JP2001209440A - Power supply with overcurrent protective device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply with a protective function device that enable the power supply to operate efficiently without a damage caused by a overcurrent. SOLUTION: A thermosensitive element 5 such as PTC thermistor is installed close to switch element and transistors of much heat producing components in a power supply circuit 3. When a voltage V2 ia applied to the series circuit composed of the thermosensitive element 5 and a resistor R4, as the voltage at the connection point of the thermosensitive element 5 and the resistor R4 changes in accordance with the change of the atmospheric temperature, the control changing the threshold of the output current in accordance with the voltage is conducted. In other word, the protective device controls the raise of a threshold if the atmospheric temperature is low and the drop of the threshold if atmospheric temperature is high, very high efficient operation in accordance with the capability of each power supply equipment becomes possible, also troubles like a damage of parts due to thermal stress can be prevented, in advance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device having an overcurrent protection function for stopping operation when an output current value exceeds a predetermined threshold value to protect a circuit.

[0002]

2. Description of the Related Art Generally, in electric and electronic devices using a semiconductor integrated circuit such as a personal computer and an AV device, a stable DC power supply of about 5 to 10 volts is required to operate the integrated circuit. Conventionally, stabilized power supply devices such as switching regulators and series regulators have been widely used as power supplies.

In such a stabilized power supply, in order to always obtain a stable output voltage irrespective of the state of the load, control is performed to measure an output voltage value and feed back this voltage value to adjust the output voltage. ing. For example, in the case of a switching regulator, when the output voltage becomes higher than a desired voltage, the voltage value is decreased by reducing the duty ratio of a pulse signal for driving the switching element to match the desired voltage. Conversely, when the output voltage becomes lower than the desired voltage, the voltage value can be raised to match the desired voltage by increasing the duty ratio of the pulse signal.

On the other hand, in a recent stabilized power supply,
When the load connected to the power supply becomes overloaded and the output current of the power supply increases, in order to prevent damage to the circuit and components constituting the circuit due to thermal stress caused by the overcurrent, A device equipped with an overcurrent protection function (OCP; overcurrent protection function) is employed.

FIG. 3 is a circuit diagram showing a configuration of a conventional power supply device having an overcurrent protection function.

As shown in FIG. 1, this power supply device 20
OCP error amplifier 11 and voltage control error amplifier 12
And a power supply circuit 13.

A reference voltage Vref3 is input to the non-inverting input terminal of the OCP error amplifier 11, and a voltage obtained by current-to-voltage conversion of the output current IOUT of the power supply circuit 13 (hereinafter referred to as voltage conversion value) is input to the inverting input terminal. Vc is supplied.

A reference voltage Vref1 is input to the non-inverting input terminal of the voltage control error amplifier 12, and the output voltage VOUT of the power supply circuit 13 is divided by the dividing resistors R11 and R12 to the inverting input terminal. The supplied voltage VP is supplied.

The output terminal of the OCP error amplifier 11 is connected to the cathode of the diode D11, the output terminal of the voltage control error amplifier 12 is connected to the cathode of the diode D12, and the anode of each of the diodes D11 and D12. Are connected to each other and to the cathode side of the light emitting diode PD11 included in the photocoupler PC11.

The anode side of the light emitting diode PD11 is connected to a DC power supply V1 via a resistor R13. The phototransistor PT11 included in the photocoupler PC11 is connected to the control unit 13a of the power supply circuit 13. The power supply device 20 can appropriately change the output voltage VOUT of the power supply circuit 13 based on a signal input from the photocoupler PC11 to the control unit 13a.

Next, the operation of the conventional power supply device having the overcurrent protection function configured as described above will be described.

At the time of normal voltage supply, the output value of the output current IOUT is smaller than the threshold value set by Vref3, so that the output of the OCP error amplifier 11 is fixed at "H" level. Therefore, no current flows from the power supply V1 to the OCP error amplifier 11, and the voltage control error amplifier 12 operates.

