JPH08317551A - Rush current preventing circuit - Google Patents

Abstract

PURPOSE: To make it possible to cope with a change in a wide range of input voltage with respect to a rush current preventing circuit to prevent a rush current to an input capacitor. CONSTITUTION: A transistor Q1 and an input capacitor C2 are connected between connecting terminals 1 and 2 to be connected to a DC power supply 5 and any rush current from the DC power supply 5 to the input capacitor C2 through the transistor Q1 can be prevented by the rush current preventing circuit, in which a capacitor C1 and a zener diode Dz1 are connected between the gate and source of the transistor Q1 , and the capacitor C1 is charged at a constant current from the DC power supply 5 through a constant current circuit 6 comprising transistors Q2 and Q3 and resistors R1 and R2 .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rush current prevention circuit having a configuration in which an input capacitor is provided between connection terminals connected to a DC power supply. In various devices such as a transmission device having a plurality of printed circuit boards on which various electronic circuit components are mounted, hot insertion and removal of the printed circuit boards are often performed. Therefore, by mounting the printed circuit board, a direct current voltage is immediately applied to the printed circuit board and supplied to each part. In that case, the power supply circuit generally uses a large-capacity capacitor in its input filter section.
Therefore, when a printed circuit board is mounted, a rush current due to a large-capacity capacitor will flow, so a rush current prevention circuit is provided to prevent it.

[0002]

BACKGROUND ART FIG. 11 is an explanatory view of a conventional example, Q _11,
Q ₁₂ is a transistor, C ₁₁ is a capacitor, C ₁₂ is an input capacitor, C ₁₃ is a smoothing capacitor, R ₁₁ is a resistor, D
z ₁₁ is a Zener diode, D ₁ and D ₂ are diodes,
L is a smoothing reactor, 10 is an inrush current prevention circuit, 1
Reference numeral 1 is a pulse width control circuit, 12 is a transformer, and 13 is a DC power supply, which is applied to a switching power supply.

The switching power supply is a pulse width control circuit 1
The output DC voltage is compared with the set reference voltage by 1 and a pulse voltage having a pulse width corresponding to the error voltage is applied to the gate of the transistor Q ₁₂ to turn on / off the current flowing through the primary winding of the transformer 12. As a result, a voltage is induced in the secondary winding of the transformer 12, and is rectified and smoothed by a rectifying / smoothing circuit composed of the diodes D ₁ and D ₂ , the reactor L, and the capacitor C _13, and becomes an output DC voltage. Are supplied to an electronic circuit (not shown).

When the transistor Q ₁₂ is turned on,
A large current flows through the primary winding of the transformer 12, but the current at that time is supplied from the DC power supply 13 and the input capacitor C _12, and by providing the input capacitor C ₁₂ having a relatively large capacitance, The voltage fluctuation of the power supply 13 can be suppressed.

The inrush current prevention circuit 10 includes a transistor Q ₁₁ , a capacitor C _11, and a Zener diode Dz _11.
And a resistor R _11, and the terminal voltage of the capacitor C ₁₁ charged via the resistor R ₁₁ is applied between the gate and source of the transistor Q ₁₁ . The Zener diode Dz ₁₁ is for preventing an excessive voltage from being applied between the gate and the source of the transistor Q ₁₁ .

FIG. 12 is a diagram for explaining the operation of the conventional example.
(A) shows the input voltage Vin, (b) shows the terminal voltage of the capacitor C ₁₁ , and (c) shows the inrush current flowing through the capacitor C ₁₁ . If without a rush current prevention circuit 10, when connecting the DC power supply 13, it is configured that the input capacitor C ₁₁ is connected directly to the DC power supply 13, an input capacitor C ₁₁
Inrush current flows to. As a result, the voltage of the DC power supply 13 changes greatly. However, when the inrush current prevention circuit 10 including the transistor Q ₁₁ is provided, immediately after the DC power supply 13 is connected, the transistor Q ₁₁ is in the off state, so that no current flows in the input capacitor C ₁₁ .

