JPH03117362A - Voltage resonance converter - Google Patents

Abstract

PURPOSE:To reduce loss in a switching element and to improve conversion efficiency by connecting a capacitor for bypassing charges, which charge the parasitic capacitance of the switching element, across a reverse blocking diode. CONSTITUTION:In a voltage resonance type converter comprising a resonance capacitor 4, a resonance coil 7, and the like, charges stored in the parasitic capacitance Cb of a switching element 6 during OFF interval of the switching element 6 are discharged through a bypath capacitor 20 connected in parallel with a reverse blocking diode 5. When the capacitance of the capacitor 20 is set higher than a predetermined value to be determined based on the circuit constants, zero voltage switching can be realized. Since current is not consumed excessively during ON interval of the switching element 6, loss can be reduced. By such arrangement, a converter which causes no degradation of conversion efficiency even in high frequency region can be obtained.

Description

[Detailed Description of the Invention] [Summary] Regarding a voltage resonant converter that converts a DC voltage to an arbitrary DC voltage, the purpose of this invention is to improve the efficiency of the converter by reducing loss in switching elements. a reactor for energy storage connected in series with a DC source, a resonant capacitor connected between one end of the reactor and a common line, a switching element for switching the DC power supply, the anode side of which is connected to one end of the reactor, a reverse blocking diode whose cathode side is connected to one of the switching elements, a resonant coil connected in series with the reactor, a rectifier diode connected in series with the resonant coil, and a common terminal connected to the output side of the rectifier diode. The output is the smoothing capacitor connected between the lines and the connection point between the diode and capacitor.
In a voltage resonant converter configured with a switching control circuit that monitors the output voltage when a load is connected and controls switching of the switching element, a parasitic capacitance of the switching element is charged across the reverse blocking diode. It is configured by connecting a bypass capacitor for the charge.

[Industrial Application Field] The present invention relates to a voltage resonant converter that converts a DC voltage to an arbitrary DC voltage.

In recent years, converters have been used to obtain arbitrary DC voltage or AC voltage from a DC power source. A circuit that generates an arbitrary DC voltage from a DC voltage is called a DC/DC converter, and a circuit that generates an arbitrary AC voltage from a DC voltage is called an inverter. Such a converter circuit generates an arbitrary voltage value from a DC voltage, and is required to have good conversion efficiency.

[Prior Art] FIG. 7 is an electric circuit diagram showing a configuration example of a voltage resonant full-wave rectifier circuit, which is a type of conventional converter. DC power supply 1
A capacitor 2 is connected to both ends of the capacitor 2. A reactor 3 is connected in series to the output of the DC power supply 1, and a resonance capacitor 4 is connected to one end of the reactor 3. The other end of the capacitor 4 is connected to the common line 14.

Further, an anode of a reverse blocking diode 5 is connected to one end of the reactor 3, and a cathode of the reverse element diode 5 is connected to a switching element 6. Here, a MOSFET is used as a switching element.

This FET 6 has a parasitic capacitance cb and a parasitic diode Db as shown in the figure. The parasitic capacitance cb and the parasitic diode Db are geometrically connected in parallel to the switching element 6 as shown in the figure. 7 is a resonant coil connected in series with the reactor 3, and 8 is a rectifying diode connected in series with the resonant coil 7.

A smoothing capacitor 9 is connected between the cathode of the diode 8 and the common line 14.

Further, the cathode of the diode 8 is connected to the load 10. The output voltage of the load 10 is input to the amplifier 11, and after the difference from the reference voltage is amplified by the amplifier 11, the output voltage is converted to V/F.
The converter 12 converts the signal into a frequency signal according to the input voltage. The drive circuit 13 applies a clock between the gate and source of the switching element 6 to drive the switching element 6 so that the input frequency is constant.

The operation of the circuit configured in this way will be explained with reference to the timing chart shown in FIG.

When an on/off signal for the switching element 6 (specifically, a voltage Vas applied between the gate and source of the FET) as shown in FIG. 8(a) is applied from the drive circuit 13, the switching element 6 The input terminal Vl (voltage of the DC power supply 1) is repeatedly turned on and off by the on-off signal.

Here, the period during which the switching element 6 is off is constant, and the period during which the switching element 6 is on is changed to change the output voltage Vo using a frequency modulation method.

During the period when the switching element 6 is on, a rectangular current 1i as shown in FIG. 8(c) flows through the reactor 3. As a result, energy is accumulated in the reactor 3. When the switching element 6 is turned off, the energy stored in the Luactor 3 is released. At this time, the resonant capacitor 4 and the resonant coil 7 constitute a resonant circuit, and the voltage V' across the capacitor 4 swings in both positive and negative directions as shown in FIG. 8 (b), becoming an alternating current voltage.
Vo in (b) is the voltage across the load 10.

