JP2002058156A - Protection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a protection circuit, capable of preventing faults in a circuit or device, even in the case of wrong connections to power supply or overvoltage in the power supply at hot plug-in. SOLUTION: The protection circuit is provided with MOSFET Q1, whose drain is connected with the input terminal of a +5 V power supply and whose source is connected with the output of the +5 V power supply and a voltage- divider circuit, consisting of resistors R1 and R2, that divides the voltage of the +12 V power supply terminals and applies it to the gate of the MOSFET Q1. When a voltage within a specified range is applied to the +12 V power supply terminals, a FET-switching element is turned on to provide a first power supply to the output. When the voltage at the +12 V power supply terminals is outside the specified range, the MOSFET Q1 is turned off, to interrupt the +5 V power supply.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a protection circuit,
In particular, the present invention relates to a protection circuit for preventing an accident caused by incorrect connection of a plurality of power supplies.

[0002]

2. Description of the Related Art In a circuit or a device in which a digital circuit and an analog circuit or a digital circuit and a mechanical control circuit are mixed, a plurality of DC power supplies of +5 V and other DC power supplies such as +12 V are often used. In a circuit or an electronic device using such a plurality of DC power supply voltages, if there is no protection circuit related to the power supply, when the + 5V and + 12V power supplies are interchanged and connected when checking the operation of the circuit or the electronic device, etc. There is a possibility that the IC may be destroyed or the circuit may generate high heat, which may lead to an accident. Also,
A similar accident may occur when an overvoltage occurs in the power supply. Furthermore, at the time of hot plug-in, there is a case where an IC used inside the device is destroyed due to voltage chattering or the like.

In order to prevent this, even if a fuse is used as a protection circuit, if the power supply is connected by mistake, or if an overvoltage occurs, IC destruction or fuse disconnection may occur. There is a fear. Further, depending on the setting of the capacity of the fuse, the disconnection may occur due to an inrush current at the time of connection.

[0004]

As described above, in an electronic device using a DC power supply, when a protection circuit is not provided or when only a fuse is used as a protection circuit, the power supply is connected by mistake. In such a case, when a high voltage is generated at the time of hot plug-in, there is a possibility that the IC may be broken, a high temperature may be generated, the wiring may be burned out, and the fuse may be disconnected. The present invention solves this problem in a relatively simple manner, and can prevent failure of a circuit or device even when a power supply is mistakenly connected or an overvoltage occurs in the power supply during hot plug-in. It is an object to realize a protection circuit.

[0005]

In order to achieve the above object, the present invention provides a protection circuit against overvoltage or erroneous connection of a power supply in an electronic circuit using a plurality of DC power supplies. An FET switching element connected to the input terminal and having a source connected to the output side of the first power supply; and a voltage dividing circuit for dividing the voltage of the second power supply terminal and applying the divided voltage to the gate of the FET switching element. Then, when a voltage within a predetermined range is applied to the second power supply terminal, the FET switching element is turned on, the first power is supplied to the output side, and the first power is supplied to the second power supply terminal. When the applied voltage is equal to or lower than a predetermined voltage, the FET switching element is turned off and the supply of the first power is cut off. Accordingly, in an electronic circuit using two types of power supplies, even if an error occurs in connecting the power supplies to each other, the supply of power is cut off, so that a failure of the circuit or the device can be prevented.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a device connected to a power source having +5 V and another DC power source voltage, for example, a device including a CD-ROM drive and a CD-RW (CD rewritable) drive, etc. High pressure +12
Since a power supply such as V is used, if the power supply is mistakenly connected, a semiconductor component such as an IC used inside the device is easily destroyed. In addition, since these power supplies generally use a switching regulator, a high voltage may be generated due to external jamming radio waves and the like. When the + 5V power supply becomes high, there is a case where an IC or the like is destroyed.

Therefore, in order to prevent the destruction of the IC regardless of which of the two phenomena occurs, the MOSFE
A protection circuit using the switching characteristics of T has been devised.
Furthermore, this circuit, by adding a capacitor,
Since the rise time of the power supply voltage can be controlled, chattering at the time of connection can be prevented, and application to a hot plug-in device can be easily realized.

Hereinafter, a protection circuit according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an embodiment of a protection circuit according to the present invention. In FIG. 1, the code Q1 is M
OSFET (field effect transistor), Q2 is a transistor, R1 to R3 are resistors, C1 is a capacitor, + 5V and + 12V are + 5V and + 12V external power supplies, respectively. FIG. 2 shows an example of a specific circuit of this embodiment. FIGS. 3, 4 and 5 show examples of the characteristics of the MOSFET.

[0010] This circuit utilizes the switching characteristics of the MOSFET to finally control the output voltage.
Voltage dividing circuits R1 and R2 for detecting whether the connection between the SFET Q1 and + 5V, + 12V are correct, and further detecting whether + 5V is within an intended voltage range, and based on the result, a circuit transistor Q2 for controlling the MOSFET Q1. , And a Zener diode ZD1.

Specifically, only when +5 V and +12 V are correctly applied from the outside to the input terminal of the power supply, the MOSF
The partial pressure ratio between R1 and R2 is adjusted so that ETQ1 turns ON. These resistors set a voltage equal to or lower than the cut-off voltage of FIG. 4 to M so that MOSFET Q1 enters a high impedance state when +5 V and +12 V are connected by mistake.
This is applied to the gate of OSFET Q1.

The reference power supply ZD1 and the transistor Q2
Detects a voltage rise of + 5V, and when the voltage exceeds a set range, the transistor Q
2 is turned on, and the MOSFET Q1 is turned into a high impedance state.
Give to the gate of TQ1.

