JP2012182967A - Power factor improvement circuit and control circuit therefor, electronic apparatus using them - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the temperature characteristics of a PFC circuit.SOLUTION: A first V/I conversion circuit 10 generates a first current I1 by applying a first voltage V1 corresponding to an AC voltage Vthat has a full-wave rectification waveform and is input into a PFC circuit 200 to a first resistor R1. A first error amplifier circuit 18 amplifies the error between a first detection voltage Vcorresponding to the output voltage Vfrom the PFC circuit 200 and a predetermined reference voltage V, to generates a second voltage V2. A second V/I conversion circuit 12 generates a second current I2 by applying the second voltage V2 to a second resistor R2. A third V/I conversion circuit 14 generates a third current I3 by applying a predetermined voltage Vto a third resistor R3. A multiplier 20 multiplies the first current I1 and the second current I2, and divides the product by the third current I3 to generate a fourth current I4, and then generates a fourth voltage V4 by feeding the fourth current I4 to a fourth resistor R4.

Description

  The present invention relates to a power factor correction circuit using a DC / DC converter.

  Various home appliances such as TVs and refrigerators, or electronic devices such as laptop computers, mobile phone terminals and PDAs (Personal Digital Assistants) operate by receiving external power, and also from an external power source. The built-in battery can be charged with the power of In home appliances and electronic devices (hereinafter collectively referred to as electronic devices), a power supply device that converts commercial AC voltage into AC / DC (AC / DC) is built-in, or the power supply device is a power source external to the electronic device. Built in the adapter (AC adapter).

  The power supply device includes a rectifier circuit (diode bridge circuit) that rectifies an AC voltage, and an insulating DC / DC converter that steps down the rectified voltage and supplies the voltage to a load. When AC / DC conversion is performed by such a power supply device, a very high amplitude current pulse is generated. Such current pulses cause problems such as radiated noise, network loss, and increase in total harmonic components. In order to solve these problems, an electronic device that consumes more than a predetermined power is required to be equipped with a PFC (power factor correction) circuit. The PFC circuit monitors the AC input voltage and the input current, and matches the phases thereof to bring the power factor closer to 100%.

  The present invention has been made in such a situation, and one of the exemplary purposes of an embodiment thereof is to improve the temperature characteristics of the PFC circuit.

  One embodiment of the present invention relates to a control circuit for a power factor correction circuit having a DC / DC converter. The control circuit applies a first voltage having a full-wave rectified waveform to a first resistor to generate a first current and an output of a power factor correction circuit (DC / DC converter). A first error amplification circuit that amplifies an error between the first detection voltage corresponding to the voltage and a predetermined reference voltage and generates a second voltage, and a second current is generated by applying the second voltage to the second resistor. A second voltage / current conversion circuit that generates a third current by applying a predetermined voltage to the third resistor, a first current multiplied by the second current, and a third A fourth current divided by the current is generated, and the fourth current is caused to flow through the fourth resistor, thereby generating a fourth voltage, and a second detection corresponding to the current flowing through the switching element of the DC / DC converter. Amplifies the error between the voltage and the fourth voltage to generate an error signal To include a second error amplifier circuit, based on the error signal, a drive circuit for driving the switching element.

  Another aspect of the present invention also relates to a control circuit for a power factor correction circuit having a DC / DC converter. The control circuit applies a first voltage having a full-wave rectified waveform to a first resistor to generate a first current and an output of a power factor correction circuit (DC / DC converter). A first error amplification circuit that amplifies an error between the first detection voltage corresponding to the voltage and a predetermined reference voltage and generates a second voltage, and a second current is generated by applying the second voltage to the second resistor. A second voltage / current conversion circuit that generates a third current by applying a predetermined voltage to the third resistor, a first current multiplied by the second current, and a third A fourth current divided by the current is generated, and the fourth current is caused to flow through the fourth resistor, thereby generating a fourth voltage, and a second detection corresponding to the current flowing through the switching element of the DC / DC converter. A comparator for comparing the voltage and the fourth voltage; To turn on the switching element in every cycle of the constant, in accordance with the output of the comparator, and a drive circuit for turning off the switching element every time the second detection voltage is higher than the fourth voltage.

  In these embodiments, when the resistance values of the first to fourth resistors are written as R1 to R4, the fourth voltage is proportional to R3 × R4 / (R1 × R2). Therefore, even if the resistance values of the first resistor to the fourth resistor fluctuate at the same rate of change due to temperature fluctuations or process fluctuations, their influence on the fourth voltage can be reduced, and the temperature characteristics of the PFC circuit can be improved. .

