JPH11164548A - Power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the flow of over-current into a switching element, when an input voltage rises abruptly. SOLUTION: When momentary interrupt of an input AC voltage occurs, a comparison means 6 does not generated pulse during such period, because a voltage is not supplied from a rectifying circuit 106 to the comparing means 6. Therefore, a pulse detecting circuit 8 is unable to detect the pulse in this case and outputs a cut-off signal. The pulse detecting circuit 8 delays this cut-off signal for about 20 msec, before it provides the output. Therefore, even if momentary interrupt is recovered, the cut-off signal is output for about 20 msec after such a recovery. When the cut-off signal is input from the pulse detecting circuit 8, a drive pulse generating circuit 125 stops the generation of a drive pulse to turn off a switching element 118.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device for rectifying an AC voltage to generate a stabilized DC voltage, and more particularly, to a PF.
It relates to a C converter.

[0002]

2. Description of the Related Art PFC (Power Factor C)
2. Description of the Related Art Orientation converters are widely used in electronic devices as a technique for reducing power supply harmonic distortion because a current flowing to an AC power supply side is close to a sine wave and has less harmonic components. FIG. 7 is a circuit diagram showing an example of a conventional PFC converter. The PFC converter 102 includes a rectifier circuit 106 for rectifying an AC voltage supplied from an AC power supply (not shown) (for example, commercial power supply) through an input terminal 104, and a diode 108 at one end connected to the output of the rectifier circuit 106. Output terminal 11 of PFC converter 102 via
0 and the output terminal 11
0 connected to the reference potential point 114
16, a switching element 118 (field-effect transistor) connected between the other end of the choke coil 112 and the reference potential point 114, a control circuit 120 for the switching element 118, an output of the rectifier circuit 106, and a reference potential point. 1
14 and a capacitor 122 connected between them. Then, the control circuit 120 generates a high-frequency drive pulse from the drive pulse generation circuit 124 and applies the drive pulse to the gate of the switching element 118.
As a result, the switching element 118 turns on and off at a high speed. Here, the control circuit 120 changes the width of the drive pulse so that a constant DC voltage is always output from the output terminal 1.
10 to be output.

In the conventional PFC converter 102, when the AC power is turned on and the input voltage rises sharply, the choke coil 112 is connected to the capacitor 116.
A very large charging current flows through the choke coil 112, so that the choke coil 112 is saturated, the inductance is greatly reduced, and a state equivalent to a short-circuit state occurs. Therefore, if the switching element 118 operates in this state, an excessive current flows through the switching element 118 when the switching element 118 is turned on, which results in overcurrent breakdown and avalanche breakdown of the switching element 118. Such an overcurrent occurs not only when the power is turned on, but also due to a momentary interruption of the AC power.

[0004]

Therefore, conventionally, a bypass diode is connected in parallel with the choke coil 112 to suppress the current flowing through the choke coil 112, or a current detecting resistor is connected in series with the switching element 118. A current flowing through the switching element 118 after connection is detected, and if an excessive current flows, the switching element 11
8 has been taken to stop the operation.

However, in the system using the bypass diode, only a part of the charging current of the capacitor 116 can be bypassed, and it is difficult to reliably prevent the saturation of the choke coil 112. On the other hand, in the method of detecting the current of the switching element 118, a time delay (for example, several hundred ns) from when an excessive current flowing through the switching element 118 is detected to when the operation of the switching element 118 is stopped.
For c), the switching element 118 cannot often be reliably protected. Therefore, conventionally, in order to prepare for a case where overcurrent protection does not function properly, the switching element 118 is used as the switching element 118, and the switching element 118 having an extremely large withstand current value is used to withstand a large current. Had become.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to reliably prevent an overcurrent from flowing through a switching element when an input voltage rises sharply. A power supply device is provided.

[0007]

In order to achieve the above object, the present invention provides a rectifier circuit and a choke having one end connected to the output of the rectifier circuit and the other end connected to an output terminal of a power supply via a diode. A coil, a capacitor connected between the output terminal and a reference potential point, a switching element connected between the other end of the choke coil and the reference potential point, and periodically turning on and off the switching element. A voltage monitoring means for detecting a sharp rise in the AC voltage supplied to the rectifier circuit and outputting a cut-off signal for a predetermined period, wherein the control circuit comprises: When the means is outputting the cutoff signal, the switching element is turned off.

