JP3565416B2 - Power factor improvement circuit - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a power factor improving circuit used for a switching power supply, and more particularly to an improvement of a power factor improving circuit for reducing noise of an input line.
[0002]
[Prior art]
FIG. 9 shows an example of a conventional circuit of the active filter system. In FIG. 9, for example, an AC voltage of 100 to 240 V is input to the EMI filter 1. Diode bridge 2 (D1) rectifies the AC voltage.
[0003]
The rectified electric signal is boosted in accordance with the switching time of the boost inductor 3 (L1) and the switching element 4 (SW1), smoothed by the flywheel diode 5 (D2) and the smoothing capacitor 6 (C1), and set to the set voltage ( For example, the voltage is boosted to 400 V) and input to the load DC / DC converter 7 connected to the subsequent stage.
[0004]
A boost voltage detecting resistor R2, R3 is connected between the DC / DC converter 7 and the common in front of the DC / DC converter 7, and a connection point of R2, R3 is connected to an input terminal of a feedback amplifier constituting the control circuit unit 8. ing. The connection point between R2 and R3 is designed so that a difference voltage of, for example, about 0.1 to 0.15 V is generated according to a load change of the DC / DC converter 7.
[0005]
The feedback amplifier 8a is composed of an error amplifier 8a 'as shown in FIG. 10, and a reference voltage Vref of, for example, about 2.5 V is connected to the non-inverting input terminal. As described above, the voltage connected to the inverting terminal of the error amplifier 8a 'changes in the range of, for example, 0.1 to 0.15V, but the error amplifier 8a' changes the voltage in the range of, for example, 0 to 5V according to the change. Output.
[0006]
Returning to FIG. 9, the controller 8 b compares the input voltage signal or a signal corresponding thereto with the voltage signal output from the error amplifier 8 a ′ to enable the power factor improvement control so that the input current becomes a sine wave. It performs arithmetic processing and converts it to a waveform that can set the boost level in phase with the input voltage waveform.
[0007]
The controller 8b has a comparator (not shown) inside. The controller 8b compares the waveform of the current flowing through the boost inductor 3 or the waveform of the current flowing through the switching element 4 (SW1) with the signal after the above-described arithmetic processing to determine the input voltage. , The on / off timing of the switching element 4 (SW1) is determined.
[0008]
When the current waveform of the boost inductor 3 or the switching element 4 (SW1) reaches the signal level after the arithmetic processing, the drive signal of the switching element 4 (SW1) output from the controller 8b is inverted, and the switching element 4 (SW1) is turned off. Let it.
[0009]
The ON timing of the switching element 4 (SW1) is performed by the following two methods. When the current of the boost inductor 3 is discontinuous, the current flowing through the boost inductor 3 decreases to zero when the switching element 4 (SW1) is turned off, so that point is detected and the switching element 4 (SW1) is turned off. Turn on. When the current of the boost inductor 3 is continuous, an oscillator (not shown) in which one cycle in which the switching element 4 (SW1) is turned on / off is set in the controller 8b, and when the time of the oscillator is up, the switching element 4 (SW1) is set. ) Is turned on.
[0010]
[Problems to be solved by the invention]
The input voltage of such a power factor correction circuit is as wide as about 100 to 240 V. For example, when the boost setting voltage is about 400 V (set by R2 and R3 and the feedback circuit), when the input voltage is low near 100 V, boosting is performed. In order to store energy in the inductor 3 (L1), the ON time of the switching element 4 (SW1) must be lengthened. As a result, the current flowing through the boost inductor 3 (L1) is increased, the loss is increased, the efficiency is reduced, the components must be increased, and the noise increases.
[0011]
By the way, in the above-mentioned circuit, the voltage input to the DC / DC converter 7 is boosted to, for example, 400 V. However, depending on the DC / DC converter, it is not always necessary to keep this input voltage constant. Some output has no effect.
The present invention presupposes a power factor improving circuit using a DC / DC converter which does not affect the output even if the input voltage fluctuates somewhat, and reduces the current flowing through the boost inductor 3 (L1) to reduce the other parts. It is an object of the present invention to provide a power factor correction circuit that does not cause any trouble including the power factor correction.
[0012]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a rectifier for inputting an AC voltage from a power supply and converting the DC voltage into a DC signal, and a booster for boosting the DC signal to a predetermined set voltage. A DC / DC converter as a load for performing DC input / DC output based on the boosted signal, load fluctuation detecting means for detecting a load fluctuation of the DC / DC converter, and an output of the load fluctuation detecting means A power factor improving circuit having control means for matching the phases of the AC voltage and the DC current based on the input voltage detecting unit for detecting a voltage change of the DC signal and a set voltage value changing unit for changing the set voltage. When the AC voltage is higher than a predetermined voltage, the boost setting value is increased, and when the AC voltage is lower than the predetermined voltage, the boost setting value is set lower, thereby reducing the load of the booster. Characterized in that it has been reduced.