The capacitor C ₁₁ is charged by the DC power supply 13 via the resistor R ₁₁ . The terminal voltage of the capacitor C ₁₁ rises as shown in (b) of FIG. 12, and when it exceeds the threshold voltage Vth of the transistor Q ₁₁ , the transistor Q _11
11 becomes conductive, and since the equivalent impedance at this time is large, a resistance is connected between the DC power supply 13 and the input capacitor C _12, and as shown in FIG. Although it flows into the input capacitor C ₁₂ , it can be significantly reduced as compared with the case where the inrush current prevention circuit 10 is not provided. Then, as the terminal voltage of the capacitor C ₁₁ rises, the equivalent impedance of the transistor Q ₁₁ becomes smaller, and finally the transistor Q ₁₁ becomes almost completely conductive.

[0008]

Various devices have been diversified, and various power supply voltages such as 24V, 48V, and 60V have been adopted. Therefore, the inrush current prevention circuit described above is configured corresponding to the power supply voltage.
Therefore, there is a problem that the cost is increased because the production of various kinds is performed.

For example, the input voltage Vi from the DC power supply 13
In the case where n is shown by the solid line in FIG. 12A, if the inrush current prevention circuit 10 can suppress the current to the current shown in FIG. 12C, the input voltage Vin becomes the dotted line in FIG. , The terminal voltage of the capacitor C ₁₁ rises as shown by the dotted line in FIG. 12 (b), and the transistor Q ₁₁ rapidly transitions to a complete conduction state, thereby causing an input capacitor The current flowing through C ₁₂ becomes large as shown by the dotted line in FIG. That is, since the rising speed of the terminal voltage of the capacitor C ₁₁ is high and the voltage applied to the input capacitor C ₁₂ is high, there is a problem that the flowing current becomes large even when the inrush current prevention circuit 10 is provided. Therefore, a structure corresponding to the input voltage Vin is required, which increases the cost.

Further, a communication device including a switching device or the like needs to be in an operating state at all times, and when a failure occurs in a part of the communication device, it is necessary to insert / remove a printed circuit board with the power source turned on. In that case, the printed circuit board is provided with a relatively large-capacity capacitor for removing noise through the power supply wiring, and therefore, an inrush current flows when the printed circuit board is mounted. As a result, the voltage of the DC power supply fluctuates, which causes malfunction of electronic circuits on other printed circuit boards. Therefore, it is necessary to prevent inrush current when mounting the printed circuit board. An object of the present invention is to suppress the inrush current even with a wide range of input voltage with a relatively simple structure.

[0011]

The inrush current prevention circuit of the present invention will be described with reference to FIG. 1. A transistor Q ₁ and an input capacitor C ₂ are connected between connection terminals 1 and 2 connected to a DC power supply 5. connect, in the circuit to prevent the inrush current flowing from the DC power source 5 to the input capacitor C ₂ through the transistor Q _1, a capacitor C ₁ connected between the gate and source of the transistor Q _1, to the capacitor C ₁ On the other hand, a constant current circuit 6 for charging with a constant current from the DC power supply 5 is provided. The constant current circuit 6 in this case is a circuit including transistors Q ₂ and Q ₃ and resistors R ₁ and R ₂ .

It is also possible to provide a quick charging circuit for rapidly charging the capacitor C ₁ to a voltage immediately before it becomes the operation starting voltage of the transistor Q ₁ .

A transistor Q ₁ and an input capacitor C ₂ are connected between the connection terminals ₁ and ₂ which are connected to the DC power supply 5, and a rush current flowing from the DC power supply 5 to the input capacitor C ₂ via the transistor Q ₁ is applied. In the circuit to prevent,
A capacitor C ₁ connected between the gate and the source of the transistor Q ₁ and a constant voltage circuit for applying a constant voltage from the DC power supply 5 to the capacitor C ₁ can be provided.

The terminal voltage of the capacitor C ₁ connected between the gate and source of the transistor Q ₁ is
Detecting _{that one} becomes a voltage which is almost fully conductive, it is possible to provide a detection circuit for notifying the next stage.

[0015]

[Action]

(1) When the connection terminals 1 and 2 are connected to the DC power source 5, the transistor Q ₁ is in the off state, but the capacitor C ₁ is charged by the DC power source 5 via the constant current circuit 6. Since this capacitor C ₁ is charged with a constant current, its terminal voltage rises linearly. When exceeding the threshold voltage of the transistor Q _1, the transistor Q ₁ is begins to conduct, the input capacitor C ₂ is charged from the DC power source 5 is started. Since the equivalent impedance of the transistor Q ₁ at that time is large, the inrush current is suppressed. Further, even when the voltage of the DC power supply 5 is significantly changed, the capacitor C ₁ is charged with a constant current, so that the capacitor C ₁ is charged with a constant time constant without being affected by the power supply voltage.
It is possible to prevent the inrush current by controlling the conduction state of the transistor Q ₁ over time. That is, it is possible to prevent inrush current corresponding to a wide range of input voltages with the same configuration.