In the power supply according to the present invention, the voltage monitoring means includes:
When a sharp rise in the AC voltage supplied to the rectifier circuit is detected, a cutoff signal is output for a predetermined period, and the control circuit turns off the switching element while the voltage monitoring means outputs the cutoff signal. To That is, in the power supply device of the present invention, the operation of the switching element is stopped by detecting a sudden rise in the input voltage that causes an overcurrent to flow through the switching element. Unlike the conventional method of stopping the switching, the operation of the switching element can be stopped before an overcurrent flows through the switching element. Also,
Rather than simply suppressing the current as in the case of using a bypass diode, the operation of the switching element is completely stopped, so that the switching element can be reliably protected.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an example of a power supply device according to the present invention. In the figure, the same elements as those in FIG. 7 are denoted by the same reference numerals, and description thereof will be omitted here. This power supply device, that is, the PFC converter 2 is different from the PFC converter 2 in FIG. 7 in the configuration of the control circuit 4. The control circuit 4 protects the switching element 118 from an overcurrent by using the present invention. It comprises a comparing means 6 (first comparing means according to the present invention) and a pulse detection circuit 8 which constitute related voltage monitoring means.

The comparing means 6 includes a voltage dividing resistor (not shown) and a comparator. The output voltage of the rectifier circuit 106 is input to one input terminal of the comparator through the voltage dividing resistor. A reference voltage is input to an input terminal from a power supply (not shown). In the present embodiment, the comparison means 6 constitutes a pulse generation circuit according to the present invention. The pulse detection circuit 8 detects the pulse output from the comparison means 6, and when the pulse is detected, the logic "
When a pulse is not detected, a signal of logic "1" is output as a cutoff signal, provided that the pulse detection circuit 8 outputs the cutoff signal for a certain period of time, for example, two.
The signal is output with a delay of about 0 msec. The drive pulse generation circuit 124 generates and outputs a high-frequency drive pulse when the cutoff signal is not input from the pulse detection circuit 8, and stops generating the drive pulse when the cutoff signal is input.

Next, the operation of the PFC converter 2 configured as described above will be described. FIG. 2 is a timing chart for explaining the operation of PFC converter 2. The comparator of the comparing means 6 compares the output voltage of the rectifier circuit 106 input through the voltage-dividing resistor with the reference voltage, and outputs a signal of logic "1" when the output voltage is larger than the reference voltage. When it is larger, a signal of logic "0" is output. As shown in FIG. 2, the output voltage of the rectifier circuit 106 has a full-wave rectified waveform in a normal state, and the comparator operates as described above, so that the comparator 6 outputs a pulse.

Here, assuming that an instantaneous interruption of the input AC voltage occurs during the period Ta as shown in FIG. 2, the voltage is not supplied from the rectifier circuit 106 to the comparing unit 6 during this period. Does not occur. Therefore,
The pulse detection circuit 8 detects a pulse during periods other than the period Ta, but cannot detect a pulse during the period Ta, and outputs a cutoff signal. However, the pulse detection circuit 8 outputs this cutoff signal by about 20
Output with a delay of msec. Therefore, the output signal of the pulse detection circuit 8 becomes logic "1" about 20 msec after the occurrence of the instantaneous interruption. And then return to logic "0". That is, when the input AC voltage rises sharply due to the elimination of the instantaneous interruption, the comparing means 6 detects this and restarts the generation of the pulse. Thereafter, the cutoff signal is output from the pulse detection circuit 8 for about 20 msec. You.

The drive pulse generating circuit 124 generates a drive pulse when the cutoff signal is not input from the pulse detection circuit 8, that is, when the rectifier circuit 106 normally outputs a voltage, and the switching element 118.
To turn on and off the switching element 118. However, when the cutoff signal is input due to the instantaneous interruption of the input AC voltage, generation of the drive pulse is stopped. Therefore, the period T during which the pulse detection circuit 8 outputs the cutoff signal
In b, the switching element 118 is turned off.

Not only in the case of the instantaneous interruption shown in FIG. 2, but also when an AC voltage is applied, a cutoff signal is generated, and the switching element 118 is turned off. In this case, since the comparing means 6 does not output a pulse before the AC voltage is applied, the pulse detection circuit 8 outputs a cutoff signal, and outputs the cutoff signal for about 20 msec even after the AC voltage is applied. Then, the output of the cutoff signal is stopped.

Therefore, in the PFC converter 2, when the input AC voltage recovers from an instantaneous interruption or when the AC voltage is applied, the switching element 118 is turned off during a period in which the voltage rises sharply, and the input AC voltage is turned off. Does not flow through the switching element 118 even when the choke coil 112 is saturated by an excessive charging current to the capacitor 116 when the voltage rises rapidly. Therefore, in this PFC converter 2, the switching element 1
18 can be reliably protected, and it is not necessary to use the switching element 118 having a large withstand current value in case the overcurrent protection does not function properly as in the related art, and as a result, the cost can be reduced.

In this embodiment, the pulse detection circuit 8 outputs the cut-off signal with a delay of about 20 msec. However, this delay time is merely an example, and the delay time of the switching element 118 depends on the characteristics of the circuit. It is, of course, possible to increase or decrease the current so as to block it properly.

