WO2008056895A1 - Circuit for output voltage error correction in smps which regulation is done by primary side control - Google Patents

Circuit for output voltage error correction in smps which regulation is done by primary side control Download PDF

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Publication number
WO2008056895A1
WO2008056895A1 PCT/KR2007/005151 KR2007005151W WO2008056895A1 WO 2008056895 A1 WO2008056895 A1 WO 2008056895A1 KR 2007005151 W KR2007005151 W KR 2007005151W WO 2008056895 A1 WO2008056895 A1 WO 2008056895A1
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WIPO (PCT)
Prior art keywords
voltage
output
current
error detection
time constant
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PCT/KR2007/005151
Other languages
French (fr)
Inventor
Chan Woong Park
Original Assignee
Chan Woong Park
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Publication date
Priority claimed from KR1020070028710A external-priority patent/KR100848685B1/en
Application filed by Chan Woong Park filed Critical Chan Woong Park
Publication of WO2008056895A1 publication Critical patent/WO2008056895A1/en

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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
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33507—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters

Definitions

  • the present invention relates to a constant- voltage error correction circuit for a primary regulation-type Switching Mode Power Supply (SMPS), which, in an inexpensive primary regulation-type SMPS, predicts variation in the load and corrects an output voltage in response to the predicted variation in the load.
  • SMPS Switching Mode Power Supply
  • an SMPS stabilizes output voltage by providing an error detection circuit in an output voltage extraction unit, detecting the error of output voltage, and feeding back detected error voltage to a power conversion unit through an optocoupler. Since this is well known, a detailed description thereof will be omitted here.
  • FIG. 1 is a diagram showing an SMPS power circuit that includes a prior art primary regulation-type output voltage stabilization circuit.
  • This primary regulation- type output voltage stabilization circuit is widely used for loads not requiring precise constant- voltage characteristics, and realizes the stabilization of output voltage by detecting voltage induced to the feedback winding T 1-3 of a transformer Tl and stabilizing the detected voltage.
  • the primary winding Tl-I of the transformer Tl is wound to be closely coupled to the secondary winding T 1-2.
  • a leakage inductance component which is not coupled to the secondary winding T 1-2, exists, and the energy stored in the leakage inductance undergoes a process of not being transferred to the secondary winding T 1-2, resonating with distributed capacity existing in the primary winding Tl-I, and extinguishing itself.
  • Both the output voltage component of the secondary winding T 1-2, attributable to the turn ratio, and a surge spike voltage component, attributable to the leakage inductance are induced to the feedback winding T 1-3 that is closely coupled to the transformer Tl.
  • FIGS. 2 and 3 are drawings illustrating examples of waveforms of voltage induced to the feedback winding T 1-3 in the output voltage stabilization circuit of FIG. 1.
  • FIG. 2 is a waveform diagram in the case of a heavy load
  • FIG. 3 is a waveform diagram in the case of a light load.
  • the period from T20 to T21 is the conduction period of the switching element U2, during which an input voltage Vi is applied to the primary winding Tl-I, and a 'negative' voltage in proportion to the turn ratio between the primary winding Tl-I and the feedback winding Tl-3 is obtained in the feedback winding Tl-3.
  • the switching element U2 is turned off at a time point T21, the winding voltage is reversed, and thus a surge voltage is generated due to the influence of the leakage inductance and reaches a peak value, and the peak value Vpeak is rectified by the diode D3, charged in the condenser C4, and is then used as a feedback value for performing voltage control.
  • the voltage charged in the condenser C4 includes an output voltage component Vo output to the secondary winding T 1-2, and a surge voltage component generated due to the leakage inductance.
  • the amount of energy stored in the primary winding Tl-I of the transformer Tl is large, and a high surge voltage is generated due to the leakage inductance.
  • the amount of energy stored in the primary winding Tl-I of the transformer Tl is small, and a low surge voltage is generated due to the leakage inductance. That is, since the surge voltage attributable to the leakage inductance varies with the magnitude of the load, variation in output voltage is inevitable in the case where control is performed such that the voltage charged in the condenser C4 is maintained at a constant value. As a result, in the case of a light load, the output voltage becomes high, while, in the case of a heavy load, the output voltage becomes low.
  • FIG. 4 is a diagram showing an SMPS power circuit including a novel primary regulation-type output voltage stabilization circuit.
  • an object of the present invention is to provide a constant- voltage error correction circuit for a primary regulation-type SMPS, which corrects a constant- voltage error that occurs in the prior art primary regulation method, thereby enabling further improved output voltage stabilization characteristics to be acquired.
  • the present invention provides a constant- voltage error correction circuit for an SMPS, the SMPS having a magnetic energy transfer element, the constant- voltage error correction circuit comprising an error detection unit for receiving detection input voltage from the winding of the magnetic energy transfer element and reference voltage and detecting the errors of output voltage of the SMPS; a time constant unit for outputting an average value of error detection voltage output from the error detection unit; and a detection input control unit for varying the detection input voltage of the error detection unit in response to the average value output from the time constant unit.
  • the present invention provides a constant- voltage error correction circuit for an SMPS, the SMPS having a magnetic energy transfer element, the constant- voltage error correction circuit comprising an error detection unit for receiving detection input voltage from the winding of the magnetic energy transfer element and reference voltage and detecting the errors of output voltage of the SMPS; a time constant unit for outputting the average value of error detection voltage output from the error detection unit; and a reference voltage control unit for varying the reference voltage of the error detection unit in response to the average value output from the time constant unit.
  • a flyback converter including one of the above-described constant- voltage error correction circuits is provided.
  • the present invention enables further improved constant- voltage characteristics to be easily acquired by predicting variation in output voltage, which is generated due to various factors, such as the influence of leakage inductance and the influence of variation in the forward voltage drop of an output diode, based on the results of experiments, and appropriately correcting the output voltage in response to the variation in the load.
  • the present invention is suitable for application to an SMPS, which does not require rapid load response characteristics because the speed of variation in the load is very low, like a battery charger.
  • FIG. 1 is a diagram of a prior art output voltage stabilization circuit for an SMPS
  • FIGS. 2 and 3 are diagrams showing the waveforms of signals in respective parts of the prior art output voltage stabilization circuit
  • FIG. 4 is a diagram showing an output voltage stabilization circuit for a novel
  • FIGS. 5 and 6 are graphs comparing the output current versus output voltage characteristics of the prior art and the present invention with each other;
  • FIGS. 7 and 8 are block diagrams showing SMPS power circuits including constant- voltage error correction circuits according to a first embodiment of the present invention
  • FIG. 9 is a diagram of a constant- voltage error correction circuit according to a second embodiment of the present invention, showing a detailed circuit diagram of the constant- voltage error correction circuits shown in FIGS. 7 and 8;
  • FIG. 10 is a diagram of a constant- voltage error correction circuit according to a third embodiment of the present invention, showing a detailed circuit diagram of the constant- voltage error correction circuits shown in FIGS. 7 and 8;
  • FIG. 11 is a diagram of a constant- voltage error correction circuit according to a fourth embodiment of the present invention, showing a detailed circuit diagram of the constant- voltage error correction circuits shown in FIGS. 7 and 8;
  • FIGS. 12 and 13 are block diagrams showing SMPS power circuits including constant- voltage error correction circuits according to a fifth embodiment of the present invention.
  • FIG. 14 is a diagram of a constant- voltage error correction circuit according to a sixth embodiment of the present invention, showing a detailed circuit diagram of the constant- voltage error correction circuits shown in FIGS. 12 and 13;
  • FIG. 15 is a diagram of a constant- voltage error correction circuit according to a seventh embodiment of the present invention, showing a detailed circuit diagram of the constant- voltage error correction circuits shown in FIGS. 12 and 13;
  • FIG. 16 is a diagram of a constant- voltage error correction circuit according to an eighth embodiment of the present invention, showing a detailed circuit diagram of the constant- voltage error correction circuits shown in FIGS. 12 and 13. Best Mode for Carrying Out the Invention
  • FIGS. 7 and 8 are block diagrams showing an SMPS power circuit including a constant- voltage error correction circuit according to a first embodiment of the present invention.