In one embodiment, the multiplier includes a differential pair composed of first and second bipolar transistors, and fourth and fifth bipolar transistors each having an emitter connected to a collector of each of the first and second bipolar transistors. A differential amplifier including a current source for supplying a tail current to the differential pair, and a current path corresponding to the third current, the emitter of which is connected to the base of the first bipolar transistor, A third bipolar transistor having a base connected to the collector of the second bipolar transistor, a sixth bipolar transistor having an emitter connected to the base of the second bipolar transistor, provided on a current path corresponding to the second current; Provided on the current path corresponding to the first current, and the emitter thereof is the base of the sixth bipolar transistor. Is connected to its base, fourth, and seventh bipolar transistor biased in common with the fifth bipolar transistor, it may include. The current flowing through the first and fourth bipolar transistors may be a fourth current, and the fourth resistor may be provided on the path of the fourth current.
According to this configuration, the fourth current can be generated by multiplying the first current by the second current and dividing by the third current.

The control circuit according to an aspect may further include an offset circuit that generates a first voltage by offsetting a voltage obtained by full-wave rectification of an AC voltage to the high potential side.
Since there is a lower limit value in the input voltage range of the current / voltage conversion circuit, the AC voltage drops to near zero volts. Therefore, if the AC voltage is directly input to the current / voltage conversion circuit, the total harmonic distortion increases. By providing the offset circuit, the total harmonic distortion can be reduced.

The first error amplifier circuit may include a first current source that is turned on when the first detection voltage is lower than the first threshold voltage and raises the second voltage.
In this case, an increase in the output voltage of the DC / DC converter can be suppressed.

The first error amplifier circuit may include a second current source that is turned on when the first detection voltage is higher than the second threshold voltage and reduces the second voltage.
In this case, it is possible to reduce the influence of steep fluctuations in the load of the DC / DC converter.

  Another aspect of the present invention is a power factor correction circuit. This power factor correction circuit includes an output circuit of a DC / DC converter including a switching element, and a control circuit according to any one of the above-described modes for driving the switching element.

  Yet another embodiment of the present invention is an electronic device. This electronic device receives the output voltage of the rectifier circuit that rectifies commercial AC voltage, the above-described power factor correction circuit that receives the output voltage of the rectifier circuit, and the power factor correction circuit, and supplies the voltage obtained by stepping down the voltage to the load. A DC / DC converter.

  Note that any combination of the above-described constituent elements and the constituent elements and expressions of the present invention replaced with each other among methods, apparatuses, systems, and the like are also effective as an aspect of the present invention.

  According to an aspect of the present invention, the temperature characteristics of the PFC circuit can be improved.

It is a circuit diagram which shows the structure of the electronic device which concerns on embodiment. It is a circuit diagram which shows the structure of the PFC circuit which concerns on embodiment. It is a circuit diagram which shows the structure of a part of control circuit. It is a circuit diagram which shows the structure of a part of control circuit. It is a circuit diagram which shows the 1st modification of a control circuit. It is a circuit diagram which shows the structure of the PFC circuit which concerns on a 2nd modification.

  The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. The embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

In this specification, “the state in which the member A is connected to the member B” means that the member A and the member B are physically directly connected, or the member A and the member B are electrically connected to each other. Including the case of being indirectly connected through other members that do not substantially affect the state of connection, or do not impair the functions and effects achieved by the combination thereof.
Similarly, “the state in which the member C is provided between the member A and the member B” refers to the case where the member A and the member C or the member B and the member C are directly connected, as well as their electric It includes cases where the connection is indirectly made through other members that do not substantially affect the general connection state, or that do not impair the functions and effects achieved by their combination.

FIG. 1 is a circuit diagram showing a configuration of an electronic apparatus 1 according to the embodiment.
The electronic device 1 is, for example, a home appliance such as a television, a refrigerator, or an air conditioner or a computer. The electronic device 1 includes a microcomputer 2, a signal processing circuit 4, a DC / DC converter 100, a rectifier circuit 102, and a PFC (power factor correction circuit) 200. The electronic device 1 is divided into a primary side and a secondary side that are insulated from each other with an insulating transformer (not shown) of the DC / DC converter 100 as a boundary.