[0016] (2) The terminal voltage of the capacitor C ₁ is applied between the gate and source of the transistor Q _1, when exceeding the threshold voltage of the transistor Q _1, is intended to transistor Q ₁ is shifts to a conductive state, By the time the threshold voltage is exceeded, the transistor Q ₁ is completely off. Therefore, in order to shorten the time, the capacitor C ₁ is rapidly charged until just before the transistor Q ₁ becomes conductive, and thereafter the constant current circuit 6 performs constant current charging.

(3) Further, a constant voltage circuit is used in place of the constant current circuit 6 described above, and a voltage converted to a constant voltage by this constant voltage circuit is applied to the capacitor C ₁ . Therefore, even when the voltage of the DC power supply 5 is changed in a wide range, the capacitor C ₁ is always charged by the constant voltage, so that the change of the equivalent impedance of the transistor Q ₁ is always the same and the input capacitor C ₁ is changed. Inrush current to ₂ can be prevented.

(4) Further, various circuits in the next stage are connected to the connection terminals 3 and 4, and it is necessary to start the operation after the voltage applied to the circuit in the next stage reaches a predetermined value. Is. Therefore, when the terminal voltage of the capacitor C ₁ is monitored and it is detected that the transistor Q ₁ has reached a voltage in which the transistor Q ₁ is in a substantially completely conductive state, the equivalent impedance of the transistor Q ₁ becomes a value close to zero, and Since a voltage having a substantially predetermined value is applied to the circuit, a signal indicating the start of operation is added.

[0019]

1 is an explanatory view of a first embodiment of the present invention, in which a DC power supply 5 is connected to connection terminals 1 and 2, and power supply for a circuit in the next stage (not shown) at connection terminals 3 and 4. The terminals are connected. In the case of the printed circuit board configuration, the connection terminals 1 and 2 are power supply connection pins of the connector, and the DC power supply 5 is connected to the power supply wiring of the back port, and the printed circuit board is mounted so that the connection terminals 1 and 2 are The DC power supply 5 is connected.

The constant current circuit 6 includes transistors Q ₂ and Q ₂ .
It is composed of ₃ and resistors R ₁ and R _2, and charges the capacitor C ₁ with a constant current when the DC power source 5 is connected. The terminal voltage Vc of the capacitor C ₁ is applied between the gate and source of the transistor Q _1, exceeds the threshold voltage of the transistor Q _1, the transistor Q ₁ is then shifted to the conductive state, the input capacitor C ₂ from the DC power source 5 And a current starts to flow in the circuit (not shown) at the next stage connected to the connection terminals 3 and 4. Since the equivalent impedance of the transistor Q ₁ at that time is large, the inrush current can be suppressed. The Zener diode Dz ₁ is for protecting the transistor Q ₁ by suppressing the terminal voltage Vc of the capacitor C ₁ to a predetermined value.

2A and 2B are diagrams for explaining the operation of the first embodiment of the present invention. FIG. 2A shows the input voltage Vin, FIG. 2B shows the terminal voltage Vc of the capacitor C ₁ , and FIG. 2C shows the input capacitor C ₂ . Indicates the flowing current. If the DC power supply 5 is connected to the connection terminals 1 and 2 at time t ₀ , the input voltage Vin rises as shown in (a), the base current of the transistor Q ₃ is supplied through the resistor R ₁ , and the transistor Q ₃ is supplied. Q ₃ is turned on, whereby the base current of the transistor Q ₂ is supplied, the transistor Q ₂ is turned on, the constant current charging of the capacitor C ₁ is started, and the terminal voltage Vc of the capacitor C ₁ is started. Is charged with a constant current, so it rises linearly.

Then, when the terminal voltage Vc of the capacitor C ₁ exceeds the threshold voltage Vth of the transistor Q ₁ at time t ₁ , the transistor Q ₁ starts to conduct, and the DC power source 5 shows the input capacitor C ₂ as shown in (c). So that the current flows. Since the equivalent impedance at the start of conduction of the transistor Q ₁ is large, the inrush current flowing in the input capacitor C ₂ can be suppressed. Further, at time t ₂ , the capacitor C ₁ is completely charged, so the charging by the constant current circuit 6 is completed.

