WO2007100193A1

WO2007100193A1 - Method for converting voltage and converter for performing the same

Info

Publication number: WO2007100193A1
Application number: PCT/KR2007/000777
Authority: WO
Inventors: Young-Chang Cho
Original assignee: Young-Chang Cho
Priority date: 2006-02-28
Filing date: 2007-02-14
Publication date: 2007-09-07
Also published as: TW200733527A; KR100724313B1

Abstract

Disclosed are method for converting a voltage and a converter for performing the same, in which power supplied from an input terminal through a switching scheme is transferred to an output terminal through a pumping scheme by means of a capacitor having small capacity, thereby improving converting efficiency and reducing shock applied to the input and output terminals. DC/AC power supplied from a power source is sequentially charged in first and second capacitors by means of a switching circuit. The power supplied from the power input terminal is dropped down and then is transferred to a load terminal through a pumping scheme. The buck-converter changes the duty or the number of pumping operations of the switching circuit so as to control the power supplied to the load terminal. In the switching circuit, the switching-on time corresponds to a period of time required for charging the capacitor. The switching circuit is maintained in an off state after the switching-on time. If the switching-off time is lengthened relative to the switching-on time, the level of voltage supplied to a load is reduced. Thus, if the switching-on time is reduced relative to the switching-off time, power supply is substantially reduced.

Description

METHOD FOR CONVERTING VOLTAGEAND CONVERTER

FORPERFORMING THE SAME

Technical Field

[1] The present invention relates to a method for converting a voltage and a converter for performing the same. More particularly, the present invention relates to a method for converting a voltage and a converter for performing the same, in which power supplied from an input terminal through a switching scheme is transferred to an output terminal through a pumping scheme by means of a capacitor having small capacity, thereby improving converting efficiency and reducing shock applied to the input and output terminals. Background Art

[2] In general, a power supplying device that supplies DC power from a power terminal to a load terminal by dropping the DC power employs a PWM (pulse width modulation) control scheme. According to the PWM control scheme, a DC voltage, which is input according to a duty output from a PWM controller, is drop down through a switching scheme such that a constant voltage can be output. That is, according to the PWM control scheme, the DC voltage is accumulated in a transformer when the PWM controller turns on a switching device, and the DC voltage is shut off when the PWM controller turns off the switching device. The accumulated DC voltage is discharged by means of counter electromotive force of the transformer, so that desired output voltage is obtained. At this time, the output voltage is determined according to the duty of the PWM pulse signal output from the PWM controller.

[3] However, according to a voltage-down circuit employing the conventional PWM control scheme, great power loss is caused during the switching operation of the switching device, so the efficiency of the power circuit is lowered and a great amount of heat is generated from the transformer, etc. Thus, the size of a heat sink or a cooling system, which are attached to the power circuit to emit the heat, is enlarged, so the whole size of the power circuit is also enlarged. Disclosure of Invention Technical Problem

[4] The present invention has been made to solve the above problems occurring in the prior art, and an object of the present invention is to provide a method for converting a voltage and a converter for performing the same, in which power of an input terminal is transferred to a load terminal through a pumping scheme by means of a capacitor having small capacity, in such a manner that stable DC power can be supplied to a load terminal by dropping down DC/AC power supplied from a power terminal through a switching scheme, thereby reducing switching noise generated from the input and output terminals and realizing the converter, except for the capacitor, as a monolithic IC semiconductor to improve the converting efficiency.

