JPH1042551A - Rush-current limiting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect a main switching device from a rush-current, when the power supply of an AC-DC conversion circuit is closed. SOLUTION: A bypass route from an input capacitor 3 to an output capacitor 8 through a thyristor 16 is provided. A switching control unit, consisting of Zener diodes 18 and 19, is connected to the gate side of the thyristor 16 for the switching control of the thyristor 16. Further, an operation stopping unit which keeps a main switching device 4 in an off-state, while a power supply is closed and the charge of the output capacitor 8 is finished is provided. If the power supply is closed, the switching of the thyristor 16 is controlled by the Zener diodes 18 and 19. During the on-period of the thyristor 16, a rush current is applied to the output capacitor 8 through the thyristor 16. The rush current is not applied to the main switching device 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inrush current limiting circuit provided in an AC / DC converter.

[0002]

2. Description of the Related Art FIG. 4 shows an example of an AC-DC converter. As shown in the figure, this AC-DC converter circuit has a bridge diode circuit 2 that is a rectifier circuit. Of four end portions of the bridge diode circuit 2, predetermined two End (input end)
Are connected to the AC power supply 1, and the remaining two ends (output ends) are connected to both ends of the input capacitor 3.

[0005] One end (output end) of the input capacitor 3 is connected to the collector of a main switch element (transistor element) 4. The emitter of the main switch element 4 is commutated with one end of a choke coil 6. The cathode sides of the diodes 7 are respectively connected. The other end of the choke coil 6 is connected to one end of an output capacitor 8. The other end of the output capacitor 8 is connected to the other end (ground side) of the input capacitor 3 via the anode of the commutation diode 7. It is connected. A load is connected to the output capacitor 8 in parallel.

A diode 14 is provided between the collector and the emitter of the main switch element 4 with its cathode facing the collector of the main switch element 4, and a control circuit 5 is mounted on the base side of the main switch element 4. It is connected via a transformer 20.

The output capacitor 8 has a voltage dividing resistor 12,
Thirteen series bodies are connected in parallel, and a series connection part of the voltage dividing resistors 12 and 13 is connected to the control circuit 5. The choke coil 6 is provided with an auxiliary winding 21, an output end of the auxiliary winding 21 is connected to an anode of the diode 10, and a cathode of the diode 10 is connected to one end of the capacitor 11. The other end of the capacitor 11 is connected to the ground side of the output capacitor 8. The control circuit 5 is connected to the connection between the diode 10 and the capacitor 11.
And one end of the starting resistor 9 is connected, and the other end of the starting resistor 9 is connected to the collector of the main switch element 4.

[0006] The AC-DC converter circuit having the above-described structure performs full-wave rectification of the output of the AC power supply 1 by the bridge diode circuit 2.
The full-wave rectified output of the bridge diode circuit 2 is smoothed through the input capacitor 3, the main switch element 4, the choke coil 6, and the output capacitor 8 to output a DC voltage to the load. By variably controlling the switch-on period, a predetermined circuit output voltage _Vout can be stably supplied to the load.

The switching control of the main switch element 4 is performed by a control circuit 5.
Detects a circuit output V _out using the voltage dividing resistors 12 and 13 and controls the control power supply source so that a predetermined circuit output voltage V _out is stably output based on the detected value e. And a circuit configuration for performing switch-on / off control (variable control of the switch-on period) of the main switch element 4 using the charging energy of the capacitor 11. For example, the switch-on timing of the main switch element 4 is performed at a predetermined constant cycle (switching cycle), and when the circuit output detection value e is lower than the set circuit output, the switch-on period is lengthened ( The ratio of the switch-on period t to the switching period T (t / T; duty (duration)) is increased) to compensate for the decrease in the circuit output, and the circuit output detection value e rises above the set circuit output. If so, the switch-on period is shortened (duty is reduced), and the rise of the circuit output is corrected.

