A DC/DC converter for outputting multiple signals

Abstract: The present invention relates to a DC/DC converter for outputting multiple signals that may produce more than two types of direct current output voltage using one pulse width modulating integrated circuit. The DC/DC converter for outputting multiple signals comprises a voltage regulator having an inductor of which charge or discharge is controlled by a switching signal generated from a pulse width modulating part, and having a condenser charged with the current which is charged in the inductor when the inductor is discharged; an output voltage sensing part capable of detecting and adjusting a level of output voltage of the voltage regulator; and an output feedback part for cutting off charge or discharge of the inductor according to a signal of the output voltage sensing part when the output voltage of the voltage regulator detected by the output voltage sensing part is beyond a predetermined level and making the condenser charged according to a switching signal from a pulse width modulating part when a level of output voltage of the voltage regulator is below a predetermined level.

Description: The present invention relates to a DC/DC converter More particularly, it relates to a DC/DC converter that may provide more than two types of output voltages by means of a pulse width modulating integrated circuit by detecting a level of output voltage to feedback, control and adjust the level of output voltage. A power supply is generally characterized as a linear power supply using a transformer having a predetermined turns ratio and a switching mode power supply having a switching method using a power transistor, in accordance with the operating principle. Although the switching mode power supply has a complicated circuit mechanism compared to the linear power supply, it is widely used as a power system of various small-sized electronic apparatus since the switching mode power supply has advantages of small size, light weight and high power density and so forth. That is because a pulse width modulating integrated circuit generating a switching waveform has been improved. Recently, as the demand for portable electronic apparatus has been increased, a DC/DC converter using a switching mode power supply that can make many types of voltages of a single power voltage of 5V or 3.3V is required. Fig. 1 is a detailed circuit diagram showing a conventional DC/DC converter. The following description is about the conventional DC/DC converter shown in FIG. 1. A power signal VCC applied to emitter of transistor Q1 is switched in accordance with a switching signal of pulse width modulating integrated circuit VPWM applied to base of transistor Q1, and the switched signal is input to base of transistor Q2 to control turn-on and turn-off operation of transistor Q2. When transistor Q2 is turned on, a circuit in which the power signal VCC is applied to transistor Q2 through inductor L is formed. At that time, inductor L is charged in accordance with the power signal VCC. While inductor L is charged, the charged voltage of condenser C is discharged. When transistor Q2 is turned off, a circuit in which the power signal VCC is applied to condenser C through inductor L and diode D is formed. At that time, diode D is turned on by instantaneous high voltage induced to inductor L and condenser C is charged with the charged current to inductor L. On the other hand, a level of output voltage of the condenser C is determined by turn-off time of transistor Q2 which is determined by turn-on time of the switching signal of pulse width modulating integrated circuit VPWM. Accordingly, the output voltage of the conventional DC/DC converter is changed according to duty ratio of the switching signal of pulse width modulating integrated circuit. Generally, the pulse width modulating integrated circuit can make one or two types of switching signal and direct current output voltage that may be generated from one pulse width modulating integrated circuit has two types at most. However, when a power supply of portable electronic apparatus is required more than three types of direct current, more than two pulse width modulating integrated circuits are needed, which increases the bulk of power supply of portable electronic apparatus and manufacturing cost. To solve conventional technical problems, it is an object of the present invention to provide a DC/DC converter that may generate more than two types of direct current output voltage using a switching signal of one pulse width modulating integrated circuit. It is another object of the present invention to provide a DC/DC converter that may produce a constant direct current output voltage by feedback and control of output voltage as well as various levels of direct current output voltage. According to the present invention there is provided a DC/DC converter for producing one voltage, selectable from more than two voltage levels, comprising: voltage regulating means having an inductor, the charge or discharge of which is controlled by a switching signal generated from a pulse width modulating means, and having a capacitor charged with current from the inductor when the inductor is discharged; output voltage sensing means for detecting and adjusting the output voltage level of the voltage regulating means; characterised by: output feedback means for cutting off the charge or discharge of the inductor according to a signal of the output voltage sensing means when the output voltage level of the voltage regulating means detected by the output voltage sensing means is beyond a predetermined level, and for charging the capacitor according to a signal from the pulse width modulating means when the output voltage level from the voltage regulating means is below a predetermined level. Further advantages and other objects of the present invention will be apparent in the following detailed description in connection with the accompanying drawings, in which: FIG. 1 is a detailed circuit diagram showing a conventional DC/DC converter; FIG. 2 is a detailed circuit diagram of a DC/DC converter for outputting multiple signals in accordance with a preferred embodiment