JPH08182318A - Switching power source - Google Patents

Abstract

PURPOSE: To provide a switching power source in which the switching loss of a switching element is reduced. CONSTITUTION: A switching power source comprises a DC power source 11, a transformer 15 having primary windings 12, 13 and a secondary winding 14, switching transistors 16, 17 connected to the other end of the windings 12, 13, a rectifier 18 connected to the winding 14 of the transformer 15, and control means 19 for detecting the voltage applied to the transistors 16, 17 to control a drive signal supplied to the transistors 16, 17 based on the detected voltage. The means 19 has voltage detectors 62, 63 for detecting the voltages applied to the transistors 16, 17 and inhibiting circuits 64, 65 for controlling the gate signals of the transistors 16, 17, and switches to zero voltage the transistor 16, 17 by means of the gate signals.

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 capable of supplying a DC high voltage power to a load.

[0002]

2. Description of the Related Art A switching power supply of this type includes a transformer in which a DC voltage is applied to a primary winding, a switching element connected to the other end of the primary winding of the transformer, and a rectifying circuit connected to the secondary winding of the transformer. And a drive circuit for supplying a drive signal to the switching element, switching is performed by the switching element to cause a current to flow in the primary winding, and the voltage boosted by this transformer is rectified by the rectifier circuit to obtain a high-voltage DC voltage. Known as one.

FIG. 4 is a circuit diagram showing an example in which a conventional switching power supply is used as a power supply for a traveling wave tube power amplifier.

This switching power supply is a DC power supply 101.
A transformer 105 having primary windings 102 and 103 and a secondary winding 104, switching elements (switching transistors) 106 and 107 connected to the other ends of the primary windings 102 and 103, and a secondary of the transformer 105. The rectifying circuit 108 is connected to the winding 104. The DC power supply 101 has a positive pole for the transformer 10.
The negative pole is connected to a common line at one common end of each of the primary windings 102 and 103. Further, the rectifier circuit 108 bridge-connects the diodes 151 to 154, and connects the two AC terminals of the bridge circuit to the secondary winding 10
A smoothing capacitor 155 is connected to the DC terminals of the bridge circuit at both ends of the bridge 4. The load 110 is connected to both ends of the smoothing capacitor 155.
Reference numeral 111 is a stray capacitance of the secondary winding 104 of the transformer 105.

The operation of such a switching power supply is shown in FIG.
Will be described with reference to. In FIG. 5, the horizontal axis represents time, and the vertical axis represents gate signals V _G1 , V _G2 and switching transistor 1.
The voltages V _D1 and V _D2 applied to the drains of 06 and 107 and the currents I _D1 and I _D2 flowing through the primary windings 102 and 103 are shown.

As shown in this figure, gate signals V _G1 , V
_{When G2} is applied to the gates of the switching transistors 106 and 107, the switching transistor 106 and
107 is on / off controlled. This makes transformer 1
Currents I _D1 and I _D2 flow through the primary windings 102 and 103 of 05 as shown in FIG. As a result, the transformer 105
A high voltage is generated in the secondary winding 104, is rectified by the bridge rectifier configured by the diodes 151 to 154 of the rectifier circuit 108, is smoothed by the smoothing capacitor 155, and supplies the DC high voltage power to the load 110.

By the way, as shown in FIG.
The switching transistors 106 and 107 from on to off or
When switching from off to on
Voltage V applied to transistors 106 and 107_D1, V_D2When,
Current I flowing through these_D1, I _D2Since and overlap
It is known that a switching loss occurs.

When the switching frequency of the switching power supply is as low as several tens [KHz], the power loss (switching loss) does not pose a problem. However, it is known that when the switching frequency is increased to several hundreds [KHz] or more in order to make the switching power source compact, this power loss increases in proportion to the switching frequency, and the efficiency of the power source decreases.

Therefore, the above-mentioned voltages V _D1 , V _D2 and current I
_In order to eliminate the overlap of _D1 and I _D2 , for example, JP-A-4-17575, JP-A-2-51356, JP-A-1-157274, JP-A-63-43567, JP-A-61-250098, Actual Kaihei No. 4-128088,
Alternatively, as disclosed in Japanese Utility Model Publication No. 4-61489, a switching power supply has been proposed in which dead time is provided by using various means to eliminate power loss.

