage.

Then, the switching element SW11 is turned on.
Immediately after the switching, the current flowing through the reactor LS is zero, so that a large current does not immediately flow even when the switching element SW11 is turned on due to the nature of the reactor LS (point B in FIG. 2).

The current increases with time, the reactor LS is excited, and magnetic energy is stored in the reactor LS. Further, since the capacitor CS is charged by the current flowing, the voltage Vcs of the capacitor CS increases. The capacitor CS is also charged so that the dot side has a positive voltage.

When the value of Vcs becomes equal to the voltage of the DC power supply 12, the current cannot flow only by the voltage of the DC power supply 12. However, because of its nature, the reactor LS keeps flowing current, so that the polarity of the reactor LS is reversed (the dot side becomes a negative voltage), and while the magnetic energy stored in the reactor LS is released, further current flows. Continue. Because the current continues to flow,
Capacitor CS is further charged, and Vcs is further increased.

Next, when the current continues to flow through the switching element SW11, the magnetic energy stored in the reactor LS decreases, so that the current decreases. Reactor L
When all the magnetic energy stored in S flows into the capacitor CS, the current flowing through the switching element SW11 becomes zero (point C in FIG. 2).

The control circuit 14 includes a switching element SW1
When the current flowing to 1 becomes zero, the switching element SW11 is turned off, and the switching element SW12 is turned off.
N (point D in FIG. 2).

When the switching element SW12 is turned on,
The capacitor CS serves as a voltage source, and a voltage is applied to the reactor LS and the smoothing capacitor C11. The reactor LS is in a state where a negative voltage is applied to the dot side. Immediately after the switching element SW12 is turned on, the current flowing through the reactor LS is zero.
Does not immediately flow a large current even when is turned on (point E in FIG. 2). Then, the current increases with time, the reactor LS is excited, and magnetic energy is stored in the reactor LS. In addition, the flow of current charges the smoothing capacitor C11. Here, when a current flows through the switching element SW12, the capacitor CS
Is discharged, the voltage Vcs of the capacitor CS decreases.

When the value of the voltage Vcs of the capacitor CS decreases to the voltage Vc11 of the smoothing capacitor C11, the current cannot flow only by the voltage of the capacitor C11.
However, due to its nature, the reactor LS keeps flowing current, so that the polarity of the reactor LS is reversed (the dot side becomes a positive voltage), and the magnetic energy stored in the reactor LS is released, and the current is further increased. Continue to pour. Since the current continues to flow, the capacitor C
S is charged in the opposite direction, so that the voltage Vcs of the capacitor CS is charged so that the dot side becomes negative.

When the current continues to flow, the magnetic energy stored in the reactor LS decreases, so that the current decreases. When all the magnetic energy stored in the reactor LS flows into the capacitors C11 and CS, the flowing current becomes zero. Here, since the smoothing capacitor C11 has a sufficiently large capacity with respect to the capacitor CS, the voltage of the capacitor C11 does not greatly increase.

When the current becomes zero, the control circuit 14 turns off the switching element SW12 and turns on the switching element SW11 (point F in FIG. 2), and thereafter repeats this operation.

The control circuit 14 detects the voltage of the capacitor C11 (the output voltage of the switching power supply), and when the voltage of the capacitor C11 has reached the voltage set by the control circuit 14, the switching element SW12 Do not turn on. And the capacitor C11
Current flows from the capacitor C11 to the load 16
Is detected, the switching element SW12 is turned on, and the operation is continued as described above (section G in FIG. 2).

The switching power supply of this embodiment can output a voltage controlled to be constant by repeating the above operation.

The switching power supply of this embodiment turns on and off the switching elements SW11 and SW12 when the current flowing through the switching elements SW11 and SW12 is zero. Therefore, unlike a conventional step-down chopper type switching power supply, the switching element is not turned on and off when a large current flows through the switching element, and no switching noise is generated. In addition, there is no overlap between the current waveform flowing through the switching element and the voltage waveform applied to the switching element during the ON conversion period and the OFF conversion period of the switching element, and there is no switching loss based on this. Thus, even if the switching frequency is increased, the loss does not increase, and a small and highly efficient switching power supply can be provided.

Next, a switching power supply according to a second embodiment of the present invention will be described with reference to FIGS. Here, the same configurations and operations as those of the above embodiment are denoted by the same reference numerals, and description thereof will be omitted. In the switching power supply of this embodiment, the capacitor CS of the circuit of the first embodiment is used.
And a diode D1 connected in parallel.

