JP2007288819A - Overvoltage/overcurrent protective circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To supply a required current to a load, while protecting the load at overvoltage or overcurrent, to automatically interrupt the load current when the overvoltage or overcurrent continues, and to import restoring function for restoring the interrupted load. <P>SOLUTION: This protective circuit is provided with first and second switching elements, connected in series and reverse polarity and inserted to a load current passage, first and second Zener diodes for detecting overvoltage, third and fourth switching elements to be conducted, when they each exceeds the Zener voltage, and a fifth switching element to be grounded by them. At overvoltage, the fifth switching element is grounded by a current flowing through the third or fourth switching element; the first and second switching elements become non-conductive, and the first or second Zener diode becomes lower than the Zener voltage; the third or fourth switching element is turned off; and the fifth switching element is released from grounded state, and the first and second switching element go into a conductive state to perform a feedback operation for conducting the load current passage. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an overvoltage overcurrent protection circuit, and more particularly, to an overvoltage overcurrent protection circuit that can cope with an overvoltage and / or overcurrent without immediately interrupting a load current.

If a surge voltage due to lightning is input, the load and other equipment will be damaged. Therefore, prevent damage to the equipment by using a lightning arrester that uses an arrester, etc., or use a triac or varistor together. ing.
However, when these arresters, varistors, triacs, etc. are used, it is finally dealt with by forcibly blowing the fuse, or these elements themselves may be short-circuited, and circuit restoration It took a long time. In general, overvoltage and overcurrent are dealt with separately.

  Therefore, Patent Document 1 presents an overvoltage overcurrent protection circuit that simultaneously realizes countermeasures against overvoltage and prevention of overcurrent, and that can be quickly and automatically restored even immediately after the protection operation is activated. Yes.

  The overvoltage overcurrent protection circuit described in Patent Document 1 is an overcurrent suppression circuit in which a pair of conduction elements are inserted in a load current path between an AC power supply and a load, and a bias voltage is applied to each of the pair of conduction elements. A self-biasing means is provided, and a conduction control element is provided that acts on the self-biasing means to control conduction / cutoff of the pair of conduction elements by detecting an overcurrent by the pair of conduction elements. When overvoltage is input to the load, the current flowing through the pair of conductive elements increases. The pair of conducting elements detect this increase in current, the conduction control element is activated by this current increase and acts on the self-bias means, and the pair of conducting elements are cut off by cutting off the bias voltage of the pair of conducting elements. The This interrupts the load current. The overvoltage suppression circuit protects the load by bypassing a current that is about to flow to the load when an overvoltage is applied to the load. This bypassed current is dealt with by the overcurrent suppression circuit.

Furthermore, in the circuit of Patent Document 1, after the above-described overcurrent suppression circuit is activated and the load current is cut off, the restoration operation is automatically performed every half cycle of AC input.
Japanese Patent No. 3672552

However, in the overvoltage overcurrent protection circuit of Patent Document 1, the load current is immediately interrupted when the overcurrent suppression circuit is activated. Although a function for recovery every half cycle is provided, the load current remains in a cut-off state until recovery. Accordingly, there is a possibility that the load current is adversely affected by being immediately interrupted and being in a disconnected state until recovery.
For example, in a server or other device, an inrush current flows when the power is turned on, but if the load current is interrupted immediately against an overcurrent, the overcurrent protection is activated due to the inrush current and the load current is interrupted. There is an inconvenience.
In addition, when the load voltage is immediately interrupted with respect to the overvoltage, if the frequency of the overvoltage is high, the load current may be momentarily interrupted each time, causing a communication device such as a server to malfunction. Become.
Furthermore, it is desirable that such a protection circuit has a function to cope with overheating.

  In view of the above situation, an object of the present invention is to provide a current necessary for a load while protecting the load in an overvoltage or overcurrent in an overvoltage overvoltage protection circuit. Another object of the present invention is to automatically cut off the load current at a certain point after a certain time has elapsed when the overvoltage or overcurrent continues. Still another object of the present invention is to provide a manual or automatic return function for returning the interrupted load current. Furthermore, it aims at making it possible to cope with overheating.

(1) The overvoltage / overcurrent protection circuit according to claim 1 is connected in reverse polarity in series, inserted into the load current path, and controlled in conjunction with the potential of one end of the fifth switching element, and the second switching element. Elements,
A first Zener for detecting a positive overvoltage generated on the load side of the load current path and a second Zener for detecting a negative overvoltage;
A third switching element that conducts when an overvoltage exceeds a Zener voltage of the first Zener, and a fourth switching element that conducts when an Zener voltage exceeds the second Zener voltage;
The fifth switching element that is conductive by conduction of the third or fourth switching element and grounded at one end;
When the overvoltage occurs, the current flowing through the third switching element that conducts and the one end of the fifth switching element is grounded, so that the first and second switching elements become non-conducting and the voltage of the load current path When the voltage drop is newly generated, the voltage applied to the first Zener is reduced to be less than the Zener voltage, whereby the third switching element is turned off, the fifth switching element is turned off, and one end of the fifth switching element is Due to the negative feedback operation in which the first and second switching elements are turned on and conducted through the load current path by being released from the ground, a voltage that can pass through the load current path by the Zener voltage of the first Zener is Controlled by the Zener voltage of the Zener,
At the time of the overvoltage, the first and second switching elements become non-conductive toward the non-conducting state due to the current flowing through the fourth switching element that is turned on and one end of the fifth switching element is grounded. When a voltage drop is newly generated, the voltage applied to the second Zener is reduced to be less than the Zener voltage, whereby the fourth switching element is turned off, the fifth switching element is turned off, and one end of the fifth switching element is The voltage that can pass through the load current path by the Zener voltage of the second Zener is reduced by the negative feedback operation in which the first and second switching elements are turned on and conducted through the load current path. It is controlled by the Zener voltage of the Zener.

(2) The overvoltage overcurrent protection circuit according to claim 2 is connected in reverse polarity in series, inserted into the load current path, and controlled in conjunction with the potential of one end of the fifth switching element, and the second switching element Elements,
A first Zener for detecting a positive overvoltage generated on the input side of the load current path and a second Zener for detecting a negative overvoltage;
A third switching element that conducts when an overvoltage exceeds a Zener voltage of the first Zener, and a fourth switching element that conducts when an Zener voltage exceeds the second Zener voltage;
The fifth switching element that is conductive by conduction of the third or fourth switching element and grounded at one end;
When the overvoltage occurs, the first and second switching elements become non-conductive by being conducted by a current flowing through the third switching element that is conducting and grounding one end of the fifth switching element.
When the overvoltage occurs, the first and second switching elements become non-conductive because the first switching element and the fifth switching element are grounded by the current flowing through the fourth switching element that is conducting, and the voltage is supplied to the load. It is characterized by blocking.

(3) The overvoltage overcurrent protection circuit according to claim 3 is connected in reverse polarity in series, inserted into the load current path, and controlled in conjunction with the potential of one end of the fifth switching element, and the second switching element Elements,
A first Zener for detecting a positive overvoltage generated on the load side of the load current path and a second Zener for detecting a negative overvoltage;
A third switching element that conducts when an overvoltage exceeds a Zener voltage of the first Zener, and a fourth switching element that conducts when an Zener voltage exceeds the second Zener voltage;
The fifth switching element that is conductive by conduction of the fourth switching element and grounded at one end,
When the overvoltage is applied, one end of the third switching element that conducts is grounded, so that the first and second switching elements become non-conducting and a voltage drop in the load current path newly occurs, thereby causing the first Zener The third switching element is turned off by lowering the applied voltage to less than the Zener voltage, one end of the third switching element is released to ground, and the first and second switching elements are turned on and the load current path is passed through. Due to the conducting negative feedback operation, the voltage that can pass through the load current path by the Zener voltage of the first Zener is controlled to the Zener voltage of the first Zener,
When the overvoltage occurs, the current flowing through the fourth switching element that is conducting is turned on and one end of the fifth switching element is grounded, so that the first and second switching elements become non-conductive and the voltage of the load current path When the voltage drop is newly generated, the voltage applied to the second Zener is reduced to be less than the Zener voltage, whereby the fourth switching element is turned off, the fifth switching element is turned off, and one end of the fifth switching element is The voltage that can pass through the load current path by the Zener voltage of the second Zener is reduced by the negative feedback operation in which the first and second switching elements are turned on and conducted through the load current path. It is controlled by the Zener voltage of the Zener.

