JP3418822B2 - Inrush current suppression circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inrush current suppressing circuit in a power supply device for suppressing an inrush current from an AC power supply and suppressing a harmonic current component to improve a power factor.
In a configuration in which a rectifier circuit and a switching power supply device are connected to an AC power supply, a peak current flows from the AC power supply side to the switching power supply device via the rectifier circuit, and contains a lot of harmonic current components. Therefore, the power factor on the AC power supply side decreases. For the purpose of improving the power factor, there is known a configuration in which a step-up type power factor improving unit is provided in the preceding stage of the switching power supply device. Even in such a configuration, since the rush current when the power is turned on is large, it is desired to suppress the rush current and shorten the start-up time of the power factor improving unit.

[0002]

2. Description of the Related Art FIG. 5 is an explanatory diagram of a switching power supply device, in which 51 is an AC power supply, 52 is a current suppressing resistor, 53 is a switch element (SW), 54 is a switch (SW) control section, and 55 is a full wave. A rectifier circuit such as a rectifier circuit, 56 is a reactor, 57 is a diode, 58 is a capacitor, 59 is a switching transistor, 60 is a current detection resistor, and 61 is a current detection resistor.
Is a switching controller, 62 is a sequence controller, 63
Is a DC-DC converter, and 64 is a load of various electronic circuits.

The resistor 52, the switch element 53, and the switch control section 54 constitute an inrush current prevention section, and the switch element 53 can be constituted by a relay contact, a field effect transistor (FET) or the like. Further, the reactor 56, the diode 57, the capacitor 58, the switching transistor 59, the resistor 60, and the switching control section 61 constitute a power factor improving section. The sequence control unit 62 includes a switch control unit 54 at the start of operation.
And a control signal is added to the switching controller 61 according to preset timing.

The DC-DC converter 63 has a load 64.
One type or a plurality of types of stabilized DC voltage are supplied in accordance with the above configuration. This DC-DC converter 6
Since 3 is usually a capacitor input type, the inflowing current waveform has a pulse shape. As a result, the harmonic current component increases, the power factor of the AC power supply 51 decreases, and the problem of an increase in reactive power occurs.

Therefore, the power factor improving section is connected to the rectifier circuit 55 and the DC.
-It is provided between the DC converter 63 and the DC converter 63. The power factor correction unit controls the switching transistor 59 to be turned on and off by the switching control unit 61, and uses the energy stored in the reactor 56 when turned on to charge the capacitor 58 via the diode 57 when turned off.
The charging voltage of the capacitor 58 is supplied to the DC-DC converter 63. Thereby, the current waveform flowing from the AC power supply 51 is approximated to a sine waveform to improve the power factor. Further, since the capacitor 59 is charged by the stored energy of the rear 56, a structure corresponding to a boost converter is obtained. Also, the ON period of the switching transistor 59 is controlled so that the current is detected by the resistor 60 and the overcurrent state does not occur.

A power switch (not shown) is turned on, and the switch element 54 is turned off by the switch control section 54 so that the resistor 52 is connected in series at the initial stage when the AC power source 51 is connected. Therefore, the inrush current is limited by the resistor 52. Then, after a predetermined time, the sequence control unit 62 applies a control signal to the switch control unit 54, and the switch control unit 54 causes the switch element 5 to operate.
3 is controlled to be turned on, and the resistor 52 is short-circuited. Thereby, the electric power is supplied from the AC power supply 51 as usual.

FIG. 6 is an explanatory view of a main part of a conventional switching control section. The same reference numerals as those in FIG.
Is a control processing unit, 66 and 67 are resistors, and 68 is a reference voltage source. The sequence control unit 62 turns on the AC power supply switch (not shown) a (switch element 53 off) → switch element 53 on b → starts the operation of the switching control unit c → starts the power factor correction unit = Vdc (output voltage The sequence control for completion of rising (start of normal operation) d) is performed.