Next, a second embodiment will be described. FIG. 3 is a circuit diagram showing the PFC converter of the second embodiment, and FIG. 4 is a timing chart for explaining the operation of the PFC converter of the second embodiment.
3, the same elements as those of FIG. 7 are denoted by the same reference numerals, and a description thereof will be omitted.

The PFC converter 12 includes a control circuit 1
4 is different from the PFC converter 102 of FIG. The control circuit 14 includes a comparing unit 16 (a second comparing unit according to the present invention), and the comparing unit 16 includes the rectifying circuit 1.
06, the first voltage dividing resistor 18 for dividing the output voltage, the second voltage dividing resistor 20 for dividing the output voltage, and the voltage divided by the first and second voltage dividing resistors 18 and 20. And a comparator 22 for comparing voltages (comparator according to the present invention).
Constitutes the voltage monitoring means according to the present invention.
Then, the comparing means 16 compares the voltage of the output terminal 110 with the output voltage of the rectifier circuit 106, and outputs a cut-off signal when the voltage of the output terminal 110 based on the output voltage of the rectifier circuit 106 is lower than a certain level. .

More specifically, as shown in FIG. 4, before the instantaneous interruption of the input AC voltage occurs during the period Ta, and during the instantaneous interruption period Ta, the second voltage dividing resistor 20 is used.
Terminal 110 supplied to the comparator 22 through the
Is higher than the output voltage of the rectifier circuit 106 supplied to the comparator 22 through the first voltage-dividing resistor 18, the comparator 22 outputs a signal of logic "0".

In the period Ta, the rectifier circuit 106 does not output a voltage, while the voltage of the output terminal 110 is
6 gradually decreases with the discharge. Then, when the instantaneous interruption is eliminated at the timing te, the input AC voltage sharply increases, and accordingly, the output voltage of the rectifier circuit 106 also sharply increases. As a result, at the timing te, the second voltage dividing resistor 2
The output voltage of 0 becomes equal to or lower than the output voltage of the first voltage-dividing resistor 18, and the comparator 22 outputs a signal of logic "1" as a cutoff signal. Thereafter, when the voltage of the output terminal 110 is restored to the normal voltage, the voltage supplied to the comparator 22 through the second voltage-dividing resistor 20 becomes larger, and the comparator 22 outputs a signal of logic “0”. Then, the drive pulse generation circuit 124 outputs
When the cut-off signal is input from 2, the generation of the drive pulse is stopped. Therefore, the switching element 118 is turned off during the period Tb during which the comparator 22 outputs the cutoff signal. Further, not only in the case of the instantaneous interruption shown in FIG.
When the AC voltage is applied, the cut-off signal is output until the input AC voltage sharply rises and thereafter the voltage of the output terminal 110 sufficiently rises.
Is turned off. Therefore, according to the second embodiment, the same effect as that of the above-described embodiment can be obtained.

Next, a third embodiment will be described. FIG. 5 is a circuit diagram showing a PFC converter according to the third embodiment, and FIG. 6 is a timing chart for explaining the operation of the PFC converter according to the third embodiment.
5, the same elements as those in FIG. 7 are denoted by the same reference numerals, and a description thereof will be omitted here. This PFC converter 24 includes current monitoring means 26,
The difference from the PFC converter shown in FIG. 7 is that the drive pulse generation circuit 124 of the control circuit 120 is controlled by the cutoff signal output from the current monitoring means 26. The current monitoring means 26 includes a resistor 28 and a comparing means 30 (third comparing means according to the present invention).
Is the output terminal 1 on the reference potential point 114 side of the rectifier circuit 106.
10, the comparator 30 is connected in series to the choke coil 112, and the comparing means 30 compares the voltage across the resistor 28 with a reference voltage and compares the voltage across the resistor 28 with the reference voltage. Outputs a cutoff signal when the voltage is exceeded.

As shown in FIG. 6, when an instantaneous interruption occurs in the input AC voltage in the period Ta and the instantaneous interruption is eliminated at the timing te, the input AC voltage, and hence the output voltage of the rectifier circuit 106, rises sharply. As a result, at this timing, as shown in FIG. 6, a large charging current instantaneously flows through the capacitor 116, the voltage across the resistor 28 also rises rapidly and exceeds the reference voltage, and the comparing means 30 outputs a cutoff signal. . Then, the drive pulse generation circuit 124 stops generating the drive pulse while the cutoff signal is being input, and the period Tb during which the comparing means 30 outputs the cutoff signal.
Then, the switching element 118 is turned off. Also,
Not only in the case of the instantaneous interruption shown in FIG. 6, but also when the AC voltage is applied, the input AC voltage rises sharply and the capacitor 11
While a large charging current flows through 6, the switching element 118 is turned off because the cutoff signal is output.
Therefore, according to the third embodiment, the same effect as that of the above-described embodiment can be obtained.

