JP3063812B2 - DC-DC converter - Google Patents

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 of the type in which a switching element is connected to a DC power supply via a reactor and the switching element is turned on / off.
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. in use.

[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, and a first capacitor connected in parallel to the first switching element via a first diode. And the first reactor and the first reactor
A second capacitor connected between a connection point with the third switching element and the third power supply terminal; and a second capacitor having one end connected to a connection point between the first switching element and the second capacitor. Reactor, a second switching element connected between the other end of the second reactor and the second power supply terminal, and a second diode connected to the other end of the second reactor and the first diode. A second diode connected between the first capacitor and a terminal connected to the first capacitor; a third diode connected in parallel to the first switching element in a reverse direction; Forming first and second control signals for on / off control of the first and second switching elements, at least a time point slightly before the end time of the off period of the first switching elements; From the first switch The second control signal is transmitted so as to control the second switching element to be turned on during a period until an end point of the off period of the switching element, and the start time of the on period of the first switching element is determined by the start time of the second switching element. And a switch control circuit in which the timing of the first and second control signals is set so as to substantially coincide with the time when the voltage of the first switching element becomes substantially zero. is there.

[0006]

The second switching element and the second reactor according to the present invention are used to discharge the electric charge of the second capacitor. When the second switching element is turned on during the off period of the first switching element, a charge of the second capacitor is discharged via the second reactor due to a resonance phenomenon between the second capacitor and the second reactor, The second capacitor is then reverse charged. When the voltage of the second capacitor is reverse-charged to cancel the voltage between the second and third power supply terminals, the voltage of the first switching element becomes substantially zero. If the first switching element is turned on at this time, zero volt switching is achieved, the switching loss becomes substantially zero, and the efficiency of the DC-DC converter increases.

[0007]

Next, a DC-DC converter according to a first embodiment of the present invention will be described with reference to FIGS. In FIG. 1, a DC power supply 1 is composed of a series circuit of first and second power supplies 2 and 3 for supplying 1/2 V, respectively, and has first, second and third power supply terminals 4, 5, and 6. The power supply 1 can be configured by connecting a series circuit of two power supply capacitors to a power supply composed of, for example, 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. Power supply 1
, The first power supply terminal 4 has the highest potential, the second power supply terminal 5 has the lowest potential (ground potential), and the third power supply terminal 6 has the first and second power supply terminals 4. , 5
Has an intermediate potential of

[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.

The output rectifying / smoothing circuit 7 comprises a first rectifying diode and a first smoothing capacitor C1.
Is connected in parallel to the switching element Q1. That is, the smoothing capacitor C1 is connected between the connection point 8 between the first reactor L1 and the first switching element Q1 and the second power supply terminal (ground terminal) 5 via the diode D1. One end and the other end of the smoothing capacitor 9 are connected to a pair of output terminals 9 and 10 for connecting a load (not shown).

A second capacitor C2 is connected between the connection point 8 and the third power supply terminal 6 for resonance.

A second reactor L2 having a smaller inductance than the first reactor L1 is provided between the connection point 8 and a second power supply terminal (ground terminal) 5 via a second switching element Q2 composed of a transistor. It is connected. That is, one end of the second reactor L2 is connected to a connection point between the second capacitor C2 and the first switching element Q1, and the second switching element Q2 is connected between the other end and the second power supply terminal 5. Is connected. A second diode D2 is connected between the other end of the second reactor L2 and a cathode of the first diode D1. Further, a third diode D3 is connected in anti-parallel to the first switching element Q1.

The control circuit 11 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 9 is connected to the control circuit 11 to control the DC output voltage between the output terminals 9 and 10 to a predetermined value.

FIG. 3 shows an example of a circuit for forming on / off control signals Vb1 and Vb2 for the first and second switching elements Q1 and Q2 shown in FIGS. 2A and 2B. FIG.
, A voltage dividing resistor R is provided between the pair of output terminals 9 and 10.
1, a voltage detection circuit 20 composed of R2 is connected.
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 shown in FIG. 4B in response to the clock pulse shown in 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. 4E generates a second control pulse (second control signal Vb2) having a time Td in response to the leading edge time t1 of the comparison output pulse of FIG. It is formed as shown and sent to the second switching element Q2. In this embodiment, the trailing edge time t2 of the second control pulse is synchronized with the leading edge time of the first control pulse.
It is also possible to extend the second control pulse of FIG. 2B to a point slightly after the time t2.

Next, referring to the waveforms of FIG.
The operation of the DC converter will be described. During the ON period of the first switching element Q1, the capacitor C2 is charged to the voltage V / 2 of the second power supply 3. When the first switching element Q1 is turned off at time 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 C2. The charging current Ic2 flows through the capacitor C2 as shown in FIG. 2 (E), and the voltage Vc2 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 Vc2 of the capacitor C2 becomes higher than the voltage of the output smoothing capacitor C1 at time ta, the diode D1 is forward-biased and conducts, and the current Id1 flows therethrough as shown in FIG. 2D. When the diode D1 turns on, the capacitor C2
Is clamped to a substantially constant value. This voltage value is V
/ 2 + αV.

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 power supply 1 and the first reactor L1 are connected. A closed circuit composed of the second reactor L2 and the second switching element Q2 is formed, and the current I2 of the second reactor L2 rises linearly with a slope as shown in FIG. Conversely, the current Id1 of the diode D1 decreases as shown in FIG.
When the current I2 of the diode D becomes equal to the current flowing through the first diode D1 during the period from ta to t1, the diode D
1 is cut off. This allows the capacitor C2
Is released, the capacitor C2, the second reactor L2, the second switching element Q2, and the second power supply 3
The discharge current of the capacitor C2 flows in a sine wave shape as shown in FIG. 2E, and the current obtained by adding the discharge current of the capacitor C2 to the second reactor L2 is shown in FIG. ). Capacitor C
2 and the voltage Vc of the first switching element Q1 are shown in FIG.
(F) and (G), which decrease in the cosine waveform, and become zero at time t2 when the voltage of the capacitor C2 becomes a value (-V / 2) which cancels the voltage of the second power supply 3. Therefore, at time t2, FIG.
As shown in (A), the first control signal Vb1 is changed to a high level to turn on the first switching element Q1. As a result, zero volt switching of the first switching element Q1 is achieved, and this loss is reduced.

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. 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 hardly occurs.

[0018]

[Modifications] The present invention is not limited to the above-described embodiment, and for example, the following modifications are possible. (1) First switching element Q1 and third diode
For example, a MOSFET with a built-in diode can be connected instead of the diode D3. (2) The control circuit 13 is not limited to FIG.
Various modifications are possible.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a DC-DC converter according to an 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 C2 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; and a first switching element connected in parallel to the first switching element via a first diode. A capacitor; and a second power supply terminal connected between a connection point between the first reactor and the first switching element and the third power supply terminal.
A second reactor having one end connected to a connection point between the first switching element and the second capacitor; and a second power supply terminal between the other end of the second reactor and the second power supply terminal. A second diode connected between the other end of the second reactor and a terminal of the first diode connected to the first capacitor. A third diode connected in reverse parallel to the first switching element; and a first and second control signal for controlling on / off of the first and second switching elements. Wherein at least a period from a point slightly before the end of the off-period of the first switching element to the end of the off-period of the first switching element, the second
The second control signal is transmitted so as to control the switching element of the first switching element to be on, and the start time of the on-period of the first switching element substantially coincides with the time when the voltage of the first switching element becomes substantially zero. And a switch control circuit in which the timings of the first and second control signals are set.