The rectifier circuit 102 is, for example, a diode rectifier circuit, receives an AC voltage such as a commercial AC voltage, and full-wave rectifies it to generate an _AC voltage VAC.

The PFC circuit 200 is a step-up DC / DC converter (switching regulator) that receives the _AC voltage VAC from the rectifier circuit 102 and generates an output voltage V _DC . PFC circuit 200 improves the power factor by matching the AC voltage _{V AC} input current _{I AC} phase.

The DC / DC converter 100 receives the output voltage _VDC of the PFC circuit 200, steps down the voltage, and supplies it to the microcomputer 2 and the signal processing circuit 4 that are loads.

  The microcomputer 2 controls the entire electronic device 1 in an integrated manner. The signal processing circuit 4 is a block that performs specific signal processing, and examples thereof include an interface circuit that performs communication with an external device, an image processing circuit, an audio processing circuit, and the like. Needless to say, the actual electronic device 1 is provided with a plurality of signal processing circuits 4 according to their functions.

  The above is the overall configuration of the electronic device 1. Next, a PFC circuit 200 that can be suitably used for such an electronic apparatus 1 will be described.

FIG. 2 is a circuit diagram showing a configuration of the PFC circuit 200 according to the embodiment.
The PFC circuit 200 includes a step-up DC / DC converter, and mainly includes a control circuit 210 and an output circuit 212. Since the output circuit 212 has a general topology including the inductor L1, the diode D1, the capacitor C1, and the switching transistor M1, detailed description thereof is omitted. By switching of the switching transistor M1, the input voltage _VAC is stepped down to generate the output voltage V _DC . Although the PFC circuit 200 can be said to be a DC / DC converter, the input voltage V _AC is a full-wave rectified AC voltage, and the output voltage V _DC is a DC voltage, so the operation is an AC / DC converter. It can be said.

The resistors R11 and R12 divide the output voltage V _DC of the PFC circuit 200 and generate a first detection voltage V _S corresponding to the output voltage V _DC . The first detection voltage V _S is input to the output voltage detection terminal (P_VS terminal) of the control circuit 210.

The detection current Rs is provided on the path of the switching transistor M1, and a second detection voltage V _I proportional to the current I _M1 flowing through the switching transistor M1 is generated between both ends thereof. The second detection voltage V _I is fed back to the current detection terminal (CS terminal) of the control circuit 210. The second detection voltage V _I has an intermittent waveform corresponding to the switching of the switching transistor M 1, but the envelope thereof may be considered to coincide with the input current I _AC of the PFC circuit 200.

Moreover, the full-wave rectified AC voltage _{V AC} is divided by the resistance R21, R22. The divided AC voltage V _BO is input to the input voltage detection terminal (P_BO terminal) of the control circuit 210.

  Hereinafter, a specific configuration of the control circuit 210 will be described. The control circuit 210 includes a first V / I conversion circuit 10, a second V / I conversion circuit 12, a third V / I conversion circuit 14, an offset circuit 16, a first error amplification circuit 18, a multiplier 20, and a second error amplification circuit 30. The drive circuit 40 is provided.

Part 1V / I conversion circuit 10 includes a first resistor R1, a first voltage V1 corresponding to the full-wave rectified AC voltage _{V AC} is input to the DC / DC converter (PFC circuit 200) to the first resistor R1 The first current I1 is generated by applying the first current I1. The first voltage V1 has a full-wave rectified waveform.
I1 = K1 × V1 / R1 (1)
K1 is a proportionality constant.

In the previous stage of the first V / I conversion circuit 10, an offset circuit 16 for offsetting the _AC voltage VAC divided by full-wave rectification to the high potential side is provided. The output of the offset circuit 16 is input to the first V / I conversion circuit 10 as the first voltage V1.

The first error amplification circuit 18 amplifies an error between the first detection voltage V _S corresponding to the output voltage V _DC of the DC / DC converter and a predetermined reference voltage V _REF to generate a second voltage V2.
The second V / I conversion circuit 12 includes a second resistor R2, and converts the second voltage V2 into a second current I2 by applying the second voltage V2 to the second resistor R2.
I2 = K2 × V2 / R2 (2)
K2 is a proportionality constant.

The third V / I conversion circuit 14 includes a third resistor R3, and generates a third current I3 by applying a predetermined voltage V _BGR (= V3) to the third resistor R3. The predetermined voltage V _BGR is preferably a constant voltage independent of temperature, and is preferably generated by a band gap reference circuit (not shown).
I3 = K3 × V _BGR / R3 (3)
K3 is a proportionality constant.

