JP3139518B2 - DC-DC converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention is, REACT Le to the DC power supply
A DC-DC converter (DC-DC converter) of a type in which a switching element is connected via a
Converter).

[0002]

2. Description of the Related Art A DC-DC converter of a type in which a switching element is connected to a DC power supply via a reactor and an output rectifying / smoothing circuit is connected in parallel with the switching element is generally called a step-up converter and used in various power supply circuits. It is used.

[0003]

When a current flows while a voltage is applied to the switching element when the switching element is turned off and on, power loss occurs and the efficiency of the converter is reduced .

Accordingly, an object of the present invention is to provide a DC-DC converter capable of reducing switching loss.

[0005]

In order to achieve the above object, the present invention provides a first and second power supply terminals for supplying a DC voltage and an intermediate potential between the first and second power supply terminals. A DC power supply having a third power supply terminal having a potential;
A first reactor connected to a power supply terminal of
A first switching element connected between the first power supply terminal and the second power supply terminal; a diode connected in parallel in the reverse direction to the first switching element; a first switching element connected to the first power supply terminal; A series circuit of a second reactor and a second switching element connected between a connection point with the first switching element and the third power supply terminal;
A capacitor connected in parallel to the switching element of
An output rectifying / smoothing circuit connected in parallel to the first switching element; and a first and a second control signal for controlling on / off of the first and second switching elements. The second switching element is provided for a period from a point slightly before the end point of the off-period of the first switching element to a point slightly after the end point of the off-period of the first switching element. The second control signal is transmitted so as to control ON of the first switching element, and the first and second control signals are transmitted so that the start time of the ON period of the first switching element substantially coincides with the discharge end time of the charge of the capacitor. DC timing of the control signal and a switch control circuit that is configured for - Ru der those related to DC converter.

[0006]

The second switching element and the second reactor according to the present invention are used for discharging the electric charge of the capacitor. When the second switching element is turned on during the off period of the first switching element, the charge of the capacitor is discharged through the second reactor due to the resonance phenomenon between the capacitor and the second reactor, and the voltage of the capacitor, that is, the first voltage Of the switching element becomes substantially zero. When you turn the first switching device at this time, zero voltage switching is achieved, the switching losses are essentially zero, DC - efficiency of the DC converter may turn high.

[0007]

[The first embodiment] Next, the onset Ming with reference to FIGS. 1 to 4
Explaining the DC-DC converter of the real施例. In FIG. 1, a DC power supply 1 is a first DC power supply for supplying V / 2 volts.
And a series circuit of second power supplies 2 and 3;
And third power supply terminals 4, 5, and 6. This power supply 1
Can be configured, for example, by connecting a series circuit of two power supply capacitors to a power supply composed of a rectifier circuit or a battery. When two power supply capacitors are used, they function as the first and second power supplies 2 and 3.
In the power supply 1, the first power supply terminal 4 has the highest potential, and the second power supply terminal 5 has the lowest potential (ground potential).
And the third power supply terminal 6 has an intermediate potential between the first and second power supply terminals 4 and 5.

[0008] A first power supply terminal is provided between first and second power supply terminals 4 and 5.
Is connected to the series circuit of the reactor L1 and the first switching element Q1. That is, the first reactor L1
Is connected to the first power supply terminal 4, and a first switching element Q1 composed of a transistor is connected between the first reactor L1 and the second power supply terminal 5.

A diode D1 and a resonance capacitor C1 are connected in parallel with the first switching element Q1.

The output rectifying / smoothing circuit 7 comprises a rectifying diode 8 and a smoothing capacitor 9, and is connected in parallel with the first switching element Q1. That is, the smoothing capacitor 9 is connected via the diode 8 between the connection point 10 between the first reactor L1 and the first switching element Q1 and the second power supply terminal 5. Note that a pair of output terminals 11 and 12 for connecting a load (not shown) are connected to one end and the other end of the smoothing capacitor 9.

Connection point 10 and third power supply terminal (intermediate terminal)
The second reactor L2 is connected between the second reactor L2 and a second switching element Q2 composed of a transistor.

The control circuit 13 is connected to control terminals (bases) of the first and second switching elements Q1 and Q2, and supplies control signals Vb1 and Vb2 shown in FIGS. 2A and 2B.
The output terminal 11 is connected to the control circuit 13 in order to control the DC output voltage between the output terminals 11 and 12 to a predetermined value.

FIG. 3 shows an example of a circuit for forming the ON / OFF control signals Vb1 and Vb2 for the first and second switching elements Q1 and Q2 shown in FIGS. 2A and 2B. FIG.
2, a voltage detection circuit 20 composed of voltage dividing resistors R1 and R2 is connected between a pair of output terminals 11 and 12. The voltage dividing points of the resistors R1 and R2 are connected to one input terminal of the error amplifier 21. The other input terminal of the error amplifier 21 is connected to a reference voltage source 22 composed of, for example, a Zener diode. The output terminal of the error amplifier 21 is connected to one input terminal of a voltage comparator (comparator) 23. The other input terminal of the comparator 23 is connected to a triangular wave (or sawtooth wave) generating circuit 24.
The triangular wave generating circuit 24 generates the triangular wave Vt of FIG. 4B in response to the clock pulse of FIG. The comparator 23 compares the triangular wave Vt with the error signal Ve obtained from the error amplifier 21 and
A comparison output pulse of the square wave of (C) is generated.

