JPH0555730U - Overload protection circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an overload protection circuit that can automatically restore the circuit operation without the need to turn the power on again when the load is restored to normal. To aim. [Structure] Overcurrent detection means 11 detects an overcurrent flowing through a semiconductor switching element Q ₂ connected in series with a load RL between a DC power supply V _CC and a ground. In accordance with this detection, the holding means 12 turns off the semiconductor switching element Q ₂ and holds the overcurrent detection state. When the overcurrent detection means 11 detects an overcurrent and the normality detection means 13 detects a normal impedance, the restoration means 14 releases the holding state by the holding means 12.

Description

[Detailed description of the device]

[0001]

[Industrial application]

 The present invention relates to an overload protection circuit that forcibly turns off a semiconductor switching element to protect it when an overcurrent flows due to a load abnormality.

[0002]

[Prior Art]

Conventionally, as this type of circuit, a circuit having a configuration shown in FIG. 4 has been proposed (Japanese Utility Model Laid-Open No. 63-120531). In the figure, the control circuit 1 inputs, for example, various signals and processes them to generate an on / off control signal for turning on / off the load. The control circuit 1 when turning on the load, Outputs an H level on the signal at its output, which in turn on the drive NPN transistor Q ₁ in response, the PNP transistor Q ₂ by on of the transistor motor Q ₁ Turn on the semiconductor switching element. When the transistor Q ₂ is turned on, a current flows from the DC power supply V _CC to the ground through the transistor Q ₂ and the load RL, and the load RL operates.

An overcurrent detection resistor R ₁ is connected between the emitter of the output transistor Q ₂ and the DC power supply V _CC, and a detection PNP transistor Q ₃ is connected in parallel with the overcurrent detection resistor R _1. The output of the control circuit 1 is lowered to the ground potential, that is, to the L level by turning on the NPN transistor Q ₄ connected between the base and the emitter of the transistor Q _{3 and} the base of the transistor Q ₃ .

With the above configuration, when an overcurrent flows through the load RL, the voltage drop at the overcurrent detection resistor R ₁ increases and the base current of the transistor Q ₃ flows. This collector current increase in Trang register Q ₃ → transistor Q ₃ and Q ₄ in an instant by the base current increases → transistors Q ₄ of the collector current increases → transistor Q ₃ of the base current positive feedback loop of increased transistor Q ₄ are Turns on. When the transistor Q ₄ is turned on, the output of the control circuit 1 is dropped to the L level, the H level on signal is dropped to the ground, the driving transistor Q ₁ is turned off, and the output transistor Q ₂ is turned off. Will be forcibly turned off and protected.

[0005]

[Problems to be solved by the device]

However, in the conventional circuit described above, once the protection operation is started, the transistors Q ₃ and Q ₄ are held in the ON state by the positive feedback action, and the output transistor Q ₂ is turned off. Therefore, even if the load RL is restored to normal, the power supply to the load RL is not started.

Therefore, in order to restore the circuit operation, it is necessary to perform a troublesome operation such as turning the power on again, and when applied to a load such as an unmanned operation, it is inefficient from the viewpoint of operation efficiency. It will be

Therefore, in view of the above-mentioned conventional problems, the present invention aims to automatically restore the circuit operation without requiring an operation such as turning the power on again when the load is restored normally. It is an object to provide an overload protection circuit that can be used.

[0008]

[Means for Solving the Problems]

In order to solve the above problems, the overload protection circuit according to the present invention is connected in series with a load RL between a DC power supply V _CC and ground and applied to a control input, as shown in the basic configuration diagram of FIG. to protect the semiconductor switching element Q ₂ to which of turning on and off controlling the current flowing to the on-off control signal load on and off by the overcurrent, over to detect an overcurrent flowing through the semi-conductor switching element Q ₂ The current detection means 11 and the overcurrent detection means 11 prevent the ON / OFF control signal from being applied to the semiconductor switching element Q ₂ in response to the detection of the overcurrent by the overcurrent detection means 11. In an overload protection circuit including a holding means 12 that holds an overcurrent detection state, a normality detection means 13 that detects that the impedance of the load RL is normal, and the overload protection circuit. When the detection unit 11 detects the overcurrent, and the normal detection unit 13 has detected the normal impedance, and characterized in that it comprises a recovery unit 14 for releasing the holding state by the holding means 12.

In the above overload protection circuit, the normality detecting means 13 is connected between the DC power supply V _CC and the load RL, and a resistor Ra for constantly flowing a current of a magnitude not operating the load RL to the load RL is provided. And a voltage monitoring means 13a for monitoring the voltage at the connection point between the resistor Ra and the load RL to detect that the impedance of the load RL is normal.

