JPH05344720A - Resonant dc-dc converter - Google Patents

Abstract

PURPOSE:To enlarge the control range of a prallel drive system resonant DC-DC converter to maintain stable activity against rising of input voltage or light load. CONSTITUTION:A series circuit consisting of a primary winding of a transformer 2, resonant inductance 3 and field effect transistor 5 is connected between terminals of a DC power supply 1. A resonance capacitor 7 is connected between of the field effect transistor 5. A series circuit consisting of a second resonant inductance 4 and a field effect transistor 6 is connected to the end of the primary of the transformer 2. A second resonance capacitor 8 is connected between main terminals of a field effect transistor 6. A third resonance capacitor 14 is connected to each drain of the field effect transistors 5 and 6.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resonance type DC-DC converter, and more particularly to a parallel drive type resonance DC-DC converter.

2. Description of the Related Art A resonance type DC-DC converter is suitable for high frequency because of its small switching loss and low noise, and it has been attracting attention as a circuit system effective for reducing the size and weight of a power supply. A method of controlling the switching frequency is generally used for voltage adjustment of this resonant converter, but in this method, it is necessary to design an output filter for the lowest frequency in the change range of the switching frequency. The drawback remains that it limits weight reduction.
Therefore, a circuit method capable of adjusting the output voltage at a fixed frequency is one of the problems of the resonance type DC-DC converter. As one method of this, for example, on September 8, 1989, the Institute of Electronics, Information and Communication Engineers Technical Research Report [Power Technology for Electronic Communications]
Parallel drive type voltage resonance type D announced at PE89-26
There is a C-DC converter. This parallel drive type voltage resonance type DC-DC converter will be explained. In FIG. 3, reference numeral 1 is a DC power source, and between its terminals, the primary winding 21 of the transformer 2, the resonance inductance 3 and the first winding 21. The field effect transistor 5, which is a switching element, is connected in series. At the end of the primary winding 21 of the transformer 2, a series circuit of a second resonance inductance 4 and a field effect transistor 6 which is a second switching element is connected in parallel. A resonance capacitor 7 is connected in parallel between the drain and the source of the field effect transistor 5 which is the first switching element, and a second resonance capacitor is similarly connected between the drain and the source of the field effect transistor 6 which is the second switching element. 8 are connected in parallel. The secondary winding 22 of the transformer 2 includes a rectifying diode 9 and a smoothing capacitor 10
Are connected in series. Both ends of the smoothing capacitor 10 are connected to the output terminals 31 and 32. The voltages at the output terminals 31 and 32 are connected to a comparison / error amplification circuit 11 that amplifies the error signal by comparing it with a reference voltage. The output signal of the comparison / error amplification circuit 11 delays the signal of the oscillation circuit 13 to control the phase difference between the field effect transistor 5 and the field effect transistor 6, and drives the field effect transistor 6.
It is connected to the. The field effect transistor 5 and the field effect transistor 6 operate at a fixed frequency and a fixed pulse width by the oscillation circuit 13, and the comparison / error amplification circuit 11 that amplifies the error signal between the output voltage and the reference voltage has the field effect transistor 5. And the phase difference between the field effect transistor 6 and the output voltage is stabilized. When the phase of the field effect transistor 5 which is the first switching element and the field effect transistor 6 which is the second switching element match, the maximum output is obtained, and on the contrary, the output is reduced as the phases are shifted.

However, such a conventional control method for a parallel drive type voltage resonance type DC-DC converter operating at a fixed frequency controls the phase difference between two switching elements. Since the power is supplied to the secondary side of the transformer when one of the two switching elements is off, the operating range is the range where the two switching elements are off. If it deviates from this control range, the transmitted power becomes almost constant and control becomes impossible. Therefore, there is a problem that when the input voltage rises or the load becomes lighter, the output voltage rises outside the control range. The present invention is a parallel drive type voltage resonance type DC-D.
An object is to expand the control range of the C converter and maintain stable operation even when the input voltage rises and the load is light.

In order to solve this problem, according to the present invention, by adding a third resonance capacitor between two resonance capacitors of a parallel drive type voltage resonance type DC-DC converter, two switching circuits are provided. By equivalently changing the resonance capacitance according to the phase difference between the elements, the output voltage can be stably controlled without significantly shifting the phases of the two switching elements.