  • the representative SMPS power circuit includes a transformer Tl configured such that a primary winding Tl-I, a secondary winding T 1-2, and a feedback winding T 1-3 are closely coupled to each other, a switching element U2 connected to the primary winding Tl-I, a diode D2 and condenser C3 configured to rectify and smooth the voltage of the secondary winding T 1-2, and a clamp circuit 13 configured to suppress surge spike voltage generated due to leakage inductance.
  • the constant- voltage error correction circuits 50 and 60 of the present embodiment operate to appropriately compensate for constant- voltage errors attributable to variation in the load in the primary regulation of stabilizing an output voltage Vo using a voltage induced to the feedback winding T 1-3, thereby improving the stability of the output voltage Vo to a desired level.
  • FIG. 5 is a diagram showing the constant- voltage characteristics of the primary regulation-type SMPS.
  • the output voltage Vo in the case of a light load, the output voltage Vo is high and the error detection voltage, output from an error detection unit 12, is increased so that a small amount of energy can be output, while, in the case of a heavy load, the output voltage Vo is low and the error detection voltage, output from the error detection unit 12, is decreased so that a large amount of energy is output. Accordingly, the range of variation in output voltage due to variation in load can be significantly reduced by appropriately increasing or decreasing the detection input of the error detection unit 12 using an error detection voltage output from the error detection unit 12, or by appropriately increasing or decreasing the reference level of the error detection unit 12.
  • 60 comprises an error detection unit 12 for detecting the error of the output voltage of the primary winding Tl-I of the transformer Tl from the voltage of the feedback winding Tl-3, and a detection input conversion unit 51 or
  • the constant- voltage error correction circuits 50 and 60 are configured to vary the detection input of the error detection unit 12 using the error detection voltage output from the error detection unit 12 so that the output voltage Vo of the primary winding Tl-I varies little.
  • the error detection unit 12 of FIG. 7 is configured to detect an error using a DC voltage, which is rectified by a diode D3 and a condenser C4 and is thus smoothed, as input
  • the error detection unit 12 of FIG. 8 is configured to receive an AC voltage from the feedback winding Tl-3 of the transformer Tl without change and detect an error.
  • the output voltage Vo is high and the error detection voltage of the error detection unit 12 is increased so that a small amount of energy can be output, while, in the case of a heavy load, the output voltage Vo is low and the error detection voltage of the error detection unit 12 is decreased so that a large amount of energy is output.
  • the amount of variation in output voltage due to variation in load can be obtained using an experimental method.
  • the detection input conversion units 51 and 61 correct the amount of variation in output voltage due to variation in load by increasing the detection input voltage of the error detection unit 12 in the case of a light load and decreasing the detection input voltage of the error detection unit 12 in the case of a heavy load, in response to the error detection voltage of the error detection unit 12.
  • the detection input conversion unit 51 or 61 comprises a time constant unit 52 or
  • a detection input control unit 53 or 63 configured to control a detection input, input to the error detection unit 12, in response to the output of the time constant unit 52 or 62, and an input resistor 54 connected between the feedback winding Tl-3 and the error detection unit 12.
  • the time constant units 52 or 62 of the detection input conversion units 51 and 61 are used to prevent the above problem. Since the time constant unit 52 or 62 obtains the average value of the output voltage of the error detection unit 12 using a time constant ranging from several tens of milliseconds to several hundreds of milliseconds, the generation of oscillation can be prevented, or can be limited to a tolerable level. Although the time constant of the time constant unit 52 or 62 is generally set to a value ranging from several milliseconds to several hundreds of milliseconds, the time constant may be appropriately increased or decreased depending on the output characteristics. Mode for the Invention
  • FIG. 9 is a diagram of a constant- voltage error correction circuit according to a second embodiment of the present invention, showing a detailed circuit diagram of the constant- voltage error correction circuits shown in FIGS. 7 and 8.
  • the constant- voltage error correction circuit comprises an error detection unit 12 and a detection input conversion unit 51, and the detection input conversion unit 51 comprises a time constant unit 52, a detection input control unit 53 and an input resistor 54.
  • the time constant unit 52 comprises a voltage-current converter
  • a transistor (TR) Ql configured to be selectively turned on and off in response to the output current of the voltage-current converter 71, a time constant setting condenser CtI configured such that the charge and discharge thereof is controlled by turning on and off of the TR Ql, a current source 13 for discharging the time constant setting condenser CtI when the TR Ql is off, a current source 12 for charging the time constant setting condenser CtI when the TR Ql is on, a second voltage-current converter 72 configured to output an output current corresponding to the voltage of the time constant setting condenser CtI and to include a TR Q2 and a resistor R2, a current mirror TR Q3 for mirroring a current output from the TR Q2, and a TR Q4 for feeding back a current, output from the TR Q2, to the output terminal of the voltage-current converter 71, and varying the level of the output voltage
  • the detection input control unit 53 of the constant- voltage error correction circuit is formed of a TR Q5.
  • the TR Q5 of the detection input control unit 53 mirrors an output current, output from the TR Q2 of the time constant unit 52, along with the current mirror TR Q3, and bypasses some of an input current, applied to the error detection unit 12, that corresponds to a mirrored current. Then, a voltage drop, corresponding to the bypassed current, occurs in the input resistor 54, and an output voltage is increased by the magnitude of the voltage drop.
  • the voltage-current converter 71 of the time constant unit 52 is set such that the output current is low when the input voltage is high, and the output current is high when the input voltage is low.
  • the output current of the voltage-current converter 71 corresponds to the output voltage of the error detection unit 12.
  • the output voltage of the voltage-current converter 71 is at the 'L' level if the mirror current of the TR Q4 is higher than the output current of the voltage-current converter 71, while the output voltage of the voltage-current converter 71 is at the 'H' level if the mirror current of the TR Q4 is lower than the output current of the voltage-current converter 71.
  • the TR Ql conducts electricity, and thus enables the time constant setting condenser CtI to be charged based on the value of the difference between the current source 12 and the current source 13.
  • the TR Ql when the output voltage of the voltage-current converter 71 is at the 'L' level, the TR Ql does not conduct electricity, and thus causes the time constant setting condenser CtI to be discharged using the current source 13.
  • An output current corresponding to the average value is output through the second voltage-current converter 72, which may be formed of the TR Q2 and the resistor R2, in response to the charge voltage of the time constant setting condenser CtI, and this output current is mirrored by the TR Q3 and the TR Q4 and fed back to the output terminal of the voltage-current converter 71.
  • the output voltage of the voltage-current converter 71 is determined depending on whether the current mirrored by the TR Q4 is lower or higher than the output current of the voltage-current converter 71.
  • the output voltage of the voltage-current converter 71 is charged in or discharged from the time constant setting condenser CtI so that the difference between the current mirrored by the TR Q4 and the output current of the voltage-current converter 71 decreases, with the result that the current mirrored by the TR Q4 is stabilized in the state in which the mirrored current continues to minutely increase and decrease slightly above and below a value such as the output current of the voltage-current converter 71.
  • the charge time constant of the time constant unit 52 is determined depending on the value of the difference between the current source 12 and the current source 13 and the time constant setting condenser CtI, and the discharge time constant is determined depending on the current source 13 and the time constant setting condenser CtI. If the current source 12 is set at 20 nA, the current source 13 is set at 10 nA and the time constant setting condenser CtI is set at 100 pF, 30 ms is taken to obtain a variation of 3V. A commonly set time constant is determined to be an experimental value and is corrected based on the degree of correction of the constant- voltage.
  • the output current of the voltage-current converter 71 can vary at any time in response to variation in load or variation in input voltage, and thus the output current of the voltage-current converter 71 can vary at any time. Accordingly, the output current of the voltage-current converter 71 has periods in which it is higher than the mirror current of the TR Q4 and periods in which it is lower than the mirror current of the TR Q4, and thus the output voltage of the voltage-current converter 71 has the 'H' level and the 'L' level.