[0008]

By the way, the above-mentioned AC-
In the DC conversion circuit, the normal circuit operation as described above cannot be performed unless the output capacitor 8 and the capacitor 11 are charged with energy of a predetermined voltage. At the time of normal power-on, since the output capacitor 8 and the capacitor 11 are not charged with energy at all,
After the operation of charging the output capacitor 8 and the capacitor 11 is performed to start the circuit, the operation shifts to the normal circuit operation as described above. In addition, the power is turned on immediately after the power is stopped due to a power failure, etc.
Since the charging energy of the output capacitor 8 and the capacitor 11 has been greatly reduced, the normal circuit operation is started after the charging operation of the output capacitor 8 and the capacitor 11 is performed as described above.

The charging operation of the output capacitor 8 and the capacitor 11 is performed as follows. For example, when the power is turned on, the output of the AC power supply 1 is supplied to the input capacitor 3 via the bridge diode circuit 2, and the voltage energy of the input capacitor 3 is charged and supplied to the capacitor 11 through the starting resistor 9. You. If the charging voltage of the capacitor 11 does not reach the predetermined voltage V _cc (the set voltage of the control power required to drive the control circuit 5), the control circuit 5
Cannot perform the circuit operation, and the main switch element 4
Is in the switch-off state, the input capacitor 3
Does not flow to the main switch element 4 side, but is entirely supplied to the capacitor 11 via the starting resistor 9.

When the charging voltage of the capacitor 11 reaches the set voltage _Vcc , the control circuit 5 starts the circuit operation.
At this time, the output capacitor 8 is empty (the stored energy is extremely low when the return power supply is turned on after a momentary power failure), and the circuit output becomes zero voltage (almost zero voltage when the return power supply is turned on).
Therefore, the control circuit 5 controls the switching of the main switch element 4 with, for example, a duty of “1” in order to compensate the circuit output.

When the main switch element 4 performs a switching operation in accordance with the switching control operation of the control circuit 5, an inrush current flows from the input capacitor 3 through the main switch element 4 and the choke coil 6 to the output capacitor 8. The output capacitor 8 is charged. When the charging voltage of the output capacitor 8 reaches a predetermined circuit output voltage, the operation shifts to the normal circuit operation as described above.

Incidentally, after the charging of the capacitor 11 is completed and the operation of the control circuit 5 is started, the choke coil 6
, The energy is output from the auxiliary winding 21 by the energization of the choke coil 6, and the energy is supplied to the capacitor 11 via the diode 10.

As described above, when the power is turned on or the power is restored after a momentary power failure, the output capacitor 8 and the capacitor 11 are turned on.
Is performed. However, in the circuit configuration shown in FIG. 4, the charging of the output capacitor 8 is performed after the charging of the capacitor 11 is completed. Therefore, the charging time from when the power is turned on to when the charging of the output capacitor 8 is completed is long.
There is a problem that it takes time for the circuit to start up.

When the control circuit 5 switches on the main switch element 4 with the duty "1" after the charging of the capacitor 11 is completed, the inrush current saturates the choke coil 6 and the choke coil 6 The inrush current cannot be controlled, and a large inrush current (overcurrent) exceeding a predetermined withstand current of the main switch element 4 may flow through the main switch element 4, and the overcurrent may damage the main switch element 4. In some cases.

Therefore, for example, the inrush current flowing through the main switch element 4 is suppressed by reducing the duty of the main switch element 4 when the power is turned on, and the main current is prevented by preventing the overcurrent from flowing through the main switch element 4. The protection of the switch element 4 can be considered. However, in such a case, the time required for charging the output capacitor 8 is increased by the amount of suppressing the inrush current, which causes a problem that the rise time of the circuit is further increased.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to prevent an overcurrent due to an inrush current at the time of power-on from flowing to a main switch element, thereby protecting the main switch element. It is another object of the present invention to provide an inrush current limiting circuit that can reduce the rise time of an AC-DC converter.

[0017]

Means for Solving the Problems In order to achieve the above object, the present invention has the following structure to solve the above problems.