[0010]

[Action]

In the above configuration, a semiconductor switching element that is connected in series with the load RL between the DC power supply V _CC and ground and that turns on / off the current flowing to the load by turning on / off by an on / off control signal applied to the control input. The overcurrent detecting means 11 detects the overcurrent flowing in Q ₂ . In response to the overcurrent detection by the overcurrent detection means 11, the holding means 12 prevents the ON / OFF control signal from being applied to the semiconductor switching element Q _2, and the overcurrent detection state by the overcurrent detection means 11 is changed. Since it is held, the semiconductor switching element Q ₂ can be turned off immediately when an overcurrent flows through the semiconductor switching element Q _{2 due} to a short circuit of the load RL.

Further, when the normality detecting means 13 detects that the impedance of the load RL is normal while the overcurrent detecting means 11 is detecting the overcurrent, the restoring means 14 releases the holding state by the holding means 12. Therefore, the ON / OFF control signal is applied to the semiconductor switching element Q ₂ blocked by the holding means 12, and the semiconductor switching element Q ₂ is automatically restored to the original ON state.

In particular, the normality detection means 13 is connected between the DC power supply V _CC and the load RL and is connected to the connection point between the resistor Ra and the load RL, which constantly flows a current of a magnitude not operating the load RL to the load RL. Since the voltage monitoring means 13a monitors the voltage and detects that the impedance of the load RL is normal, the operation of the load RL is not affected.

[0013]

【Example】

 Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a circuit diagram showing an embodiment of an overload protection circuit according to the present invention. The same parts as those of the conventional one described above with reference to FIG. 4 are designated by the same reference numerals.

In FIG. 2, an output transistor Q ₂ which is a semiconductor switching element whose emitter is connected to the DC power supply V _CC via the overcurrent detection resistor R _{1 and} whose collector is connected to the ground via the load RL is The ON / OFF control signal is input to the base, which is the control input, to control the ON / OFF control of the current flowing to the load RL. Voltage dividing resistors R ₂ and R ₃ are connected in parallel to the overcurrent detecting resistor R ₁ , and an emitter is connected to the DC power supply V _CC at the interconnection point of the voltage dividing resistors R ₂ and R _3. The base of the transistor Q ₃ is connected. The collector of the detection transistor Q ₃ has a resistor R ₄ . It is connected to ground via R ₅ and R ₆ .

When a large current flows to the output transistor Q _{2 due} to an overload, the detection transistor Q ₃ is turned on due to a large voltage drop, and the overcurrent flowing through the output transistor Q ₂ along with the resistor R _1. Functions as the overcurrent detecting means 11 for detecting

The resistance R_FiveAnd R₆At the interconnection point of the₃Resistance R at the base of₇And a reverse current blocking diode D connected through₁A transistor Q connected to the output of the control circuit 1 via_FourConnected to the base of. Therefore, this transistor Q_FourIs the detection transistor Q₃Is turned on when the overcurrent is detected, the ON / OFF control signal output from the control circuit 1 is dropped to ground by this ON, and the output transistor Q ₂ Is prevented from being applied to the base of the₃Is held in the ON state, which is the overcurrent detection state. Therefore, the transistor Q_FourFor example, the on / off control signal is output transistor Q in response to overcurrent detection.₂It functions as a holding unit 12 that holds the overcurrent detection state of the overcurrent detection unit 11 while being prevented from being applied to.

[0017] Between the collector of the output transistor Q ₂ and the output terminal OUT is an interconnection point of the load RL and the DC power supply V _CC, a sufficiently large value for the impedance value R _L of the normal load RL Is connected to a resistor Ra. The resistance Ra has such a large value that the load RL does not operate even if the voltage of the DC power supply V _CC is applied thereto.

Further, a first judgment circuit 13, a second judgment circuit 14a, a logic circuit 14b, and a switch circuit 14c are added. First judging circuit 13, the voltage of the output terminal OU T, the voltage value determined by the resistance division ratio of the impedance value R _L and the resistor Ra of the load RL of the normal, i.e. [R _L / (R _L + Ra) ] It functions as a normality detecting means for detecting that the voltage of the output terminal OUT is higher than the judgment voltage by comparing with a value slightly lower than V _CC and detecting that the impedance of the load R L is normal.