(4) The overvoltage overcurrent protection circuit according to claim 4 is connected in reverse polarity in series, inserted into the load current path, and controlled in conjunction with the potential of one end of the fifth switching element, and the second switching element Elements,
A first Zener for detecting a positive overvoltage generated on the input side of the load current path and a second Zener for detecting a negative overvoltage;
A third switching element that conducts when an overvoltage exceeds a Zener voltage of the first Zener, and a fourth switching element that conducts when an Zener voltage exceeds the second Zener voltage;
The fifth switching element that is conductive by conduction of the fourth switching element and grounded at one end,
When one end of the third switching element that conducts at the time of the overvoltage is grounded, the first and second switching elements become non-conducting,
When the overvoltage occurs, the first and second switching elements become non-conductive because the first switching element and the fifth switching element are grounded by the current flowing through the fourth switching element that is conducting, and the voltage is supplied to the load. It is characterized by blocking.

(5) The overvoltage overcurrent protection circuit according to claim 5 is connected in series with reverse polarity and is arranged in the load current path and controlled in conjunction with the potential of one end of the sixth or seventh switching element. A switching element and a first resistance element connected in series to the load current path;
When the voltage between the terminals of the first resistance element is detected and the potential at one end of the first resistance element is higher than the potential at the other end, the sixth switching element that can conduct and the potential at one end of the first resistance element are other The seventh switching element capable of conducting when lower than the potential at the end, and
When an overcurrent flows through the load current path and the voltage across the first resistance element reaches a voltage that forward biases the control terminal of the sixth switching element and makes the sixth switching element conductive, the sixth One end of the switching element is grounded,
When an overcurrent flows through the load current path and the voltage across the first resistance element reaches a voltage that forward biases the control terminal of the seventh switching element and makes the seventh switching element conductive, the seventh When one end of the switching element is grounded, the first and second switching elements become non-conductive, and the current in the load current path is limited, so that the voltage drop of the first resistance element is reduced and the sixth or The seventh switching element is turned off, one end of the sixth or seventh switching element is released from the ground, and the first and second switching elements suppress the overcurrent by the negative feedback operation toward the conduction of the load current path, thereby reducing the load current. It is characterized by conducting.

(6) An overvoltage overcurrent protection circuit according to a sixth aspect of the present invention is the overvoltage overcurrent protection circuit according to any one of the first to fifth aspects, wherein the eighth switching element has one end connected to a DC power source,
A first rectifying element connected to one end of the fifth or sixth and seventh switching elements and connected in series; a second resistance element; and a capacitive element having one end connected to the other end of the eighth switching element;
A second rectifying element having one end connected to the other end of the eighth switching element;
A ninth switching element configured such that a DC voltage is applied to one end and the potential of the other end of the capacitive element can be transmitted to the control end; forward biasing from the other end of the ninth switching element to the control end is possible; A tenth switching element configured to be able to transmit a potential at one end of the capacitive element via the second rectifying element, and forward biased from the other end of the tenth switching element to the control end; Or an eleventh switching element configured to be able to transmit to one end of the sixth and seventh switching elements, and the other end having a ground potential,
When one end of the fifth, sixth, or seventh switching element is grounded, the capacitor element is charged by the current path formed by the first rectifying element, the second resistance element, the capacitor element, and the eighth switching element. And after the elapse of time based on the time constant of the second resistive element and the capacitive element, the control terminal of the ninth switching element is forward-biased, whereby the ninth switching element becomes conductive and the tenth and tenth elements When the eleventh switching element is turned on, the second rectifying element is turned on, whereby the control end of the ninth switching element is further forward-biased, and the ninth, tenth and eleventh switching elements are kept conductive and the fifth switching element is turned on. Alternatively, one end of each of the sixth and seventh switching elements is held at ground, and the first and second switching elements are cut off and held.

(7) The overvoltage overcurrent protection circuit according to claim 7 is the overvoltage overcurrent protection circuit according to claim 6, further comprising a switch element between one end of the eighth switching element and the other end of the capacitive element, and conducting the switch element. To discharge the electric charge of the capacitive element through one end of the tenth switching element, and reverse-bias the control end of the ninth switching element to cut off the conduction of the tenth and eleventh switching elements. The control terminal is forward-biased, and the capacitive element is discharged in the current path of the second resistance element, the first rectifying element, the fourth resistance element, and the eighth switching element to return to the initial state at the normal time. One end of the eleventh switching element is released from the ground, and the first and second switching elements are released from the cutoff state.

(8) An overvoltage overcurrent protection circuit according to an eighth aspect is the circuit according to any one of the first to fifth aspects, wherein the overvoltage overcurrent protection circuit is provided between one end of the fifth or sixth and seventh switching elements and the other end of the capacitive element. A third resistance element connected;
A third rectifying element connected between a connection point of one end of the fifth or sixth and seventh switching elements and one end of the eleventh switching element;
A fifth resistance element connected to one end of the eleventh switching element and capable of forward-biasing the control ends of the first switching element and the second switching element by the DC power supply;
In a state where one end of the fifth, sixth or seventh switching element is held at ground,
When one end of each of the fifth, sixth, and seventh switching elements is released from the ground, the third resistance element, the capacitive element, and the second rectifying element are generated by a potential at one end of the fifth, sixth, or seventh switching element. The capacitor element is reversely charged in the current path formed by the tenth and eleventh switching elements, so that the ninth switching element after the passage of time based on the time constant of the third resistor element and the capacitor element. The control terminal is reverse-biased, and the ninth, tenth, and eleventh switching elements are turned off, so that one end of the eleventh switching element is released to ground, and the potential at the one end is restored, so that the first and second switching elements are restored. The control end of the element is forward-biased to release the cutoff holding of the first and second semiconductor elements.

(9) The overvoltage overcurrent protection circuit according to claim 9 is the overvoltage overcurrent protection circuit according to any one of claims 6 to 8, wherein one end is connected to the control end of the tenth switching element, and a DC voltage is applied to the other end and the control end. A twelfth switching element;
A temperature-sensitive element having one end connected to the control end of the twelfth switching element and the other end connected to the first and / or second switching element;
When the resistance value of the temperature sensitive element decreases, the twelfth switching element is turned on and the tenth switching element is turned on, whereby the tenth and eleventh switching elements are turned on and one end of the eleventh switching element is It is grounded, and the first and second switching elements are cut off and held.

(10) An overvoltage overcurrent protection circuit according to a tenth aspect of the present invention is the overvoltage overcurrent protection circuit according to the fifth aspect, wherein an overcurrent is detected using a current transformer instead of the first resistance element, and the sixth and / or seventh switching elements are It is characterized by on-off driving.

  In the overvoltage overcurrent protection circuit according to the present invention, as a basic component, a pair of first and second switching elements are inserted in a load current path, and the load voltage is controlled by controlling the conduction cutoff operation of these switching elements. / It is possible to keep the load current at a predetermined value or cut it off. The first and second switching elements are shared by a plurality of partial circuits that respectively realize the overvoltage suppression function, overcurrent suppression function, and overheat suppression function of the circuit, and contribute to simplification of the circuit. is doing.

The circuit according to claim 1 or 3 has an overvoltage suppression function for detecting an overvoltage and controlling a load current path based on the detection. As a circuit element that realizes an overvoltage suppression function, the first and second Zeners that detect positive and negative overvoltages generated on the load side of the load current path, respectively, and the first and second Zeners detect the overvoltages, respectively. The third switching element and the fourth switching element are provided which are electrically connected to each other. Furthermore, the 5th switching element by which conduction | electrical_connection interruption | blocking is controlled by the 3rd or 4th switching element is provided. These circuit elements detect the overvoltage and control the first and second switching elements corresponding thereto. That is, the first and second switching elements are controlled by the one-end potential of the fifth switching element.

  According to such a configuration, for example, when a positive overvoltage is detected by the first Zener and the third switching element is turned on, the fifth switching element is turned on and the potential at one end thereof is grounded. The first and second switching elements Since the voltage applied to the first Zener is lowered due to the non-conducting state, the third switching element is turned off, the one end potential of the fifth switching element is released to ground, and the first and second switching elements are brought into the conducting state. A negative feedback operation of heading is realized. This negative feedback operation sets the load voltage to a constant value. This means that this circuit blocks only the difference between the overvoltage and the normal voltage. As a result, the load current is not momentarily interrupted when an overvoltage is applied, and an appropriate load current is maintained, thereby avoiding an adverse effect on the load. In the case of a negative overvoltage, the same negative feedback operation is performed.