That is, in the first invention, the output of the AC power supply is received by the input capacitor via the rectifier circuit, and the output of the input capacitor is supplied to the output capacitor via the main switch element, and smoothed by the output capacitor. An inrush current limiting circuit that is provided in an AC-DC conversion circuit that outputs to the outside, and suppresses a current that intrudes from an input capacitor to an output capacitor through a main switch element when power is turned on. A charging operation switch element provided on a bypass path between the rectifier circuit and the output capacitor that bypasses a main path to the output capacitor via the output capacitor via the output capacitor, and subtracting a charging voltage of the output capacitor from a voltage of the input capacitor. When the difference voltage reaches a predetermined voltage The charging operation switch element is switched on, and when the difference voltage becomes zero voltage, the charging operation switch element is switched off to perform switching control of the charging operation switch element, and the charging operation switch element is controlled. A charge control unit for supplying power of the rectifier circuit output of the AC power supply to an output capacitor through a bypass path sequentially passing through an input capacitor and a charging operation switch element during a switch-on period of the AC power supply; and A main switch element operation stop circuit for maintaining the main switch element in a switch-off state during a period from when the charging operation of the control section is started to when the charging voltage of the output capacitor reaches the set circuit output voltage. The configuration having the above is a means for solving the above problem.

According to a second aspect of the present invention, the charge control section forming the first aspect of the invention has a series connection structure in which the anode side of the first Zener diode is connected in series with the cathode side of the second Zener diode. This series connection is the first
Is connected in parallel to the charging operation switch element, with the Zener diode being an input capacitor side. The charging operation switch element is constituted by a thyristor or a triac, and the gate side of the switch element is the first and second Zener diodes. Is a means for solving the above-mentioned problem with the configuration connected to the series connection part.

According to a third aspect of the present invention, the gate side of a thyristor or a triac, which is a switching element at the time of charging forming the second aspect of the present invention, includes a level shift diode for equivalently increasing a switch-on driving voltage of the switching element. The configuration is connected to the series connection of the first and second Zener diodes of the charging control unit via the charging control unit, and is a means for solving the above problem.

According to a fourth aspect of the present invention, there is provided the first, second or third aspect.
The charging operation switch element according to the present invention has a structure in which a resistor for protecting the charging operation switch element is connected in series, thereby providing means for solving the above-mentioned problem.

According to a fifth aspect of the present invention, there is provided the first, second or third aspect.
Alternatively, the charging control section forming the fourth invention is configured to solve the above-mentioned problem by a configuration in which a resistor for protecting the charging control section is connected in series.

In the present invention having the above configuration, for example, when the power of the AC-DC converter circuit is turned on from a state where the voltage of the output capacitor is zero voltage, the charge control unit performs switching control of the switch element during charging. During the switch-on period of the switch element during charging, the power of the output of the rectifier circuit of the AC power supply is charged and supplied to the output capacitor through a bypass path bypassing the main switch element. During a period from the start of charging of the output capacitor to the completion of charging, the operation stop circuit keeps the main switch element in a switch-off state.

As described above, during the charging period of the output capacitor when the power is turned on, the main switch element is maintained in the switch-off state by the operation stop circuit, and the rush current of the rectifier circuit output passes through the bypass path bypassing the main switch element. Since the current flows into the output capacitor, the inrush current does not flow through the main switch element, so that an overcurrent due to the inrush current does not flow through the main switch element, and the main switch element can be protected. In addition, since the value of the inrush current can be set without considering the adverse effect of the inrush current on the main switching element, the inrush current can be made larger than before, thereby shortening the charging period of the output capacitor. It is possible to achieve.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. In the description of the present embodiment, the same reference numerals are given to the same parts as those in the conventional example, and the overlapping description will be omitted.

FIG. 1 shows the AC-
The inrush current limiting circuit of the present embodiment is shown in a state incorporated in a DC conversion circuit. This inrush current limiting circuit 25
Are a starting resistor 9, a capacitor 11, a resistor 15, a thyristor 16 which is a switching element at the time of charging, and a resistor 17.
And a Zener diode 18 as a first Zener diode and a Zener diode 19 as a second Zener diode.