Therefore, as described above, the switch (not shown) with the AC power source 51 is turned on, the switch element 53 is turned off by the switch control unit 54, and the switch element 53 is turned on after a predetermined time elapses. Resistance 52
Is short-circuited, and then a start signal is applied to the switching control unit 61 to start the on / off operation of the switching transistor 59, and after a predetermined time, if no abnormality occurs, a normal operation state is entered.

The switching control unit 61 divides the sum of the voltage across the resistor 60 for detecting the current Ir and the voltage of the reference voltage source 68 by the resistors 66 and 67, and the divided voltage is sent to the control processing unit 65. input. The control processing unit 65 starts operation by the activation signal from the sequence control unit 62,
Turning on the switching transistor 59 (see FIG. 5),
Start off operation. At this time, when the current Ir increases, the divided voltage by the resistors 66 and 67 increases, and when the current Ir exceeds a set current, the ON period of the switching transistor 59 is shortened so as to suppress the current Ir.

[0010]

The inrush current flowing from the AC power supply 51 can be suppressed by connecting the resistor 52 in series as described above, and the output capacity of the AC power supply 51 can be reduced. In that case, the effect of suppressing the inrush current is increased by increasing the resistance 52. However, it takes a long time for the charging voltage of the capacitor 58 of the power factor correction unit to reach a predetermined value, whereby the DC-DC converter 63 operates normally and the stabilized DC voltage is supplied to the load 64. There is a problem that it takes a long time to complete. In order to solve this problem, if the resistance 52 is made small, the inrush current becomes large. Therefore, it is necessary to prepare the AC power supply 51 having an output capacity that can tolerate this inrush current. Also, when the switch element 53 is turned on and the resistor 52 is short-circuited, a large inrush current flows again for a shorter time than the initial inrush current. Further, an inrush current flows (which is suppressed to some extent by soft start or the like) when the power factor correction section is started. An object of the present invention is to suppress the inrush current and shorten the rise time of the power factor correction section.

[0011]

The inrush current suppressing circuit of the present invention comprises (1) a current suppressing resistor 5 for suppressing an alternating current from an alternating current power source, and a switch element 6 for short-circuiting the resistor 5.
And a rush current prevention unit that includes a switch control unit 7 that controls ON / OFF of the switch element 6, a rectification circuit 2 that rectifies an AC voltage that is input via the rush current prevention unit 1, and the rectification circuit. A capacitor 10 for applying the rectified output voltage from the circuit 2 via the reactor 8 and the diode 9.
And a switching transistor 11 that stores energy in the reactor 8 and switches the stored energy to be input to the capacitor 10 via the diode 9.
And a switching control unit 13 for detecting the current and controlling the ON / OFF ratio of the switching transistor so as not to exceed the set current.
The switch element 6 of the inrush current prevention unit 1 is turned off at the start of the operation, the switching transistor 11 of the power factor correction unit 3 is turned on / off after a predetermined time, and the inrush current prevention is performed after a predetermined time. The sequence control unit 4 is provided to control the timing so that the switch element 6 of the unit 1 is turned on and the current suppressing resistor 5 is short-circuited.

(2) The switching control section 13 of the power factor correction section 3 has a time constant circuit for starting charging of the capacitor 10 in response to a start signal from the sequence control section 4, and a sum of the detected current voltage and the reference voltage. The voltage divider circuit that divides the voltage and the start signal that starts operation and the divided voltage of the voltage divider circuit is input to switch the current so that it does not exceed the set current.
The control processing unit that controls ON / OFF of the transistor 11 and the state in which the voltage dividing ratio of the voltage dividing circuit is reduced so as to reduce the set current is divided by the start signal delayed according to the time constant of the time constant circuit. It is possible to provide a switching element that switches to increase the pressure ratio and increase the set current.