[0010]

As described above, in the former switching power supply of the related art, when the switching frequency is increased in order to reduce the size and weight, the power supply efficiency is lowered, and conversely, the power supply efficiency is kept high. In that case, the switching frequency cannot be increased, which results in a large power supply.

In the conventional switching power supply in which the dead time is provided to reduce the power loss, the dead time is not set by directly detecting the voltage applied to the switching transistor. However, there is a drawback that the switching efficiency is also lowered.

Therefore, an object of the present invention is to provide a switching power supply in which the switching loss of the switching element is reduced.

[0013]

According to a first aspect of the present invention, there is provided a switching power supply comprising: a transformer in which a DC voltage is applied to a primary winding; a switching element connected to the other end of the primary winding of the transformer; It is equipped with a rectifier circuit connected to the secondary winding, and a drive circuit that gives a drive signal to the switch 1 element. The switching element switches the current to flow in the primary winding, and the voltage boosted by this transformer is rectified by the rectifier circuit. In a switching power supply that obtains a high-voltage DC voltage by rectification, a control means that detects the voltage applied to the switching transistor and controls the drive signal supplied to both switching transistors based on the detected voltage is provided. The feature is that zero voltage switching is performed by the action.

According to another aspect of the present invention, the control means includes a voltage detection circuit for detecting the voltage applied to the switching element, and an inhibit circuit for controlling the drive signal of the switching element by the detection signal from the voltage detection circuit. It is characterized by.

The parameters of the transformer according to claim 3 are:
The primary winding inductance of the transformer and the stray capacitance of the transformer, and these values are set such that the current flowing through the switching element and the voltage applied to the switching element do not overlap.

A switching element according to a fourth aspect is a switching transistor.

According to a fifth aspect of the present invention, there is provided a switching power source, wherein a DC voltage is applied to a primary winding of the transformer, and a switching element connected to the other end of the primary winding of the transformer.
A rectifier circuit connected to the secondary winding of the transformer and a drive circuit that gives a drive signal to the switching element,
In a switching power supply that switches by a switching element to pass a current through the primary winding and rectifies the voltage boosted by this transformer with a rectifier circuit to obtain a high-voltage DC voltage,
A control means is provided that includes a voltage detection circuit that detects the voltage applied to the switching element and an inhibit circuit that controls the drive signal of the switching element based on the detection signal from the voltage detection circuit. It is characterized in that zero voltage switching is performed.

In the present invention, the zero voltage switching is performed by utilizing the charging action by the excitation energy of the winding to the floating capacitance of the transformer, and in order to detect this voltage,
A voltage detection circuit is provided, and the drive signal from the drive circuit is taken into the inhibit circuit. The detection signal from the voltage detection circuit forms the drive signal for the switching element from the drive signal, and this drive signal causes the switching element to perform zero voltage switching. It is done.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

FIG. 1 is a block diagram showing an example in which an embodiment of the switching power supply of the present invention is used as a power supply for a traveling wave tube power amplifier.

The switching power supply shown in this figure has a DC power supply 11, primary windings 12 and 13 and a secondary winding 14, and a transformer in which the DC power supply 11 is connected to a common one terminal of the primary windings 12 and 13. 15, switching elements (switching transistors) 16 and 17 respectively connected to the other ends of the primary windings 12 and 13, a rectifying circuit 18 connected to the secondary winding 14 of the transformer 15, and a switching transistor 16 , 17 for detecting the voltage applied to the switching transistors 16 and 17 and controlling the drive signal supplied to the switching transistors 16 and 17 based on the detected voltage.

More specifically, the DC power supply 11 has a positive pole connected to one common end of the primary windings 12 and 13 of the transformer 15 and a negative pole connected to a common line. Further, in the switching transistors 16 and 17, each drain is connected to each other terminal of the transformer 15 and each source is connected to a common line. The rectifier circuit 18 is configured by connecting diodes 51 to 54 in a bridge connection, connecting two AC terminals of the bridge circuit to both ends of the secondary winding 14, and connecting a smoothing capacitor 55 to a DC terminal of the bridge circuit. . The load 20 is connected to both ends of the smoothing capacitor 55. Further, reference numeral 21 is a transformer 1.
5 is the stray capacitance of the secondary winding 14.