As shown in FIG. 1, one end of the resistor 17 is connected to the collector of the main switch element 4 and
Is connected to the cathode side of a Zener diode 18, the anode side of the Zener diode 18 is connected to the cathode side of a Zener diode 19, and the anode side of the Zener diode 19 is connected to the choke coil 6 and the output capacitor 8. Connected to the connection.

One end of a resistor 15 is connected to the connection between the resistor 17 and the collector of the main switch element 4, and the anode of a thyristor 16 is connected to the other end of the resistor 15. The cathode of the thyristor 16 is connected to the connection between the anode of the Zener diode 19 and the output capacitor 8, and the gate of the thyristor 16 is connected to the series connection X of the Zeners 18 and 19.

One end of a starting resistor 9 is connected to the connection between the cathode of the thyristor 16 and the output capacitor 8, and the other end of the starting resistor 9 is connected to the capacitor 11. Since the circuit configuration of the AC-DC conversion circuit other than the above is the same as that of the conventional example, the duplicated description will be omitted.

Among the circuit components constituting the inrush current limiting circuit 25, a Zener diodes 18 and 19 constitute a charge control section, and this charge control section controls the switching of the thyristor 16 which is a switch element during charging. To charge the output capacitor 8. The start-up resistor 9 and the capacitor 11 constitute an operation stop circuit. This circuit operates during a charging period of the output capacitor 8 (the charging voltage of the output capacitor 8 after the charging of the output capacitor 8 is started is determined by a predetermined circuit output). Main switch element 4 is maintained in a switch-off state during a period from when voltage _Vout is reached to when charging is completed.

The inrush current limiting circuit of this embodiment is configured as described above. Hereinafter, the circuit operation of the inrush current limiting circuit will be briefly described with reference to the time chart of FIG.

For example, when the power of the AC-DC converter is turned on from the state where the input capacitor 3, the output capacitor 8 and the capacitor 11 are at zero voltage (time t _{1 in} FIG. 2), the output of the AC power source 1 is bridged. The voltage V ₁ of the input capacitor 3 is supplied to the input capacitor 3 via the diode circuit 2 and rises in accordance with the output of the full-wave rectified waveform of the bridge diode circuit 2 as shown in FIG. Go.

The difference voltage ΔV (ΔV) obtained by subtracting the voltage V ₂ of the output capacitor 8 from the voltage V ₁ of the input capacitor 3
V = V ₁ −V ₂ ) is the resistance 17 and the Zener diode 18,
When the divided voltage is applied to 19 and the applied voltage of the Zener diodes 18 and 19 exceeds the predetermined ON drive voltage of the Zener diodes 18 and 19, and the Zener diodes 18 and 19 are both switched on ( At time t _{2 in} FIG. 2, a trigger signal for turning on the thyristor 16 is applied to the gate of the thyristor 16 from the series connection portion X of the Zener diodes 18 and 19, and the thyristor 16 is turned on.
Is turned on, and as shown in FIG. 2B, an inrush current corresponding to the magnitude of the differential voltage ΔV starts flowing from the input capacitor 3 side in a bypass path passing through the resistor 15 and the thyristor 16 in order.

The rush current that flows into the thyristor 16 when the thyristor 16 is switched on first has a constant value (rise current value) I _{th at the} starting position A shown in FIG. 2B, and is expressed by the following equation. be able to.

I _th ≒ (ZD ₁ + ZD ₂ ) / R ₁

Here, ZD ₁ represents the switch-on drive voltage of the Zener diode 18, ZD ₂ represents the switch-on drive voltage of the Zener diode 19, and R ₁ represents the resistor 15.
Represents the resistance value.

The rush current flowing through the thyristor 16 branches to the output capacitor 8 and the starting resistor 9, and the rush current split to the output capacitor 8 flows into the output capacitor 8 to charge the output capacitor 8. Then, the voltage V ₂ of the output capacitor 8 is changed as shown in FIG.
Going up. At the same time, the rush current shunted to the starting resistor 9 flows into the capacitor 11 via the starting resistor 9 to charge the capacitor 11.