The circuit according to claim 2 or 4 also has an overvoltage suppression function for detecting an overvoltage and controlling a load current path based on the detection. The circuit element for realizing the overvoltage suppression function is the same as that of the circuit of claim 1, but the negative feedback operation is not performed. Therefore, when the one end potential of the fifth switching element is grounded, the first and second switching elements are brought into a non-conductive state, the load current is immediately cut off, and the voltage supply to the load is also cut off at the same time. This circuit can be used when there is no harmful effect even if there is an instantaneous interruption of the load current. When the overvoltage disappears, the load current is supplied immediately.

The circuit according to claim 5 has an overcurrent suppression function for detecting an overcurrent and controlling a load current path based on the detection. As a circuit element for realizing the overcurrent suppression function, the first resistance element connected in series to the load current path, the one end potential of the first resistance element or the other end potential is high, and the voltage between the terminals is a forward bias voltage. The sixth and seventh switching elements are connected to each other and the potential is grounded at one end.
These circuit elements perform detection of overcurrent and control of the first and second switching elements corresponding thereto. That is, the first and second switching elements are controlled by the one end potential of the sixth switching element for the positive current and by the one end potential of the seventh switching element for the negative current.

  According to such a configuration, for example, when a positive overcurrent is detected by the first resistance element, the sixth switching element is turned on, the potential at one end thereof is grounded, and the first and second switching elements are turned off. The negative feedback operation in which the voltage between the terminals of the first resistance element is reduced by turning to the state, the sixth switching element is turned off, the potential at one end thereof is released to ground, and the first and second switching elements are turned on. Realized. This negative feedback operation sets the load current to a constant value. This means that only the difference between overcurrent and normal current is cut off by this circuit. As a result, when an overcurrent flows, the load current is not momentarily interrupted, and an appropriate load current is maintained, thereby avoiding an adverse effect on the load. For example, even when the inrush current at the time of power-on is large in a rectifying load such as a server, it is possible to avoid inability to start the load device. In the case of a negative overcurrent, the same negative feedback operation is performed.

The circuit according to claim 6 has a timer function, the timer is started from the time when the overvoltage detection function or the overcurrent detection function is activated, and the load current is completely cut off after a predetermined time has elapsed. . Therefore, an appropriate load current flows through the load for a certain period of time after the overvoltage or overcurrent occurs, but if the overvoltage or overcurrent continues beyond this certain period of time, the load current can be cut off and Prevents harmful effects caused by continuation and reduces the load and load on this circuit.

  In the circuit of claim 6, for example, a first rectifying element, a second resistance element, and a capacitive element are sequentially connected in series to one end of the fifth switching element in the overvoltage detection function, and one end of the capacitive element is It is connected to an eighth switching element having one end connected to the DC power supply. Therefore, when the potential of one end of the fifth switching element is grounded, a current flows from the DC power source to the eighth switching element, the capacitive element, the second resistive element, and the first rectifying element, whereby charging of the capacitive element is started. The

  The time based on the time constant of charging corresponds to the timer operating period, and can be set by the second resistance element and the capacitive element. During the timer operation period, even if an overvoltage continues to be applied, the overvoltage suppression function (overvoltage suppression according to claim 1 or 3) operates, and the load current is not interrupted. In the case of overvoltage suppression according to claim 2 or 4, there is an instantaneous interruption of the load current.

  Further, since the ninth switching element to which a DC voltage is applied to one end is controlled by the other end potential of the capacitive element, it is forward-biased by the other end potential of the charged capacitive element after the time based on the above time constant. And the ninth switching element becomes conductive.

  Further, since the tenth switching element controlled by the other end potential of the ninth switching element and the eleventh switching element controlled by the other end potential of the tenth switching element are provided, the tenth and eleventh switching elements are provided. Both elements are turned on at the same time as the ninth switching element is turned on.

  One end potential of the capacitive element is applied to one end of the tenth switching element via a second rectifier element connected to the other end of the eighth switching element. Therefore, when the tenth and eleventh switching elements are turned on, the second rectifier element is turned on, so that the other end potential shifts further deeply forward biasing the ninth switching element via the one end potential of the capacitive element. As a result, the conduction state of the ninth, tenth and eleventh switching elements can be maintained.

Furthermore, since the eleventh switching element can transmit the potential at one end to one end of the fifth switching element and the other end is at the ground potential, if the conduction state of the eleventh switching element is maintained, One end holds the ground potential. As a result, the first and second switching elements are held in the cut-off state, the load current is cut off, and the state is held.
In the circuit according to the sixth aspect, the same timer operation and shut-off holding operation are also performed when the one end potentials of the sixth and seventh switching elements in the overcurrent detection function are grounded.

The circuit according to claim 7 is obtained by adding a manual return function to the timer function of the circuit according to claim 6. By adding this manual return function, it is possible to easily return to the normal initial state at a desired point in time after the circuit enters the cut-off holding state.
The switch element for manual return is provided between one end of the eighth switching element and the other end of the capacitive element. When the switch element is turned on, the capacitive element is reversely charged by the DC power source, the ninth switching element is reverse-biased by the potential at the other end of the capacitive element and shut off, and then the tenth and eleventh switching elements are also shut off. The eighth switching element is conductive. Thereby, current flows from the capacitive element to the second resistive element, the first rectifying element, the fourth resistive element, and the eighth switching element, and the capacitive element is discharged. Thereby, this circuit can return to the normal initial state, and the first and second switching elements can be released from the cut-off holding state by releasing the one end potential of the eleventh switching element from the ground.

The circuit according to claim 8 has a timer function to which an automatic return function is added. By adding this automatic return function, it is possible to automatically return to the normal initial state without the need for manual operation after the circuit enters the cut-off holding state.
As a circuit element for the automatic return function, a third resistance element is further connected between one end of the fifth or sixth and seventh switching elements and the other end of the capacitive element. In addition, one end of the fifth or sixth and seventh switching elements is connected to the other end of the third rectifying element having one end connected to one end of the eleventh switching element. Further, an eighth resistance element connected to one end of the eleventh switching element and capable of forward biasing the control ends of the first and second switching elements by a DC power supply is provided.
According to such a configuration, it is assumed that after one end of the fifth, sixth, or seventh switching element is grounded, one end of all of these switching elements is released from grounding. At this time, a current flows to the third resistor element, the capacitor element, the second rectifier element, the tenth and eleventh switching elements due to the one-end potential of the fifth or sixth and seventh switching elements, and the capacitor elements are reversely charged. .

  The time based on the time constant of charging corresponds to the automatic recovery period, and can be set by the third resistance element (having a resistance value that is more dominant than the fourth resistance element (R6)) and the capacitance element. More precisely, this time constant is approximately the capacitance value of the capacitive element × (the third resistance element + the resistance value of the fourth resistance element). During the automatic recovery period, even if one end of the fifth, sixth and seventh switching elements is released from the ground, one end of the eleventh switching element is in the ground holding state, and therefore the first and second switching elements are also forward biased. It remains in the shut-off holding state.

  The ninth switching element controlled by the other end potential of the capacitive element is reverse-biased by the other end potential of the reversely charged capacitive element after the time based on the time constant, and the ninth switching element is turned off. The eleventh switching element is also turned off. As a result, one end of the eleventh switching element is released from grounding. As a result, the first and second switching elements are forward-biased via the eighth resistance element, thereby releasing the cutoff holding state.

The circuit according to claim 9 has an overheat suppression function that performs overheat detection and control of the load current path based on the detection, and a part of the circuit configuration of the timer function for controlling the load current path is provided. Use. This prevents damage due to overheating of the circuit elements and contributes to simplification of the circuit.
As a circuit element for realizing the overheat suppression function, a twelfth switching element having one end connected to the control end of the tenth switching element of the timer circuit and a DC voltage applied to the other end and the control end, and the first and / or second A temperature sensitive element temperature-coupled to the switching element, one end of the temperature sensitive element being a control end of the twelfth switching element and the other end being a ground potential.

  In such a configuration, when the resistance of the temperature sensitive element decreases (when overheated), the twelfth switching element is turned on and the tenth switching element is turned on, whereby the tenth and eleventh switching elements are turned on. As a result, the one end potential of the eleventh switching element is grounded, and the first and second switching elements are shut off. This cut-off state is maintained until the twelfth switching element is cut off.

