JP6488432B1 - Overcurrent protection circuit - Google Patents

Abstract

  An overcurrent protection circuit according to an embodiment of the present invention includes a current supply line, a protection transistor, and a voltage generation unit. The current supply line includes a first switch and a current detection resistor. The first switch includes a field effect transistor or an insulated gate bipolar transistor. The current detection resistor detects an overcurrent to the load. The current supply line supplies a current from a first current supply source to the load. The protection transistor is connected in parallel with the current detection resistor. The protection transistor has an emitter connected to the current supply line and a collector connected to a gate of the first switch, and the first switch is turned off to limit an overcurrent to the load. It is possible to switch between.

Description

  The present invention relates to an overcurrent protection circuit that limits energization to a load when an overcurrent is detected.

  For example, a protection circuit that limits energization to a load when an overcurrent is detected due to a ground fault in a circuit on the load side is known. For example, Patent Document 1 discloses a main transistor connected between a power source and a load, a load current detection resistor for detecting an overcurrent to the load, and an overcurrent detection voltage in which a voltage drop in the load current resistor is predetermined. An overcurrent protection circuit is disclosed that includes a first transistor that operates when the current reaches the first transistor and switches the main transistor to an off state.

JP 2011-78235 A

  In the conventional overcurrent protection circuit, the threshold voltage of the first transistor is set to a magnitude corresponding to the overcurrent detection voltage in the load current detection resistor. For this reason, it is difficult to reduce the amount of heat generated by the overcurrent detection resistor when the overcurrent protection function is activated by the operation of the first transistor, and as a result, a relatively large resistance is added to the overcurrent detection resistor in consideration of the amount of heat generation. Need to be used, or the mechanism for heat dissipation of the overcurrent detection resistor must be enlarged.

  In view of the circumstances as described above, an object of the present invention is to provide an overcurrent protection circuit that can reduce the amount of heat generated by a load current detection resistor.

In order to achieve the above object, an overcurrent protection circuit according to an aspect of the present invention includes a current supply line, a protection transistor, and a voltage generator.
The current supply line includes a first switch and a current detection resistor. The first switch includes a field effect transistor or an insulated gate bipolar transistor. The current detection resistor detects an overcurrent to the load. The current supply line supplies a current from a first current supply source to the load.
The protection transistor is connected in parallel with the current detection resistor. The protection transistor has an emitter connected to the current supply line and a collector connected to a gate of the first switch, and the first switch is turned off to limit an overcurrent to the load. It is possible to switch between.
The voltage generator is connected to a base of the protection transistor and generates a reference voltage lower than a threshold voltage at which the protection transistor is switched on.

  Since the overcurrent protection circuit includes a voltage generator, the resistance value of the current detection resistor can be made smaller than that of the conventional one. Thereby, it is possible to reduce the amount of heat generated by the current detection resistor when the overcurrent protection function is activated.

The voltage generation unit includes a reference voltage generation source that generates a first voltage that is equal to or higher than the threshold voltage, and a voltage dividing circuit unit that divides the first voltage into a second voltage corresponding to the reference voltage. May be.
As a result, when an overcurrent occurs, the first switch can be stably switched to the off state.

The first switch may be composed of a P-type field effect transistor connected between the current detection resistor and the load. In this case, the reference voltage generation source is connected between an output terminal of the current detection resistor and a ground terminal, the protection transistor is an emitter connected to the first current supply source, and the first And a PNP bipolar transistor having a collector connected to the gate of the switch and a base connected to the voltage dividing circuit section.
With this configuration, it is possible to generate a voltage equal to or higher than the threshold voltage of the protection transistor between the base and the emitter of the protection transistor when an overcurrent is detected.

  The voltage dividing circuit unit may include a first resistance element and a second resistance element. The first resistance element is connected between an output terminal of the current detection resistor and the ground terminal. The second resistance element is connected between the first resistance element and the ground terminal, and has a larger resistance value than the current detection resistance.

  The reference voltage generation source includes a rectifier element connected in parallel with the first resistance element and the second resistance element between an output terminal of the current detection resistor and the ground terminal, and generates the voltage The unit may further include a third resistance element connected between the second resistance element and the ground terminal.

The reference voltage generation source may further include a fourth resistance element connected in series with the rectifying element.
Thereby, the circuit characteristic of a voltage generation part can be adjusted.

The voltage generation unit may further include a switching circuit unit including a second switch that can cut off a connection between the third resistance element and the ground terminal.
As a result, it is possible to realize a standby mode that limits the current flowing to the load by maintaining the first switch in an off state other than when an overcurrent is detected, and the current in the voltage generator in the standby mode is Consumption can be suppressed.

  The second switch includes a field effect transistor, and the switching circuit unit further includes a fifth resistance element connected between a gate of the first switch and a source of the second switch. You may have.

In this case, the fifth resistance element may have a larger resistance value than the third resistance element.
As a result, the occurrence of peaking of the current flowing through the current detection resistor can be suppressed, and for example, excessive supply of current when power is supplied to the load can be prevented.

The overcurrent protection circuit may further include an impedance element connected between a source and a gate of the first switch.
Thereby, the first switch can be protected from the surge current when the overcurrent is detected.

The rectifying element may be a diode-connected transistor having a threshold voltage substantially the same as the threshold voltage of the protection transistor.
Alternatively, the rectifying element may be composed of a diode having an operating voltage substantially the same as the threshold voltage of the protection transistor.

On the other hand, the first switch may be composed of an N-type field effect transistor connected between the first current supply source and the current detection resistor. In this case, the reference voltage generation source is connected between a second current supply source and the input terminal of the current detection resistor, and the protection transistor is an emitter connected to the output terminal of the current detection resistor. And an NPN bipolar transistor having a collector connected to the gate of the first switch and a base connected to the voltage dividing circuit section.
With this configuration, it is possible to generate a voltage equal to or higher than the threshold voltage of the protection transistor between the base and the emitter of the protection transistor when an overcurrent is detected.

  The voltage dividing circuit unit may include a first resistance element and a second resistance element. The first resistance element is connected between the second current supply source and an input terminal of the current detection resistor. The second resistance element is connected between the first resistance element and the second current supply source, and has a larger resistance value than the current detection resistance.

  The reference voltage generation source includes a rectifying element connected in parallel with the first resistance element and the second resistance element between the second current supply source and an input terminal of the current detection resistor. The voltage generation unit may further include a third resistance element connected between the second current supply source and the second resistance element.

The voltage generation unit may further include a switching circuit unit including a second switch that can cut off a connection between the second current supply source and the third resistance element.
As a result, it is possible to realize a standby mode that limits the current flowing to the load by maintaining the first switch in an off state other than when an overcurrent is detected, and the current in the voltage generator in the standby mode is Consumption can be suppressed.

  On the other hand, the first switch may be composed of an N-type field effect transistor connected between the load and the current detection resistor. In this case, the current detection resistor is connected between the load and the ground terminal, and the reference voltage generation source is connected between a second current supply source and an input terminal of the current detection resistor, The protection transistor includes an emitter connected to the output terminal of the current detection resistor, a collector connected to the gate of the first switch, and a base connected to the voltage dividing circuit section. It is composed of transistors.

  Also in this case, the voltage dividing circuit unit may include a first resistance element and a second resistance element. The first resistance element is connected between the second current supply source and an input terminal of the current detection resistor. The second resistance element is connected between the first resistance element and the second current supply source, and has a larger resistance value than the current detection resistance.

  The reference voltage generation source includes a rectifying element connected in parallel with the first resistance element and the second resistance element between the second current supply source and an input terminal of the current detection resistor. But you can. In this case, the voltage generating unit further includes a third resistance element connected between the second current supply source and the rectifying element, and the reference voltage generating source is in series with the rectifying element. A fourth resistance element connected is further included.

The overcurrent protection circuit may further include a heat transfer member that thermally connects the protection transistor and the voltage generation source.
Alternatively, the overcurrent protection circuit may further include a package body that seals the protection transistor and the voltage generation source in common.
As a result, the protection transistor and the voltage generation source can be maintained in a common temperature environment.