(3) The switching control section 13 of the power factor correction section 3 starts its operation by a voltage dividing circuit for dividing the sum of the detected voltage of the current and the reference voltage and a start signal from the sequence control section 4. In addition, by inputting the divided voltage of the voltage dividing circuit, the control processing unit that controls ON / OFF of the switching transistor 11 so that the current does not exceed the set current, and the voltage dividing circuit that reduces the set current. And a field effect transistor that switches so as to increase the voltage division ratio and increase the set current after a delay time based on the parasitic capacitance when a start signal is input to the gate from a state in which the voltage division ratio is reduced. You can

[0014]

1 is an explanatory view of a first embodiment of the present invention, in which 1 is an inrush current prevention unit, 2 is a rectifier circuit,
3 is a power factor correction unit, 4 is a sequence control unit, 5 is a resistor for suppressing current, 6 is a switch element such as a relay or transistor, 7 is a switch control unit, 8 is a reactor, 9 is a diode, 10 is a capacitor, 11 Is a switching transistor such as a field effect transistor, 12 is a resistor for detecting an output current, and 13 is a switching controller. Note that power
The load connected through the rate improvement circuit 3 is not shown.

The sequence control unit 4 is composed of a time constant circuit, a timer and the like, and an AC power switch (not shown) is turned on a (switch element 6 is off) → operation start of the switching control unit c → switch element 6 on b. → Sequence control of completion of activation of power factor improving unit = completion of rise of Vdc (output voltage) (start of normal operation) d is performed. The sequence control unit 62 of the conventional example uses a → b → c → d.
The timing control is performed according to the sequence. The switching control unit 13 controls the switching transistor 11 so that the current detected by the resistor 12 does not exceed the set current, and has a configuration in which the set current is automatically switched to a small value in the initial stage of startup. I have it.

2A and 2B are operation explanatory diagrams of the conventional example and the embodiment of the present invention. FIG. 2A shows the operation of the conventional example, FIG. 2B shows the operation of the embodiment of the present invention, and a is an AC power supply. The switch is turned on, b is a switch element for short-circuiting the current suppressing resistor, c is the operation of the power factor improving unit, d is the completion of the start of the power factor improving unit = Vdc (output voltage) rise completion (normal). Operation start). Iin is the current from the AC power supply, and Vdc is the terminal voltage of the capacitor of the power factor correction unit, that is, the output voltage.

That is, in the conventional example of (A), the sequence control unit 54 (see FIG. 5) is a switch element for short-circuiting the current suppressing resistor 52 after the time T1 from the turning on of the AC power switch. 53 is turned on b, and after that, the operation of the power factor improving section c is started after time T3, that is, the on / off operation of the switching transistor 59 is started, and after time T2, the start of the power factor improving section is completed = Vdc (output voltage).
Is completed (normal operation start) d.

Therefore, the inrush current of the current Iin from the AC power supply is suppressed by the current suppressing resistor 52 when the AC power switch is on a, but the inrush current is again generated when the switch element 53 is on b. Flowing. Then, inrush current flows even at the start of operation c of the power factor correction unit. The output voltage Vdc approaches a normal value when the operation of the power factor correction section starts. In this case, if the resistance 52 is increased in order to sufficiently suppress the inrush current at the timing a, it is necessary to lengthen the time T1 and the inrush current at the timing b is also increased.

Further, as shown in (B), in the embodiment of the present invention, after the sequence control unit 4 turns on the AC power switch, the power factor improving unit 3 is turned on after time t1.
The operation is started c, and then the switch element 6 is turned on b. That is, the timing control is performed according to the sequence of a → c → b → d.

In this case, the current suppressing resistor 5 is increased to sufficiently suppress the inrush current when the AC power switch is turned on a, and the switching transistor 11 of the power factor improving section 3 is also provided.
The current is detected by the resistor 12 at the start of the on / off operation of the switching controller 1 so that the current is limited.
The operation of 3 suppresses the inrush current at the timing of c. Further, when the switch element 6 is turned on b, the power factor correction unit 3 has started to operate, so the output voltage Vdc has also started to rise, and therefore the inrush current when the current suppressing resistor 5 is short-circuited. Can also be suppressed. Then, it is possible to shorten the period from the turning on of the AC power switch to the completion of the start of the power factor correction unit = the completion of the rise of Vdc (output voltage) (start of normal operation) d.