The circuit according to claim 10 uses a current transformer in place of the first resistance element for overcurrent detection in the overcurrent suppression function according to claim 5. Thereby, compared with the case where a resistive element is used, a voltage drop and power loss can be reduced.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, in order to clarify the correspondence between each element in this circuit and the constituent elements in the claims, the names in the claims are attached in parentheses after the names of the elements in various places.

(1) First Embodiment (1-1) Overall Configuration of Circuit and Normal Operation <Overall Configuration of Entire Circuit>
FIG. 1 is a circuit diagram showing an example of a first embodiment of an overvoltage overcurrent protection circuit of the present invention. This circuit is a circuit inserted between an AC power supply and a load. The input terminals on the AC power supply side of this circuit are referred to as terminals 1 and 2, and the output terminals on the load side are referred to as terminals 3 and 4. The load current paths are between the terminals 1 and 3 and between the terminals 2 and 4 respectively. This circuit includes, in addition to an input unit 10 having a general noise removal and overvoltage protection element and an output unit 11 having a general overvoltage protection element, an overvoltage suppression unit 12 and an overcurrent which are main parts of the present invention. A suppression unit 13, a timer unit 14, an overheat suppression unit 15, a field effect transistor (hereinafter referred to as “FET”) Q 1 and FET Q 2, and a buffer amplifier 16 are provided.

  In the input unit 10, a common mode transformer is connected to the terminals 1 and 2 of the AC power supply via a fuse, and cancels the common-mode noise input to the terminals 1 and 2, respectively. The triac TRi and the pair of zener diodes ZD in the input unit 10 operate against an overvoltage that is much higher (for example, about twice) than the target overvoltage of the overvoltage suppression unit 12 according to the present invention. In addition, a capacitor and a varistor are connected in parallel between the terminal 3 and the terminal 4 in the output unit 11 to protect the load from overvoltage. The configurations of the input unit 10 and the output unit 11 are general and are not essential elements of the present invention.

  The FET Q1 (first switching element) and the FET Q2 (second switching element) are connected in series reverse polarity and are inserted in the load current path between the terminal 1 and the terminal 3. The drain of the FET Q1 is connected to the terminal 1 side, the drain of the FET Q2 is connected to the terminal 3 side, and the sources of the FET Q1 and the FET Q2 are connected via the resistor R1, and the gates of the FET Q1 and the FET Q2 Connected to the end.

  In addition, regarding the overvoltage suppression unit 12, the overcurrent suppression unit 13, the timer unit 14, the overheat suppression unit 15 and the buffer amplifier 16 of the present invention, the load current path of the terminal 3 line in which the FETQ1 and the FETQ2 are inserted is used as the ground potential point. . In this case, the voltage drop due to the resistor R1 can be ignored.

  The buffer amplifier 16 is an emitter follower buffer amplifier including a transistor Q3 which is an npn type bipolar transistor and a transistor Q4 which is a pnp type bipolar transistor. The collector of the transistor Q3 is connected to the DC power source + Vcc, and the collector of the transistor Q4 is connected to the ground potential point on the load current path. The connection point between the bases of the transistors Q3 and Q4 is the input terminal of the buffer amplifier 16, that is, the point C. The connection point between the emitters of the transistors Q3 and Q4 is the output terminal of the buffer amplifier, and is connected to the gates of the FETs Q1 and Q2. The buffer amplifier 16 controls the gates of the FET Q1 and the FET Q2 by the potential at the point C.

  The point C is connected to the DC power source + Vcc through the resistor R6. The point C is also connected to each collector which is one end of a transistor Q9 (fifth switching element) of the overvoltage suppressing unit 12 and transistors Q5 and Q6 (sixth and seventh switching element) of the overcurrent suppressing unit 13, which will be described later. Yes. The point C is also connected to a collector which is one end of a transistor Q13 (an eleventh switching element) of a timer unit described later.

<Normal circuit operation>
First, the normal operation of the entire circuit will be described. Under normal conditions, all transistors Q9, Q5, Q6 and Q13 connected to the point C are off (non-conducting or cut off). Therefore, the potential of the DC power source + Vcc (hereinafter referred to as “high potential”) is applied to the point C via the resistor R6. Thus, transistor Q3 is forward biased and on (conducting), while transistor Q4 is reverse biased and off.

  At this time, since the emitters of the transistors Q3 and Q4 are held at a high potential, the gates of the FETs Q1 and Q2 (first and second switching elements) are held at an on potential. Therefore, FETQ1 and FETQ2 are kept on.

  When the FETs Q1 and Q2 are in the ON state, the conduction state of the load current path is ensured, so that the voltage of the AC power supply is applied to the load, and a normal load current flows.

(1-2) Configuration and operation of overvoltage suppression unit <Configuration>
In the overvoltage suppressing unit 12, a Zener diode Z1 (first Zener), a Zener diode Z2 (second Zener), and appropriate resistors R9 and R10 are provided between the terminals 3 and 4 on the drain side of the FET Q2, that is, the load side. Are connected in series. The two Zener diodes Z1 and Z2 are connected so as to have opposite polarities. That is, the Zener diode Z1 is connected with the cathode on the terminal 3 side and the anode on the terminal 4 side, while the Zener diode Z2 is connected with the cathode on the terminal 4 side and the anode on the terminal 3 side. The resistor R9 is connected between the Zener diode Z1 and the terminal 3, and the resistor R10 is connected between the Zener diode Z2 and the terminal 4.

  The overvoltage suppression unit 12 further includes an npn bipolar transistor Q7 (third switching element), a pnp bipolar transistor Q8 (fourth switching element), and an npn bipolar transistor Q9 (fifth switching element). Element).

  The base of the transistor Q7 is connected to the connection point between the Zener diode Z2 and the resistor R10, the collector is connected to the emitter of the transistor Q9 via the resistor R17 and the diode D17, and the emitter is connected to the terminal 4.

  The base of the transistor Q8 is connected to the connection point of the Zener diode Z2 and the resistor R10, the collector is connected to the base of the transistor Q9 via the resistor R18 and the diode D18, and the emitter is connected to the terminal 4.

  The base of the transistor Q9 is connected to the point A (one end of the resistor R1) on the load current path via the resistor R5, the collector is connected to the point C, and the emitter is connected to the point A via the diode D3. The emitter of the transistor Q9 is also connected to the collector of the transistor Q7 via a resistor R17 and a diode D17.

<Operation: Positive overvoltage>
First, an overvoltage suppression operation when a positive overvoltage (positive overvoltage) is applied to the terminal 3 line with the terminal 4 line as a reference potential will be described.
In this case, when a voltage exceeding the Zener voltage is applied to the Zener diode Z1 (first Zener), the Zener diode Z1 becomes conductive. As a result, a current flows through the resistor R10, the base of the transistor Q7 is forward-biased, and the transistor Q7 (third switching element) is turned on. At this time, the current path is as follows: terminal 3 line → resistor R9 → zener diode Z1 → zener diode Z2 → transistor Q7 (base → emitter) → terminal 4 line.

  When the transistor Q7 is turned on, the emitter potential of the transistor Q9 (fifth switching element) is substantially lowered to the potential of the terminal 4. At the same time, since the base of the transistor Q9 is forward-biased through the resistor R5, the transistor Q9 is turned on. The current path at this time is point A → resistance R5 → transistor Q9 (base → emitter) → transistor Q7 (collector → emitter) → terminal 4 line.

  The potential at the point C is normally high as described above, but when the transistor Q9 is turned on, the potential at the point C is grounded via the transistor Q9 and the diode D3. The current path at this time is point C → transistor Q9 (collector → emitter) → transistor Q7 (collector → emitter) → terminal 4 line.

  When the point C becomes the ground potential, the FETs Q1 and Q2 go to the off state (non-conducting state) by the control through the buffer amplifier 16, but here, the negative feedback operation unique to this circuit works as follows. Transistor Q3 is reverse biased and tends to turn off, while transistor Q4 is forward biased and tends to turn on. As a result, the emitters of the transistors Q3 and Q4 are directed to the ground potential, and the gates of the FETs Q1 and Q2 (first and second switching elements) are directed to the off potential.

  Thereby, FETQ1 and FETQ2 go to an OFF state (non-conduction state). As a result, a new voltage drop occurs between the terminal 1 and the terminal 3, so that the voltage applied to the Zener diode Z1 becomes equal to or lower than the Zener voltage and becomes non-conductive. As a result, the transistors Q7 and Q9 are turned off, and the point C is released from the ground and becomes a high potential.

