US20010015637A1 - Power supply circuit in which ripple reducing ability is maintained even when power supply voltage drops - Google Patents
Power supply circuit in which ripple reducing ability is maintained even when power supply voltage drops Download PDFInfo
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- US20010015637A1 US20010015637A1 US09/782,426 US78242601A US2001015637A1 US 20010015637 A1 US20010015637 A1 US 20010015637A1 US 78242601 A US78242601 A US 78242601A US 2001015637 A1 US2001015637 A1 US 2001015637A1
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/12—Arrangements for reducing harmonics from ac input or output
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J1/00—Circuit arrangements for dc mains or dc distribution networks
- H02J1/10—Parallel operation of dc sources
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
- H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
- H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
- H02M3/1563—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators without using an external clock
Definitions
- the present invention relates to power supply circuits. More specifically, the present invention relates to a power supply circuit which is particularly suitable for supplying a voltage to, for example, a voltage-controlled oscillator in a cellular phone.
- FIG. 4 is a circuit diagram of a conventional power supply circuit.
- the power supply circuit includes a voltage stabilizer circuit 31 and a ripple reducing circuit 32 , each implemented in the form of an integrated circuit.
- the voltage stabilizer circuit 31 has a first voltage input terminal 31 a, a first voltage output terminal 31 b, and a first control voltage input terminal 31 c.
- a high-level control signal is applied to the first control voltage input terminal 31 c
- a voltage input to the first voltage input terminal 31 a is stabilized to a particular voltage, for example, 3 volts, before being output from the first voltage output terminal 31 b.
- the first control voltage input terminal 31 c is connected to a power supply voltage input terminal 33 .
- the power supply voltage input terminal 33 is supplied with a voltage, for example, 3.6 volts, from a power supply (not shown), for example, a battery.
- the ripple reducing circuit 32 has a second voltage input terminal 32 a, a second voltage output terminal 32 b, and a second control voltage input terminal 32 c.
- a high-level control voltage is applied to the second control voltage input terminal 32 c, a voltage input to the second voltage input terminal 32 a is caused to have reduced ripple before being output from the second voltage output terminal 32 b.
- the second control voltage input terminal 32 c is connected to the power supply voltage input terminal 33 .
- the second voltage input terminal 32 a is connected to the first voltage output terminal 31 b of the voltage stabilizer circuit 31 .
- the second voltage output terminal 32 b is connected to a load voltage output terminal 34 .
- the load voltage output terminal 34 is connected to a load (not shown), for example, a voltage-controlled oscillator.
- the minimal voltage drop between the first voltage input terminal 31 a and the first voltage output terminal 31 b of the voltage stabilizer circuit 31 is on the order of 0.15 volt.
- a voltage of 3 volts is constantly output from the first voltage output terminal 31 b; however, when the power supply voltage is below 3.15 volts, a voltage which is 0.15 volt lower than the power supply voltage is output from the first voltage output terminal 31 b.
- the minimal voltage drop between the second voltage input terminal 32 a and the second voltage output terminal 32 b of the ripple reducing circuit 32 is on the order of 0.25 volt.
- a voltage which is 0.25 volt lower than a voltage input to the second voltage input terminal 32 a is output from the second voltage output terminal 32 b.
- the battery is often used for a period long enough to render the output voltage of the voltage stabilizer circuit 31 lower than the rated voltage (3 volts), for example, as low as 2.5 volts.
- the voltage stabilizer circuit 31 When the voltage stabilizer circuit 31 outputs a voltage below the rated voltage, the voltage stabilizer circuit 31 diminishes its ability to reduce ripple, as shown in FIG. 5, increasing ripple which enters the ripple reducing circuit 32 . Then, the ripple reducing circuit 32 fails to sufficiently remove the ripple, thus outputting a voltage containing considerable ripple to the load voltage output terminal 34 .
- the present invention provides a power supply circuit including a power supply voltage input terminal; a load voltage output terminal; a voltage stabilizer circuit having a first voltage input terminal and a first voltage output terminal, which stabilizes a voltage input to the first voltage input terminal and which outputs a rated voltage from the first voltage output terminal; and a ripple reducing circuit having a second voltage input terminal and a second voltage output terminal, which reduces ripple in a voltage input to the second voltage input terminal and outputs from the second voltage output terminal.
- the first voltage input terminal and the second voltage input terminal are connected to the power supply voltage input terminal, while the first voltage output terminal and the second voltage output terminal are connected to the load voltage output terminal.
- the voltage stabilizer circuit is activated when a power supply voltage input to the power supply voltage input terminal is a predetermined value or higher, while the ripple reducing circuit is activated when the power supply voltage is lower than the predetermined value.