  • the amount of variation in the charge and discharge voltage of the time constant setting condenser CtI for a specific period corresponds to the difference between the period of the 'H' level and the period of the 'L' level, with the result that the voltage charged in the time constant setting condenser CtI reaches a value corresponding to the average value of the output current of the voltage-current converter 71.
  • the time constant unit 52 obtains the average value of the output current of the voltage-current converter 71 using the time constant depending on the time constant setting condenser CtI, the current source 12 and the current source 13, and outputs the average value. Then, an average value output current is mirrored by the TR Q3 and the TR Q5, and thus the TR Q5 bypasses the current through the input resistor 54 in a superimposed manner, with the result that the voltage drop in the input resistor 54 increases and the detection input voltage decreases. As a result, this acts to increases the output voltage, and the increase in the output voltage is determined based on the current mirrored by the TR Q5.
  • This circuit has an advantage in that integration can be easily realized using a piece of silicon material having a small area because the circuit is relatively simple and can acquire a relatively large time constant using a low-capacity condenser, and another advantage in that adjustment can be made by a user using a semiconductor because an input resistor 54 capable of adjusting the amount of correction of the output voltage is present outside the circuit.
  • FIG. 10 is a diagram of a constant- voltage error correction circuit according to a third embodiment of the present invention, showing a detailed circuit diagram of the constant- voltage error correction circuits shown in FIGS. 7 and 8.
  • the constant- voltage error correction circuit comprises an error detection unit 12 and a detection input conversion unit 51-1, and the detection input conversion unit 51-1 comprises a time constant unit 52-1, a detection input control unit 53-1 and an input resistor 54.
  • the time constant unit 52-1 comprises a voltage-current converter 71-1 for converting an error detection voltage, fed back from the error detection unit 12 to a control unit 11, into a current value, a TR Ql configured to be selectively turned on and off in response to the output current of the voltage-current converter 71-1, a time constant setting condenser CtI configured such that the charge and discharge thereof is controlled by turning on and off of the TR Ql, a current source 13 for discharging the time constant setting condenser CtI when the TR Ql is off, a current source 12 for charging the time constant setting condenser CtI when the TR Ql is on, a second voltage-current converter 72 configured to output an output current corresponding to the voltage of the time constant setting condenser CtI and to include a TR Q2 and a resistor R2, a current mirror TR Q3 for mirroring a current output from the TR Q2, and a TR Q4 for feeding back a current, output from the TR Q2, to
  • the detection input control unit 53-1 subtracts the current of the TR Q2 from the current of a current source 14, and mirrors the remaining current using a current mirror TR Q7 and TR Q5 for a current mirror through a TR Q6 for a voltage drop. Therefore, the voltage-current converter 71-1 of the time constant unit 52-1 is configured such that the mirror current of the TR Q5 is low when the input voltage is high and the mirror current of the TR Q5 is large when the input voltage is low, and bypasses some of the input current, applied to the error detection unit 12, that corresponds to a mirrored current. A voltage drop, corresponding to the magnitude of the bypassing, occurs in the input resistor 54, so that the output voltage increases by the magnitude of the voltage drop.
  • the constant- voltage error correction circuit of FIG. 10 includes a detection input control unit 53-1, which is fabricated by adding circuit elements to the detection input control unit 53 in the case where the constant- voltage error detection circuit of Fig. 10 has the opposite of the input-output characteristics of the voltage-current converter 71 of the constant- voltage error correction circuit of FIG. 9 are the opposite of each other.
  • the constant- voltage error correction circuit of FIG. 10 has the same operational effects as the constant- voltage error correction circuit of FIG. 9, and has a detailed operation corresponding to that of FIG. 9.
  • FIG. 11 is a diagram of a constant- voltage error correction circuit according to a fourth embodiment of the present invention, showing a detailed circuit diagram of the constant- voltage error correction circuits shown in FIGS. 7 and 8.
  • the constant- voltage error correction circuit comprises an error detection unit 12 and a detection input conversion unit 51-2, and the detection input conversion unit 51-2 comprises a time constant unit 52-2, a detection input control unit 53-2 and an input resistor 54.
  • the time constant unit 52-2 sets a time constant using a resistor R81 and a condenser C81, obtains the average value of the output of the error detection unit 12, outputs a current corresponding to the average value using a voltage- current converter 81, which can be formed of a TR Q81 and a resistor R82, performs mirroring using TR Q82 and a current mirror TR Q83, and bypasses some of an input current, applied to the error detection unit 12, that corresponds to a mirrored current.
  • a voltage drop, corresponding to the magnitude of the bypassing occurs in an input resistor 54, so that the output voltage further increases by the magnitude of the voltage drop.
  • FIGS. 12 and 13 are block diagrams showing a fifth embodiment of the constant- voltage error correction circuit according to the present invention.
  • each of constant-voltage error correction circuits 90 and 100 comprises an error detection unit 12 for detecting the error of the output voltage of the primary winding Tl-I of the transformer Tl from the voltage of the feedback winding Tl-3, and a reference voltage conversion unit 91 for converting the reference voltage of the error detection unit 12 in response to an error detection voltage output from the error detection unit 12. That is, the constant- voltage error correction circuits 90 and 100 are configured to vary the reference voltage of the error detection unit 12 using the error detection voltage output from the error detection unit 12 so that the output voltage Vo of the primary winding Tl-I varies little.
  • the error detection unit 12 of FIG. 12 detects the error of an output voltage Vo using a DC voltage, which is rectified by a diode D3 and a condenser C4 and is thus smoothed, as input, the error detection unit 12 of FIG. 13 receives an AC voltage from the feedback winding T 1-3 of the transformer Tl without change and detects the error of the output voltage Vo.
  • correction is performed in such a way as to decrease the output voltage by decreasing the reference voltage output from the reference voltage conversion unit 91 in the case where the error detection voltage output from the error detection unit 12 is high in the case of a light load, and in such a way as to increase the output voltage by increasing the reference voltage output from the reference voltage conversion unit 91 in the case where when the error detection voltage output from the error detection unit 12 is low in the case of a heavy load.
  • the reference voltage conversion unit 91 comprises a time constant unit 92 for obtaining the average value of an error detection voltage output from the error detection unit 12 and a reference voltage control unit 93 for outputting a reference voltage corresponding to the average value.
  • FIG. 14 is a diagram of a constant- voltage error correction circuit according to a sixth embodiment of the present invention, showing a detailed circuit diagram of the constant- voltage error correction circuits shown in FIGS. 12 and 13.
  • a time constant unit 92 is configured to obtain the average value of the output current of a voltage-current converter 111 and output the average value.
  • the output characteristic of the voltage-current converter 111 of FIG. 14 is the opposite of the output characteristics of the voltage- current converter 71. That is, the voltage-current converter 111 of FIG. 14 is set such that the output current is high in the case where the input voltage is high, and the output current is low in the case where the input voltage is low.
  • the output current of the time constant unit 92 of FIG. 14 has a value equal to a value obtained by averaging the output current of the voltage-current converter 111 using a large time constant, and this current is mirrored by the TR Q5 of a reference voltage control unit 93 and flows through a resistor R2 connected to a reference voltage Vref2, thereby varying an output reference voltage by controlling a voltage drop in the resistor R2.
  • this circuit decreases the output voltage in the case of a light load and increases the output voltage in the case of a heavy load, thus achieving the correction of the constant- voltage characteristics.
  • FIG. 15 is a diagram of a constant- voltage error correction circuit according to a seventh embodiment of the present invention, showing a detailed block diagram of the constant- voltage error correction circuits shown in FIGS. 12 and 13.
  • the time constant unit 92-1 of FIG. 15 has the same construction as the time constant unit 92 of FIG. 14, the output characteristics of the voltage-current converter 111-1 of FIG. 15 are the opposite of those of the voltage-current converter 111 of FIG. 14. That is, the voltage-current converter 111-1 of the time constant unit 92- 1 is set such that the output current is low when the input voltage is high, and the output current is high when the input voltage is low, and is inverted in accordance with characteristics required by a reference voltage control unit 93-1 and then controls the reference voltage.
