JPH06311737A - Dc/dc converter - Google Patents

Abstract

PURPOSE:To reduce a power loss at turn-on or turn-off, by using a resonance control circuit for interrupting current resonance of a resonance circuit while DC power is turned on and off in a cycle from continuity to breake through a relay circuit. CONSTITUTION:When energy stored in a resonance inductance element 3 is discharged through current resonance and a diode 8 is reversely biased, the resonance is interrupted for a time and the resonance energy is stored in the resonance capacitor 7. During the breaking time of the resonance, a DC/DC converter functions similarly to an ordinary on-on converter at an on-state so as to reduce a power loss. Then, a sub-transistor 9 is turned on to discharge the energy stored in the resonance capacitor 7. Then, a current flowing in a main transistor 4 is reduced, and at the same time, a power loss at the turn- off is also reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC / DC converter using current resonance (hereinafter referred to as a DC-DC converter).

[0002]

2. Description of the Related Art In DC-DC converters, the frequency is being increased to reduce the size and weight, but the power loss at turn-off increases in proportion to the frequency. Therefore, DC-DC using current resonance as shown in FIG.
Converters have been proposed. This DC-DC converter is shown in FIG. 6 when the main transistor 4 is turned off.
Since there is no overlap between the current waveform and the voltage waveform as shown in (a), it is possible to almost eliminate the power loss at turn-off.

[0003]

However, the current I _D1 flowing through the main transistor 4 is 5 to 6 times the output current I _O , resulting in a large power loss. Since the ON time T _ON of the main transistor 4 is fixed to a fixed time,
To adjust the output voltage constant according to the input voltage,
Frequency control is required to control the off-time T _OFF with respect to the on-time T _ON of the main transistor 4, which complicates the circuit configuration. Furthermore, when the input voltage is high and the load is low, there is a low frequency region, and it becomes substantially impossible to increase the frequency. Further, the voltage V _C across the resonance capacitor is 2 times the battery voltage V _B as shown in FIG. 6B.
Since the voltage is doubled, there is a problem that a high withstand voltage resonance capacitor or diode is required. The present invention has been made to solve the above problems, and an object of the present invention is to provide a DC-DC converter capable of reducing power loss at the time of turning on or turning off.

[0004]

As a specific configuration for achieving the above object, an intermittent circuit for intermittently converting a DC power supply voltage into an AC voltage and a rectifying diode for half-wave rectifying the AC voltage, In a DC-DC converter including a smoothing circuit that smoothes the half-wave rectified voltage, a resonance circuit including a resonance inductance serially connected to the rectifying diode and a resonance capacitor, and the intermittent circuit. A DC-DC converter is provided, which is provided with a resonance control circuit for interrupting the current resonance operation of the resonance circuit during one cycle from conduction to interruption of the DC power supply.

[0005]

According to the above DC-DC converter, the resonance operation by the resonance inductance and the resonance capacitor is started by the conduction of the DC power supply by the intermittent circuit and is ended by the interruption. Then, the resonance operation is interrupted by the resonance control circuit during one cycle of the resonance operation, and the resonance operation is limited to a predetermined period at the beginning and end of the conduction period of the DC power supply. Therefore, it is possible to suppress the turn-off loss of the intermittent circuit and the current peak value during the ON period to reduce the power loss, and it becomes possible to perform control at a constant frequency, thereby increasing the frequency at which the intermittent circuit is turned on and off. And so on.

[0006]

(First Embodiment) A first embodiment of the present invention will be described with reference to FIGS. In the circuit diagram of FIG. 1, 1
Is a DC power source such as a battery, 2 is an exciting coil of a transformer,
Reference numeral 3 is a resonance inductance, which can be replaced by a leakage inductance attached to the exciting coil 2. Reference numeral 4 is a main transistor for turning on / off the connection with the DC power supply 1 and supplying it as an AC voltage to the secondary side. 5
Is a rectifying diode for half-wave rectifying the AC voltage supplied to the secondary side by turning on / off the main transistor 4.

A resonance control circuit 6 is composed of a resonance capacitor 7, a diode 8 and a sub-transistor 9. The resonance capacitor 7 is connected in series with the rectifying diode 5 together with the diode 8 to form a resonance circuit with the resonance inductance 3. The sub-transistor 9 is provided in a circuit that bypasses the diode 8.

