JP4539433B2 - Power supply device with overvoltage protection function and overvoltage protection circuit - Google Patents

Description

  The present invention relates to a power supply device having an overvoltage protection function for protecting circuit elements from overvoltage and an overvoltage protection circuit.

  Conventionally, a configuration using a relay is known as one of measures for protecting circuit elements from overvoltage. Hereinafter, an overvoltage protection function according to a conventional technique using a relay will be described with reference to FIG.

  In the power supply device 1 shown in FIG. 4, a battery 102 is connected to the input terminal 101. The input terminal 101 is connected to the midpoint of the primary coil of the transformer T via the power line 103. Note that an input capacitor C <b> 1 is connected to the power line 103.

  Transistors M1 and M2 are connected to the primary coil of the transformer T. The transistors M1 and M2 are controlled by a set of control signals generated by the control IC 104. On the secondary side of the transformer T, diodes D1 and D2 for rectifying the output of the transformer T and an output capacitor C2 for smoothing the output voltage are provided.

  In the power supply device 100 configured as described above, the power line 103 is provided with a relay 111. Further, the control IC 104 includes a comparator 113 that compares the input voltage Vin (the detection voltage Vh obtained by the input voltage detection circuit 112 including the resistors R1 and R2) with a threshold voltage (voltage V1). Further, a transistor M3 controlled by the output of the comparator 113 is connected to the exciting coil of the relay 111. A resistor R3 is provided between the relay 111 and the transistor M3, and the gate of the transistor M3 is grounded by the resistor R4.

When the input voltage Vin exceeds the threshold voltage, the transistor M3 is controlled to be turned off, and the contact of the relay 111 is turned off (released). Thereby, the input from the battery 102 is interrupted, and the circuit elements (transistors M1, M2, control IC 104, input capacitor C1, etc.) constituting the power supply apparatus 100 are protected from overvoltage. In addition, the structure which protects a circuit element from overvoltage using a relay is described in patent document 1, for example.
Japanese Patent Laid-Open No. 5-260537 (FIG. 1, paragraphs 0010 to 0016 of the specification)

  In the power supply device 100 shown in FIG. 4, a delay time inevitably occurs after the signal for turning off the relay 111 is generated until the relay 111 is actually turned off. For this reason, when the input voltage Vin increases rapidly, the voltage applied to the circuit elements constituting the power supply apparatus 100 increases until the relay 111 is actually turned off. Therefore, it is necessary to determine the breakdown voltage of these circuit elements in anticipation of the voltage increase described above.

Further, in the above-described configuration, the relay 111 is turned off in a state where a large current flows through the relay 111, so that the contact may be welded.
An object of the present invention is to avoid welding of relay contacts and to use a circuit element having a low withstand voltage in a power supply device having an overvoltage protection circuit using a relay.

  The power supply device with an overvoltage protection function of the present invention includes a power circuit, a relay, a comparison circuit, and a control means. The power circuit generates an output voltage by controlling a current using a switching element. The relay is provided between the input power supply and the power circuit. The comparison circuit compares the input voltage of the power circuit with a predetermined threshold value. The control means controls the switching element so that the power circuit generates an output voltage if the input voltage is less than or equal to a first threshold, and if the input voltage exceeds the first threshold, the switching circuit When the element is controlled to be turned off and the input voltage exceeds a second threshold value that is higher than the first threshold value, the relay is controlled to be turned off.

  In the power supply device having the above configuration, when the input voltage rises and exceeds the first threshold value, the switching element is controlled to be turned off, and the current flowing through the power circuit is reduced. When the input voltage further rises and exceeds the second threshold value, the relay is controlled to be turned off, the input power supply and the power circuit are disconnected, and the circuit element is protected from the overvoltage. Thus, since the switching element is controlled to be turned off before the relay is turned off, the current flowing through the relay is sufficiently small when the relay contact is released.

  In the power supply device with an overvoltage protection function, when the input voltage exceeds a third threshold value that is higher than the second threshold value, the input voltage is a predetermined clamp voltage or more than that. Alternatively, the switching element may be switched so as to match the low voltage.