[5] In order to accomplish the above object, the present invention provides a method of converting a voltage, the method comprising the steps of: charging an input capacitor with a DC voltage by switching an input DC power; charging an output capacitor connected to a DC output terminal with a voltage by transferring the voltage charged in the input capacitor to the output capacitor through a switching scheme; detecting the DC voltage output from the output capacitor; and increasing a switching frequency when the DC voltage output from the output capacitor is less than a predetermined reference level, and reducing the switching frequency when the DC voltage output from the output capacitor is equal to the predetermined reference level or above. Brief Description of the Drawings

[6] The above and other advantages of the present invention will become readily apparent with reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:

[7] FlG. 1 is a schematic view illustrating a DC-DC converter according to a first embodiment of the present invention;

[8] FlG. 2 is a schematic view illustrating an AC-DC converter according to a first embodiment of the present invention;

[9] FlG. 3 is a block diagram illustrating the structure of a DC-DC converter according to a first embodiment of the present invention;

[10] FlG. 4 is a circuit view illustrating the structure of a DC-DC converter according to a first embodiment of the present invention;

[11] FlG. 5 is a block diagram illustrating the structure of an AC-DC converter according to a second embodiment of the present invention; and

[12] FlG. 6 is a circuit view illustrating the structure of an AC-DC converter according to a second embodiment of the present invention. Best Mode for Carrying Out the Invention

[13] Hereinafter, exemplary embodiments of the present invention will be explained in detail with reference to the accompanying drawings.

[14] FlG. 1 is a schematic view illustrating a DC-DC converter, which is an example of a buck-converter according to the first embodiment of the present invention, FlG. 2 is a schematic view illustrating an AC-DC converter, which is another example of the buck-converter according to the first embodiment of the present invention, FlG. 3 is a block diagram illustrating the structure of a DC-DC converter, which is an example of the buck-converter according to the first embodiment of the present invention, FlG. 4 is a circuit view illustrating the structure of a DC-DC converter, which is an example of the buck-converter according to the first embodiment of the present invention, FlG. 5 is a block diagram illustrating the structure of an AC-DC converter, which is an example of the buck-converter according to the second embodiment of the present invention, and FlG. 6 is a circuit view illustrating the structure of an AC-DC converter, which is another example of the buck-converter according to the second embodiment of the present invention.

[15] Referring to FIGS. 1 and 2, the buck-converter according to the present invention includes a switching circuit 110 that changes a switching on/off duty by detecting an input voltage of a power terminal and an output voltage of a load terminal, and first and second capacitors 120 and 130 which are sequentially charged with electric charges according to the switching operation of the switching circuit 110.

[16] According to the present invention, DC/AC power supplied from the power terminal is sequentially charged in the first and second capacitors 120 and 130 by using the switching circuit 110. At this time, the power supplied from the power terminal is dropped down such that the power can be transferred to the load terminal through the pumping scheme.

[17] That is, the buck-converter according to the present invention changes the switching on/off frequency or duty by using the switching circuit 110 to control the power supplied to the load terminal. For example, referring to FlG. 2, the switching circuit 110 alternatively performs the on/off switching operation relative to contacts a and b. If the number of switching operations is reduced (for instance, if the switching-on time is shorter than the switching-off time), the voltage level supplied to the load terminal is lowered.

[18] Accordingly, if the switching-on time is shorter than the switching-off time, the supply power is substantially reduced.

[19] Referring again to FlG. 1, if the switching terminal of the switching circuit 110 is connected to the terminal a, the DC voltage of the input terminal is charged in the first capacitor 120 through the pumping scheme. In addition, if the switching terminal of the switching circuit 110 is connected to the terminal b, the voltage charged in the second capacitor 130 may vary according to the electric charge conservation law Q = C x V, wherein Q is amount of electric charges, C is capacitance of capacitor and V is voltage.

[20] For instance, in the case where the DC voltage of the input terminal is 141 V, capacitance of the first capacitor 120 is lOμf, capacitance of the second capacitor 130 is 90μf, the DC voltage 14.1V is charged in and output from the second capacitor 130 without causing loss during the charging operation. At this time, the switching circuit 110 detects the voltage that is changed in and output from the second capacitor 130. If the detected voltage is lower than the desired voltage, the switching terminal is switched to the contact a. In this state, the above-mentioned operation is repeated. If a load (not shown) connected to the output terminal of the second capacitor 130 does not consume power, the switching circuit 110 may not operate. Thus, power consumption rarely occurs in the no-load state. In addition, the input/output terminals is subject to the shock noise corresponding to the voltage charged in the first and second capacitors

120 and 130, so that ripple and noise characteristics can be improved as compared with the general switching scheme.