FIG. 3 is an explanatory view of the main part of the second embodiment of the present invention, showing the structure of the main part of the switching control part. In the figure, RI is a current detection resistor (corresponding to the resistor 12 in FIG. 1), Ir is a current, 13 is a switching control unit, 21 is a control processing unit, R1 to R8 are resistors, C1 is a capacitor, and Q1 is Transistors, D1 and D2 are diodes, CMP is a comparison circuit, Vr is a reference voltage, and VD is a divided voltage.

The control processing section 21 starts its operation in response to a start signal ("0") from the sequence control section, and controls the on / off operation of the switching transistor 11 (see FIG. 1). The current Ir flows in the direction of the arrow, and the voltage across the resistor RI is added to the reference voltage Vr. When the transistor Q1 is off, the divided voltage VD divided by the resistors R1 and R2 is generated. It is input to the control processing unit 21. Therefore, the divided voltage VD when the current Ir is in the overcurrent state is compared and determined in the control processing unit 21, and the ON period of the switching transistor 11 is shortened to limit the current Ir.

Further, the resistors R5 to R8, the capacitor C1, the diodes D1 and D2, and the comparison circuit CMP constitute a time constant circuit for delaying the start signal from the sequence controller. That is, since the diode D1 is in the reverse bias state before the activation signal (“0”) is input from the sequence control unit, the capacitor C1 is charged by the reference voltage Vr via the resistor R7 and the diode D2. And the terminal voltage of this capacitor C1 and resistors R5 and R
The divided voltage of the reference voltage Vr according to 6 is compared in the comparison circuit CMP, and at this time, the output signal of the comparison circuit CMP is configured to be high level (“1”). Therefore, since the base current flows through the resistor R4, the transistor Q1 is turned on. As a result, the resistor R3 is connected in parallel with the resistor R2, and the voltage division ratio is reduced.

Thus, when the transistor Q1 is on,
From the voltage division ratio of the resistors R1 and R2, the resistor R3 is the resistor R2.
As described above, the voltage division ratio is reduced by being connected in parallel, the divided voltage VD is increased even with the same current Ir, and in the control processing unit 21, the current Ir flowing through the resistor RI is an overcurrent. When the current is smaller than the set current of the state, the overcurrent state is controlled and the ON period of the switching transistor 11 is controlled to suppress the current Ir.

That is, as shown in FIG. 2B, the activation signal ("0") from the sequence control unit 4 is applied to the switching control unit 13 after a lapse of time t1 from turning on the AC power switch. In the initial state, the transistor Q1 is on. Therefore, when the control processing unit 21 starts the on / off operation of the switching transistor 11, it operates to suppress the current Ir, thereby suppressing the inrush current. can do.

Then, a forward voltage ("0") from the sequence controller 4 causes a forward voltage to be applied to the diode D1, and the capacitor C1 is discharged through the resistor R8 and the diode D1. This capacitor C
When the terminal voltage of the capacitor C1 drops according to the time constant of 1 and the resistor R8 and becomes lower than the divided voltage of the resistors R5 and R6, the output signal of the comparison circuit CMP becomes "0" and the base current of the transistor Q1 stops flowing. .

As a result, the transistor Q1 is turned off, the divided voltage VD by the resistors R1 and R2 is applied to the control processing unit 21, and the current Ir is suppressed when the current Ir exceeds the normal set current. As described above, the ON period of the switching transistor 11 is controlled. In this case, the time constant is equal to or less than the time T2 and needs to correspond to the time after the timing of b.

While the switch element 6 of the inrush current prevention unit 1 is off, the output voltage Vdc does not rise to a predetermined value due to the voltage drop across the resistor 5, but this switch element 6
Is turned on at the timing of b in FIG. 2B, the output voltage Vdc rises to a predetermined value. Further, the inrush current at this time does not occur as in the conventional example because the terminal voltage of the capacitor 10 of the power factor improving section has already risen to some extent. And in the conventional example, T1 + T3
Although the time of + T2 is used as the rise time, according to the present invention, the rise time is t1 (<T1) + T2, and the rush current can be suppressed and the rise time can be shortened.

