JPH0740784B2 - Series resonance converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial field of application" The present invention is particularly suitable for high power, and controls a switching element to flow a half wave of series resonance current to convert direct current to alternating current DC-AC.
The present invention relates to a series resonant converter that converts a conversion circuit and full-wave rectifies the converted AC output to obtain a DC output.

“Prior Art” Conventionally, in order to reduce loss in a direct current-direct current (DC-DC) converter, a MOS-FET is used in an output circuit of a forward type converter as shown in FIG. In this converter, a DC power supply 1 is connected to a primary side of a main transformer 3 via a main switch 2, and a rectifying MO on a secondary side of the main transformer 3 is synchronized with turning on / off of the main switch 2.
By turning on / off S-FET4 and 5 alternately, MOS-FET
The rectifying action is performed at. MOS-FE with low on-resistance
By using T, the loss is reduced compared to the PN diode.

Secondary voltage V _t and the rectifying element of the main transformer 3 (MOS-FE
The waveforms of the currents i ₂ and i ₃ flowing through T) 4,5 are shown in FIG. When the voltage V _t generated on the secondary side of the main transformer 3 is positive, the MOS-
On the FET 4, and turns off the MOS-FET 5 power supply from the primary side of the main transformer 3 to the secondary side to charge the output capacitor 7 through the output reactor 6, the period the voltage V _t of the negative MOS-
By turning off the FET 4 and turning on the MOS-FET 5, the current flowing in the output reactor 6 can be passed through the MOS-FET 5 to the output capacitor 7.

Since the MOS-FETs 4 and 5 have a body diode as a parasitic element and this diode has a long recovery time, a large recovery current flows when a reverse voltage is applied when a current flows through the body diode. FIG. 6 shows an enlarged view of the time axis when the current is switched in FIG. Since the current flowing through the output reactor 6 is continuous, there are periods T ₁ and T ₂ during which the currents i ₂ and i ₃ flowing through the MOS-FETs 4 and 5 simultaneously flow. this period
Since T ₁ and T ₂ change depending on the load current, the gate signals G ₂ and G ₃ of the MOS-FETs 4 and 5 must be changed according to the changes of the periods T ₁ and T ₂ to the body diodes of the MOS-FETs 4 and 5. There was a problem that the current flows and the recovery current becomes large, and the loss at the time of high frequency increases. Further, since the periods T ₁ and T ₂ change according to the change of the load current, it is very difficult to generate the gate signals G ₂ and G ₃ according to the change.

In addition, as shown in JP-A-60-183977, the transformer 2
There is also one that detects the voltage on the secondary side and controls the opening and closing of the FET gate by this, but this is effective for rectifying a signal that is weak power. However, when using this as a power rectifier, the current flowing in the transformer is affected by the reactance of the transformer and is delayed in time more than the voltage, so the body diode current flows and the power conversion efficiency deteriorates. I can't.

The object of the present invention is to provide an MO that can achieve high efficiency with a simple driving method.
It is to provide a series resonant converter using an S-FET in a rectifier circuit.

[Means for Solving the Problems] According to the present invention, a MOS-FET is used in a rectifier circuit that obtains an AC output of a half-wave series resonance current by a DC-AC conversion circuit and rectifies the AC output. Furthermore, the primary side of the main transformer is connected to the output side of the DA-AC conversion circuit, and both ends of the secondary side of the main transformer are connected to one end of the output capacitor through the first and second MOS-FETs, respectively. The other end of the output capacitor is connected to the midpoint of the secondary side of the main transformer,
First and second current detectors flowing through the first and second MOS-FETs are provided, and the detection outputs of the first and second current detectors are supplied to the resonance current width detection circuit, and the output of the resonance current width detection circuit Thus, the drive control of the first and second MOS-FETs is performed. What is different from the conventional technology is that a low loss MOS-FET rectifier circuit can be realized with a simple drive circuit.

