JPH07123581A - Reverse voltage protective circuit - Google Patents

Abstract

PURPOSE:To provide a circuit for protecting an electronic circuit, e.g. a semiconductor integrated circuit, positively against reverse voltage while suppressing the voltage drop during normal operation. CONSTITUTION:The reverse voltage protective circuit connected between the terminals A, B of a power supply 1 and protecting an electronic circuit, e.g. a semiconductor integrated circuit, being fed with power therefrom against reverse voltage comprises a bias circuit 4 for operating a transistor 3, connected in series with the electronic circuit 2, in the saturation region when a voltage of normal polarity is applied thereto and turning the transistor 3 OFF when a reverse voltage is applied thereto.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reverse voltage protection circuit for protecting an electronic circuit such as a semiconductor integrated circuit from a reverse voltage.
A reverse voltage may be applied to an electronic circuit such as a semiconductor integrated circuit due to a surge voltage or the like, and the reverse voltage may damage an active element such as a transistor or a passive element such as a capacitor in the electronic circuit. Therefore, it is necessary to protect the electronic circuit when a reverse voltage is applied to the electronic circuit.

[0002]

2. Description of the Related Art FIG. 4 is an explanatory view of a conventional example.
Is a diode 4 in series with a semiconductor integrated circuit (IC) 41.
In the normal state, a forward current of the diode 42 flows in the semiconductor integrated circuit 41 due to the grounding G of the power source (not shown) and the negative voltage V _EE by connecting the two. When a reverse voltage such as a surge voltage is applied, a reverse voltage is applied to the diode 42, the current flowing through the semiconductor integrated circuit 41 is cut off, and the semiconductor integrated circuit 41 can be protected from the reverse voltage. it can.

A configuration in which the diode 42 described above is realized by connecting the base and collector of a transistor formed in a semiconductor integrated circuit is known, for example, in Japanese Patent Laid-Open No. 59-65464.

FIG. 4B shows a semiconductor integrated circuit (I
C) A Zener diode 43 is connected in parallel with 41 to protect against overvoltage of the power supply by the Zener voltage of the Zener diode 43, and against a reverse voltage, a current flowing in the forward direction of the Zener diode 43 causes a semiconductor integrated circuit. The reverse voltage applied to 41 is reduced.

A structure in which the Zener diode 43 described above is formed on the back surface of a semiconductor substrate to protect transistors and the like is known, for example, from Japanese Patent Laid-Open No. 60-98657.

FIG. 4C shows a semiconductor integrated circuit (I
C) A configuration is shown in which a resistor 44 is connected in series with 41, and the resistor 44 limits the current that flows when a reverse voltage is applied to the semiconductor integrated circuit 41.

[0007]

Problems to be Solved by the Invention As shown in FIG.
In the configuration shown in, the forward voltage of the diode 42 is 0.7V.
The operating voltage of the semiconductor integrated circuit 41 is 3 to 5V.
Since the degree is general, the diode 4 in normal condition
The forward voltage of 2 cannot be ignored. That is, it becomes necessary to raise the power supply voltage by the amount of the forward voltage of the diode 42.

The structure shown in FIG. 4B can protect the overvoltage and the reverse voltage. However, when the reverse voltage is applied to the semiconductor integrated circuit 41, the zener diode 4
The reverse voltage can only be reduced to the forward voltage of 3, and the semiconductor integrated circuit 41 can be reliably against the reverse voltage.
There is a drawback that cannot be protected.

The configuration shown in FIG. 4 (c) utilizes the voltage drop due to the resistor 44, but there is a problem that the resistor 44 consumes power even in a normal state.
There is also a problem that heat is generated accordingly. It is an object of the present invention to have a small voltage drop in a normal state and surely protect an electronic circuit from a reverse voltage.