- the voltage stabilizer circuit further has a first control voltage input terminal to which a high-level control signal for activating the voltage stabilizer circuit is applied, while the ripple reducing circuit further has a second control voltage input terminal to which a high-level control signal for activating the ripple reducing circuit is applied.
- the power supply voltage input terminal and the first control voltage input terminal are connected via a first switching device, while the power supply voltage input terminal and the second control voltage input terminal are connected via a second switching device.
- the first switching device is turned on and the second switching device is turned off when the power supply voltage is the predetermined value or higher, while the first switching device is turned off and the second switching device is turned on when the power supply voltage is lower than the predetermined value.
- the power supply circuit further includes a voltage divider circuit for dividing a voltage output from the first voltage output terminal to produce a divided voltage.
- the first switching device is implemented by a first PNP transistor and the second switching device is implemented by a second PNP transistor, the emitters of each of the first and second PNP transistors being connected to the power supply voltage input terminal, the collector of the first PNP transistor being connected to the first control voltage input terminal and to the base of the second PNP transistor, the collector of the second PNP transistor being connected to the second control voltage input terminal.
- the divided voltage is applied to the base of the first PNP transistor, the divided voltage being so determined that the first PNP transistor is turned on when the power supply voltage is the predetermined value or higher and is turned off when the power supply voltage is lower than the predetermined value.
- the predetermined value of the power supply voltage is the sum of the rated voltage of the voltage stabilizer circuit and a voltage drop between the second voltage input terminal and the second voltage output terminal of the ripple reducing circuit.
- FIG. 1 is a circuit diagram of a power supply circuit according to an embodiment of the present invention
- FIG. 2 is a graph showing input-output characteristics of the power supply circuit according to the embodiment
- FIG. 3 is a graph showing ripple reduction characteristics of the power supply circuit according to the embodiment.
- FIG. 4 is a circuit diagram of a conventional power supply circuit
- FIG. 5 is a graph showing ripple reduction characteristics of the conventional power supply circuit.
- FIG. 1 is a circuit diagram of a power supply circuit according to the preferred embodiment.
- the power supply circuit includes a voltage stabilizer circuit 1 implemented in the form of an integrated circuit.
- the voltage stabilizer circuit has a first voltage input terminal 1 a, a first voltage output terminal 1 b, and a first control voltage input terminal 1 c.
- a high-level control voltage is applied to the first control voltage input terminal 1 c, a voltage input to the first voltage input terminal 1 a is stabilized to a particular voltage before being output from the first voltage output terminal 1 b.
- the output voltage is substantially free of ripple.
- the minimal voltage drop between the first voltage input terminal 1 a and the first voltage output terminal 1 b of the voltage stabilizer circuit 1 is on the order of 0.15 volt.
- the rated output voltage to be output from the first voltage output terminal 1 b is 3 volts
- the rated output voltage i.e., 3 volts
- the voltage which is input to the first voltage input terminal 1 a is 3.15 volts or higher
- the rated output voltage i.e., 3 volts
- the first voltage input terminal 1 a is connected to a power supply voltage input terminal 2
- the first voltage output terminal 1 b is connected to a load voltage output terminal 3 .
- the power supply voltage input terminal 2 is supplied with a voltage, for example, 3 volts, from a power supply (not shown), for example, a battery.
- the load voltage output terminal 3 is connected to a load (not shown), for example, a voltage-controlled oscillator.
- a first PNP transistor 4 as first switching means.
- the emitter of the first PNP transistor 4 is connected to the power supply voltage input terminal 2
- the collector of the PNP transistor 4 is connected to the first control voltage input terminal 1 c.
- a voltage divider circuit 5 constituted of two resistors 5 a and 5 b connected in series with each other.
- a divided voltage obtained by the voltage divider circuit 5 i.e., a voltage at the node between the resistors 5 a and 5 b, is supplied to the base of the first PNP transistor 4 .
- the power supply circuit also includes a ripple reducing circuit 6 implemented in the form of an IC.
- the ripple reducing circuit 6 has a second voltage input terminal 6 a, a second voltage output terminal 6 b, a second control voltage input terminal 6 c.
- a high-level control voltage is applied to the second control voltage input terminal 6 c, a voltage input to the second voltage input terminal 6 a is caused to have reduced ripple before being output from the second voltage output terminal 6 b.
- the minimal voltage drop between the second voltage input terminal 6 a and the second voltage output terminal 6 b is on the order of 0.25 volt.
- a voltage output from the second voltage output terminal 6 b is always 0.25 volt lower than the voltage input to the second voltage input terminal 6 a.