[Embodiment] FIG. 1 is a circuit diagram for explaining an embodiment of the present invention. A series circuit of resonance capacitors 10 and 10 'is connected to both ends of the DC power supply 1, and diodes 11 and 11' for clamping the voltage are connected in parallel with the resonance capacitors 10 and 10 ', respectively. A series circuit of main switches 13 and 13 'is connected to both ends of the DC power supply 1, and a resonance reactor 12 is provided between the connection of the resonance capacitors 10 and 10' and the connection point of the main switches 13 and 13 '. The primary side of the main transformer 14 is connected. Main transformer 14
Both ends of the secondary side of are connected to each other through MOS-FET rectifier elements 15 and 15 ', and an output capacitor 16 is connected between the connection point and the middle point of the secondary side of the main transformer 14,
A load 17 is connected in parallel with 16. The control circuit 18 detects the voltage of the load 17 and changes the operating frequency of the main switches 13 and 13 'to perform constant voltage control. The resonance current width detection circuit 19 detects the resonance current flowing through the rectifier elements 15 and 15 ′ by the detector 20,
The width of the resonance current is obtained by detecting with 20 ', and the MOS-FET rectifying elements 15 and 15' are driven.

The resonance capacitors 10, 10 ', the diodes 11, 11', the resonance reactor 12, and the main switches 13, 13 'are series resonance type DC-AC.
It constitutes the conversion circuit 21.

Since MOS-FET rectifiers 15 and 15 'have body diodes as parasitic elements, they are connected so that current flows from the source to the drain. By alternately turning on and off the main switches 13 and 13 'every half cycle, a resonance current is passed through the main transformer 14. That is, when the main switch 13 is turned on while the resonance capacitor 10 is charged and the resonance capacitor 10 'is discharged, the DC power supply 1 and the resonance capacitor 10 are connected to the main switch 13-resonance reactor 12 -Primary side of main transformer 14-A series resonance current flows through the resonance capacitor 10 ', the resonance capacitor 10 is discharged, and the resonance capacitor 10' is charged. When the resonance current becomes zero, the main switch 13 is automatically turned off, then the main switch 13 'is turned on, the resonance current flows in the same manner, the resonance capacitor 10 is charged, and the resonance capacitor 10' is charged. 10 'is discharged, and the resonance current flowing in the primary side of the main transformer 14 is in the opposite direction.

The voltage induced on the secondary side of the main transformer 14 is full-wave rectified by the MOS-FET rectifying elements 15, 15 '. That is the main transformer 1
When a voltage is induced on the secondary side of 4, a current flows through one of the MOS-FET rectifier elements 15 and 15 'through its body diode according to the polarity of the voltage. At this time, the main transformer 14
FIG. 2 shows the currents I ₄ and I ₅ flowing through the MOS-FET rectifying elements 15 and 15 'connected to the secondary side of the. As shown in FIG. 2, these currents I ₄ and I ₅ have a half-sine wave shape, and the MOS-FET rectifier 1
There are periods T ₃ and T _{4 in} which current does not flow at the same time in 5,15 ′. The resonance currents I ₄ and I ₅ are determined by the voltage of the direct current 1, the voltage of the load 17, the resonance reactor 12, and the resonance capacitors 10 and 10 ′. MOS-FET for diode 11,11 'to clamp the voltage of resonance capacitor 10,10' to the voltage of DC power supply 1
The current flowing through 15,15 'has a half-sine wave shape. Resonance current I
₄ and I ₅ are detected by the detectors 20 and 20 ', the period during which the resonance current is flowing is found by the resonance current width detection circuit 19, and the
By driving 5'with signals A and B as shown in FIG. 2, the MOS-FET can be turned on without passing a current through the body diode of the MOS-FET. That is, the ends of the drive signals A and B may be matched with the ends of the resonance currents I ₄ and I ₅ (when they reach zero).

Detects the currents I ₄ and I ₅ flowing in the MOS-FET rectifiers 15 and 15 ′,
If the operating frequency for controlling the main switches 13, 13 'is controlled by the control circuit 18 so that the currents I ₄ , I ₅ do not turn on at the same time, the resonance currents I ₄ , I ₅ flow simultaneously even if the load current changes. There is no such thing. Therefore, the recovery current does not flow when the MOS-FET turns off, and the problem of increased loss at high frequencies is eliminated, and the rectifiers 4 and 5 are turned on at the same time as in conventional forward converters, and load current is reduced. There is no need to perform complicated control such as controlling the period of simultaneous ON in accordance with the change of.