Since the input capacitor 3 has a small capacity, its voltage V ₁ varies in accordance with the output of the bridge diode circuit 2 by drawing a full-wave rectified waveform as shown in FIG. After the voltage V ₁ of the input capacitor 3 reaches a predetermined peak voltage V _p of the input capacitor 3,
It is going down. Then, when the voltage V ₁ of the input capacitor 3 becomes equal to the charging voltage V ₂ of the output capacitor 8 and the difference voltage ΔV becomes zero (time t ₃ in FIG. 2), FIG.
As shown in (b), the thyristor 16 is turned off, the supply of the rush current is stopped, and the charging operation of the output capacitor 8 and the capacitor 11 is stopped.

Thereafter, the voltage V ₁ of the input capacitor 3 decreases and tends to be lower than the charging voltage V ₂ of the output capacitor 8. However, the voltage V ₁ of the input capacitor 3 is changed by the diode 14 to the charging voltage of the output capacitor 8. It is clamped to V _2.

After that, as shown in FIG. 2A, the input capacitor 3 is changed according to the output of the bridge diode circuit 2.
Voltage V ₁ of the begins to rise again, in the same manner as described above, when the Zener diode 18 and 19 from the differential voltage ΔV of the input capacitor 3 and the output capacitor 8 are both turned the switch ON state (time t ₄ in FIG. 2), A trigger signal is applied to the gate of the thyristor 16 from the series connection part X side of the Zener diodes 18 and 19, the thyristor 16 switches on, and an inrush current starts flowing from the input capacitor 3 side through the resistor 15 and the thyristor 16, The charging of the output capacitor 8 and the capacitor 11 is restarted.

As described above, the Zener diodes 18 and 19 repeatedly perform the switching control of the thyristor 16 by using the difference voltage ΔV between the input capacitor 3 and the output capacitor 8 to charge the output capacitor 8 and the capacitor 11 as shown in FIG.
(A) as shown in FIG. Then, when the charging voltage of the output capacitor 8 reaches the set output voltage _Vout of the AC-DC conversion circuit and the charging voltage of the capacitor 11 reaches the predetermined control power voltage _Vcc (time t in FIG. 2).
₁₁ ), the AC-DC converter circuit starts up and shifts to the normal circuit operation as described above, and the circuit operation of the rush current limiting circuit is stopped.

In this embodiment, the starting resistor 9 of the operation stop circuit is set as follows so that the charging of the capacitor 11 is completed at the same time as the charging of the output capacitor 8 is completed, and the control circuit 5 starts up. During the charging period of the capacitor 8, the main switch element 4 is maintained in the switch-off state.

The amount of current shunted from the thyristor 16 and flowing into the starting resistor 9 during the switch-on period of the thyristor 16 can be determined by the resistance value of the starting resistor 9. The resistance value of the starting resistor 9 is set so that the charging of 11 is completed, and the length of the charging period of the capacitor 11 is determined by the amount of current flowing into the capacitor 11 via the starting resistor 9. This is done by setting the capacitor 11
Since the control circuit 5 cannot switch on the main switch element 4 unless the charging of the output capacitor 8 is completed, the operation stop circuit including the starting resistor 9 and the capacitor 11 operates after the charging of the output capacitor 8 is started (from power-on). This is because the main switch element 4 can be kept in the switch-off state until the charging is completed.

In this embodiment, the difference voltage ΔV between the input capacitor 3 and the output capacitor 8 is a value ΔV ′ (ΔV ′) obtained by subtracting the set circuit output voltage V _out from the predetermined peak voltage V _{p of the} input capacitor 3. = V _p −
_V.sub.out ) (.DELTA.V> .DELTA.V '), the Zener diodes 18 and 19 are both switched on, a trigger signal for switching on the thyristor 16 is applied to the gate of the thyristor 16, and the thyristor 16 is switched on. So, thyristor 16, resistor 17, and Zener diode
Circuit constants 18 and 19 are set.