  When the input voltage increases rapidly, the voltage further increases within the operation delay time of the relay. However, when the input voltage exceeds the third threshold, the input voltage is clamped to a predetermined clamp voltage or a lower voltage.

  The overvoltage protection circuit of the present invention is used in a power supply device that controls an output voltage by controlling a current using a switching element, and has a comparison circuit and a control means. The comparison circuit compares the input voltage with a predetermined threshold value. When the input voltage exceeds a first threshold, the control unit controls the switching element to be in an OFF state. When the input voltage exceeds a second threshold that is higher than the first threshold, the input power supply and the The relay provided between the power supply apparatus is controlled to be in an off state. Further, when the input voltage exceeds a third threshold value that is higher than the second threshold value, the control means causes the input voltage to match a predetermined clamp voltage or a lower voltage. It may be switched to control the switching element. The operation of these overvoltage protection circuits is as described above.

  In the power supply device with overvoltage protection function or the overvoltage protection circuit, when the input voltage exceeds the third threshold value within a predetermined time after the input voltage exceeds the second threshold value, the input voltage is set in advance. The switching element may be switched so as to be matched with a predetermined clamp voltage or a lower voltage. According to this configuration, when the input voltage rapidly rises and reaches an overvoltage, the input voltage is clamped to a predetermined clamp voltage or a voltage lower than that.

According to the present invention, since the current flowing through the relay is sufficiently reduced before the relay is turned off for overvoltage protection, the relay contact is not welded when released.
Further, when the input voltage further rises within the operation delay time of the relay, the voltage is clamped to a predetermined value, so that the breakdown voltage of the circuit elements constituting the power supply device can be lowered.

  FIG. 1 is a diagram showing a configuration of a power supply device with an overvoltage protection function according to the present invention. Here, the power supply device 1 shown in FIG. 1 is a DC / DC converter, and a battery 102 as an input power supply is connected to an input terminal 101 thereof. The power supply device 1 also includes a power circuit 10, an input voltage detection circuit 20, a control IC 30, a relay 111, and the like. The basic configuration of the power supply device 1 shown in FIG. 1 is the same as that of the power supply device 100 shown in FIG. 4, but the control IC 30 that provides the characteristic functions of the present invention is different from the control IC 104 shown in FIG. Yes.

  The power circuit 10 includes an input capacitor C1, a transformer T, transistors M1 and M2 as switching elements, diodes D1 and D2, and an output capacitor C2. Here, the input terminal 101 is connected to the midpoint of the primary coil of the transformer T via the relay 111 and the power line 103. One end of the primary coil of the transformer T is connected to the drain of the transistor M1, and the other end of the primary coil of the transformer T is connected to the drain of the transistor M2. Furthermore, the sources of the transistors M1 and M2 are grounded (or connected to the negative electrode of the battery 102). Control signals cont1 and cont2 generated by the control IC 30 are applied to the gates of the transistors M1 and M2, respectively.

The input voltage detection circuit 20 includes resistors R1 and R2 for dividing the input voltage Vin. The detection voltage Vh obtained by dividing the input voltage Vin is applied to the VH terminal of the control IC 30. The relationship between the input voltage Vin and the detection voltage Vh is expressed by the following equation (1).
Vin = Vh × {(R1 + R2) / R2} (1)
The control IC 30 includes a comparison circuit 31 and a control circuit 40, which will be described later, and generates a control signal cont1, a control signal cont2, and a relay control signal Recont. Control signal cont1 and control signal cont2 are output via output terminal OUT1 and output terminal OUT2, respectively, and are provided to the gates of transistor M1 and transistor M2 of power circuit 10. Also, the relay control signal Recont is output via the output terminal Relay_out and is given to the gate of the transistor M3.

  Relay 111 is provided between battery 102 and power circuit 10 and is controlled to be on (conductive state) or off (cut off state) according to the state of transistor M3. A resistor R3 is provided between the relay 111 and the transistor M3, and the gate of the transistor M3 is grounded by the resistor R4.