of the present invention; FIGS. 3A to 3E are waveforms of each portion of FIG. 2; and FIG. 4 is a block diagram of a power supply having a DC/DC converter for outputting multiple signals in accordance with a preferred embodiment of the present invention. FIG. 2 is a detailed circuit diagram of a DC/DC converter for outputting different types of output voltage in accordance with a preferred embodiment of the present invention. In the inventive DC/DC converter as shown in FIG. 2, a power signal VCC is applied to inductor L connected with diode D and condenser C in series; a switching signal VPWM of pulse width modulation integrated circuit passed through resistance R5 is applied to base of transistor Q1; resistance R4 is connected to base-emitter of transistor Q1; and the power signal VCC is applied to emitter of transistor Q1. Further, two transistors Q3 and Q4 that are in Darlington connection are connected to collector of transistor Q1; two resistances R3s having the same resistance value are respectively connected to emitter-base of transistors Q3 and Q4 that are connected by Darlington method; common collector of transistors Q3 and Q4 that are connected by Darlington method is connected to base of transistor Q2 of which collector is connected to node between inductor L and diode D; and node between two resistances R1 and R2 connected with condenser C in parallel is connected with base of transistor Q4. FIGs. 3A to 3E are wave forms of each portion of the DC/DC converter in accordance with the preferred embodiment of the present invention. FIGS. 3A and 3B have a common time scale and FIGS. 3C to 3E have another common time scale along their horizontal axes. The following description is about the operation of the inventive DC/DC converter. The power signal VCC is applied to inductor L and emitter of transistor Q1, and the switching signal of pulse width modulation integrated circuit VPWM as FIG. 3A is applied to emitter of transistor Q1 through resistance R5. The above power signal VCC is a system power of direct current applied from a battery of portable electronic apparatus. Switching signal VPWM is reversed into a level of the power signal VCC by the above transistor Q1. The switching signal VA reversed by the above transistor Q1 is as shown in FIG. 3B, and its size decreases as much as the size of voltage drop between a level of the power signal VCC and emitter-collector of transistor Q1. Two resistances R1 and R2 connected with condenser C of an output terminal are to detect the size of an output voltage VOUT3, and voltage component VB may be expressed as the equation: VB=VOUT3 X (1+R1/R2) Accordingly, voltage component VB is changed in proportion to the output voltage VOUT3 of condenser C. Two transistors Q3 and Q4 are turned on if voltage component VB-VA is greater than 2V BE , and two transistors Q3 and Q4 are turned off if VB-VA is smaller than 2V BE . The above V BE is voltage value of threshold of each transistor Q3 and Q4. Accordingly, the on/off operation of transistor Q2 is controlled by reversed switching signal VA if VB-VA is greater than 2V BE and two transistors Q3 and Q4 that are connected by Darlington method are turned on. The power signal VCC is applied to inductor L if the above transistor Q2 is turned on by reversed switching signal in FIG. 3B, and diode D is turned on by inductor L instantaneously having high voltage and condenser C is charged by voltage including the voltage supplied from inductor L, and the power signal VCC. FIG. 3C shows an on/off signal VC applied to base of transistor Q2, and FIG. 3D shows a current I L flowing through inductor L, and FIG. 3E shows an output voltage VOUT3 of condenser C. The reversed switching signal VA is applied to base of transistor Q2 if VB-VA is greater than 2V BE and two transistors Q3 and Q4 is turned on. If VB-VA is smaller than 2V BE and two transistors Q3 and Q4 is turned off, the above transistor Q2 is turned off, the power signal VCC is applied to condenser C through inductor L and diode D, and the above condenser C is charged by the power signal VCC. Accordingly, the operation for charging as much as the amount of voltage of the power signal only occurs if two transistors Q3 and Q4 are turned off. The rated output voltage of the above condenser C is the output voltage VOUT3 of condenser C in case that two transistors Q3 and Q4 that are connected by Darlington method, and the above output voltage VOUT3 of condenser C may be expressed as the equation: VOUT3=(VA+2V BE ) X (1+R1/R2) Accordingly, it is possible to control voluntarily the output voltage VOUT3 of condenser C by controlling a resistance value ratio of two resistances R1 and R2 to detect the output voltage VOUT3 of condenser C. FIG. 4 is a block diagram showing a power supply including the DC/DC converter for outputting voltages in accordance with the preferred embodiment of the present invention. In FIG. 4, first and second regulators 10 and 20 to which an output signal of 2-channel pulse width modulating part 60 is applied are relating to the conventional art, a third regulator 30, output voltage feedback part 50, and output voltage sensing part 40 are the DC/DC converter for outputting voltages in accordance with the preferred embodiment of the present invention. Two types of output voltages VOUT1 and VOUT2 are generated by the above first and second regulators 10 and 20, and another level of output voltage VOUT3 is generated by the inventive DC/DC converter of the preferred embodiment of the present invention. Additionally, it is possible to connect two DC/DC converters or more of the preferred embodiment of the present invention in parallel to the above output terminal of 2-channel pulse width modulating part to obtain more various output voltages. Accordingly, the present invention provides the DC/DC converter of which the level of the output voltage may be voluntarily controlled, thereby obtaining various levels of output voltage using a single pulse width modulating circuit. Although only a preferred embodiment of the invention has been disclosed and described, it is apparent that other embodiments of the invention are possible within the scope of the appended claims.