The multiplier 20 multiplies the first current I1 and the second current I2, and generates a fourth current I4 divided by the third current I3. The multiplier 20 includes a fourth resistor R4, and generates a fourth voltage V4 by causing the fourth current I4 to flow through the fourth resistor R4.
V4 = I4 × R4 (4)

The second error amplification circuit 30 amplifies an error between the second detection voltage V _I corresponding to the current I _M1 flowing through the switching transistor M1 of the output circuit 212 and the fourth voltage V4 from the multiplier 20, and the error voltage V Generate _ERR .

The drive circuit 40 drives the switching transistor M1 based on the error voltage _VERR . The drive circuit 40 generates a drive signal S _DRV having a duty ratio corresponding to the error voltage V _ERR by a pulse modulation method such as pulse width modulation (PWM) or pulse frequency modulation (PFM), and performs switching from the output terminal SWOUT. Output to the gate of the transistor M1. The configuration of the drive circuit 40 is not particularly limited, and a known technique may be used.

FIG. 2 shows an example of a PWM drive circuit 40. The drive circuit 40 includes a ramp waveform generator 42, a comparator 44, an oscillator 46, an RS flip-flop 48, and a driver 50.
The ramp waveform generation unit 42 generates a sawtooth wave having a predetermined frequency (for example, 65 kHz) or a periodic voltage V _RAMP having a triangular wave. The comparator 44 compares the error voltage V _ERR and the periodic voltage V _RAMP and generates a reset signal S _RST whose level changes at each intersection. The reset signal S _RST has a positive edge every time V _ERR crosses V _RAMP from below.

The oscillator 46 generates a set signal S _SET having a predetermined frequency. The RS flip-flop 48 receives a set signal S _SET at its set terminal (S) and a reset signal S _RST at its reset terminal (R). The output (Q) of the RS flip-flop 48 transitions to a high level for each positive edge of the set signal S _SET and transitions to a low level for each positive edge of the reset signal S _RST .

The generation of the set signal S _SET is not limited to that by the oscillator 46. For example, instead of the oscillator 46, a zero cross comparator may be provided that generates a set signal S _SET whose level transitions (positive edge) when the current of the inductor L1 drops to substantially zero. For example, the current of the inductor L1 can be suitably detected by providing an auxiliary winding in the inductor L1. In this case, compared with the case where the oscillator 46 is used, the energy stored in the inductor L1 can be used more efficiently. The set signal S _SET may be generated by yet another method. The same applies to a modified example of FIG. 5 described later.

The output of the RS flip-flop 48 is a pulse width modulated signal S _PWM . The driver 50 switches the switching transistor M1 based on the PWM signal _SPWM .
The duty ratio of the PWM signal S _PWM is such that the first detection voltage V _S matches the reference voltage V _REF by the feedback loop including the first error amplification circuit 18 and the feedback loop including the second error amplification circuit 30. envelope waveform of the current I _M1 flowing through the switching transistor M1 is adjusted to match the full-wave rectified input voltage V _AC waveform.

  The above is the overall configuration of the PFC circuit 200. Next, a specific configuration example of the control circuit 210 will be described.

FIG. 3 is a circuit diagram showing a configuration of part of the control circuit 210.
Offset circuit 16 via the resistor R1, it receives an input voltage V _BO of the full-wave rectified AC voltage V _AC is divided, and generates a first voltage V1 to offset it.

The first V / I conversion circuit 10 includes a transistor M11, an operational amplifier OA1, and a current mirror circuit CM1 in addition to the first resistor R1. One end of the first resistor R1 is grounded. One end (source) of the transistor M11 is connected to the first resistor R1 and the inverting input terminal of the operational amplifier OA1. The first voltage V1 is input to the non-inverting input terminal of the operational amplifier OA1. A current I _M11 flows through the transistor M11 and the resistor R1.
I _M11 = V1 / R1

The current mirror circuit CM1 is a cascoat type including transistors M12 to M15 and a resistor R2, and folds back the current I _M11 and outputs the first current I1. When the mirror ratio of the current mirror circuit CM1 is 1, K1 = 1 and equation (1a) is established.
I1 = V1 / R1 (1a)