[0010]

The reverse voltage protection circuit of the present invention will be described with reference to FIG. 1. An electronic circuit connected between terminals A and B of a power supply 1 and supplied with operating power from the power supply 1. In the reverse voltage protection circuit for protecting the electronic circuit 2 when the reverse voltage is applied to the transistor 2, the transistor 3 is connected in series to the electronic circuit 2 so that the voltage of the power source 1 is applied to the electronic circuit 2.
When the voltage of normal polarity is applied to the electronic circuit 2, the transistor 3 is operated in the saturation region,
There is provided a bias circuit 4 for turning off the transistor 3 when a reverse voltage is applied to.

The bias circuit 4 includes a transistor 3 between the base of the transistor 3 and one terminal A of the power source 1.
Has a resistance for operating in the saturation region.

[0012]

The electronic circuit 2 such as a semiconductor integrated circuit and the transistor 3 are connected in series, and the transistor 3 is operated in the saturation region to supply the operating power from the power supply 1 to the electronic circuit 2. At that time, the collector-emitter voltage of the transistor 3 operating in the saturation region is about 0.02 to 0.1 V, so that the voltage drop due to the transistor 3 can be ignored even when the voltage of the power supply 1 is several V. become. When a reverse voltage due to a surge voltage or the like is applied to the electronic circuit 2, the base current of the transistor 3 does not flow, so that the transistor 3 is turned off and the electronic circuit 2 can be protected.

The bias circuit 4 supplies a base current so that the transistor 3 operates in a saturation region when a voltage of normal polarity is applied to the electronic circuit 2, and a base current is supplied when a reverse voltage is applied. By not flowing, the transistor 3 is turned off, and the electronic circuit 2 can be protected from the reverse voltage.

[0014]

FIG. 2 is an explanatory view of an embodiment of the present invention.
Reference numeral 1 is a power source, 12 is a driving unit including an amplifier 15 and the like, 22 is a light emitting unit including a semiconductor laser 26 and a transistor 25, 1
3 and 23 are npn-type transistors, and 14 and 24 are resistors forming a bias circuit. One terminal A of the power supply 11 is a ground G terminal and the other terminal B is a negative voltage V.
_Shows the case of _EE pin. Further, the drive unit 12 and the light emitting unit 22
And correspond respectively to the electronic circuit 2 of FIG.
4 respectively correspond to the bias circuit 4 of FIG. Further, the driving unit 12 can be made into a semiconductor integrated circuit.

A voltage of regular polarity is supplied from the power source 11 to the drive unit 12.
When applied to the light emitting portion 22, sufficient current is supplied to the bases of the transistors 13 and 23 through the resistors 14 and 24 that form the bias circuit 4, and the transistors 13 and 2 are
3 is operated in the saturation region. Therefore, transistor 1
The collector-emitter voltage of 3, 23 is about 0.02V.

The light emitting section 22 has a structure in which a transistor 25 is connected in parallel with the semiconductor laser 26, and the semiconductor laser 2 is connected from the power source 11 via the transistor 23 in the saturation region.
A voltage is applied to 6 and the transistor 25. When the semiconductor laser 26 is used as a pumping light source for an optical amplifier made of an optical fiber doped with a rare earth element such as erbium (Er) (not shown), the drive current of the semiconductor laser 26 is
Since it can be controlled by the bypass current flowing through the transistor 25, the drive unit 12 can control the transistor 25 to control the gain of the optical amplifier. In this case, compared with the configuration in which the transistor 25 is connected in series to the semiconductor laser 26 to control the drive current, the power supply 11
There is an advantage that the voltage of can be set low.

The drive unit 12 includes an amplifier 15 and the like, and operates by applying the voltage of the power supply 11 to the amplifier 15 and the like via the transistor 13 through which the base current flows so as to operate in the saturation region. Then, the gain control signal from the circuit configuration (not shown) is amplified by the amplifier 15, and the light emitting unit 22
The transistor 25 of FIG. That is, the drive unit 12 can control the light emitting unit 22 to control the gain of the optical amplifier to a predetermined value.

Further, when the surge voltage or the like is superposed on the voltage of the normal polarity of the power source 11, a voltage having a reverse polarity may be applied to the drive unit 12 and the light emitting unit 22. In that case, a voltage is applied in the opposite direction to the pn junction between the base and emitter of the transistors 13 and 23, and the base current stops flowing, so the transistors 13 and 23 are turned off. Therefore, the reverse voltage is not applied to the drive unit 12 and the light emitting unit 22. That is, the electronic circuits such as the driving unit 12 and the light emitting unit 22 can be protected from the reverse voltage.

