JPH05328714A - DC-DC converter - Google Patents

Abstract

(57) [Summary] [Object] The present invention stores energy from a DC power supply in a choke coil by turning on and off a main switching element,
In addition, a step-up DC- which discharges this and supplies power to the load
The purpose is to reduce the loss and noise of this type of DC-DC converter such as a DC converter. According to the present invention, a capacitor and a diode are provided in parallel with a main switching element, and a circuit including an auxiliary switching element that discharges the capacitor charge to a load side or a DC power source side before turning on the main switching element is provided. Has been achieved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to lowering the switching loss and switching noise of a converter of this type such as a step-up DC-DC converter.

[0002]

2. Description of the Related Art DC-DC converters such as step-up DC
The DC converter turns on / off the main switching element SW ₁ such as FET as shown in FIG. 5 as shown in FIG.
During the ON period, the DC power supply E causes a current to flow through the choke coil L ₀ to store energy therein. Further, during the off period of the main switching element SW ₁ , the energy accumulated in the on choke coil L ₀ is transferred to the commutation diode D _0.
It is discharged to the output side through a capacitor C for smoothing.
_{It is} smoothed by ₀ and supplied to the load. Since the output voltage of the DC-DC converter is the sum of the voltage V _E of the DC power supply E and the voltage e generated in the choke coil L ₀ , that is, e = L ₀ di / dt, it is widely used as a step-up circuit for the DC power supply. ing.

[0003]

As is well known, in this circuit, as shown in FIGS. 6B and 6C, the main switching element SW ₁ shown in FIG. 6A is turned on and turned off. Switching efficiency as shown in FIG. 6 (d) is generated due to the overlap of the voltage of SW _{1 and} the waveform of the current flowing therethrough, thereby lowering the conversion efficiency.
As well known, in order to prevent this, one method is to shorten the switching time of the main switching element SW ₁ . However, in this method, as the switching time is shortened, a larger surge voltage is generated, which causes a large surge noise, and the switching loss and the switching noise have a so-called trade-off relationship. Therefore, it is difficult to suppress both by this method. Therefore, in the conventional case, the switching time is shortened, and the main switching element SW ₁ has the structure shown in FIG.
Resistor R ₁ indicated by, R _2, a capacitor C _1, C _2, the diode D such as by connecting the surge absorption circuit called snubber circuit _1, also the resistance in parallel to the commutating diode D ₀ R
_A snubber circuit consisting of a series circuit of ₃ and a capacitor C ₃ is connected to reduce switching loss and switching noise. However, this method has a drawback in that even if the surge noise is suppressed, an increase in power loss due to the resistors R ₁ and R ₃ forming the snubber circuit cannot be avoided. Further, in the case of a FET having a parasitic diode and a parasitic capacitance such as an FET widely used as a main switching element, when the main switching element SW ₁ is turned on,
The electric charge accumulated in the parasitic capacitance is released to the circuit of the main switching element SW ₁ , which causes a loss, which also causes a problem of lowering conversion efficiency.

[0004]

An object of the present invention is to provide a low-loss, low-noise DC-DC converter which solves the above problems.

[0005]

In the present invention, a main switching element having a parasitic diode and a parasitic capacitance such as an FET is used as the main switching element, or in the case of a main switching element having neither of them. Connects a diode and a capacitor in parallel. In addition, the load discharge circuit to the output side of the capacitor, which consists of auxiliary switching in parallel with the main switching element, that is, it turns on before the main switching element turns on, and the charging energy of the capacitor charged when the main switching element is off is rapidly To discharge to the output side or DC power supply side to enable zero voltage switching of the main switching element, and also to turn off before turning off the main switching element, divert the current flowing through the main switching element to the capacitor, and A DC-DC converter with low loss and low noise is provided by providing an auxiliary switching element that enables turn-off at low voltage, and without taking a means for reducing loss accompanied by generation of surge voltage such as shortening switching time. It is characterized by that. Next, the present invention will be specifically described with reference to an embodiment circuit.