[21] FlG. 2 is a schematic view showing the principle of converting AC power to DC power according to the present invention. FlG. 2 is substantially identical to FlG. 1, except that a wave rectifier 121 for rectifying AC power and a charge condenser C are installed between an AC input terminal and the first capacitor 120. The wave rectifier

121 rectifies the AC power to convert the AC power into the DC power and the DC power is charged in the charge condenser C. In this state, the power is converted and output similarly to FlG. 1.

[22] As shown in FlG. 3, in a DC-DC converter which is the converter according to the first embodiment of the present invention, the first capacitor 120 is connected to the DC input terminal so as to be charged with electric charges, and the second capacitor 130 is connected to the DC output terminal so as to output the charges by receiving the charges of the first capacitor 120 through the switching scheme. The switching circuit 110 is connected to one side of the second capacitor 130 so as to change the switching on/off duty by detecting the voltage output from the second capacitor 130.

[23] The switching circuit 110 includes a switching controller 112 that changes the switching on/off duty according to the voltage by detecting the voltage output from the second capacitor 130, and first and second switching units 114 and 116 performing the switching operation according to the control signal of the switching controller 112. The first switching unit 114 is installed between the DC input terminal and the first capacitor 120 in order to perform the switching operation such that the voltage of the DC input terminal can be charged in the first capacitor 120, and the second switching unit 116 is installed between the first and second capacitors 120 and 130 in order to perform the switching operation such that the voltage of the first capacitor 120 can be charged in the second capacitor 130.

[24] Here, a current limiter 102 can be further installed between the DC input terminal and the first switching unit 114 so as to protect the DC input terminal by preventing surge current from being applied to the DC input terminal. The first capacitor 120 has great inductance, and the second capacitor 130 includes non-inductive winding capacitor. Thus, the switching shock applied to the input and output terminals can be reduced.

[25] The DC-DC converter having the above construction according to the first embodiment of the present invention receives DC power from the DC input terminal. If the DC power passes through the current limiter 102, the switching controller 112 operates the first switching unit 114 such that a predetermined amount of DC power can be charged in the first capacitor 120. The voltage charged in the first capacitor 120 is transferred to the second capacitor 130 by means of the second switching unit 115 under the control of the switching controller 112. In the case where capacitance of the first capacitor 120 is lOμf, capacitance of the second capacitor 130 is 90μf, and the DC voltage is 100V, the total amount of electric charges is expressed as Q = lOμf x 100V = (lOμf + 90μf) x 10V according to the electric charge conservation law Q = C x V, so the voltage charged in the second capacitor 130 is 10V.

[26] Since the second capacitor 130 is the non-inductive winding capacitor having inductance components lower than those of the first capacitor 120, spike noise can be reduced. The switching controller 112 controls the switching operation by detecting the DC output voltage. If the detected output voltage is lower than the predetermined reference voltage, the number of switching operations is increased, that is the duty is changed, so that the voltage can be rapidly charged in the first capacitor 120 from the DC input terminal. If the detected output voltage exceeds the predetermined reference voltage, the switching controller 112 stops the switching operation, thereby preventing the voltage greater than the reference voltage from being output. Recently, as high- voltage switching devices have been developed, the switching operation can be efficiently performed. According to the present invention, simple high- voltage switching devices are prepared in the form of a monolithic semiconductor, except for the first and second capacitors 120 and 130, so that the DC power supply can be achieved by using one semiconductor chip and two capacitors having small capacitance.

[27] The DC-DC converter shown in FlG. 3 according to the first embodiment of the present invention can also be embodied by using the circuit shown in FlG. 4. Referring to the circuit structure shown in FlG. 4, the first capacitor 120 connected to the DC input terminal makes contact with collector terminals of a fifth transistor Q5 and a third transistor Q3, which are NPN transistors, through a resistor R9. A base terminal of the fifth transistor Q5 is connected to an emitter terminal of the third transistor Q3 through a resistor R8, and an emitter terminal of the fifth transistor Q5 is connected to the DC input terminal.