The current flowing through the resonant coil 7 in response to this AC voltage is I
L The result will be as shown in Figure 8 (d).

Drain (D) and source (S) of switching element 6
) The die pressure Vds becomes as shown in FIG. 8(e).

Here, while the switching element 6 is off, the drain-source voltage v[,5 of the switching element 6 increases following the voltage Vr across the resonance capacitor 40. This voltage charges the parasitic capacitance cb of the switching element 6 to the peak voltage Vcp of the resonance capacitor 4. Here, if there is no reverse element diode 5,
Resonance capacitor! Among the voltages applied to both ends of (2), the negative voltage is clamped by the parasitic diode Db and therefore does not appear. Therefore, a reverse element diode 5 is connected in series with the switching element 6 to eliminate the influence of the parasitic diode Db. Therefore, the discharge of the electric charge charged in the parasitic capacitance cb is prevented.

As a result, the parasitic capacitance IICb is connected to (
1/2)CbVc,2 energy is stored. Here, cb was used as is as the capacitance of the parasitic capacitance Cb.

This energy is released inside the switching element 6 when the switching element 6 is turned on by the drive circuit 13. This emission results in energy loss.

On the other hand, during the period when the switching element 6 is off, the reactor 3
The charges accumulated in the resonant coil 7 flow through the diode 8. At this time, the current IL flowing through the resonant coil 7 is
The result will be as shown in Figure (d).

Next, the human power/output voltage conversion characteristics of the voltage resonant converter will be explained. FIG. 9 is a human power/output voltage conversion characteristic diagram of the voltage resonant converter.

(a) shows the characteristics of the voltage resonance full waveform, and (b) shows the characteristics of the voltage resonance half waveform. In the figure, the vertical axis shows Vo/VI, and the horizontal axis shows FS/FN. The parameter is R1-/Zn. In the figure, RL is the load resistance, Zn is the characteristic impedance of the circuit, and r is r (Lr is the inductance of the resonant coil, and Cr is the capacitance of the resonant capacitor). Vl is the input voltage, vO is the output voltage, FS is the switching frequency, F
N is the resonant frequency of the circuit.

In the case of the voltage resonance half waveform shown in (b), when the parameter (load RL) is changed, the characteristic curve changes. However, the voltage resonance full waveform shown in (a) has an advantageous characteristic for constant voltage control in that the input voltage Vl to output voltage VO conversion characteristic does not depend on the load RL. This characteristic shows that this circuit system has constant voltage characteristics even when the conversion frequency is kept constant without any control over fluctuations in the load RI. In other words, when performing feedback control to control the output voltage to a constant value, it is only necessary to control the fluctuations in the input voltage (conversion frequency control; increase the frequency to lower the output voltage), and control the control range (conversion frequency control; increase the frequency to lower the output voltage). (frequency change width) can be made extremely small. Therefore, by using the voltage resonance full waveform method, it is possible to downsize the filter circuit, magnetic components, etc. necessary for the converter.

[Problems to be Solved by the Invention] In the conventional system shown in FIG. 7, a reverse blocking diode 5 is inserted in series with the switching element 6 in order to maintain the AC waveform appearing at both ends of the resonant capacitor 4. Because of this reverse blocking diode 5, the charge accumulated in the parasitic capacitance cb of the switching element 6 cannot be discharged when the switching element is turned off. As a result, this charge flows through the switching element 6 and is discharged when the switching element 6 is turned on. Therefore, the loss of the switching element 6 increases. Here, the peak voltage Vcp applied to the resonance capacitor 4 varies depending on the load 10, but the input power supply voltage VlO
The loss reaches several times to several tens of times, and increases in proportion to the higher the conversion frequency.

This causes a decrease in the efficiency of the converter, making it difficult to increase the frequency. Furthermore, since the loss increases, the switching element may generate abnormal heat and may be thermally destroyed.

The present invention has been made in view of these problems, and an object of the present invention is to provide a voltage resonant converter that does not cause a decrease in conversion efficiency even in a high frequency range.

[Means to solve the problem] FIG. 1 is an electrical circuit diagram showing the principle of the present invention.

Components that are the same as those in FIG. 7 are designated by the same reference numerals.

In the figure, 1 is a DC power supply, 3 is an energy storage reactor connected in series with the DC source 1, 4 is a resonance capacitor connected between one end of the reactor 3 and the common line 14, and 6 is the DC power supply. A switching element for switching the power supply 1; 5 is an inverse element diode whose anode side is connected to one end of the reactor 3; and its cathode side is connected to one end of the switching element 6; 7 is a resonant coil connected in series with the reactor 3; , 8 is a rectifying diode connected in series with the resonant coil 7, and 9 is a smoothing capacitor connected between the output side of the rectifying diode 8 and the common line 14.