  FIG. 2 shows an embodiment of the comparison circuit 31 provided in the control IC 30. The comparison circuit 31 includes comparators 32-34. The positive input terminals of the comparators 32 to 34 are connected to the VH terminal of the control IC 30 and are supplied with a detection voltage Vh obtained by dividing the input voltage Vin. Reference voltages V11, V22, and V33 are applied to the negative input terminals of the comparators 32, 33, and 34, respectively. Here, these reference voltages are set so as to satisfy “V11 <V22 <V33”. Further, if a value lower than the breakdown voltage of the transistors M1, M2, the control IC 30, and the input capacitor C1 is set as the reference voltage V33, each circuit element can be protected from overvoltage.

The comparators 32, 33, and 34 compare the detected voltage Vh with the corresponding reference voltages V11, V22, and V33. As comparison results, the first overvoltage determination signal comp_OUT11, the second overvoltage determination signal comp_OUT22, and the third Outputs overvoltage judgment signal comp_OUT33. Here, if the detection voltage Vh is equal to or lower than the corresponding reference voltage, the first to third overvoltage determination signals are “L” indicating that the input voltage Vin is not an overvoltage, and the detection voltage Vh indicates the corresponding reference voltage. If it exceeds, the input voltage Vin becomes “H” indicating an overvoltage. That is, the comparison circuit 31 monitors the level of the overvoltage in three stages. Here, considering the relational expression (1) described above, the three threshold values for determining whether or not the input voltage Vin is an overvoltage are as follows.
First threshold value: V11 × {(R1 + R2) / R2}
Second threshold value: V22 × {(R1 + R2) / R2}
Third threshold value: V33 × {(R1 + R2) / R2}
In the power supply device 1 having the above-described configuration, the control IC 30 uses the control signals cont1 and cont2 to set the output voltage of the power circuit 10 to a desired value (here, when the input voltage Vin is equal to or lower than the first threshold value). Then, the voltage required by the load 200 is maintained. At this time, the transistors M1 and M2 of the power circuit 10 are alternately turned on / off according to the control signals cont1 and cont2. As a result, a current corresponding to the control signals cont1 and cont2 flows through the primary coil of the transformer T. Then, electric power is transmitted from the primary side of the transformer T to the secondary side. Then, the output of the transformer T is rectified by the diodes D1 and D2, further smoothed by the output capacitor C2, and supplied to the load 200. As described above, the power supply device 1 generates a corresponding output voltage by controlling the current on the input side using the transistors M1 and M2.

  The operation when an overvoltage occurs is as follows. That is, when the input voltage Vin exceeds the first threshold value, the control IC 30 controls the transistors M1 and M2 to be turned off using the control signals cont1 and cont2. As a result, the current on the primary side of the transformer T is greatly reduced, and accordingly, the current flowing through the relay 111 is also reduced.

  Subsequently, when the input voltage Vin exceeds the second threshold value, the signal comp_OUT22 output from the comparator 33 shown in FIG. 2 changes from “L” to “H”. This signal comp_OUT22 is output via the output terminal Relay_out and is given to the gate of the transistor M3 as the relay control signal Recont. Then, the transistor M3 is turned off and the relay 111 is turned off. As a result, since the battery 102 is disconnected from the power supply device 1, the circuit elements (transistors M1, M2, control IC 30, and input capacitor C1) constituting the power supply device 1 are protected from overvoltage. Further, at this time, the current flowing through the relay 111 is greatly reduced by controlling the transistors M1 and M2 to be in the OFF state, so that the welding of the contact is avoided.