Although the case where the activation signal from the sequence control unit 4 is "0" is shown, the opposite logic "1" can be applied. In that case, for example, the polarities of the diodes D1 and D2 are reversed and the comparison circuit CMP is used.
When the start signal is not input, the capacitor C1 is not charged by the reference voltage Vr when the comparison logic is inverted.
Becomes a reverse bias state, and accordingly, the capacitor C1 is charged through the resistors R7 and R8, and the output signal of the comparison circuit CMP is changed from "1" to "0" by utilizing the time constant at that time.
The configuration can be reversed.

FIG. 4 is an explanatory view of the essential parts of a third embodiment of the present invention, in which the same symbols as in FIG. 3 indicate the same parts, and R11
~ R15 is a resistor, Q2 is a field effect transistor, C2 is a capacitor, D3 is a diode. This embodiment utilizes the parasitic capacitance of the field effect transistor Q2,
A case where the activation signal from the sequence control unit is delayed to turn off the field effect transistor Q2 is shown. When this parasitic capacitance is not a sufficient value, the capacitor C2 can be connected as shown by the dotted line.

When the activation signal ("0") from the sequence controller is not applied, the field effect transistor Q2 divides the reference voltage Vr by the resistor (R15 + RI) via the resistor R14 and the diode D3. The applied voltage is applied to the gate to turn on, and the parasitic capacitance is charged. This parasitic capacitance is generally about several thousand pF. Alternatively, when the capacitor C2 shown by the dotted line is connected, this capacitor C2 is also charged. Then, the field effect transistor Q2 in the ON state connects the resistor R12 in parallel with the resistor R12 to reduce the voltage division ratio.

In this state, when the activation signal ("0") is applied from the sequence control unit, the control processing unit 21 starts its operation, and the current Ir is suppressed to a small value as in the case shown in FIG. So that the switching transistor 11
The on / off operation (see FIG. 1) is controlled. Then, since the diode D3 is in the reverse bias state, when the charged charge of the parasitic capacitance of the field effect transistor Q2 (or the charged charge of the capacitor C2) is discharged through the resistor R15 and falls below the threshold value of the field effect transistor Q2, The field effect transistor Q2 is turned off. Thereby, the resistance R
The divided voltage of 11 and R12 is input to the control processing unit 21, and ON / OFF control of the switching transistor 11 is performed so as not to exceed the set current.

Switching by the sequence control unit
The start of the operation of the power factor correction unit by the start of the on / off operation of the transistor 11 and the operation of short-circuiting the current suppressing resistor 5 by the switch element 6 are the same as those in the above-described embodiment. Therefore, duplicate description will be omitted.

The present invention is not limited to the above-mentioned respective embodiments, and various additions and modifications can be made. For example, in order to delay the activation signal from the sequence control unit, various configurations are possible. The time constant circuit can be applied, and a function called a timer can also be used. Further, it is also possible to adopt a configuration in which the timing signal is output from the sequence control unit so that the transistor Q1 in FIG. 3 and the field effect transistor Q2 in FIG. 4 are turned off after the time of the time constant circuit. . The timing signal in this case is timing b (see FIG. 2).
This can be dealt with by setting the time constant, timer, etc. of the sequence control unit so that the signal is output between the timing d and the timing d, and the circuit configuration can be simplified. The reference voltage Vr
Is indicated by a battery, but it is also possible to apply a constant voltage using a Zener diode or the like. Further, although the switching transistor 11 of the power factor correction unit 3 is shown as a field effect transistor, it is of course possible to use a bipolar transistor.

