JP2519969B2 - DC-DC converter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a resonance type DC-DC converter capable of reducing loss and switching noise in a switching element and controlling an output voltage at a fixed operating frequency. .

(Prior Art) A DC-DC converter is applied to a circuit for converting a DC voltage into a DC voltage having different polarities or different voltage values, aiming at downsizing, weight reduction, and high efficiency. DC-DC
In the converter, by increasing the conversion frequency, it is possible to reduce the size and weight of the transformer and output filter.

Currently, the most frequently used circuit type of the DC-DC converter is a forward type or flyback type in which the current flowing through the switching element is forcibly cut off by turning off the switching element. These circuit types have the advantage that the output voltage can be kept constant by pulse width control even if the load resistance and the input voltage change, but there are the following problems when increasing the frequency.

(I) Since a spike-shaped current due to the recovery current of the rectifying diode flows when the switching element is turned on, loss and noise at the time of turn-on are large.

(Ii) Since the load when the switching element is turned off is inductive due to the leakage inductance of the transformer and the inductance component distributed in the circuit, the loss in the switching element and snubber circuit is large.

Due to these problems, even if MOS-FET is used as a switching element up to an output capacity of about 100 W, the conversion frequency is limited to about 500 kHz and above 1 kW to about 100 kHz. In order to further increase the conversion frequency, there are many items to be considered, such as improving the characteristics of switching elements and rectifying elements, manufacturing a transformer with less leakage inductance, mounting components with less stray inductance, and lowering the snubber circuit loss. For this reason, DC-DC converters, which can reduce the loss and noise when the switching element turns on and off by making the waveform of the current flowing through the switching element sinusoidal with a capacitor and an inductor, have been actively studied. The circuit type of this DC-DC converter is called a series resonance converter.

FIG. 3 shows a circuit configuration of a series resonance converter which is generally considered. Here, 1 is a DC power supply, 2 and 3 are feedback diodes, 4 and 5 are switching elements, 6 is a transformer, 7 and 8 are resonance capacitors, 9 is a resonance inductor, and 1 is a resonance inductor.
Reference numerals 0 and 11 are rectifying diodes, 12 is a smoothing capacitor, and 13 is a load resistance.

Next, the operation will be described. When the switching element 4 is turned on while the resonance capacitor 7 is charged with the power supply voltage, the resonance capacitor 7-the switching element 4
-Primary winding of transformer 6-Resonance inductor 9-Resonance capacitor 7 loop and DC power supply 1-Switching element 4-Primary winding of transformer 6-Resonance inductor 9-Resonance capacitor 8-DC power supply 1 loop Resonance current flows at. When the switching element 5 is turned on, the resonance capacitor 8-resonance inductor 9-the primary winding of the transformer 6-switching element 5-loop of the resonance capacitor 8 and DC power supply 1-resonance capacitor 7-resonance inductor 9 -Primary winding of transformer 6-Switching element 5-
A resonance current flows in the loop of the DC power supply 1. Transformer 6
If the ratio of the number of primary windings to the number of secondary windings is n, n times the resonance current flows in the secondary winding of the transformer, so this resonance current is rectified by the rectifying diodes 10 and 11 and smoothed. The capacitor 12 is charged to supply a DC voltage to the load resistor 13.

(Problems to be Solved by the Invention) When the voltage of the DC power supply 1 is E, the resonance capacitor 7
Alternatively, if the charging voltage of 8 is 3E / 2 or less, no current flows in the feedback diode 2 or 3. In this mode, the output voltage is constant even if the load resistance 13 is changed, and is given by E / (2n). Since E and n cannot be freely changed, the output voltage cannot be controlled in this mode. The charging voltage of the resonance capacitors 7 and 8 increases as the load resistance 13 is reduced, and when it reaches 3E / 2, the resonance capacitor 7-DC power supply 1-
Feedback diode 3-primary winding of transformer 6-loop of resonance inductor 9 or resonance capacitor 8-resonance inductor 9-primary winding of transformer 6-feedback diode 2-loop of DC power supply 1 Flow out. In this mode, the output current is constant even if the load resistance 13 is changed, and is given by 8f _s CnE. However, f _s is the operating frequency, and the resonance frequency is f _r, is the case of f _r> 2f _s. C is the capacitance of the resonance capacitors 7 and 8. When the load resistance value is R, the output voltage V _out is 8f _s CnER. It is necessary to change the operating frequency f _s to keep the output voltage V _out constant even if the load resistance value R changes. That is, the load resistance value R
Since the operating frequency f _s decreases with increasing, there is a problem that annoying noise is generated in the audible frequency range.