Further, the control means 19 detects the drive circuit 61 for generating the first drive signal D ₁ and the second drive signal D ₂ and the drain voltages V _D1 and V _D2 of the switching transistors 16 and 17, respectively. The voltage detection circuits 62 and 63 for outputting the respective detection signals, and the first circuit from the drive circuit 61
Drive signal D ₁ and the second drive signal D ₂ of FIG. 1 and inhibit circuits 64 and 65 for forming gate signals V _G1 and V _G2 based on the respective detection signals.

The operation of such an embodiment is shown in FIGS.
Will be described with reference to. FIG. 2 shows the operation of the embodiment of the present invention, in which the horizontal axis represents time, the vertical axis represents drive signals D ₁ and D ₂ , gate signals V _G1 and V _G2 , drain voltages V _D1 and V _D2. , Drain currents I _D1 and I _D2 are shown. FIG. 3 is an enlarged view showing the relationship between the primary winding inductance and the stray capacitance of the transformer of the embodiment.

First, the DC voltage supplied from the DC power supply 11 is supplied to the drains of the switching transistors 16 and 17 via the primary windings 12 and 13 of the transformer 15. Here, when the switching transistors 16 and 17 are switched by the gate signals V _G1 and V _G2 , a rectangular wave AC flows in the primary windings 12 and 13 of the transformer 15. The voltage boosted in the secondary winding 14 of the transformer 15 is rectified by the diode bridge circuit including the diodes 51 to 54 of the rectifier circuit 18, smoothed by the smoothing capacitor 55, and becomes a high voltage DC voltage. This high-voltage DC voltage is applied to the load 2
0 is supplied.

Since the transformer 15 used here generates a high voltage, the number of turns of the secondary winding 14 increases. Therefore, the stray capacitance 21 generated between the secondary winding 104 is
Is a relatively large value compared to that for low pressure.

[0027] Here, the voltage V _D1 or V _D2, as shown in FIG. 3, the inductance Lp of the primary winding 12, 13 of the electrostatic capacitance value Cs and the transformer 15 of the stray capacitance 21 is large, the voltage V _D1 , V _D2 has a large rising or falling slope, and conversely, when the capacitance value Cs or the inductance Lp is small, the rising slope or the like becomes small. As described above, the slopes of the rising edges of the voltages V _D1 and V _D2 are determined by the capacitance value Cs and the inductance Lp. Therefore, the excitation inductance Lp of the primary windings 12, 13 of the transformer 15 is matched with the value of the electrostatic capacitance Cs of the stray capacitance 21 so that the relationships between the voltages V _D1 , V _D2 and the currents I _D1 , I _D2 do not overlap. I will decide appropriately. As a result, the exciting energy stored in the primary windings 12 and 13 of the transformer 15 charges the stray capacitance 21 during a period in which both the switching transistors 16 and 17 are at rest. In order to detect such a state, the voltage waveforms V _D1 and V _D2 of the switching transistors 16 and 17 are _supplied to the voltage detection circuit 62 of the control means 19,
Detect at 63. When the input voltages (voltages V _D1 and V _D2 ) are higher than zero, the voltage detection circuits 62 and 63 output signals for inhibiting the drive signals D ₁ and D ₂ from the inhibit circuits 64 and 65, and the input voltages ( When the voltages V _D1 , V _D2 ) become substantially zero, a signal for releasing the drive signal blocking state of the inhibit circuits 64, 65 is output. The inhibit circuits 64 and 65 form the gate signals V _G1 and V _G2 as shown in FIG. 2, which block the passage of a part of the drive signals D ₁ and D ₂ of the drive circuit 61 output at a duty of approximately 50%. To do.

The switching transistors 16 and 17 perform a switching operation by such gate signals V _G1 and V _G2 . Then, the switching transistors 16 and 17
As shown in FIG. 2, after the drain voltages V _D1 and V _D2 become zero (time t ₁₁ , t ₁₃ , ..., Time t ₂₁ , t ₂₂ ,
...) and turned on (time t ₃₁ , t ₃₃ , ..., time t ₄₁ ,
t ₄₃ , ...) and the currents I _D1 and I _D2 start to flow (time t
₅₁ , t ₅₃ , ..., Times t ₆₁ , t ₆₃ , ...), the switching transistors 16 and 17 do not generate switching loss at the start of switching. Further, even when the switching transistors 16 and 17 are turned off, as shown in FIG. 2, the currents I _D1 and I _D2 are cut off (time t ₅₂ , t ₅₄ , ..., Time t ₆₂ , t _64). ,…), Voltage V _D1 , V
_{Since D2} rises (time t ₁₂ , t ₁₄ , ..., Time t ₂₂ , t ₂₄ , ...), no switching loss occurs.

