JP3143847B2 - 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 for converting the voltage of a DC power supply on the input side and outputting a DC power supply voltage.

[0002]

2. Description of the Related Art According to a transformer type DC-DC converter, a pulse is generated by an input DC power supply on a primary side,
It is possible to transform and rectify the pulse whose pulse width is controlled according to the voltage to be output to the secondary side, and to convert it into a desired constant-voltage DC power supply voltage. However, in the case of using a transformer, the clipping circuit is required to protect the switching element from a spike voltage caused by the leakage magnetic flux of the transformer.

On the other hand, in order to avoid this problem, a reactor type DC-DC converter as shown in FIG. In this case, the coil L1 connected to the battery E1 is connected to the switching element S1 as shown in FIG.
And a boost type in which an induced voltage superimposed on the power supply voltage is rectified by a diode D1 and smoothed by a smoothing capacitor C1 to output a DC voltage, and an induced voltage subtracted from the power supply voltage as shown in FIG. Is categorized into a step-down type that rectifies and smoothes

[0004]

That is, in the case of a reactor type DC-DC converter, conversion can be performed only in a voltage range higher or lower than the power supply voltage.

SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to provide a reactor type DC-DC converter capable of converting an input power supply voltage into a voltage higher or lower than the input power supply voltage.

[0006]

In order to achieve this object, the present invention provides a reactor coil having one terminal connected to a DC power supply, and a switching element for connecting the other terminal of the coil to a reference potential. , Connect to the other terminal,
A CL coupling circuit composed of a coupling capacitor and a reactor coil; a rectifying element for rectifying an output voltage of the reactor coil of the CL coupling circuit; a smoothing capacitor for smoothing the rectified output; A constant voltage control circuit that compares the output voltage with an output voltage reference voltage as an input, and controls a ratio of an on / off period of the switching element according to the difference.

[0007]

During the ON period of the switching element, a current flows through the switching element in accordance with the inductance and the input power supply voltage of the coils functioning as both reactors, and energy is accumulated. When the switching element is turned off, the energy stored in both of these coils is supplied to the output current through the rectifying element to the load, and is smoothed by the smoothing capacitor. The constant voltage control circuit controls the ratio of the ON period and the OFF period of the switching element to output a constant voltage in a state where the input DC power supply is separated by the coupling capacitor of the CL coupling circuit. It is converted to a desired constant voltage output power supply voltage that is higher or lower than the voltage.

When the load becomes heavy and the output current is supplied over the entire off period, the output current is held during the next on period and added to the input currents of both coils, so that the output current is correspondingly increased. The constant voltage control is performed with the ratio of the off period to the on period kept constant.

[0009]

FIG. 1 shows a DC-D according to an embodiment of the present invention.
The C converter will be described. E10 is a battery as an input DC power supply. L10 has one terminal connected to the battery E1.
0 and the other terminal is F
This is a reactor coil that is conducted to the reference potential by the ET transistor Q10. C10 and L11 are a coupling capacitor and a reactor coil constituting an L-shaped CL coupling circuit. D10 is a diode as a rectifying element for rectifying the output voltage of the CL coupling circuit. C11 is a smoothing capacitor for smoothing the rectified output. Reference numeral 10 denotes a constant voltage control circuit which compares the output DC voltage V ₀ smoothed by the smoothing capacitor C11 with an output DC voltage reference voltage, and converts the output DC voltage V ₀ to a constant voltage according to the difference. FET transistor Q10
A switching signal for controlling the ratio of the on-off periods of the switching signals. In this embodiment, the ON period T ₁ in the control cycle T,
That is, the pulse width of the switching signal is controlled.

The operation of the DC-DC converter thus configured will be described with reference to FIG. FIG. 7A shows the operation waveforms of each part when the load is light. Slope of current corresponding to the inductance and the input DC voltage V _I to the coil L10 during the on-period T ₁ of the in the control period T is excited flows through FET transistor Q10. At the same time, a negative voltage corresponding to the input DC voltage V _I at the charging voltage by connection to the reference potential of the capacitor C10 is applied to the coil L11,
A current having a gradient corresponding to the inductance and the applied voltage flows through the FET transistor Q10 to be excited.
Therefore, the sum of these becomes the input current I _I, and energy is stored in the associated coils L10 and L11.

When the FET transistor Q10 enters the OFF period, the reverse voltage of the other terminal of the coil L10 rises stepwise higher than the input power supply voltage, and passes through the diode D10 while the DC voltage of the battery E10 is separated by the capacitor C10. feeding the load over energy release period T _2. At the same time, a reverse voltage is generated in a stepwise manner in the coil L11, and the output current I _O of the sum of the two is changed to the diode D10.
It is supplied to the load over the energy release period T ₂ through, during which the ripple voltage is smoothed by the smoothing capacitor C12, a subsequent resting period T _3. The capacitance value of the capacitor C10 is set to be large enough to exhibit a sufficiently low impedance with respect to the pulse components of the input / output currents I _I and I _O , thereby ensuring highly efficient voltage conversion.

In the constant voltage control circuit 10, when the output DC voltage V _O is set equal to the input DC voltage V _I , as shown in the figure, the output current I _O has the same maximum amplitude as the input current I _I in the reverse direction. in the same gradient, it is controlled to T ₁ = T _2. In this state, when the load becomes lighter, the relationship of T ₁ = T ₂ is maintained, and both of these periods become shorter, and the load becomes heavier and longer.