  Thus, when the input voltage Vin rises, the relay 111 is turned off, and overvoltage is avoided. However, for example, when the output voltage of the battery 102 suddenly increases, the input voltage Vin further increases during the period from when the input voltage Vin exceeds the second threshold until the relay 111 is actually turned off. Will rise. When the input voltage Vin exceeds the third threshold value within a predetermined time (for example, preferably set to about 1 to 5 seconds) after the input voltage Vin exceeds the second threshold value, the control IC 30 The transistors M1 and M2 are controlled so that the input voltage Vin matches a predetermined clamp voltage (or a voltage lower than that). Here, the clamp voltage is set lower than the withstand voltages of the transistors M1 and M2, the control IC 30, and the input capacitor C1. That is, in this case, the input voltage Vin is clamped to a predetermined value, and circuit elements constituting the power supply device 1 are protected from overvoltage.

  Therefore, it is not necessary to increase the withstand voltage of the circuit elements constituting the power supply device 1 more than necessary. As a result, since inexpensive parts can be used as circuit elements constituting the power supply device 1, the cost of the power supply device as a whole can be reduced.

  FIG. 3 shows an embodiment of a control circuit (control means) 40 provided in the control IC 30. Note that FIG. 3 illustrates a control circuit for generating the control signal cont1, but the control circuit for generating the control signal cont1 and the control circuit for generating the control signal cont2 are basically the same as each other. It is a configuration. Therefore, description of the control circuit for generating the control signal cont2 is omitted.

  The control signal cont3 is, for example, a PWM signal having a predetermined period, and is given to one input terminal of each of the OR gates 41 and 42. Note that the control signal cont3 is generated by a known technique based on the output voltage of the power circuit 10, for example. A first overvoltage determination signal comp_OUT11 is supplied to the other input terminal of each of the OR gates 41 and. The output of the OR gate circuit 41 is given to the gate of the transistor M4 through the buffer 43.

  The output of the OR gate 42 is given to one input terminal of the AND gate 44. Further, a third overvoltage determination signal comp_OUT33 whose logic is inverted by the inverting circuit 45 is supplied to the other input terminal of the AND gate 44. The output of the AND gate 44 is given to the gate of the transistor M5 through the buffer 46.

  The transistors M4 and M5 are a pMOS transistor and an nMOS transistor, respectively, and are connected in series. The connection point of the transistors M4 and M5 is connected to the output terminal OUT1 shown in FIG.

  The amplifier 48 operates when the third overvoltage determination signal comp_OUT33 is “H”, and stops its operation when the third overvoltage determination signal comp_OUT33 is “L”. The non-inverting input terminal of the amplifier 48 is supplied with a fixed voltage Vk (for example, 3 V), and the inverting input terminal is supplied with a detection voltage Vh. The output of the amplifier 48 is connected to the output terminal OUT1 through the signal line 47. The signal line 47 is grounded via a resistor R5.

  In the control circuit 40 having the above configuration, if the input voltage Vin is equal to or lower than the first threshold value, the first overvoltage determination signal comp_OUT11 becomes “L”, so that the control signal cont3 passes through the OR gates 41 and 42. To do. In this case, since the third overvoltage determination signal comp_OUT33 is also “L”, the output of the OR gate 42 passes through the AND gate 44. That is, the control signal cont3 is given to the gates of the transistors M4 and M5. Thus, the transistors M4 and M5 are alternately turned on / off. Further, the amplifier 48 does not operate. Therefore, in this case, the control circuit 40 outputs signals corresponding to the control signal cont3 as the control signal cont1 and the control signal cont2. As a result, the transistors M1 and M2 shown in FIG. 1 are controlled so that the power circuit 10 generates a voltage required by the load 200.

  When the input voltage Vin exceeds the first threshold, the first overvoltage determination signal comp_OUT11 becomes “H”. If the input voltage Vin is equal to or lower than the third threshold, the third overvoltage determination signal comp_OUT33 is “L”. In this case, since the transistor M4 is turned off and the transistor M5 is turned on, the output terminal OUT1 and the output terminal OUT2 become “L”. Therefore, since the transistors M1 and M2 are given “L” as the control signal cont1 and the control signal cont2, respectively, both are controlled to be in the off state. As a result, the current flowing through the primary side of the transformer T is greatly reduced.