When the input voltage Vin is a high voltage system as shown by the dotted line in FIG. 2A, the terminal voltage V of the capacitor C ₁
c increases as shown by the solid line in (b) regardless of the drastic change in the input voltage Vin. Therefore, at the same time t ₁ as when the input voltage Vin is the solid line, the transistor Q ₁ shifts to the conducting state and a current flows through the input capacitor C ₂ . At that time, as the input voltage Vin is higher, the current becomes larger as indicated by the dotted line in (c).

However, in the conventional example, the input voltage Vi
The rise in n speeds up the rise of the terminal voltage of the capacitor C ₁ , the transistor Q ₁ rapidly shifts to a nearly complete conduction state, and since the input voltage Vin is high, the current flowing through the input capacitor C ₂ is the inrush current. Even if a protection circuit is provided, it will be very large. On the other hand, as in the first embodiment of the present invention, the capacitor C _{1 is connected} to the constant current circuit 6
The input voltage Vin
The transistor Q ₁ can be gradually controlled to be conductive at a predetermined speed even by making a drastic change in Therefore,
It is possible to provide a rush current prevention circuit that supports a wide range of input voltage Vin.

FIG. 3 is an explanatory view of the second embodiment of the present invention. The same reference numerals as those in FIG. 1 indicate the same parts, Q ₄ and Q ₅ are transistors, R _{3 to} R ₅ are resistors, and Dz ₂ is Dz _2. It is a Zener diode. When the connection terminals 1 and 2 are connected to the DC power source 5, first the transistor Q ₄ is turned on and the capacitor C ₁ is turned on.
Is rapidly charged through the resistor R ₃ and the transistor Q ₄ . Then, the terminal voltage Vc of the capacitor C ₁ becomes equal to the zener voltage of the zener diode Dz ₂ and the transistor Q ₅
When the value of the sum of the base-emitter voltage of the above is exceeded, the transistor Q ₅ is turned on and the transistor Q ₄ is turned off. Then, the charging of the capacitor C ₁ is continued via the constant current circuit 6.

When the terminal voltage Vc of the capacitor C ₁ exceeds the threshold voltage Vth, the transistor Q ₁ starts to conduct, and the DC power source is supplied to the next stage circuit connected to the input capacitor C ₂ and the connection terminals 3 and 4. Current starts to flow from 5. At that time, since the equivalent impedance of the transistor Q ₁ is large, the inrush current can be suppressed. Then, as the terminal voltage Vc of the capacitor C ₁ gradually rises, the equivalent impedance of the transistor Q ₁ becomes smaller, and finally becomes a value close to zero, and the power supply in the steady state is supplied from the DC power supply 5. Is done.

FIG. 4 is an operation explanatory diagram of the second embodiment of the present invention. (A) is the input voltage Vin, (b) is the terminal voltage Vc of the capacitor C ₁ , and (c) is the input capacitor C ₂ . Indicates the flowing current. When the connection terminals 1 and 2 are connected to the DC power supply 5, the input voltage Vin rises immediately and the capacitor C
₁ is rapidly charged through the transistor Q _4, just before the threshold voltage Vth, (b), the capacitor C ₁
The terminal voltage Vc of is increased.

When the terminal voltage Vc of the capacitor C ₁ becomes a value immediately before the threshold voltage Vth, the transistor Q ₅ is turned on and the transistor Q ₄ is turned off as described above, so that the constant current circuit 6 is used. Then, the capacitor C ₁ is charged by the preset constant current, and the terminal voltage Vc thereof gradually rises. Then, when the terminal voltage Vc exceeds the threshold voltage Vth, the transistor Q ₁ starts conducting, and a current flows through the input capacitor C ₂ as shown in (c). Since the transistor Q ₁ at this time has a large equivalent impedance as in the case of the above-described embodiment, the inrush current can be suppressed.

When the input voltage Vin is high as shown by the dotted line in (a), the capacitor C is connected via the transistor Q _4.
1 is rapidly charged, and the time required for the terminal voltage Vc to rise immediately before the threshold voltage Vth is further shortened. After that, constant current charging is performed via the constant current circuit 6, so in the case of the input voltage indicated by the solid line. Similarly, the terminal voltage Vc gradually rises. That is, the configuration of the inrush current prevention circuit can be made the same even if the input voltage Vin is drastically changed.
Moreover, it is possible to shorten the time from when the connection terminals 1 and 2 are connected to the DC power supply 5 until the transistor Q ₁ starts conducting.

