JPH10108451A - Input ac voltage detecting method and apparatus of switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute excessive voltage rise operation control for surely preventing the switching operation in which an excessive current flows into a switching element in the voltage rising operation, where an input AC voltage is lower than the predetermined voltage. SOLUTION: An alternate current from a line filter is both-wave rectified with rectifying diodes D21, D22 and is then divided by resistors R21, R22 and then input to a LPF 21. An input AC-detecting voltage Vr, corresponding to an effective voltage sent from an LPF 21 is output on the basis of its cutoff frequency characteristic and response characteristic. This input AC-detecting voltage Vr is compared in a comparator 22 with the reference voltage value. When the input AC-detecting voltage Vr exceeds the reference voltage value, an input AC-detecting voltage Vra, corresponding to the effective voltage on which the rating of the excessive voltage rise operation control depends is output to the control section from the output end. When the input AC detecting voltage Vra is lower than the predetermined value of the input AC voltage which is not input to the control section, the switching operation in which an excess current flows into the switching element is stopped, and the excessive voltage rise operation control is executed for shortening the on period.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a step-up switching power supply that obtains a voltage higher than an input voltage. The present invention relates to a method and an apparatus for detecting an input AC voltage of a switching power supply for detecting an input AC voltage for performing suppression control.

[0002]

2. Description of the Related Art Conventionally, in a switching power supply of a boost type or the like, when an input alternating current (AC) voltage drops, a switching element tries to output a constant boosted voltage by its closed loop control, and an excessive boost in which an excessive current flows. Operation may be performed. For this reason, the input AC voltage is monitored, and when the voltage drops below a predetermined value, the switching operation of the switching element is stopped so that an excessive current does not flow, and the suppression control (hereinafter, referred to as excessive (Referred to as boost control suppression control). In other words, to perform the switching operation from an appropriate input AC voltage,
Controls switching elements.

FIG. 6 is a block diagram showing a configuration of a conventional switching power supply for performing control for suppressing excessive boosting operation. This switching power supply is of a well-known external excitation type, and outputs a high voltage (+ HV) and a low voltage (+ LV) boosted by pulse width (PWM) control.

In this operation, first, an alternating current from a commercial AC power supply or the like is supplied to a line filter 1, where noise is removed, waveform shaping is performed, etc., and then a bridge rectifier 2 is turned on.
To perform a double-wave rectification, and apply it to one end of a primary coil (operating as a choke coil) L1 of the transformer T.

A switching element 3 such as a field effect transistor (FET) is connected in series to the other end of the primary coil L1. At the time of the OFF operation of the switching (ON / OFF) operation of the switching element 3, the energy stored in the primary coil L <b> 1 in the previous ON operation is rectified by the rectifier 4. Further, this rectified voltage is supplied to the electrolytic capacitor C2.
High voltage (+
HV) is output.

In this case, control for keeping the output high voltage constant is performed. First, the output high voltage is input to the control unit 5, where it is compared with a reference voltage value by a comparator (not shown) or the like. Based on the comparison value here, the gate when the switching element 3 is an FET is driven by PWM control,
Performs closed-loop control to stabilize the fluctuation of the output high voltage due to the fluctuation of the input AC voltage and the fluctuation of the current to the load. Further, the alternating current induced in the secondary coil L2 of the transformer T is rectified by the low-voltage rectifier circuit 6, and a low voltage (+ LV) smoothed by the electrolytic capacitor C3 is output.

Further, in this switching power supply, operation control for power factor improvement is performed. The operation control of this power factor improvement
When the current detector 8 such as a current transformer has a high voltage (-H
V) line, and the detection current and the output voltage from the bridge rectifier 2 and the electrolytic capacitor C1 are input to the control unit 5 respectively. The control unit 5 controls the switching element 3 to perform operation control for power factor improvement to make the current waveform and the voltage waveform similar. Further, the control unit 5 controls the low-voltage rectifier circuit 6 through the start circuit 7 and performs start control for supplying the low voltage (+ LV) from a specified voltage to the load.

Further, this switching power supply performs suppression control for an excessive boosting operation, and an input AC voltage detecting unit 10 for this is provided. As shown in FIG. 7, the input AC voltage detector 10 rectifies the alternating current from the line filter 1 with both rectifier diodes D1 and D2, divides the alternating current to a specified voltage with resistors R1 and R2, and performs impedance matching and the like. Do. Further, a noise component in the divided input AC detection voltage is removed by the capacitor C4, and the input AC detection voltage is output. This input AC detection voltage is input to the minus input terminal of the comparator (operation amplifier) 10a.