By setting the circuit constants in this manner, the charging voltage of the output capacitor 8 can be charged to the set circuit output voltage _Vout when the power is turned on.
After the charging of the output capacitor 8 is completed and the AC-DC conversion circuit starts up, it is possible to prevent a current from flowing from the input capacitor 3 side to the output capacitor 8 side via the rush current limiting circuit 25, thereby allowing normal circuit operation. Sometimes inrush current limiting circuit
The occurrence of power loss in the inrush current limiting circuit 25 due to the energization of 25 can be avoided.

Further, the resistance of the resistor 17 is set so that a current exceeding a predetermined withstand current does not flow through the Zener diodes 18 and 19. From this, the Zener diodes 18 and 19 can be protected.

Further, in a current region in which the inrush current flowing through the thyristor 16 during the switch-on period of the thyristor 16 does not exceed a predetermined withstand current, the optimum value of the inrush current that allows the output capacitor 8 to be charged more quickly is known in advance. The resistance value of the resistor 15 is set so that the above-mentioned optimal rush current flows through the resistor 15 and the thyristor 16 during the switch-on period of the thyristor 16. The length of the charging period of the output capacitor 8 can be determined.

According to this embodiment, the inrush current limiting circuit is provided in the AC-DC conversion circuit, and when the power is turned on or the power is restored after a momentary power failure, the input is performed while maintaining the main switch element 4 in the OFF state. Since the inrush current flows through the bypass path from the capacitor 3 side to the output capacitor 8 and the capacitor 11 side through the thyristor 16 to charge the output capacitor 8 and the capacitor 11, the output capacitor 8 and the capacitor 11 are charged. Inrush current does not pass through the main switching element 4 during the charging period from the start of the charging to the completion of charging, and an overcurrent due to the inrush current as described in the conventional example passes through the main switching element 4 and passes through the main switching element 4. Can be reliably avoided.

Also, the main switching element 4
Therefore, it is not necessary to use a switch element having a large withstand current as the main switch element 4 in order to protect the main switch element 4. Since the main switch element having a small withstand current is inexpensive, the circuit cost can be reduced.

Further, in this embodiment, as described above, the output capacitor 8 and the capacitor 11 are charged by inrush current flowing through the bypass path bypassing the main switch element 4, and are provided on the bypass path. The thyristor 16 has a higher withstand current than the main switch element (transistor element) 4 and can use an inexpensive element. Therefore, the rush current can be controlled without considering the adverse effect of the rush current on the main switch element 4. , And the inrush current can be made larger than before.

Of course, even if the inrush current is increased in such a manner, the withstand current of the thyristor 16 is much larger than that of the main switch element 4. Therefore, the thyristor 16 is not damaged by the large inrush current. By increasing the current, it is easy to shorten the charging period of the output capacitor 8. Moreover, the output capacitor 8
And the charging of the capacitor 11 are performed at the same time, so that the period from when the power is turned on to when the charging of the output capacitor 8 and the capacitor 11 is completed and the AC-DC conversion circuit starts up is significantly shorter than in the conventional example. be able to.

Further, the resistor 15 is provided in series with the thyristor 16, and the resistance of the resistor 15 is set so that an inrush current larger than the withstand current of the thyristor 16 does not flow through the thyristor 16. It is possible to prevent a problem that the thyristor 16 is damaged due to an overcurrent that exceeds the withstand current flowing through the 16.

Further, a resistor 17 is connected in series to a series connection of the Zener diodes 18 and 19,
Since the resistance value of the resistor 17 is set to an optimal value so that a current larger than a predetermined withstand current does not flow through the resistors 18 and 19, the Zener diodes 18 and 19 can be protected by the resistor 17.

Since the Zener diodes 18 and 19 can be protected by the resistor 17 in this manner, the Zener diode 18 having a small withstand current can be replaced by merely changing the setting of the resistance value of the resistor 17. , 19
Can be adopted as In addition, since the Zener diodes 18 and 19 are connected in series, the voltage applied to one Zener diode can be suppressed lower than when only one Zener diode is provided, and the protection of the Zener diode is more reliably performed. In addition, a Zener diode having a lower withstand voltage can be used.