The voltage control error amplifier 12 outputs the output voltage V
A voltage VP obtained by dividing OUT by resistors R11 and R12 is compared with a reference voltage Vref1, and a voltage signal proportional to the difference is output. The value of the voltage VP increases and the reference voltage V
When the difference from ref1 increases, the voltage control error amplifier 1
2 decreases, the current flowing from the power supply V1 into the voltage control error amplifier 12, that is, the current flowing through the resistor R13 increases, and accordingly, the light emitting diode P
The light emission amount of D11 increases, and the signal level input from the photocoupler PC11 to the control unit 13a increases. In this case, the control unit 13a controls the driving of a predetermined circuit of the power supply circuit 13 in a direction to decrease the output voltage VOUT. As a result, the output voltage VOUT of the power supply circuit 13 decreases.

Conversely, when the value of the voltage VP decreases and the difference from Vref1 decreases, the output voltage of the voltage control error amplifier 12 increases. , That is, the current flowing through the resistor R13, the amount of light emitted by the light emitting diode PD11 decreases, and the photocoupler P
The signal level input from C11 to the control unit 13a decreases. In this case, the control unit 13a controls driving of a predetermined circuit of the power supply circuit 13 in a direction to increase the output voltage VOUT. As a result, the output voltage VOUT of the power supply circuit 13 increases.

Here, the load (not shown) connected to the power supply circuit 13 becomes overloaded, and the output current IOU of the power supply circuit 13 is increased.
When T becomes an overcurrent, the voltage conversion value Vc of the output current IOUT input to the OCP error amplifier 11 increases and becomes larger than the reference voltage Vref3, so that the output of the OCP error amplifier 11 becomes the "L" level. And the current supplied from the power supply V1 flows into the OCP error amplifier 11 side.

As a result, no current flows into the voltage control error amplifier 12. As a result, the output current becomes constant by the error amplifier 11 for OCP, overcurrent can be prevented, and safety can be ensured.

However, in the conventional power supply having the overcurrent protection function, the threshold value of the voltage conversion value Vc of the output current IOUT is set in advance regardless of the surrounding environment, and the voltage conversion value Vc is set to this threshold value. Since the output voltage VOUT is reduced when the value exceeds the value, the operation is stopped despite the fact that stable operation is possible without receiving much thermal stress. Even though each component has already reached the operation limit due to the thermal stress, there may be a problem that the operation is continued and the thermal stress is continuously applied.

For example, when the power supply circuit 13 is installed in a place where the ambient temperature is extremely low, even if the output current IOUT becomes large, the components of the circuit are not subjected to much thermal stress, so that the operation can be continued. . On the other hand, when the power supply circuit 13 is installed in a place where the ambient temperature is high, even if the output current IOUT does not become so large, since each component is actually subjected to a lot of thermal stress, it can withstand continuous operation. Disappears. When a plurality of power supply circuits are connected in parallel and operated, heat is applied to each of the power supply circuits due to the mounting position of each power supply circuit and the degree of contact with cooling air supplied from a cooling fan. Since there are various situations in which stress is applied, there are cases where driving is possible continuously and cases where driving must be stopped.

That is, the thermal stress applied to each component of the power supply circuit varies not only due to the magnitude of the output current but also due to the surrounding environment. In a conventional power supply circuit having an overcurrent protection function, However, a method of controlling by taking in data caused by the surrounding environment has not been adopted.

[0020]

As described above, in the conventional power supply device having an overcurrent protection function, when the output current exceeds a predetermined threshold value regardless of the surrounding environment. Is a configuration in which operation is forcibly stopped.Therefore, the operation is stopped even though the components are not receiving much heat stress. May be continued, and efficient operation may not be performed, and a problem that components of the power supply circuit may be damaged may occur.