  When the input voltage Vin exceeds the third threshold, the first overvoltage determination signal comp_OUT11 and the third overvoltage determination signal comp_OUT33 are both “H”. Then, the transistors M4 and M5 are both turned off, and the output terminal OUT1 and the output terminal OUT2 are in a high impedance state. Further, when the third overvoltage determination signal comp_OUT33 becomes “H”, the amplifier 48 generates an error signal for making the error between the voltage Vk and the detection voltage Vh zero, and the error signal is the control signal cont1, cont2. Is output as

  When the control signals cont1 and cont2 generated in this way are given, the transistors M1 and M2 operate so as to make the detection voltage Vh coincide with the voltage Vk. Here, considering the relational expression (1) described above, the transistors M1 and M2 operate so as to make the input voltage Vin coincide with “Vk × {(R1 + R2) / R2}”. That is, the input voltage Vin is held at a predetermined clamp voltage “Vk × {(R1 + R2) / R2}”. Here, for example, assuming that “Vk = 3 volts” and “R1 = R2”, the clamp voltage is 6 volts.

  As described above, in the power supply device 1, when the input voltage Vin exceeds the first threshold value, the transistors M1 and M2 are controlled to be turned off, the current on the primary side of the transformer T is decreased, and the second threshold value is further increased. If exceeded, the relay 111 is controlled to be in an OFF state, and an overvoltage is avoided. At this time, since the relay contact is released after the current flowing through the relay 111 is sufficiently reduced, the contact is not welded.

  Further, when the input voltage Vin suddenly rises and exceeds the third threshold before the relay 111 is actually turned off, the transistors M1 and M2 are set so that the input voltage Vin matches the predetermined clamp voltage. Is controlled. Here, if a value lower than the withstand voltage of the transistors M1, M2, the control IC 30, and the input capacitor C1 is set as the clamp voltage, each circuit element protection can be protected from an overvoltage. In other words, the breakdown voltage of each circuit element can be lowered by setting an appropriate clamp voltage.

  In the above-described embodiment, a DC / DC converter is shown as an example of a power supply device, but the present invention is not limited to this. That is, the present invention is applicable to a power circuit that controls an output using a switching element.

It is a figure which shows the structure of the power supply device with an overvoltage protection function which concerns on this invention. It is an Example of the comparison circuit provided in control IC. It is an Example of the control circuit provided in control IC. It is a figure which shows the conventional power supply device provided with the overvoltage protection function.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Power supply device 10 Power circuit 20 Input voltage detection circuit 30 Control IC
31 Comparison Circuit 32-33 Comparator 40 Control Circuit 101 Input Terminal 102 Battery 111 Relay 200 Load

Claims (2)

A power circuit that includes a switching element and generates an output voltage by a current that flows when the switching element is turned on and off ;
A relay provided between the input power source and the power circuit;
A comparison circuit for comparing the input voltage of the power circuit with a predetermined threshold;
If the input voltage is equal to or less than the first threshold value, on of the switching element so as to generate an upper Kide force voltage, by controlling the off and the input voltage exceeds the first threshold value, the switching element Control means for controlling the relay to an off state when the input voltage exceeds a second threshold value higher than the first threshold value.
I have a,
When the input voltage exceeds the third threshold value within a predetermined time after the input voltage exceeds the second threshold value, the control means sets the input voltage to a predetermined clamp voltage or a lower voltage. A power supply device with an overvoltage protection function , wherein on / off of the switching element is controlled so as to match . An overvoltage protection circuit used in a power supply device that includes a switching element and controls an output voltage by a current that flows when the switching element is turned on and off .
A comparison circuit that compares the input voltage with a predetermined threshold;
When the input voltage exceeds a first threshold, the switching element is controlled to be in an OFF state, and when the input voltage exceeds a second threshold that is higher than the first threshold, the input power source and the power supply device Control means for controlling the relay provided between them in an off state;
I have a,
When the input voltage exceeds the third threshold value within a predetermined time after the input voltage exceeds the second threshold value, the control means sets the input voltage to a predetermined clamp voltage or a lower voltage. An overvoltage protection circuit that controls on and off of the switching element so as to coincide with each other .

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