[28] In addition, the second capacitor 130 connected to the DC input terminal makes contact with collector terminals of a sixth transistor Q6 and a fourth transistor Q4, which are PNP transistors, through a resistor Rl 1. A base terminal of the sixth transistor Q6 is connected to an emitter terminal of the fourth transistor Q4 through a resistor RlO, and an emitter terminal of the sixth transistor Q6 is connected between the first capacitor 120 and the resistor R9.

[29] A base terminal of the third transistor Q3 is connected to a collector terminal of a first transistor Ql, which is an NPN transistor, connected to both ends of the DC input terminal, and a base terminal of the fourth transistor Q4 is connected to a collector terminal of a second transistor Q2, which is an NPN transistor, connected to both ends of the DC input terminal

[30] The resistor R9, which is connected between the first capacitor 120 and collector terminals of the fifth transistor Q5 and the third transistor Q3, which are NPN transistors, and the resistor Rl 1, which is connected between the second capacitor 130 and the sixth and fourth transistors Q6 and Q4, which are PNP transistors, regulate the current when the current instantaneously flows due to the characteristics of the condenser such that the current has a stable value.

[31] In addition, the fifth transistor Q5 and the third transistor Q3, which are NPN transistors, are designed such that they are operated inversely to the sixth and fourth transistors Q6 and Q4, which are PNP transistors. That is, if the fifth transistor Q5 is connected, the sixth transistor Q6 is disconnected, or vice versa.

[32] In addition, a variable resistor R2 is connected to one side of the second capacitor

130 through a resistor Rl so as to set the value of current output from the second capacitor 130. An output side of the variable resistor R2 is connected to an input side of a V/F (voltage-to-frequency) controller 113 that converts voltage signals to frequency signals, and an output side of the V/F controller 113 is connected to the base terminal of the first transistor Ql . One of input terminals of the V/F controller 113 is connected to the DC output terminal through a resistor R 12. In stead of the V/F controller 113, a mono-stable oscillator or a timer, which is operated when the voltage is low, can be employed.

[33] Hereinafter, the operation of the converter having the above construction according to the first embodiment of the present invention will be explained. If the voltage output from the second capacitor 130 is lower than the predetermined reference voltage, which is preset by the variable resistor R2, the V/F controller 113 repeatedly outputs the turn-on and turn-off signals to the first transistor Ql with a predetermined frequency (number of switching operations) inversely proportional to the differential voltage between the output voltage and the predetermined reference voltage. As the turn-on signal is applied to the first transistor Ql from the V/F controller 113, the first transistor Ql is turned on, so that the second transistor Q2 is also turned on. As the first and second transistors Ql and Q2 are turned on, the third and fifth transistors Q3 and Q5 are also turned on, so that the first capacitor 120 is charged with the voltage supplied from the DC input terminal. [34] In addition, as the turn-off signal is applied to the first transistor Ql from the V/F controller 113 that repeatedly outputs the turn-on and turn-off signals, the first transistor Ql is turned off, so that the second transistor Q2 is also turned off. As the second transistor Q2 is turned off, the fourth and sixth transistors Q4 and Q6 are turned on, so that the voltage charged in the first capacitor 120 is transferred to the second capacitor 130.

[35] That is, if a low- voltage is output from the second capacitor 130, the V/F controller

113 outputs a higher frequency. At this time, if the voltage output from the second capacitor 130 through the resistor Rl is lower than the reference voltage, which is preset by the variable resistor R2, the V/F controller 113 outputs the turn-on and turn- off signals to the first transistor Ql by increasing the frequency (duty ratio) of the turn- on and turn-off signals, so that a constant DC voltage is output from the second capacitor 130.

[36] In addition, the V/F controller 113 detects the current output from the second capacitor 130 by using the resistor RIl. If the detected current is within a predetermined reference range, the operation of the V/F controller 113 is stopped in such a manner that the current having a value within the predetermined reference range can be output from the second capacitor 130. A typical timer IC or circuits capable of outputting on/off signals according to the voltage can be used instead of the V/F controller 113.