FIG. 1 shows an embodiment of the present invention, which will be described below with reference to FIG. In the figure, 1 is a DC power supply, and between its terminals, the primary winding 21 of the transformer 2,
The resonance inductance 3 and the field effect transistor 5 as the first switching element are connected in series, and the series circuit of the resonance inductance 4 and the field effect transistor 6 as the second switching element is connected to the end of the primary winding 21 of the transformer 2. Are connected in parallel. A resonance capacitor 7 is connected in parallel between the drain and source of the field effect transistor 5,
Similarly, the second resonance capacitor 8 is connected in parallel between the drain and source of the field effect transistor 6. Further, a third resonance capacitor 14 is connected between the drain of the field effect transistor 5 and the drain of the field effect transistor 6. A rectifier diode 9 and a smoothing capacitor 10 are connected in series to the secondary winding 22 of the transformer 2. An error amplification circuit 11 that amplifies an error signal between the voltage of the smoothing capacitor 10 and the reference voltage, and an oscillator 13 based on the signal of the error amplification circuit 11.
A phase control circuit 12 for delaying the signal of FIG. 1 and controlling the phase difference between the field effect transistor 5 and the field effect transistor 6 to drive the field effect transistor 6 is connected between the oscillator 13 and the gate of the field effect transistor 6. .. The field effect transistor 5 and the field effect transistor 6 are the oscillator 13
Operates with a fixed frequency and a fixed pulse width. An error amplification circuit 11 that amplifies an error signal between the output voltage and the reference voltage determines the phase difference between the field effect transistor 5 and the field effect transistor 6 and stabilizes the output voltage. The maximum output is obtained when the phases of the field effect transistor 5 and the field effect transistor 6 match, and conversely, the output decreases as the phases are shifted. The operation will be described in more detail. FIG. 2 shows a primary side equivalent circuit for each operation mode when the phase difference between the field effect transistors 5 and 6 which are two switching elements of the resonance type DC-DC converter of the present invention is not zero. The operation when the phase difference between the two field effect transistors 5 and 6 is zero is a normal resonance type converter having a single switching element, and therefore the description thereof is omitted. Mode 1 is a primary side equivalent circuit when the field effect transistors 5 and 6 are both turned on. Mode 2 is a primary side equivalent circuit when the field effect transistor 5 is off and the field effect transistor 6 is on. Here, the third resonant capacitor 14 is
And the resonance frequency of the first resonance inductance 3 and the first resonance capacitor 7 becomes low. Mode 3 is a field effect transistor 5,
6 is an equivalent circuit of the primary side when both 6 are turned off. At this time, the third resonance capacitor 14 has a higher voltage at the contact point with the first resonance capacitor 7. Mode 4 is
In the equivalent circuit of the primary side when the field effect transistors 5 and 6 are both turned off, the voltage of the third resonance capacitor 14 is in mode 3
And the opposite polarity. In modes 4 and 5, the first
By changing the voltage difference between the second resonance capacitor and the second resonance capacitor, the third resonance capacitor 14 is involved in the resonance phenomenon. Mode 5 is a primary side equivalent circuit when the field effect transistor 5 is on and the field effect transistor 6 is off. At this time, the third resonance capacitor 14 is connected in parallel with the second resonance capacitor 8, and the resonance frequency of the resonance circuit of the second resonance inductance 4 and the second resonance capacitor 8 becomes low. After this mode 1
Then, the operation from mode 1 to mode 5 is repeated. In all of these modes, in modes 4 and 5, the first resonant capacitor 7 and the second resonant capacitor 8
The third resonance capacitor 14 is involved in the resonance phenomenon due to the change in the voltage difference between the third resonance capacitor 14 and the third resonance capacitor 14. Mode 2 to Mode 5
In, the potential difference is generated between the first resonance capacitor 7 and the second resonance capacitor 8 due to the phase difference between the two field effect transistors 5 and 6, and the electric charge is stored in the third resonance capacitor 14. The larger the phase difference, the more time the charge is stored in the third resonance capacitor 14. That is,
As the phase difference increases, the time taken for the third resonance capacitor 14 to participate in the resonance phenomenon increases, and it is considered that the resonance capacitance is equivalently increased as the phase difference increases when the resonance circuit is viewed comprehensively. When the resonance capacitance is large, the resonance frequency is low and the off-time of the two field effect transistors 5 and 6 is long. Therefore, when operating at a fixed frequency, the amount of energy stored in the primary winding 21 of the transformer 2 decreases and the output power also decreases. The situation when the phase difference is large may be when the load is light or when the input voltage is high. In such a case, the resonance capacitance is equivalently increased by the third resonance capacitor 14 to reduce the output power.
The output voltage can be controlled without increasing the phase difference between the two field effect transistors 5 and 6. By this,
It is possible to widen the controllable range of the output voltage and prevent problems caused by the phase difference between the two switching elements, for example, generation of power loss due to circulating current flowing between the two switching elements and excessive resonance voltage.

As described above, according to the present invention, in a fixed frequency parallel drive type resonance DC-DC converter for stabilizing the output voltage by controlling the phase difference between two switching elements. By adding the third resonance capacitor, the controllable range of the output voltage can be widened and the problems caused by the phase difference of the switching elements can be improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of a resonance type DC-DC converter according to the present invention.

FIG. 2 is a primary-side equivalent circuit for each operation mode of the circuit shown in FIG.

FIG. 3 is a circuit diagram of a conventional parallel drive type resonant DC-DC converter.

[Explanation of symbols]

1 ... DC power supply 2 ... Transformer 3, 4 ... Resonance inductance 5, 6 ... Field effect transistor 7, 8 ... Resonance capacitor 9 ... Rectifier diode 10 ... Capacitor 11 ... Comparison / error amplification circuit 12 ... Phase control circuit 13 ... Oscillation circuit 14 ... Resonant capacitor 31, 32 ... Output terminal

Claims (1)

[Claims] 1. A resonance type DC-DC in which a pair of resonance switches composed of an inductance, a capacitor and a switching element are connected in parallel, the pair of switching elements are driven at the same frequency, and output power is controlled by the phase difference between them.
A resonant DC-DC converter comprising a third resonant capacitor connected to the ends of the pair of capacitors.