JPH0360329A - Reverse power supply preventing circuit - Google Patents

Abstract

PURPOSE:To supply a circuit with source voltage with small voltage drop by inserting a switch means having small voltage drop between a power supply terminal and the circuit to be supplied with power, judging the polarity of the power supply and controlling the switch means. CONSTITUTION:A reverse power supply preventing circuit X is inserted between a power supply terminal 1 and a circuit 2 to be supplied with power and power supply is blocked when the power is supplied with reverse polarity to the power supply terminal 1. In this case, switch means 3 having small voltage drop, for example, a transistor, is inserted between the power supply terminal 1 and the circuit 2. The switch means 3 is controlled by the output from a polarity judging means 4 for judging the polarity of the power supply. That is, the switch means 3 is turned on when the power supply has a forward polarity and turned off when the power supply has a reverse polarity. Thus, power supply is blocked and the circuit is protected against damage.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a power supply reverse input protection circuit.

[Prior Art] Conventionally, as shown in FIG. 5, this type of power supply reverse input protection circuit has been designed to connect a power supply terminal 1 and a power supplied circuit 2 such as an electronic circuit formed by an IC or the like. A diode D1 for blocking reverse current is provided between them, and when the power supply voltage Vin applied to the power supply terminal 1 has forward polarity, power is supplied to the power supply circuit 2 through the diode D, and when the power supply voltage Vin applied to the power supply terminal 1 has reverse polarity, the power is supplied to the power supply circuit 2. There is a device in which power supply is blocked by D to prevent circuit breakdown due to application of a power supply voltage of opposite polarity to the power supplied circuit 2.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional example, since there is a forward voltage drop of about 0°6 V in the diode D for blocking reverse current, this voltage drop makes the circuit operation unstable. For example, common I used in electronic equipment
C is guaranteed to operate within ±5% of the power supply voltage.
If the power supply voltage is 5V, it is necessary to suppress voltage fluctuations to ±0.25V or less. However, in the case of the above-mentioned conventional example, the voltage drop due to the reverse current blocking diode D1 is 0.
Since there is 6V, the power supply voltage Vin input to power supply terminal 1
When the voltage is set to 5V, there is a problem in that the power supply voltage supplied to the power supplied circuit 2 becomes lower than the guaranteed operation voltage. Note that it is conceivable to increase the power supply voltage Vin input to the power supply terminal 1 by 0.6 V to ensure operation guaranteed voltage, but the adjustment work to adjust the power supply voltage Vin is troublesome, and adjustment may not be possible. A problem arises.

The present invention has been made in view of the above points, and its object is to provide a power supply reverse input that can supply the power supply voltage applied to the power supply terminal to the power supply circuit with a small voltage drop. The purpose is to provide a protection circuit.

[Means for Solving Problem R] The power supply reverse input protection circuit of the present invention is inserted between a power supply terminal and a power supplied circuit, and prevents power input from being input when a power supply of reverse polarity is input to the power supply terminal. In the power supply reverse input protection circuit designed to prevent reverse input, a switch means with a small voltage drop is inserted between the power supply terminal and the power supplied circuit, and a polarity determination means output that determines the polarity of the power input to the power supply terminal. The switch means is turned on when the polarity is forward, and the switch means is turned off when the polarity is reversed.

[Function] The present invention is configured as described above, and a switch means with a small voltage drop is inserted between the power supply terminal and the power supplied circuit, and a polarity switch means for determining the polarity of the power input to the power supply terminal is inserted between the power supply terminal and the power supplied circuit. Since the switch means is controlled by the output of the determination means, it is possible to provide a power supply reverse input protection circuit that can supply the power supply voltage applied to the power supply terminal to the power supplied circuit with a small voltage drop. It looks like this 6 [
Embodiment] FIG. 1 shows an embodiment of the present invention, which is inserted between a power supply terminal 1 and a power supplied circuit 2, and is connected to the power supply terminal when a power supply of opposite polarity is input to the power supply terminal 1. In the power supply reverse input protection circuit X designed to prevent reverse input, a switch means 3 with a small voltage drop is inserted between the power supply terminal 1 and the power supplied circuit 2, and the polarity of the power input to the power supply terminal 1 is determined. controlling the switch means 3 with the output of the polarity determining means 4;
When the polarity is forward, the switch means 3 is turned on, and when the polarity is reversed, the switch means 3 is turned off.