[37] According to the preferred embodiment of the present invention, a charge capacitor can be further provided in the input/output terminals of the power source shown in FIG. 4, and a switching unit, which is controlled by the switching controller 112 shown in FIG. 3, can be provided in the input/output terminals in order to operate the charge capacitor. If the charge capacitor and the switching unit are further provided in the input/output terminals of the power source, shock applied to the input/output terminals during the charging operation can be reduced or prevented. In this case, the switching operation is performed according to the on/off operations of the switching controller 112 shown in FIG. 3.

[38] In addition, according to another embodiment of the present invention, as shown in

FIG. 5, a converter capable of outputting DC voltage when AC power is applied to the input terminal is provided. The structure of the converter shown in FIG. 5 is substantially identical to the structure of the converter shown in FIG. 3, except for a rectifier 104 for rectifying AC power applied to the AC input terminal and a DC- charge capacitor 106 for storing the DC voltage output from the rectifier 104. The same reference numerals will be assigned to the same elements.

[39] Referring again to FIG. 5, when the input AC voltage passes through the rectifier

104, the AC voltage takes a root-mean square, so that a voltage that is times of the input voltage is charged in the DC-charge capacitor 106. The voltage charged in the DC-charge capacitor 106 is transferred to the first capacitor 120 by means of the first switching unit 114. The voltage charged in the first capacitor 120 is inversely proportional to the capacitance of the DC-charge capacitor 106 and the first capacitor 120 and is dropped down according to the electric charge conservation law Q = C x V (if the DC-charge capacitor 106 and the first capacitor 120 have the same capacitance, the voltage is dropped down by 1/2). In the same manner, if a current limiter (not shown) is provided in the AC input terminal, rush shock can be absorbed relative to the input power due to current limitation.

[40] The voltage charged in the first capacitor 120 is transferred to the second capacitor

130 by means of the second switching unit 116 which is controlled by the switching controller 112. At this time, the voltage charged in the second capacitor 130 is inversely proportional to the capacitance of the DC-charge capacitor 106 and the second capacitor 130 and is dropped down according to the electric charge conservation law Q = C x V. For instance, in the case where the capacitance of the first capacitor 120 is lOμf, the capacitance of the second capacitor 130 is 90μf, and the DC voltage is 100V, the total amount of electric charges is expressed as Q = lOμf x 100V = (lOμf + 90μf) x 10V according to the electric charge conservation law Q = C x V, so the voltage charged in the second capacitor 130 is precisely dropped down to 10V. In this case, the amount of current is increased by 10 times. Thus, by taking lead and capacitance of the second capacitor 130 into consideration, a non-inductive winding type capacitor, rather than a typical electrolytic capacitor, is used as the second capacitor 130 so as to reduce spike noise in the output voltage.

[41] The AC-DC converter according to the second embodiment of the present invention can realize the DC power supply capable of reducing loss and outputting superior DC voltage without causing current impact to the AC power. The elements of the AC-DC converter, except for the capacitors, can be prepared in the form of a monolithic IC semiconductor. Referring to FIG. 5, the converter according to the second embodiment of the present invention consists of one semiconductor and three capacitors.

[42] The converters shown in FIGS. 3 and 5 can significantly reduce loss of power as compared with the conventional converter employing a transformer, and can supply high-quality DC power using capacitors having small capacitance. In addition, similarly to an SMPS (switch mode power supply), the converters according to the present invention can reduce noise generated from the input/output terminals and can improve the operational efficiency.

[43] FIG. 6 is a circuit view corresponding to the block diagram shown in FIG. 5. The circuit structure shown in FIG. 6 is substantially identical to the circuit structure shown in FlG. 3, except that a wave rectifier 104 for rectifying AC power and a DC-charge condenser 106 for storing the DC voltage output from the rectifier 104 are installed at the AC input terminal, and transistors Q3 to Q6 are NPN transistors. Thus, the structure and operation of the circuit shown in FlG. 6 will be omitted below.