FIG. 5 is an explanatory view of the third embodiment of the present invention. The same reference numerals as those in FIG. 1 denote the same parts, 7 is a constant voltage circuit, Q ₆ is a transistor, R ₆ and R ₇ are resistors, Dz ₃ is a Zener diode. The constant voltage circuit 7 is shown to be composed of the transistor Q ₆ , the resistor R _7, and the Zener diode Dz ₃ , but the constant voltage circuit may have another structure.

When the connection terminals 1 and 2 are connected to the DC power source 5, the transistor Q ₁ is in the off state, but the constant voltage from the constant voltage circuit 7 is applied to the capacitor C ₁ via the resistor R _6. Will be charged. When the terminal voltage Vc of the capacitor C ₁ exceeds the threshold voltage Vth, the transistor Q ₁ starts conducting, and the DC power source 5 connects the input capacitor C ₂ and the connection terminals 3 and 4 to the next stage circuit (not shown). ) Current flows. At that time, as described above, since the equivalent impedance of the transistor Q ₁ is large, the inrush current can be suppressed. Then, as the terminal voltage Vc of the capacitor C ₁ gradually rises, the transistor Q
The equivalent impedance of ₁ becomes small and finally becomes a value close to zero.

6A and 6B are operation explanatory diagrams of the third embodiment of the present invention. FIG. 6A is an input voltage Vin, FIG. 6B is a terminal voltage Vc of the capacitor C ₁ , and FIG. 6C is an input capacitor C ₂ . Indicates the flowing current. When the connection terminals 1 and 2 are connected to the DC power supply 5, the input voltage Vin rises immediately and the capacitor C ₁
Is charged from the constant voltage circuit 7 via the resistor R ₆ . Therefore, the terminal voltage Vc of the capacitor C ₁ rises according to the time constant of R ₆ · C ₁ as shown in (b). And
When the terminal voltage Vc exceeds the threshold voltage Vth, the transistor Q ₁ starts conducting, and a current flows in the input capacitor C ₂ as shown in (c).

Further, even when the input voltage Vin is largely changed as shown by the dotted line in (a), the capacitor C ₁ is charged by the voltage regulated by the constant voltage circuit 7, so that R ₆ · C ₁ Since the terminal voltage Vc rises according to the time constant of and the timing of starting conduction of the transistor Q ₁ does not change, the inrush current can be suppressed. The current flowing through the input capacitor C ₂ increases as the input voltage Vin is high as shown by the dotted line in (c), but can be suppressed to a sufficiently small value as compared with the conventional example.

FIG. 7 is an explanatory view of the fourth embodiment of the present invention, in which the same symbols as in FIG. 5 indicate the same parts, Dz ₄ is a Zener diode, and R ₈ is a resistor. In this embodiment, the threshold voltage Vth of the transistor Q ₁ is apparently increased, and the conduction of the transistor Q ₁ is started in a portion where the rising characteristic of the terminal voltage Vc of the capacitor C ₁ is gentle.

[0035] That is, when connecting the connection terminals 1 and 2 to the DC power supply 5, the constant voltage voltage by the constant voltage circuit 7, the charging of the capacitor C ₁ is started via a resistor R _6, the capacitor C ₁ The terminal voltage Vc rises according to the time constant of R ₆ · C ₁ . Also the gate of transistor Q ₁
The source-to-source voltage is the voltage across the resistor R ₈ when the Zener diode Dz ₄ is conducting.

Therefore, the terminal voltage Vc of the capacitor C ₁ rises, the terminal voltage Vc causes the Zener diode Dz ₄ to conduct, and when the voltage across the resistor R ₈ exceeds the threshold voltage Vth of the transistor Q ₁ , the transistor Q ₁
Will start conducting, and the Zener diode Dz
By selecting the Zener voltage of ₄ , the capacitor C
_{In the} part where the rising characteristic of the terminal voltage Vc of ₁ is gentle,
The conduction of the transistor Q ₁ can be started.

FIG. 8 is an operation explanatory diagram of the fourth embodiment of the present invention. (A) is the input voltage Vin, (b) is the terminal voltage Vc of the capacitor C ₁ , and (c) is the input capacitor C ₂ . Indicates the flowing current. When the connection terminals 1 and 2 are connected to the DC power supply 5, the input voltage Vin rises immediately as shown in (a), and the terminal voltage Vc of the capacitor C ₁ is changed to a constant voltage by the constant voltage circuit 7. It is charged through the resistor R ₆ and rises according to the time constant of R ₆ · C ₁ as shown in (b).

