JP2003199345A - Switching power supply apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To properly practice a soft switching operation and realize reduction of switching loss and switching noise in any one of a current continuous mode, a critical mode, and a current discontinuous mode in a flyback converter, a forward converter, and a boost converter. <P>SOLUTION: This switching power supply apparatus has a first diode, which rectifies surge energy instantaneously generated, when a main switch is turned off, and a storage capacitor, in which the rectified current is stored. A current, made to flow through a regenerating winding provided in a transformer to regenerate the charge stored in the storage capacitor, is further made to flow to an auxiliary switch via an inductor and a second diode for regeneration. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soft switching technique which contributes to high efficiency and low noise in a switching power supply device which operates as a flyback converter, a forward converter and a boost converter.

[0002]

2. Description of the Related Art A power supply device of this type is disclosed in Japanese Patent Laid-Open No. 10-46.
No. 79 is disclosed. FIG. 1 is a conventional example of soft switching related to a flyback converter.
This is called T (Zero Voltage Transition). This switching power supply device is provided with a main switch and a sub switch, turns on the sub switch slightly before turning on the main switch, and turns on the main switch when the voltage applied to the main switch drops to near zero. That is. In this example, in the current continuous mode of the flyback converter, the switching loss of both the main switch and the sub switch can be effectively reduced both at the time of turn-on and at the time of turn-off, and at the same time, noise can be reduced. Detailed description of the operation of the ZVT of FIG. 1 is omitted because it has the same contents as the above publication. Also,
As another conventional example, the surge energy generated when the main switch is turned off is regenerated to the input power source through the sub-transformer, as disclosed in JP-A-10-178777 and JP-A-11-178.
Although there is also a No. 341, in the former, the main switch and the sub switch are soft switching only in the current continuous mode, and in the latter, the sub switch is always hard switching.

[0003]

As described above, the ZVT in the flyback converter operates very conveniently in the continuous current mode. However, quasi-resonance (Quasi resonan
When operating in the critical mode called t) or in the discontinuous current mode, the ZVT deviates from the soft switching operation. It is preferable that the ZVT does not operate the auxiliary switch in the current critical mode. In addition, the ZVT is a main switch and a sub switch that are driven at a timing when the sub switch is turned on slightly before the timing of turning on the main switch and is turned off shortly after the main switch is turned on.
Requires one drive circuit (illustrated in the timing chart of FIG. 1).

[0004]

In order to solve the above-mentioned problems, the present invention provides a power supply device according to the first invention, wherein in a flyback converter, a forward converter or a boost converter, an input power source is connected to the input power source. The main switch for turning on / off the current flowing through the primary winding of the transformer, the first rectifying diode for rectifying surge energy from the transformer generated when the main switch is turned off, and the current rectified by the diode. An electric storage capacitor for accumulating is provided, and the electric charge accumulated in the electric storage capacitor is passed through a regeneration winding provided in the main transformer and further connected to an auxiliary switch through an inductor and a second diode for preventing backflow. It was configured.

In a switching power supply device according to a second aspect of the invention, a secondary winding is provided on the inductor of the first aspect of the invention to change the configuration of the transformer, and the secondary winding of the transformer is surge energy through a third diode. Was regenerated to the input power source.

In the switching power supply device according to the third invention, the main switch and the sub switch are driven by the same drive circuit.

The switching power supply device according to the fourth aspect of the present invention exceeds the current critical mode as the load current increases,
When the current continuous mode is entered, the auxiliary switch is turned on earlier than the main switch is turned on.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 shows an embodiment of the present invention, and the operation of each part will be described with reference to FIG. The circuit shown in FIG. 2 is a power supply device for a flyback converter, and is turned off after the main switch 104 is turned on by a control signal 119. This power supply device has a primary winding 103 of a transformer 102 generated immediately after a main switch 104 is turned off.
First diode 117 for rectifying surge energy due to a leakage inductor (not shown) between the secondary winding 113 and the secondary winding 113, and the capacitor 11 for storing the rectified charge.
8 is provided. The electric charge stored in the capacitor 118 is connected to the sub switch 110 through the regeneration winding 109, the inductor 107, and the second backflow prevention diode 108 provided in the transformer 102 and flows. Since the input gate of the sub switch 110 is basically connected in parallel with the main switch 104, a regenerative current starts flowing through the sub switch 110 at the same timing as when the main switch 104 is turned on. At this time, the regenerative current flowing through the sub switch 110 resonates with the storage capacitor 118 and the inductor 107, and a current having a waveform obtained by half-wave rectifying the sine wave flows as shown by A-110 in FIG. Therefore, the actual current flowing through the main switch 104 is A-1 shown in FIG. 2 obtained by subtracting this half-wave regenerative current from the normal triangular wave.
The current waveform is 04. This subtracted current waveform component is reduced from the input current, and the efficiency is improved.