The second determination circuit 14a inputs the collector side voltage of the detection transistor Q ₃ and determines the presence or absence of this collector side voltage. The logic circuit 14b inputs the outputs of the first and second determination circuits 13 and 14a, determines that the first determination circuit 13 has a higher voltage at the output terminal OUT than the determination voltage, and performs the second determination. circuit 14a generates an output signal when it is determined that there collector voltage tiger Njisuta Q _3. The switch circuit 14c is driven by the output of the logic circuit 14b and connects the base of the transistor Q ₄ to the ground potential. Therefore, the second determination circuit 14a, the logic circuit 14b and the switch circuit 14c hold the holding means 12 when the overcurrent detecting means 11 detects the overcurrent and the normality detecting means 13 detects the normal impedance. Functioning as a recovery means 14 for releasing the holding state of the transistor Q ₄ constituting the above, that is, the ON state.

The first determination circuit 13, a comparator CP1 and resistor Rb, is constituted by the Rc, the determination voltage is lower than the above-mentioned _{[R L / (R L + Ra} ) ] · V _CC. This judgment voltage is a load current value at which abnormality detection is started, that is, a load corresponding to a current value generated at the resistor R ₁ that causes a voltage drop that is the on-start voltage of the transistor Q ₃ set by the resistors R ₂ and R _3. 'when a, [R _L' impedance value R _L are set by / (R _L '+ Ra)] · V _CC resistor Rb so that the value higher than the voltage value determined by, R c.

The second determination circuit 14a divides the collector voltage of the comparator CP2 and the detection transistor Q ₃ into resistors Rd and Re for preventing the input voltage of the comparator CP2 from exceeding the rated voltage. When the resistance Rf for setting the determination voltage are constituted by a Rg, determination voltage is set to a value lower than the input voltage of the comparator CP2 when oN of the transistor Q _3.

The logic circuit 14b is composed of a diode logic, an AND gate IC and the like. In the figure, an AND circuit based on diode logic is used, but the NOR gate or EX-OR gate may be used by changing the input terminal polarities of the comparators CP1 and CP2.

The switch circuit 14c is composed of an NPN transistor Q ₅ and a resistor. The base of the transistor Q ₅ is connected to the logic circuit output through the resistor, the collector is connected to the base of the transistor Q ₄ , and the emitter is connected to the ground. Each is connected.

The operation of the circuit configured as described above will be described below for each load state with reference to the time chart of FIG. 3 showing the state of each unit.

(A) Under normal load Overcurrent detection resistor R₁The voltage drop of the resistor R₂, R₃Transistor Q set in₃Transistor Q does not reach the on-state voltage of₃Is off, therefore transistor Q _Four Is also off, and output transistor Q₂Turns on / off according to a signal from the control circuit 1, and supplies a current to the load RL. Generally, overcurrent detection resistor R₁Is set to a small value, the transistor Q₂Is on, that is, the current is supplied to the load RL, the voltage at the output terminal OUT is the power supply voltage V_CCThe output voltage of the first judgment circuit 13 becomes H level because it becomes a slightly lower value and higher than the judgment voltage of the first judgment circuit 13. Also, the transistor Q₃Is off so transistor Q₃Since the collector voltage of the second judgment circuit 14a becomes L level and the output of the logic circuit 14b becomes L level, the collector voltage of the second judgment circuit 14a becomes L level._FiveRemains off.

Next, when the transistor Q ₂ is in the off state, the voltage of the output terminal OUT becomes the value of [ _RL / ( _RL + Ra)] · V _CC , which is determined by the determination voltage of the first determination circuit 13. Since it is a large value, the output of the first determination circuit 13 is at H level, and the collector potential of the transistor Q ₃ is also at ground potential, so the output of the second determination circuit 14a is at L level. and thus the output of the logic circuit 14b is at the L level, the transistor Q ₅ of the switch circuit 14c remains off. As described above, when the load RL is normal, the transistor Q ₅ of the switch circuit 14c is off, and the output transistor Q ₂ turns on / off the current supplied to the load RL in response to the signal from the control circuit 1. Control.

(B) Load Abnormality Next, a case where the load RL becomes abnormal for some reason will be described. When the load current increases for some reason, such as a short circuit, the voltage drop across overcurrent detection resistor R ₁ increases, the resistance R _2, exceeds the ON voltage of the R ₃ transistor Q ₃ which is set in, the transistor Q ₃ a base current starts to flow, the collector current of the transistor Q ₃ are become the base current of the transistor Q _4, the positive feedback effect of the collector current of the transistor Q ₄ increases the base current of bets transistor Q _3, transistor Q _3, Q ₄ is The transistor Q ₄ is turned on instantly, and at the same time, the transistor Q ₄ blocks the signal from the control circuit 1, so that the output transistor Q ₂ is turned off and the current supply to the load RL is stopped.

On the other hand, the impedance of the load RL is Kuna' smaller than the value R _L of the normal by a load failure, so that the output terminal voltage smaller than the value of [R _L / (R _L + Ra)] · V _CC It should be a value.