The threshold voltage Vth of the transistor Q ₁ is
By selecting the Zener voltage of Zener diode Dz ₄ ,
It becomes apparently larger like Vth ′ with respect to the terminal voltage Vc of the capacitor C ₁ . Therefore, the transistor Q
₁ indicates that the terminal voltage Vc of the capacitor C ₁ is the threshold voltage Vt.
When h ′ is exceeded, conduction is started, and as shown in (c), current flows through the input capacitor C ₂ and the equivalent impedance of the transistor Q ₁ is large, so that inrush current can be suppressed. In that case, since the equivalent impedance of the transistor Q ₁ gradually decreases in accordance with the rising characteristic of the terminal voltage Vc of the capacitor C ₁ , it is possible to reliably suppress the inrush current.

When the input voltage Vin is significantly changed as shown by the dotted line in (a), the terminal voltage Vc of the capacitor C ₁ is the voltage converted to a constant voltage by the constant voltage circuit 7 as described above. Since it is charged by, it rises as shown in (b), the timing at which the transistor Q ₁ starts conducting is the same, and as much as the input voltage Vin rises, as shown by the dotted line in (c). The current increases. Therefore, the inrush current can be prevented by the inrush current prevention circuit having the same configuration even for a wide range of input voltage Vin.

FIG. 9 is an explanatory view of the fifth embodiment of the present invention. The same reference numerals as those in FIG. 1 denote the same parts, Q ₇ and Q ₈ are transistors, R ₉ and R ₁₀ are resistors, and 8 is an output. It is a terminal.
By the transistor Q _7, Q _8, monitors the voltage between the gate and source of the transistor Q _1, it is detected that the transistor Q ₁ is was almost fully conductive, and notifies the next stage of the circuit .

That is, the connection terminals 1 and 2 are connected to the DC power source 5, the capacitor C ₁ is charged through the constant current circuit 6,
The terminal voltage Vc is the threshold voltage Vth of the transistor Q _1.
Then, the transistor Q ₁ starts conducting, and a current is supplied from the DC power supply 5 to the next stage circuit (not shown) connected to the input capacitor C ₂ and the connection terminals 3 and 4, and the current at that time is supplied. Is suppressed by the large equivalent impedance of the transistor Q ₁ .

As the terminal voltage Vc of the capacitor C ₁ rises, the equivalent impedance of the transistor Q ₁ becomes smaller and finally becomes a value close to zero, and the DC power source 5 is connected to the connection terminals 3 and 4. In addition, the operation power is supplied to the circuit at the next stage, which is a steady state. In such a state, the terminal voltage Vc of the capacitor C ₁ turns on the transistor Q _7, which turns on the transistor Q ₈ and detects from the output terminal 8 that the transistor Q ₁ is almost completely conductive. The generated signal is sent to the circuit at the next stage. The circuit at the next stage starts operation by this detection signal. Since the transistors Q ₇ and Q ₈ only send the detection signal, the transistors can be small in size and small in capacity.

Before such a steady state is reached,
Due to the large equivalent impedance of the transistor Q ₁ , a voltage lower than the steady-state voltage is supplied to the circuit in the next stage, and when the operation starts due to this low voltage, malfunction may occur. Therefore, it is detected that the equivalent impedance of the transistor Q ₁ is sufficiently small and the voltage of the circuit of the next stage does not cause a malfunction, and the detection signal that enables the operation of the circuit of the next stage is started. The signal is sent from the output terminal 8 to the next stage circuit.

FIG. 10 is a diagram for explaining the operation of the fifth embodiment of the present invention. (A) is the input voltage Vin, (b) is the terminal voltage Vc of the capacitor C ₁ , and (c) is the input capacitor C ₂ . Flowing current, (d) is the terminal voltage of the input capacitor C ₂ ,
(E) shows a detection signal. When the connection terminals 1 and 2 are connected to the DC power source 5 at time t ₀ , the capacitor C ₁ is charged with a constant current through the constant current circuit 6, and its terminal voltage Vc is
It rises linearly as shown in (b).