It is a circuit diagram which shows the basic composition of the overcurrent protection circuit which concerns on one Embodiment of this invention. It is a circuit diagram which shows the overcurrent protection circuit which concerns on a comparative example. 1 is a circuit diagram showing an overcurrent protection circuit according to a first embodiment of the present invention. It is a circuit diagram which shows the overcurrent protection circuit which concerns on the 2nd Embodiment of this invention. It is a figure which shows an example of the relationship between the power supply voltage and output current in the said overcurrent protection circuit. It is a circuit diagram which shows the overcurrent protection circuit which concerns on the 3rd Embodiment of this invention. It is a circuit diagram which shows the overcurrent protection circuit which concerns on the 4th Embodiment of this invention. It is a figure which shows an example of the relationship with the power supply potential in each part of the said overcurrent protection circuit. It is a figure explaining one effect | action of the said overcurrent protection circuit. It is a figure explaining one effect | action of the said overcurrent protection circuit. It is a circuit diagram which shows the overcurrent protection circuit which concerns on the 5th Embodiment of this invention. It is a figure explaining the example of 1 structure of the principal part of the overcurrent protection circuit which concerns on the 6th Embodiment of this invention. It is a figure explaining the other structural example of the principal part of the said overcurrent protection circuit. It is a circuit diagram which shows the overcurrent protection circuit which concerns on the 7th Embodiment of this invention. It is a circuit diagram which shows the overcurrent protection circuit which concerns on the 8th Embodiment of this invention. It is a circuit diagram which shows the overcurrent protection circuit which concerns on the 9th Embodiment of this invention. It is a circuit diagram which shows the overcurrent protection circuit which concerns on the 10th Embodiment of this invention. It is a circuit diagram which shows the overcurrent protection circuit which concerns on the 11th Embodiment of this invention. It is a circuit diagram which shows the other structural example of the said overcurrent protection circuit. It is a circuit diagram which shows the further another structural example of the said overcurrent protection circuit. It is a figure explaining the example of 1 structure of the principal part of the overcurrent protection circuit which concerns on the 12th Embodiment of this invention. It is a figure explaining the other structural example of the principal part of the said overcurrent protection circuit. It is a circuit diagram which shows the modification of a structure of the overcurrent protection circuit which concerns on one Embodiment of this invention. It is a circuit diagram which shows the other modification of a structure of the said overcurrent protection circuit. It is a circuit diagram which shows the further another modification of the structure of the said overcurrent protection circuit. It is a circuit diagram which shows the further another modification of the structure of the said overcurrent protection circuit.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<First Embodiment>
[Basic configuration]
FIG. 1 is a circuit diagram showing a basic configuration of an overcurrent protection circuit according to an embodiment of the present invention.

  The overcurrent protection circuit 100 of the present embodiment includes a current supply line 21, a protection transistor Q11, and a voltage generation unit X10.

The current supply line 21 includes a main switch (first switch) M11 connected between the power source 10 (first current supply source) and the output port 11 connected to the load L, and an overcurrent to the load L. Current detection resistor Rs.
The protection transistor Q11 is connected in parallel with the current detection resistor Rs between the power supply 10 and the load L (output port 11).
The voltage generator X10 is connected to the base of the protection transistor Q11, and is configured to be able to generate a reference voltage (Vref) that is smaller than the threshold voltage (Vbe) at which the protection transistor Q11 switches to the on state.

  Details of each part will be described below.

In the present embodiment, the power source 10 is constituted by a DC power source such as a battery.
The main switch M11 is connected between the current detection resistor Rs and the output port 11 (load L). The main switch M11 is a P-type MOSFET having a gate connected to the collector of the protection transistor Q11 via the control line 22, a source connected to the current detection resistor Rs, and a drain connected to the output port 11. (Metal-Oxide-Semiconductor Field-Effect-Transistor).
The protection transistor Q11 includes a base connected to the voltage generator X10, an emitter connected to the current supply line 21 between the power supply 10 and the current detection resistor Rs, and a gate of the main switch M11 via the control line 22. And a collector connected to the PNP bipolar transistor.

The main switch M11 is configured to be switchable between an on state in which current is supplied from the power source 10 to the load L and an off state in which the current supplied from the power source 10 to the load L is limited by the protection transistor Q11.
Here, “limit the current” means that the current supplied to the load L is restricted to a predetermined current value or less in the present embodiment, but is not limited thereto, and the current supplied to the load L is not limited thereto. The main switch M11 may be configured to shut off the output current (set the output current to zero).

The overcurrent protection circuit 100 has an input port 12 connected to the gate of the main switch M11 via the control line 22. The input port 12 is configured to be capable of inputting an input signal capable of controlling on / off of the main switch M11.
The gate of the main switch M11 adjusts the impedance between the source and drain of the main switch M11. The impedance of the input signal (voltage) applied to the input port 12 is higher than the impedance when the emitter and collector of the protection transistor Q11 are conducted, and the operation of the protection transistor Q11 is preferentially performed. .

  The protection transistor Q11 has a threshold voltage (Vbe) that is switched on when the voltage drop of the current detection resistor Rs reaches a predetermined overcurrent detection voltage, and the voltage between the base and the emitter is the threshold voltage (Vbe). ) The main switch M11 can be switched to the off state at the above time.

  The voltage generator X10 is connected between the current supply line 21 between the current detection resistor Rs and the main switch M11 and the base of the protection transistor Q11. The voltage generator X10 generates a reference voltage (Vref). The reference voltage (Vref) is set to an appropriate level that does not satisfy the threshold voltage (Vbe) of the protection transistor Q11. Further, when the voltage drop in the current detection resistor Rs reaches a predetermined magnitude (hereinafter also referred to as an overcurrent detection voltage (ΔVrs)), the reference voltage (Vref) is equal to the overcurrent detection voltage (ΔVrs) and the reference voltage. The value added to (Vref) is set to a value that is equal to or higher than the threshold voltage (Vbe) of the protection transistor Q11.

  Thereby, in a normal time when a predetermined amount of current (not an overcurrent) is supplied to the load L, the protection transistor Q11 is maintained in the off state. On the other hand, when the voltage drop of the current detection resistor Rs reaches a predetermined overcurrent detection voltage (ΔVrs), the sum of the overcurrent detection voltage (ΔVrs) and the reference voltage (Vref) is the base of the protection transistor Q11. -The protection transistor Q11 is configured to be turned on by being input between the emitters.

  As described above, the overcurrent protection circuit 100 according to the present embodiment includes the voltage generation unit X10 that inputs the reference voltage (Vref) to the base of the protection transistor Q11, so that the voltage drop at the current detection resistor Rs is compared. Even in a case where the size is small, it is possible to switch the main transistor M11 to the off state by switching the protection transistor Q11 to the on state.

  As a comparative example, an overcurrent protection circuit 1 that does not include the voltage generator X10 is shown in FIG.

  As shown in the figure, in the overcurrent protection circuit 1 of the comparative example, the output terminal (current supply line 10) of the current detection resistor Rs and the base of the protection transistor Q11 are directly connected. In the overcurrent protection circuit 1, when the voltage drop at the current detection resistor Rs becomes equal to or higher than the threshold voltage (Vbe) of the protection transistor Q11, the protection transistor Q11 is turned on. As a result, the main switch M11 is switched to an off state that limits the current supplied from the power supply 10 to the load L.

  In the overcurrent protection circuit 1 of the comparative example, the amount of heat generated by the current detection resistor Rs becomes a problem when an overcurrent occurs. The current value of the overcurrent is Imax [A], the resistance value of the current detection resistor Rs is Rs1 [Ω], the threshold voltage of the protection transistor Q11 is Vbe [V], and the amount of heat generated by the current detection resistor Rs when an overcurrent occurs Assuming that Pmax1 [W], the overcurrent protection circuit 1 satisfies the following relationship.

Imax = Vbe / Rs1 (1)
Pmax1 = (Imax) ²・ Rs1
= (Vbe) ² / Rs1 (2)

  In the overcurrent protection circuit 1 of the comparative example, the current under the condition that the threshold voltage (Vbe) of the protection transistor Q11 is 0.6 [v], the resistance value of the current detection resistor Rs, and the loss at the current detection resistor Rs Table 1 shows the relationship of power.

  On the other hand, the overcurrent protection circuit 100 of the present embodiment is capable of converting the overcurrent detection voltage in the current detection resistor Rs into a voltage (Vref) that is equal to or higher than the threshold voltage (Vbe) of the protection transistor Q11. Have For this reason, it is possible to use a resistance element having a resistance value lower than that of the comparative example for the current detection resistor Rs, thereby suppressing the heat generation amount of the current detection resistor Rs when an overcurrent is generated to be lower than the heat generation amount of the comparative example. be able to.

  For example, the resistance value of the current detection resistor Rs in the overcurrent protection circuit 100 of this embodiment is Rs100 (= Rs1 / (1 + a) [Ω] (coefficient a is a positive number)), and the current detection resistor Rs at the time of overcurrent occurrence Assuming that the heat generation amount is Pmax100 [W], the heat generation amount Pmax100 is reduced to 1 / (1 + a) times the heat generation amount Pmax1 in the comparative example as follows.

Imax = Vbe / Rs100 = Vbe / Rs1 / (1 + a) (3)
Pmax100 = (Imax) ²・ Rs100
= [Vbe / {Rs1 / (1 + a)}] ² · Rs1 / (1 + a)
= Pmax1 / (1 + a) (4)

[Voltage generator]
Details of the voltage generator X10 will be described below.

  FIG. 3 is a circuit diagram showing an overcurrent protection circuit 101 including the voltage generator X11 of the present embodiment. In the figure, portions corresponding to those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted. Hereinafter, the threshold voltage of the protection transistor Q11 is described as “Vbe1”.

  The voltage generator X11 is connected between the output terminal of the current detection resistor Rs and the base of the protection transistor Q11. The voltage generation unit X11 includes a reference voltage generation source VS and a voltage dividing circuit unit VD.

  The reference voltage generation source VS is configured to be able to generate a first voltage that is equal to or higher than the threshold voltage (Vbe1) of the protection transistor Q11. The voltage dividing circuit unit VD is configured to be able to divide the first voltage into a second voltage corresponding to the reference voltage (Vref).