The second V / I conversion circuit 12 and the third V / I conversion circuit 14 are configured in the same manner as the first V / I conversion circuit 10. In the second V / I conversion circuit 12 (third V / I conversion circuit 14), the current mirror circuit CM2 (CM3) includes transistors M22 and M23 (M32 and M33), respectively. Of course, the current mirror circuits CM2 and CM3 may be configured as a cascode type. Conversely, the current mirror circuit CM1 of the first V / I conversion circuit 10 may be configured similarly to the current mirror circuits CM2 and CM3. When the mirror ratio of the current mirror circuits CM2 and CM3 is 1, equations (2a) and (3a) are established.
I2 = V2 / R2 (2a)
I3 = V _BGR / R3 (3a)

The first error amplifier circuit 18 includes an error amplifier EA1, an output buffer 19, a first current source CS1, and a second current source CS2.
The error amplifier EA1 amplifies an error between the reference voltage V _REF and the first detection voltage V _S. The output buffer 19 has a push-pull format and generates the second voltage V2 corresponding to the output of the error amplifier EA1.

The first current source CS1 is turned on when the first detection voltage _{V S} is less than a predetermined first threshold voltage _{V TH1.} The first threshold voltage _{V TH1} is lower than the reference voltage _{V REF,} be a low value of about 15% than for example the reference voltage _{V REF} desirable. In the ON state, the first current source CS1 raises the second voltage V2 by supplying current to the output terminal of the first error amplifier circuit 18. When the second voltage V2 increases, the output voltage _VDC of the PFC circuit 200 increases.

The second current source CS2 is turned on when the first detection voltage V _S is higher than a predetermined second threshold voltage V _TH2 , and the second voltage source CS2 draws a current from the output terminal of the first error amplification circuit 18, thereby generating the second voltage. Decrease V2. When the second voltage V2 decreases, the output voltage _VDC of the PFC circuit 200 decreases.

The comparator CMP1 compares the first detection voltage V _S with the threshold voltage V _TH1 and generates a low voltage lockout signal (VSUVLO signal) that becomes a high level when V _S > V _TH1 . The first current source CS1 is turned on when the VSUVLO signal is at a low level. Further, the comparator CMP2 compares the first detection voltage V _S with the threshold voltage V _TH2 and generates an overvoltage protection signal (DOVP signal) that becomes a high level when V _S > V _TH2 . The second current source CS2 is turned on when the DOVP signal is at a high level.

  FIG. 4 is a circuit diagram showing a configuration of part of the control circuit 210. In addition to the fourth resistor R4, the multiplier 20 includes bipolar transistors Q1 to Q9, a current source 22, a resistor R5, and current mirror circuits CM41 to CM43.

  The current mirror circuits CM41 to CM43 fold back the first current I1 to the third current I3, respectively. Transistors Q1, Q2, Q4, Q5 and current source 22 form a differential amplifier. The first transistor Q1 and the second transistor Q2 constitute a differential pair. The fourth transistor Q4 and the fifth transistor Q5 are loads of the first transistor Q1 and the second transistor Q2, respectively. The emitters of the transistors Q4 and Q5 are connected to the collectors of the transistors Q1 and Q2, respectively. The current source 22 supplies a tail current to the differential pair (Q1, Q2).

  The third transistor Q3 is provided on a path of a current I3 'corresponding to the third current I3, and its emitter is connected to the base of the first transistor Q1, and its base is connected to the collector of the second transistor Q2. The sixth transistor Q6 is provided on the path of a current I2 'corresponding to the second current I2, and its emitter is connected to the base of the second transistor Q2. The seventh transistor Q7 is provided on the path of the current I1 ′ corresponding to the first current I1, and its emitter is connected to the base of the sixth transistor Q6, and the base of the fourth transistor Q4 and the fifth transistor Q5. Biased in common with the base.

The eighth transistor Q8 and the ninth transistor Q9 form a current mirror circuit CM44, and the current I4 ′ (= I _C1 ) flowing through the path formed by the first transistor Q1 and the fourth transistor Q4 is folded back to generate a fourth current I4. . The fourth resistor R4 is provided on the path of the fourth current I4. Voltage drop _{V R4} of the fourth resistor R4 is output as the fourth voltage V4.