Claims: A DC/DC converter for producing one voltage, selectable from more than two voltage levels, comprising: voltage regulating means (30) having an inductor (L), the charge or discharge of which is controlled by a switching signal (VA) generated from a pulse width modulating means (VPWM), and having a capacitor (C) charged with current from the inductor when the inductor is discharged; output voltage sensing means (40) for detecting and adjusting the output voltage level (VOUT3) of the voltage regulating means; characterised by: output feedback means (50) for cutting off the charge or discharge of the inductor according to a signal of the output voltage sensing means (40) when the output voltage level (VOUT3) of the voltage regulating means detected by the output voltage sensing means is beyond a predetermined level, and for charging the capacitor (C) according to a signal (VA) from the pulse width modulating means when the output voltage level from the voltage regulating means is below a predetermined level. A DC/DC converter according to Claim 1, wherein said output voltage sensing means includes first and second resistances (R 1 ,R 2 ) connected in series with each other across the capacitor (C) and detects a voltage component to control an on/off operation of the output voltage feedback means, and controls an output voltage of the capacitor by controlling resistance value ratios of the first and second resistances. A DC/DC converter according to Claim 1 or Claim 2, wherein said output voltage feedback means includes first and second transistors (Q 3 ,Q 4 ) that are connected by a Darlington connection. A DC/DC converter according to any one of Claims 1 to 3, in combination with at least one further DC/DC converter of similar type, the DC/DC converters being connected to an output terminal of the pulse width modulating means, thereby forming a power supply for outputting multiple signals in which each DC/DC converter produces a different output voltage to each other. A DC/DC converter as claimed in any of the preceding claims, wherein; the pulse width modulating means generates a respective switching signal at each output terminal thereof; the voltage regulating means has a first switch element (Q 2 ) controlled by the switching signal from said pulse width modulating means, and has a selectively conductive second switch element (D) for conducting the current flowing from said inductor to charge said capacitor to generate the output voltage of said voltage regulating means thereacross; the output feedback means includes first and second transistors (Q 3 ,Q 4 ) that are connected by Darlington connection with a base electrode of said first transistor having an emitter electrode of the second transistor connected thereto, with a base electrode of said second transistor connected to receive a control voltage supplied from said output voltage sensing means (40), with an emitter electrode of said first transistor connected to receive the switching signal generated by said pulse width modulating means (VPWM) and with an interconnection of the collector electrodes of said first and second transistors connected to said first switch element for controlling the conduction thereof. A DC/DC converter according to Claim 2 or Claim 5 when dependent upon Claim 2, wherein the first and second resistances are arranged to detect at their interconnection with each other a voltage component applied to the base of said second transistor to control an on/off operation of the output voltage feedback means, and to control an output voltage across said capacitor. A DC/DC converter according to Claim 5 or to Claim 6 when dependent upon Claim 5, in combination with at least one further DC/DC converter of similar type, each of said DC converters converting from the same direct current input voltage, sharing the same pulse width modulating means, having the first switch elements in their respective voltage regulating means controlled by the same switching signal from said pulse width modulator, and differing in their output voltage sensing means to provide different independently-regulated direct-current output voltages across their respective capacitors. The DC/DC converter according to Claim 5 or to any of Claims 6 or 7 when dependent upon Claim 5, wherein said DC/DC converter has input, output and common terminals; wherein said inductor (L) has a winding with a first end connected to said input terminal and with a second end; wherein said capacitor has first and second plates respectively connected to said output terminal and to said common terminal; wherein said first switch element is a third transistor (Q 2 ) having a base electrode connected to the interconnection of the collector electrodes of said first and second transistors, having an emitter electrode connected to said common terminal, and having a collector electrode connected to the second end of said winding; and wherein said second switch element is a rectifier diode (D) having first and second electrodes connected to the second end of said winding and to said output terminal.

Inventors: MOON SEUNG HWAN, MOON, SEUNG HWAN
Applicants: SAMSUNG ELECTRONICS CO LTD, SAMSUNG ELECTRONICS CO., LTD.
Application year: 1995
Main classification: H02M3
IPC codes: H02M3