  • FIG. 16 is a diagram of a constant- voltage error correction circuit according to an eighth embodiment of the present invention, showing a detailed circuit diagram of the constant- voltage error correction circuits shown in FIGS. 12 and 13.
  • FIG. 16 is another example of the reference voltage conversion unit 91-2.
  • This reference voltage conversion unit 91-2 sets a time constant using a resistor R121 and a condenser C 121, obtains the average value of the output of the error detection unit 12, and performs conversion into a current corresponding to the average value using a voltage-current converter 121, which may be formed of a TR Q 121 and a resistor R 122, with the result that the converted current causes a voltage drop in a resistor R 123, and thus varies an output reference voltage.
  • Each of the voltage-current converters shown in FIGS. 9, 10, 14 and 15 may be replaced by an output mirrored by a mirror output mirrored by a current mirror using a voltage-current converter included in a control circuit from the point of view of the construction of a circuit. Since the output current is formed to finally correspond to the output of the error detection unit regardless of the location of the voltage-current converter, it will be apparent that the voltage-current converter can be considered to be disposed at one of the locations shown in FIGS. 9, 10, 14 and 15.
  • the present invention can be applied to an SMPS power circuit including a primary regulation-type output voltage stabilization circuit.

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Abstract

The present invention relates to a constant- voltage error correction circuit for a primary regulation-type Switching Mode Power Supply (SMPS), which, in an inexpensive primary regulation-type SMPS, predicts variation in the load and corrects an output voltage in response to the predicted variation in the load. The constant- voltage error correction circuit for an SMPS, which has a magnetic energy transfer element, includes an error detection unit for receiving detection input voltage from the winding of the magnetic energy transfer element and reference voltage and detecting the errors of output voltage of the SMPS; a time constant unit for outputting the average value of error detection voltage output from the error detection unit; and a detection input control unit for varying the detection input voltage of the error detection unit in response to the average value output from the time constant unit.

Description

Description
CIRCUIT FOR OUTPUT VOLTAGE ERROR CORRECTION IN SMPS WHICH REGULATION IS DONE BY PRIMARY SIDE
CONTROL
Technical Field
[1] The present invention relates to a constant- voltage error correction circuit for a primary regulation-type Switching Mode Power Supply (SMPS), which, in an inexpensive primary regulation-type SMPS, predicts variation in the load and corrects an output voltage in response to the predicted variation in the load. Background Art
[2] In general, an SMPS stabilizes output voltage by providing an error detection circuit in an output voltage extraction unit, detecting the error of output voltage, and feeding back detected error voltage to a power conversion unit through an optocoupler. Since this is well known, a detailed description thereof will be omitted here.
[3] However, since a device for performing feedback, such as an optocoupler, is expensive, technologies for implementing an SMPS power circuit, not requiring high- precision output voltage, at low cost are being investigated.
[4] FIG. 1 is a diagram showing an SMPS power circuit that includes a prior art primary regulation-type output voltage stabilization circuit. This primary regulation- type output voltage stabilization circuit is widely used for loads not requiring precise constant- voltage characteristics, and realizes the stabilization of output voltage by detecting voltage induced to the feedback winding T 1-3 of a transformer Tl and stabilizing the detected voltage.
[5] With regard to the operation of the circuit of FIG. 1, during the conduction period of a switching element U2, magnetic energy is stored in the primary winding Tl-I of the transformer Tl, while, during the non-conduction period of the switching element U2, the magnetic energy stored in the primary winding Tl-I is transferred to a closely coupled secondary winding T 1-2, is rectified by a diode D2, is stored in a condenser C3, and is then supplied to a load. Meanwhile, the voltage, drawn from the feedback winding Tl-3 and charged in a condenser C4 through a diode D3, is compared with a reference voltage Vref 1 in an error detection unit 12, and the results of the comparison are applied to a control unit 11. The control unit 11 increases or decreases the amount of energy output to the load by controlling the switching frequency or the amount of current of the switching element U2, thereby performing control so that the voltage charged in the condenser C4 can be maintained at a constant value.
[6] Meanwhile, the primary winding Tl-I of the transformer Tl is wound to be closely coupled to the secondary winding T 1-2. However, actually, a leakage inductance component, which is not coupled to the secondary winding T 1-2, exists, and the energy stored in the leakage inductance undergoes a process of not being transferred to the secondary winding T 1-2, resonating with distributed capacity existing in the primary winding Tl-I, and extinguishing itself. Both the output voltage component of the secondary winding T 1-2, attributable to the turn ratio, and a surge spike voltage component, attributable to the leakage inductance, are induced to the feedback winding T 1-3 that is closely coupled to the transformer Tl.
[7] FIGS. 2 and 3 are drawings illustrating examples of waveforms of voltage induced to the feedback winding T 1-3 in the output voltage stabilization circuit of FIG. 1. FIG. 2 is a waveform diagram in the case of a heavy load, and FIG. 3 is a waveform diagram in the case of a light load.
[8] In FIG. 2, the period from T20 to T21 is the conduction period of the switching element U2, during which an input voltage Vi is applied to the primary winding Tl-I, and a 'negative' voltage in proportion to the turn ratio between the primary winding Tl-I and the feedback winding Tl-3 is obtained in the feedback winding Tl-3. When the switching element U2 is turned off at a time point T21, the winding voltage is reversed, and thus a surge voltage is generated due to the influence of the leakage inductance and reaches a peak value, and the peak value Vpeak is rectified by the diode D3, charged in the condenser C4, and is then used as a feedback value for performing voltage control. Accordingly, the voltage charged in the condenser C4 includes an output voltage component Vo output to the secondary winding T 1-2, and a surge voltage component generated due to the leakage inductance.
[9] In the case of a heavy load, during the conduction period of the switching element
U2, the amount of energy stored in the primary winding Tl-I of the transformer Tl is large, and a high surge voltage is generated due to the leakage inductance. In the case of a light load, the amount of energy stored in the primary winding Tl-I of the transformer Tl is small, and a low surge voltage is generated due to the leakage inductance. That is, since the surge voltage attributable to the leakage inductance varies with the magnitude of the load, variation in output voltage is inevitable in the case where control is performed such that the voltage charged in the condenser C4 is maintained at a constant value. As a result, in the case of a light load, the output voltage becomes high, while, in the case of a heavy load, the output voltage becomes low. In general output voltage control based on primary regulation, when the output voltage is 5 V in the case of the maximal load, the output voltage generally increases to about 8 ~ 10 V in the case of no load, so that the range of variation in the output voltage attributable to the magnitude of the load is about 60% ~ 100%.
[10] FIG. 4 is a diagram showing an SMPS power circuit including a novel primary regulation-type output voltage stabilization circuit.
[11] Recently, as shown in the circuit of FIG. 4, a circuit for stabilizing output voltage by detecting the voltage of a secondary winding T 1-2 from the voltage induced to the feedback winding T 1-3 of a transformer Tl without being affected by leakage inductance and feeding back the detected voltage to a control unit has been disclosed. In this circuit, the stability of output voltage is significantly improved compared to that of the case of FIG. 1. However, this circuit has a problem in that the stability thereof is lower than a secondary regulation-type circuit for detecting an error on a secondary side and performing feedback. Disclosure of Invention Technical Problem
[12] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a constant- voltage error correction circuit for a primary regulation-type SMPS, which corrects a constant- voltage error that occurs in the prior art primary regulation method, thereby enabling further improved output voltage stabilization characteristics to be acquired. Technical Solution
[13] In order to accomplish the above object, the present invention provides a constant- voltage error correction circuit for an SMPS, the SMPS having a magnetic energy transfer element, the constant- voltage error correction circuit comprising an error detection unit for receiving detection input voltage from the winding of the magnetic energy transfer element and reference voltage and detecting the errors of output voltage of the SMPS; a time constant unit for outputting an average value of error detection voltage output from the error detection unit; and a detection input control unit for varying the detection input voltage of the error detection unit in response to the average value output from the time constant unit.