As is clear from this result, by using a MOS-FET as the rectifying element of the series resonant converter, a simple driving circuit compared to the conventional technology can drive the body diode of the MOS-FET rectifying element without passing a current. A low-loss MOS-FET that can be used and does not increase loss even at high frequencies
A rectifier circuit can be realized. Note MOS-FET15,15 'driving signals A for resonance current I ₄ B respectively, to within a period during which I ₅ is flowing, MOS-FET15,15' drive signal resonance current I ₄ of, I
_{This is because when} the ON width of ₅ or more is reached, the output capacitor 16 serves as a power source and a feedback current flows through the main transformer 14 to the primary side to prevent an increase in loss.

The series resonance type DC-AF conversion circuit 21 for converting direct current into alternating current is not limited to the one shown in FIG. 1, and various types can be used. Further, when supplying the output alternating current of the DC-AC conversion circuit 21 to the rectifier circuit, without using a main transformer,
A full-wave rectification circuit in which four MOS-FET rectification elements are bridge-connected may be used. From the viewpoint of minimizing the loss of the rectifier circuit, it is better to use the main transformer 14.

[Advantages of the Invention] As described above, by using a MOS-FET as a rectifying element of a DC resonant converter, a low loss rectifying circuit can be realized with a simple driving circuit even for high power, and therefore a series resonant converter It is possible to further improve efficiency. Further, the converter of the present invention has less loss in the rectifier circuit than in the case where a fast recovery diode is used as the rectifier element. That is, the voltage of the DC power supply 1 is 250 V, the output voltage V ₀ of the output capacitor 16 is −54 V, and the rectifying element is a MOS.
Fig. 3 shows the loss of each rectifier circuit when using -FET15,15 'and when using a fast recovery diode instead. Since the loss increases when a current is applied to the body diode of the MOS-FET, make sure that the on-voltage of the MOS-FET is lower than the forward voltage drop of the body diode.
The on resistance of the MOS-FETs 15 and 15 'is selected. As is clear from Fig. 3, compared to the fast recovery diode
In MOS-FET, low loss is achieved and output current I ₀ = 10A
At that time, the loss is about 60% when using the MOS-FET and when using the fast recovery diode. MOS-
Since the on resistance of the FET can be reduced by parallel connection, the loss can be further reduced.

By driving the MOS-FETs 115 and 15 'by determining the period during which the resonance current is flowing by the resonance current width detection circuit 19, the MOS-FET can be turned on without passing a current through the body diode.

[Brief description of drawings]

FIG. 1 is a connection diagram showing a configuration example of a series resonance converter of the present invention, FIG. 2 is a waveform diagram of a current flowing through the rectifier circuit of FIG. 1 and a drive signal waveform diagram, and FIG. 3 is a loss characteristic diagram of the rectifier circuit. Fig. 4 is a connection diagram showing a conventional forward converter using a MOS-FET in a rectifier circuit, Fig. 5 is a voltage / current waveform diagram of the MOS-FET rectifier circuit in Fig. 4, and Fig. 6 is time in Fig. 5. It is a figure which shows an axis expansion and a MOS-FET rectifying element drive signal.

Claims (1)

[Claims] 1. A series resonance in which a switching element is controlled to flow a series resonance current, direct current is converted into alternating current by a DC-AC conversion circuit, and the converted alternating current is full-wave rectified by a rectifying element to obtain a direct current output. In the converter, the primary side of the main transformer is connected to the output side of the DC-AC conversion circuit, and both ends of the secondary side of the main transformer are the first and second MOSs.
-Connected to one end of the output capacitor through each of the FETs, the other end of the output capacitor is connected to the midpoint of the secondary side of the main transformer, and the first and the second that flow through the first and second MOS-FETs.
A second current detector is provided, the detection outputs of the first and second current detectors are supplied to the resonance current width detection circuit, and the output of the resonance current width detection circuit causes the resonance current to flow during the above period. A series resonant converter characterized in that the first and second MOS-FETs are drive-controlled.