- the second voltage input terminal 6 a is connected to the power supply voltage input terminal 2 , and the second voltage output terminal 6 b is connected to the load voltage output terminal 3 .
- a second PNP transistor 7 as second switching means.
- the emitter of the second PNP transistor 7 is connected the power supply voltage input terminal 2
- the collector of the second PNP transistor is connected to the second control voltage input terminal 6 c.
- the base of the PNP transistor 7 is connected to the first control voltage input terminal 1 c of the voltage stabilizer circuit 1 , and is connected via a resistor 8 to the ground.
- the collector of the second PNP transistor is also connected to the ground via a resistor 9 .
- the ripple reducing circuit 6 is provided with a filter 10 for reducing ripple.
- the minimal voltage drop in the voltage stabilizer circuit 1 is 0.15 volt
- ripple tends to appear in the voltage output from the first voltage output terminal 1 b.
- the input voltage should be maintained above a level which is on the order of 0.25 volt higher than the rated voltage in order that the voltage stabilizer circuit 1 exhibits a ripple reducing ability equivalent to that of the ripple reducing circuit 6 .
- the divided voltage of the voltage divider circuit 5 is so determined that the first PNP transistor 4 is turned on until the voltage on the first voltage input terminal 1 a drops to 3.25 volts and is turned off when the voltage is below 3.25 volts; thus, the divided voltage is set to 2.55 (3.25 ⁇ 0.7) volts.
- the first PNP transistor 4 remains turned on until the power supply voltage drops to 3.25 volts; accordingly, a voltage substantially equivalent to the power supply voltage, i.e., a high-level signal, is applied to the first control voltage input terminal 1 c.
- the rated voltage i.e., 3 volts
- the second PNP transistor 7 is turned off.
- a low-level signal (0 volt) is applied to the second control voltage input terminal 6 c, inhibiting the output of voltage from the second voltage output terminal 6 b.
- the rated output voltage i.e., 3 volts
- the impedance at the second voltage output terminal 6 b is very high; thus, the voltage output from the first voltage output terminal 1 b is prevented from being applied to the second voltage output terminal 6 b.
- the first PNP transistor 4 is turned off. Then, the voltage at the first control voltage input terminal 1 c of the voltage stabilizer circuit 1 falls to a low level (0 volt), inhibiting the output of voltage from the first voltage output terminal 1 b. Meanwhile, the second PNP transistor 7 is turned on. Thus, a voltage substantially equivalent to the power supply voltage, i.e., a high-level signal, is applied to the second control voltage input terminal 6 c of the ripple reducing circuit. Accordingly, a voltage which is substantially free of ripple is output from the second voltage output terminal 6 b. In this state, the impedance at the first voltage output terminal 1 b of the voltage stabilizer circuit 1 is very high; thus, the voltage output from the second voltage output terminal 6 b is prevented from being applied to the first voltage output terminal 1 b.
- the output voltage i.e., voltage on the load voltage output terminal 3
- the input voltage i.e., power supply voltage
- ripple is reduced in the voltage stabilizer circuit 1 until the input voltage drops to 3.25 volts, and is reduced in the ripple reducing circuit 6 when the input voltage is below 3.25 volts.
- the voltage output to the load voltage output terminal 3 is substantially free of ripple, although the voltage is somewhat lower. If, for example, a voltage-controlled oscillator is connected as the load, a voltage on the order of 2.75 volts is sufficient for satisfactory performance. Thus, the battery can be used for a longer period, in this case, until the battery voltage drops to 3 volts.
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Abstract
A power supply circuit includes a power supply voltage input terminal; a load voltage output terminal; a voltage stabilizer circuit having a first voltage input terminal and a first voltage output terminal, which stabilizes a voltage input to the first voltage input terminal and which outputs a rated voltage from the first voltage output terminal; and a ripple reducing circuit having a second voltage input terminal and a second voltage output terminal, which reduces ripple in a voltage input to the second voltage input terminal and outputs from the second voltage output terminal. The first voltage input terminal and the second voltage input terminal are connected to the power supply voltage input terminal, while the first voltage output terminal and the second voltage output terminal are connected to the load voltage output terminal. The voltage stabilizer circuit is activated when a power supply voltage input to the power supply voltage input terminal is a predetermined value or higher, while the ripple reducing circuit is activated when the power supply voltage is lower than the predetermined value.
Description
- 1. Field of the Invention
- The present invention relates to power supply circuits. More specifically, the present invention relates to a power supply circuit which is particularly suitable for supplying a voltage to, for example, a voltage-controlled oscillator in a cellular phone.