[14] Furthermore, the present invention provides a constant- voltage error correction circuit for an SMPS, the SMPS having a magnetic energy transfer element, the constant- voltage error correction circuit comprising an error detection unit for receiving detection input voltage from the winding of the magnetic energy transfer element and reference voltage and detecting the errors of output voltage of the SMPS; a time constant unit for outputting the average value of error detection voltage output from the error detection unit; and a reference voltage control unit for varying the reference voltage of the error detection unit in response to the average value output from the time constant unit.
[15] Furthermore, according to the present invention, a flyback converter including one of the above-described constant- voltage error correction circuits is provided. [16] The present invention enables further improved constant- voltage characteristics to be easily acquired by predicting variation in output voltage, which is generated due to various factors, such as the influence of leakage inductance and the influence of variation in the forward voltage drop of an output diode, based on the results of experiments, and appropriately correcting the output voltage in response to the variation in the load. The present invention is suitable for application to an SMPS, which does not require rapid load response characteristics because the speed of variation in the load is very low, like a battery charger.
Advantageous Effects
[17] According to the present invention, further improved output characteristics can be acquired by correcting the constant- voltage stabilization characteristics of a primary regulation-type output voltage stabilization circuit to a level desired by a designer using an actually measured experimental value, so that appropriate regulation can be achieved without using a complicated and expensive secondary regulation circuit, thereby enabling a reduction in cost. Furthermore, constant- voltage stabilization characteristics, equal to those acquired in a secondary regulation method, can be acquired by further improving the constant- voltage stabilization characteristics of novel primary regulation-type output voltage stabilization circuits, disclosed recently, using a simple correction circuit embedded in an integrated circuit, so that advantages can be obtained in that the circuit is simplified and the assembly cost and time can be reduced. Brief Description of the Drawings
[18] FIG. 1 is a diagram of a prior art output voltage stabilization circuit for an SMPS;
[19] FIGS. 2 and 3 are diagrams showing the waveforms of signals in respective parts of the prior art output voltage stabilization circuit;
[20] FIG. 4 is a diagram showing an output voltage stabilization circuit for a novel
SMPS, which has recently been disclosed;
[21] FIGS. 5 and 6 are graphs comparing the output current versus output voltage characteristics of the prior art and the present invention with each other;
[22] FIGS. 7 and 8 are block diagrams showing SMPS power circuits including constant- voltage error correction circuits according to a first embodiment of the present invention;
[23] FIG. 9 is a diagram of a constant- voltage error correction circuit according to a second embodiment of the present invention, showing a detailed circuit diagram of the constant- voltage error correction circuits shown in FIGS. 7 and 8;
[24] FIG. 10 is a diagram of a constant- voltage error correction circuit according to a third embodiment of the present invention, showing a detailed circuit diagram of the constant- voltage error correction circuits shown in FIGS. 7 and 8;
[25] FIG. 11 is a diagram of a constant- voltage error correction circuit according to a fourth embodiment of the present invention, showing a detailed circuit diagram of the constant- voltage error correction circuits shown in FIGS. 7 and 8;
[26] FIGS. 12 and 13 are block diagrams showing SMPS power circuits including constant- voltage error correction circuits according to a fifth embodiment of the present invention;
[27] FIG. 14 is a diagram of a constant- voltage error correction circuit according to a sixth embodiment of the present invention, showing a detailed circuit diagram of the constant- voltage error correction circuits shown in FIGS. 12 and 13;
[28] FIG. 15 is a diagram of a constant- voltage error correction circuit according to a seventh embodiment of the present invention, showing a detailed circuit diagram of the constant- voltage error correction circuits shown in FIGS. 12 and 13; and
[29] FIG. 16 is a diagram of a constant- voltage error correction circuit according to an eighth embodiment of the present invention, showing a detailed circuit diagram of the constant- voltage error correction circuits shown in FIGS. 12 and 13. Best Mode for Carrying Out the Invention
[30] The constant- voltage error correction circuits of a primary regulation-type SMPS according to embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
[31] [First embodiment]
[32] FIGS. 7 and 8 are block diagrams showing an SMPS power circuit including a constant- voltage error correction circuit according to a first embodiment of the present invention.
[33] The representative SMPS power circuit, to which the present invention is applied, includes a transformer Tl configured such that a primary winding Tl-I, a secondary winding T 1-2, and a feedback winding T 1-3 are closely coupled to each other, a switching element U2 connected to the primary winding Tl-I, a diode D2 and condenser C3 configured to rectify and smooth the voltage of the secondary winding T 1-2, and a clamp circuit 13 configured to suppress surge spike voltage generated due to leakage inductance.
[34] The constant- voltage error correction circuits 50 and 60 of the present embodiment operate to appropriately compensate for constant- voltage errors attributable to variation in the load in the primary regulation of stabilizing an output voltage Vo using a voltage induced to the feedback winding T 1-3, thereby improving the stability of the output voltage Vo to a desired level.
[35] FIG. 5 is a diagram showing the constant- voltage characteristics of the primary regulation-type SMPS. In this drawing, in the case of a light load, the output voltage Vo is high and the error detection voltage, output from an error detection unit 12, is increased so that a small amount of energy can be output, while, in the case of a heavy load, the output voltage Vo is low and the error detection voltage, output from the error detection unit 12, is decreased so that a large amount of energy is output. Accordingly, the range of variation in output voltage due to variation in load can be significantly reduced by appropriately increasing or decreasing the detection input of the error detection unit 12 using an error detection voltage output from the error detection unit 12, or by appropriately increasing or decreasing the reference level of the error detection unit 12. [36] Referring to FIGS. 7 and 8, each of constant- voltage error correction circuits 50 and
60 according to the present invention comprises an error detection unit 12 for detecting the error of the output voltage of the primary winding Tl-I of the transformer Tl from the voltage of the feedback winding Tl-3, and a detection input conversion unit 51 or
61 for converting the detection input voltage of the error detection unit 12 in response to the error detection voltage output from the error detection unit 12. That is, the constant- voltage error correction circuits 50 and 60 are configured to vary the detection input of the error detection unit 12 using the error detection voltage output from the error detection unit 12 so that the output voltage Vo of the primary winding Tl-I varies little.
[37] Although the error detection unit 12 of FIG. 7 is configured to detect an error using a DC voltage, which is rectified by a diode D3 and a condenser C4 and is thus smoothed, as input, the error detection unit 12 of FIG. 8 is configured to receive an AC voltage from the feedback winding Tl-3 of the transformer Tl without change and detect an error.
[38] In FIGS. 7 and 8, in the case of a light load, the output voltage Vo is high and the error detection voltage of the error detection unit 12 is increased so that a small amount of energy can be output, while, in the case of a heavy load, the output voltage Vo is low and the error detection voltage of the error detection unit 12 is decreased so that a large amount of energy is output. The amount of variation in output voltage due to variation in load can be obtained using an experimental method. The detection input conversion units 51 and 61 correct the amount of variation in output voltage due to variation in load by increasing the detection input voltage of the error detection unit 12 in the case of a light load and decreasing the detection input voltage of the error detection unit 12 in the case of a heavy load, in response to the error detection voltage of the error detection unit 12.
[39] The detection input conversion unit 51 or 61 comprises a time constant unit 52 or
62 configured to obtain the average value of the output voltage of the error detection unit 12 using a given time constant, a detection input control unit 53 or 63 configured to control a detection input, input to the error detection unit 12, in response to the output of the time constant unit 52 or 62, and an input resistor 54 connected between the feedback winding Tl-3 and the error detection unit 12.
[40] In general, immediately varying the detection input or reference voltage of the error detection unit 12 using the output voltage of the error detection unit 12 may cause positive feedback, thus resulting in undesired oscillation.