The present invention has been made to solve such a conventional problem.
An object of the present invention is to provide a power supply device having an overcurrent protection function that can prevent damage due to overcurrent and that can operate efficiently.

[0022]

This and other objects are achieved by the present invention which is defined below as (1) to (5).

(1) In a power supply device having an overcurrent protection function for protecting a circuit by forcibly lowering an output voltage when an output current exceeds a threshold value, a predetermined portion of the power supply device or Temperature detecting means for detecting a temperature in the vicinity of the power supply device, and threshold value changing means for changing the threshold value according to the temperature detected by the temperature detecting means;
A power supply device having an overcurrent protection function, comprising:

(2) In a power supply device having an overcurrent protection function for protecting a circuit by forcibly lowering the output voltage when the output current exceeds a threshold value, a predetermined portion of the power supply device or Temperature detection means for detecting the temperature in the vicinity of the power supply device, the threshold value at the time of the reference temperature is set, and if the temperature detected by the temperature detection means is lower than the reference temperature, The threshold value is increased with respect to the threshold value at the reference temperature, and when the temperature detected by the temperature detecting means is higher than the reference temperature, the threshold value is set at the reference temperature. A power supply device having an overcurrent protection function, comprising: a threshold value changing unit that lowers a threshold value.

(3) A resistor, an output voltage is compared with a first reference value, a first amplifying means for flowing a current corresponding to the difference through the resistor, and a current based on the current flowing through the resistor. Control means for controlling the output voltage value to be constant, and a predetermined threshold value. When the output current exceeds the threshold value, the control means controls the output voltage value regardless of the operation of the first amplification means. A second amplifying means for increasing a current flowing through the resistor, and an overcurrent protection function for forcibly reducing the output voltage to protect the circuit when the value of the current flowing through the resistor increases. In the power supply device provided, a heat-sensitive element whose resistance value changes according to a temperature at a predetermined location of the power supply device or in the vicinity of the power supply device, and a DC voltage is applied to the heat-sensitive element, and a voltage across the heat-sensitive element is applied. Is detected, and the threshold is set in accordance with the detected value. A power supply device having an overcurrent protection function, comprising: a threshold value changing means for changing the threshold value.

(4) The threshold value changing means calculates a difference between a DC power supply for applying a DC voltage to the thermosensitive element, a voltage generated at both ends of the thermosensitive element, and a second reference value. When the voltage across the thermal element increases and the output value of the third amplifying means increases, the threshold value is increased, and when the output value decreases, Is a power supply device having an overcurrent protection function according to the above (3), which performs a process of lowering the threshold value.

(5) The threshold value changing means is configured to increase the threshold value as the temperature detected by the temperature detecting means decreases. A power supply device provided with an overcurrent protection function according to (1).

[0028]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a configuration of an embodiment of a power supply device having an overcurrent protection function to which the present invention is applied.

As shown in FIG.
An OCP error amplifier (second amplifier) 1, a voltage control error amplifier (first amplifier) 2, a threshold setting amplifier (third amplifier) 4, a power supply circuit 3, Is provided.

A reference voltage Vref3 for setting the threshold value of the output current IOUT is input to the non-inverting input terminal of the OCP error amplifier 1 via a resistor R6, and the power supply circuit 3 is connected to the inverting input terminal. (Hereinafter referred to as a voltage conversion value) Vc which is a current-voltage conversion of the output current IOUT.

The reference voltage (first reference value) Vref1 is input to the non-inverting input terminal of the voltage control error amplifier 2, and the output voltage VOUT of the power supply circuit 3 is input to the inverting input terminal.
Is supplied by the voltage dividing resistors R1 and R2.

The output terminal of the OCP error amplifier 1 is connected to the cathode of the diode D1, the output terminal of the voltage control error amplifier 2 is connected to the cathode of the diode D2, and the anodes of the diodes D1 and D2 are connected to each other. It is connected to the cathode side of the light emitting diode PD1 included in the photocoupler PC1.