  When the point C becomes a high potential, the FETs Q1 and Q2 are turned on (conductive state) by the control through the buffer amplifier 16. As a result, the voltage on the terminal 3 side increases. By this negative feedback operation, the voltage between the terminals 3 and 4 is balanced at a constant voltage (in this case, the Zener voltage of the Zener diode Z1). Since this negative feedback operation is performed instantaneously, it immediately balances to a constant voltage at the time of transition from the normal voltage to the overvoltage, and the constant voltage is maintained as long as the overvoltage continues. Therefore, in this circuit, only the difference between the normal voltage and the overvoltage is suppressed, and an appropriate current continues to be supplied to the load. That is, even if an overvoltage is applied, the load current is not immediately cut off.

  As another circuit example (not shown) having the same operation as this, the other end of the resistor R17 having one end connected to the anode of the diode D17 is connected to the point C (that is, connected to the emitter of the transistor Q9). The other end of the resistor R17 is changed to the point C), and a circuit in which the diode D3 connected between the emitter of the transistor Q9 and the point A is made through (short-circuited) can be configured. Also in this case, when a positive overvoltage is applied, the transistor Q7 is turned on, so that the point C can be set to a low potential without using the transistor Q9, and the FETQ1 and the FETQ2 are turned off as described above. Overvoltage suppression is possible. The current for grounding at point C is point C → resistor R17 → diode D17 → transistor Q7 (collector → emitter).

<Operation: Negative overvoltage>
Next, an overvoltage suppression operation in the case where a negative overvoltage (negative overvoltage) is applied to the terminal 3 line with the terminal 4 line as a reference potential will be described.
In this case, when a voltage exceeding the Zener voltage is applied to the Zener diode Z2 (second Zener), the Zener diode Z2 becomes conductive. As a result, a current flows through the resistor R10, the base of the transistor Q8 is forward-biased, and the transistor Q8 (fourth switching element) is turned on. The current path at this time is: terminal 4 line → transistor Q8 (emitter → base) → zener diode Z2 → zener diode Z1 → resistor R9 → terminal 3 line.

  When the transistor Q8 is turned on, the potential of the terminal 4 is applied to the base of the transistor Q9 (fifth switching element). On the other hand, since the emitter of the transistor Q9 has a potential of approximately point A via the diode D3, the transistor Q9 is turned on by being forward-biased. The current path at this time is terminal 4 line → transistor Q8 (emitter → collector) → transistor Q9 (base → emitter) → diode D3 → point A.

  The potential at the point C is normally high as described above, but when the transistor Q9 is turned on, the potential at the point C is grounded via the transistor Q9 and the diode D3. The current path at this time is point C → transistor Q9 (collector → emitter) → diode D3 → point A.

  The subsequent operation is the same as in the case of positive overvoltage. That is, the negative feedback operation balances the voltage between the terminal 3 and the terminal 4 with a constant voltage (in this case, the Zener voltage of the Zener diode Z2).

(1-3) Configuration and operation of overcurrent suppression unit <Configuration>
In the overcurrent suppression unit 13, a resistor R1 (first resistance element) is connected in series to the load current path. One end of the resistor connected to the input terminal 1 side is a point A, and the other end is a point B. The overcurrent suppression unit 13 further includes a transistor Q5 (sixth switching element) that is an npn-type bipolar transistor and a transistor Q6 (seventh switching element) that is an npn-type bipolar transistor.

  The base of the transistor Q5 is connected to the point A through the base resistance, the collector is connected to the point C, and the emitter is connected to the point B through an appropriate resistance.

  The base of the transistor Q6 is connected to the point B through the base resistance, the collector is connected to the point C, and the emitter is connected to the point A.

  A current transformer may be provided instead of the resistor R1. In that case, the primary side of the current transformer is magnetically coupled to the load current path so that the potential of one end of the secondary side is applied to the base of the transistor Q5, and the potential of the other end of the secondary side is applied to the base of the transistor Q6. To be applied. At this time, the transistor Q5 is forward biased when the potential at one end of the secondary side becomes a high potential, and the transistor Q6 is forward biased when the potential at the other end of the secondary side becomes a high potential.

<Operation: Positive overcurrent>
First, an overcurrent suppression operation when an overcurrent (positive overcurrent) flows from the point A to the point B in the resistor R1 will be described.
At this time, the voltage between the terminals of the resistor R1 is such that the potential at the point A is higher than the potential at the point B. Further, since the inter-terminal voltage Vab = current I × resistance R1, the transistor Q5 is turned on and the collector current flows when the inter-terminal voltage exceeds the forward bias voltage (about 0.6 V) of the base of the transistor Q5.

  The potential at the point C is normally high as described above, but when the transistor Q5 is turned on, the potential at the point C is grounded through the transistor Q5.

  When the point C becomes the ground potential, the FET Q1 and the FET Q2 are turned off by the control via the buffer amplifier 16, but the negative feedback operation unique to this circuit works as follows. Transistor Q3 is reverse biased and tends to turn off, while transistor Q4 is forward biased and tends to turn on. As a result, the emitters of the transistors Q3 and Q4 are directed to the ground potential, and the gates of the FETs Q1 and Q2 (first and second switching elements) are directed to the off potential.

  Thereby, FETQ1 and FETQ2 go to an OFF state (non-conduction state). As a result, the current on the load current path decreases, the voltage across the resistor R1 decreases, and becomes equal to or lower than the forward bias voltage of the transistor Q5. As a result, the transistor Q5 is turned off, and the point C is released from the ground and becomes a high potential.

  When the point C becomes a high potential, the FETs Q1 and Q2 are turned on (conductive state) by the control through the buffer amplifier 16. As a result, the current on the load current path increases. By this negative feedback operation, the load current is balanced with a constant current (in this case, the current when the transistor Q5 is forward biased). Since this negative feedback operation is performed instantaneously, it immediately balances to a constant current when it shifts from a normal current to an overcurrent, and the constant current is maintained as long as the overcurrent continues. Therefore, in this circuit, only the difference between the normal current and the overcurrent is suppressed, and an appropriate current continues to be supplied to the load. That is, even if an overcurrent is applied, the load current is not immediately interrupted.

<Operation: Negative current overload>
Next, an overcurrent suppression operation in the case where an overcurrent (negative overcurrent) flows from the point B to the point A in the resistor R1 will be described.
At this time, the voltage between the terminals of the resistor R1 is such that the potential at the point B is higher than the potential at the point A. When the inter-terminal voltage exceeds the forward bias voltage at the base of the transistor Q6, the transistor Q6 is turned on and a collector current flows.

  The potential at the point C is normally high as described above, but when the transistor Q6 is turned on, the potential at the point C is grounded through the transistor Q6.

  The subsequent operation is the same as in the case of positive overcurrent. That is, due to the negative feedback operation, the load current is balanced with a constant current (in this case, the current when the transistor Q6 is forward biased).

(1-4) Configuration and operation of timer unit <Configuration>
The timer unit 14 includes a transistor Q10 (eighth switching element) that is an npn-type bipolar transistor. The collector of the transistor Q10 is connected to the DC power source + Vcc, and the base is also connected to the DC power source + Vcc via the resistor R4.

  Furthermore, a diode D1 (first rectifier element), a resistor R2 (second resistor element), and a capacitor C1 (capacitor element) connected in series to the point C (the collector of the transistor Q9 or Q5 and Q6). The diode D1 has a cathode connected to the point C and an anode connected to the resistor R2. A point D, which is one end of the capacitor C1, is connected to the emitter of the transistor Q10.

  Further, the timer unit 14 includes a diode D2 (second rectifying element), and has an anode connected to the emitter of the transistor Q10 and a cathode connected to the base of the transistor Q10.

  Further, the timer unit 14 includes a transistor Q11 (ninth switching element) that is a pnp bipolar transistor, a transistor Q12 (tenth switching element) that is an npn bipolar transistor, and a transistor Q13 (eleventh switching element) that is an npn bipolar transistor. ).

  The transistor Q11 has a base connected to a point E that is the other end of the capacitor C1, an emitter connected to the DC power source + Vcc via a diode D5 and a resistor R3, and a collector connected to the base of the transistor Q12.

  Transistor Q12 has a base connected to the collector of transistor Q11, a collector connected to the cathode of diode D2, and an emitter connected to the base of transistor Q13.

  The base of transistor Q13 is connected to the emitter of transistor Q12, the collector is connected to point C (the collector of transistor Q9 or Q5 and Q6), and the emitter is grounded. Transistors Q12 and Q13 are Darlington connected.

  Further, a reset switch RS (switch element) is connected between the collector of the transistor Q10 and the point E which is the other end of the capacitor C1.