The present invention is a DC-DC converter capable of maintaining a constant output voltage by bypassing a part of the charging / discharging current of a resonance condenser from the primary winding of a transformer and controlling the energy transmitted to the secondary side of the transformer. Is provided.

(Means for Solving the Problems) The present invention is for achieving the above-mentioned object.
Connecting a series circuit of switching elements, a second series circuit of two switching elements, a series circuit of two resonance capacitors, and a series circuit of two feedback diodes to a DC power supply; The connection point of the series circuit of the two feedback diodes and the connection point of the series circuit of the second two switching elements are connected to form a connection point a, and the connection point of the first two switching elements is connected. The primary winding of the transformer and the series circuit of the first resonance inductor between the connection point a and the connection point a, and between the connection point a and the connection point of the series circuit of the two resonance capacitors. Is connected to a second resonance inductor, and a full-wave rectifier circuit and a smoothing capacitor are connected to the secondary winding of the transformer.
The main point is the DC-DC converter.

(Operation) The present invention has the above-described configuration, the resonance inductor is divided into two, and the switching element is connected to the connection point of these two resonance inductors so that part of the charging / discharging current of the resonance capacitor is used as the switching element. The most important feature is that the output voltage can be kept constant even at a fixed operating frequency by controlling the energy that is bypassed and transmitted to the secondary side of the transformer.

(Examples) Examples of the present invention will be described below with reference to the drawings. Needless to say, the embodiment is merely an example, and various modifications and improvements can be made without departing from the spirit of the present invention.

FIG. 1 is a connection diagram of an embodiment of the present invention, in which 1 is a DC power supply, 2 and 3 are feedback diodes, 4,5, 15 and 16 are switching elements (4,5 are first switching elements, 15, 16 is a second switching element), 6 is a transformer, 7 and 8 resonance capacitors, 10 and 11 are rectifying diodes, 12 is a smoothing capacitor, 13 is a load resistor, and 9 and 14 are resonance inductors ( (9 is the first resonance inductor, 14 is the second resonance inductor)
Is.

FIG. 2 shows the switching elements 4, 5, 15, 16 in FIG.
It is a figure which shows the phase relationship of the signal which drives.

Next, the operation will be described. When the resonance capacitor 7 is charged to the voltage of the DC power supply 1 and the drive signal V _{G1 of} FIG. 2 is applied to the switching element 4 to turn it on, the resonance capacitor 7-the switching element 4-the primary winding of the transformer 6- Resonance inductors 9,14-Loop of resonance capacitor 7 and DC power supply 1-Switching element 4-Primary winding of transformer 6-Resonance inductor 9,14-Resonance capacitor 8
-Resonant current flows in the loop of the DC power supply 1. The resonance current i ₀ is given by the following equation, where t = 0 is the time when the switching element 4 is turned on.