The anode side of the light emitting diode PD1 is connected to a DC power supply V1 via a resistor (resistor) R3.

The phototransistor PT1 included in the photocoupler PC1 is connected to a control section (control means) 3a of the power supply circuit 3. The power supply device 10 can appropriately change the output voltage VOUT of the power supply circuit 3 based on a signal input from the photocoupler PC1 to the control unit 3a.

A reference voltage (second reference value) Vref2 is supplied to a non-inverting input terminal of the threshold setting amplifier 4, and a thermosensitive element (temperature detecting means) 5 is supplied to an inverting input terminal.
The connection point between the resistor and the resistor R4 is connected. Since the voltage V2 is applied to the series connection circuit of the thermal element 5 and the resistor R4, the voltage Vs generated at both ends of the thermal element 5 is applied to the inverting input terminal of the threshold setting amplifier 4. Is applied. The output terminal of the threshold setting amplifier 4 is OC
It is connected to the non-inverting input terminal of the P error amplifier 1.

A resistor R8 is interposed between the output terminal of the threshold setting amplifier 4 and the inverting input terminal of the threshold setting amplifier 4. Output terminal is connected to the OCP error amplifier 1 via the resistor R7.
Is connected to the non-inverting side input terminal of.

As the heat-sensitive element 5, an element such as a thermistor (for example, a PTC thermistor) whose resistance value changes according to the ambient temperature is used. It is preferable that the thermal element 5 be disposed in an element or a component that receives a large amount of thermal stress, such as a MOS-FET, a transistor, or a transformer in the power supply circuit 3 or in the vicinity thereof.

Next, the operation of the power supply device 10 of the present embodiment will be described. During normal voltage supply, the output current IOU
Since the voltage conversion value Vc of T is smaller than the threshold value set by the reference voltage Vref3 and the output voltage of the threshold setting amplifier 4 at the reference temperature, the output of the OCP error amplifier 1 is "H". Fixed at the level. Therefore, the power supply V
1 does not flow into the OCP error amplifier 1 side,
The voltage control error amplifier 2 operates.

The voltage control error amplifier 2 has an output voltage VOU
T is divided by resistors R1 and R2 into a voltage VP and a reference voltage Vre
f1 and outputs a voltage signal proportional to this difference. When the value of the voltage VP increases and the difference from the reference voltage Vref1 increases, the output voltage of the voltage control error amplifier 2 decreases, so that the current flows from the power supply V1 into the voltage control error amplifier 2, that is, flows through the resistor R3. As the current increases, the light emission amount of the light emitting diode PD1 increases, and the signal level input from the photocoupler PC1 to the control unit 3a increases. In this case, the control unit 3a
Controls the driving of a predetermined circuit of the power supply circuit 3 in the direction of decreasing the output voltage VOUT. As a result, the output voltage VOUT of the power supply circuit 3 decreases.

On the contrary, when the value of the voltage VP decreases and the difference from Vref1 decreases, the output voltage of the voltage control error amplifier 2 increases. , That is, the current flowing through the resistor R3, the light emission amount of the light emitting diode PD1 decreases, and the signal level input from the photocoupler PC1 to the control unit 3a decreases. In this case, the control unit 3a controls driving of a predetermined circuit of the power supply circuit 3 in a direction to increase the output voltage VOUT. As a result, the output voltage VOUT of the power supply circuit 3 increases.

As described above, the power supply circuit 3 operates in a direction to decrease the output voltage VOUT when the output voltage VOUT is higher than the target value, and operates when the output voltage VOUT is lower than the target value. It operates in a direction to increase this. That is, the control section 3a controls the output voltage VOUT to be always constant.