The base-emitter voltages of the first transistor Q1 to the seventh transistor Q7 are VF1 to VF7, and collector currents flowing through the transistors are I _{C1 to} I _C7 .
VF1 + VF3 + VF5 = VF2 + VF8 + VF7 (5)
Holds. The collector current flowing in the bipolar transistor is
I _C ∝Is × exp (V _F / V _T ) (6)
V _T = kT
Is: saturation current q: charge of the electron (1.602 × 10 ⁻¹⁹ [C])
k: Boltzmann constant (1.38 × 10 ⁻²³ [J / K]
T: Absolute temperature ([K])

From equations (5) and (6), equation (7) is obtained.
_IC1 * _IC3 * _IC5 = _IC2 * _IC6 * _IC7 (7)
Here, since the transistors Q2 and Q5 are provided on the same current path, I _C2 = I _C5 is established, and Expressions (8) and (9) are obtained.
I _C1 × I _C3 = I _C6 × I _C7 (8)
I _C1 = I _C6 × I _C7 / I _C3 (9)

For simplicity, all the mirror ratios of the current mirror circuits CM41 to CM43 are set to 1. Then
I _C7 = I1 ′ = I1
I _C6 = I2 ′ = I2
I _C3 = I3 ′ = I3
Therefore, Expression (10) is obtained.
I _C1 = I2 × I1 / I3 (10)
When the current I _C1 flowing through the first transistor Q1 has a mirror ratio of 1 in the current mirror circuit CM44 including the transistors Q8 and Q9, Expression (11) is obtained.
I4 = I _C1 = I2 × I1 / I3 (11)

Substituting the formulas (1a) to (3a) into the formula (11), the formula (12) is obtained.
I4 = (V1 × V2) / V3 × R3 / (R1 × R2) (12)

Equation (13) is obtained from Equation (4) and Equation (12).
V4 = (V1 × V2) / V3 × (R3 × R4) / (R1 × R2) (13)

  The second error amplifier circuit 30 includes an error amplifier EA2 and an output buffer 32, and is configured similarly to the first error amplifier circuit 18 of FIG.

  The above is the configuration of the PFC circuit 200 according to the embodiment. Next, the operation of the PFC circuit 200 will be described.

The first voltage V1 has the same full-wave rectification waveform as the _AC voltage VAC, and the second voltage V2 and the third voltage V3 are both DC voltages. Therefore, the fourth voltage V4 is a full-wave rectified waveform having the same phase as the _AC voltage VAC.

As described above, the duty ratio of the PWM signal S _{PWM is controlled} by the system including the second error amplifier circuit 30 so that the envelope of the current I _M1 flowing through the switching transistor M1 matches the fourth voltage V4. Is done. Therefore, the current I _M1 flowing through the switching transistor M1, and thus the waveform and phase of the input current I _AC of the PFC circuit 200 match the _AC voltage VAC, and the power factor is improved.

Here, attention is paid to equation (13). Resistors R1 to R4 are formed by pairing. Therefore, even if temperature variation or process variation (referred to as temperature variation or the like) occurs, the respective resistance values vary while maintaining their ratio. That is, in the term of (R3 × R4) / (R1 × R2) in the equation (13), the influence of temperature variation and the like is canceled between the denominator and the numerator, so that the value is kept substantially constant. That can reduce the influence of temperature variation to the fourth voltage V4, it is possible to reduce the influence of temperature variation to thus input current I _AC waveform.

The PFC circuit 200 further has the following advantages.
Since the divided AC voltage V _BO has a full-wave rectified waveform, it drops to substantially zero volts. If the AC voltage V _BO is directly input to the first V / I conversion circuit 10, it is out of the input voltage range of the operational amplifier OA 1 and operates in the dead band. Therefore, the first current I 1 is a clean full-wave rectified waveform. Will be distorted. This distortion exacerbates total harmonic distortion (THD). On the other hand, the control circuit 210 according to the embodiment can prevent the first V / I conversion circuit 10 from operating in the dead zone by providing the offset circuit 16, and can improve the total harmonic distortion.

Further, since the PFC circuit 200 is required to respond to an envelope of about 50 Hz to 60 Hz, the response speed of the feedback loop is very low. Therefore, the feedback control using only the error amplifiers EA1 and EA2 cannot suppress the decrease in the output voltage V _{DC and} the increase in the output voltage V _DC due to the steep load fluctuation. In contrast, in the control circuit 210 according to the embodiment, the first current source CS1 is turned on in the low voltage state (V _S <V _TH1 ), and the second voltage V2 is increased faster than the response by the error amplifier EA1. As a result, the output voltage _VDC can be quickly increased. Further, by turning on the second current source CS2 in the overvoltage state (V _S > V _TH2 ) and reducing the second voltage V2 faster than the response by the error amplifier EA1, the output voltage V _DC can be quickly reduced. .