- 2. Description of the Related Art
- FIG. 4 is a circuit diagram of a conventional power supply circuit. The power supply circuit includes a
voltage stabilizer circuit 31 and a ripple reducing circuit 32, each implemented in the form of an integrated circuit. Thevoltage stabilizer circuit 31 has a firstvoltage input terminal 31 a, a firstvoltage output terminal 31 b, and a first controlvoltage input terminal 31 c. When a high-level control signal is applied to the first controlvoltage input terminal 31 c, a voltage input to the firstvoltage input terminal 31 a is stabilized to a particular voltage, for example, 3 volts, before being output from the firstvoltage output terminal 31 b. The first controlvoltage input terminal 31 c is connected to a power supplyvoltage input terminal 33. The power supplyvoltage input terminal 33 is supplied with a voltage, for example, 3.6 volts, from a power supply (not shown), for example, a battery. - The ripple reducing circuit32 has a second
voltage input terminal 32 a, a second voltage output terminal 32 b, and a second control voltage input terminal 32 c. When a high-level control voltage is applied to the second control voltage input terminal 32 c, a voltage input to the secondvoltage input terminal 32 a is caused to have reduced ripple before being output from the second voltage output terminal 32 b. The second control voltage input terminal 32 c is connected to the power supplyvoltage input terminal 33. The secondvoltage input terminal 32 a is connected to the firstvoltage output terminal 31 b of thevoltage stabilizer circuit 31. The second voltage output terminal 32 b is connected to a loadvoltage output terminal 34. The loadvoltage output terminal 34 is connected to a load (not shown), for example, a voltage-controlled oscillator. - In accordance with the above configuration, the minimal voltage drop between the first
voltage input terminal 31 a and the firstvoltage output terminal 31 b of thevoltage stabilizer circuit 31 is on the order of 0.15 volt. Thus, when the power supply voltage is 3.15 volts or higher, a voltage of 3 volts is constantly output from the firstvoltage output terminal 31 b; however, when the power supply voltage is below 3.15 volts, a voltage which is 0.15 volt lower than the power supply voltage is output from the firstvoltage output terminal 31 b. - The minimal voltage drop between the second
voltage input terminal 32 a and the second voltage output terminal 32 b of the ripple reducing circuit 32 is on the order of 0.25 volt. Thus, a voltage which is 0.25 volt lower than a voltage input to the secondvoltage input terminal 32 a is output from the second voltage output terminal 32 b. - When the power supply circuit is used in, for example, a cellular phone, the battery is often used for a period long enough to render the output voltage of the
voltage stabilizer circuit 31 lower than the rated voltage (3 volts), for example, as low as 2.5 volts. - When the
voltage stabilizer circuit 31 outputs a voltage below the rated voltage, thevoltage stabilizer circuit 31 diminishes its ability to reduce ripple, as shown in FIG. 5, increasing ripple which enters the ripple reducing circuit 32. Then, the ripple reducing circuit 32 fails to sufficiently remove the ripple, thus outputting a voltage containing considerable ripple to the loadvoltage output terminal 34. - Consequently, C/N ratio decreases for signals generated by the voltage-controlled oscillator (or other types of signal generator) connected to the load voltage output terminal, thereby degrading performance of the cellular phone.
- Accordingly, it is an object of the present invention to provide a power supply circuit in which the ripple reducing ability is maintained even when an output of a voltage stabilizer circuit in the power supply circuit drops below a rated voltage due to a decrease in power supply voltage.
- To this end, the present invention provides a power supply circuit including a power supply voltage input terminal; a load voltage output terminal; a voltage stabilizer circuit having a first voltage input terminal and a first voltage output terminal, which stabilizes a voltage input to the first voltage input terminal and which outputs a rated voltage from the first voltage output terminal; and a ripple reducing circuit having a second voltage input terminal and a second voltage output terminal, which reduces ripple in a voltage input to the second voltage input terminal and outputs from the second voltage output terminal. In the power supply circuit, the first voltage input terminal and the second voltage input terminal are connected to the power supply voltage input terminal, while the first voltage output terminal and the second voltage output terminal are connected to the load voltage output terminal. The voltage stabilizer circuit is activated when a power supply voltage input to the power supply voltage input terminal is a predetermined value or higher, while the ripple reducing circuit is activated when the power supply voltage is lower than the predetermined value.
- Preferably, in the power supply circuit, the voltage stabilizer circuit further has a first control voltage input terminal to which a high-level control signal for activating the voltage stabilizer circuit is applied, while the ripple reducing circuit further has a second control voltage input terminal to which a high-level control signal for activating the ripple reducing circuit is applied. The power supply voltage input terminal and the first control voltage input terminal are connected via a first switching device, while the power supply voltage input terminal and the second control voltage input terminal are connected via a second switching device. The first switching device is turned on and the second switching device is turned off when the power supply voltage is the predetermined value or higher, while the first switching device is turned off and the second switching device is turned on when the power supply voltage is lower than the predetermined value.