[0013]
In claim 2, Te claim 1, wherein the power factor correction circuit smell, change settings voltage is characterized in that to carry out stepwise.
[0014]
According to a third aspect of the present invention, in the power factor improving circuit according to the first aspect, the set voltage is changed in an analog manner.
According to a fourth aspect of the present invention, in the power factor correction circuit according to the first aspect, the setting voltage is changed in a stepwise manner and an analog manner in accordance with the voltage of the AC power supply.
[0015]
【Example】
FIG. 1 shows a configuration of a power factor correction circuit according to the present invention, which differs from the conventional example shown in FIG. 9 in that an input voltage correction circuit 10 is provided. The one end of the input voltage correction circuit 10 is connected to the dialog diode bridge 2 (D1) and the boost inductor 3 connection point (L1) (A), the other end connected between the boosted voltage detecting resistors R2, R3 and the common potential Is done.
[0016]
FIG. 2 shows the details of the input voltage correction circuit 10. The input voltage from point A is connected to a common potential via resistors R5 and R6, and a capacitor C2 is connected to both ends of the resistor R6 connected to the common potential. Both ends are connected. The gate of the transistor 11 functioning as the switch SW2 is connected to a connection point between R5 and R6, a resistor R4 is connected between the collector and the emitter, and the collector is connected to the resistor R3 and the emitter is connected to the common potential.
[0017]
The input voltage correction circuit 10 is provided with an input voltage detection unit (E unit enclosed by a two-dot chain line) so that the voltage at the connection point of R2 and R3 can be reduced as the input voltage increases and the boost setting value can be increased. It is composed of a step-up setting change section (F section surrounded by a two-dot chain line). The input voltage detection unit E detects the input voltage directly, or detects the zero current or zero voltage of the boost inductor 3 (L1), or the auxiliary winding wound around L1 to be used for an auxiliary power supply or the like. The input voltage is indirectly detected using a line (not shown).
[0018]
The boost set value changing unit changes the set value variably or stepwise according to the input voltage. This circuit includes an operational amplifier and a comparator using the transistor 11 (SW2).
For example, the transistor 11 is switched to R3 or R3 + R4 by using the transistor 11 so that the boost setting value becomes 220 V at 100 Vac or more and the boost setting value becomes 400 V at 200 Vac or more.
[0019]
The input voltage from point A is divided by resistors R5 and R6, but a switching point is set according to the input voltage. The divided voltage has a pulsating waveform, and the boost setting value is switched every cycle, so that the boost voltage cannot be obtained stably. The capacitor C2 smoothes the DC voltage to obtain a stable boosted voltage.
[0020]
This voltage is applied between the base and the emitter of the transistor 11 (SW2) to turn ON / OFF the SW2. In a 100 V system with a low input voltage, SW1 is turned off, and the boost setting resistance is R3 + R4. When the input voltage is 200 Vac or more, the transistor is turned on and R4 is short-circuited, so that the boost setting resistor switches to R3.
[0021]
The boosted voltage is detected by the switched resistance and R2, and the negative feedback control is performed via the error amplifier of the feedback unit 8a so that the boosted voltage becomes substantially constant. If a more stable operation is required, a measure such as providing a hysteresis circuit in the detection unit in FIG. 2 is taken as shown in a G section surrounded by a two-dot chain line in FIG.
[0022]
FIG. 3B shows the change of the boosted value with respect to the input voltage in the case where the hysteresis circuit G is provided. In FIG. 3A, when the input voltage shifts from the high input voltage to the low input voltage, b. This shows a case where migration has occurred.
[0023]
FIG. 4 is an input voltage correction circuit showing another embodiment. Here as well as connected to a non-inverting input terminal of the error amplifier through a resistor R 7 to the input voltage from the A point connects one end of the non-inverting resistor connected in parallel to the input terminal R8 and the capacitor C2, the other The ends are connected to a common potential.
[0024]
That is, the reference voltage terminal of the error amplifier of the feedback unit 8a is linearly varied according to the input voltage in accordance with the input voltage to change the boost setting value. Then, similarly to the embodiment shown in FIG. 2, the input voltage is divided by the resistors R7 and R8, and the voltage smoothed by the capacitor C2 is applied to the reference voltage terminal of the error amplifier of the feedback unit 8a.
[0025]
With this configuration, the reference voltage increases with an increase in the input voltage. Therefore, when the input voltage is low, the boosted voltage can be set low, and when the input voltage is high, the boosted voltage can be set high.
[0026]
FIG. 5A shows the relationship between the voltage Vc1 applied to both ends of the conventional smoothing capacitor (C1) and the voltage at the point A (input voltage) with the set voltage being constant, and FIG. 5B shows that the set voltage is variable. The relationship between Vc1 of the present invention and the voltage at point A (input voltage) is shown. FIG. 6A is a diagram showing an example in which the set voltage is performed in an analog manner, and FIG. 6B is a diagram showing an example in which a portion performed in a stepwise manner and a portion performed in an analog manner are mixed according to the voltage of the AC power supply. It is.
