JP3143848B2 - 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 a voltage of a DC power supply on an input side and outputting a DC power supply voltage through a synchronous rectifier.

[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 is known 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 Further, a DC / DC converter that recovers energy on the output side by using the diode D1 as a bidirectional synchronous rectifying element that is turned on when the switching element S1 is turned off is also known.

[0004]

In a reactor type DC-DC converter using such a synchronous rectifying element, either the voltage higher or lower than the power supply voltage is used as in the case of rectification by a diode. In addition to being able to convert only to the range, when the operation of the DC-DC converter is stopped, if the output DC voltage is gradually decreased in order to absorb the charging energy of the output-side capacitor, the operation is particularly performed in the step-up type. Since the lower limit of the voltage is limited, there is a problem that energy cannot be sufficiently recovered to the input side.

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 using a synchronous rectifier capable of converting an input power supply voltage into a voltage higher or lower than the input power supply voltage. And

[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 bidirectional coil for connecting the other terminal of the coil to a reference potential. And a CL coupling circuit connected to the other terminal and comprising a coupling capacitor and a reactor coil, and a bidirectional synchronous rectifier for rectifying an output voltage of the reactor coil of the CL coupling circuit. The element, a smoothing capacitor for smoothing the rectified output thereof, and a synchronous control of the synchronous rectifying element so that the synchronous rectifying element is turned on during the OFF period of the switching element. And a constant voltage control circuit for controlling the ratio of the on / off periods of the switching elements 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 to the load through the synchronous rectifying element,
It 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 capacitor of the CL coupling circuit, thereby controlling the input power supply voltage. To a higher or lower output power supply voltage of a desired constant voltage.

When the power supply ends in the middle of the OFF period due to a small load, current flows from the smoothing capacitor to the input side during the remaining period. When the load becomes heavy and the output current is supplied over the entire period of the off period, the current is held during the next on period and added to the input current of both coils to increase the output current accordingly, Constant voltage control is performed while keeping the ratio of the off period to the on period constant.

When the output DC voltage exceeds the set output DC voltage due to the inertia of the output side, energy can be quickly recovered to the input side by constant voltage control for extending the OFF period. If the OFF period is automatically and gradually increased when the operation is stopped, sufficient recovery of energy to the input side is performed.

[0010]

FIG. 1 shows a DC-D according to an embodiment of the present invention.
The C converter will be described. E10 is a storage battery as an input DC power supply. L10 is a reactor coil having one terminal connected to the storage battery E10 and the other terminal electrically connected to the reference potential by the FET transistor Q10 as a bidirectional switching element. C10 and L11 are
These are a coupling capacitor and a reactor coil that constitute an L-shaped CL coupling circuit. Q11 is this C
It is a FET transistor as a switching element that exhibits bidirectionality as a synchronous rectification element that rectifies the output voltage of the L-coupled circuit. C11 is a smoothing capacitor for smoothing the rectified output.

Reference numeral 10 denotes a constant voltage control circuit, which controls the FET transistor Q11 during the ON period of the FET transistor Q10.
Performs synchronous control to turn off, as compared with the output DC voltage reference voltage output DC voltage V _O which is smoothed by the smoothing capacitor C11, a constant voltage output DC voltage V _O in accordance with 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 during the control cycle T,
That is, the pulse width of the switching signal of the FET transistor Q10 is controlled. The constant voltage control circuit 10 is configured to collect the accumulated energy of the forced close to the T gradually longer T ₂ smoothing capacitor C11 during the operation stop.

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. FET transistor Q11 is in the on-period T ₁ of the in the control period T is turned off, the OFF period T ₂ are turned on. In the on period T _1, by a reverse current flows through the voltage charged in the smoothing capacitor C11 through the FET transistor Q11 in the OFF period T ₂ of the immediately preceding, according to the inductance and the input DC voltage V _I to the coil L10 A current that changes from a negative slope to a positive slope flows through the FET transistor Q10 and is excited. At the same time, it applied to the negative voltage coil L11 corresponding to the input DC voltage V _I at the charging voltage by connection to a reference potential of the capacitor C10, the inclination corresponding to the inductance and the voltage applied through FET transistor Q10 - from then at the + A certain current flows and is excited. Therefore, the sum of these becomes the input current I _I ,
Energy is stored in the associated coils L10, L11.

When the FET transistor Q10 is in the off period T ₂
, The FET transistor Q11 turns on, the reverse voltage of the other terminal of the coil L10 rises stepwise higher than the input power supply voltage, and a load is applied through the FET transistor Q11 in a state where the DC voltage of the storage battery E10 is separated by the capacitor C10. To the power supply. At the same time coil L1
A reverse voltage is generated in the step 1 in a step-like manner, and the output current _IO of the sum of the two is supplied to the load through the FET transistor Q11, and the ripple voltage during this period is smoothed by the smoothing capacitor C12. When the power supply is terminated halfway, the electric charge accumulated in the smoothing capacitor C10 with the same gradient flows back to the coils L10 and L11 by the same time constant and the same reverse voltage, and the current gradually increases from the -current at the next ON. . 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 FIG. 2A, the output current I _O becomes the input current I _I
Are controlled so that T ₁ = T ₂ with the same amplitude and the same gradient in the opposite direction. In this state, if the load gradually increases from no load,
While maintaining the relationship of T ₁ = T ₂ , the on and off periods T ₁ ,
T ₂ of the return period T _3, T ₄ becomes gradually shorter than 1/2 of T _1, T _2.