In terms of circuit configuration, the first example is different from the conventional example shown in FIG.
The rectifier diode 117 and the storage capacitor 118 are added, but with such a configuration, soft switching operation can be performed in both the main switch and the sub switch in both the discontinuous current mode and the critical mode. Further, since the operation timings of the main switch and the sub switch may be almost the same, the drive circuit of the main switch and the sub switch can be made common, and the circuit configuration can be simplified. In an actual drive circuit, in order to reduce the switching noise of the main switch 104, the
Generally, a circuit in which a parallel circuit of a resistor 150 and a diode 151 is inserted in the gate to delay turn-on and advance turn-off is commonly used. Therefore, strictly speaking, a slight timing difference occurs,
Basically, they can be driven by the same drive circuit. As in the present invention, the surge energy is regenerated with a half cycle delay, and the rounded regenerative current waveform like A-110 in FIG. 2 becomes a triangular wave without a half cycle delay and is a triangular wave. There is an essential difference in the operation from the conventional example of -110. As a matter of course, since the regenerative winding 109, the inductor 107, and the backflow prevention diode 108 are in series, the operation is the same even if the connecting order is changed.

Next, the flyback converter shown in FIG. 2 will be described in more detail taking as an example a quasi-resonant switching power supply that operates in a current critical mode. First, when the main switch 104 is turned on, the current from the input power supply 101 passes through the primary winding 103 of the transformer 102 and stores excitation energy in the transformer 102. When the main switch 104 is turned off, this excitation energy is charged from the secondary winding 113 of the transformer 102 through the secondary side rectifying diode 114 into the secondary capacitor 115 and supplied to the load 116.

When the main switch 104 is turned on, the energy stored in the leakage inductor (not shown) between the primary winding 103 and the secondary winding 113 becomes surge energy at the moment when the main switch 104 is turned off. Main switch 104
Tries to bounce up the voltage of. However, the surge energy charges the first storage capacitor 118 through the first diode 117, and thus rises slightly slowly. This reduces the switching loss when the main switch 104 is turned off and reduces noise. When the discharge on the secondary side is completed, the voltage of the main switch 104 slowly drops. This curve resonates with the primary inductor of the main transformer 102 and the inter-electrode capacitance of the main switch or the external capacitor 106, and takes the form of a sine wave peak to valley (V-104 in FIG. 2) at the resonance frequency. . In the vicinity of the lowest voltage of the main switch 104, the main switch 1
Turn-on 04 can reduce the turn-on loss. This is the operating principle of quasi-resonance. The capacitor 112 is an inter-electrode capacitor of the sub switch 110 or an external capacitor, and the diodes 105 and 11
Reference numeral 1 is a diode parasitic on the switch or an external diode.

On the other hand, the sub switch 110 is a storage capacitor 11 that stores surge energy during the secondary side discharge period.
A second switching power supply circuit that uses 8 as a power supply and regenerates surge energy is formed. The third winding 109 for regeneration wound around the transformer 102, the leakage inductor or the external inductor 107, and the reverse switch diode 108 are connected to the sub switch 110, and when the sub switch 110 is turned on, a regenerative current starts to flow. The waveform of this regenerative current is the same as the storage capacitor 118 and the inductor 10.
Half wave of sine wave of resonance frequency resonating at 7 (A in FIG. 2)
-110). The voltage when the sub-switch 110 is turned on quickly becomes 0 V (V-110 in FIG. 2), but the current waveform rises slowly and flows because it is a half-wave of a sine wave as described above. Therefore, the switching loss generated by voltage × current does not occur. By selecting an appropriate circuit constant, the electric charge of the storage capacitor 118 can be extracted until it becomes zero, and soft switching operation is possible for both the main switch and the sub switch in both the discontinuous current mode and the critical mode. As a result, since the switching noise can be reduced, the noise filter to be inserted into the device can be made simple and small, or it can be omitted in some cases, which makes it possible to achieve high efficiency and downsizing.