  Further, a resistor R6 (fourth resistor element) is connected between the collector of the transistor Q10 and the cathode of the diode D1. The collector of the transistor Q10 is connected to a DC power supply, and the base is forward biased by a resistor R4.

  Further, a resistor R7 (third resistance element) is connected between the point C and the point E which is the other end of the capacitor C1.

<Operation: Normal>
When normal, the potential at point C is high as described above. At this time, the transistor Q10 is in the ON state because the DC power supply + Vcc is applied to the collector and the DC power supply + Vcc forward biases the base via the resistor R4. However, since the emitter potential is a high potential at the point C via the resistor R7, no current flows. The capacitor C1 is also in an initial state (uncharged), but is not charged because no voltage is generated between both ends. That is, the timer is not operating.

<Operation: Overvoltage or overcurrent>
At the time of overvoltage or overcurrent, the collector of the transistor Q9, Q5 or Q6 (fifth, sixth or seventh switching element) is grounded, and the point C becomes the ground potential. As a result, the potential at point E drops and current starts to flow through transistor Q10 (eighth switching element), and charging of capacitor C1 (capacitance element) is started. The current path at this time is DC power supply + Vcc → transistor Q10 (collector → emitter) → capacitor C1 → resistance R2 → diode D1 → point C → transistor Q9 (collector → emitter → diode D3), Q5 or Q6 (collector → emitter) → Point A

  The time constant at this time is determined by capacitor C1 × resistor R2. Note that the resistance R7 is sufficiently larger than the resistance R2. The time constant is 200 ms, for example, and this corresponds to the timer operation period. During the timer operation period, the overvoltage suppression unit and the overcurrent suppression unit operate as described above. If overvoltage and overcurrent conditions are eliminated during this time and the collectors of transistors Q9, Q5 and Q6 are all grounded, point C returns to a high potential and returns to normal operation. The timer unit 14 also returns to the initial state.

  When the overvoltage or overcurrent state continues, the capacitor C1 is charged, and the potential at the point E drops toward the potential at the point C (ground potential). When the timer operation period corresponding to the time constant has elapsed, the potential at the point E forward biases the base of the transistor Q11 (the ninth switching element), and the transistor Q11 is turned on.

  When transistor Q11 is turned on and collector current flows, this current flows to the Darlington circuit formed by transistors Q12 and Q13 (tenth and eleventh switching elements), and transistors Q12 and Q13 are turned on. As a result, the capacitor C1 starts to discharge via the diode D2 (second rectifying element). The current path at this time is point D of capacitor C1 → diode D2 → transistor Q12 (collector → emitter) → transistor Q13 (base → emitter) → ground point (point A).

  When a discharge current flows through this current path, the potential at the point D (the positive side of the capacitor C1) that is one end of the capacitor C1 becomes substantially the ground potential, and at the same time, the potential at the point E that is the other end of the capacitor C1 drops further deeply. To do. As a result, the transistor Q11 is further forward-biased, and the transistors Q12 and Q13 are similarly enhanced in the ON state. By this positive feedback operation, the potential dropped deeply at the point E is held as it is, and the transistors Q11, Q12, and Q13 are locked in the on state (hereinafter referred to as “on-lock state”). As a result, the potential at the point C connected to the collector of the transistor Q13 is held at the ground potential. That is, FETQ1 and FETQ2 are kept off, and the load current path remains cut off.

  After the timer operation time has elapsed and the on-lock state is established, the circuit does not return to the normal state even if the overvoltage and overcurrent are eliminated (that is, the collectors of the transistors Q9, Q5, and Q6 are released to ground). As a result, it is possible to avoid an adverse effect caused by the overvoltage or overcurrent state lasting for a certain period of time.

  When the diode D2 is turned on, as described above, the base of the transistor Q10 becomes the ground potential and is reverse-biased, so that the transistor Q10 is turned off.

  Here, with reference to FIG. 2, the circuit operation of the timer unit 14 after the on-lock state is set will be supplementarily described. FIG. 2 is a circuit diagram equivalently showing the timer unit 14 in the on-lock state. Transistors Q12 and Q13 are equivalently shown as short circuits or PN junction elements. Since transistor Q10 is turned off, the charging path of capacitor C1 through transistor Q10 is cut off. Further, the capacitor C1 has a current path of DC power source + Vcc → resistor R3 → diode D5 → transistor Q11 (emitter → base) → resistor R2 → diode D1 → point C → transistor Q13 (collector → emitter) → ground point (point A). Reverse charged. However, this reverse charging does not increase the potential at point E. This is because the value of the resistor R2 becomes substantially 1 / hfe of the current amplification factor hfe due to the current amplification effect of the transistor Q11. Therefore, the point E is equivalent to being almost grounded. As a result, since the emitter of the transistor Q11 is at a high potential, the base of the transistor Q11 is maintained in the forward bias state.

<Operation: Manual return>
With reference to FIG. 1 again, the operation of the timer unit 14 at the time of manual return will be described.
When the reset switch RS is pushed and made conductive in the on-lock state described above, a DC power source is connected to one end of the reset switch, so that a voltage of the DC power source + Vcc is applied to the point E of the capacitor C1. It is reverse charged. The current path at this time is DC power supply + Vcc → reset switch RS → capacitor C1 → diode D2 → transistor Q12 (collector → emitter) → transistor Q13 (base → emitter) → ground point (point A).

  The potential at the point E rises due to reverse charging of the capacitor C1, and the transistor Q11 is reverse biased and turned off, thereby turning off the transistors Q12 and Q13. When the collector of the transistor Q13 is released from the ground, the point C is released from the ground. As a result, the conduction of the load current path is restored.

  Further, since the transistor Q12 is turned off, the collector of Q12 is released from the ground, so that the transistor Q10 is forward biased again and turned on, and a current flows through the transistor Q10, whereby the reversely charged capacitor C1 is discharged. The current path at this time is capacitor C1 (point E) → resistor R2 → diode D1 → resistor R6 → transistor Q10 (collector → emitter) → capacitor C1 (point D). As a result, the timer unit returns to the initial state.

  This manual return operation is effective when the overvoltage and overcurrent are eliminated. That is, the point C is not grounded by the transistor Q9, Q5 or Q6 and is grounded only by the transistor Q13. Accordingly, the point C is released from the ground by turning off the transistor Q13.

  If the overvoltage or overcurrent is not eliminated, the point C is not released from the ground even when the transistor Q13 is turned off by the manual return operation.

  Even if an overcurrent flows due to the inrush current of the load device immediately after the manual return, the timer unit is activated again, so that the load current is not interrupted during the timer operation period. If the overcurrent due to the inrush current is eliminated during the timer operation period, the normal operation is performed thereafter.

(1-5) Overheat suppression part <Configuration>
The overheat suppression unit 15 includes a thermistor th (temperature sensitive element) that is temperature-coupled to the FET Q1 and / or the FET Q2, and a transistor Q14 (twelfth switching element) that is a pnp bipolar transistor. One end of the thermistor th is connected to the base of the transistor Q14, and the other end is grounded. The collector of the transistor Q14 is connected to the base of the transistor Q12 of the timer unit, and a DC voltage obtained from a DC power source + Vcc is applied to the emitter and the base.

<Operation>
When the temperature is normal, the base is reverse-biased by the divided voltage of the base bias resistor and the thermistor, and the transistor Q14 is turned off.
As the temperature rises, the resistance of the thermistor decreases. When the resistance value of the thermistor falls below a certain value, the base is forward biased and the transistor Q14 is turned on. When the transistor Q14 is turned on, a DC voltage from the DC power source + Vcc is applied to the emitter of the transistor Q14, and a collector current flows. As a result, the transistors Q12 and Q13 (the tenth and eleventh switching elements) are forward biased and turned on. When the transistor Q13 is turned on, the point C connected to its collector is grounded. Thereby, FETQ1 and FETQ2 are interrupted | blocked.

  When the transistors Q12 and Q13 are turned on, the transistor Q10 (eighth switching element) is reverse-biased and turned off. Therefore, the timer does not operate during the overheat suppression operation.

(2) Modification of First Embodiment <Configuration>
Although not shown, a modification of the embodiment shown in FIG. 1 will be described. This is a form in which there is no negative feedback operation in the overvoltage suppression unit 12. In the modification, the resistor R9 in the overvoltage suppressing unit 12 and the connection point G of the terminal 3 line are disconnected, and one end of the resistor R9 is connected to the drain side of the FET Q1. That is, the Zener diodes Z1 and Z2 are connected to the input side of the FET Q1. Other configurations are the same as those in the embodiment of FIG.