When the load further increases in the state of V _O = V _I , the state shifts to the state of FIG. 1B through a critical state in which the backflow periods T ₃ and T ₄ become just zero. That is, in order to increase the input current I _I in response to an increasing load, T ₁
If the control period T is fixed, the power supply period T ₂ is shortened, and the output current I _O cannot be increased. Therefore, at the end of the off period T _{2 in} the state of T ₁ = T ₂ in maintaining its current to the coil L10, L11 on-time followed by an output current I _O flowing still, the input current I _I
Are switched in a state in which a corresponding step current is superimposed, and an output current I _O in which the step current is superimposed is supplied.

Further, when the input and output DC voltages are different, V _{O
= (T 1 / T 2)} T 1 in response to V _I is controlled. For example, when V _O > V _I , when T ₁ > T ₂ , the output current I _O is supplied with the same amplitude as the input current I _I, and with a steeper gradient according to V _O > V _I. At that time, the coils L10, L11
, The reverse step voltage during T ₂ becomes higher than that shown in the figure depending on 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
To be supplied the output current I _O at a gentle slope at the same maximum amplitude, the reverse step voltage maintains the relationship _{V I × T 1 = V O} × T 2 is low.

In such a state, when the load is a DC motor, if the V _{O is} to be reduced for speed adjustment, the terminal voltage due to the inertia of the DC motor is set to T ₁ by constant voltage control. The regenerative braking is performed by controlling in a smaller direction, and is absorbed by the storage battery E10. If the input DC power supply is not a storage battery, the input DC power supply is recovered by an input-side smoothing capacitor attached to the power supply. When the operation of the DC-DC converter is stopped, T ₁ is automatically and gradually reduced to T ₂
= T, and stops after the energy of the smoothing capacitor C12 or the large capacitive load is absorbed by the storage battery E10. FIG. 3A shows a waveform diagram of the input / output current during such a current recovery operation when the load is small, and FIG. 3B shows a waveform diagram when the load is large.

Although the inductance values of the coils L10 and L11 do not have to be the same, 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. As the bidirectional switching element, a normal switching transistor in which diodes are connected in parallel can be used. 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. 4 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
When 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, the back electromotive force is clamped, and each winding simply acts as a reactor. There is no spike voltage due to leakage inductance. The operation is
It operates according to the above description based on FIG. 2 and FIG.

[0020]

According to the present invention, in a reactor type DC-DC converter in which a synchronous rectifier is used as a rectifier according to the present invention, energy on the output side is absorbed on the input side, an input DC power supply is coupled to a coupling capacitor and a reactor coil. The power supply voltage can be output at either high or low DC output, and the coil of the CL coupling circuit works together with the switching coil with the energy as a reactor without losing the conversion efficiency. To supply the output current to the load. For example, the present invention can be used as a general-purpose charging device that switches and charges a storage battery charging voltage to 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 the storage 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. Furthermore, the regenerative braking of the DC motor and the recovery of the energy stored in the output-side capacity are reliably performed without limiting the constant voltage control range.

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 parts is reduced and the coils are downsized, and in some cases, commercially available products Can also be used.

[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 points during normal operation of the converter.

FIG. 3 is a diagram showing input / output current waveforms during a current recovery operation of the converter.

FIG. 4 is a diagram showing a circuit configuration of a DC-DC converter according to another embodiment.

FIG. 5 shows a circuit configuration of a conventional reactor type converter. FIG. 5A shows a boost type, and FIG. 5B shows a step-down type.

[Explanation of symbols]

 E10 Storage battery L10, L11 Coil Q10, Q11 FET transistor T10 Pulse transformer

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-58-224559 (JP, A) JP-A-5-76167 (JP, A) (58) Fields investigated (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 bidirectional switching element connecting the other terminal of the coil to a reference potential, and a coupling connected to the other terminal. Coupling circuit composed of a capacitor for use and a coil for a reactor, and the CL
A bidirectional synchronous rectifier for rectifying the output voltage of the reactor coil of the coupling circuit, a smoothing capacitor for smoothing the rectified output, and synchronizing the synchronous rectifier so that the synchronous rectifier is turned on during the off period of the switching element. A constant voltage control circuit for controlling the output voltage of the smoothing capacitor as an input, comparing the output voltage with an output voltage reference voltage, and controlling a ratio of an on / off period of the switching element according to the difference. DC-DC converter. 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 bidirectional switching element connecting the other terminal of the coil to a reference potential, and a CL coupling circuit connected to the other terminal. A bidirectional synchronous rectifier connected to a CL coupling circuit, a smoothing capacitor for smoothing the rectified output thereof, and a synchronous control for synchronously controlling the synchronous rectifier so that the synchronous rectifier is turned on during an off period of the switching element; A constant voltage control circuit that compares the output voltage of the switching element 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.
A DC-DC converter, 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. .