[0006]

【Example】

1 is a circuit diagram of an embodiment of the present invention in a step-up chopper type DC-DC converter using an FET as a main switching element. In the figure, E is a DC power supply, L
₀ is choke coil, SW ₁ is main switching element, C
_S is its parasitic capacitance, D _S is a parasitic diode, D ₀ is a commutation diode, C ₀ is a smoothing capacitor,
These perform the same function as the conventional circuit shown in FIG.
Reference numerals SW _{2 and} below are provided for the present invention. Among them, SW ₂ is an auxiliary switching element such as MO.
It is an S-transistor and is controlled by a control circuit (not shown).
As shown in (a) and (b), the main switching element SW ₁
Of the main switching element SW ₁ is turned on before turning on and the main switching element SW ₁ is turned off after turning on. T is an energy discharging transformer, N ₁ is its primary coil, N ₂ is a secondary coil, L ₂ is a second choke coil, D
₂ is a reverse current blocking diode, SW ₂ , N ₁ , L ₂ , D
₂ is connected in series to form a parallel circuit with the capacitor C _S, and the second choke coil L ₂ prevents the electric charge of the capacitor C _{S from} being rapidly discharged to the auxiliary switching element SW ₂ as shown in FIG. 2C. The rise of the current flowing through this series circuit is controlled. L ₁ is a first choke coil, which is connected in series with the main switching element SW ₁ and has a capacitor C formed by the auxiliary switching element SW ₂ as shown in FIG.
_It is made so that the flowing current gradually rises before the turn-off of the auxiliary switching element SW ₂ so as to hardly affect the discharge of _S. Next, the operation of this circuit will be described with reference to FIG.

[0007]

[Operation] [Operation from turn-on of auxiliary switching element to turn-on of main switching element] Fig. 2 (a)
When the main switching element SW ₁ and the auxiliary switching element SW ₂ shown in (b) are off, electric power is supplied to the load and at the same time, the capacitor C _{S is connected} to the main switching element SW ₁ via the _first choke coil L ₁ . Charge to the terminal voltage. At time t ₁ in FIG. 2 prior to turning on the main switching element SW ₁ , when the auxiliary switching element SW ₂ is turned on as shown in FIG. 2B, the DC power source E causes the choke coil L ₀ , the first choke coil L ₁ ,
Diode D _2, 1 coil N ₁ of the second choke coil L ₂ transformer T, a series circuit of the auxiliary switching element SW _2, the capacitor C _S, diode D _2, the second choke coil L _2, the transformer T 1 primary coil A circuit for discharging the electric charge of the capacitor C _S , which is composed of N ₁ and the auxiliary switching element SW _2, is formed. However, as described above, the current suppressing action of the first choke coil L ₁ is set larger than that of the second choke coil. Therefore, the rise of the current i _L1 flowing in the first choke coil L ₁ is shown in FIG.
As shown in (d), it is significantly gentler than that of the second choke coil L ₂ . Therefore, in order to simplify the explanation, it is assumed that the commutation diode D ₀ is ideal, and S
Main switching element SW when W ₁ and SW ₂ are off
₁ of the terminal voltage V _S1, therefore if voltage and the output voltage V ₀ which the output end of the choke coil L ₀ are equal, circuits parentheses by the broken line in FIG. 1 is a circuit equivalent to FIG. 3 (a). Therefore, as shown in FIG. 2E, the charge charged in the capacitor C _S is rapidly discharged, and the energy based on this is discharged to the load side by the secondary coil N ₂ of the transformer T. The discharge ends its voltage of the capacitor at time t ₂ in FIG. 2, i.e. the diode D _S becomes zero volts as the main switching element SW ₁ of the terminal voltage V _S1 Figure (f)
Becomes conductive. Therefore, if the main switching element SW ₁ is turned on after the time when the diode D _S is turned on, for example, at the time t ₃ in FIG. 2A, zero volt switching is performed, so that the switching loss is remarkably reduced. You can When the auxiliary switching element SW ₂ is turned on, the choke coil L ₂
As a result, the current gradually rises, so the loss is small. Even if capacitor C _S is parasitic capacitance of the main switching element SW _1, never resulting in losses due to discharge of the main circuit of the switching elements SW ₁ as described above. When the discharge of the capacitor C _S ends at time t ₂ and the diode D _S becomes conductive, the circuit in parentheses in FIG. 1 becomes equivalent to the circuit in FIG. 3 (b), and the circuit of the second choke coil L ₂ becomes The current flowing in the circuit is -V ₀ · (N ₁ /
The slope of N ₂ ) / L ₂ decreases as shown in FIG. 2 (c) and finally becomes zero. Therefore, in this state, the auxiliary switching element S
If W ₂ is turned off, the switch loss will be very small. On the other hand, the main switching element SW at time t ₂
After _one turn-on, the current flowing through the first choke coil L ₁ is made gradually larger by the action of L ₁ as shown in FIG. 2 (d), the choke coil L ₀ first choke coil L _1, all current flowing through, Therefore, as shown in FIG. 2 (g), the current flows to the main switching element SW ₁ and accumulates energy in the choke coil L ₀ .

