JP2001211058A - Electronic switch - Google Patents

Abstract

(57) Abstract: To provide an electronic switch to which a capacitive element is connected and which can prevent a switch element from being damaged by a large inrush current. SOLUTION: In a FET or a bipolar transistor used as a switch element of an electronic switch, F
In ET, a capacitor and a resistor are connected in parallel between the source and gate, and in a bipolar transistor, a capacitor and a resistor are connected in parallel between the emitter and the base.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a video camera and a V
The present invention relates to an electronic switch used for a small electronic device such as a TR.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing an example of a conventional electronic switch. In the figure, a positive electrode 1A of a DC power supply 1 for generating a DC voltage of 10V to 20V is provided with a P-channel field effect transistor 2 serving as a switch element of an electronic switch.
(Hereinafter abbreviated as FET2) source S is connected. The drain D of FET2 is connected to the output terminal 3,
The gate G is connected to the control circuit 4. The resistor 5 is connected between the gate G and the source S. The gate G of the FET 2 is connected to the negative electrode 1B of the DC power supply 1 via the control circuit 4. The FET 2 is turned off when the potential of the source S (hereinafter, source potential) and the potential of the gate G (hereinafter, gate potential) are the same. When the source potential becomes higher than the gate potential by several volts or more, FET2 turns on. That is, FE
By setting the gate potential of T2 lower than the source potential by several volts or more, the conduction between the source S and the drain D can be made conductive. The gate potential is controlled by the control circuit 4. When the FET 2 is turned on, the voltage of the DC power supply 1 is output to the output terminal 3. Generally, the rise time of an electronic switch using a P-channel field-effect transistor is several tens nanoseconds to several hundred nanoseconds, and the rise time when it is turned on is short. Therefore, a large inrush current may flow depending on the load. FIG. 3 is a graph showing a temporal change of an inrush current, which is commonly used in the description of the related art and the present invention. The horizontal axis in FIG. 3 indicates time, and the vertical axis indicates inrush current. In FIG. 3, an example of an inrush current flowing through the FET 2 is shown by a curve a. According to the curve a, the rush current of the peak current A1 flows during the time T1.

As another conventional example, an electronic switch using a bipolar transistor 10 shown in FIG. 5 is known. The configuration in FIG. 5 is obtained by replacing the FET 2 in FIG. 4 with a bipolar transistor 10. The bipolar transistor 10 is turned off when the emitter potential and the base potential are the same. When the base potential becomes lower than the emitter potential by several volts or more, the base current flows, and the collector current according to the current amplification factor flows and turns on. By controlling the control circuit 4 so that a sufficient base current flows, the emitter E
And the collector C can be made conductive. The rise time of a bipolar transistor is several hundred nanoseconds or more, which is slightly longer than that of an FET. An example of an inrush current of an electronic switch using a bipolar transistor is shown by a dotted curve b in FIG.
Indicated by In this example, the rush current of the peak current A2 flows during the time T2.

[0004]

On the load side of an electronic switch, a low-impedance, large-capacity electrolytic capacitor 7 is usually provided.
Is connected. When the electronic switch is turned on, a large inrush current flows in a short time to charge the electrolytic capacitor 7. When the current capacity of the DC power supply 1 is large, the rush current becomes 50 A or more, and sometimes exceeds 100 A in some cases. This large inrush current causes FET2
In some cases, switch elements such as the transistor and the bipolar transistor 10 may be destroyed. If a large switch element is used to prevent destruction, the size of the electronic switch becomes large, and it is difficult to incorporate the electronic switch into a small electronic device. An object of the present invention is to provide an electronic switch in which a large inrush current does not flow when a large-capacity capacitor is connected to the load side of the electronic switch.

[0005]

An electronic switch according to the present invention comprises a field effect transistor as a switch element, a capacitor and a resistor connected in parallel between a source and a gate of the field effect transistor, and the field effect transistor. And a control circuit that is connected between the gate and the source and controls a potential between the gate and the source. Since the electronic switch of the present invention has a capacitor and a resistor connected in parallel between the source and the gate, when the control circuit controls the gate potential to be lower than the source potential to turn on the electronic switch, the capacitor And the time during which the potential of the gate is reduced becomes longer by the time determined by the time constant of the resistance. Therefore, the time during which the inrush current flows becomes longer, the values of the inrush current are averaged, and the peak value becomes lower.