The first control signal forming circuit 26 has a structure shown in FIG.
(C) The trailing edge time t4 of the comparison output pulse from the time t2 after a predetermined delay time Td from the leading edge time t1 of the comparison output pulse.
A first control pulse (first control signal Vb1) having a time width up to and including the first control pulse is formed as shown in FIG.
To the switching element Q1. Note that instead of synchronizing the end point of the first control pulse with the trailing edge of the comparison output pulse, the end point of the first control pulse may be synchronized with the clock pulse in FIG. 4A or the apex or start point of the triangular wave in FIGS. it can. Second
The control signal forming circuit 27 of FIG. 4 responds to the leading edge time t1 of the comparison output pulse of FIG. 4C by using the second control pulse (second control signal Vb2) having a time width Ts slightly longer than Td.
Is formed as shown in FIG. 4 (E) and sent to the second switching element Q2. Trailing edge time t of the second control pulse
3 is between the leading edge time t1 and the trailing edge time t4 of the first control pulse, and is the time when the current I2 of the second reactor L2 becomes substantially zero.

Next, referring to the waveforms of FIG.
The operation of the DC converter will be described. When the first switching element Q1 is turned off at the time point t0 in FIG. 2, the current I1 of FIG. 2C flowing to the first switching element Q1 through the first reactor L1 is transferred to the resonance capacitor C1. The charging current Ic flows through the capacitor C1 as shown in FIG. 2 (E), and the voltage Vc rises linearly from zero volt with a slope as shown in FIG. 2 (F). Therefore, zero volt switching at the time of turning off the first switching element Q1 is achieved, and the switching loss at this time is extremely small. When the voltage Vc of the capacitor C1 becomes higher than the voltage of the output smoothing capacitor 9 at the time point ta, the diode 8 is forward-biased and conducts, and a current Id flows therethrough as shown in FIG. When the diode 8 is turned on, the voltage of the capacitor C1 is clamped at a substantially constant value.

Thereafter, at time t1, as shown in FIG. 2B, the second control signal Vb2 changes to a high level, and when the second switching element Q2 is turned on, the first power supply 2 and the first power supply 2 are turned on.
Reactor L1, second switching element Q2 and second
A current I2 of the second reactor L2 rises linearly with a slope as shown in FIG. 2 (G), and conversely, the current I2 of the diode 8 rises.
d decreases as shown in FIG. 2D and becomes zero at time tb. When the diode 8 is cut off at tb,
The clamp by the output voltage of the capacitor C1 is released,
A resonance circuit including the capacitor C1, the second switching element Q2, the second reactor L2, and the second power supply 3 is formed, and the discharge current of the capacitor C1 flows in a sine wave form as shown in FIG. A current obtained by adding the discharge current of the capacitor C1 flows to the second reactor L2 as shown in FIG. Here, the inductance of reactor L1 is set to be larger than the inductance of reactor L2. The voltage Vc of the capacitor C1 and the first switching element Q1 decreases with a cosine waveform shown in FIG. 2 (F) and becomes zero at time t2. Therefore, at time t2, the first control signal Vb1 is changed to a high level as shown in FIG. 2A, and the first switching element Q1 is turned on. As a result, zero volt switching of the first switching element Q1 is achieved, and this loss is reduced. Note that the second switching element Q2 and the second reactor L
In the conventional circuit having no 2 provided, the discharge current of the capacitor C1 flows through the first switching element Q1, and switching loss occurs.

After the time point t2, the second switching element Q
2 is maintained, the current I2 flowing therethrough becomes zero at time t3 as shown in FIG. 2 (G). Then, at time t3, the control signal Vb2 of the second switching element Q2 is returned to a low level. Thereby, zero volt switching of the second switching element Q2 can also be achieved. Therefore, the increase in loss due to the addition of the second switching element Q2 is not Na hardly generated.

[0018]

[Modifications] The present invention is not limited to the above-described embodiment, and for example, the following modifications are possible. (1) The control circuit 13 is not limited to FIG. 3 and can be variously modified. (2) The diode D1 connected in antiparallel to the first switching element Q1 can be built in the switching element Q1. For example, the first switching element Q1 is an insulated gate field effect transistor (FET), in which a diode D1 is incorporated.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a DC-DC converter according to a first embodiment.

FIG. 2 is a waveform diagram showing a state of each unit in FIG.

FIG. 3 is a block diagram illustrating a control circuit of FIG. 1;

FIG. 4 is a waveform chart showing a state of each unit in FIG. 3;

[Explanation of symbols]

 Reference Signs List 1 power supply 4, 5, 6 first, second and third power supply terminals 7 output rectifying and smoothing circuit L1, L2 first and second reactors Q1, Q2 first and second switching elements C1 resonance capacitor

Claims (1)

(57) [Claims] 1. A first and a second power supply for supplying a DC voltage.
A DC power supply having a power supply terminal and a third power supply terminal having a potential intermediate between the potentials of the first and second power supply terminals; a first reactor connected to the first power supply terminal; A first switching element connected between the first reactor and the second power supply terminal; a diode connected in reverse parallel to the first switching element; a diode connected to the first reactor; A second switching element connected between the connection point with the first switching element and the third power supply terminal;
A series circuit of a reactor and a second switching element; a capacitor connected in parallel to the first switching element; an output rectification smoothing circuit connected in parallel to the first switching element; Forming a first and a second control signal for controlling on / off of the first and second switching elements, wherein the first and second switching elements generate a first and second control signal, and a time point slightly before an end time of an off period of the first switching element; And transmitting the second control signal so as to control the second switching element to be on in a period from a time point after the end time of the off period of the first switching element to a time point slightly after the end time of the first switching element; The timing of the first and second control signals is set so that the start time of the ON period of the switching element substantially coincides with the end time of the discharge of the capacitor. DC and a pitch control circuit - DC converter.