FIG. 2 shows a specific circuit example, in which the switch means 3 is formed by a transistor Q, and the polarity determination means 4 is formed by a transistor Q2 and resistors R1 to R3. When a power supply voltage Vin of forward polarity is applied, a forward bias is applied between the base and emitter of the transistor Q2, and the transistor Q2 is turned on, and the transistor Q is turned on and power is supplied to the power supplied circuit 2. At this time, since the voltage drop caused by the transistor Q1 is about 0.1V, the voltage drop is much lower than that in the conventional example, and the operation of the power supply circuit 2 can be guaranteed.

On the other hand, when a power supply voltage Vin of opposite polarity is applied to the power supply terminal 1, the base and emitter of the transistor Q2 become reverse biased, and the transistor Q2 is turned off, and the transistor Q1 is turned off, and the power supply circuit 2 is turned off. This prevents the circuit from being damaged due to the application of a power supply voltage of opposite polarity.

FIG. 3 shows another embodiment, in which the polarity determination means 4 is formed by a diode D2 and a relay Ry, and the switch means 3
is formed by the normally open contact r of the relay R3/.

Now, when the power supply voltage Vin is of forward polarity, current flows to the relay Ry via the diode D2, the normally open contact r of the relay Ry is turned on, and the power supply voltage is supplied to the power supply circuit 2. In this case, The voltage drop due to the normally open contact r is almost negligible. On the other hand, when the power supply voltage Vin has the opposite polarity, no current flows through the relay Ry, so the normally open contact r remains off, and power supply to the power supply circuit 2 is blocked.

FIG. 4 shows still another embodiment, in which the polarity determining means 4 is formed by a photocoupler PC, and the photocoupler P
It is also possible to control the transistor Q by the C output.

Now, when the power supply voltage Vin is of forward polarity, a current flows through the photodiode of the photocoupler PC, turning on the phototransistor, turning on the transistor Q, and supplying the power supply voltage Vin to the power supply circuit 2. Ru. On the other hand, when the power supply voltage Vin has the opposite polarity, no current flows to the photodiode of the photocoupler PC, so the phototransistor is turned off, and the transistor Q is also turned off, blocking power supply to the power supply circuit 2. Ru.

[Effects of the Invention] The present invention is configured as described above, and a switch means with a small voltage drop is inserted between the power supply terminal and the power supplied circuit, and the polarity of the power input to the power supply terminal is determined. Since the switch means is controlled by the output of the polarity determining means, it is possible to provide a power supply reverse input protection circuit that can supply the power supply voltage applied to the power supply terminal to the power supply circuit with a small voltage drop. There is an effect that it can be done.

[Brief explanation of drawings]

Fig. 1 is a block circuit diagram of one embodiment of the present invention, Fig. 2 is a specific circuit diagram of the same as above, Fig. 3 is a specific circuit diagram of another embodiment, and Fig. 4 is a specific circuit diagram of yet another embodiment. , FIG. 5 is a circuit diagram of a conventional example. 1 is a power supply terminal, 2 is a power supplied circuit, 3 is a switch means, and 4 is a polarity determination means.

Claims (1)

[Claims] (1) In a power supply reverse input protection circuit that is inserted between a power supply terminal and a power-supplied circuit to prevent power input when a power supply of reverse polarity is input to the power supply terminal, A switch means with a small voltage drop is inserted between the supply circuit and the switch means is controlled by the output of the polarity determination means for determining the polarity of the power input to the power supply terminal,
At the same time as turning on the switch means when the polarity is forward,
A power supply reverse input protection circuit characterized in that the switch means is turned off when the polarity is reversed.