A threshold value, which is a reference voltage value divided by resistors R3 and R4, is set at the plus input terminal of the comparator 10a. This threshold value is set to the input AC detection voltage from the capacitor C4. When the peak value is exceeded, a pulse is output from the output terminal. This pulse is integrated by a resistor R5 and a capacitor C6 at the subsequent stage, and this constant voltage value is further compared by a comparator (operating amplifier) 10b to determine a threshold value of a reference voltage value divided by the resistors R3 and R4. When it exceeds, an input AC detection voltage indicating that the input AC is a normal value equal to or higher than a specified voltage is output to the control unit 5.

The control unit 5 performs PWM control for driving the switching element 3 on and off based on the input AC detection voltage, and the boosting operation is performed. The control unit 5
When the input AC detection voltage is not input to the control unit 5,
That is, by performing control to output a predetermined boosted voltage when the input AC voltage falls below a predetermined value, control is performed to prevent a switching operation in which an excessive current flows through the switching element. That is, the switching element 3 is set to F
At the time of ET, a cutoff voltage is sent to the gate to stop the switching operation, and control for suppressing an excessive boosting operation such as shortening the ON time of the switching element to limit the output voltage to a predetermined output voltage is performed. .

[0011]

However, in the above-described conventional switching power supply, the input AC voltage detector 10 shown in FIG. 7 uses the rectifier diodes D1 and D2 to perform the double-wave rectification (pulsating current) peak voltage value. Is compared with the reference voltage threshold,
Since the input AC detection voltage is obtained, it is difficult to appropriately control the excessive boosting operation.

This is because a switching power supply with large power consumption is often connected to an AC line for supplying AC to the line filter 1, and the maximum value portion of the AC waveform is destroyed by the switching ON / OFF operation. . That is, as shown in FIG. 8, the waveform that has been subjected to the dual-wave rectification by the rectifier diodes D1 and D2 of the input AC voltage detection unit 10 collapses with respect to the normal waveform including the dotted line as shown by the solid line. In this case, if the reference voltage value (threshold) BV is set to detect the peak voltage, the input AC voltage cannot be detected.

The control for suppressing the excessive boosting operation by detecting the peak voltage operates according to the rating depending on the effective voltage. When the input AC waveform is distorted as shown in FIG. There is a problem that the control may not be performed despite the rating in which the suppression control of the excessive boosting operation can be performed.

It is an object of the present invention to prevent a switching operation in which an excessive current flows through a switching element when an input AC voltage is distorted and its effective voltage is obtained when the input AC voltage drops below a predetermined value. It is an object of the present invention to provide a method and an apparatus for detecting an input AC voltage of a switching power supply, which can surely control the excessive boosting operation.

[0015]

In order to achieve the above object, the present invention monitors an input AC voltage and suppresses a switching operation in which an excessive current flows through a switching element when the input AC detection voltage drops. In an input AC voltage detection method in a switching power supply that detects an input AC voltage to perform operation suppression control, the input AC voltage is double-wave rectified, and then corresponds to an effective voltage, and
A substantially constant input AC detection voltage is generated, and suppression control of an excessive boosting operation is performed based on the input AC detection voltage.

The present invention also monitors an input AC voltage and detects an input AC voltage for performing a control for suppressing an excessive boosting operation for suppressing a switching operation in which an excessive current flows through a switching element when the input AC detection voltage decreases. In the input AC voltage detecting device of the switching power supply, the rectifying means for performing the dual-wave rectification of the input AC voltage and the dual-wave rectified voltage from the rectifying means correspond to the effective voltage and perform the control of suppressing the excessive boosting operation. And an input AC detection voltage generating means for generating and outputting a substantially constant input AC detection voltage.

In the present invention, the input AC voltage is double-wave rectified,
Corresponding to the effective voltage from this rectified output, and detecting a substantially constant input AC voltage, when the input AC detection voltage has dropped below a predetermined value, that is, the input AC voltage has dropped below a predetermined value In such a case, control is performed to suppress an excessive boosting operation such as stopping a switching operation in which an excessive current flows through the switching element, shortening the ON time of the switching element, and limiting the switching voltage to a predetermined output voltage.

Therefore, the input AC voltage is distorted and
When the effective voltage is obtained, it is possible to reliably control the excessive boosting operation to prevent a switching operation in which an excessive current flows through the switching element when the input AC voltage falls below a predetermined value.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a method and an apparatus for detecting an input AC voltage in a switching power supply according to the present invention will be described. FIG. 1 is a circuit diagram showing a configuration of an embodiment of a method and an apparatus for detecting an input AC voltage in a switching power supply according to the present invention. The configuration shown in FIG. 1 is based on input AC voltage detecting section 10 in the switching power supply shown in FIG.
It corresponds to. Hereinafter, FIG. 6 will be described repeatedly.