<Operation>
When the Zener diode Z1 (first Zener) detects an overvoltage, the transistor Q7 (third switching element) is turned on and the transistor Q9 (fifth switching element) is turned on. When the zener diode Z2 (second zener) detects an overvoltage, the transistor Q8 (fourth switching element) is turned on and the transistor Q9 (fifth switching element) is turned on. When the transistor Q9 is turned on, the point C becomes the ground potential.

  When the point C becomes the ground potential, the gates of the FET Q1 and the FET Q2 become the ground potential, and the FET Q1 and the FET Q2 are turned off. As a result, the load current of the terminal 3 line is immediately cut off. The voltage drop on the load side due to the load current interruption is not reflected in the applied voltage to the Zener diodes Z1 and Z2. Therefore, the negative feedback operation does not work.

  Also in this modified embodiment, the timer unit starts to operate when the point C becomes the ground potential. If the overvoltage is eliminated before the period corresponding to the time constant elapses, the circuit returns to a normal state. However, after the period corresponding to the time constant elapses, the transistor Q13 is turned on. C is held at ground. If the point C is held at the ground, the circuit will not recover even if the overvoltage is eliminated. In that case, it is manually reset by the reset switch RS.

(3) Second Embodiment <Configuration>
FIG. 3 is a circuit diagram showing an example of the second embodiment of the overvoltage overcurrent protection circuit of the present invention. In the second embodiment, the overvoltage suppression unit 12, the overcurrent suppression unit 13, the overheat suppression unit 15, the FETQ1 and the FETQ2, and the buffer amplifier 16 have the same configuration, but the configuration related to the timer unit 14 is different. An automatic return operation can be performed when the unit 14 is in a lock-on state.

  In the circuit of FIG. 3, the timer unit 14 is not provided with a manual reset switch. Further, between the point C which is the collector of the transistor Q9 (fifth switching element) and the transistors Q5 and Q6 (sixth and seventh switching element) and the point F which is the collector of the transistor Q13 (eleventh switching element). A diode D4 (third rectifying element) is connected. The diode D4 has an anode connected to the point F and a cathode connected to the point C. Point F is also the input point of buffer amplifier 16. The buffer amplifier 16 controls the gates of the FETQ1 and the FETQ2 (first and second switching elements).

  Further, the collector of the transistor Q13, that is, the point F is connected to the DC power source + Vcc through the resistor R8. Therefore, the resistor R8 can apply an ON voltage to the gates of the FETQ1 and the FETQ2.

<Operation: Normal, overvoltage and overvoltage>
The normal operation is the same as in the embodiment of FIG. 1, and both point C and point F are at a high potential.
The operation of the overvoltage suppression unit 12 at the time of overvoltage is the same as in the embodiment of FIG. 1, and when an overvoltage is detected, the transistor Q9 is turned on and the point C is grounded. Further, the operation of the overcurrent suppression unit 13 at the time of overcurrent is the same as that in the form of FIG. 1, and when the overcurrent is detected, the transistor Q5 or Q6 is turned on and the point C is grounded. At this time, the point F is also grounded through the diode D4.

  When the point C is grounded, the timer unit 14 operates in the same manner as in FIG. 1, the transistor Q13 is turned on, and the point F is held at the ground.

<Automatic return operation>
It is assumed that when the transistor Q13 is in the on-lock state and the point F is held at the ground, the overvoltage and the overcurrent are restored and the point C is restored to the high potential.
At this time, since the diode D4 has a reverse polarity with respect to the potential difference between the point C and the point F, the point F remains at the ground potential, and the FET Q1 and the FET Q2 are off, that is, the load current path is cut off.

  However, when the point C becomes high potential, current flows in the current path of DC power source + Vcc → resistor R6 → resistor R7 → capacitor C1 → diode D2 → transistor Q12 → transistor Q13 → ground point (point A), and the capacitor C1 Reverse charged. As a result, the potential at the point E, which is the other end of the capacitor C1, starts to rise. The time constant at this time is determined by capacitor C1 × (resistor R7 + resistor R6). The time constant is about several seconds, for example, and this corresponds to the automatic return period. After the automatic return period has elapsed, when the potential at point E rises to a constant value, the base of transistor Q11 is reverse-biased and turned off. When the transistor Q11 is turned off, the transistors Q12 and Q13 are also turned off, and the point F returns to a high potential. As a result, the on-voltage is applied to the gates of FETQ1 and FETQ2 via the buffer amplifier 16, and the FETQ1 and FETQ2 become conductive. Thus, the conduction of the load current path is restored.

  If an overvoltage or overcurrent occurs again during this automatic recovery period, the reverse charging current of the capacitor C1 does not flow because the point C is grounded. As a result, the potential at point E does not increase, and the on-lock state is not released. Accordingly, the conduction of the load current path is not restored.

  According to this automatic return operation, after the overvoltage suppression unit or overcurrent suppression unit is activated and the load current path is interrupted and held by the timer unit, the load current is automatically detected after an appropriate period of time without requiring manual operation. Road continuity is restored.

  The FET and bipolar transistor shown in the circuit example of the present invention are examples, and an N-channel FET may be used as a P-channel FET, an npn-type bipolar transistor as a pnp type, and a pnp-type bipolar transistor as an npn type. Is possible. In this case, it can be realized by reversing the polarity of the DC power supply and reversing the polarity of the diode.

It is a circuit diagram showing an example of a 1st embodiment of an overvoltage overcurrent protection circuit of the present invention. FIG. 2 is a circuit diagram equivalently showing a timer unit in an on-lock state in the circuit of FIG. 1. It is a circuit diagram which shows an example of 2nd Embodiment of the overvoltage overcurrent protection circuit of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Input part 11 Output part 12 Overvoltage suppression part 13 Overcurrent suppression part 14 Timer part 15 Overheat suppression part 16 Buffer amplifier Q1, Q2 FET (1st, 2nd switching element)
Q3, Q4 Bipolar transistor Q5, Q6 Bipolar transistor (6th, 7th switching element)
Q7, Q8 Bipolar transistor (3rd, 4th switching element)
Q9 Bipolar transistor (5th switching element)
Q10 Bipolar transistor (8th switching element)
Q11, Q12, Q13 Bipolar transistors (9th, 10th, 11th switching elements)
Q14 Bipolar transistor (12th switching element)
D1 to D5 Diode RS Reset switch th Thermistor Z1, Z2 Zener diode

Claims (10)