- More preferably, the power supply circuit further includes a voltage divider circuit for dividing a voltage output from the first voltage output terminal to produce a divided voltage. The first switching device is implemented by a first PNP transistor and the second switching device is implemented by a second PNP transistor, the emitters of each of the first and second PNP transistors being connected to the power supply voltage input terminal, the collector of the first PNP transistor being connected to the first control voltage input terminal and to the base of the second PNP transistor, the collector of the second PNP transistor being connected to the second control voltage input terminal. The divided voltage is applied to the base of the first PNP transistor, the divided voltage being so determined that the first PNP transistor is turned on when the power supply voltage is the predetermined value or higher and is turned off when the power supply voltage is lower than the predetermined value.
- More preferably, in the power supply circuit, the predetermined value of the power supply voltage is the sum of the rated voltage of the voltage stabilizer circuit and a voltage drop between the second voltage input terminal and the second voltage output terminal of the ripple reducing circuit.
- Thus, even when the power supply voltage drops to such an extent that the voltage stabilizer circuit no longer outputs a rated voltage, a voltage substantially free of ripple is output from the ripple reducing circuit, which serves to expand the life of a battery for the power supply. In accordance with the decrease in the power supply voltage, the voltage stabilizer circuit and the ripple reducing circuit are automatically switched therebetween for operation, without changing the output voltage of the power supply circuit at the time of switching.
- FIG. 1 is a circuit diagram of a power supply circuit according to an embodiment of the present invention;
- FIG. 2 is a graph showing input-output characteristics of the power supply circuit according to the embodiment;
- FIG. 3 is a graph showing ripple reduction characteristics of the power supply circuit according to the embodiment;
- FIG. 4 is a circuit diagram of a conventional power supply circuit; and
- FIG. 5 is a graph showing ripple reduction characteristics of the conventional power supply circuit.
- A preferred embodiment of the present invention will now be described with reference to the accompanying drawings.
- FIG. 1 is a circuit diagram of a power supply circuit according to the preferred embodiment. Referring to FIG. 1, the power supply circuit includes a
voltage stabilizer circuit 1 implemented in the form of an integrated circuit. The voltage stabilizer circuit has a firstvoltage input terminal 1 a, a firstvoltage output terminal 1 b, and a first controlvoltage input terminal 1 c. When a high-level control voltage is applied to the first controlvoltage input terminal 1 c, a voltage input to the firstvoltage input terminal 1 a is stabilized to a particular voltage before being output from the firstvoltage output terminal 1 b. The output voltage is substantially free of ripple. - The minimal voltage drop between the first
voltage input terminal 1 a and the firstvoltage output terminal 1 b of thevoltage stabilizer circuit 1 is on the order of 0.15 volt. Thus, assuming that the rated output voltage to be output from the firstvoltage output terminal 1 b is 3 volts, if the voltage which is input to the firstvoltage input terminal 1 a is 3.15 volts or higher, the rated output voltage, i.e., 3 volts, is output from the firstvoltage output terminal 1 b; on the other hand, if the voltage which is input to the firstvoltage input terminal 1 a is lower than 3 volts, a voltage which is 0.15 volt lower than the input voltage is output from the firstvoltage output terminal 1 b. - The first
voltage input terminal 1 a is connected to a power supplyvoltage input terminal 2, and the firstvoltage output terminal 1 b is connected to a loadvoltage output terminal 3. The power supplyvoltage input terminal 2 is supplied with a voltage, for example, 3 volts, from a power supply (not shown), for example, a battery. The loadvoltage output terminal 3 is connected to a load (not shown), for example, a voltage-controlled oscillator. Between the power supplyvoltage input terminal 2 and the first controlvoltage input terminal 1 c, there is provided afirst PNP transistor 4 as first switching means. The emitter of thefirst PNP transistor 4 is connected to the power supplyvoltage input terminal 2, and the collector of thePNP transistor 4 is connected to the first controlvoltage input terminal 1 c. Between the firstvoltage output terminal 1 b and the ground, there is provided avoltage divider circuit 5 constituted of tworesistors voltage divider circuit 5, i.e., a voltage at the node between theresistors first PNP transistor 4. - The power supply circuit also includes a