The input AC voltage detector 20 shown in FIG. 1 is provided with rectifier diodes D21 and D22 for rectifying the AC from the line filter 1 in FIG. further,
The two-wave rectified (pulsating current) voltage output from the rectifier diodes D21 and D22 is divided into a specified voltage so that the circuit at the subsequent stage can easily process the impedance, and the cathodes of the rectifier diodes D21 and D22 are grounded to achieve impedance matching. And resistors R21 and R22 connected in series.

Further, a low-pass filter (LPF) which receives a double-wave rectified (pulsating current) voltage from the connection point between the resistors R21 and R22 and outputs an input AC detection voltage Vr corresponding to the effective voltage. 21 are connected. This L
The PF 21 responds to the double-wave rectified waveforms from the rectifier diodes D21 and D22, for example, so that the second harmonic (double-wave rectified waveform) of the 50 Hz AC waveform of the commercial AC power supply is sufficiently reduced, for example, a cutoff frequency. It has a frequency characteristic of 60 Hz.

Further, there is provided a comparator (differential amplifier) 22 to which the output side of the LPF 21 and the minus input terminal are connected. A positive input terminal of the comparator 22 has series-connected resistors R23 and R24 for setting a reference voltage value (threshold value) obtained by dividing the voltage (Vcc) of the power supply line with the ground. Are connected.

FIG. 2 is a circuit diagram showing a detailed configuration example of the LPF 21. This example is a known resistor input type active (active) filter to which a resistor and a capacitor are connected. As shown in FIG. 2, the active filter includes a resistor R30 / capacitor C30, a resistor R31 / capacitor C31, a resistor R32 / capacitor C32, an operational amplifier (op-amp) 34, and a resistor R35 / capacitor C3.
5, a fifth-order configuration including a resistor R36 / capacitor C36, an operational amplifier (op-amp) 37, and feedback resistors R37 and R38. LPF2 of this active filter
1 has a cutoff frequency of 60 Hz and a gain of, for example, 1
The frequency and gain characteristics are set to 00 times.

Next, the operation of this embodiment will be described. AC from a commercial AC power supply or the like is supplied to the line filter 1 shown in FIG. The line filter 1 removes noise components, performs a waveform shaping process and the like, and rectifies the noise with a bridge rectifier 2. This rectified voltage is smoothed by the electrolytic capacitor C1 and applied to one end of a primary coil (operating as a choke coil) L1 of the transformer T.

When the switching element 3 connected to the other end of the primary coil L1 is turned off in the switching (on / off) operation, the energy stored in the primary coil L1 during the previous on operation is rectified by the rectifier 4. Further, the rectified voltage is smoothed through the electrolytic capacitor C2, and the boosted high voltage (+ HV) is output.

The output high voltage is also input to the control unit 5. The control unit 5 performs closed loop control for making the output high voltage constant, operation control for improving the power factor, and suppression control for excessive boosting operation for preventing a switching operation in which an excessive current flows through the switching element when the input AC voltage falls below a predetermined value. Done.

The control unit 5 compares the output high voltage with a threshold value of a reference voltage value by a comparator (not shown) or the like. A well-known PWM control signal corresponding to this comparison value drives the gate when the switching element 3 is an FET. By the switching (on / off) operation time by this drive, the output high voltage is stably output. Further, the AC induced in the secondary coil L2 of the transformer T is rectified by the low-voltage rectifier circuit 6, and a low voltage (+ LV) smoothed by the electrolytic capacitor C3 is output.

In the operation control of the power factor improvement, the detection current from the current detector 8 and the output voltage through the bridge rectifier 2 and the electrolytic capacitor C1 are input to the control unit 5 shown in FIG. The control unit 5 controls the switching element 3 to perform operation control for power factor improvement to make the current waveform and the voltage waveform similar. Further, the control unit 5 controls the low-voltage rectifier circuit 6 through the start circuit 7 and performs start control for supplying the low voltage (+ LV) from a specified voltage to the load.

Next, in the control for suppressing the excessive boosting operation, FIG.
Rectifier diode D2 of the input AC voltage detector 20 shown in FIG.
1 and D22 perform double-wave rectification of the AC from the line filter 1 shown in FIG.
Then, the voltage is divided so that the signal processing in the LPF 21 of the subsequent active filter is easy, and the output is performed after performing impedance matching or the like.