  In the present embodiment, the reference voltage generation source VS is configured to be able to generate a voltage (hereinafter also referred to as a standard voltage) corresponding to the threshold voltage (Vbe1) of the protection transistor Q11 as the first voltage. The The reference voltage generation source VS includes a voltage generation transistor Q12 connected between the output terminal of the current detection resistor Rs and the ground terminal (GND). The voltage generating transistor Q12 is composed of a rectifying element, and in this embodiment is composed of a diode-connected bipolar transistor.

  More specifically, the voltage generating transistor Q12 includes an emitter connected to the current supply line 21 (the output terminal of the current detection resistor Rs), a collector connected to the ground terminal (GND) via the resistor R3, a collector And a PNP bipolar transistor having a base connected to.

  The standard voltage corresponds to a threshold voltage (Vbe2) at which the voltage generating transistor Q12 is turned on. In this embodiment, the standard voltage is set to the same value as the threshold voltage (Vbe1) of the protection transistor Q11 (hereinafter referred to as the above-mentioned standard voltage). Standard voltage is also called standard voltage (Vbe2). The voltage generating transistor Q12 is typically composed of the same transistor element as the protecting transistor Q11. As a result, variations in characteristics between the transistors Q11 and Q12 due to changes in ambient temperature or the like can be prevented.

  The voltage dividing circuit VD is connected in parallel with the reference voltage generation source VS between the current supply line 21 (the output terminal of the current detection resistor Rs) and the ground terminal (GND). The voltage dividing circuit unit VD includes two resistors R1 (first resistor element) and resistor R2 (second resistor element) connected in series with each other, and a connection point between these two resistors R1 and R2 is for protection. Connected to the base of transistor Q11. As a result, the standard voltage (Vbe2) is divided into the reference voltage (Vref) in the voltage dividing circuit unit VD.

  The resistor R1 is connected between the output terminal of the current detection resistor Rs and the ground terminal (GND), and the resistor R2 is connected between the resistor R1 and the ground terminal (GND). The resistance values of the resistors R1 and R2 are not particularly limited as long as they can input a voltage equal to or higher than the threshold voltage (Vbe1) of the protection transistor Q11 to the base of the protection transistor Q11 when overcurrent is detected. Typically, the resistance value (R1) of the resistor R1 is set larger than the resistance value (R2) of the resistor R2. In the present embodiment, the resistance value of the resistor R2 is set to a value larger than the resistance value of the current detection resistor Rs. The resistance value of the resistor R2 works when the current flowing through the current detection resistor Rs increases and the potential difference of the current detection resistor Rs becomes larger than the potential difference generated at the resistor R2 (protection function) It is preferably set to a value that turns on transistor Q11.

  As an example, when the threshold voltage (Vbe1) and the standard voltage (Vbe2) of the protection transistor Q11 are both 0.6 [v] and the overcurrent detection voltage in the current detection resistor Rs is 0.1 [v], the resistor R1 , R2 are set to resistance values that can divide the standard voltage (Vbe2) so that a reference voltage (Vref) of 0.5 [v] or more and less than 0.6 [v] is obtained. As a result, when a voltage drop of 0.1 [v] occurs in the voltage detection resistor Rs, the potential difference between both ends of the voltage detection resistor Rs is added to the reference voltage (Vref), so that the protection transistor Q11 is turned on. Switch to state.

  The voltage generator X11 includes a resistor R3 (third resistor element). The resistor R3 is connected between the resistor R2 and the ground terminal (GND). The resistance value of the resistor R3 is not particularly limited as long as the reference voltage generation source VS can generate the above-described standard voltage (Vbe2).

[Operation of overcurrent protection circuit]
Subsequently, a typical operation of the overcurrent protection circuit 101 of the present embodiment configured as described above will be described.

  In a normal state in which a predetermined amount of current is supplied from the power supply 10 to the load L, a signal voltage that maintains the main switch M11 in the on state is input to the input port 12. As a result, the current supplied from the power supply 10 is supplied to the output port 11 and the load L connected thereto via the current supply line 21 including the current detection resistor Rs and the main switch M11. .

  The voltage generator X11 generates a reference voltage (Vref) from the current flowing from the output terminal of the current detection terminal Rs to the ground terminal (GND). More specifically, the voltage generation unit X11 generates a standard voltage (Vbe2) in the reference voltage generation source VS, and divides it into the reference voltage (Vref) in the voltage dividing circuit unit VD. The reference voltage (Vref) thus obtained is input to the base (between the base and the emitter) of the protection transistor Q11.

  When the load L is grounded, the power supply potential (Vcc) with respect to the load L is increased and the output current (Iout) is increased. As a result, the voltage drop at the current detection resistor Rs is also increased. A reference voltage (Vref) is input in advance between the base and emitter of the protection transistor Q11, and this reference voltage (Vref) is protected by the base-emitter voltage when added to the overcurrent detection voltage (ΔVrs). Is set to a value equal to or higher than the threshold voltage (Vbe1) of the transistor Q11.

  Therefore, when the voltage drop in the current detection resistor Rs increases to a predetermined overcurrent detection voltage (ΔVrs), the added value of the reference voltage (Vref) in the voltage generator X11 and the voltage drop in the current detection resistor Rs is for protection. The threshold voltage (Vbe1) of transistor Q11 is reached. As a result, the protection transistor Q11 is turned on, and a control signal (collector current) for switching the main switch M11 to the off state is input to the gate of the main switch M11 via the control line 22. Thereby, since the current value supplied from the power supply 10 to the load L is limited, the load L can be protected from overcurrent.

  When the ground fault of the load L is resolved, the power supply potential (Vcc) with respect to the load L returns to the normal potential, so the magnitude of the current supplied from the power supply 10 to the load L is reduced to a predetermined amount during normal operation. Therefore, the voltage drop in the current detection resistor Rs is also reduced. As a result, the protection transistor Q11 is turned off, and the main switch M11 is turned on again. As a result, the overcurrent protection circuit 101 can be automatically returned from the current output stop (limit) mode to the normal current output operation mode.

  As described above, since the overcurrent protection circuit 101 of the present embodiment includes the voltage generation unit X11, the resistance value of the current detection resistor Rs is made smaller than that of the overcurrent protection circuit 1 of the comparative example (see FIG. 2). be able to. Thereby, it is possible to reduce the amount of heat generated by the current detection resistor Rs when the overcurrent protection function is activated.

  For example, the current under the condition that the threshold voltage (Vbe1) and the standard voltage (Vbe2) of the protection transistor Q11 are both 0.6 [v] and the ratio of the resistor R1 to the resistor R2 is 9: 1, Table 2 shows the relationship between the detection resistor Rs and the power loss in the current detection resistor Rs.

  As shown in Table 2, according to the present embodiment, compared with the overcurrent protection circuit 1 of FIG. 2, the power loss at the current detection resistor Rs can be reduced to 1/10. As a result, the amount of heat generated by the current detection resistor Rs can be significantly reduced, and thus the current detection resistor Rs can be configured with a smaller resistance element. In addition, the heat dissipation mechanism can be reduced in size and simplified.

<Second Embodiment>
FIG. 4 is a circuit diagram showing an overcurrent protection circuit 102 according to the second embodiment of the present invention. Hereinafter, the configuration different from the first embodiment will be mainly described, and the same configuration as the first embodiment will be denoted by the same reference numeral, and the description thereof will be omitted or simplified.

  The overcurrent protection circuit 102 of the present embodiment is different from the first embodiment in the configuration of the voltage generator X12. In the present embodiment, the reference voltage generation source VS of the voltage generation unit X12 further includes a resistor R4 (fourth resistance element) connected in series with the voltage generation transistor Q12. In the present embodiment, the resistor R4 is connected between the voltage generating transistor Q12 and the resistor R3, but is not limited thereto, and may be connected to the emitter side of the voltage generating transistor Q12.

  The threshold voltages (Vbe1, Vbe2) of the protection transistor Q11 and the voltage generation transistor Q12 have temperature dependency and tend to increase (increase) as the temperature decreases. The voltage generation unit X12 can adjust the change in the standard voltage (Vbe2) of the reference voltage generation source VS according to the increase of the power supply voltage (Vcc) with respect to the load L, depending on the resistance value of the resistor R4.

  5A to 5C show experimental results showing the relationship between the power supply voltage (Vcc) and the output current (Iout) with respect to the load L in the overcurrent protection circuit 102. FIG. Here, for simplicity, the resistance value of the resistor R4 is “small”, “medium”, and “large”, and the ambient temperature (ambient air temperature: ta) is −40 ° C. and 25 ° C., respectively. The measured value of the output current at 85 ° C. was plotted.

  As shown in FIGS. 5A to 5C, regardless of the size of the resistor R4, the output current (Iout) tends to increase as the power supply voltage (Vcc) increases as the environmental temperature decreases. Further, as the resistance value of the resistor R4 increases, the output current (Iout) tends to decrease as the power supply voltage (Vcc) increases.

