JPH06252725A - Power supply changeover circuit - Google Patents

Abstract

PURPOSE:To provide a power supply changeover circuit of a system configured in duplicate having a very small voltage loss and leakage current and switched uninterruptibly. CONSTITUTION:Emiteres of two sets of transistors (TRs) 1,2 being components of a switch circuit of each power supply are respectively connected to input power supplies 12,13 and bases are connected to a bias resistor 5 through TRs 3.4. The other end of the bias resistor 5 is connected to a GND 15. Collectors of the TRs 1,2 are connected together, and the connecting point is used for an output voltage terminal 14. Moreover, diodes 10,11 are connected in a polarity to block a current flowing reversely to an input power supply and resistors 8,9 are connected to control a bias voltage. Thus, the two power supplies are switched uninterruptibly and the power supply changeover circuit is realized, in which a voltage loss and a leakage current are very small.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to power circuits, and more particularly to
The present invention relates to a power supply switching circuit of a power supply by a dual backup system in which one is in use when the other is in standby.

[0002]

2. Description of the Related Art As a conventional dual power supply switching circuit, the following is known.

First of all, as shown in FIG. 2, diodes 21 and 22 are connected in series to two input power supplies 23 and 24, respectively, and a series voltage is applied to an output terminal 25 by connecting these series circuits in parallel. It is what is output.

Secondly, the two power sources are simply switched by a relay.

Next, as a third method, Japanese Patent Application Laid-Open No. 62-24571.
The technique disclosed in Japanese Patent No. 9 has been proposed. This technical content is to switch using two transistors 31 and 32 of the same kind as shown in FIG. That is,
Two sets of transistors 31, 32 and two diodes 3
Two types of power supply 3 from 3, 34 and one bias resistor 35
Two sets of switching circuits for Nos. 6 and 37 are configured, and are connected so as to add a difference in input voltage as a difference in control voltage of the switching circuits. With this configuration, the comparison of two input voltages and the connection operation to the larger voltage side are simultaneously realized, and the one with the larger input voltage is selected and output.

[0006]

Among the above circuits, the first conventional example using the diode has a drawback that the voltage drops due to the forward voltage characteristic of the diode, and the second switching method is performed by the relay. In the conventional example, a momentary interruption occurs when switching.

The third transistor using two transistors
In the conventional example, there is no voltage loss and switching can be performed without interruption, but when one side of the power supply is "OFF," the reverse β characteristic of the transistor causes a leakage current to occur in the power supply that is "OFF." There is. This leakage current depends on the type capacity of the transistor, but when it is large, it is about 10
The current is about mA, and there is a risk that the transistor used for this current may be extremely heated to stabilize the operation or be destroyed.

The present invention has been made in view of the above-mentioned conventional circumstances. Therefore, the object of the present invention is to eliminate the above-mentioned drawbacks inherent in the prior art, to reduce the voltage loss and the leakage current extremely, and to eliminate them. It is to provide a new power supply switching circuit capable of instantaneous interruption switching.

[0009]

In order to achieve the above object, a power supply switching circuit according to the present invention connects two types of power supplies of the same polarity to the emitters of two sets of first transistors, respectively. Two sets of second transistors for "ON / OFF" control of the transistors are respectively connected to respective bases of the first transistors, and the two sets of the first transistors are connected.
It is characterized in that the collectors of the transistors are connected to each other, and this connection point is configured as an output voltage terminal.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be specifically described with reference to the drawings for each of its preferred embodiments.

FIG. 1 is a circuit configuration diagram showing a first embodiment according to the present invention. The first embodiment is one in which the voltages of the power supplies 12 and 13 are positive, and the switching transistors 1 and 2 are of PNP type, and the control transistors 3 and 4 are of NPN type. .

Referring to FIG. 1, two power supplies 12 and 1 are provided.
The emitters of the two sets of switching transistors 1 and 2 which form the switch circuit of FIG.
3 is connected to the base of the control transistor 3,
It is connected to the bias resistor 5 through 4. The other end of the bias resistor 5 is connected to the GND 15. The collectors of the switching transistors 1 and 2 are connected to each other, and the connection point is configured as an output voltage terminal 14.

The diodes 10 and 11 are connected to the input power source 1
2 and 13 are “OFF” or input power sources 13 that are different from each other,
Resistors 8 and 9 are connected to control the bias voltage, respectively, in order to block the current flowing back to the input power supplies 12 and 13 from the bias circuit by the bias resistor 5 when the voltage is lower than 12.