A smoothing circuit 10 includes diodes 11,
It is composed of a smoothing coil 12 and a smoothing capacitor 13, and smoothes the AC voltage half-wave rectified by the rectifying diode 5 and outputs it to the load 14.

The operation of the DC-DC converter having the above structure will be described with reference to the operation waveform diagram of FIG. V _DS1 , V _C
And V _DS2 are voltage waveform diagrams, and I _D1 , I _D2, and I _D3 are current waveform diagrams, respectively, showing the voltage value between the circuits shown in FIG. 1 and the current value flowing through the circuits. Further, V _GS1 indicates a drive signal for the main transistor 4, and V _GS2 indicates a drive signal for the sub-transistor 9. The periods t _{0 to} t ₅ are the resonance start period t _{0 to} t ₂ , the resonance interruption period t _{2 to} t _3, and the resonance end period t.
_It is divided into _{3 to} t ₅ .

[0010] In the resonance starting period t ₀ ~t _2, the main transistor 4 is turned on at t _0, the current I _D1 flowing through the main transistor 4 at t ₀ ~t ₁ period <output current I _O becomes, t ₁ ~
During the period t ₂ , a current resonance operation (hereinafter referred to as resonance operation) occurs due to the resonance inductance 3 and the resonance capacitor 7. The current I _D1 flowing through the main transistor 4 is from t ₀ to
In the t ₁ period, I _D1 = V _B · t / L _l (V _B : DC power supply voltage,
L _l : resonance inductance), which increases with the passage of time. Assuming that the capacitance of the resonance capacitor 7 is C _C , t _{1 to} t ₂ = 2π√ (L _l C _C ) / 2, and the resonance current ID ₂ is the resonance inductance 3 → rectification diode 5 →
The current flows from the diode 8 to the resonance capacitor 7, and the energy stored in the resonance inductance 3 is released by the resonance operation. Once resonant operation the diode 8 is reverse biased is interrupted, the resonant capacitor 7 (2V _B) ^2/2
The resonance energy of C _C (joule) is accumulated.

No resonance operation is present during the resonance interruption period of t _{2 to} t ₃ , and the same operation as the ON period of a normal on-on converter is performed. Next, the resonance end period t _{3 to} t ₅ is started when the sub-transistor 9 is turned on at t ₃ , and the energy stored in the resonance capacitor 7 is discharged,
The current I _D1 flowing through the main transistor 4 is reduced to reduce power loss when the main transistor 4 is turned off. During the period from t _{3 to} t ₄ , the resonance current I _D3 flows through the resonance capacitor 7 → the sub-transistor 9 → the rectifying diode 5 → the resonance inductance 3 → the DC power supply 1 → the main transistor 4, and t _{3 to} t ₄ = 2π√. (L _l C _C ) / 4. t
₄ period ~t _5, the current I _D1 flowing through the main transistor 4 t ₄ is started when the turn-off becomes ≒ 0,
The output current I _O flows from the resonance capacitor 7 to the subtransistor 9. The voltage V _C applied to the load 14 is V _C = −I
_O・ t / C _C decreases with time.

As described above, in the first embodiment, t _{2 to} t ₃
The resonance operation is limited to the beginning and end of the ON period of the main transistor 4 by providing the resonance interruption period of
Since the current flowing through the main transistor 4 decreases immediately before turn-off, the loss at the time of turn-off can be reduced, and the peak value of the current I _D1 flowing through the main transistor 4 can be suppressed to reduce the power loss. Although the periods t _{1 to} t ₂ and the periods t _{3 to} t ₄ are constant, the on period t _{0 to} t 4 of the main transistor ₄ is variable and control at a constant frequency is possible, so that high frequency is also possible. .

(Second Embodiment) The configuration of the second embodiment of the present invention is shown in the circuit diagram of FIG. The resonance capacitor 27 is provided in series with the resonance control circuit 6, and the capacitance (C _B ) of the energy storage capacitor 28 provided in the resonance control circuit 6 is set to the capacitance of the resonance capacitor 27. It is different from the configuration (FIG. 1) of the first embodiment in that it is larger than (C _C ). Therefore, the same components will be assigned the same reference numerals as those in FIG. 1 and detailed description thereof will be omitted.