20 is a bypass capacitor for the charge charged in the switching element 6 connected to both ends of the reverse blocking diode 50, and 21 is the output voltage at the connection point between the diode 8 and the capacitor 9, and the output voltage when the load 10 is connected. This is a switching control circuit that monitors and controls switching of the switching element 6.

[Operation] During the period when the switching element 6 is off, the electric charge charged in the parasitic capacitance ff1Cb is discharged via the bypass capacitor 20 connected in parallel to the reverse blocking diode 5 as shown in FIG. That is, since the capacitor 20 forms a path through which the current i as shown in the figure flows, the charge accumulated in the parasitic capacitance cb is discharged via the capacitor 20. Therefore, when the switching element 6 is turned on, no extra current is consumed, and losses can be reduced. Therefore, even if the conversion frequency becomes high, the loss does not increase, and it is possible to provide a voltage resonant converter that does not cause a decrease in conversion efficiency even in a high frequency range.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 3 is an electrical circuit diagram showing one embodiment of the present invention. Components that are the same as those in FIG. 1 are designated by the same reference numerals. In the figure, 2 is an input capacitor connected between the DC power supply 1 and the common line 14.

The switching control circuit 21 includes an amplifier 11. It is composed of a V/F converter 12 that converts the output of the amplifier 11 into a frequency signal, and a drive circuit 13 that drives the switching element 6 at a frequency corresponding to the output of the V/F converter 12. The other circuits are the first
Same as the figure. The operation of the circuit configured as described above will be explained as follows.

First, the operating principle will be explained. FIG. 4 shows an equivalent circuit when the switching element 6 shown in FIG. 3 is off. In the figure, Cr is the capacitance of the resonant capacitor 4, Vds is the voltage applied across the switching element 6, Lr is the inductance of the resonant coil 7, and cd is the capacitance of the capacitor 20. The state when the switching element 6 is off is divided into state 1 as shown in (.r) and state 2 as shown in (b) as shown in the figure. State 1 is a period in which the parasitic capacitance cb of the switching element 6 is charged to the peak voltage Vcp, and state 2 is a period in which the parasitic capacitance cb is discharged through the capacitor 20 (Cd).

Here, if Zn-f■]-wn-1/Fr7t]-(Lr is the inductance of the resonant coil 7, C
r is the capacity ff1 of the resonance capacitor 4), state 1 (0≦w
nt≦π/2), the voltage Vd applied across the capacitor Cb
s is Vds (t) − Vo+Zn I i sin (wn t)
(1) Here, Vo is the voltage across the load 10, and Ii is the current flowing from the current source, that is, the reactor 3.

The voltage Vds applied across capacitor ff1Cb in state 2 is V
ds (t)= Vo+ [Cb/ (Cd+Cb)] Zn In
+ [Cd/ (Cd+Cb)] Zn I nX
c o s (wn t-π/2) (2)
If the off-period of the switching element 6 is wnt-3π/2, then from equation (2), Vd5-V immediately before turn-on.

[Cd/ (Cd+Cb)] Zn I n (3
) remains in the parasitic capacitance cb. Therefore, this residual voltage Vds is Vds≦0, that is, Cd≧Cb (Zn I i+Vo)x1/ (Zn
If the capacitance ff1cd of the capacitor 20 is selected so that I1-Vo) (4), zero-voltage switching of the switching element 6 becomes possible. Therefore, zero-voltage switching of the switching element 6 is possible without generating loss during turn-off, and while maintaining the constant voltage load characteristic that is a characteristic of the voltage resonance full waveform (see Figure 9). It becomes possible to

Next, the operation of the embodiment shown in FIG. 3 will be explained with reference to the timing chart shown in FIG. As shown in the equalization circuit of FIG. 4, the input section can be regarded as a current source that flows current Ii by the action of input terminal 9 (reactor 3). When the switching element 6 is turned off as shown in FIG. 3(a), the resonance capacitor 4 is charged with the current 1i and rises as shown in FIG. 5(b). and,
When the voltage V' across the resonance capacitor 4 reaches the output voltage VO (period from T to T in FIG. 5), the rectifier diode 8 is turned on, and the resonance circuit of the resonance capacitor 4 and the resonance coil 7 is activated. is formed.

As a result, the voltage Vr across the resonance capacitor 4 and the voltage (
The current I flowing through the vibrating coil 7 has a sinusoidal waveform (see FIGS. 5(b) and (d), period from T to T2).