[44] When the DC output voltage is dropped below a predetermined level, the converter according to the present invention increases the output frequency of the V/F controller 113 or the timer IC, which is used as the switching controller. In addition, if the DC output voltage increases to a proper level, the converter according to the present invention reduces the output frequency of the V/F controller 113 or the timer IC, so that the voltage of the output terminal can be constantly maintained regardless of the load current. Industrial Applicability

[45] As described above, according to the converter of the present invention, power of the input terminal is transferred to the load terminal through a pumping scheme by means of capacitors having small capacity, in such a manner that stable DC power can be supplied to a load terminal by dropping down DC/AC power supplied from a power terminal through a switching scheme, thereby reducing switching noise generated from the input and output terminals and realizing the converter, except for the capacitor, as a monolithic IC semiconductor. Thus, the converter according to the present invention can improve the converting efficiency and can be fabricated in a small size and light weight without causing power loss.

[46] Although the exemplary embodiments of the present invention have been described, it is understood that the present invention should not be limited to these exemplary embodiments but various changes and modifications can be made by one ordinary skilled in the art within the spirit and scope of the present invention as hereinafter claimed.

Claims

[1] A method of converting a voltage, the method comprising the steps of: charging an input capacitor with a DC voltage by switching an input DC power; charging an output capacitor connected to a DC output terminal with a voltage by transferring the voltage charged in the input capacitor to the output capacitor through a switching scheme; detecting the DC voltage output from the output capacitor; and increasing a switching frequency when the DC voltage output from the output capacitor is less than a predetermined reference level, and reducing the switching frequency when the DC voltage output from the output capacitor is equal to the predetermined reference level or above.

[2] The method as claimed in claim 1, further comprising the steps of rectifying an

AC power such that the AC power is converted into a DC power, and charging a charge capacitor with the DC power, before charging the input capacitor with the DC voltage.

[3] A converter comprising: a first capacitor connected to a DC input terminal so as to receive power from the

DC input terminal through a switching scheme; a second capacitor connected to a DC output terminal so as to receive charges from the first capacitor through a switching scheme and then output the charges to the DC output terminal; a switching controller for converting a switching on/off frequency (duty) of the switching scheme by detecting a voltage output from the second capacitor, such that the first and second capacitors are charged with the voltage according to a predetermined reference voltage; a first switching unit for switching a power supplied to the first capacitor from the DC input terminal according to a control signal of the switching controller; and a second switching unit for switching a power supplied to the second capacitor from the first capacitor according to a control signal of the switching controller.

[4] The converter as claimed in claim 3, further comprising a current limiter provided between the DC input terminal and the first switching unit so as to protect the DC input terminal by preventing a surge current from being applied to the DC input terminal.

[5] The converter as claimed in claim 3, further comprising a wave rectifier provided at a front end of the DC input terminal for rectifying an AC power to convert the AC power into a DC power, and a charge capacitor provided at the front end of the DC input terminal to receive the DC power.

[6] The converter as claimed in claim 3, wherein the first capacitor includes an electrolytic capacitor having a relatively great amount of inductance components, and the second capacitor includes a non-inductive winding type capacitor, so that switching shock is reduced at the DC input terminal and the DC output terminal.

[7] The converter as claimed in claim 3, wherein elements of the converter, except for the capacitors, are prepared as a monolithic IC.

[8] The converter as claimed in claim 3, further comprising at least one charge capacitor provided between the first and second capacitors and a switching unit installed between first and second capacitors in order to switch a charging operation of the charge capacitor under a control of the switching controller, thereby reducing shock noise at input and output terminals.

[9] The converter as claimed in claim 3, wherein the switching controller includes a

V/F controller which outputs frequencies according to the DC output voltage that is provided to the V/F controller through a feed-back scheme.

[10] The converter as claimed in claim 3, wherein the switching controller includes a timer IC which outputs signals according to the DC output voltage that is provided to the timer IC a feed-back scheme.