JPH0937456A - Inrush current prevention circuit - Google Patents

Abstract

The present invention relates to an inrush current prevention circuit, and an object thereof is not to give a current stress to a field effect transistor at the time of repeatedly making and releasing a power switch and to prevent drooping of a power supply voltage. . Two smoothing capacitors C1 are connected between lines to supply a DC voltage to a load circuit.
And a field-effect transistor 23 without a body diode provided on one of the power supply lines and two power supply lines 20 and 26 on the power supply side of the field-effect transistor 23, and the gate of the field-effect transistor 23 is connected. A resistance voltage dividing circuit 10 having a resistance voltage dividing output terminal connected thereto is provided, and a capacitor C2 connected between the voltage dividing output terminal and one power supply line which is a power supply side of the field effect transistor 23. It is characterized by being configured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inrush current prevention circuit for preventing formation of an energizing circuit to a smoothing capacitor connected in parallel with a load when a power switch is released. When the switch is turned on and the DC power supply is connected to the load circuit, if the input impedance of the load circuit is small,
A large inrush current flows through the load circuit. In order to prevent such a large inrush current, a conventional inrush current prevention circuit is provided between the DC power supply and the load.

[0002]

2. Description of the Related Art In a conventional inrush current prevention circuit, as shown in FIG. 3, a field effect transistor 22 having a body diode is provided in a feed line 20 for a load current, and a gate of such a field effect transistor 22 is provided. The whole is constructed by connecting a circuit for giving a gate voltage. The circuit for providing the gate voltage consists of a resistor R1, a resistor R2 and a capacitor C2. The resistor R1 is
The resistor R2 and the capacitor C2 are connected between the power supply line 26 and the gate of the field effect transistor 22, and the resistor R2 and the capacitor C2 are connected to the gate of the field effect transistor 22 and the field effect transistor 22.
Connected to the source of. The source of the field effect transistor 22 is connected to the power source side. The drain of the field effect transistor 22 is connected to the load side. 28 is a body diode of the field effect transistor 22. The capacitor C1 (smoothing capacitor) and the load circuit 24 are connected between the power supply line 20 and the power supply line 26. 30 is a DC power supply, and SW is a switch.

The operation of the inrush current prevention circuit is as follows. When the switch SW is turned on to supply power to the load circuit, the capacitor C2 is charged through the resistor R1 and the gate-source voltage of the field effect transistor 22 gradually increases. The gate voltage is the field effect transistor 22.
Above the threshold voltage of
Starts to conduct, and a current gradually starts to flow in the capacitor C1. The capacitor C2 is charged to the input voltage Ei supplied from the DC power supply 30. In addition, current also flows through the load circuit 24.

As described above, since the gate voltage is gradually increased, a large inrush current can be prevented from flowing to the load circuit 24 when the switch SW is turned on.

[0005]

However, when the switch SW is released after the current is supplied to the load circuit 24 as described above, the capacitor C1 is released.
The electric charge that has been charged into the battery is discharged through the resistor R1, the resistor R2, and the body diode 28. During this discharging, the electric charge charged in the capacitor C2 remains undischarged, and after the voltage applied between the capacitors C2 and the voltage proportionally distributed by the resistors R1 and R2 to the capacitor C1 are balanced. , The electric charge of the capacitor C2 is discharged through the resistor R2.

Therefore, it takes a considerably long time for the gate voltage applied to the gate of the field effect transistor 22 to drop below the threshold value (see the conventional circuit in FIG. 4). In the above-mentioned inrush current prevention circuit, when the switch SW is released, the gate voltage of the field effect transistor 22 remains above the threshold value for a long time.
The field-effect transistor 22 remains in the conductive state, and an excessive rush current may flow in the load circuit 24 to give a current stress to the field-effect transistor 22.

The present invention has been made in view of the above technical problem, and prevents inrush current from being applied to the field effect transistor when the power switch is repeatedly turned on and off so as not to cause drooping of the power supply voltage. Its purpose is to provide a circuit.

[0008]

FIG. 1 is a block diagram showing the principle of the present invention.