Next, the operation of the switching power supply of this embodiment will be described. First, in the first embodiment, when the switching elements SW11 and SW12 are turned ON and OFF, the switching element SW11 is turned ON while the dot side of the capacitor CS is negatively charged (H in FIG. 2).
point). Therefore, when the switching element SW11 is turned on, “(charging voltage of the capacitor CS) + (voltage of the DC power supply 12)” is applied to the reactor LS, and therefore, the charging voltage of the capacitor CS for each cycle. Rises. According to a simulation result in which a predetermined numerical value is set for each electronic element, as shown in FIG. 2, the charging voltage of the capacitor CS increases to about 500 V. The current flowing through the switching elements SW11 and SW12 was about 100 A at the peak.

On the other hand, in the switching power supply circuit of the second embodiment, when a reverse voltage is applied to the dot side of the capacitor CS, the capacitor CS is not charged and a current flows through the diode D1. As a result, unlike the circuit of the first embodiment (the circuit of FIG. 1), the capacitor CS is not charged in reverse. Therefore, when the switching element SW11 is turned on, only the voltage of the DC power supply 12 is applied to the reactor LS, and the charging voltage of the capacitor CS does not increase every cycle. According to the simulation result shown in FIG. 4, the capacitor CS is charged only up to 24 V, and the current flowing through the switching element SW11 has a peak.
The current flowing through the switching element SW12 was about 5 A, and the peak was about 10 A.

The switching power supply of the second embodiment, like the switching power supply of the first embodiment, turns on and off the switching elements SW11 and SW12 when the current flowing through the switching elements SW11 and SW12 is zero. There is no occurrence of switching or switching loss. Further, the charging voltage of the capacitor CS decreases, and the switching elements SW11, SW
12, the current flowing through the capacitor C
It is possible to use a small element having a low withstand voltage and a low allowable current value for S and the switching elements SW11 and SW12,
This can also contribute to downsizing of the entire switching power supply.

Note that a switching element may be connected in parallel with the diode D1. Further, only the switching element may be connected instead of the diode D1. In this case, control is performed such that the switching element is turned ON only at a timing when a forward current flows through the diode D1.

Next, a switching power supply according to a third embodiment of the present invention will be described with reference to FIGS. Here, the same configurations and operations as those of the above embodiment are denoted by the same reference numerals, and description thereof will be omitted. In the switching power supply of this embodiment, a reactor LS2 is further added to the circuit of the first embodiment, and when one switching element SW11 is turned on and the other switching element SW12 is turned off.
This is a switching power supply circuit in which the reactor through which current flows differs when N is performed. Also, a diode D1 was connected in parallel to the capacitor CS of this switching power supply circuit, as in the second embodiment. Further, a switching element may be connected in parallel to replace the diode D1.

Next, the operation of the switching power supply of this embodiment will be compared with the operation of the switching power supply circuit of the second embodiment. First, in the switching power supply circuit of the second embodiment, when the switching element SW11 is ON, a current flows from the dot side of the reactor LS to the non-dot side to charge the capacitor CS, and the switching element SW1 is turned on.
When 2 is ON, a current flows from one without a dot to one with a dot, and the capacitor CS is discharged. That is,
When the switching element SW11 is ON and when the switching element SW12 is ON, a current reciprocating in one reactor LS flows. Switching element SW11 is O
Since the reactor LS through which the current flows is the same both when N and when the switching element SW12 is ON, the ratio of the peak value of the current flowing through the switching element SW11 to the peak value of the current flowing through the switching element SW12 is:
The value is determined by the ratio between the input voltage and the output voltage of the switching power supply.

On the other hand, in the circuit of the third embodiment,
When the switching element SW11 is ON, the reactor L
When a current flows through S1, the capacitor CS is charged. When the switching element SW12 is ON, a current flows through the reactor LS2 and the capacitor CS is discharged. That is,
Reactors LS1 and LS2 only flow current in one direction, and the reactors through which the current passes in the charging path and the discharging path of capacitor CS are different. The fact that the reactor through which the current passes when the switching element SW11 is ON and when the switching element SW12 is ON is different from the peak value of the current flowing through the switching element SW11 by adjusting the values of the reactors LS1 and LS2. The ratio of the peak value of the current flowing through the switching element SW12 can be adjusted.