The operation of the DC-DC converter having the above structure will be described with reference to the operation waveform chart of FIG. Similar to the first embodiment, V _DS1 , V _C1 , V _C2 and V _DS2 are voltage waveform diagrams,
I _C1 , I _C2 , I _D1 and I _D2 are current waveform diagrams showing the voltage value between the circuits and the current value flowing through the circuits shown in FIG. 3, respectively. Further, V _GS1 indicates a drive signal for the main transistor 4, and V _GS2 indicates a drive signal for the sub-transistor 9. Period t ₀ ~t _5, the resonance starting period t ₀ ~t _3, is divided into resonance interruption period t ₃ ~t ₄ and the resonance end period t ₄ ~t _5.

The resonant starting period t main transistor 4 is turned on at ₀ ~t ₃ At t _0, t ₀ ~t ₁ current I _D1 flowing through the main transistor 4 during the period <output current I _O, and the current flowing through the main transistor 4 I _D1 is I _D1 = V _B · t /
L _l (V _B : DC power supply voltage, L _l : resonance inductance), which increases with time t and reaches a peak value at t ₂ . In the period from t _{1 to} t ₂ , the resonance operation by the resonance inductance 3 and the resonance capacitor 27 continues until V _C1 = V _C2 .

Since the capacitance C _B of the energy storage capacitor 28 is large, the capacitor voltage V _C2 is fixed at a substantially constant value. Therefore, in the period from t ₂ to t ₃ , the current I _D1 flowing through the main transistor 4 is I _D1 = (V _C2 −V _B ) ·
The energy becomes t / L _{1 and} decreases with the lapse of time, and the energy stored in the resonance inductance 3 is released and shunted from the diode 8 to the energy storage capacitor 28 and stored. The emission of the energy causes the diode 8 to be reverse-biased and the resonance to end.

In the resonance interruption period t _{3 to} t ₄ , there is no resonance operation, and the same operation as the ON period of a normal ON-ON converter is performed. Then, the resonance end period t ₄ ~t ₅ is started when the sub-transistor 9 is turned on. When the sub-transistor 9 is turned on, the energy storage capacitor 28 → the sub-transistor 9 → the resonance capacitance inductance 3
And resonates in the path of, and releases the energy stored in the energy storage capacitor 28. At this time, the current I _D3 flowing through the sub-transistor 9 is I _D3 = (V _C2 −V _B ) ·
Since it increases with the lapse of time due to t / L ₁ , on the contrary, the current I _D1 flowing through the main transistor 4 gradually decreases and turns off at t ₅ .

As described above, in the second embodiment, the resonance capacitor 27 and the energy storage capacitor 28 are separated, so that V _C1 ≉V _B can be fixed and the resonance voltage can be clamped at a constant level. By adopting the withstand voltage resonance capacitor 27, the energy storage capacitor 28, and the low withstand voltage diode 11, it is possible to reduce the cost and improve the characteristics, and to improve the efficiency of the DC-DC converter.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a first embodiment.

FIG. 2 is an operation waveform diagram of the first embodiment.

FIG. 3 is a circuit diagram of a second embodiment.

FIG. 4 is an operation waveform diagram of the second embodiment.

FIG. 5 is a circuit diagram of a conventional example.

FIG. 6 is an operation waveform diagram of a conventional example.

[Explanation of symbols]

1 ... DC power supply, 3 ... Resonance inductance,
4 ... main transistor, 5 ... rectifier diode,
6 ... Resonance control circuit, 7, 27 ... Resonance capacitor 9 ... Sub-transistor, 10 ... Converter circuit, 1
4 ... load

Claims (1)

[Claims] 1. A direct current circuit comprising: an intermittent circuit for intermittently converting a DC power supply voltage into an AC voltage; a rectifying diode for rectifying the AC voltage in a half-wave; and a smoothing circuit for smoothing the half-wave rectified voltage. In a DC converter, a resonance circuit including a resonance inductance connected in series to the rectifying diode and a resonance capacitor, and a current resonance of the resonance circuit during one cycle from conduction to interruption of the DC power source by the interrupt circuit. A DC / DC converter comprising a resonance control circuit for interrupting operation.