[0023]

As described above, in the power supply device of the present invention, the voltage monitoring means outputs a cutoff signal for a predetermined period when detecting a sharp rise in the AC voltage supplied to the rectifier circuit, and Turns off the switching element while the voltage monitoring means outputs the cutoff signal. That is, in the power supply device of the present invention, the operation of the switching element is stopped by detecting a sudden rise in the input voltage that causes an overcurrent to flow through the switching element. Unlike the conventional method of stopping the switching, the operation of the switching element can be stopped before an overcurrent flows through the switching element. Further, the operation of the switching element is completely stopped instead of simply suppressing the current as in the case of using the bypass diode, so that the switching element can be surely protected. Therefore, it is not necessary to use a switching element having a large withstand current value in preparation for a case where overcurrent protection does not function properly as in the related art, and as a result, cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an example of a power supply device according to the present invention.

FIG. 2 is a timing chart for explaining the operation of the PFC converter of FIG.

FIG. 3 is a circuit diagram showing a PFC converter according to a second embodiment.

FIG. 4 is a timing chart for explaining an operation of the PFC converter according to the second embodiment.

FIG. 5 is a circuit diagram showing a PFC converter according to a third embodiment.

FIG. 6 is a timing chart for explaining an operation of the PFC converter according to the third embodiment.

FIG. 7 is a circuit diagram showing an example of a conventional PFC converter.

[Explanation of symbols]

2 PFC converter, 4 control circuit, 6 comparison means, 8 pulse detection circuit, 12 PFC converter, 14 control circuit, 16 comparison means, 18 first part Piezoresistor, 20 second divide resistor, 22
Comparator 24 PFC converter 26 current monitoring means 28 resistor 30 comparison means 10
2 ... PFC converter, 104 ... Input terminal, 106
... Rectifier circuit, 108, Diode, 110, Output terminal, 112, Choke coil, 114, Reference potential point, 116, Capacitor, 118, Switching element, 120, Control circuit, 122, Capacitor , 12
4 ... Drive pulse generation circuit.

Claims (8)

[Claims] 1. A rectifier circuit, a choke coil having one end connected to the output of the rectifier circuit and the other end connected to an output terminal of a power supply device via a diode, and between the output terminal and a reference potential point. A power supply device comprising: a connected capacitor; a switching element connected between the other end of the choke coil and the reference potential point; and a control circuit for periodically turning on and off the switching element. Voltage monitoring means for detecting a sudden rise in AC voltage supplied to the power supply and outputting a cutoff signal for a predetermined period, wherein the control circuit is configured to switch the switching element when the voltage monitoring means outputs the cutoff signal. A power supply device. 2. The voltage monitoring device according to claim 1, wherein the pulse generation circuit generates a pulse having a cycle equal to a fluctuation cycle of the output voltage of the rectifier circuit based on the output voltage of the rectifier circuit. A pulse detection circuit that outputs the cutoff signal when the output is stopped, and stops the output of the cutoff signal after a delay time when the pulse generation circuit starts outputting the pulse. The power supply device according to claim 1, wherein: 3. The pulse generating circuit includes a first comparing unit that outputs a signal of a different level when the output voltage of the rectifier circuit is higher than a reference voltage and when the output voltage is lower than a reference voltage,
3. The power supply according to claim 2, wherein said pulse is generated based on an output signal of said first comparing means. 4. The voltage monitoring means compares an output voltage of the rectifier circuit with a voltage of the output terminal, and when a voltage of the output terminal is equal to or lower than a predetermined level with reference to an output voltage of the rectifier circuit. 2. The power supply device according to claim 1, further comprising a second comparing unit that outputs a cutoff signal. 5. The second comparing means includes a first voltage dividing resistor for dividing an output voltage of the rectifier circuit, a second voltage dividing resistor for dividing a voltage of the output terminal, and a first voltage dividing resistor. And the second
5. The power supply device according to claim 4, further comprising: a comparator for comparing voltages divided by said voltage dividing resistors. 6. The voltage monitoring means comprises current monitoring means for detecting a current flowing through the choke coil and outputting a cutoff signal when a current exceeding a reference value flows through the choke coil. Item 7. The power supply according to Item 1. 7. The current monitoring means includes: a resistor connected in series with a choke coil; and a voltage across the resistor being compared with a reference voltage, and a voltage across the resistor being adjusted to the reference voltage. 7. The power supply device according to claim 6, further comprising: a third comparing unit that outputs the cutoff signal when the power supply voltage exceeds the threshold. 8. The power supply device according to claim 7, wherein the resistor is connected in series to an output terminal on the reference potential point side of the rectifier circuit.