Note that the present invention is not limited to the above-described embodiment, but can adopt various embodiments. For example, in the above-described embodiment, the charge control unit is configured by the Zener diodes 18 and 19, but the input capacitor 3
And the voltage of the output capacitor 8 is detected, and the thyristor 16 is switched on when the difference voltage ΔV between these voltages reaches a predetermined drive voltage. Good.

In the above-described embodiment, a thyristor is used as the charging operation switch element, but a triac may be used instead of the thyristor. Even when a triac is adopted, the triac switching control can be performed by using the zener diodes 18 and 19 as in the above-described embodiment.

Furthermore, in the above embodiment, the resistor 17 is connected in series to the Zener diodes 18 and 19;
When a Zener diode having a large withstand current is used, the resistor 17 may be omitted. Furthermore, in the above-described embodiment, the resistor 15 is connected in series to the anode side of the thyristor 16, but when a thyristor having a large withstand current is used, the resistor 15 may be omitted.

Further, in the above embodiment, the operation stopping circuit of the main switch element 4 is constituted by the starting resistor 9 and the capacitor 11, but the operation stopping circuit starts charging the output capacitor 8 after the power is turned on. A configuration other than the above embodiment may be used as long as the circuit is configured to maintain the main switch element 4 in the switch-off state during the charging period until the termination.

Further, a level shift diode 22 may be provided between the gate of the thyristor 16 and the series connection X of the Zener diodes 18 and 19 as shown by a dotted line in FIG. The level shift diode 22 is disposed with its cathode facing the gate side of the thyristor 16, and can equivalently increase the switch-on drive voltage of the thyristor 16.

As shown in FIG. 3, the thyristor 16 has a voltage signal (trigger signal) higher than the switch-on drive voltage at the gate.
Is applied, a current flows from the anode side to the cathode side.However, when the thyristor 16 is heated and heated by energization or the like, the driving voltage decreases, and when the thyristor 16 is in the switch-off state, the Zener diode 18,
Only when a voltage due to a very small leak current flowing into 19 is applied to the gate of the thyristor 16, the thyristor 16 is rarely switched on despite the switch-off period of the thyristor 16.

On the other hand, when the level shift diode 22 is provided as described above, the level shift diode 22
Since the driving voltage of the thyristor 16 can be equivalently increased by the predetermined forward voltage, the above problem can be reliably prevented. However, since the above problem hardly occurs in normal operation, the occurrence of the above problem can be substantially avoided without providing the level shift diode 22.

[0062]

According to the present invention, the inrush current limiting circuit is provided in the AC-DC conversion circuit, and the power of the output of the rectifier circuit of the AC power supply is supplied to the output capacitor by the bypass path bypassing the main switch element by the inrush current limiting circuit. The main switch element is maintained in the switch-off state during the charging period from the start of the charging operation of the output capacitor to the completion of the charging of the output capacitor, while charging the output capacitor by charging the output capacitor. However, when the power is turned on, the rush current flowing from the rectifier circuit side to the output capacitor does not flow through the main switch element, and the problem that the main switch element is damaged by the overcurrent due to the rush current as described in the conventional example. This can be reliably prevented, and the main switch element can be protected.

As described above, since the main switch element can be reliably protected from inrush current, a switch element having a small withstand current can be used as the main switch element, and such a switch element is inexpensive. Therefore, it is possible to reduce the circuit cost.

Further, as described above, since the rush current does not flow through the main switch element, the rush current can flow without considering the adverse effect of the rush current on the main switch element. Thus, a larger inrush current can flow than in the conventional example, and the charging time of the output capacitor can be reduced as compared with the conventional example.

Further, a charging operation switch element is provided on a bypass path through which an inrush current flows, and a charging control unit for performing switching control of the charging operation switch element is provided. After the DC conversion circuit starts up, the charging operation switch element can be maintained in the switch-off state, whereby the rush current limiting circuit is energized during the normal circuit operation of the AC-DC conversion circuit. Will not be
It is possible to prevent a power loss from occurring in the inrush current limiting circuit due to energization of the inrush current limiting circuit during normal circuit operation, and prevent an increase in power loss in the entire AC-DC conversion circuit.

