JPH08149691A - Inrush current prevention circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an inrush current prevention circuit that reliably prevents an inrush current and improves the reliability of the device regardless of the state of the voltage across the terminals of the input smoothing capacitor. [Configuration] Without relay driver RL ₁ is controlled by a discharge current of the input smoothing capacitor C _1, as controlled by the current due to the input voltage V _in, a rush prevention resistor R ₁
And a diode D between the relay drive unit RL ₁ and
Inrush current is prevented regardless of the state of the input smoothing capacitor C ₁ .

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 for preventing an accident caused by an excessive current flowing into a power supply circuit or the like.

[0002]

2. Description of the Related Art An inrush current prevention circuit is provided to prevent an excessive inrush current from flowing through an input smoothing capacitor such as a power supply circuit to blow a fuse in the circuit or damage a switch contact. . Conventionally, a circuit as shown in FIG. 3 has been used as the inrush current prevention circuit.
Reference numeral 1 is a power supply circuit or the like, to which an input smoothing capacitor C ₁ is connected in parallel. The input smoothing capacitor C ₁ charges and discharges according to the time constant determined by the inrush prevention resistor R ₁ .
Further, in order to prevent wasteful power consumption by the rush prevention resistor R _1, a relay for short-circuiting the inrush prevention resistors R ₁ are provided. The relay is a two-contact output relay, one contact rl _1-1 is provided to short-circuit R ₁ as described above, and the other contact rl _1-2 is connected in series with the capacitor C ₂ . The capacitor C ₂ is used to control the relay. Further, the drive unit RL _{1 of the} relay is controlled by the transistor TR,
The base voltage of the transistor TR increases or decreases according to the voltage across the terminals of the capacitor C ₂ . The capacitor C ₂ is a resistor R ₂
The battery is charged according to the time constant determined by and the time constant is C ₁
Set it to be larger than the time constant defined in. First, the switch SW in a state where the input voltage V _in is applied O
At N, the charging current flows through the input smoothing capacitor C ₁ , but this is limited by the inrush prevention resistor R ₁ and the fuse F
Also, the contacts of the switch SW are protected. Then, the voltage between the terminals of the capacitor C ₂ increases in accordance with the time constant determined by the resistance R _2, and the voltage between the terminals turns on the transistor TR.
Voltage value to be reached (about 0.7 V), preventing the loss in the relay driver RL ₁ is operated, projecting ingress-preventing resistor R ₁ that contact rl _1-1 is shorted rush prevention resistor R ₁ To do. Further, the relay contacts rl _1-2 are switched at the same time as the relay contacts rl _1-1 , and the transistor C ₂ is discharged through the resistor R ₄ . When the switch SW is turned off, the capacitor C
₁ is discharged, and the voltage between its terminals is input to the transistor TR as a divided voltage of the resistors R ₂ and R ₃ . The partial pressure is about 0.
When the voltage becomes 7 V or less, the relay driving unit RL ₁ operates and the relay contact rl _1-1 is opened, so that a current flows through the capacitor C ₁ through the inrush prevention resistor R ₁ . In addition, relay contact r
l _1-2 is switched to the transistor TR side, and charging is performed again.

However, the above-described conventional inrush current prevention circuit has the following problems.
That is, the input voltage V _in of instantaneous interruption or middle input voltage V _in again of the discharge input by ON / OFF operation at short intervals of the switch SW smoothing capacitor C ₁ is applied, the relay contacts rl _1-1 Inrush current may flow into the power supply circuit or the like while the circuit is short-circuited, and the fuses and switch contacts may be damaged.
FIG. 4 is a signal waveform diagram of each part in FIG.
₁ indicates a section _in which the input voltage Vin is normally applied,
The time T ₂ are shown a section input voltage V _in is not applied. Further, t _1, t ₃ is a timing which supplied the input voltage V _in, t ₂ denotes the timing of the input voltage V _in is instantaneously interrupted. Incidentally, the switch SW in FIG. 3 is always kept ON. First, when the input voltage V _in is applied at t ₁ ,
Since the relay contact rl _1-1 is open, the current I _in flows through the inrush prevention resistor R ₁ and no inrush current occurs. The voltage V ₁ across the capacitor C ₁ is the inrush prevention resistor R ₁ and the capacitor C ₁
It gradually increases with a time constant determined by. At the same time, the voltage across the capacitor C ₂ also increases, and after the charging of the capacitor C ₁ is completed, the voltage value across the capacitor C ₂ reaches the base voltage (about 0.7 V) of the transistor and the relay drive unit RL is reached.
₁ operates and shorts relay contacts rl _1-1 . Then the input smoothing capacitor C ₁ is discharged upon interruption of t ₂ the input voltage V _in. The voltage V ₂ applied between the terminals of the series circuit of the resistor R ₂ and the resistor R ₃ is equal to the voltage V ₁ between the terminals of the input smoothing capacitor C ₁ , so that the base voltage V _{B of the} transistor TR gradually increases with the voltage V _1. , But at t ₃ the voltage V _B
If the input voltage V _in is applied again before the voltage drops to turn off the transistor TR, the relay contact rl _1-1 remains short-circuited and the current I _in changes to the relay contact rl _1-1.
Flow into the input smoothing capacitor C ₁ to generate an inrush current. Therefore, the rush current is generated as described above, which has been a problem of causing a failure of the device such as the power supply circuit.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide an inrush current prevention circuit that reliably prevents an inrush current regardless of the state of the voltage across the terminals of an input smoothing capacitor. To aim.