Here, A ₀ ; the constant of the voltage of the DC power supply 1, the inductance of the resonance inductors 9 and 14, and the capacitance of the resonance capacitors 7 and 8 L ₁ ; the inductance of the resonance inductor 9 L ₂ ; the inductance of the resonance inductor 14 C: Capacitance of resonance capacitors 7 and 8 (C ₁ = C ₂ = C
And ) When the drive signal V _G2 is applied to the switching element 15 at t = t ₁ while the resonance current i ₀ is flowing to turn it on, the series circuit of the switching element 4, the primary winding of the transformer 6 and the resonance inductor 13 is short-circuited. Therefore, the current flowing through this series circuit is linearly attenuated according to the following equation.

i ₁ = I ₀ −nV _out (t−t ₁ ) / L ₁ (2) where I ₀ ; current V _out ; of the series circuit of the transformer 6 and the inductor 9 immediately before the switching element 15 is turned on. Voltage of smoothing capacitor 13 (output voltage) n; ratio of primary winding number N _{1 of} transformer 6 to secondary winding number N ₂ (n
= N ₁ / N ₂ ) At time t ₂ when this current becomes zero, t ₂ = t ₁ + (I ₀ L ₁ / nV _out ) (3) according to equation (2) That is, the current flows through the switching element 4. The current becomes zero even if the switching element 4 does not turn off. Therefore, by removing the drive signal V _G1 of the switching element 4 at the time t = t ₂ when the current becomes zero, the loss at the turn-off is theoretically determined. It can be zero.

The output current I _out is given by equation (1), where T is one cycle.
It is given by the following equation from (2) and (3).

Since the output voltage V _out is given by the product of the output current I _out and the load resistance value R, V _out = I _out R (5) In order to keep the output voltage V _out constant, the time to turn on the switching element 15 from the equations (4) and (5)
It can be seen that it is sufficient to control t ₁ .

The feedback diode 2 prevents the reverse voltage from being applied to the switching element when the resonance capacitor 8 is charged to a voltage higher than the voltage of the DC power supply 1, and prevents the feedback current from flowing in the primary winding of the transformer. , To stabilize the circuit operation. The switching elements 5 and 16, the operation of the feedback diode 3 and the flowing current are as follows.
15, The description is omitted because it is exactly the same as the feedback diode 2.

(Effects of the Invention) As described above, the present invention provides a first series circuit of two switching elements, a second series circuit of two switching elements, and a series circuit of two resonance capacitors. ,
A series circuit of two feedback diodes is connected to a DC power source, and a connection point of the series circuits of the two feedback diodes and a connection point of the series circuit of the second two switching elements are connected. As a connection point a, the primary winding of the transformer and the series circuit of the first resonance inductor are connected between the connection point of the first two switching elements and the connection point a,
A second resonance indexer is connected between the connection point a and the connection point of the series circuit of the two resonance capacitors, and a full-wave rectification circuit and a smoothing capacitor are connected to the secondary winding of the transformer. By connecting the DC-DC converter, the current flowing through the circuit is determined by the inductance and capacitance, and the circuit current is not forcibly cut off by the switching element. Since the generation of high frequency noise can be reduced and the output voltage can be controlled without changing the operating frequency, there is an advantage that audible noise is not generated even at a light load.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a connection diagram of an embodiment of the present invention, FIG. 2 is a drive signal of a switching element in FIG. 1, and FIG. 3 is a connection diagram of a conventional series resonance converter. 1 ... DC power source 2, 3 ... Feedback diode 4,5 ... First switching element 15, 16 ... Second switching element 6 ... Transformer 7,8 ... Resonance capacitor 9 ... First Resonance inductor 14 …… Second resonance inductor 10,11 …… Rectifying diode 12 …… Smoothing capacitor 13 …… Load resistance

Claims (1)

(57) [Claims] 1. A series circuit of a first two switching elements, a series circuit of a second two switching elements, a series circuit of two resonance capacitors, and a series of two feedback diodes. And a circuit connected to a DC power source, and a connection point of the series circuit of the two feedback diodes and a connection point of the series circuit of the second two switching elements are connected to each other to form a connection point a.
The primary winding of the transformer and the series circuit of the first resonance inductor are connected between the connection point of the first two switching elements and the connection point a, and the connection point a and the second resonance inductor are connected to each other. The second resonance indexer is connected between the resonance circuit and the connection point of the series circuit, and the full-wave rectifier circuit and the smoothing capacitor are connected to the secondary winding of the transformer. DC-DC converter.