According to the first aspect of the present invention, as shown in FIG. 1, two smoothing capacitors C1 are connected between the lines to supply a DC voltage to the load circuit. It is connected between the field effect transistor 23 having no body diode interposed in the electric wire and the two power supply lines 20 and 26 on the power source side of the field effect transistor 23, and the gate of the field effect transistor 23 has a resistance component. A resistance voltage dividing circuit 10 having a voltage output terminal connected thereto, and a capacitor C2 connected between the voltage dividing output terminal and the one power supply line which is on the power supply side of the field effect transistor 23 are provided. It is characterized by being configured.

According to the first aspect of the present invention, when the direct current is supplied to the load circuit, when the power switch is turned on to supply the direct current to the load circuit, the gate voltage of the field effect transistor 23 is gradually increased. Therefore, a large inrush current is not supplied to the load circuit when the power switch is turned on. Further, even if the power switch is repeatedly turned on and off, the electric charge accumulated in the smoothing capacitor does not flow through the resistance voltage dividing circuit, so that the electric charge of the capacitor C2 that is the power supply source for the gate voltage is changed to the resistance voltage dividing circuit 10. Is rapidly discharged through the resistor.

Therefore, unlike the conventional case, an excessive current does not flow through the field effect transistor 23, and a current stress is not applied to the field effect transistor 23.

Since the DC power supply voltage can be prevented from drooping, it does not adversely affect other devices.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 shows an embodiment of the invention described in claim 1. In this embodiment, a field effect transistor 23 having no body diode is used instead of the field effect transistor 22 having a body diode of the conventional inrush current protection circuit shown in FIG.

According to this inrush current prevention circuit, the operation from turning on the switch SW to supplying the load current to the load circuit 24 is the same as the operation described with reference to FIG. That is, when the switch SW is turned on to supply the load current to the load circuit 24, the gate voltage of the field effect transistor 23 gradually increases due to the large charging time constant of the capacitor C2, and a large rush into the load circuit 24 occurs. It is possible to prevent the inconvenience of passing a current.

The gate voltage of the field effect transistor 23 becomes a constant value (see FIG. 4), and a direct current corresponding to the gate voltage is supplied to the load circuit 24. When such power supply is stopped, the switch SW is released. Since the field effect transistor 23 does not have a body diode, unlike the conventional inrush current prevention circuit, the smoothing capacitor C1 is used.
Through resistor R1 and resistor R2 to smoothing capacitor C
The current path to 1 is not formed. Smoothing capacitor C1
Is discharged through the load circuit 24. Therefore, the electric charge stored in the capacitor C2 rapidly drops through the resistor R2 (see the circuit of the present invention in FIG. 4), and the gate voltage of the field effect transistor 23 is kept above the threshold value for a long time. Therefore, the field effect transistor 23 is instantly turned off.

Even if the switch SW is repeatedly turned on / off, the field effect transistor 23 does not become conductive. Therefore, the current stress is not given to the field effect transistor 23. In addition, drooping of the DC power supply can be prevented, and no adverse effect is given to other devices.

[0017]

As described above, according to the present invention, the gate voltage applied to the gate of the field effect transistor of the inrush current prevention circuit can be determined only by the inrush current circuit. It is possible to eliminate the influence of the capacitor for use, prevent an excessive current from flowing through the field effect transistor, and prevent the current stress generated in the field effect transistor. Since it is possible to prevent the DC power supply from drooping, it is possible to eliminate adverse effects on other devices.

[Brief description of drawings]

FIG. 1 is a principle block diagram of the invention according to claim 1;

FIG. 2 is a diagram showing an embodiment of the invention described in claim 1;

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

FIG. 4 is a diagram showing the progress of the voltage applied to the gate of the inrush current prevention circuit.

[Explanation of symbols]

 10 Resistance Dividing Circuit 20 Feed Line 23 Field Effect Transistor 24 Load Circuit 26 Feed Line C1 Smoothing Capacitor C2 Capacitor R1 Resistor R2 Resistor SW Switch

Claims (1)

[Claims] 1. A two-feed line connecting a smoothing capacitor between the lines to supply a DC voltage to a load circuit, a field-effect transistor without a body diode interposed in one of the feed lines, and the electric field. A resistance voltage dividing circuit connected between the two power supply lines on the power supply side of the effect transistor and having a resistance voltage dividing output terminal connected to the gate of the field effect transistor; the voltage dividing output terminal; An inrush current prevention circuit comprising an electric wire and a capacitor connected between the electric field supply transistor and a power supply line on the power supply side.