Here, when the load (not shown) connected to the power supply circuit 3 becomes overloaded and the output current IOUT of the power supply circuit 3 becomes overcurrent, the voltage conversion of the output current IOUT input to the OCP error amplifier 1 is performed. The value Vc increases, and this voltage conversion value Vc becomes larger than the threshold set by the reference voltage Vref3 and the output voltage of the threshold setting amplifier 4 at the time of the reference temperature. 1 becomes "L" level. As a result, the current supplied from the power supply V1 flows into the OCP error amplifier 1.

As a result, no current flows into the voltage control error amplifier 2. As a result, the output current is made constant by the OCP error amplifier 1, the overcurrent can be prevented, and safety can be ensured.

FIG. 2 is a characteristic curve showing the relationship between the output current IOUT of the power supply circuit 3 and the output voltage VOUT.

As shown in FIG. 5, when the output current IOUT rises and exceeds the threshold value Imax, the output voltage VOUT drops sharply and the operation of the power supply circuit 3 is stopped.

Here, when the ambient temperature of the thermal element 5 is lower than the reference temperature, the resistance value of the thermal element 5 decreases, so that the voltage Vs generated at both ends of the thermal element 5 decreases. As a result, the difference between the reference voltage Vref2 and the voltage Vs increases, the output voltage of the threshold setting amplifier 4 increases, and the voltage supplied to the non-inverting input terminal of the OCP error amplifier 1 decreases. Increase. At this time, the gain of the threshold setting amplifier 4 is limited in order to prevent the voltage Va applied to the non-inverting input terminal of the OCP error amplifier 1 from increasing sharply.

As a result, the voltage conversion value V of the output current IOUT
The threshold value of c increases from the threshold value at the reference temperature. That is, the threshold value Imax shown in FIG. 2 is shifted to the right in the figure as compared with the case of the reference temperature. The threshold value after the change (after the shift) increases as the ambient temperature of the thermal element 5 decreases. Therefore, even when the output current IOUT increases, the ambient temperature of the thermosensitive element 5 (mainly the MOS-FET
, Transistors, transformers, and other elements and components that are easily subjected to thermal stress), the components of the power supply circuit 3 do not receive much thermal stress, and can continue to operate.

On the contrary, when the ambient temperature of the thermal element 5 is higher than the reference temperature, the OC
Since the voltage value supplied to the non-inverting input terminal of the P error amplifier 1 decreases, the threshold value of the voltage conversion value Vc of the output current IOUT decreases from the threshold value at the reference temperature. That is, the threshold value Imax shown in FIG. 2 is shifted to the left in the figure from that at the time of the reference temperature. Therefore, even when the output current IOUT does not increase so much, when the ambient temperature of the thermal element 5 is high, each component of the power supply circuit 3 is subjected to a lot of thermal stress. And stop the operation. Thus, an efficient operation according to the ambient temperature is realized.

As described above, in the power supply device 10 having the overcurrent protection function according to the present embodiment, the threshold value of the current serving as the reference for stopping the operation of the power supply circuit 3 is set to the ambient temperature of the thermosensitive element 5. Therefore, the operation can be performed very efficiently according to the capacity and state of the power supply circuit 3. Further, it is possible to prevent troubles such as damage to each component of the power supply circuit 3 due to thermal stress.

Further, in the case where the power supply devices having the overcurrent protection function are connected in parallel and operated, for example, the power supply devices received by the respective power supply devices may be different due to a difference in hitting of the cooling air sent from the cooling fan. Although the thermal stress may be different, even in such a case, it is possible to perform an efficient operation according to the capacity and state of each power supply device. Further, occurrence of troubles such as damage to circuit components due to thermal stress can be prevented.