In the first embodiment, when the voltage of the input power source 12 is higher than that of the input power source 13, a current flows through the transistors 1 and 3, the switching transistor 1 is turned on, and the output terminal 14 is turned on. The voltage of the input power supply 12 is output to. On the contrary, when the voltage of the input power supply 13 is higher than that of the input power supply 12, the transistor 2,
Current flows through the switching transistor 2 and
N ″, and the voltage of the input power supply 13 is output.

When the input power supplies 12 and 13 are the same, the transistors 1 and 2 are both turned "ON", and no switching interruption occurs.

Here, when the input power supply 12 is "OFF" or when the voltage of the input power supply 12 is lower than that of the input power supply 13, the switching transistor 1 is turned "OFF" by the control transistor 3 and the leak current is reduced. Does not occur. Further, when the input power supply 13 is "OFF" or when the voltage of the input power supply 13 is lower than that of the input power supply 12, the switching transistor 2 is turned "OFF" by the control transistor 4 and no leak current is generated. .

FIG. 2 is a circuit configuration diagram showing a second embodiment according to the present invention.

Referring to FIG. 2, the second embodiment is one in which the voltages of the power supplies 12 'and 13' are negative, and the switching transistors 1'and 2'are of the NPN type for control. PNP type transistors are used for the transistors 3'and 4 ', respectively.

The operation of the second embodiment is almost the same as that of the first embodiment except that the flow of current is opposite.

In both the first and second embodiments described above, bipolar type transistors are used as the switching transistors and the control transistors, but it is clear that FETs and the like can also be used.

[0021]

As described above, according to the present invention,
It is possible to switch between the two power supplies without interruption, and it is possible to obtain the effect of realizing a power supply switching circuit with extremely small voltage loss and leak current.

That is, by using the present invention, the base current of the switching transistor is cut off by the control transistor, and the current leaking due to the inverse β characteristic is reduced from several tens mA to an unmeasurable state. I was able to.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing a first embodiment according to the present invention.

FIG. 2 is a circuit configuration diagram showing a second embodiment according to the present invention.

FIG. 3 is a circuit diagram of a conventional power supply switching circuit using a diode.

FIG. 4 is a circuit diagram of a conventional power supply switching circuit using a transistor.

[Explanation of symbols]

 1, 2, 3 ', 4' ... PNP type transistors 1 ', 2', 3, 4 ... NPN type transistors 5, 6, 7, 8, 9 ... Bias resistors 5 ', 6', 7 ', 8', 9 '... Bias resistance 12, 13, 12', 13 '... Input power supply 14, 14' ... Output voltage terminal 15 ... GND

Claims (5)

[Claims] 1. An emitter of two sets of transistors is respectively connected to two kinds of input power supplies of the same polarity, and another two sets are biased by the input power supplies separately from the bases of the transistors. The respective collectors of the transistors are connected to each other, the common bias resistors are connected to the emitters of the other two sets of transistors to form two sets of switching circuits, and the collectors of the two sets of transistors are connected to each other. A power supply switching circuit characterized by being configured as an output voltage terminal. 2. A first switching transistor having an emitter connected to a first input power source and a collector connected to an output terminal; and a collector connected to a base of the first switching transistor and an emitter connected to a bias circuit. A first whose base is biased by the first input power supply
And a second switching transistor having an emitter connected to a second power supply having the same polarity as the first input power supply and a collector connected to the output terminal.
A power supply switching circuit comprising a second control transistor having a collector connected to the base of the second switching transistor, an emitter connected to the bias circuit, and a base biased by the second input power supply. . 3. The first power source is connected to the first power source by “O”.
First backflow blocking means for blocking a current flowing back from the bias circuit at the time of "FF" is connected, and the current flows backward from the bias circuit to the second power source when the second power source is "OFF". 3. The power supply switching circuit according to claim 2, further comprising a second backflow blocking unit that blocks a current. 4. The first and second power supplies are positive voltage power supplies, and the first and second switching transistors are PN.
4. The power supply switching circuit according to claim 2, further comprising a P-type transistor, wherein the first and second control transistors are NPN-type transistors. 5. The first and second power supplies are negative voltage power supplies, and the first and second switching transistors are NP.
4. The power supply switching circuit according to claim 2, further comprising an N-type transistor and the first and second control transistors being PNP-type transistors.