The charge control section is constituted by a series connection of first and second zener diodes, and the switch element at the time of charging is constituted by a thyristor or a triac. Switching operation of the switch element at the time of charging can be performed to perform the charging operation of the output capacitor.

When a level shift diode is provided on the gate side of the thyristor or triac,
Since the drive voltage for switching on the thyristor or triac can be equivalently increased by the switch-on drive voltage for the level shift diode, even if the drive voltage for switch-on decreases due to the temperature rise of the thyristor or triac, The thyristor or the triac can be reliably prevented from being accidentally switched on by the voltage of a very small leak current flowing from the charge control unit, and the reliability of the circuit operation can be improved.

In the case where a resistor is connected in series with the switch element during charging, the inrush current flowing through the switch element during charging during the switch-on period of the switch element during charging is determined by the switch element during charging. The inrush current can be suppressed by setting the resistance value of the resistor so as not to be equal to or larger than the predetermined withstand current, and the charge-time operation switch element can be reliably protected.

In the case where a resistor is connected in series to the charge control section, the current of more than a predetermined withstand current does not flow through each circuit component constituting the charge control section. By setting the resistance value of the resistor, each circuit component of the charge control unit can be protected. This makes it possible to form each circuit component of the charge control unit with an element having a small withstand current, and since such an element is inexpensive, the circuit cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a time chart showing an example of a charging operation of an output capacitor of the circuit shown in FIG. 1;

FIG. 3 is a graph showing electrical characteristics of a thyristor.

FIG. 4 is a circuit diagram showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 AC power supply 2 Bridge diode circuit 3 Input capacitor 4 Main switch element 8 Output capacitor 9 Starting resistor 11 Capacitor 15, 17 Resistor 16 Thyristor 18, 19 Zener diode 22 Level shift diode

Claims (5)

[Claims] An AC power supply receives an output of an AC power supply via an input capacitor via a rectifier circuit, further supplies an output of the input capacitor to an output capacitor via a main switch element, smoothes the output by the output capacitor, and outputs the output to the outside. A rush current limiting circuit provided in a DC conversion circuit for suppressing a current rushing from an input capacitor to an output capacitor via a main switch element when power is turned on. A charging operation switch element provided on a bypass path between the rectifier circuit and the output capacitor bypassing the main path to the output capacitor, and a differential voltage obtained by subtracting a charging voltage of the output capacitor from a voltage of the input capacitor is predetermined. When the set voltage is reached, the charging operation switch element Is turned on, and when the differential voltage becomes zero voltage, the charging operation switch element is switched off to perform switching control of the charging operation switch element, and during the switch-on period of the charging operation switch element. A charge control unit that supplies power of the output of the rectifier circuit of the AC power supply to an output capacitor through a bypass path through an input capacitor and a charge operation switch element in order, and a charging operation of the charge control unit connected to the main switch element And a main switch element operation stop circuit for maintaining the main switch element in a switch-off state during a period from the start of the operation until the charging voltage of the output capacitor reaches a set circuit output voltage. Inrush current limiting circuit. 2. The charge control section includes a series connection body in which an anode side of a first zener diode is connected in series with a cathode side of a second zener diode, and the series connection body includes a first zener diode. Is connected in parallel to the charging operation switch element with the input capacitor side. The charging operation switch element is constituted by a thyristor or a triac, and the gate side of the switch element is connected in series with the first and second Zener diodes. 2. The inrush current limiting circuit according to claim 1, wherein the inrush current limiting circuit is connected to the first and second sections. 3. A gate of a thyristor or a triac, which is a switch element operated at the time of charging, via a level shift diode for equivalently increasing a switch-on drive voltage of the switch element. 3. The rush current limiting circuit according to claim 2, wherein the rush current limiting circuit is connected to a series connection of the Zener diode. 4. The charging operation switch element according to claim 1, wherein a resistor for protecting the charging operation switch element is connected in series. Inrush current limiting circuit. 5. The charge control unit according to claim 1, wherein a resistor for protecting the charge control unit is connected in series. Inrush current limiting circuit.