Although the power supply device having the overcurrent protection function of the present invention has been described based on the illustrated embodiment, the present invention is not limited to this, and the configuration of each part has the same function. It can be replaced by any configuration having

[0052]

As described above, according to the present invention,
Temperatures of various components constituting the power supply device and the surroundings are detected by a temperature detecting means, and a threshold value of an output current for stopping the operation is appropriately changed in accordance with the detected temperature. For example, when the temperature detected by the temperature detecting means is low, even if the output current is large, the various components constituting the power supply device are not subjected to much thermal stress, so that the power supply device can be continuously operated. Conversely, when the temperature detected by the temperature detecting means is high, even if the output current is small, various parts constituting the power supply device may be subjected to a lot of thermal stress, and thus the threshold value is lowered. Thus, the operation of the power supply device is stopped at a low output current value.

Therefore, extremely efficient operation according to the capacity and state of the power supply unit can be performed, and troubles such as damage to parts due to thermal stress can be prevented.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a power supply device having an overcurrent protection function according to an embodiment of the present invention.

FIG. 2 is a characteristic curve showing a relationship between an output current and an output voltage of a power supply device having an overcurrent protection function according to an embodiment of the present invention.

FIG. 3 is a circuit diagram showing a configuration of a power supply device having a conventional overcurrent protection function.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 OCP error amplifier (second amplifying means) 2 voltage control error amplifier (first amplifying means) 3, 13 power supply circuit 3 a control unit (control means) 4 threshold setting amplifier (third amplifying means) 5) Thermal element (temperature detecting means) 10, 20 Power supply circuit 11 OCP error amplifier 12 Voltage control error amplifier 13a Controller D1, D2, D11, D12 Diode PC1, PC11 Photocoupler PD1, PD11 Light emitting diode PT1, PT11 Photo Transistors R1, R2, R4, R6, R7, R8 Resistance R3 Resistance (resistor) R11, R12, R13 Resistance

Claims (5)

[Claims] 1. A power supply device having an overcurrent protection function for protecting a circuit by forcibly lowering an output voltage when an output current exceeds a threshold value. Overcurrent, comprising: temperature detecting means for detecting a temperature near the power supply device; and threshold changing means for changing the threshold according to the temperature detected by the temperature detecting means. Power supply device with protection function. 2. A power supply device having an overcurrent protection function for forcibly lowering an output voltage and protecting a circuit when an output current exceeds a threshold value. Temperature detection means for detecting a temperature in the vicinity of the power supply device, wherein the threshold value at the time of the reference temperature is set, and when the temperature detected by the temperature detection means is lower than the reference temperature, The threshold value is raised with respect to the threshold value at the reference temperature, and when the temperature detected by the temperature detecting means is higher than the reference temperature, the threshold value is raised at the reference temperature. A power supply device having an overcurrent protection function, comprising: a threshold value changing unit that lowers a threshold value. 3. A resistor, an output voltage is compared with a first reference value, a first amplifying means for flowing a current corresponding to the difference through the resistor, and a current flowing through the resistor. Control means for controlling the output voltage value so as to be constant; and a predetermined threshold value. When the output current exceeds the threshold value, the resistance value is controlled regardless of the operation of the first amplification means. A second amplifying means for increasing a current flowing through the body, comprising an overcurrent protection function for forcibly reducing the output voltage and protecting the circuit when the value of the current flowing through the resistor increases. A heat-sensitive element whose resistance changes according to the temperature at a predetermined location of the power supply or near the power supply; applying a DC voltage to the heat-sensitive element; And changes the threshold value according to the detected value. A power supply device having an overcurrent protection function. 4. The method according to claim 1, wherein the threshold value changing unit includes: a DC power supply for applying a DC voltage to the thermosensitive element; and a third reference value for calculating a difference between a voltage generated at both ends of the thermosensitive element and a second reference value. When the output voltage of the third amplifying unit increases, the threshold value is increased, and when the output value decreases, the output voltage of the third amplifying unit increases. 4. The power supply device having an overcurrent protection function according to claim 3, wherein the power supply device performs processing for lowering the threshold value. 5. The filter according to claim 1, wherein the threshold value changing unit is configured to increase the threshold value as the temperature detected by the temperature detecting unit decreases. Power supply device with current protection function.