As a result, the parasitic capacitance Cb of the switching element 6 is charged to the peak voltage Vcp as shown in FIG. 5(c), but is completely discharged by the action of the added capacitor 20. Then, since the energy stored in the parasitic capacitance Cb at turn-off becomes 0, zero voltage switching is maintained.

Further, the energy remaining in the resonant coil 7 is discharged to the load 10 during the period from T2 to T.

Next, the stabilizing operation of the output voltage will be explained.

The output voltage vO is raised and compared with a reference voltage by the amplifier 11, the difference (error) between Vo and the reference voltage is calculated, and the error is amplified. The output of this amplifier 11 is applied to a V/F converter 12 and converted into a clock frequency corresponding to the error. The V/F converter 12 converts this clock frequency into a pulse train with a constant on time and supplies it to the drive circuit 13. The drive circuit 13 amplifies this human power pulse,
The gate of the switching element 6 is driven. And the ninth
As is clear from the characteristics in Figure (a), when the output voltage Vo becomes higher than the reference voltage, feedback control is performed to lower the conversion frequency to keep the output voltage Vo constant.

FIG. 6 is an electrical circuit diagram showing another embodiment of the present invention.

Components that are the same as those in FIG. 3 are designated by the same reference numerals. In the embodiment shown in the figure, the resonant coil portion is replaced with an isolation transformer 30, and the output voltage Vo is extracted from the DC power supply 1 in an electrically insulated manner. In order to achieve complete insulation, for example, a photocoupler or the like is used to insulate between the V/F converter 12 and the drive circuit 13.

This system has the advantage that it is not necessary to provide a special resonance coil because the inductance L of the resonance coil can be the cage inductance between the primary and secondary windings of the isolation transformer 30.

In the above embodiment, a MOS is used as a switching element.
Although the case where an FET is used is taken as an example, the present invention is not limited to this, and other high-speed switching elements such as a junction type FET can be used.

It is also possible to use a bipolar transistor or the like.

[Effects of the Invention] As described above in detail, according to the present invention, a capacitor is connected across the reverse blocking diode of the voltage full-wave resonant converter in order to bypass the electric charge charged in the parasitic capacitance of the switching element. By doing so, it is possible to significantly reduce the loss when the switching element is turned on, and therefore it is possible to provide a voltage resonant converter that does not cause a decrease in conversion efficiency even in a high frequency region. According to the present invention, there is little reduction in conversion efficiency even when the frequency is increased, so it is possible to miniaturize the circuit.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of the principle of the present invention, Fig. 2 is an explanatory diagram of the operation of the present invention, Fig. 3 is an electric circuit diagram showing an embodiment of the present invention, and Fig. 4 is an equivalent diagram when the switching element is off. 5 is a timing chart showing the operating waveforms of each part of the circuit shown in FIG. 3, FIG. 6 is an electric circuit diagram showing another embodiment of the present invention, and FIG. 7 is an electric circuit diagram showing an example of the configuration of a conventional circuit. A circuit diagram, FIG. 8 is a timing chart showing operating waveforms of each part, and FIG. 9 is an input/output voltage conversion characteristic diagram of the voltage resonant converter. In Figure 1, 1 is a DC power supply, 3 is a reactor, 4 is a resonant capacitor, 5 is a reverse blocking diode, 6 is a switching element, 7 is a resonant coil, 8 is a diode, 9 is a capacitor, 10 is a load, 14 is a A common line, 20 a capacitor, and 21 a switching control circuit. Figure 3: A swimming chart showing the operation of each part of the circuit Figure 5: Figure 7 Figure] 0

Claims (1)

[Claims] A DC power source (1), an energy storage reactor (3) connected in series with the DC source (1), and between one end of the reactor (3) and a common line (14). The connected resonance capacitor (4) and the DC power supply (
1); a reverse blocking diode (5) whose anode side is connected to one end of the reactor (3) and whose cathode side is connected to one end of the switching element (6); and the reactor (3). Resonant coils connected in series (
7), a rectifier diode (8) connected in series with the resonant coil (7), and a common line (1) connected to the output side of the rectifier diode (8).
4) The connection point between the smoothing capacitor (9), the diode (8), and the capacitor (9) connected between them is used as an output, and the output voltage when the load (10) is connected is monitored and the switching element is (6) In a voltage resonant converter configured with a switching control circuit (21) that performs switching control, there is a bypass for the electric charge charged in the parasitic capacitance of the switching element (6) across the reverse blocking diode (5). A voltage resonant converter characterized in that a capacitor (20) is connected thereto.