The terminal voltage Vc of the capacitor C ₁ is at time t ₁
To exceeds the threshold voltage Vth of the transistor Q _1, the transistor Q ₁ is begins to conduct, current shown in the DC power source 5 to the input capacitor C ₂ (c) flows, the terminal voltage of the input capacitor C ₂ is (d ) As shown in (). When the terminal voltage Vc of the capacitor C ₁ exceeds the voltage Vs at time t ₂ , the transistors Q ₇ and Q ₈ are turned on,
As shown in (e), the detection signal is sent from the output terminal 8 to the next stage circuit.

The means for detecting that the transistor Q ₁ is in the almost completely conductive state is as described in the second to the second.
It is also applicable to the fourth embodiment, and it is also possible to add a configuration in which the transistors Q ₇ and Q ₈ are turned off when the operation of the circuit in the next stage is started.

[0047]

As described above, according to the present invention, the capacitor C ₁ is connected between the gate and the source of the transistor Q ₁ for suppressing the current flowing from the DC power source 5 to the input capacitor C ₂ , and the capacitor C ₁ is connected to the capacitor C ₁ . by charging with a constant current by the constant current circuit 6, the inrush current can be reliably prevented, even when the input voltage Vin becomes significant changes, because charging the capacitor C ₁ with a constant current of the transistor Q ₁ Since the timing of starting conduction does not change, there is an advantage that it can be used as it is without changing the configuration of the inrush current prevention circuit. That is, since the inrush current prevention circuit having the same configuration can be used for various voltage systems, there is an advantage that the cost can be reduced.

Further, by charging the capacitor C ₁ with the voltage converted into a constant voltage by the constant voltage circuit 7, the input voltage Vi
Capacitor C with the same characteristics even when the value of n is changed drastically.
_Since the terminal voltage Vc of ₁ rises, the timing of the start of conduction of the transistor Q ₁ does not change. Therefore, the inrush current prevention circuit having the same configuration can be used for various voltage systems, which leads to cost reduction. There is an advantage that can be achieved.

Further, the terminal voltage V of the capacitor C _{1 at which} the transistor Q ₁ for preventing the inrush current becomes almost completely conductive.
By detecting c and notifying it to the circuit at the next stage, there is an advantage that malfunction in the transient state when the DC power supply 5 is connected can be prevented.

[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 the first embodiment of the present invention.

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

FIG. 4 is an operation explanatory diagram of the second embodiment of the present invention.

FIG. 5 is an explanatory diagram of a third embodiment of the present invention.

FIG. 6 is an operation explanatory diagram of the third embodiment of the present invention.

FIG. 7 is an explanatory diagram of a fourth embodiment of the present invention.

FIG. 8 is an operation explanatory diagram of the fourth embodiment of the present invention.

FIG. 9 is an explanatory diagram of a fifth embodiment of the present invention.

FIG. 10 is an operation explanatory diagram of the fifth embodiment of the present invention.

FIG. 11 is an explanatory diagram of a conventional example.

FIG. 12 is an operation explanatory diagram of a conventional example.

[Explanation of symbols] 1-4 connection terminals 5 DC power supply 6 constant voltage circuit Q ₁ transistor Q ₂ , Q ₃ transistor C ₁ capacitor C ₂ input capacitor Dz ₁ Zener diode R ₁ , R ₂ resistance

Claims (4)

[Claims] 1. A circuit in which a transistor and an input capacitor are connected between connection terminals connected to a DC power source to prevent an inrush current flowing from the DC power source to the input capacitor through the transistor, An inrush current prevention circuit comprising: a capacitor connected between a gate and a source; and a constant current circuit for charging the capacitor with a constant current from the DC power supply. 2. The inrush current prevention circuit according to claim 1, further comprising a rapid charging circuit for rapidly charging the capacitor to a voltage immediately before becoming an operation start voltage of the transistor. 3. A circuit in which a transistor and an input capacitor are connected between connection terminals connected to a DC power supply to prevent an inrush current flowing from the DC power supply to the input capacitor through the transistor, An inrush current prevention circuit comprising: a capacitor connected between a gate and a source; and a constant voltage circuit for applying a constant voltage from the DC power source to the capacitor. 4. A detection circuit that detects when the terminal voltage of the capacitor connected between the gate and source of the transistor has reached a voltage at which the transistor is in a substantially completely conductive state and notifies the next stage. The inrush current prevention circuit according to claim 1, wherein the inrush current prevention circuit is provided.