Therefore, according to this embodiment, the switching loss of the switching transistors 16 and 17 can be made almost zero.

[0030]

As described above, according to the first aspect of the invention, since the switching loss of the switching element does not increase even if the switching frequency of the power supply is increased, it is possible to obtain a highly efficient, compact and lightweight power supply. There is an effect that can be done.

According to the second aspect of the present invention, the voltage applied to the switching element is detected, and the drive signal for the switching element is formed by the inhibit circuit based on the detection signal, so that the switching element is switched to zero voltage. Can be made.

According to the third aspect of the invention, the primary winding inductance of the transformer and the stray capacitance of the transformer are set to values such that the current flowing through the switching element and the voltage applied to the switching element do not overlap. Therefore, the switching element can be brought into a state in which zero voltage switching can be performed.

In the fourth aspect of the invention, since the switching element is composed of the switching transistor, the switching drive signal can be easily obtained.

According to the fifth aspect of the present invention, a control including a voltage detection circuit for detecting the voltage applied to the switching element and an inhibit circuit for controlling the drive signal of the switching element by the detection signal from the voltage detection circuit. Since the means is provided and the zero voltage switching is performed by the interaction with the parameter of the transformer, the switching loss of the switching element does not increase even if the switching frequency of the power source is increased, so that a highly efficient, compact and lightweight power source can be obtained. There is an effect that can be.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a switching power supply according to the present invention.

FIG. 2 is various signal waveform diagrams for explaining the operation of the embodiment.

FIG. 3 is an explanatory diagram showing an enlarged switching voltage of the embodiment.

FIG. 4 is a block diagram showing a conventional switching power supply.

FIG. 5 is various signal waveform diagrams for explaining the operation of the conventional switching power supply.

[Explanation of symbols]

 11 DC power supply 12, 13 Primary winding 14 Secondary winding 15 Transformer 16, 17 Switching transistor 18 Rectifier circuit 19 Control means 51-54 Diode 55 Smoothing capacitor 61 Drive circuit 62, 63 Voltage detection circuit 64, 65 Inhibit circuit

Claims (5)

[Claims] 1. A transformer in which a DC voltage is applied to a primary winding, a switching element connected to the other end of the primary winding of the transformer, a rectifier circuit connected to the secondary winding of the transformer, and a drive signal to the switching element. And a drive circuit that supplies a current to the primary winding by switching with a switching element, and a voltage boosted by the transformer is rectified by a rectifier circuit to obtain a high-voltage DC voltage, which is applied to the switching transistor. The switching power supply is characterized in that it is provided with a control means for detecting the voltage to be applied and controlling the drive signal to be supplied to both switching transistors based on the detected voltage, and that the zero voltage switching is performed by the interaction with the parameter of the transformer. . 2. The control means includes a voltage detection circuit that detects a voltage applied to the switching element, and an inhibit circuit that controls a drive signal of the switching element according to a detection signal from the voltage detection circuit. The switching power supply according to claim 1, which is characterized in that. 3. The transformer parameters are the primary winding inductance of the transformer and the stray capacitance of the transformer,
The switching power supply according to claim 1, wherein a value is set so that a current flowing through the switching element and a voltage applied to the switching element do not overlap each other. 4. The switching power supply according to claim 1, wherein the switching element is a switching transistor. 5. A transformer in which a DC voltage is applied to the primary winding, a switching element connected to the other end of the primary winding of the transformer, a rectifier circuit connected to the secondary winding of the transformer, and a drive signal to the switching element. And a drive circuit that supplies a current to the primary winding by switching with a switching element, and the voltage boosted by this transformer is rectified by a rectifier circuit to obtain a high-voltage DC voltage. A control means comprising a voltage detection circuit for detecting the voltage that is detected and an inhibit circuit for controlling the drive signal of the switching element by the detection signal from the voltage detection circuit, and zero voltage switching is performed by the interaction with the parameters of the transformer. Switching power supply characterized by doing so.