  The output current (Iout) depends on the output characteristic of the main switch M11, and the output characteristic of the main switch M11 depends on the output characteristic of the protection transistor Q11. Furthermore, the output characteristics of the protection transistor Q11 have a strong correlation with the circuit characteristics of the voltage generation unit X12 when overcurrent is detected. For this reason, for example, when the output characteristics of the voltage generator X12 greatly depend on the voltage between the power supply 10 and the load L, the output characteristics of the voltage generator X12 are optimized by optimizing the resistance value of the resistor R4. Can be adjusted.

  Also in the overcurrent protection circuit 102 of the present embodiment configured as described above, the same operational effects as those of the first embodiment described above can be obtained. According to this embodiment, since the reference voltage generation source VS has the resistor R4, desired circuit characteristics of the voltage generator X12 can be obtained by adjusting the value of the resistor R4.

<Third Embodiment>
FIG. 6 is a circuit diagram showing an overcurrent protection circuit 103 according to the third embodiment of the present invention. Hereinafter, the configuration different from the second embodiment will be mainly described, and the same configuration as the second embodiment will be denoted by the same reference numeral, and the description thereof will be omitted or simplified.

  The overcurrent protection circuit 103 of the present embodiment is different from the second embodiment in the configuration of the voltage generator X13. The voltage generation unit X13 of the present embodiment further includes a switching circuit unit SC including a changeover switch M12 (second switch). The overcurrent protection circuit 103 further includes a standby port 13.

The changeover switch M12 is formed of a switching element that can cut off the connection between the resistor R3 and the ground terminal (GND). In the present embodiment, the changeover switch M12 is configured by an N-type MOSFET connected between a resistor R3 and a ground terminal (GND). The changeover switch M12 has a gate connected to the standby port 13, a drain connected to the resistor R3, and a source connected to the ground terminal (GND).
The standby port 13 is configured to be able to input a standby signal that can turn on / off the changeover switch M12.

  The overcurrent protection circuit 103 according to the present embodiment switches between a standby state mode, a current output operation mode, and a current output stop mode by adjusting the potential of an external signal input to the input port 12 and the standby port 13. Configured to be possible. Table 3 shows the relationship between the input signal and standby signal and the current output.

  In the standby mode, the signal (I signal) input to the input port 12 is adjusted to a potential that turns off the main switch M11, and the signal (Standby signal) input to the standby port 13 turns off the changeover switch M12. It is adjusted to a potential that limits the current flowing to the ground terminal (GND). In this mode, the power supply current output from the output port 11 is limited by the main switch M11, and the dark current of the resistor R3 is also suppressed. For this reason, current consumption of the power supply 10 can be minimized when the device is not operating.

  In the current output operation mode, the signal (I signal) input to the input port 12 is adjusted to the potential for turning on the main switch M11, and the signal (Standby signal) input to the standby port 13 turns on the changeover switch M12. The potential is adjusted. In this mode, the overcurrent protection circuit 103 is enabled during the operation of the device, and when the ground fault occurs, the main switch M11 is switched off by the operation of the voltage generation unit X13, so that an appropriate overcurrent protection function is provided. can get.

  In the current output stop mode, the signal (I signal) input to the input port 12 is adjusted to a potential for turning off the main switch M11, and the signal (Standby signal) input to the standby port 13 turns on the changeover switch M12. The potential is adjusted. In this mode, for example, when it is desired to stop the operation of the device for a reason other than a ground fault, the main switch M11 is shifted to the OFF state by the input signal from the input port 12 to limit the current supply to the load. Applies to

  As described above, according to the present embodiment, the same operational effects as those of the second embodiment can be obtained, and the normal mode (current output) can be obtained by connecting the overcurrent protection circuit 103 to the external control circuit. It is possible to execute other operation modes other than (operation mode).

  Note that the input port 12 may not be connected to the control circuit. In this case, the input port 12 is connected to the ground terminal via an appropriate resistance element.

  The change-over switch M12 is not limited to being configured by an FET, and may be configured by a switching element such as a bipolar transistor, a photocoupler, or a photoMOS. Alternatively, the changeover switch M12 may be configured by a mechanical relay as long as it is a switch element that can be easily controlled by the CPU.

<Fourth Embodiment>
FIG. 7 is a circuit diagram showing an overcurrent protection circuit 104 according to the fourth embodiment of the present invention. Hereinafter, the configuration different from the third embodiment will be mainly described, and the same configuration as the third embodiment will be denoted by the same reference numeral, and the description thereof will be omitted or simplified.

  The overcurrent protection circuit 104 of the present embodiment is different from the third embodiment in that the installation of the input port 12 is omitted and the function of the input port 12 is added to the standby port 13. In the circuit example of FIG. 7, the standby signal for turning off the changeover switch M12 in the standby port 13 also serves as an input signal for turning off the main switch M11. Thereby, the structure of the external control circuit for switching control of the main switch M11 and the changeover switch M12 can be simplified.

  The switching circuit unit SC of the voltage generation unit X14 in this embodiment further includes a resistor R5 (fifth resistance element). The resistor R5 is connected between the control line 22 and the source of the changeover switch M12. The resistor R5 is for applying a predetermined bias potential to the ground of the main switch M11.

  Furthermore, the voltage generation unit X14 further includes a resistor R6 (sixth resistor element) connected between the source and base of the main switch M11. The resistor R6 is configured as an impedance element that absorbs a surge generated in the current supply line 21 when the main switch M11 is switched to the off state. As a result, the main switch M11 can be protected from surge current when an overcurrent is detected.

  When a potential for turning on the changeover switch M12 is input to the standby port 13, the current output operation mode is turned on in which the main switch M11 is turned on. As a result, a predetermined value of current is supplied from the power supply 10 to the load via the output port 11.

8A to 8D are diagrams illustrating an example of the relationship with the power supply voltage in each part of the overcurrent protection circuit 104. A is a current (I _RS ) flowing through the current detection resistor Rs, B is a collector current (I _Q1 ) of the protection transistor Q11, and C is a resistor R1, R2 in the current detection resistor Rs and the voltage dividing circuit unit VD. the voltage _{(V RS, V R1, V} R2) and, D is show voltage of the resistor R4 to (V _R4), respectively.

  Here, the threshold voltages (Vbe1, Vbe2) of the protection transistor Q11 and the voltage generation transistor Q12 are both 0.6 V, and the resistance R1 is set so that the current value of the current detection resistor Rs at the time of overcurrent detection is 5A. An example in which .about.R6 is set is shown. In this example, the operating point of the reference voltage generation source VS (voltage generation transistor Q12) is about 4V, and the current limit start voltage by the protection transistor Q11 is about 8V.

In the overcurrent protection circuit 104 shown in FIGS. 8A to 8D, the power supply voltage dependence characteristics of the Rs current (I _RS ) measured by varying the magnitude relationship between the resistance values of the resistors R3 and R5 are shown in FIGS.

  In the figure, A indicates when the resistance value (R3) of the resistor R3 is greater than the resistance value (R5) of the resistor R5 (R3> R5), B indicates when R3 = R5, and C indicates that R3 < Each time is R5. Specifically, A is R3 = 100 kΩ, R5 = 82 kΩ, B is R3 = R5 = 100 kΩ, and C is R3 = 82 kΩ and R5 = 100 kΩ. In the figure, a two-dot chain line, a solid line, and a broken line indicate when the environmental temperature (ta) is −25 ° C., 25 ° C., and 75 ° C., respectively. The current detection resistor Rs was adjusted so that the Rs current was 5 A when the temperature was 25 ° C. and the power supply voltage (Vcc) was 14V. The resistance value of the load L (see FIG. 1) connected to the output port 11 was set to 0.1Ω.

  As shown in FIGS. 9A to 9C, the Rs current tends to increase as the environmental temperature becomes lower. This depends on the temperature characteristics of the threshold voltages (Vbe1, Vbe2) of the protection transistor Q11 and the voltage generation transistor Q12, and matches the current characteristics of the output current (Iout) described with reference to FIGS. To do.

  Further, when the resistance values of the resistors R3 and R5 are in the relationship of R3> R5, it was confirmed that peaking occurred in the Rs current at low temperature (−25 ° C.) (see the region indicated by P in FIG. 9A). Due to the occurrence of peaking, a large current flows through the current detection resistor Rs, so that the supply of current to the load becomes excessive, which may cause malfunction or malfunction of the load (device).

  On the other hand, when the resistance values of the resistors R3 and R5 are in the relationship of R3 ≦ R5, the occurrence of peaking is prevented. In particular, when R3 <R5, the Rs current rises slowly. As a result, it is possible to reliably prevent excessive current supply when power is supplied to the load.

The relationship between the Rs current (I _RS ) and the resistance value (R4) of the resistor R4 is shown in FIGS. A shows when R4 = 0Ω, B shows when R4 = 30Ω, and C shows when R4 = 100Ω.

  10A to 10C, the resistance values of the resistor R3 and the resistor R5 have a relationship of R3 <R5, and here, R3 = 82 kΩ and R5 = 100 kΩ. In the figure, a two-dot chain line, a solid line, and a broken line indicate when the environmental temperature (ta) is −25 ° C., 25 ° C., and 75 ° C., respectively. The current detection resistor Rs was adjusted so that the Rs current was 5 A when the temperature was 25 ° C. and the power supply voltage (Vcc) was 14V.