The LPF 21 includes rectifier diodes D21 and D21.
4 corresponding to the double-wave rectified waveform shown in FIG. 3 from FIG.
The cutoff frequency (fc) is set so that the second harmonic (double-wave rectified waveform) of the AC waveform of z is sufficiently reduced and the noise can be removed. For example, the cutoff frequency is set to 60 Hz, and
As shown in FIG. 5, the delay time is, for example, 16 m / sec.
Response characteristics.

The LPF 21 outputs an input AC detection voltage Vr indicated by a solid line in FIG. 3 based on the cutoff frequency characteristic shown in FIG. 4 and the response characteristic shown in FIG. This input AC detection voltage Vr is input to the minus input terminal of the comparator 22. A resistor R2 is connected to the positive input terminal of the comparator 22.
3, a reference voltage value (threshold value) divided by R24 is set, and when the input AC detection voltage Vr from the LPF 21 exceeds this reference voltage value, a rating of the control for suppressing the excessive boosting operation from the output end. Outputs an input alternating current (AC) detection voltage Vra corresponding to the effective voltage to which the control unit 5 depends.

The control unit 5 receives the input AC detection voltage Vra
Drives the switching element 3 by PWM control based on
The boost operation is performed. Also, the input AC detection voltage Vr
When a is not input to the control unit 5 or when it is extremely low, that is, when the input AC voltage is lower than a predetermined value or less, the switching element 3 prevents a switching operation in which an excessive current flows to output a boosted voltage. . That is, the control for stopping the switching operation and for suppressing the excessive boosting operation for limiting the output voltage to a predetermined output voltage by shortening the ON time of the switching element is performed.

In this control, the control unit 5 sends a cut-off voltage to the gate when the switching element 3 is an FET, or sends a PWM signal for performing a predetermined boosting.
The control for suppressing the excessive boosting operation is performed.

Since the LPF 21 of the active filter has a low cutoff frequency and a high input impedance,
A more accurate effective voltage can be obtained. In other words, more accurate suppression control of the excessive boosting operation becomes possible. in this case,
An accurate high-order constant can be set, and an effective value of the effective voltage can be obtained with more effective noise removal. If the voltage comparator 22 has hysteresis, it operates more stably.

As described above, in this embodiment, after the two-wave rectification is performed by the rectification diodes D21 and D22, the rectification diodes D21 and D22 are passed through the LPF 21 to input the input AC detection voltage Vr corresponding to the effective voltage.
Have gained. Therefore, the line filter 1 shown in FIG.
When the effective voltage is obtained when the input AC voltage supplied to the switching element is distorted, a reliable over-boost operation for preventing a switching operation in which an excessive current flows through the switching element 3 when the input AC voltage falls below a predetermined value. Can be suppressed.

In the above embodiment, the reference voltage (threshold) is set in the comparator 22 by dividing the voltage by the resistors R23 and R24 in FIG.
Other means can be used instead of the 24 serially connected configuration. For example, even if a low-voltage stabilizing circuit is used and the stabilized DC voltage from here is set as a reference voltage value, the same operation is performed, and the operation and effect are the same.

In the above embodiment, the active filter having the fifth order configuration shown in FIG. 2 has been described as the LPF 21. However, the order may be reduced and the cutoff frequency may be lowered. In this case, the response time differs and the detection time is delayed. Therefore, the order of the filter may be selected in consideration of the drop fluctuation of the input AC voltage, the switching operation capability (capacity) of the switching element 3, the supply current to the load, and the like.

Further, depending on the state of the control for suppressing the excessive boosting operation, a passive filter including only a resistor and a capacitor can be used without using the operational amplifiers 34 and 37 in FIG. Further, depending on the frequency of the input AC supplied to the line filter 1 shown in FIG. 6, an LC low-pass filter including a coil and a capacitor may be used.

[0039]

As described above, according to the present invention, the input AC voltage corresponds to the effective voltage from the rectified output obtained by performing the double-wave rectification,
In addition, a substantially constant input AC detection voltage is generated. When the input AC voltage falls below a predetermined value, the switching operation in which an excessive current flows through the switching element is stopped, or the ON time of the switching element is shortened,
Suppression control of an excessive boosting operation such as limiting to a predetermined output voltage is performed. As a result, when the input AC voltage is distorted and its effective voltage is obtained, it is possible to reliably control the excessive boosting operation when the input AC voltage drops below a predetermined value.