[41] The time constant units 52 or 62 of the detection input conversion units 51 and 61 are used to prevent the above problem. Since the time constant unit 52 or 62 obtains the average value of the output voltage of the error detection unit 12 using a time constant ranging from several tens of milliseconds to several hundreds of milliseconds, the generation of oscillation can be prevented, or can be limited to a tolerable level. Although the time constant of the time constant unit 52 or 62 is generally set to a value ranging from several milliseconds to several hundreds of milliseconds, the time constant may be appropriately increased or decreased depending on the output characteristics. Mode for the Invention
[42] [Second embodiment]
[43] FIG. 9 is a diagram of a constant- voltage error correction circuit according to a second embodiment of the present invention, showing a detailed circuit diagram of the constant- voltage error correction circuits shown in FIGS. 7 and 8.
[44] The constant- voltage error correction circuit comprises an error detection unit 12 and a detection input conversion unit 51, and the detection input conversion unit 51 comprises a time constant unit 52, a detection input control unit 53 and an input resistor 54.
[45] Referring to FIG. 9, the time constant unit 52 comprises a voltage-current converter
71 for converting an error detection voltage, fed back from the error detection unit 12 to a control unit 11, into a current value, a transistor (TR) Ql configured to be selectively turned on and off in response to the output current of the voltage-current converter 71, a time constant setting condenser CtI configured such that the charge and discharge thereof is controlled by turning on and off of the TR Ql, a current source 13 for discharging the time constant setting condenser CtI when the TR Ql is off, a current source 12 for charging the time constant setting condenser CtI when the TR Ql is on, a second voltage-current converter 72 configured to output an output current corresponding to the voltage of the time constant setting condenser CtI and to include a TR Q2 and a resistor R2, a current mirror TR Q3 for mirroring a current output from the TR Q2, and a TR Q4 for feeding back a current, output from the TR Q2, to the output terminal of the voltage-current converter 71, and varying the level of the output voltage of the voltage-current converter 71 depending on whether the feedback current is higher or lower than the output of the voltage-current converter 71. The time constant unit 52 is configured to obtain the average value of the output current of the voltage-current converter 71 for a set period and to output the average value.
[46] The detection input control unit 53 of the constant- voltage error correction circuit is formed of a TR Q5. The TR Q5 of the detection input control unit 53 mirrors an output current, output from the TR Q2 of the time constant unit 52, along with the current mirror TR Q3, and bypasses some of an input current, applied to the error detection unit 12, that corresponds to a mirrored current. Then, a voltage drop, corresponding to the bypassed current, occurs in the input resistor 54, and an output voltage is increased by the magnitude of the voltage drop.
[47] The operation of the time constant unit 52 shown in FIG. 9 will be described below.
[48] The voltage-current converter 71 of the time constant unit 52 is set such that the output current is low when the input voltage is high, and the output current is high when the input voltage is low.
[49] The output current of the voltage-current converter 71 corresponds to the output voltage of the error detection unit 12. The output voltage of the voltage-current converter 71 is at the 'L' level if the mirror current of the TR Q4 is higher than the output current of the voltage-current converter 71, while the output voltage of the voltage-current converter 71 is at the 'H' level if the mirror current of the TR Q4 is lower than the output current of the voltage-current converter 71. When the output voltage of the voltage-current converter 71 is at the 'H' level, the TR Ql conducts electricity, and thus enables the time constant setting condenser CtI to be charged based on the value of the difference between the current source 12 and the current source 13. In contrast, when the output voltage of the voltage-current converter 71 is at the 'L' level, the TR Ql does not conduct electricity, and thus causes the time constant setting condenser CtI to be discharged using the current source 13. An output current corresponding to the average value is output through the second voltage-current converter 72, which may be formed of the TR Q2 and the resistor R2, in response to the charge voltage of the time constant setting condenser CtI, and this output current is mirrored by the TR Q3 and the TR Q4 and fed back to the output terminal of the voltage-current converter 71. The output voltage of the voltage-current converter 71 is determined depending on whether the current mirrored by the TR Q4 is lower or higher than the output current of the voltage-current converter 71. As a result, the output voltage of the voltage-current converter 71 is charged in or discharged from the time constant setting condenser CtI so that the difference between the current mirrored by the TR Q4 and the output current of the voltage-current converter 71 decreases, with the result that the current mirrored by the TR Q4 is stabilized in the state in which the mirrored current continues to minutely increase and decrease slightly above and below a value such as the output current of the voltage-current converter 71.
[50] Here, the charge time constant of the time constant unit 52 is determined depending on the value of the difference between the current source 12 and the current source 13 and the time constant setting condenser CtI, and the discharge time constant is determined depending on the current source 13 and the time constant setting condenser CtI. If the current source 12 is set at 20 nA, the current source 13 is set at 10 nA and the time constant setting condenser CtI is set at 100 pF, 30 ms is taken to obtain a variation of 3V. A commonly set time constant is determined to be an experimental value and is corrected based on the degree of correction of the constant- voltage.
[51] In general, the output current of the voltage-current converter 71 can vary at any time in response to variation in load or variation in input voltage, and thus the output current of the voltage-current converter 71 can vary at any time. Accordingly, the output current of the voltage-current converter 71 has periods in which it is higher than the mirror current of the TR Q4 and periods in which it is lower than the mirror current of the TR Q4, and thus the output voltage of the voltage-current converter 71 has the 'H' level and the 'L' level. The amount of variation in the charge and discharge voltage of the time constant setting condenser CtI for a specific period corresponds to the difference between the period of the 'H' level and the period of the 'L' level, with the result that the voltage charged in the time constant setting condenser CtI reaches a value corresponding to the average value of the output current of the voltage-current converter 71.
[52] In summary, the time constant unit 52 obtains the average value of the output current of the voltage-current converter 71 using the time constant depending on the time constant setting condenser CtI, the current source 12 and the current source 13, and outputs the average value. Then, an average value output current is mirrored by the TR Q3 and the TR Q5, and thus the TR Q5 bypasses the current through the input resistor 54 in a superimposed manner, with the result that the voltage drop in the input resistor 54 increases and the detection input voltage decreases. As a result, this acts to increases the output voltage, and the increase in the output voltage is determined based on the current mirrored by the TR Q5.
[53] This circuit has an advantage in that integration can be easily realized using a piece of silicon material having a small area because the circuit is relatively simple and can acquire a relatively large time constant using a low-capacity condenser, and another advantage in that adjustment can be made by a user using a semiconductor because an input resistor 54 capable of adjusting the amount of correction of the output voltage is present outside the circuit. [54] [Third embodiment]
[55] FIG. 10 is a diagram of a constant- voltage error correction circuit according to a third embodiment of the present invention, showing a detailed circuit diagram of the constant- voltage error correction circuits shown in FIGS. 7 and 8.
[56] The constant- voltage error correction circuit comprises an error detection unit 12 and a detection input conversion unit 51-1, and the detection input conversion unit 51-1 comprises a time constant unit 52-1, a detection input control unit 53-1 and an input resistor 54.
[57] Referring to FIG. 10, the time constant unit 52-1 comprises a voltage-current converter 71-1 for converting an error detection voltage, fed back from the error detection unit 12 to a control unit 11, into a current value, a TR Ql configured to be selectively turned on and off in response to the output current of the voltage-current converter 71-1, a time constant setting condenser CtI configured such that the charge and discharge thereof is controlled by turning on and off of the TR Ql, a current source 13 for discharging the time constant setting condenser CtI when the TR Ql is off, a current source 12 for charging the time constant setting condenser CtI when the TR Ql is on, a second voltage-current converter 72 configured to output an output current corresponding to the voltage of the time constant setting condenser CtI and to include a TR Q2 and a resistor R2, a current mirror TR Q3 for mirroring a current output from the TR Q2, and a TR Q4 for feeding back a current, output from the TR Q2, to the output terminal of the voltage-current converter 71-1, and varying the level of the output voltage of the voltage-current converter 71-1 depending on whether the feedback current is higher or lower than the output of the voltage-current converter 71-1. The voltage-current converter 71-1 is set such that the output current is high when the error detection voltage is high, and the output current is low when the error detection voltage is low.