According to the switching power supply of the third embodiment, like the switching power supplies of the first and second embodiments,
ON / OFF of switching elements SW11 and SW12
Is performed when the current flowing through the switching elements SW11 and SW12 is zero, so that switching noise and switching loss do not occur. Furthermore, since the peak value of the current flowing through the switching elements SW11 and SW12 can be adjusted by the value of the reactors LS1 and LS2 to be used, the switching elements SW11 and SW1 can be adjusted.
Second, an element having a small allowable current value can be used.

The circuit of the switching power supply according to the present invention is not limited to the above-described embodiment, but couples two reactors of the switching power supply circuit according to the third embodiment, that is, sets two sets to one core. May be used as a switching power supply circuit. Further, a switching element may be connected in parallel to the capacitor CS of this circuit. Further, the switching element may be replaced with the diode D1 and connected.

In this switching power supply circuit, the reactor LS1 emits all the excitation energy temporarily stored while the switching element SW11 is ON. Similarly, reactor LS2 also emits all the excitation energy once stored during the period when switching element SW11 is ON. Therefore, reactor LS1,
Even if LS2 is wound around one core, it does not affect the circuit operation.

The reactor LS1 and the reactor LS
By forming 2 with one core, the number of cores used can be reduced, which can contribute to downsizing of the switching power supply.

[0045]

According to the switching power supply of the present invention, the switching element is turned on and off when no current is flowing through the switching element, so that the generation of switching noise can be reduced. In addition, since the current waveform flowing through the switching element and the voltage waveform applied to the switching element do not overlap during the ON conversion period and the OFF conversion period of the switching element, no switching loss occurs due to this. Therefore, even if the switching frequency is increased, the loss does not increase. Therefore,
A small and efficient switching power supply can be supplied.

Further, by providing a diode or a switching element in parallel with a capacitor between the switching elements, the charging voltage can be reduced, and the current flowing through the switching element is reduced. In addition, it is possible to use a small element having a low withstand voltage and a low allowable current value, which can contribute to downsizing of the entire switching power supply.

[Brief description of the drawings]

FIG. 1 is a schematic circuit diagram of a switching power supply according to a first embodiment of the present invention.

FIG. 2 is a diagram showing operation waveforms of various parts of the switching power supply according to the embodiment.

FIG. 3 is a schematic circuit diagram of a switching power supply according to a second embodiment of the present invention.

FIG. 4 is a diagram showing operation waveforms of various parts of the switching power supply according to the embodiment.

FIG. 5 is a schematic circuit diagram of a switching power supply according to a third embodiment of the present invention.

FIG. 6 is a diagram showing operation waveforms of each unit of the switching power supply according to the embodiment.

FIG. 7 is a schematic circuit diagram of a conventional switching power supply.

[Explanation of symbols]

 2,12 DC power supply 4,14 Control circuit 6,16 Load 20 LC circuit SW1, SW11, SW12 Switching element L1, LS reactor C1, C11 Smoothing capacitor CS capacitor

Claims (6)

[Claims] An output terminal of a DC power supply is connected to one end of a first switching element, and the other end of the first switching element not connected to the DC power supply; An LC circuit in which a reactor and a first capacitor are connected in series is connected between the other output terminal to which no switching element is connected, and the other end of the first switching element is connected to a second switching element. Connecting one end of an element, connecting a second capacitor between the other end of the second switching element to which the first switching element is not connected, and the other output terminal of the DC power supply, The first and second switching elements are alternately turned on by O
N. A switching power supply, comprising: a control circuit for turning OFF; and a load connected in parallel with the second capacitor. 2. The switching power supply according to claim 1, further comprising a diode connected in parallel with said first capacitor. 3. One end of a first switching element is connected to one of output terminals of the DC power supply, and a first reactor is connected to the other end of the first switching element that is not connected to the DC power supply. A second reactor is connected to one end of the first reactor to which the first switching element is not connected, between the first reactor and the second reactor, and the DC power supply A first capacitor is connected between the other output terminal to which the first switching element is not connected, and a second switching element at one end of the second reactor where the first reactor is not connected. And a second capacitor is connected between one end of the second switching element to which the second reactor is not connected and the other output terminal of the DC power supply. The first, O the second switching element alternately with each other
N. A switching power supply, comprising: a control circuit for turning OFF; and a load connected in parallel with the second capacitor. 4. The switching power supply according to claim 3, further comprising a diode connected in parallel with said first capacitor. 5. The switching power supply according to claim 3, wherein the first reactor and the second reactor have a magnetically coupled structure. 6. The switching power supply according to claim 1, further comprising a third switching element connected in parallel with said first capacitor.