A load current value at which abnormality detection is started, that is, a load impedance value corresponding to a current value at the resistor R ₁ that causes a voltage drop that is an on-start voltage of the transistor Q ₃ set by the resistors R ₂ and R _3. Is _RL ', the determination voltage of the first determination circuit 13 is [ _RL / ( _RL + Ra)]. V _CC or less and [ _RL ' / ( _RL '+ Ra)]. V _CC or more. Since the resistors Rb and Rc are set so that, the voltage at the output terminal OUT becomes equal to or lower than the judgment voltage, so that the output of the first judgment circuit 13 becomes L level.

Since the transistor Q ₃ is on, its collector potential becomes almost the power supply voltage, and the second determination circuit 14a outputs H level. However, since the output of the first determination circuit 13 is L level, it is a logic circuit. The output of 14b is at L level, and the transistor Q ₅ of the switch circuit 14c is off. Therefore, the transistors Q ₃ and Q _{4 both} remain in the ON state, and the output transistor Q ₂ remains off.

(C) At the time of load recovery When the load RL is recovered, its impedance becomes R _L , so that the voltage of the output terminal OU T becomes [ _RL / ( _RL + Ra)] · V _CC and becomes the first Since the voltage becomes equal to or higher than the determination voltage of the determination circuit 13, the output of the first determination circuit 13 becomes H level.

At this time, the transistors Q ₃ and Q ₄ are on, so the output of the second determination circuit 14 a is in the H level state, and therefore the output of the logic circuit 14 b becomes the H level and the switching circuit The transistor Q ₅ of 14c is turned on. Thus the transistor Q ₄ for the base is a ground potential of the transistors Q ₄ are turned off, to release the state where the blocking signal from the control circuit 1. Further, the transistor Q ₃ also turns off because the base current due to the transistor Q ₄ disappears and the load RL is in the reset state, and the base current due to the voltage drop at the resistor R ₁ does not flow.

When a series of these operations is completed, the collector of the transistor Q ₃ returns to the ground potential, so that the output of the second determination circuit 14a becomes L level and the transistor Q ₅ of the switch circuit 14c is turned off to load the load RL. To the normal state.

As described above, when the load RL is normal, the output transistor Q ₂ is turned on / off according to the signal from the control circuit 1 to supply current to the load RL, and when the load RL is abnormal (short circuit). If the output transistor Q ₂ is turned off and the load RL returns to normal, it is possible to automatically restore normal operation without troublesome operations such as turning the power on again. As the load RL to which the circuit of the present invention is applied, an incandescent lamp load having a small impedance when not in operation (non-lighting) is not suitable, and a buzzer, a relay, a solenoid or the like is suitable.

[0035]

[Effect of the device]

 As described above, according to the present invention, the overcurrent flowing in the semiconductor switching element connected in series with the load is detected, and the semiconductor switching element is immediately turned off in response to the overcurrent detection. Can be protected from load. Also, when the load is restored to normal, the semiconductor switching elements that were turned off are automatically restored to the original on state, so operations such as turning on the power again are required when the load is restored to normal. Without, the circuit operation can be automatically restored.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a basic configuration of an overload protection circuit according to the present invention.

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

FIG. 3 is a diagram showing a state of each unit in the circuit of FIG.

FIG. 4 is a circuit diagram showing an example of a conventional overload protection circuit.

[Explanation of symbols]

V _CC DC power supply RL load Q ₂ semiconductor switching element (transistor for output) 11 overcurrent detection means 12 holding means 13 normality detection means (first determination circuit) 14 recovery means Ra resistance 13a voltage monitoring means

Claims (2)

[Scope of utility model registration request] 1. An overcurrent semiconductor switching element that is connected in series with a load between a DC power source and ground and is turned on / off by an on / off control signal applied to a control input to control on / off of a current flowing to a load. To protect the semiconductor switching element, an overcurrent detecting means for detecting an overcurrent flowing in the semiconductor switching element, and the on / off control signal applied to the semiconductor switching element in response to the overcurrent detection by the overcurrent detecting means. In the overload protection circuit that includes a holding unit that holds the overcurrent detection state by the overcurrent detection unit and a normal detection unit that detects that the impedance of the load is normal, the overcurrent detection unit When an overcurrent is detected and the normality detection means detects a normal impedance, the holding state by the holding means is released. Overload protection circuit; and a recovery unit that. 2. The normality detecting means includes a resistor connected between the DC power source and the load, which constantly allows a current of a magnitude not operating the load to flow through the load, and a voltage at a connection point between the resistor and the load is detected. An overload protection circuit comprising: a voltage monitoring unit that monitors and detects that the impedance of the load is normal.