The waveforms in FIGS. 1 and 2 are from the top, the voltage of the main switch 104, the current, the gate voltage, and the auxiliary switch 1.
There are 10 voltages, currents, and gate voltages.

FIG. 3 is a modification of FIG. In the case of the circuit shown in FIG. 2, when the input voltage 101 is as low as DC141V, there is no particular problem in the circuit. However, when the input voltage 101 becomes high, for example, DC390V, the surge energy generated at the moment when the main switch 104 is turned off resonates with the inductor 107 and the internal capacitor 112 of the sub switch 110, and the storage capacitor 1
From the inevitable voltage which is the sum of 18 and regenerative winding 109,
Further, it jumps up and joins the sub switch 110. Under the condition that this exceeds the maximum rating of the auxiliary switch 110, the secondary winding 107 is connected to the inductor 107 for the purpose of limiting the surge voltage applied to the auxiliary switch 110.
c, the inductor 107 is connected to the primary winding 107b,
The configuration of the transformer 107a having the secondary winding 107c is changed. Then, the secondary winding 10 of the transformer 107a
The voltage generated from 7c is rectified by the third diode 123 and regenerated to the input power supply 101, so that the auxiliary switch 11
The surge voltage applied to 0 can be limited. Naturally, the regenerative current of the secondary winding 107c is the diode 12
It is also possible to regenerate the secondary side DC output (both ends of the capacitor 115) through 3. In the example of FIG. 3, input voltage 1
Secondary winding 1 depending on the value of 01, load current and circuit constant
No current flows through 07c, and 107a simply operates as an inductor. Thus, the embodiment of FIG. 3 in which the inductor 107 is replaced with the transformer 107a is the transformer 107a.
Although the operation is provided, the main switch and the sub switch become soft switching only in the continuous current mode of Japanese Patent Laid-Open No. 10-178777 which regenerates with a transformer, and the sub switch of Japanese Patent Laid-Open No. 11-178341 always operates. Regeneration to the power supply by hard switching is fundamentally different from the operation of the conventional example in which the regeneration winding 109 is not used. The difference between FIG. 2 and FIG. 3 lies in the inductor and the transformer as described above, and the other operations are the same, so a detailed description of the operation of FIG. 3 will be omitted.

When the quasi-resonant control is performed by the flyback converters of FIGS. 2 and 3, if the minimum frequency is set so that the frequency does not become too low when the load current is large, the load current is large. In this case, the current continuous mode is entered. At this time, if the main switch and the sub switch continue to drive at the same timing, turn-on of the main switch shifts to hard switching. Of course, as it is, turn-off is soft switching, so good operation can be achieved. However, in the present invention, when the current continuous mode is entered, the on timing of the sub switch is controlled to be relatively earlier than the on timing of the main switch, so that in the current continuous mode, it is almost the same as the operation of the ZVT shown in FIG. It can operate and maintain soft switching even at turn-on. Note that if the upper limit of the frequency is set so that the frequency does not become too high when the load current is reduced by the quasi-resonant control, the mode shifts to the current discontinuous mode when the load is light. The circuit of 3 maintains the soft switching operation for both the main switch and the sub switch.

The current value at the time of entering the continuous current mode can be known in advance from the input voltage and the current flowing through the main switch. Therefore, in order to perform the control for maintaining the soft switching even in the current continuous mode in the simplest manner, the current value in the critical mode is stored in the table, and the DSP is stored.
If you switch to continuous mode with (Digital Signal Processing), you can calculate the optimal time difference and make the on-timing of the sub-switch relatively earlier than the on-timing of the main switch. Of course, the same function can be calculated by an analog circuit.