Further, since the active low-pass filter is used to generate the input AC detection voltage corresponding to the effective voltage for controlling the excessive boosting operation, a more accurate constant can be set, the cut-off frequency is low, In addition, a low-pass filter having a high input impedance is formed. As a result, it is possible to form an effective low-pass filter capable of obtaining an accurate effective voltage with better noise removal.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a configuration of an embodiment of a method and an apparatus for detecting an input AC voltage in a switching power supply according to the present invention.

FIG. 2 is a circuit diagram showing a detailed configuration of an LPF in FIG. 1;

FIG. 3 is a diagram for explaining a double-wave rectified waveform and an input AC detection voltage of an LPF output in FIG. 1;

FIG. 4 is a frequency characteristic diagram showing a cutoff frequency of the LPF shown in FIG.

FIG. 5 is a response characteristic diagram showing a delay state of the LPF shown in FIG. 1;

FIG. 6 is a block diagram illustrating a configuration example of a conventional switching power supply that performs suppression control of an excessive boosting operation.

FIG. 7 is a circuit diagram illustrating a detailed configuration of an input AC voltage detection unit in FIG. 6;

8 is a waveform diagram showing a rectified waveform in the input AC voltage detection section shown in FIG.

[Explanation of symbols]

1 ... line filter, 2 ... bridge rectifier, 3 ...
Switching element, 4 ... Rectifier, 5 ... Control unit, 6 ...
... low voltage rectifier circuit, 7 ... start circuit, 20 ... input AC voltage detector, 21 ... low-pass filter, 22 ... comparators, 34, 37 ... operational amplifiers, C1, C2, C3 ...
... Electrolytic capacitors, C30-C32, C35, C36 ...
... capacitors, D21, D22 ... rectifier diodes, R
21 to R24, R30 to R32, R35 to R38 ... resistor, L1 ... primary coil, L2 ... secondary coil,
T: transformer, Vr, Vra: input AC detection voltage.

Claims (8)

[Claims] 1. A switching power supply for monitoring an input AC voltage and detecting an input AC voltage for performing control for suppressing an excessive boosting operation for suppressing a switching operation in which an excessive current flows through a switching element when the input AC detection voltage decreases. In the input AC voltage detection method, the input AC voltage is double-wave rectified, and a substantially constant input AC voltage corresponding to an effective voltage is detected from the rectified output,
A method for detecting an input AC voltage of a switching power supply, wherein the control for suppressing the excessive boosting operation is performed based on the input detection voltage. 2. The system according to claim 1, wherein the input AC detection voltage is compared with a reference voltage value, and when the input AC detection voltage falls below the reference voltage value, suppression control of an excessive boosting operation is performed. Method of detecting the input AC voltage of a switching power supply. 3. A switching power supply that monitors an input AC voltage and detects an input AC voltage for performing a suppression control of an excessive boosting operation for suppressing a switching operation in which an excessive current flows through a switching element when the input AC detection voltage decreases. In the input AC voltage detection device, a rectifying unit that double-wave rectifies the input AC voltage, a substantially constant voltage corresponding to an effective voltage from the double-wave rectified voltage of the rectifying unit, and performing a suppression control of an excessive boosting operation. An input AC voltage detection device for a switching power supply, comprising: input AC detection voltage generation means for detecting and outputting an input AC voltage. 4. A comparing means and a reference voltage setting means are provided,
The comparing means compares the input AC detection voltage from the input AC detection voltage generating means with a reference voltage value, and when the input AC detection voltage drops to the reference voltage value, an output voltage for performing suppression control of excessive boosting operation 4. The input AC voltage detecting device for a switching power supply according to claim 3, wherein said reference voltage setting means sets a reference voltage value to said comparing means. 5. The input AC voltage detecting device for a switching power supply according to claim 3, wherein a low-pass filter is used as said input AC detected voltage generating means. 6. A passive low-pass filter of a resistor input type using a resistor and a capacitor set at a cutoff frequency at which a signal component of a double-wave rectified waveform is not extracted from the low-pass filter. 6. The input AC voltage detection device for a switching power supply according to claim 5. 7. A low-pass filter comprising a resistor and a capacitor set at a cutoff frequency at which a signal component of a double-wave rectified waveform is not extracted, and an active low-pass filter including an amplifier. 6. The input AC voltage detection device for a switching power supply according to claim 5. 8. The device according to claim 4, wherein a resistor connected in series between a power supply and ground is used as said reference voltage setting means, and a divided voltage at the series connection point is used as a reference voltage value. Input AC voltage detector for switching power supplies.