As shown in FIGS. 10A to 10C, refer to FIGS. 5A to 5C for the fact that the Rs current (I _RS ) tends to decrease as the power supply voltage (Vcc) increases as the resistance value of the resistor R4 increases. This matches the current characteristic of the output current (Iout) described above. When the resistance values of the resistors R3 and R5 are in a relationship of R3 <R5, the peaking of the Rs current can be suppressed regardless of the resistance value (R4) of the resistor R4.

<Fifth Embodiment>
FIG. 11 is a circuit diagram showing an overcurrent protection circuit 105 according to the fifth embodiment of the present invention. Hereinafter, the configuration different from the fourth embodiment will be mainly described, and the same configuration as the fourth embodiment will be denoted by the same reference numeral, and the description thereof will be omitted or simplified.

  Similar to the fourth embodiment, the overcurrent protection circuit 105 of the present embodiment includes a voltage generation unit X15 and a switching circuit unit SC. The overcurrent protection circuit 105 of this embodiment is different from that of the fourth embodiment in that it further includes first and second impedance elements Z1, Z2 and a resistor R7 (seventh resistor element).

  The first impedance element Z1 is connected between the source and gate of the main switch M11 in place of the resistor R6 of the fourth embodiment. The second impedance element Z2 is connected between the gate and the source of the changeover switch M12. The resistor R7 is connected between the collector of the protection transistor Q11 and the gate of the main switch M11.

  The first and second impedance elements Z1 and Z2 are provided in order to protect the main switch M11 and the changeover switch M12 from external noise and the load of the use environment. In particular, the first impedance element Z1 and the resistor R7 set a time constant capable of absorbing a surge generated in the current supply line 21 when the main switch M11 is switched to the off state. As a result, the main switch M11 can be protected from surge current when an overcurrent is detected.

  The first and second impedance elements are constituted by a parallel circuit in which two or more passive elements such as a resistance element, a capacitance element, and a rectifying element are appropriately combined. Although not shown, a radio wave absorber such as a ferrite bead may be separately provided between the drain of the main switch M11 and the output port 11.

<Sixth Embodiment>
FIG. 12 is a circuit diagram showing an overcurrent protection circuit according to the sixth embodiment of the present invention. Hereinafter, the configuration different from the first embodiment will be mainly described, and the same configuration as the first embodiment will be denoted by the same reference numeral, and the description thereof will be omitted or simplified.

[Basic configuration]
The overcurrent protection circuit 200 according to the present embodiment includes a current supply line 21, a protection transistor Q21, and a voltage generator X20.

The current supply line 21 includes a main switch (first switch) M21 connected between the power source 10 (first current supply source) and the output port 11 connected to the load L, and an overcurrent to the load L. Current detection resistor Rs.
The protection transistor Q21 is connected in parallel with the current detection resistor Rs between the power supply 10 and the load L (output port 11).
The voltage generator X20 is connected to the base of the protection transistor Q21 and is configured to be able to generate a reference voltage (Vref) that is smaller than the threshold voltage (Vbe) at which the protection transistor Q21 switches to the on state.

  Details of each part will be described below.

The main switch M21 is connected between the power supply 10 and the current detection resistor Rs. The main switch M21 is an N-type MOSFET having a gate connected to the collector of the protection transistor Q21 via the control line 22, a source connected to the current detection resistor Rs, and a drain connected to the power supply 10. Composed.
The protection transistor Q21 includes a base connected to the voltage generator X20, an emitter connected to the current supply line 21 between the current detection resistor Rs and the output port 11, and the main switch M21 via the control line 22. An NPN bipolar transistor having a collector connected to the gate.

The main switch M21 is configured to be switchable between an on state in which a current is supplied from the power source 10 to the load L and an off state in which the current supplied from the power source 10 to the load L is limited by the protection transistor Q21.
Here, “limit the current” means that the current supplied to the load L is regulated to a predetermined current value or less as in the first embodiment, but is not limited to this, and the load L is not limited to this. The main switch M21 may be configured to cut off the supplied current (set the output current to zero).

  The overcurrent protection circuit 200 has an input port 12 connected to the gate of the main switch M21 via the control line 22. The input port 12 is configured to be able to input an input signal capable of controlling on / off of the main switch M21.

  The protection transistor Q21 has a threshold voltage (Vbe) that switches to an ON state when the voltage drop of the current detection resistor Rs reaches a predetermined overcurrent detection voltage (ΔVrs), and the voltage between the base and the emitter is the threshold value The main switch M21 can be switched to the off state when the voltage (Vbe) or higher.

  The voltage generator X20 is connected between the current supply line 21 between the current detection resistor Rs and the main switch M21 and the base of the protection transistor Q21. The voltage generator X20 is further connected to an auxiliary power source 20 (second current supply source) for generating a reference voltage (Vref). The reference voltage (Vref) is set to an appropriate level that does not satisfy the threshold voltage (Vbe) of the protection transistor Q21. Further, when the voltage drop in the current detection resistor Rs reaches a predetermined magnitude (overcurrent detection voltage (ΔVrs)), the reference voltage (Vref) is calculated from the overcurrent detection voltage (ΔVrs) and the reference voltage (Vref). Is set to a value that is equal to or higher than the threshold voltage (Vbe) of the protection transistor Q21.

  Thereby, in a normal time when a predetermined amount of current (not an overcurrent) is supplied to the load L, the protection transistor Q21 is maintained in the OFF state. On the other hand, when the voltage drop of the current detection resistor Rs reaches a predetermined overcurrent detection voltage (ΔVrs), the sum of the overcurrent detection voltage (ΔVrs) and the reference voltage (Vref) is the base of the protection transistor Q21. The protection transistor Q21 is configured to be turned on by being input between the emitters.

[Voltage generator]
Details of the voltage generator X20 will be described below.

  FIG. 13 is a circuit diagram illustrating an overcurrent protection circuit 201 including the voltage generation unit X21 of the present embodiment. In the figure, portions corresponding to those in FIG. 12 are denoted by the same reference numerals, and detailed description thereof is omitted. Hereinafter, the threshold voltage of the protection transistor Q21 will be described as “Vbe1”.

  The voltage generator X21 is connected between the input terminal of the current detection resistor Rs and the base of the protection transistor Q21. Similar to the first embodiment, the voltage generation unit X21 includes a reference voltage generation source VS and a voltage dividing circuit unit VD.

  The reference voltage generation source VS is configured to be able to generate a first voltage that is equal to or higher than the threshold voltage (Vbe1) of the protection transistor Q21. The voltage dividing circuit unit VD is configured to be able to divide the first voltage into a second voltage corresponding to the reference voltage (Vref).

  In the present embodiment, the reference voltage generation source VS is configured to be able to generate a voltage (standard voltage) corresponding to the threshold voltage (Vbe1) of the protection transistor Q21 as the first voltage. The reference voltage generation source VS includes a voltage generation transistor Q22 connected between the auxiliary power supply 20 and the input terminal of the current detection resistor Rs. The voltage generating transistor Q22 is composed of a rectifying element, and in this embodiment is composed of a diode-connected bipolar transistor.

  More specifically, the voltage generating transistor Q22 is connected to the emitter connected to the current supply line 21 (the input terminal of the current detection resistor Rs), the collector connected to the auxiliary power source 20 via the resistor R3, and the collector. And an NPN-type bipolar transistor having a formed base.

  As shown in FIG. 13, the auxiliary power source 20 is configured by a DC power source connected between the resistor R <b> 3 of the voltage generation unit X <b> 21 and the output port 11. The voltage (Vp) of the auxiliary power supply 20 is typically higher than the voltage (Vcc) of the power supply 10. For example, when the power supply 10 is 12V, a 22V DC power supply is used as the auxiliary power supply 20. The circuit configuration of the auxiliary power supply 20 is not particularly limited, and is typically configured by a charge pump or a DC-DC converter.

  The standard voltage corresponds to a threshold voltage (Vbe2) at which the voltage generating transistor Q22 is turned on. In this embodiment, the standard voltage is set to the same value as the threshold voltage (Vbe1) of the protection transistor Q21 (hereinafter referred to as the above-mentioned standard voltage). Standard voltage is also called standard voltage (Vbe2). Similarly to the first embodiment, the voltage generation transistor Q22 is configured by the same transistor element as the protection transistor Q21.

  The voltage dividing circuit unit VD is connected in parallel with the reference voltage generation source VS between the current supply line 21 (the input terminal of the current detection resistor Rs) and the auxiliary power supply 20. The voltage dividing circuit unit VD includes two resistors R1 (first resistor element) and resistor R2 (second resistor element) connected in series with each other, and a connection point between these two resistors R1 and R2 is for protection. Connected to the base of transistor Q21. As a result, the standard voltage (Vbe2) is divided into the reference voltage (Vref) in the voltage dividing circuit unit VD.