Further, a capacitor C1 is added and MOSF
The rise time of the gate bias voltage of ETQ1 is controlled. As a result, the rise time of the + 5V CONTROL output terminal voltage can be controlled.
When incorporated in the power supply unit of the hot plug-in compatible device, malfunction and destruction due to chattering at the time of connection can be prevented.

In this case, the MOSFET Q1 has VGS ≒ 2
In order to be turned on at V, a relatively large capacitance is required for the capacitor C1. In this case, the rise time constant T
Is expressed as T = C1 · R1 in a pseudo manner.

The advantage of this circuit is that a special control circuit is not required, and it can be easily added to an existing circuit later. CD-ROM, CD-R
In a device in which a W, HD (Hard Disk), FD (Floppy Dis) drive or the like is incorporated together with a computer, it is possible to prevent damage to the device due to incorrect connection of the power connector.

Further, as shown in FIG. 5, the MOSFET Q1 has a very low ON resistance between the drain and the source of about 20 mΩ, so that the voltage loss is made negligibly small as compared with the case where a transistor is used. be able to.

When a switching regulator is used as a power supply, the switching regulator may malfunction due to an increase in voltage due to radiation of radio waves from the outside. Even in such a case, the upper limit of the voltage rise is set at about 5.6V. By setting the voltage, the voltage can be automatically reduced, so that destruction of the IC can be prevented.

Furthermore, if the connection is made by mistake while the power is on, the rise time of the voltage can be delayed, thereby preventing malfunction or destruction. A similar effect can be expected by mounting this circuit on a hot plug-in compatible device.

The circuit of the present invention is not limited to the +5 V and +12 V power supply devices, and similar effects can be expected for devices of other voltages by changing the setting of the constant. Further, by providing a plurality of such circuits, the present invention can be applied to two or more multi-supply voltage devices. In addition, the circuit of the present invention always operates when the applied voltage returns to within the normal range.
There is an advantage that the voltage of the ONCONTROL voltage output terminal automatically returns to the normal state (+5 V). FIG. 6 shows CD-
An application example of the present invention to a circuit having a ROM and a CD-RW drive will be described.

[0020]

As described above, according to the first aspect of the present invention, in a protection circuit against overvoltage or erroneous connection of a power supply in an electronic circuit using a plurality of DC power supplies, a drain of the first power supply is provided. An FET switching element connected to the input terminal and having a source connected to the output side of the first power supply;
A voltage dividing circuit for dividing the voltage of the second power supply terminal and applying the divided voltage to the gate of the FET switching element, wherein when a voltage within a predetermined range is applied to the second power supply terminal,
The switching element is turned on, the first power is supplied to the output side, and when the voltage applied to the second power terminal is equal to or lower than a predetermined voltage, the FET switching element is turned off to supply the first power. Is cut off. By this, when two power supplies are connected by mistake, FET
Since the switching element enters the high impedance state, it is possible to prevent a high voltage from being applied to the output side by mistake.

According to a second aspect of the present invention, the collector is connected to the gate of the FET switching element, the emitter is connected to a predetermined reference voltage, and the base is connected to the first through a resistor.
When the voltage applied to the input terminal of the first power supply exceeds a predetermined value, the transistor is turned on and a reference voltage is applied to the gate of the FET switching element, The switching element is turned off and supply of the first power is cut off. Thereby, the rise of the first power supply voltage is detected, and when the first power supply voltage exceeds the set range, the FET switching element enters a high impedance state.
It is possible to prevent a high voltage from being applied to the output side.

According to a third aspect of the present invention, there is provided the FE having a capacitor between the gate of the FET switching element and ground.
It is characterized in that the time until conduction of the T switching element is controlled. As a result, the rise time of the output terminal voltage of the first power supply can be controlled, and malfunction and destruction due to chattering at the time of connection with a hot plug-in compatible device can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of a protection circuit according to the present invention.

FIG. 2 is a circuit diagram of an embodiment of a protection circuit according to the present invention.

FIG. 3 shows an example of characteristics of a MOSFET used in the present invention.

FIG. 4 shows an example of characteristics of a MOSFET used in the present invention.

FIG. 5 shows an example of characteristics of a MOSFET used in the present invention.

FIG. 6 is a circuit block diagram showing an application example of the protection circuit of the present invention.

[Explanation of symbols]

C1: capacitor, Q1: MOSFET (field effect transistor), Q2: transistor, R1 to R3: resistor,
+ 5V ... + 5V external power supply, + 12V ... + 12V external power supply.

Claims (3)

[Claims] An electronic circuit using a plurality of DC power supplies, the protection circuit corresponding to overvoltage or erroneous connection of a power supply, wherein a drain is connected to an input terminal of the first power supply, and a source is an output of the first power supply. And a voltage dividing circuit that divides the voltage of the second power supply terminal and applies the divided voltage to the gate of the FET switching element, wherein a voltage within a predetermined range is applied to the second power supply terminal. Is applied, the FET switching element is turned on and the first
Is supplied to the output side, and when the voltage applied to the second power supply terminal is equal to or lower than a predetermined voltage, the FET switching element is turned off and the supply of the first power supply is cut off. And protection circuit. 2. A transistor having a collector connected to a gate of the FET switching element, an emitter connected to a predetermined reference voltage, and a base connected to an input terminal of the first power supply via a resistor, When the voltage applied to the input terminal of the first power supply exceeds a predetermined value, the transistor is turned on, the reference voltage is applied to the gate of the FET switching element, and the FET switching element is turned off, and the first switching element is turned off. The protection circuit according to claim 1, wherein the supply of the power is cut off. 3. The protection circuit according to claim 1, further comprising a capacitor between a gate of the FET switching element and ground, and controlling a time until the FET switching element is turned on.