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are within the scope of the present invention. is there. Hereinafter, such modifications will be described.

Although the control circuit 210 that performs so-called average current mode control has been described with reference to FIG. 2, the present invention is not limited thereto and can be applied to the peak current mode. FIG. 5 is a circuit diagram showing a PFC circuit including the control circuit 210a according to the first modification. The peak current mode control circuit 210a includes a comparator 45 instead of the second error amplification circuit 30 of FIG. The comparator 45 includes a fourth voltage V4 comparing the second detection voltage _{V I,} generates a reset signal _{S RST} which becomes high level when V I> V4. This reset signal _SRST is input to the reset terminal of the RS flip-flop 48 of the drive circuit 40a. That is, the drive circuit 40a turns on the switching transistor M1 at predetermined intervals according to the set signal S _SET from the oscillator 46, and the second detection voltage V _I is higher than the fourth voltage V4 according to the reset signal S _RST. The switching transistor M1 is turned off every time.

In the control circuit 210a of FIG. 5, feedback is applied so that the peak value of the second detection voltage V _I , in other words, the peak value of the current I _M1 flowing through the switching transistor M1 coincides with the fourth voltage V4, and the output voltage V _DC Is stabilized. The control circuit 210a in the peak current mode can increase the efficiency as compared with the average current mode.

  FIG. 6 is a circuit diagram showing a configuration of a PFC circuit 200b according to the second modification. A rectifier circuit 102 and a filter 101 are provided in front of the PFC 200b. Needless to say, the filter 101 may be provided before the PFC circuit 200 already described with reference to FIG.

AC voltage V _AC noise is removed by the filter 101, full-wave rectified by the rectifier circuit 102, is smoothed by the smoothing capacitor C30. The smoothed voltage (referred to as input voltage _VIN ) is input to the PFC circuit 200b. In this modification, the PFC circuit 200b operates as a DC / DC converter that converts a DC voltage into a DC voltage.

  The PFC circuit 200b mainly includes a control circuit 210b and an output circuit 212. As the control circuit 210b, the average current mode control circuit 210 of FIG. 2 or the peak current mode control circuit 210a of FIG. 5 can be used.

  In parallel with the capacitor C30, a resistor R31 and a capacitor C31 are provided in series. The potential Vcc at the connection point between the resistor R31 and the capacitor C31 is supplied to the power supply terminal VCC of the control circuit 210.

The detection resistor Rs is provided between the source of the switching transistor M1 and the output terminal P32 of the rectifier circuit 102. The detection resistor Rs, a current flowing through the switching transistor M1, the current _{I M1} corresponding to the input current of the PFC circuit 200b in other words flow, is across the sense resistor Rs, according to the current _{I M1} flowing through the switching transistor M1 second detection voltage (voltage drop) _{V I} is generated. The second detection voltage V _I is fed back to the current detection terminal (CS terminal) of the control circuit 210. The detection resistor Rs may be provided between the source of the switching transistor M1 and the ground terminal, as in the above-described embodiment. Conversely, in the embodiment described above, the detection resistor Rs may be arranged at the position shown in FIG.

Diodes D21, D22 is a commercial AC voltage _{V AC} input to the rectifier circuit 102 full-wave rectification. The full-wave rectified AC voltage V _BO is divided by resistors R 21 and R 22 and input to the input voltage detection terminal (P_BO terminal) of the control circuit 210.

  The above is the configuration of the PFC circuit 200b according to the second modification. Also by this modification, the same effect as the PFC circuit 200 of the embodiment can be obtained.

  In the embodiment, the case where the DC / DC converter 100 is mounted on the electronic device 1 has been described. However, the present invention is not limited thereto, and can be applied to various power supply apparatuses. For example, the DC / DC converter 100 can be applied to an AC adapter that supplies power to an electronic device. Examples of the electronic device in this case include a laptop computer, a desktop computer, a mobile phone terminal, and a CD player, but are not particularly limited.