FIG. 5 shows an example of a circuit in which the sub switch 110 is turned on relatively earlier than the main switch when the current continuous mode is entered. The drive signal 119 drives the sub switch 110 through the sub switch drive circuit 166. At the same time, the drive signal 119 also drives the main switch 104 through the variable delay circuit 164 and the main switch drive circuit 165. The signal from the voltage detection circuit 162 that detects the input voltage 101 and the signals detected by the resistor 160 and the current detection circuit 161 that detect the switch current are the delay amount calculation circuit 163.
Is calculated and enters the variable delay circuit 164. When the signal detected by the voltage detection circuit 162 and the current detection circuit 161 indicates that the operation is in the discontinuous current mode, the variable delay circuit 164 does not delay. However, when the operation result in the current continuous mode is obtained, the optimum delay amount is calculated and the optimum delay is performed by the variable delay circuit 164. If the circuit configuration of FIG. 5 is adopted, both of the main switch and the sub switch can be soft-switched in any of the current discontinuous mode, the current critical mode, and the current continuous mode. Of course, as described with reference to FIG. 3, the inductor 107 is changed to the configuration of the transformer 107a, the primary winding 107b is connected to the auxiliary switch, and the secondary winding is regenerated to the input power supply 101 through the diode 123. It can be regenerated to the DC output on the secondary side (both ends of the capacitor 115).

Even if the polarity of the secondary winding 113 is reversed and the free wheel diode 113 and the free wheel inductor 131 are provided to form a forward converter (FIG. 4A), an appropriate soft switching operation can be performed. In addition, if the secondary circuit is eliminated and the capacitor 115 is directly charged from the drain of the main switch element 104 through the diode 114 (FIG. 4).
B), can be applied to boost converter.

[0019]

EFFECT OF THE INVENTION In the current discontinuous mode and the current critical mode,
Soft switching operation is possible in any mode. Therefore, switching loss and switching noise can be reduced, and a simple noise filter can be set. In the case of this operation, the drive circuit of the main switch and the drive circuit of the sub switch can be made common, so that the drive circuit can be made very simple. In addition, if the load current increases and the current continuous mode is entered, the auxiliary switch is turned on earlier than the main switch so that both the main switch and the auxiliary switch can be operated in the continuous current mode of the flyback converter or in the forward converter. It can be soft switching.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of a conventional example and its operation waveform.

FIG. 2 is a circuit diagram showing a configuration of a first embodiment of the present invention and operation waveforms thereof.

FIG. 3 is a modification of FIG. 2 and shows a circuit diagram showing a configuration of a second embodiment of the present invention and an operation waveform thereof.

FIG. 4 is a circuit diagram showing a configuration of third and fourth embodiments of the present invention and operation waveforms thereof.

FIG. 5 is a circuit diagram showing a fifth embodiment.

[Explanation of symbols]

101 Input power source 102, 107a Transformer 103, 107b Primary winding 104 of transformer 104 Main switch 105, 111 Switch parasitic diode or external diode 106, 112 Switch parasitic capacitor or external capacitor 107, 131 Inductor 108, 114, 117, 123 , 130, 132, 1
51 diode 109 transformer regenerative winding 110 secondary switch 113, 107c secondary winding 115, 118 capacitor 116, 133, 150, 160 resistance 119, 120 drive signal 161 current detection circuit 162 voltage detection circuit 163 delay amount calculation circuit 164 Variable delay circuit 165 Main switch drive circuit 166 Sub switch drive circuit

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Claims (4)

[Claims] 1. A flyback converter, a forward converter, or a boost converter,
A first rectifying diode that rectifies surge energy from the main winding of the transformer that occurs when the main switch is turned off, and a storage capacitor that stores the current rectified by the diode are provided, and the charge stored in the storage capacitor is stored. The switching power supply device is characterized in that the regenerative winding provided in the main transformer is further connected to the sub switch through an inductor and a second diode for preventing backflow. 2. The power supply device according to claim 1, wherein the inductor is provided with a secondary winding to change to a transformer configuration, and the secondary winding of the transformer receives a surge energy from an input power source through a third diode. A power supply device characterized by being regenerated. 3. The power supply device according to claim 1 or 2, wherein the main switch and the sub switch are driven by the same drive circuit. 4. The power supply device according to claim 1,
As the load current increases, the current critical mode is exceeded,
A power supply device comprising control means for turning on the sub switch earlier than turning on the main switch when the current continuous mode is entered.