  The resistor R1 is connected between the input terminal of the current detection resistor Rs and the auxiliary power source 20, and the resistor R2 is connected between the resistor R1 and the auxiliary power source 20. The resistance values of the resistors R1 and R2 are not particularly limited as long as a voltage equal to or higher than the threshold voltage (Vbe1) of the protection transistor Q21 can be input to the base of the protection transistor Q21 when overcurrent is detected. Typically, the resistance value (R1) of the resistor R1 is set larger than the resistance value (R2) of the resistor R2, and the resistance value of the resistor R2 is set larger than the resistance value of the current detection resistor Rs. The The resistance value of the resistor R2 works when the current flowing through the current detection resistor Rs increases and the potential difference of the current detection resistor Rs becomes larger than the potential difference generated at the resistor R2 (protection function) It is preferably set to a value that turns on transistor Q21.

  The voltage generator X21 has a resistor R3 (third resistor element). The resistor R3 is connected between the resistor R2 and the auxiliary power source 20. The resistance value of the resistor R3 is not particularly limited as long as the reference voltage generation source VS can generate the above-described standard voltage (Vbe2).

[Operation of overcurrent protection circuit]
Next, a typical operation of the overcurrent protection circuit 201 of the present embodiment configured as described above will be described.

  In a normal state in which a predetermined amount of current is supplied from the power supply 10 to the load L, a signal voltage that maintains the main switch M21 in the on state is input to the input port 12. As a result, the current supplied from the power supply 10 is supplied to the output port 11 and the load L connected thereto via the current supply line 21 including the main switch M21 and the current detection resistor Rs. .

  On the other hand, the voltage generator X21 generates a reference voltage (Vref) from the current supplied from the auxiliary power supply 20. More specifically, the voltage generation unit X21 generates a standard voltage (Vbe2) in the reference voltage generation source VS, and divides it into the reference voltage (Vref) in the voltage dividing circuit unit VD. The reference voltage (Vref) thus obtained is input to the base (between the base and emitter) of the protection transistor Q21.

  When the load L is grounded, the output current (Iout) increases, and as a result, the voltage drop at the current detection resistor Rs also increases. A reference voltage (Vref) is input in advance between the base and emitter of the protection transistor Q21. The reference voltage (Vref) is protected by the base-emitter voltage when added to the overcurrent detection voltage (ΔVrs). Is set to a value equal to or higher than the threshold voltage (Vbe1) of the transistor Q21.

  Therefore, when the voltage drop in the current detection resistor Rs increases to a predetermined overcurrent detection voltage (ΔVrs), the added value of the reference voltage (Vref) in the voltage generator X21 and the voltage drop in the current detection resistor Rs is for protection. The threshold voltage (Vbe1) of transistor Q21 is reached. As a result, the protection transistor Q21 is turned on, and the gate potential of the main switch M21 is discharged to the current supply line 21 via the control line 22, so that the main switch M21 is turned off. Thereby, since the current value supplied from the power supply 10 to the load L is limited, the load L can be protected from overcurrent.

  When the ground fault of the load L is eliminated, the magnitude of the current supplied from the power supply 10 to the load L is reduced to a predetermined amount at the normal time, and thus the voltage drop in the current detection resistor Rs is also reduced. As a result, the protection transistor Q21 is turned off, and the main switch M21 is turned on again. Thereby, the overcurrent protection circuit 201 can be automatically returned from the current output stop (limit) mode to the normal current output operation mode.

  In the overcurrent protection circuit 201 of this embodiment, the same operation effect as that of the first embodiment can be obtained, and the resistance value of the current detection resistor Rs is set higher than that of the overcurrent protection circuit 1 of the comparative example (see FIG. 2). Can be small. Thereby, it is possible to reduce the amount of heat generated by the current detection resistor Rs when the overcurrent protection function is activated.

<Seventh Embodiment>
FIG. 14 is a circuit diagram showing an overcurrent protection circuit according to the seventh embodiment of the present invention. Hereinafter, the configuration different from the sixth embodiment will be mainly described, and the same configuration as the sixth embodiment will be denoted by the same reference numeral, and the description thereof will be omitted or simplified.

  The overcurrent protection circuit 202 of the present embodiment is different from the sixth embodiment in the configuration of the voltage generator X22. In the present embodiment, the reference voltage generation source VS of the voltage generation unit X22 further includes a resistor R4 (fourth resistance element) connected in series with the voltage generation transistor Q22. In the present embodiment, the resistor R4 is connected between the voltage generating transistor Q22 and the resistor R3, but is not limited thereto, and may be connected to the emitter side of the voltage generating transistor Q22.

  Also in the overcurrent protection circuit 202 of the present embodiment, it is possible to obtain the same operational effects as those of the above-described sixth embodiment. Further, according to the present embodiment, since the reference voltage generation source VS has the resistor R4, the value of the resistor R4 can be adjusted as in the second embodiment described with reference to FIG. Desired circuit characteristics of the voltage generator X22 can be obtained.

<Eighth Embodiment>
FIG. 15 is a circuit diagram showing an overcurrent protection circuit according to the eighth embodiment of the present invention. Hereinafter, the configuration different from the seventh embodiment will be mainly described, and the same configuration as the seventh embodiment will be denoted by the same reference numeral, and the description thereof will be omitted or simplified.

  The overcurrent protection circuit 203 of the present embodiment is different from the seventh embodiment in the configuration of the voltage generator X23. The voltage generation unit X23 of the present embodiment further includes a switching circuit unit SC including a changeover switch M22 (second switch). The overcurrent protection circuit 203 further includes a standby port 13.

The changeover switch M22 is formed of a switching element that can cut off the connection between the auxiliary power supply 20 and the resistor R3. In the present embodiment, the changeover switch M22 includes a P-type MOSFET having a gate connected to the standby port 13, a source connected to the auxiliary power source 20, and a drain connected to the resistor R3.
The standby port 13 is configured to be able to input a standby signal capable of controlling the changeover switch M22 on and off.

  The overcurrent protection circuit 203 according to the present embodiment switches between the standby state mode, the current output operation mode, and the current output stop mode by adjusting the potential of the external signal input to the input port 12 and the standby port 13. Configured to be possible. Table 4 shows the relationship between the input signal and standby signal and the current output.

  In the standby mode, the signal (I signal) input to the input port 12 is adjusted to a potential that turns off the main switch M21, and the signal (Standby signal) input to the standby port 13 turns off the changeover switch M22. It is adjusted to a potential that limits the current flowing from the auxiliary power supply 20 to the voltage generator X23. In this mode, the power supply current output from the output port 11 is limited by the main switch M21, and the dark current of the resistor R3 is also suppressed. For this reason, the current consumption of the auxiliary power supply 20 can be minimized when the device is not operating.

  In the current output operation mode, the signal (I signal) input to the input port 12 is adjusted to a potential for turning on the main switch M21, and the signal (Standby signal) input to the standby port 13 turns on the changeover switch M22. The potential is adjusted. In this mode, the overcurrent protection circuit 203 is enabled during operation of the device, and when the ground fault occurs, the main switch M21 is switched off by the operation of the voltage generation unit X23, so that an appropriate overcurrent protection function is provided. can get.

  In the current output stop mode, the signal (I signal) input to the input port 12 is adjusted to a potential that turns off the main switch M21, and the signal (Standby signal) input to the standby port 13 turns on the changeover switch M22. The potential is adjusted. In this mode, for example, when it is desired to stop the operation of the device for a reason other than the ground fault, the main switch M21 is changed to the OFF state by the input signal from the input port 12, and the current supply to the load is limited. Applies to

  As described above, according to the present embodiment, the same operational effects as those of the seventh embodiment can be obtained, and the normal mode (current output) can be obtained by connecting the overcurrent protection circuit 203 to the external control circuit. It is possible to execute other operation modes other than (operation mode).

  The change-over switch M22 is not limited to being configured by an FET, and may be configured by a switching element such as a bipolar transistor, a photo color, or a photo MOS. Alternatively, the changeover switch M22 may be configured by a mechanical relay as long as it is a switch element that can be easily controlled by the CPU.

<Ninth Embodiment>
FIG. 16 is a circuit diagram showing an overcurrent protection circuit according to the ninth embodiment of the present invention. Hereinafter, configurations different from those of the eighth embodiment will be mainly described, and configurations similar to those of the eighth embodiment will be denoted by the same reference numerals, and description thereof will be omitted or simplified.

  The overcurrent protection circuit 204 of this embodiment is different from that of the eighth embodiment in that the installation of the input port 12 is omitted and the function of the input port 12 is added to the standby port 13. In the circuit example of FIG. 16, the standby signal that causes the standby port 13 to turn off the changeover switch M22 also serves as an input signal that turns off the main switch M21. Thereby, the structure of the external control circuit for switching control of the main switch M21 and the changeover switch M22 can be simplified.

  The switching circuit SC of the voltage generator X24 in the present embodiment further includes a resistor R5 (fifth resistor element). The resistor R5 is connected between the control line 22 and the source of the changeover switch M22. The resistor R5 is for adjusting the output current from the changeover switch M22 input to the gate of the main switch M21 to an appropriate value.

  When a potential for turning on the changeover switch M22 is input to the standby port 13, the current switch is switched to a current output operation mode in which the main switch M21 is turned on. As a result, a predetermined value of current is supplied from the power supply 10 to the load via the output port 11.