  Although the present invention has been described using specific terms based on the embodiments, the embodiments only illustrate the principles and applications of the present invention, and the embodiments are defined in the claims. Many variations and modifications of the arrangement are permitted without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Electronic device, EA1 ... Error amplifier, I1 ... 1st electric current, M1 ... Switching transistor, R1 ... 1st resistance, CS1 ... 1st current source, 2 ... Microcomputer, I2 ... 2nd electric current, R2 ... 2nd resistance, CS2 ... second current source, I3 ... third current, R3 ... third resistor, 4 ... signal processing circuit, R4 ... fourth resistor, 46 ... oscillator, 48 ... RS flip-flop, 50 ... driver, 100 ... DC / DC Converter 102 rectifier circuit 200 PFC circuit 210 control circuit 212 output circuit OA operational amplifier CM current mirror circuit

Claims (8)

A control circuit for a power factor correction circuit having a DC / DC converter,
A first voltage / current conversion circuit that generates a first current by applying a first voltage having a full-wave rectified waveform to a first resistor;
A first error amplification circuit that amplifies an error between a first detection voltage corresponding to an output voltage of the DC / DC converter and a predetermined reference voltage and generates a second voltage;
A second voltage / current conversion circuit for generating a second current by applying the second voltage to a second resistor;
A third voltage / current conversion circuit for generating a third current by applying a predetermined voltage to the third resistor;
A multiplier that multiplies the first current and the second current, generates a fourth current divided by the third current, and generates a fourth voltage by flowing the fourth current through a fourth resistor;
A second error amplifying circuit for amplifying an error between a second detection voltage corresponding to a current flowing through the switching element of the DC / DC converter and the fourth voltage and generating an error signal;
A drive circuit for driving the switching element based on the error signal;
A control circuit comprising: A control circuit for a power factor correction circuit having a DC / DC converter,
A first voltage / current conversion circuit that generates a first current by applying a first voltage having a full-wave rectified waveform to a first resistor;
A first error amplification circuit that amplifies an error between a first detection voltage corresponding to an output voltage of the DC / DC converter and a predetermined reference voltage and generates a second voltage;
A second voltage / current conversion circuit for generating a second current by applying the second voltage to a second resistor;
A third voltage / current conversion circuit for generating a third current by applying a predetermined voltage to the third resistor;
A multiplier that multiplies the first current and the second current, generates a fourth current divided by the third current, and generates a fourth voltage by flowing the fourth current through a fourth resistor;
A comparator for comparing the second detection voltage corresponding to the current flowing through the switching element of the DC / DC converter and the fourth voltage;
A driving circuit that turns on the switching element every predetermined period and turns off the switching element every time the second detection voltage becomes higher than the fourth voltage in accordance with the output of the comparator;
A control circuit comprising: The multiplier is
A differential pair composed of first and second bipolar transistors, fourth and fifth bipolar transistors each having an emitter connected to a collector of each of the first and second bipolar transistors, and a tail in the differential pair A current source for supplying current, and a differential amplifier comprising:
A third bipolar transistor provided on a current path corresponding to the third current, an emitter thereof connected to a base of the first bipolar transistor, and a base connected to a collector of the second bipolar transistor;
A sixth bipolar transistor provided on a current path corresponding to the second current, the emitter of which is connected to the base of the second bipolar transistor;
A seventh bipolar transistor provided on a current path corresponding to the first current, having an emitter connected to a base of the sixth bipolar transistor, and a base biased in common with the fourth and fifth bipolar transistors; A transistor,
Including
Generating the fourth current in response to a current flowing through the first and fourth bipolar transistors;
The control circuit according to claim 1, wherein the fourth resistor is provided on a path of the fourth current.   4. The control circuit according to claim 1, further comprising an offset circuit that offsets a voltage obtained by full-wave rectification of an AC voltage to a high potential side and generates the first voltage. 5. .   5. The first error amplifier circuit includes a first current source that is turned on when the first detection voltage is lower than a first threshold voltage and raises the second voltage. 6. The control circuit according to any one of the above.   6. The first error amplifier circuit includes a second current source that is turned on when the first detection voltage is higher than a second threshold voltage and reduces the second voltage. The control circuit according to any one of the above. An output circuit of a DC / DC converter including a switching element;
The control circuit according to any one of claims 1 to 6, which drives the switching element;
A power factor correction circuit comprising: A rectifier circuit for rectifying commercial AC voltage;
The power factor correction circuit according to claim 7, which receives an output voltage of the rectifier circuit;
A DC / DC converter that receives an output voltage of the power factor correction circuit and supplies a voltage obtained by stepping down the output voltage to a load;
An electronic device comprising:

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