In addition, a voltage is supplied from the power source 11 with regular polarity to the drive unit 1.
2 and the light emitting part 22 are applied to the transistor 1
Since 3 and 23 operate in the saturation region, the collector-emitter voltage is about 0.02V. Therefore, the voltage V _EE
Is -5V, for example, 4.98V is applied to the drive unit 12 and the light emitting unit 22. In that case, the voltage drop due to the transistors 13 and 23 is 0.4% of the voltage of the power supply 11, so that it is negligible.

FIG. 3 is an explanatory view of another embodiment of the present invention, in which 32 is an electrolytic capacitor 35 and a MOS transistor 3.
An electronic circuit including 6 and the like, 33 is a pnp type transistor,
Reference numeral 34 is a resistor forming a bias circuit.

The embodiment shown in FIG. 2 is a case where an npn-type transistor is used, but this embodiment is a case where a pnp-type transistor is used, and the electronic circuit 32 includes active elements such as various transistors. It can be configured to include, a configuration including only passive elements such as the electrolytic capacitor 35, or a single configuration.

Also in this embodiment, the transistor 33 is used.
The value of the resistor 34 is selected so as to operate in the saturation region. Therefore, the emitter-collector voltage of the transistor 33 is about 0.02V as described above, and assuming that the voltage of the power supply (not shown) is 5V, the voltage drop by the transistor 33 is 0.4%. It becomes too much and can be ignored.

When a surge voltage or the like is superimposed on the voltage of the power supply and a voltage of reverse polarity is applied to the electronic circuit 32, the base current of the transistor 33 does not flow, so the transistor 33 is turned off. The reverse voltage is not applied to the electronic circuit 32. That is, the electronic circuit 32 can be protected from reverse voltage.

Although each of the above-described embodiments shows the case of using npn-type and pnp-type bipolar transistors, it is also possible to use transistors such as field effect transistors. For example, the transistor 1 of the embodiment shown in FIG.
Instead of 3, 23, an n-channel enhancement type MOS transistor can be used. Further, a p-channel enhancement type MOS transistor can be used instead of the transistor 33 of the embodiment shown in FIG.

[0025]

As described above, according to the present invention, by connecting the transistor 3 in series with various electronic circuits 2 and operating the transistor 3 in the saturation region, the voltage effect by the transistor 3 can be ignored. And power supply 1
Therefore, a voltage of normal polarity can be applied to the electronic circuit 2 to operate the electronic circuit. Further, when a surge voltage or the like is superimposed on the voltage of the power source 1 and a reverse voltage is applied to the electronic circuit 2, the transistor 3 is turned off.
Can be protected from reverse voltage. Therefore, there is an advantage that the structure is simple and the power loss can be ignored.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is an explanatory diagram of an embodiment of the present invention.

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

FIG. 4 is an explanatory diagram of a conventional example.

[Explanation of symbols]

 1 power supply A, B power supply terminal 2 electronic circuit 3 transistor 4 bias circuit

Claims (2)

[Claims] 1. A reverse voltage is applied to an electronic circuit (2) connected between terminals (A) and (B) of a power supply (1) and supplied with operating power from the power supply (1), In a reverse voltage protection circuit for protecting an electronic circuit (2), a transistor (3) is connected in series to the electronic circuit (2) so that the voltage of the power source (1) is applied to the electronic circuit (2). And a transistor (3) is operated in a saturation region when a voltage of normal polarity is applied to the electronic circuit (2), and a reverse voltage is applied to the electronic circuit (2). A reverse voltage protection circuit comprising a bias circuit (4) for turning off (3). 2. The bias circuit (4) operates the transistor (3) in a saturation region between the base of the transistor (3) and one terminal (A) of the power supply (1). 2. The resistance of claim 1
Reverse voltage protection circuit described.