  The overcurrent protection circuit 204 of this embodiment is different from that of the eighth embodiment in that it further includes first and second impedance elements Z1, Z2 and a resistor R7 (seventh resistor element). The first impedance element Z1 is connected between the source and gate of the main switch M21. The second impedance element Z2 is connected between the gate and source of the changeover switch M22. The resistor R7 is connected between the collector of the protection transistor Q21 and the gate of the main switch M21.

  The first and second impedance elements Z1 and Z2 are configured by a parallel circuit in which two or more passive elements such as a resistance element, a capacitance element, and a rectifying element are appropriately combined. The first and second impedance elements Z1 and Z2 are provided in order to protect the main switch M21 and the changeover switch M22 from external noise and load of the use environment. In particular, the first impedance element Z1 and the resistor R7 set a time constant that can absorb a surge generated in the current supply line 21 when the main switch M21 is switched to the off state. Thereby, the main switch M21 can be protected from the surge current when the overcurrent is detected.

<Tenth Embodiment>
FIG. 17 is a circuit diagram showing an overcurrent protection circuit according to the tenth embodiment of the present invention. Hereinafter, the configuration different from the sixth embodiment will be mainly described, and the same configuration as the sixth embodiment will be denoted by the same reference numeral, and the description thereof will be omitted or simplified.

  The overcurrent protection circuit 301 of this embodiment is different from that of the sixth embodiment in that the main switch M31 is composed of an IGBT (insulated gate bipolar transistor).

  That is, the main switch M31 is connected between the power supply 10 and the current detection resistor Rs, and has a gate connected to the collector of the protection transistor Q21 via the control line 22, and an emitter connected to the current detection resistor Rs. And an N-type IGBT having a collector connected to the power source 10.

The main switch M31 is configured to be switchable between an on state in which current is supplied from the power source 10 to the load L and an off state in which the current supplied from the power source 10 to the load L is limited by the protection transistor Q21.
Here, “limit the current” means that the current supplied to the load L is regulated to a predetermined current value or less as in the first embodiment, but is not limited to this, and the load L is not limited to this. The main switch M31 may be configured to cut off the supplied current (set the output current to zero).

  Also in the overcurrent protection circuit 301 of the present embodiment configured as described above, the same operational effects as those of the sixth embodiment can be obtained. In the present embodiment, since the main switch M31 is composed of an IGBT, it can be suitably used as an overcurrent protection circuit provided in a current supply line through which a relatively large current flows.

  Similarly, in the seventh to tenth embodiments described above, the overcurrent protection circuits 202 to 204 are configured by replacing the main switch M21 configured by an N-type MOSFET with a main switch M31 configured by an N-type IGBT. Also good.

<Eleventh embodiment>
FIG. 18 is a circuit diagram showing an overcurrent protection circuit according to the eleventh embodiment of the present invention. Hereinafter, configurations different from those of the fifth embodiment will be mainly described, and configurations similar to those of the fifth embodiment will be denoted by the same reference numerals, and description thereof will be omitted or simplified.

  The overcurrent protection circuit 106 of the present embodiment is configured by installing a monitoring circuit MC in the overcurrent protection circuit 105 according to the fifth embodiment described with reference to FIG.

  The monitoring circuit MC has a monitoring transistor Q13 connected in parallel to the protection transistor Q11 between the power supply 10 and the main switch M11. The monitoring transistor Q13 is a PNP bipolar transistor having a base connected to the monitoring port 14, an emitter connected to the power source 10, and a collector connected to the gate of the main switch M11 via the control line 22. Is done.

  The monitoring circuit MC monitors the magnitude of the output current (Iout) from the main switch M11, and turns on the monitoring transistor Q13 from the monitoring port 14 when detecting that this is a current value corresponding to a predetermined overcurrent. An input signal for switching to the state is input to the base of the monitoring transistor Q13. Thereby, the main switch M11 is switched to the OFF state, and the load L can be protected from overcurrent.

  The timing at which the monitoring transistor Q13 is turned on may be the same as or earlier than the timing at which the protection transistor Q11 is turned on when the overcurrent detection voltage is detected by the current detection resistor Rs. May be. By using the monitoring circuit MC together, the load L can be quickly protected from overcurrent when overcurrent is detected. Further, the main switch M11 can be effectively protected from the surge current when the overcurrent is detected by the first impedance element Z1 and the resistor R7.

An overcurrent protection circuit 205 shown in FIG. 19 corresponds to the overcurrent protection circuit 204 according to the tenth embodiment described with reference to FIG. 16 provided with a monitoring circuit MC.
In this example, the monitoring circuit MC includes a monitoring transistor Q23 connected in parallel to the protection transistor Q21 between the auxiliary power supply 20 and the load L (output port 11). The monitoring transistor Q23 is formed of an NPN bipolar transistor having a base connected to the monitoring port 14, an emitter connected to the output port 11, and a collector connected to the auxiliary power source 20.
In this example as well, the same effect as described above can be obtained.

  An overcurrent protection circuit 302 illustrated in FIG. 20 corresponds to a circuit in which the main switch of the overcurrent protection circuit 205 illustrated in FIG. 19 is replaced with a main switch M31 configured with an N-type IGBT. The rest of the configuration is the same as the configuration in FIG.

  The monitoring transistors Q13 and Q23 are not limited to being configured with bipolar transistors, but may be configured with switching elements such as FETs, photocouplers, and photoMOSs.

<Twelfth Embodiment>
In the overcurrent protection circuit of each of the embodiments described above, the protection transistors Q11 and Q21 (hereinafter collectively referred to as Q1) and the voltage generation transistors Q12 and Q22 (hereinafter collectively referred to as Q2) have their threshold voltages (Vbe1 Vbe2) has temperature characteristics (for example, about -2 mV / ° C). For this reason, in order to prevent variations in the element characteristics of both transistors due to these temperature characteristics, it is preferable that both transistors be formed of a common transistor element.

  On the other hand, the voltage generator in the overcurrent protection circuit may be configured as a separate circuit component externally attached to the overcurrent protection circuit 1 shown in FIG. 2, for example, as shown in FIGS. Is possible. In this case, the protection transistor Q1 and the voltage generation transistor Q2 are often composed of different package components. For this reason, a temperature difference is likely to occur between both transistors, and this causes a difference in the threshold voltages of both transistors. If the difference becomes large, the target operation as an overcurrent protection circuit can be ensured. There is a risk of disappearing.

  Therefore, as shown in FIG. 21, the overcurrent protection circuit 601 of the present embodiment includes a first package component 61 incorporating a protection transistor Q1, a second package section 62 incorporating a voltage generation transistor Q2, A heat transfer member 63 that thermally connects the two package components 61 and 62 is provided.

The first package component 61 includes a package body 610 that seals the protection transistor Q1, and external terminals 611 to 613 connected to the base, emitter, and collector of the protection transistor Q1, respectively.
Similarly, the second package component 62 includes a package body 620 that seals the voltage generating transistor Q2, and external terminals 621 to 623 connected to the base, emitter, and collector of the voltage generating transistor Q2, respectively.
The arrangement of the external terminals of the package parts 61 and 62 is not limited to the illustrated example, and can be changed to an arbitrary position. Further, the terminal arrangement of elements in the same package may be changed.

  The heat transfer member 63 is typically made of a metal material having a relatively high heat transfer property such as copper or aluminum. The heat transfer member 63 is typically formed in a plate shape, but is not limited thereto, and may be a box shape, a rod shape, a mesh shape, or the like. For example, a heat conductive adhesive is used for the connection between the package parts 61 and 62 and the heat transfer member 63, but the connection is not limited thereto. May be formed.

  In the overcurrent protection circuit 601 of the present embodiment, since both the package parts 61 and 62 are connected to each other by the heat transfer member 63, occurrence of a temperature difference between the both package parts 61 and 62 is suppressed. As a result, since the protection transistor Q1 and the voltage generation transistor Q2 can be maintained in a common temperature environment, the operation variation due to the temperature difference can be suppressed, and the target overcurrent protection operation can be stably secured. Can do.

  On the other hand, the first and second package parts 61 and 62 may be constituted by a single common package part. For example, the package component 64 shown in FIGS. 22A and 22B includes a package body 640 for sealing the protection transistor Q1 and the voltage generation transistor Q2, and a base, an emitter, and a collector of the protection transistor Q1 and the voltage generation transistor Q2, respectively. It has external terminals 611 to 613 and 621 to 623 to be connected.

  According to the above configuration, since the protection transistor Q1 and the voltage generation transistor Q2 are accommodated in the common package body 640, generation of a temperature difference between the protection transistor Q1 and the voltage generation transistor Q2 can be prevented as much as possible. it can. When temperature distribution can occur in the package main body 64, as shown in FIG. 22B, the surface of the package main body 64 is covered with a heat transfer member 65 made of a copper plate, copper foil, or the like. It is possible to suppress the occurrence of temperature distribution in

  As mentioned above, although embodiment of this invention was described, this invention is not limited only to the above-mentioned embodiment, Of course, a various change can be added.

  For example, in the second to fifth, seventh to ninth, and eleventh embodiments described above, the resistor R4 in the voltage generating unit is connected between the voltage generating transistors Q12 and Q22 and the resistor R3, but the present invention is not limited to this. For example, a voltage generating transistor Q12 may be connected between the resistor R4 and the resistor R3 as in the voltage generating unit X16 shown in FIG. This configuration can be similarly applied to circuit examples described later with reference to FIGS.