[0027]
FIGS. 7 and 8 show the results of experiments using the input voltage correction circuit 10 of FIG. 2. In both the input voltages 100 Vac (FIG. 7) and 240 Vac (FIG. 8), the input current waveform becomes sinusoidal, and the power factor is improved. This indicates that there is no problem even when the present invention is implemented.
[0028]
Further, according to the configuration of the present invention, there is also a loss improvement effect. That is, when the input voltage is low, the voltage applied to the boost inductor 3 is lower than in the conventional method, and the core loss of the inductor is reduced. In addition, the effective value of the current flowing through the inductor can be reduced and the copper loss can be reduced as compared with the conventional method.
[0029]
Since the loss can be reduced in this way, the inductance can be reduced to about 1/2 and the size of the inductor can be reduced. Despite the downsizing of the inductor, an efficiency of 95.5% min or more equivalent to that of the conventional circuit was obtained at an input voltage of 100 Vac.
[0030]
The foregoing description of the present invention has been presented by way of illustration and example only of particular preferred embodiments. Thus, it will be apparent to one skilled in the art that the present invention may be modified or modified in many ways without departing from its essentials. The scope of the present invention defined by the description of the claims is intended to cover alterations and modifications within the scope.
[0031]
【The invention's effect】
The effects confirmed when the DC / DC converter 7 has a load power of 60 W will be described below.
{Circle around (1)} Even if the boost setting value is varied according to the input voltage, there is no problem in improving the power factor.
{Circle around (2)} By reducing the boosted voltage at the time of low input voltage, the energy stored in the boost inductor is reduced, and the core loss and the copper loss of the boost inductor can be reduced.
(3) The inductance and size of the boost inductor can be reduced by reducing the loss. The boost inductor was reduced in size to a bottom area of -40% and a volume of -57%. The efficiency in the example was equal to or higher than that of the conventional example, and as a result of calculation using a power meter or the like, it was 95.5% min at an input voltage of 100 Vac.
[0032]
(4) Since the energy stored in the boost inductor is small, the current peak value is small. As a result, the normal mode component of the conduction noise returning to the input is reduced, and the EMI filter can be downsized. Cost reduction can be achieved by downsizing these components.
[Brief description of the drawings]
FIG. 1 is a main part configuration diagram showing an example of an embodiment of a power factor correction circuit according to the present invention.
FIG. 2 is a circuit diagram showing an example of an input correction circuit used in the power factor correction circuit of the present invention.
FIG. 3 is a diagram showing an embodiment in which a hysteresis circuit is provided in the circuit of FIG. 2;
FIG. 4 is a circuit diagram showing another embodiment of the input correction circuit used in the power factor correction circuit of the present invention.
FIG. 5 is a diagram showing a relationship between Vc1 of the conventional example in which the set voltage is constant and a voltage of the point A (input voltage) of the present invention in which the set voltage is variable.
FIG. 6 is a diagram illustrating an example in which a set voltage is performed in an analog manner, and an example in which a part that performs a stepwise operation and a part that performs an analog operation in accordance with the voltage of an AC power supply are mixed.
FIG. 7 is a diagram showing an example of a current waveform with respect to a voltage of the power factor correction circuit to which the present invention is applied.
FIG. 8 is a diagram showing another example of the current waveform with respect to the voltage of the power factor correction circuit to which the present invention is applied.
FIG. 9 is a diagram showing an example of a conventional power factor correction circuit.
FIG. 10 is a diagram illustrating an example of an error amplifier included in a feedback circuit.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 EMI filter 2 diode bridge 3 boost inductor 4 switching element 5 flywheel diode 6 smoothing capacitor 7 DC / DC converter 8 control circuit section 8a feedback circuit 8b controller 10 input voltage correction circuit

Claims (4)

A rectifier for inputting an AC voltage from a power supply and converting the DC signal into a DC signal, a booster for boosting the DC signal to a predetermined voltage, and a load for performing DC input / DC output based on the boosted signal DC / DC converter, load fluctuation detecting means for detecting a load fluctuation of the DC / DC converter, and control means for matching the phases of the AC voltage and the DC current based on the output of the load fluctuation detecting means. In the rate improvement circuit, an input voltage detection unit that detects a voltage fluctuation of the DC signal and a set voltage value change unit that changes the set voltage are provided, and when the AC voltage is higher than a predetermined voltage, a boost set value is increased. A power factor improving circuit , wherein when the AC voltage is lower than a predetermined voltage, a load of the boosting means is reduced by setting a boost setting value to be low . 2. The power factor improving circuit according to claim 1, wherein the setting voltage is changed stepwise . 2. The power factor improving circuit according to claim 1, wherein the setting voltage is changed in an analog manner. 2. The power factor correction circuit according to claim 1, wherein a change in the set voltage is performed in a stepwise manner and a part in an analog manner in accordance with the voltage of the AC power supply .

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