When the load gradually increases in the state of V _O = V _I , the state shifts to the state of FIG. 2C through a critical state without the pause T ₃ shown in FIG. 2B. That is, in order to increase the input current I _I in response to the increasing load, T
_{On the} other hand, if the control period T is fixed, the energy release period T ₂ becomes short, and the output current I _O cannot be increased. Therefore, the energy release period T _{2 in} the state of T ₁ = T ₂ can be increased. The output current I _O still flowing at the end of the current is maintained in the coils L10 and L11 at the subsequent ON time, and the switching is performed in a state where the corresponding step current is superimposed on the input current I _I, and the step current is superimposed. An output current _IO is supplied.

Furthermore, input and output DC voltage load is a light state may yl, T ₁ in response to _{V O = (T 1 / T} 2) V it is controlled. For example, in the case of V _O> V _I, in the output current I _O is the input current I _I of the same maximum amplitude in the state (T _1> T ₂₎ where T ₂ is longer than T ₁ in FIG. 2A, the gradient V
Supply more steeply according to _O > V _I. At that time, reverse step voltage in T ₂ generated in the coil L10, L11 is higher than that shown depending on the T ₁ / T _2. Similarly, when the load becomes heavier, a step current is superimposed on I _I and I _{O according} to the magnitude. When V _O <V _I is set, T ₁ <T ₂ , and the output current I _O is supplied with the same maximum amplitude and a gentle gradient, and V _I × T ₁ = V _O × T ₂
And the reverse step voltage decreases.

The inductance values of the coils L10 and L11 do not have to be the same. However, if any one of the inductance values becomes small and the current waveform is not a triangular wave but saturates stepwise on the way, the voltage control range It is conceivable to shorten the control cycle T so as not to limit the control cycle T. An ordinary switching transistor can be used as the switching element. The power supply voltage can be configured to generate a negative power supply voltage by setting the input power supply voltage to a negative voltage and setting the polarity of the switching element accordingly.

FIG. 3 shows another embodiment using, as the coils L10 and L11, a pulse transformer T10 having the same number of turns on the primary and secondary sides and having a 1: 1 transformation ratio and having the same phase. That is, 1
The secondary winding 11 functions as the coil L10, and the secondary winding 12 functions as the coil L11. At this time, the primary winding 11
And the terminal of the secondary winding 12 on the switching side of the in-phase terminal is short-circuited by the large-capacity capacitor C10, so that each winding simply acts as a reactor, and therefore the spike voltage caused by the leakage inductance. Does not occur.

[0017]

According to the reactor type DC-DC converter of the present invention, the input DC power supply is separated by the CL coupling circuit composed of the coupling capacitor and the reactor coil, thereby reducing the power supply voltage. Thus, the DC output of either the high or the low can be output, and the coil of the CL coupling circuit, together with the switching coil, accumulates energy as a reactor and supplies an output current to the load without impairing the conversion efficiency. For example, the present invention can be used as a general-purpose charging device that switches a battery charging voltage between a high voltage and a low voltage with respect to a constant input power voltage by using a common input DC power supply supplied by a commercial power supply.
In addition, when a battery is used as a power source, a constant DC voltage can be output even when the voltage drops due to discharge below the voltage to be output. At this time, by using the primary and secondary windings of the pulse transformer for the switching and CL coupling circuit coils, the number of components is reduced and the coils are downsized. You can also.

[Brief description of the drawings]

FIG. 1 is a diagram showing a circuit configuration of a DC-DC converter according to one embodiment of the present invention.

FIG. 2 is a diagram showing waveforms at various parts of the converter.

FIG. 3 is a diagram showing a circuit configuration of a DC-DC converter according to another embodiment.

4A and 4B show a circuit configuration of a conventional reactor type converter. FIG. 4A shows a step-up type and FIG. 4B shows a step-down type.

[Explanation of symbols]

 E10 Battery L10, L11 Coil Q10 FET transistor T10 Pulse transformer

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-58-224559 (JP, A) JP-A-6-250748 (JP, A) JP-A 5-76167 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H02M 3/155

Claims (3)

(57) [Claims] 1. A reactor coil having one terminal connected to a DC power supply, a switching element connecting the other terminal of the coil to a reference potential, a coupling capacitor connected to the other terminal, and a coupling capacitor and a reactor. Coupling circuit composed of an inductor coil, a rectifying element for rectifying the output voltage of the reactor coil of the CL coupling circuit, a smoothing capacitor for smoothing the rectified output, and an output voltage output from the smoothing capacitor. A DC-DC converter comprising: a constant-voltage control circuit that compares the reference voltage with a voltage and controls a ratio of an on / off period of the switching element according to a difference between the reference voltage and the voltage. 2. A reactor coil connected to a DC power supply and a reactor coil forming a CL coupling circuit are one in number.
2. The DC-DC converter according to claim 1, wherein the number of windings on the secondary side and the secondary side is the same and configured by a pulse transformer having the same phase. 3. A coil having one terminal connected to a DC power supply, a switching element connecting the other terminal of the coil to a reference potential, a CL coupling circuit connected to the other terminal, and a CL coupling circuit connected to the other terminal. A rectifying element to be connected, a smoothing capacitor for smoothing the rectified output thereof, and an output voltage of the smoothing capacitor as an input, which is compared with an output voltage reference voltage, and a ratio of an on / off period of the switching element is controlled in accordance with the difference. A constant voltage control circuit, wherein the coil connected to the DC power supply and the coil forming the CL coupling circuit are constituted by pulse transformers having the same number of turns on the primary and secondary sides and having the same phase. A DC-DC converter characterized by the above-mentioned.