The voltage generating transistor Q12 constituting the reference voltage generating source VS is not limited to an example constituted by a PNP bipolar transistor. For example, as in the voltage generation unit X17 shown in FIG. 24, the voltage generation transistor Q14 may be formed of an NPN bipolar transistor. Also in this case, the voltage generation transistor Q14 has the same threshold voltage as that of the protection transistor Q11, and is configured as a rectifying element by connecting the base and the collector (diode connection). Thereby, the same effect as each above-mentioned embodiment can be acquired.
Similarly, the voltage generating transistor Q22 (see, for example, FIG. 12) configured by an NPN bipolar transistor may be configured by a PNP bipolar transistor.

  The rectifying element constituting the reference voltage generation source VS is not limited to a transistor. For example, like the voltage generation unit X18 shown in FIG. 25, the rectifying element that configures the reference voltage generation source VS may be configured by a diode D1. The diode has an operating voltage (Vf) equivalent to the threshold voltage (Vbe) of the first transistor Q1, so that the current flow from the current supply line 21 (current detection resistor Rs) to the resistor R4 is in the forward direction. Connected to. Even with such a configuration, it is possible to obtain the same effects as those of the above-described embodiments.

  In each of the above embodiments, the main switches M1 and M2 are configured by P-type MOSFETs or N-type MOSFETs. However, each main switch may be replaced by a complementary MOSFET (CMOS: Complementary MOS). Also, by replacing each main switch with a complementary MOSFET, the high potential (power supply terminal) side is replaced with a low potential (ground terminal) side, and the low potential (ground terminal) side is replaced with a high potential (power supply terminal) side. An overcurrent protection circuit having a similar function may be realized.

Further, in each of the above-described embodiments, the high-side drive type overcurrent protection circuit in which the main switch is installed on the power supply 20 side with respect to the load L has been described as an example. The present invention is also applicable to a low-side drive overcurrent protection circuit installed on the ground side with respect to L.
In this case, like the overcurrent protection circuit 107 shown in FIG. 26, the main switch M3 is formed of an N-type MOSFET. The protection transistor Q31 is formed of an NPN type bipolar transistor, and the voltage generation transistor Q32 in the voltage generation unit X19 is also formed of an NPN type bipolar transistor.

In the overcurrent protection circuit 107, the main switch M3 and the current detection resistor Rs are connected in series between the load L and the ground terminal (GND), and the main switch M3 is connected between the load L and the current detection resistor Rs. Is done.
The protection transistor Q31 is connected in parallel with the current detection resistor Rs, has an emitter connected to the current supply line 21 and a collector connected to the gate of the main switch M3, and limits overcurrent to the load L. The main switch M3 can be switched to the off state.
The voltage generator X19 is connected to the base of the protection transistor Q31 and generates a reference voltage (Vref) that is smaller than the threshold voltage (Vbe1) at which the protection transistor Q31 switches to the on state. In this example, the voltage generation unit X19 has the same configuration as the voltage generation unit X24 in the ninth embodiment described with reference to FIG. Includes a voltage generating transistor Q32.
Other configurations are the same as those in FIG. 16, and thus detailed description thereof is omitted.
Even in such a configuration, it is possible to obtain the same effects as those of the above-described embodiments.

Claims (20)

A first switch configured by a field effect transistor or an insulated gate bipolar transistor; and a current detection resistor for detecting an overcurrent to the load, and supplying a current from the first current supply source to the load. A current supply line;
An emitter connected in parallel with the current sensing resistor, connected to the current supply line, and a collector connected to the gate of the first switch, to the off state for limiting overcurrent to the load; A protective transistor capable of switching the first switch;
A voltage generation unit connected to a base of the protection transistor and generating a reference voltage lower than a threshold voltage at which the protection transistor switches to an on state,
The voltage generation unit includes a reference voltage generation source that generates a first voltage that is equal to or higher than the threshold voltage, and a voltage dividing circuit unit that divides the first voltage into a second voltage corresponding to the reference voltage. Overcurrent protection circuit. The overcurrent protection circuit according to claim 1,
The first switch includes a P-type field effect transistor connected between the current detection resistor and the load.
The reference voltage generation source is connected between an output terminal of the current detection resistor and a ground terminal,
The protection transistor includes a PNP bipolar having an emitter connected to the first current supply source, a collector connected to the gate of the first switch, and a base connected to the voltage dividing circuit section. Overcurrent protection circuit composed of transistors. The overcurrent protection circuit according to claim 2,
The voltage dividing circuit section is
A first resistance element connected between the output terminal of the current detection resistor and the ground terminal;
An overcurrent protection circuit comprising: a second resistance element connected between the first resistance element and the ground terminal and having a resistance value larger than the current detection resistance. The overcurrent protection circuit according to claim 3,
The reference voltage generation source includes a rectifier element connected in parallel with the first resistor element and the second resistor element between an output terminal of the current detection resistor and the ground terminal,
The voltage generation unit further includes a third resistance element connected between the second resistance element and the ground terminal. The overcurrent protection circuit according to claim 4,
The reference voltage generation source further includes a fourth resistance element connected in series with the rectifying element. The overcurrent protection circuit according to claim 4,
The voltage generation unit further includes a switching circuit unit including a second switch that can cut off a connection between the third resistance element and the ground terminal. The overcurrent protection circuit according to claim 6,
The second switch includes a field effect transistor,
The switching circuit unit further includes a fifth resistance element connected between a gate of the first switch and a source of the second switch. The overcurrent protection circuit according to claim 7,
The fifth resistance element has a larger resistance value than the third resistance element. The overcurrent protection circuit according to claim 2,
An overcurrent protection circuit, further comprising an impedance element connected between a source and a gate of the first switch. The overcurrent protection circuit according to claim 4,
The rectifying element is formed of a diode-connected bipolar transistor having a threshold voltage substantially the same as the threshold voltage of the protection transistor. The overcurrent protection circuit according to claim 4,
The rectifying element is configured by a diode having an operating voltage substantially the same as a threshold voltage of the protection transistor. The overcurrent protection circuit according to claim 1,
The first switch includes an N-type field effect transistor connected between the first current supply source and the current detection resistor,
The reference voltage generation source is connected between a second current supply source and an input terminal of the current detection resistor,
The protection transistor includes an emitter connected to the output terminal of the current detection resistor, a collector connected to the gate of the first switch, and a base connected to the voltage dividing circuit section. Overcurrent protection circuit composed of transistors. The overcurrent protection circuit according to claim 12,
The voltage dividing circuit section is
A first resistance element connected between the second current supply source and an input end of the current detection resistor;
An overcurrent protection circuit comprising: a second resistance element connected between the first resistance element and the second current supply source and having a resistance value larger than the current detection resistance. The overcurrent protection circuit according to claim 13,
The reference voltage generation source includes a rectifying element connected in parallel with the first resistance element and the second resistance element between the second current supply source and an input terminal of the current detection resistor. ,
The voltage generation unit further includes a third resistance element connected between the second current supply source and the second resistance element. The overcurrent protection circuit according to claim 14,
The voltage generation unit further includes a switching circuit unit including a second switch capable of disconnecting a connection between the second current supply source and the third resistance element. The overcurrent protection circuit according to claim 1,
The first switch includes an N-type field effect transistor connected between the load and the current detection resistor,
The current detection resistor is connected between the load and the ground terminal,
The reference voltage generation source is connected between a second current supply source and an input terminal of the current detection resistor,
The protection transistor includes an emitter connected to the output terminal of the current detection resistor, a collector connected to the gate of the first switch, and a base connected to the voltage dividing circuit section. Overcurrent protection circuit composed of transistors. The overcurrent protection circuit according to claim 16,
The voltage dividing circuit section is
A first resistance element connected between the second current supply source and an input end of the current detection resistor;
An overcurrent protection circuit comprising: a second resistance element connected between the first resistance element and the second current supply source and having a resistance value larger than the current detection resistance. The overcurrent protection circuit according to claim 17,
The reference voltage generation source includes a rectifying element connected in parallel with the first resistance element and the second resistance element between the second current supply source and an input terminal of the current detection resistor. ,
The voltage generation unit further includes a third resistance element connected between the second current supply source and the rectifying element,
The reference voltage generation source further includes a fourth resistance element connected in series with the rectifying element. A first switch configured by a field effect transistor or an insulated gate bipolar transistor; and a current detection resistor for detecting an overcurrent to the load, and supplying a current from the first current supply source to the load. A current supply line;
An emitter connected in parallel with the current sensing resistor, connected to the current supply line, and a collector connected to the gate of the first switch, to the off state for limiting overcurrent to the load; A protective transistor capable of switching the first switch;
A voltage generator that is connected to a base of the protection transistor and generates a reference voltage lower than a threshold voltage at which the protection transistor switches to an on state;
An overcurrent protection circuit comprising: a heat transfer member that thermally connects the protection transistor and the voltage generator. The overcurrent protection circuit according to any one of claims 1 to 19,
An overcurrent protection circuit, further comprising a package body that seals the protection transistor and the voltage generator in common.

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