[58] The detection input control unit 53-1 subtracts the current of the TR Q2 from the current of a current source 14, and mirrors the remaining current using a current mirror TR Q7 and TR Q5 for a current mirror through a TR Q6 for a voltage drop. Therefore, the voltage-current converter 71-1 of the time constant unit 52-1 is configured such that the mirror current of the TR Q5 is low when the input voltage is high and the mirror current of the TR Q5 is large when the input voltage is low, and bypasses some of the input current, applied to the error detection unit 12, that corresponds to a mirrored current. A voltage drop, corresponding to the magnitude of the bypassing, occurs in the input resistor 54, so that the output voltage increases by the magnitude of the voltage drop.
[59] The constant- voltage error correction circuit of FIG. 10 includes a detection input control unit 53-1, which is fabricated by adding circuit elements to the detection input control unit 53 in the case where the constant- voltage error detection circuit of Fig. 10 has the opposite of the input-output characteristics of the voltage-current converter 71 of the constant- voltage error correction circuit of FIG. 9 are the opposite of each other. The constant- voltage error correction circuit of FIG. 10 has the same operational effects as the constant- voltage error correction circuit of FIG. 9, and has a detailed operation corresponding to that of FIG. 9.
[60] [Fourth embodiment]
[61] FIG. 11 is a diagram of a constant- voltage error correction circuit according to a fourth embodiment of the present invention, showing a detailed circuit diagram of the constant- voltage error correction circuits shown in FIGS. 7 and 8.
[62] The constant- voltage error correction circuit comprises an error detection unit 12 and a detection input conversion unit 51-2, and the detection input conversion unit 51-2 comprises a time constant unit 52-2, a detection input control unit 53-2 and an input resistor 54.
[63] Referring to FIG. 11, the time constant unit 52-2 sets a time constant using a resistor R81 and a condenser C81, obtains the average value of the output of the error detection unit 12, outputs a current corresponding to the average value using a voltage- current converter 81, which can be formed of a TR Q81 and a resistor R82, performs mirroring using TR Q82 and a current mirror TR Q83, and bypasses some of an input current, applied to the error detection unit 12, that corresponds to a mirrored current. A voltage drop, corresponding to the magnitude of the bypassing, occurs in an input resistor 54, so that the output voltage further increases by the magnitude of the voltage drop.
[64] Although this circuit is simple, the size of the resistor R81 or the condenser C81 must be large in order to acquire a time constant of several tens of milliseconds using the resistor R81 and the condenser C81, so that it is difficult to embed the circuit in a semiconductor, with the result that the circuit is suitable for the case where an external condenser is used as the condenser C81.
[65] [Fifth embodiment]
[66] FIGS. 12 and 13 are block diagrams showing a fifth embodiment of the constant- voltage error correction circuit according to the present invention.
[67] Referring to FIGS. 12 and 13, each of constant-voltage error correction circuits 90 and 100 according to the present invention comprises an error detection unit 12 for detecting the error of the output voltage of the primary winding Tl-I of the transformer Tl from the voltage of the feedback winding Tl-3, and a reference voltage conversion unit 91 for converting the reference voltage of the error detection unit 12 in response to an error detection voltage output from the error detection unit 12. That is, the constant- voltage error correction circuits 90 and 100 are configured to vary the reference voltage of the error detection unit 12 using the error detection voltage output from the error detection unit 12 so that the output voltage Vo of the primary winding Tl-I varies little.
[68] Although the error detection unit 12 of FIG. 12 detects the error of an output voltage Vo using a DC voltage, which is rectified by a diode D3 and a condenser C4 and is thus smoothed, as input, the error detection unit 12 of FIG. 13 receives an AC voltage from the feedback winding T 1-3 of the transformer Tl without change and detects the error of the output voltage Vo.
[69] In FIGS. 12 and 13, correction is performed in such a way as to decrease the output voltage by decreasing the reference voltage output from the reference voltage conversion unit 91 in the case where the error detection voltage output from the error detection unit 12 is high in the case of a light load, and in such a way as to increase the output voltage by increasing the reference voltage output from the reference voltage conversion unit 91 in the case where when the error detection voltage output from the error detection unit 12 is low in the case of a heavy load.
[70] Comparing the fifth embodiment of the constant- voltage error correction circuits of
FIGS. 12 and 13 with the first embodiment of the present invention shown in FIGS. 7 and 8, the two embodiments are the same in operation and advantage except that the first embodiment controls the detection input while the fifth embodiment controls the reference voltage.
[71] The reference voltage conversion unit 91 comprises a time constant unit 92 for obtaining the average value of an error detection voltage output from the error detection unit 12 and a reference voltage control unit 93 for outputting a reference voltage corresponding to the average value.
[72] [Sixth embodiment]
[73] FIG. 14 is a diagram of a constant- voltage error correction circuit according to a sixth embodiment of the present invention, showing a detailed circuit diagram of the constant- voltage error correction circuits shown in FIGS. 12 and 13.
[74] Referring to FIG. 14, a time constant unit 92 is configured to obtain the average value of the output current of a voltage-current converter 111 and output the average value.
[75] Although the construction of the time constant unit 92 of FIG. 14 is the same as that of the time constant unit 52 of FIG. 9, the output characteristic of the voltage-current converter 111 of FIG. 14 is the opposite of the output characteristics of the voltage- current converter 71. That is, the voltage-current converter 111 of FIG. 14 is set such that the output current is high in the case where the input voltage is high, and the output current is low in the case where the input voltage is low.
[76] As in the time constant unit 52 of FIG. 9, the output current of the time constant unit 92 of FIG. 14 has a value equal to a value obtained by averaging the output current of the voltage-current converter 111 using a large time constant, and this current is mirrored by the TR Q5 of a reference voltage control unit 93 and flows through a resistor R2 connected to a reference voltage Vref2, thereby varying an output reference voltage by controlling a voltage drop in the resistor R2.
[77] As a result, this circuit decreases the output voltage in the case of a light load and increases the output voltage in the case of a heavy load, thus achieving the correction of the constant- voltage characteristics.
[78] [Seventh embodiment]
[79] FIG. 15 is a diagram of a constant- voltage error correction circuit according to a seventh embodiment of the present invention, showing a detailed block diagram of the constant- voltage error correction circuits shown in FIGS. 12 and 13.
[80] Although the time constant unit 92-1 of FIG. 15 has the same construction as the time constant unit 92 of FIG. 14, the output characteristics of the voltage-current converter 111-1 of FIG. 15 are the opposite of those of the voltage-current converter 111 of FIG. 14. That is, the voltage-current converter 111-1 of the time constant unit 92- 1 is set such that the output current is low when the input voltage is high, and the output current is high when the input voltage is low, and is inverted in accordance with characteristics required by a reference voltage control unit 93-1 and then controls the reference voltage.
[81] [Eighth embodiment]
[82] FIG. 16 is a diagram of a constant- voltage error correction circuit according to an eighth embodiment of the present invention, showing a detailed circuit diagram of the constant- voltage error correction circuits shown in FIGS. 12 and 13.
[83] FIG. 16 is another example of the reference voltage conversion unit 91-2. This reference voltage conversion unit 91-2 sets a time constant using a resistor R121 and a condenser C 121, obtains the average value of the output of the error detection unit 12, and performs conversion into a current corresponding to the average value using a voltage-current converter 121, which may be formed of a TR Q 121 and a resistor R 122, with the result that the converted current causes a voltage drop in a resistor R 123, and thus varies an output reference voltage.
[84] That is, in the case of a light load, since the current of the TR Q121 is high, the voltage drop in a resistor R 123 is high, and thus the reference voltage is decreased, with the result that the output voltage is decreased. In contrast, in the case of a heavy load, since the current of the TR Q 121 is low, the voltage drop in the resistor R 123 is low, and thus the reference voltage is increased, with the result that the output voltage is increased.