[Main switching element SW₁Turn off
Operation at time] Main switching element SW₁At time t_bsmell
The main switching element SW₁Flow to
The current was SW as shown in Fig. 2 (d) and Fig. 2 (e).₁When
Parallel capacitor C_SIt flows to and charges this. others
Main switching element SW ₁Voltage and current of Fig. 2 (f)
As in (g), there is almost no overlap between them, so SW
₁The loss at turn-off is significantly less. Since
From the above description, according to the present invention, the switching time can be shortened.
Low loss without using a surge voltage
, Low loss and low noise DC-DC converter
Can be realized. Above, one embodiment of the present invention is explained.
As mentioned, the first and second choke coils L₁, L₂As
Use leakage inductance of wiring and transformer T
You may do it. Further, the above embodiment is a step-up DC-D.
Although it is an application example to a C converter,
Buck-boost converter, and high-frequency transformer for buck-boost
The same effect can be obtained by applying it to a DC-DC converter using
You can play the fruit. Next, as another embodiment, a step-down type
An application example to the DC-DC converter circuit will be described.

[0009]

[Other Embodiments] This DC-DC converter stores energy in L ₀ when the main switching element SW ₁ shown in FIG. 4 is turned on and a current is passed through the choke coil L ₀ to load, and when SW _{1 is} turned off. It is a DC-DC converter adapted to release the energy stored in L ₀ . The output voltage of this circuit is the voltage V _{E of the} DC power supply _E and the choke coil L
_It is used for stepping down the DC power supply because it has a voltage difference e = L ₀ di / dt generated at ₀ , and has the following circuit configuration. That is, the diode D ₂ , the primary coil N _{1 of the} transformer T, and the auxiliary switching element SW ₂ such as MO in parallel with the main switching capacitor SW ₁ such as FET.
A series circuit of S transistors is connected, and a series circuit of a secondary coil N ₂ of a transformer T and a diode D ₃ is connected in parallel to a DC power source E. Then, the auxiliary switching element SW ₂ is turned on before the main switching element SW ₁ is turned on to discharge the charge of the parasitic capacitance to the DC power source E side to enable zero voltage switching, and when the main switching element SW ₁ is turned off. The current of SW ₁ is commutated to the parasitic capacitance C _S to reduce the loss.
In this example, the wiring and the transformer T are used as the _first and second choke coils L ₁ and L ₂ in the embodiment described in FIG.
The leakage inductance of is used.

[0010]

As described above, according to the present invention, it is possible to provide a low-loss and low-noise DC-DC converter, and to be applied to a DC power supply device in a field requiring a high-efficiency and low-noise power supply, for example, a power supply device for a communication device. The effect is large when used.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a circuit according to an embodiment of the present invention.

FIG. 2 is a waveform example diagram for explaining the operation of the circuit according to the embodiment of the present invention.

FIG. 3 is a partial equivalent circuit diagram of a circuit according to an embodiment of the present invention.

FIG. 4 is a circuit diagram of another embodiment of the present invention.

FIG. 5 is an explanatory diagram of a conventional circuit.

FIG. 6 is a waveform example diagram for explaining the operation of the conventional circuit.

[Explanation of symbols]

E DC power supply L ₀ Choke coil SW ₁ Main switching element C _S Capacitor or parasitic capacitance of main switching element D _S diode or parasitic diode of main switching element D ₀ Commutation diode C ₀ Smoothing capacitor L ₁ 1st choke coil L ₂ second choke coil D ₂ reverse-blocking diode D ₃ reverse blocking diode T trans N ₁ 1 primary coil N ₂ 2 coil

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yasuyuki Koizumi 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation (72) Inventor Shizuo Ozora 1-6-1, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] 1. A DC for storing energy from a DC power supply in a choke coil by turning on / off a main switching element and discharging the energy to supply power to a load.
-In the DC converter, a switching element having a parasitic capacitance and a parasitic diode or a switching element in which a capacitor and a diode instead of these are connected is used as the main switching element, and a first switching element is connected in series to the main switching element.
A choke coil is provided, a reverse current blocking diode is provided in parallel with the main switching element, a choke coil having a smaller current suppressing action than the first choke coil, a primary coil of a transformer, and a series circuit of an auxiliary switching element are provided. The switching element has a function of turning before turning on of the main switching element and turning off after turning on of the main switching element, and the secondary coil of the transformer is connected in parallel to the output side or the power supply side via a reverse current blocking diode. A DC-DC converter comprising a charge discharging circuit for the capacitor connected to the.