ripple reducing circuit 6 implemented in the form of an IC. Theripple reducing circuit 6 has a secondvoltage input terminal 6 a, a secondvoltage output terminal 6 b, a second controlvoltage input terminal 6 c. When a high-level control voltage is applied to the second controlvoltage input terminal 6 c, a voltage input to the secondvoltage input terminal 6 a is caused to have reduced ripple before being output from the secondvoltage output terminal 6 b. The minimal voltage drop between the secondvoltage input terminal 6 a and the secondvoltage output terminal 6 b is on the order of 0.25 volt. Thus, a voltage output from the secondvoltage output terminal 6 b is always 0.25 volt lower than the voltage input to the secondvoltage input terminal 6 a. The secondvoltage input terminal 6 a is connected to the power supplyvoltage input terminal 2, and the secondvoltage output terminal 6 b is connected to the loadvoltage output terminal 3. Between the power supplyvoltage input terminal 2 and the second controlvoltage input terminal 6 c, there is provided a second PNP transistor 7 as second switching means. The emitter of the second PNP transistor 7 is connected the power supplyvoltage input terminal 2, and the collector of the second PNP transistor is connected to the second controlvoltage input terminal 6 c. - The base of the PNP transistor7 is connected to the first control
voltage input terminal 1 c of thevoltage stabilizer circuit 1, and is connected via a resistor 8 to the ground. The collector of the second PNP transistor is also connected to the ground via aresistor 9. Theripple reducing circuit 6 is provided with afilter 10 for reducing ripple. - Although the minimal voltage drop in the
voltage stabilizer circuit 1 is 0.15 volt, when the voltage input to the firstvoltage input terminal 1 a is on the order of 0.15 volt higher than the rated voltage, ripple tends to appear in the voltage output from the firstvoltage output terminal 1 b. The input voltage should be maintained above a level which is on the order of 0.25 volt higher than the rated voltage in order that thevoltage stabilizer circuit 1 exhibits a ripple reducing ability equivalent to that of theripple reducing circuit 6. - Accordingly, the divided voltage of the
voltage divider circuit 5 is so determined that thefirst PNP transistor 4 is turned on until the voltage on the firstvoltage input terminal 1 a drops to 3.25 volts and is turned off when the voltage is below 3.25 volts; thus, the divided voltage is set to 2.55 (3.25−0.7) volts. - In accordance with the above configuration, the
first PNP transistor 4 remains turned on until the power supply voltage drops to 3.25 volts; accordingly, a voltage substantially equivalent to the power supply voltage, i.e., a high-level signal, is applied to the first controlvoltage input terminal 1 c. Thus, the rated voltage, i.e., 3 volts, is output from the firstvoltage output terminal 1 b. Meanwhile, the second PNP transistor 7 is turned off. Thus, a low-level signal (0 volt) is applied to the second controlvoltage input terminal 6 c, inhibiting the output of voltage from the secondvoltage output terminal 6 b. Accordingly, the rated output voltage, i.e., 3 volts, is fed from the firstvoltage output terminal 1 b of thevoltage stabilizer circuit 1 to the load (not shown). In this state, the impedance at the secondvoltage output terminal 6 b is very high; thus, the voltage output from the firstvoltage output terminal 1 b is prevented from being applied to the secondvoltage output terminal 6 b. - On the other hand, when the power supply voltage drops below 3.25 volts, the
first PNP transistor 4 is turned off. Then, the voltage at the first controlvoltage input terminal 1 c of thevoltage stabilizer circuit 1 falls to a low level (0 volt), inhibiting the output of voltage from the firstvoltage output terminal 1 b. Meanwhile, the second PNP transistor 7 is turned on. Thus, a voltage substantially equivalent to the power supply voltage, i.e., a high-level signal, is applied to the second controlvoltage input terminal 6 c of the ripple reducing circuit. Accordingly, a voltage which is substantially free of ripple is output from the secondvoltage output terminal 6 b. In this state, the impedance at the firstvoltage output terminal 1 b of thevoltage stabilizer circuit 1 is very high; thus, the voltage output from the secondvoltage output terminal 6 b is prevented from being applied to the firstvoltage output terminal 1 b. - When operation switches from the
voltage stabilizer circuit 1 to theripple reducing circuit 6 at a power supply voltage of 3.25 volts, since the voltage drop in theripple reducing circuit 6 is 0.25 volt, theripple reducing circuit 6 outputs a voltage of 3 volts, which is equivalent to the voltage output from thevoltage stabilizer circuit 1 before operation is switched. Thus, output voltage of the power supply circuit does not change at the time of switching. - When the power supply voltage is below 3.25 volts, a voltage which is 0.25 volt lower than the power supply voltage is output from the second
voltage output terminal 6 b. - As shown in FIG. 2, the output voltage (i.e., voltage on the load voltage output terminal3) is constantly 3 volts until the input voltage (i.e., power supply voltage) drops to 3.25 volts, and is 0.25 volt lower than the input voltage when the input voltage is below 3.25 volts.