An electronic switch according to another aspect of the present invention is a bipolar transistor as a switch element, a capacitor and a resistor connected in parallel between an emitter and a base of the bipolar transistor, and a base and an emitter of the bipolar transistor. A control circuit connected between the base and the emitter to control a potential between the base and the emitter. In the electronic switch according to another aspect of the present invention, since a capacitor and a resistor are connected in parallel between the emitter and the base, the control circuit controls the base potential to be lower than the emitter potential in order to turn on the electronic switch. Then, the time during which the base potential decreases by the time determined by the time constant of the capacitor and the resistor becomes longer. As a result, the inrush current flows for a longer time,
The values of the inrush current are averaged, and the peak value becomes lower.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a circuit diagram of an electronic switch according to an embodiment of the present invention. In the figure, P is applied to the positive electrode 1A of the DC power supply 1 having an output voltage of 10V to 20V.
The source S of the channel field effect transistor 2 (hereinafter abbreviated as FET2) is connected. An electrolytic capacitor 7 as a load is connected between the output terminal 3 connected to the drain D of the FET 2 and the negative electrode 1B of the DC power supply 1. A control circuit 4 is connected between the gate G of the FET 2 and the negative electrode 1B of the DC power supply 1. The terminal of the control circuit 4 connected to the negative electrode 1B is substantially connected to the source S via the DC power supply 1. The control circuit 4 is a circuit for setting the potential of the gate G to the potential of the positive electrode 1A or the potential of the negative electrode 1B of the DC power supply 1. The control circuit 4 is, for example, a switch that connects / disconnects the gate G to / from the negative electrode 1B of the DC power supply 1. Source S
A resistor 5 and a capacitor 6 are connected in parallel between the gate G.

Next, the operation will be described. When the control circuit 4 is off and the gate G is not connected to the negative electrode 1B, since the gate G is connected to the positive electrode 1A via the resistor 5, the source S and the gate G are at the same potential, and the FET 2 is non-conductive. State (off). When the control circuit 4 is turned on, the gate G is connected to the negative electrode 1B, so that the potential of the gate G (gate potential) becomes lower than the potential of the source S (source potential). At the moment when the control circuit 4 is turned on, the gate potential becomes negative 1 after a time determined by the time constant of the resistor 5 and the capacitor 6.
B potential. Generally, the FET 2 is turned on when the gate potential becomes lower than the source potential by several volts or more. Therefore, if the above-mentioned time constant is set so that the time until the gate potential becomes several volts lower than the source potential from the moment when the control circuit 4 is turned on becomes a desired time, for example, 1 second, the rush current Can flow for a desired length of time. Since the charge for charging the load capacitor 7 is a constant value depending on the capacitance and the power supply voltage, the peak value of the current is reduced by increasing the time during which the rush current flows. A curve c in FIG. 3 shows an inrush current of a measurement example of the electronic switch according to the present embodiment. The time during which the rush current flows is T3, which is much longer than the times T1 and T2. The peak value of the inrush current was A3, which was significantly lower than the peak values A1 and A2.

FIG. 2 is a circuit diagram showing another example of the embodiment of the present invention. 2, the FET 2 in FIG. 1 is replaced with a bipolar transistor 10, the emitter E is connected to the positive electrode of the DC power supply 1, and the collector C is connected to the output terminal 3. The base B is connected to the control circuit 4. Other configurations are the same as those of FIG. 1, and the operation is substantially the same as that of FIG.

[0010]

As described in detail in the above embodiment,
According to the present invention, the rush current when the electronic switch is turned on can be suppressed by changing the gate voltage or the base voltage of the switch element of the electronic switch in a time based on the time constant of the capacitor and the resistor.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an electronic switch according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of another example of an electronic switch according to the embodiment of the present invention.

FIG. 3 is a graph showing temporal changes of respective currents flowing through a conventional electronic switch and an electronic switch of the present invention.

FIG. 4 is a circuit diagram of a conventional electronic switch.

FIG. 5 is a circuit diagram of another example of a conventional electronic switch.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC power supply 1A Positive electrode 1B Negative electrode 2 FET 3 Output terminal 4 Control circuit 5 Resistance 6 Capacitor 10 Bipolar transistor

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5G013 AA02 AA17 BA01 CA10 5G065 BA04 BA07 BA08 EA01 GA02 HA07 HA17 LA02 NA01 NA04 5J055 AX25 AX32 AX55 BX16 CX12 DX05 DX12 DX55 EY01 EY10 EZ01 GX01 GX04

Claims (4)

[Claims] 1. A field effect transistor as a switch element for controlling power supply from a DC power supply to a load, a capacitor and a resistor connected in parallel between a source and a gate of the field effect transistor, and the electric field Connected between the gate and the source of the effect transistor,
An electronic switch including a control circuit that controls a potential between a gate and a source. 2. An end of the control circuit is connected to a gate,
2. The electronic switch according to claim 1, wherein the other end is connected to a terminal that is not connected to a source of the DC power supply. 3. A bipolar transistor as a switch element for controlling power supply from a DC power supply to a load, a capacitor and a resistor connected in parallel between an emitter and a base of the bipolar transistor, and the bipolar transistor. An electronic switch comprising a control circuit connected between the base and the emitter of the semiconductor device and controlling a potential between the base and the emitter. 4. An end of the control circuit is connected to a base,
4. The electronic switch according to claim 3, wherein the other end is connected to a terminal that is not connected to an emitter of the DC power supply.