[0035]

As described above, according to the present invention, the inrush current prevention unit 1 including the switch control unit 7 that controls the switch element 6 that short-circuits the current suppressing resistor 5, the rectifying circuit 2,
The power factor correction unit 3 and the sequence control unit 4 are included, the switch element 6 is turned off at the start of the operation, and after a predetermined time, the switching transistor 11 of the power factor correction unit 3 is turned on and off, and then the rush operation is performed. The sequence control unit 4 controls so that the switch element 6 of the current prevention unit 1 is turned on, and the rise time can be shortened even when the current suppressing resistor 5 is increased to reduce the inrush current. There are advantages.

Further, the switching control section 13 for inputting the start signal from the sequence control section 4 and for turning on / off the switching transistor 11 of the power factor correction section 3 which starts the operation by the start signal is constituted by a time constant circuit. By controlling ON / OFF to suppress the current to a small value during the delay time, there is an advantage that the rush current at the time of starting the power factor correction unit 3 can be suppressed.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a first embodiment of the present invention.

FIG. 2 is an operation explanatory diagram of an embodiment of the present invention as a conventional example.

FIG. 3 is an explanatory diagram of a main part of a second embodiment of the present invention.

FIG. 4 is an explanatory diagram of a main part of a third embodiment of the present invention.

FIG. 5 is an explanatory diagram of a switching power supply device.

FIG. 6 is an explanatory diagram of a main part of a conventional switching control unit.

[Explanation of symbols]

1 Inrush current prevention unit 2 rectifier circuit 3 Power Factor Improvement Department 4 Sequence control unit 5 Current suppression resistor 6 switch elements 7 Switch control section 8 reactor 9 diode 10 capacitors 11 switching transistors 12 Current detection resistor 13 Switching controller

Front page continuation (58) Fields surveyed (Int.Cl. ⁷ , DB name) H02M 7/06 H02M 3/155 H02M 7/217

Claims (3)

(57) [Claims] 1. An inrush current prevention unit including a current suppressing resistor for suppressing an AC current from an AC power source, a switch element for short-circuiting the resistor, and a switch control unit for controlling ON / OFF of the switch element, A rectifier circuit that rectifies an AC voltage that is input through the inrush current prevention unit, a capacitor that applies a rectified output voltage by the rectifier circuit through a reactor and a diode, and energy is stored in the reactor to store the energy. A switching transistor that switches the input current to the capacitor through the diode, and
A power factor correction unit including a switching control unit that controls the on / off ratio of the switching transistor so that the output current does not exceed a set current, and the switch element of the inrush current prevention unit at the start of operation. Is turned off, and after turning on and off the switching transistor of the power factor correction unit after a predetermined time,
Rush current suppression circuit, characterized in that it includes a sequence control section for controlling the timing to short-circuit the resistor the current suppressing the switching element of the inrush current prevention unit as an on after a predetermined time. 2. The time constant circuit for starting charging of the capacitor by the activation signal from the sequence controller and the output current detected by the switching controller of the power factor improving unit.
A voltage divider circuit that divides the sum of the detected voltage and the reference voltage,
A control processing unit that starts operation by the start signal and inputs the divided voltage of the voltage dividing circuit to control the on / off ratio of the switching transistor so that the output current does not exceed a set current. And, the setting current is increased by increasing the voltage dividing ratio by the start signal delayed according to the time constant of the time constant circuit from the state where the voltage dividing ratio of the voltage dividing circuit is decreased so as to decrease the setting current. The inrush current suppressing circuit according to claim 1, further comprising a switch element for switching to a larger value. 3. The switching control section of the power factor correction section operates according to a voltage divider circuit that divides the sum of a detection voltage that has detected an output current and a reference voltage, and the start signal from the sequence control section. A control processing unit that starts and inputs the divided voltage of the voltage dividing circuit to control the on / off ratio of the switching transistor so that the current does not exceed the set current, and the set current is reduced. As described above, after the delay time based on the parasitic capacitance due to the activation signal being input from the state in which the voltage dividing ratio of the voltage dividing circuit is reduced, the voltage dividing ratio is increased and the setting current is increased. The inrush current suppressing circuit according to claim 1, further comprising a field effect transistor.