[0005]

SUMMARY OF THE INVENTION In order to achieve this object, an inrush current prevention circuit according to the present invention has a transistor that is not controlled by a voltage across terminals when an input smoothing capacitor is discharged.
A diode is provided between the input smoothing capacitor and the base terminal of the transistor so as to be controlled by the input voltage, and the discharge voltage of the input smoothing capacitor is blocked by the diode, so that inrush current is reliably prevented. Is something that can be done.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the embodiments shown in the drawings. It should be noted that the same components as those of the related art are designated by the same reference numerals and the description thereof is omitted. FIG. 1 is a block diagram showing the configuration of an inrush current prevention circuit according to the present invention. In the figure, a diode D prevents the discharge voltage of the input smoothing capacitor C _{1 from} affecting the base voltage of the transistor TR, and the diode D is placed between the inrush prevention resistor R ₁ and the resistor R _2. To be installed.

First, when the switch SW is turned on, a charging current flows through the input smoothing capacitor C ₁ , but this is limited by the inrush prevention resistor R ₁ and the contacts of the fuse F and the switch SW are protected. Then, after a lapse of time determined by the resistor R ₂ and the capacitor C ₂ (however, the time is set to be equal to or longer than the time when C ₁ completes charging), the transistor TR is turned on, the relay driving unit RL ₁ operates, and its contact rl _{1 -1} shorted rush prevention resistor R ₁ to prevent the loss in the projecting ingress-preventing resistor R _1. Also, at the same time as the relay contact rl _{1-1, the} relay contact rl _1-2
And the discharge of the capacitor C ₂ takes place through the resistor R ₄ . Up to this point, there is no difference from the conventional circuit operation.

Next, when the switch SW is turned off, the input smoothing capacitor C ₁ starts discharging, but the discharging current is blocked by the diode D ₂ , so that the discharging current flows to the power supply circuit 1 and the like and is consumed. To be done. At this time, the resistance R
_Since the voltage applied between the terminals of the series circuit of ₂ and the resistor R ₃ is equal to the input voltage V _in , the base voltage V _{B of the} transistor TR is
Becomes zero, the transistor TR is turned off, and the relay driving unit RL ₁ opens the relay contact rl _1-1 and switches the relay contact rl _1-2 to the R ₃ side. That is, the short circuit of the inrush prevention resistor R ₁ is released at the same time when the switch SW is turned off. Therefore, even if the input voltage is momentarily cut off or an ON / OFF operation occurs at a short SW interval, the relay driving unit RL ₁ performs the switching operation regardless of the voltage of the input smoothing capacitor C ₁ , so that the input voltage V _in When applied, the input smoothing capacitor C ₁ can be surely charged through the inrush resistance R ₁ to prevent the inrush current.

[0009] Figure 2 is a signal waveforms diagram in FIG. 1, the time T ₁ indicates a state in which the input voltage V _in is applied correctly, also the time T ₂ are the input voltage V _in is instantaneously interrupted Indicate the case. Further, t _1, t ₃ is a timing which supplied the input voltage V _in, t ₂ denotes the timing of the input voltage V _in is instantaneously interrupted. In addition, in FIG. 1, the switch SW is always kept ON. First, when the input voltage V _in is applied at t ₁ , the relay contact rl _1-1 is opened first, so that the current I _in
Flows through the inrush prevention resistor R ₁ and no inrush current occurs. Voltages V ₁ across capacitor C ₁ increases gradually with a time constant determined by a rush prevention resistor R ₁ and capacitor C _1,
After the charging of the capacitor C ₁ is completed, the voltage value between the capacitors C ₂ becomes the base voltage of the transistor TR (about 0.7 V).
And the relay drive unit RL ₁ operates and the relay contact rl
_1-1 short circuit. Then the capacitor C ₁ at the time of instantaneous interruption of t ₂ the input voltage V _in is discharged but, since it is prevented the voltage across the terminals of the capacitor C ₁ at this time by the diode D _1, a series circuit of resistors R ₂ and the resistor R ₃ The voltage V ₂ across the terminals of the transistor T becomes equal to the input voltage V _in and becomes zero, so that the transistor T
The base voltage V _{B of} R becomes zero like the input voltage V _in .
Therefore, the input voltage V _in to a short break at the same time the relay contact rl
_{Since 1-1 is} also opened, even if the input voltage V _in is applied again at t ₃ , the current always flows through the inrush prevention resistor R ₁ , so that no inrush current is generated.

[0010]

As described above, according to the present invention, when the input smoothing capacitor is discharged, the voltage between its terminals does not affect the transistor and the rush current can be surely prevented by the configuration and operation as described above. Therefore, there is a remarkable effect in improving the reliability of the device.

[0011]

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an inrush current prevention circuit according to the present invention.

FIG. 2 is a signal waveform diagram of each part in the inrush current prevention circuit according to the present invention.

FIG. 3 is a block diagram showing a configuration of a conventional inrush current prevention circuit.

FIG. 4 is a signal waveform diagram of each part in a conventional inrush current prevention circuit.

[Explanation of symbols]

1 ... Power supply circuit F ... Fuse SW ... Switch RL ... Relay control unit rl ... Relay contact D ... Diode C ... Capacitor R ... Resistance

Claims (1)

[Claims] 1. An inrush prevention resistor for preventing an inrush current from flowing when an input smoothing capacitor connected in parallel to a power supply circuit or the like is charged, a relay for short-circuiting the inrush prevention resistor, and a drive for the relay. In an inrush current prevention circuit including a transistor for controlling a section, the input smoothing capacitor and the base terminal of the transistor are connected so that the relay driver is not controlled by the voltage at the time of discharging the input smoothing capacitor. An inrush current prevention circuit characterized by having a diode provided therebetween.