A first switching element and a second switching element which are connected in series with opposite polarity and inserted into the load current path and controlled in conjunction with the potential of one end of the fifth switching element;
A first Zener for detecting a positive overvoltage generated on the load side of the load current path and a second Zener for detecting a negative overvoltage;
A third switching element that conducts when an overvoltage exceeds a Zener voltage of the first Zener, and a fourth switching element that conducts when an Zener voltage exceeds the second Zener voltage;
The fifth switching element that is conductive by conduction of the third or fourth switching element and grounded at one end;
When the overvoltage occurs, the current flowing through the third switching element that conducts and the one end of the fifth switching element is grounded, so that the first and second switching elements become non-conducting and the voltage of the load current path When the voltage drop is newly generated, the voltage applied to the first Zener is reduced to be less than the Zener voltage, whereby the third switching element is turned off, the fifth switching element is turned off, and one end of the fifth switching element is Due to the negative feedback operation in which the first and second switching elements are turned on and conducted through the load current path by being released from the ground, a voltage that can pass through the load current path by the Zener voltage of the first Zener is Controlled by the Zener voltage of the Zener,
At the time of the overvoltage, the first and second switching elements become non-conductive toward the non-conducting state due to the current flowing through the fourth switching element that is turned on and one end of the fifth switching element is grounded. When the voltage drop is newly generated, the voltage applied to the second Zener is reduced to be less than the Zener voltage, whereby the fourth switching element is turned off, the fifth switching element is turned off, and one end of the fifth switching element is The voltage that can pass through the load current path by the Zener voltage of the second Zener is reduced by the negative feedback operation in which the first and second switching elements are turned on and conducted through the load current path. An overvoltage overcurrent protection circuit controlled by a Zener voltage of a Zener. A first switching element and a second switching element which are connected in series with opposite polarity and inserted into the load current path and controlled in conjunction with the potential of one end of the fifth switching element;
A first Zener for detecting a positive overvoltage generated on the input side of the load current path and a second Zener for detecting a negative overvoltage;
A third switching element that conducts when an overvoltage exceeds a Zener voltage of the first Zener, and a fourth switching element that conducts when an Zener voltage exceeds the second Zener voltage;
The fifth switching element that is conductive by conduction of the third or fourth switching element and grounded at one end;
When the overvoltage occurs, the first and second switching elements become non-conductive by being conducted by a current flowing through the third switching element that is conducting and grounding one end of the fifth switching element.
When the overvoltage occurs, the first and second switching elements become non-conductive because the first switching element and the fifth switching element are grounded by the current flowing through the fourth switching element that is conducting, and the voltage is supplied to the load. An overvoltage overcurrent protection circuit characterized by shutting off. A first switching element and a second switching element which are connected in series with opposite polarity and inserted into the load current path and controlled in conjunction with the potential of one end of the fifth switching element;
A first Zener for detecting a positive overvoltage generated on the load side of the load current path and a second Zener for detecting a negative overvoltage;
A third switching element that conducts when an overvoltage exceeds a Zener voltage of the first Zener, and a fourth switching element that conducts when an Zener voltage exceeds the second Zener voltage;
The fifth switching element that is conductive by conduction of the fourth switching element and grounded at one end,
When the overvoltage is applied, one end of the third switching element that conducts is grounded, so that the first and second switching elements become non-conducting and a voltage drop in the load current path newly occurs, thereby causing the first Zener The third switching element is turned off by lowering the applied voltage to less than the Zener voltage, one end of the third switching element is released to ground, and the first and second switching elements are turned on and the load current path is passed through. Due to the conducting negative feedback operation, the voltage that can pass through the load current path by the Zener voltage of the first Zener is controlled to the Zener voltage of the first Zener,
At the time of the overvoltage, the first and second switching elements become non-conductive toward the non-conducting state due to the current flowing through the fourth switching element that is turned on and one end of the fifth switching element is grounded. When the voltage drop is newly generated, the voltage applied to the second Zener is reduced to be less than the Zener voltage, whereby the fourth switching element is turned off, the fifth switching element is turned off, and one end of the fifth switching element is The voltage that can pass through the load current path by the Zener voltage of the second Zener is reduced by the negative feedback operation in which the first and second switching elements are turned on and conducted through the load current path. An overvoltage overcurrent protection circuit controlled by a Zener voltage of a Zener. A first switching element and a second switching element which are connected in series with opposite polarity and inserted into the load current path and controlled in conjunction with the potential of one end of the fifth switching element;
A first Zener for detecting a positive overvoltage generated on the input side of the load current path and a second Zener for detecting a negative overvoltage;
A third switching element that conducts when an overvoltage exceeds a Zener voltage of the first Zener, and a fourth switching element that conducts when an Zener voltage exceeds the second Zener voltage;
The fifth switching element that is conductive by conduction of the fourth switching element and grounded at one end,
When one end of the third switching element that conducts at the time of the overvoltage is grounded, the first and second switching elements become non-conducting,
When the overvoltage occurs, the first and second switching elements become non-conductive because the first switching element and the fifth switching element are grounded by the current flowing through the fourth switching element that is conducting, and the voltage is supplied to the load. An overvoltage overcurrent protection circuit characterized by shutting off. A first resistor connected in series to the load current path and the first and second switching elements connected in series with opposite polarity and arranged in the load current path and controlled in conjunction with the potential of one end of the sixth or seventh switching element. Elements,
When the voltage between the terminals of the first resistance element is detected and the potential at one end of the first resistance element is higher than the potential at the other end, the sixth switching element that can conduct and the potential at one end of the first resistance element are other The seventh switching element capable of conducting when lower than the potential at the end, and
When an overcurrent flows through the load current path and the voltage across the first resistance element reaches a voltage that forward biases the control terminal of the sixth switching element and makes the sixth switching element conductive, the sixth One end of the switching element is grounded,
When an overcurrent flows through the load current path and the voltage across the first resistance element reaches a voltage that forward biases the control terminal of the seventh switching element and makes the seventh switching element conductive, the seventh When one end of the switching element is grounded, the first and second switching elements become non-conducting and the current in the load current path is limited, so that the voltage drop of the first resistance element is reduced and the sixth or The seventh switching element is turned off, one end of the sixth or seventh switching element is released from the ground, and the first and second switching elements suppress the overcurrent by the negative feedback operation toward the conduction of the load current path, thereby reducing the load current. An overvoltage overcurrent protection circuit characterized by conducting. An eighth switching element having one end connected to a DC power source;
A first rectifying element connected to one end of the fifth or sixth and seventh switching elements and connected in series; a second resistance element; and a capacitive element having one end connected to the other end of the eighth switching element;
A second rectifying element having one end connected to the other end of the eighth switching element;
A ninth switching element configured such that a DC voltage is applied to one end and the potential of the other end of the capacitive element can be transmitted to the control end; forward biasing from the other end of the ninth switching element to the control end is possible; A tenth switching element configured to be able to transmit a potential at one end of the capacitive element via the second rectifying element, and forward biased from the other end of the tenth switching element to the control end; Or an eleventh switching element configured to be able to transmit to one end of the sixth and seventh switching elements, and the other end having a ground potential,
When one end of the fifth, sixth, or seventh switching element is grounded, the capacitor element is charged by the current path formed by the first rectifying element, the second resistance element, the capacitor element, and the eighth switching element. And after the elapse of time based on the time constant of the second resistive element and the capacitive element, the control terminal of the ninth switching element is forward-biased, whereby the ninth switching element becomes conductive and the tenth and tenth elements When the eleventh switching element is turned on, the second rectifying element is turned on, whereby the control end of the ninth switching element is further forward-biased, and the ninth, tenth and eleventh switching elements are kept conductive and the fifth switching element is turned on. Alternatively, one end of each of the sixth and seventh switching elements is held at ground, and the first and second switching elements are cut off and held. To overvoltage overcurrent protection circuit according to any one of the 5.   A switch element is provided between one end of the eighth switching element and the other end of the capacitive element, and by making the switch element conductive, the charge of the capacitive element is discharged through one end of the tenth switching element. 9 reversely biasing the control terminal of the switching element to cut off the conduction of the tenth and eleventh switching elements and forward biasing the control terminal of the eighth switching element, the second resistance element, the first rectifying element, The capacitive element is discharged in the current path of the fourth resistance element and the eighth switching element to return to the normal initial state, and one end of the eleventh switching element is released to ground, and the first and second switching elements are The overvoltage overcurrent protection circuit according to claim 6, wherein the overvoltage protection is released. A third resistance element connected between one end of the fifth or sixth and seventh switching elements and the other end of the capacitive element;
A third rectifying element connected between a connection point of one end of the fifth or sixth and seventh switching elements and one end of the eleventh switching element;
A fifth resistance element connected to one end of the eleventh switching element and capable of forward biasing the control ends of the first switching element and the second switching element by the DC power supply;
In a state where one end of the fifth, sixth or seventh switching element is held at ground,
When one end of each of the fifth, sixth, and seventh switching elements is released from the ground, the third resistance element, the capacitive element, and the second rectifying element are generated by a potential at one end of the fifth, sixth, or seventh switching element. The capacitor element is reversely charged in the current path formed by the tenth and eleventh switching elements, so that the ninth switching element after the passage of time based on the time constant of the third resistor element and the capacitor element. The control terminal is reverse-biased, and the ninth, tenth, and eleventh switching elements are turned off, so that one end of the eleventh switching element is released to ground, and the potential at the one end is restored, so that the first and second switching elements are restored. 6. The overload according to claim 1, wherein the control end of the element is forward biased to release the cutoff holding of the first and second semiconductor elements. -Pressure-current protection circuit. A twelfth switching element having one end connected to the control end of the tenth switching element and a DC voltage applied to the other end and the control end;
A temperature-sensitive element having one end connected to the control end of the twelfth switching element and the other end connected to the first and / or second switching element;
When the resistance value of the temperature sensitive element decreases, the twelfth switching element is turned on and the tenth switching element is turned on, whereby the tenth and eleventh switching elements are turned on and one end of the eleventh switching element is 9. The overvoltage overcurrent protection circuit according to claim 6, wherein the overvoltage overcurrent protection circuit is grounded to cut off and hold the first and second switching elements.   6. The overvoltage overcurrent protection circuit according to claim 5, wherein an overcurrent is detected using a current transformer instead of the first resistance element, and the sixth and / or seventh switching element is driven on and off.

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