- As shown in FIG. 3, ripple is reduced in the
voltage stabilizer circuit 1 until the input voltage drops to 3.25 volts, and is reduced in theripple reducing circuit 6 when the input voltage is below 3.25 volts. - Accordingly, even when the power supply voltage, for example, from a battery, drops to on the order of 3 volts, the voltage output to the load
voltage output terminal 3 is substantially free of ripple, although the voltage is somewhat lower. If, for example, a voltage-controlled oscillator is connected as the load, a voltage on the order of 2.75 volts is sufficient for satisfactory performance. Thus, the battery can be used for a longer period, in this case, until the battery voltage drops to 3 volts.
Claims (6)
1. A power supply circuit comprising:
a power supply voltage input terminal;
a load voltage output terminal;
a voltage stabilizer circuit having a first voltage input terminal and a first voltage output terminal, which stabilizes a voltage input to said first voltage input terminal and which outputs a rated voltage from said first voltage output terminal; and
a ripple reducing circuit having a second voltage input terminal and a second voltage output terminal, which reduces ripple in a voltage input to said second voltage input terminal and outputs from said second voltage output terminal,
wherein said first voltage input terminal and said second voltage input terminal are connected to said power supply voltage input terminal, while said first voltage output terminal and said second voltage output terminal are connected to said load voltage output terminal, and wherein said voltage stabilizer circuit is activated when a power supply voltage input to said power supply voltage input terminal is a predetermined value or higher, while said ripple reducing circuit is activated when said power supply voltage is lower than said predetermined value.
2. A power supply circuit according to , wherein said voltage stabilizer circuit further has a first control voltage input terminal to which a high-level control signal for activating said voltage stabilizer circuit is applied, while said ripple reducing circuit further has a second control voltage input terminal to which a high-level control signal for activating said ripple reducing circuit is applied, wherein said power supply voltage input terminal and said first control voltage input terminal are connected via first switching means, while said power supply voltage input terminal and said second control voltage input terminal are connected via second switching means, and wherein said first switching means is turned on and said second switching means is turned off when said power supply voltage is said predetermined value or higher, while said first switching means is turned off and said second switching means is turned on when said power supply voltage is lower than said predetermined value.
claim 1
3. A power supply circuit according to , further comprising:
claim 1
a voltage divider circuit for dividing a voltage output from said first voltage output terminal to output a divided voltage,
wherein said first switching means is implemented by a first PNP transistor and said second switching means is implemented by a second PNP transistor, the emitters of each of said first and second PNP transistors being connected to said power supply voltage input terminal, the collector of said first PNP transistor being connected to said first control voltage input terminal and to the base of said second PNP transistor, the collector of said second PNP transistor being connected to said second control voltage input terminal, and wherein said divided voltage is applied to the base of said first PNP transistor, said divided voltage being so determined that said first PNP transistor is turned on when said power supply voltage is said predetermined value or higher and is turned off when said power supply voltage is lower than said predetermined value.
4. A power supply circuit according to , wherein said predetermined value of said power supply voltage is the sum of said rated voltage of said voltage stabilizer circuit and a voltage drop between said second voltage input terminal and said second voltage output terminal of said ripple reducing circuit.
claim 1
5. A power supply circuit according to , wherein said predetermined value of said power supply voltage is the sum of said rated voltage of said voltage stabilizer circuit and a voltage drop between said second voltage input terminal and said second voltage output terminal of said ripple reducing circuit.
claim 2
6. A power supply circuit according to , wherein said predetermined value of said power supply voltage is the sum of said rated voltage of said voltage stabilizer circuit and a voltage drop between said second voltage input terminal and said second voltage output terminal of said ripple reducing circuit.