[85] Although this circuit is simple, the size of the resistor R121 or condenser C121 must be large in order to acquire a time constant of several tens of milliseconds using the resistor R 121 and the condenser C 121, so that it is difficult to embed the circuit in a semiconductor, with the result that the circuit is suitable for the case where an external condenser is used as the condenser C 121.
[86] Each of the voltage-current converters shown in FIGS. 9, 10, 14 and 15 may be replaced by an output mirrored by a mirror output mirrored by a current mirror using a voltage-current converter included in a control circuit from the point of view of the construction of a circuit. Since the output current is formed to finally correspond to the output of the error detection unit regardless of the location of the voltage-current converter, it will be apparent that the voltage-current converter can be considered to be disposed at one of the locations shown in FIGS. 9, 10, 14 and 15.
[87] Referring to FIG. 5, it can be seen that the constant- voltage characteristics of the output voltage are significantly improved in the case where the present invention is applied to the prior art SMPS power circuit, as shown in FIGS. 7 and 12. Furthermore, referring to FIG. 6, it can be seen that the constant- voltage characteristics of the output voltage are improved, even when the present invention is applied to a novel SMPS power circuit, as shown in FIGS. 8 and 13.
[88] Although the technical spirit of the present invention has been described in conjunction with the accompanying drawings above, the description is intended to describe the preferred embodiments of the present invention for illustrative purposes only, and is not intended to limit the present invention. Furthermore, it will be apparent to those skilled in the art that various variations and modifications are possible within a range that does not depart from the scope of the technical spirit of the present invention.
Industrial Applicability
[89] The present invention can be applied to an SMPS power circuit including a primary regulation-type output voltage stabilization circuit.

Claims

Claims
[1] A constant- voltage error correction circuit for a Switching Mode Power Supply
(SMPS), the SMPS having a magnetic energy transfer element, the constant- voltage error correction circuit comprising: an error detection unit for receiving detection input voltage from winidings of the magnetic energy transfer element and reference voltage and detecting errors of output voltage of the SMPS; a time constant unit for outputting an average value of error detection voltage output from the error detection unit; and a detection input control unit for varying the detection input voltage of the error detection unit in response to the average value output from the time constant unit.
[2] The constant- voltage error correction circuit as set forth in claim 1, wherein: the time constant unit comprises a resistor and a condenser connected in series to an output terminal of the error detection unit, and obtains an average value of the error detection voltage using a time constant set based on the resistor and the condenser; and the detection input control unit comprises a voltage-current converter for outputting a current value corresponding to the average value obtained by the time constant unit and a current mirror for varying the detection input voltage by mirroring current, output from the voltage-current converter, to the detection input terminal.
[3] The constant- voltage error correction circuit according to claim 1, wherein the time constant unit comprises a first voltage-current converter for converting the error detection voltage of the error detection unit into a first current value, a switching element configured to be selectively turned on and off in response to the output voltage of the first voltage-current converter, a time constant setting condenser configured to be selectively charged and discharged in response to the turning on and off of the switching element, a charge current source for charging the time constant setting condenser when the switching element is turned on, a discharge current source for discharging the time constant setting condenser when the switching element is turned off, a second voltage-current converter for converting a charge voltage of the time constant setting condenser into a second current value and outputting the second current value to the detection input control unit, and a first current mirror for varying the output voltage of the first voltage-current converter in response to a value of the mirrored current value by mirroring the output current of the second voltage-current converter and thus connecting the mirrored output to an output terminal of the first voltage-current converter.
[4] The constant- voltage error correction circuit according to claim 3, wherein the detection input control unit comprises a second current mirror for varying the detection input voltage by mirroring output current of the first current mirror to the error detection unit.
[5] A constant- voltage error correction circuit for an SMPS, the SMPS having a magnetic energy transfer element, the constant- voltage error correction circuit comprising: an error detection unit for receiving detection input voltage from a winding of the magnetic energy transfer element and reference voltage and detecting errors of output voltage of the SMPS; a time constant unit for outputting an average value of error detection voltage output from the error detection unit; and a reference voltage control unit for varying the reference voltage of the error detection unit in response to the average value output from the time constant unit.
[6] The constant- voltage error correction circuit according to claim 5, wherein: the time constant unit comprises a resistor and a condenser connected in series to an output terminal of the error detection unit and obtains an average value of the error detection voltage using a time constant set based on the resistor and the condenser; and the reference voltage control unit comprises a voltage-current converter for outputting a current value corresponding to the average value obtained by the time constant unit and a resistor for varying the reference voltage by generating a voltage drop based on current output from the voltage-current converter.
[7] The constant- voltage error correction circuit according to claim 5, wherein the time constant unit comprises a first voltage-current converter for converting the error detection voltage of the error detection unit into a first current value, a switching element configured to be selectively turned on and off in response to the output voltage of the first voltage-current converter, a time constant setting condenser configured to be selectively charged and discharged in response to the turning on and off of the switching element, a charge current source for charging the time constant setting condenser when the switching element is turned on, a discharge current source for discharging the time constant setting condenser when the switching element is turned off, a second voltage-current converter for converting a charge voltage of the time constant setting condenser into a second current value and outputting the second current value to the reference voltage control unit, and a first current mirror for varying the output voltage of the first voltage-current converter in response to a value of the mirrored current value by mirroring the output current of the second voltage-current converter and thus connecting the mirrored output to an output terminal of the first voltage-current converter.
[8] The constant- voltage error correction circuit according to claim 7, wherein the reference voltage control unit comprises a second current mirror for varying the reference voltage by mirroring output current of the first current mirror to the error detection unit.
[9] A flyback converter including the constant- voltage error correction circuit according to any one of claims 1 to 8, wherein the magnetic energy transfer element is a transformer, and the error detection unit detects errors of output voltage using a primary winding voltage of the transformer.
[10] The flyback converter according to claim 9, wherein the error detection unit detects the errors of output voltage using an Alternating Current (AC) signal from the primary winding of the transformer.
[11] The flyback converter according to claim 9, wherein the error detection unit detects the errors of output voltage using a Direct Current (DC) signal obtained by rectifying an AC signal from the primary winding of the transformer.
[12] A flyback converter having the constant- voltage error correction circuit according to any one of claims 1 to 8, wherein the magnetic energy transfer element is a transformer, and the error detection unit detects errors of output voltage using voltage of a feedback winding of the transformer.
[13] The flyback converter according to claim 12, wherein the error detection unit detects the errors of output voltage using an AC signal from the feedback winding of the transformer.
[14] The flyback converter according to claim 12, wherein the error detection unit detects the errors of output voltage using DC signals that are obtained by rectifying an AC signal output from the feedback winding of the transformer.
PCT/KR2007/005151 2006-11-06 2007-10-19 Circuit for output voltage error correction in smps which regulation is done by primary side control WO2008056895A1 (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
KR20060108972 2006-11-06
KR10-2006-0108972 2006-11-06
KR10-2007-0028710 2007-03-23
KR1020070028710A KR100848685B1 (en) 2006-11-06 2007-03-23 circuit for output voltage error correction in SMPS which regulation is done by primary side control

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20020026139A (en) * 2000-09-28 2002-04-06 후지 덴끼 가부시키가이샤 Power supply circuit
US20060082943A1 (en) * 2004-10-15 2006-04-20 Po-Han Chiu Multi-input single-output power converter and method thereof
KR20060042200A (en) * 2004-09-30 2006-05-12 미쓰미덴기가부시기가이샤 Regulator circuit
US7054170B2 (en) * 2004-01-05 2006-05-30 System General Corp. Power-mode controlled power converter

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20020026139A (en) * 2000-09-28 2002-04-06 후지 덴끼 가부시키가이샤 Power supply circuit
US7054170B2 (en) * 2004-01-05 2006-05-30 System General Corp. Power-mode controlled power converter
KR20060042200A (en) * 2004-09-30 2006-05-12 미쓰미덴기가부시기가이샤 Regulator circuit
US20060082943A1 (en) * 2004-10-15 2006-04-20 Po-Han Chiu Multi-input single-output power converter and method thereof

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