claim 3
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2000-048975 | 2000-02-21 | ||
JP2000048975A JP2001236130A (en) | 2000-02-21 | 2000-02-21 | Power supply circuit |
Publications (2)
Publication Number | Publication Date |
---|---|
US20010015637A1 true US20010015637A1 (en) | 2001-08-23 |
US6445166B2 US6445166B2 (en) | 2002-09-03 |
Family
ID=18570976
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US09/782,426 Expired - Fee Related US6445166B2 (en) | 2000-02-21 | 2001-02-13 | Power supply circuit in which ripple reducing ability is maintained even when power supply voltage drops |
Country Status (5)
Country | Link |
---|---|
US (1) | US6445166B2 (en) |
EP (1) | EP1128533A3 (en) |
JP (1) | JP2001236130A (en) |
KR (1) | KR100393536B1 (en) |
CN (1) | CN1156986C (en) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN102214996A (en) * | 2011-05-03 | 2011-10-12 | 深圳可立克科技股份有限公司 | Micro-voltage-difference linear voltage-stabilizing power circuit |
WO2014013292A1 (en) * | 2012-07-19 | 2014-01-23 | Freescale Semiconductor, Inc. | System on a chip, apparatus and method for voltage ripple reduction on a power supply line of an integrated circuit device operable in at least two modes |
CN105353816A (en) * | 2014-08-20 | 2016-02-24 | 联想(北京)有限公司 | Method for stabilizing power supply, power supply and electronic device |
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JP4726460B2 (en) * | 2004-10-22 | 2011-07-20 | 株式会社リコー | Constant voltage power circuit |
US7233130B1 (en) * | 2005-08-05 | 2007-06-19 | Rf Micro Devices, Inc. | Active ripple reduction switched mode power supplies |
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US8564256B2 (en) * | 2009-11-18 | 2013-10-22 | Silicon Laboratories, Inc. | Circuit devices and methods of providing a regulated power supply |
JP2013181831A (en) | 2012-03-01 | 2013-09-12 | Advantest Corp | Test device |
CN106300971A (en) * | 2016-08-29 | 2017-01-04 | 合肥惠科金扬科技有限公司 | A kind of driving mu balanced circuit of liquid crystal display module |
CN106208691A (en) * | 2016-08-29 | 2016-12-07 | 合肥惠科金扬科技有限公司 | A kind of liquid crystal display screen power supply |
CN106130345A (en) * | 2016-08-29 | 2016-11-16 | 合肥惠科金扬科技有限公司 | A kind of anti-power failure liquid crystal display screen power supply |
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DE3804252C1 (en) * | 1988-02-11 | 1989-05-24 | Siemens Ag, 1000 Berlin Und 8000 Muenchen, De | Low-loss voltage comparator |
US5126652A (en) * | 1991-04-15 | 1992-06-30 | Square D Company | Universal input voltage power supply |
JPH07110132B2 (en) * | 1991-08-22 | 1995-11-22 | 日本モトローラ株式会社 | Voltage converter |
JP3444903B2 (en) | 1992-02-27 | 2003-09-08 | 富士通株式会社 | Power supply switching circuit for mobile phones |
JP3747381B2 (en) * | 1994-11-10 | 2006-02-22 | 富士通株式会社 | Power supply control circuit for electronic devices with built-in batteries |
US5929606A (en) * | 1997-08-29 | 1999-07-27 | Compaq Computer Corporation | Ripple-suppressed converting battery module |
FR2768527B1 (en) * | 1997-09-18 | 2000-07-13 | Sgs Thomson Microelectronics | VOLTAGE REGULATOR |
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-
2000
- 2000-02-21 JP JP2000048975A patent/JP2001236130A/en not_active Withdrawn
-
2001
- 2001-01-31 EP EP01300834A patent/EP1128533A3/en not_active Withdrawn
- 2001-02-13 CN CNB011018895A patent/CN1156986C/en not_active Expired - Fee Related
- 2001-02-13 US US09/782,426 patent/US6445166B2/en not_active Expired - Fee Related
- 2001-02-20 KR KR10-2001-0008450A patent/KR100393536B1/en not_active IP Right Cessation
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN102214996A (en) * | 2011-05-03 | 2011-10-12 | 深圳可立克科技股份有限公司 | Micro-voltage-difference linear voltage-stabilizing power circuit |
WO2014013292A1 (en) * | 2012-07-19 | 2014-01-23 | Freescale Semiconductor, Inc. | System on a chip, apparatus and method for voltage ripple reduction on a power supply line of an integrated circuit device operable in at least two modes |
US9337717B2 (en) | 2012-07-19 | 2016-05-10 | Freescale Semiconductor, Inc. | System on a chip, apparatus and method for voltage ripple reduction on a power supply line of an integrated circuit device operable in at least two modes |
CN105353816A (en) * | 2014-08-20 | 2016-02-24 | 联想(北京)有限公司 | Method for stabilizing power supply, power supply and electronic device |
Also Published As
Publication number | Publication date |
---|---|
CN1310522A (en) | 2001-08-29 |
JP2001236130A (en) | 2001-08-31 |
KR20010083199A (en) | 2001-08-31 |
US6445166B2 (en) | 2002-09-03 |
KR100393536B1 (en) | 2003-08-02 |
EP1128533A3 (en) | 2003-12-10 |
CN1156986C (en) | 2004-07-07 |
EP1128533A2 (en) | 2001-08-29 |
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