JP3709858B2 - Circuit for current control type semiconductor switching element - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a circuit using a current control type semiconductor switching element, and more particularly to a circuit having an overvoltage protection function and an overcurrent protection function.
[0002]
[Prior art]
As a circuit for protecting the current control type power transistor from overvoltage or overcurrent, there is a circuit as shown in FIG. In the circuit shown in FIG. 4A, the control terminal IN, the OR gate 3, the transistor driving power source 1, the P-type MOSFET 4, the N-type MOSFET 5, the Zener diode 6, the load 7, and the load 7 are driven. Power supply 2, main power transistor 8, mirror transistor 9, resistor 10, differential amplifier 11, and level conversion circuit 12.
[0003]
The circuit shown in FIG. 4A has an overvoltage protection function when the transistor 8 is off and an overcurrent protection function when the transistor 8 is on, in addition to the function of driving the transistor 8. In a normal operation that is neither an overcurrent state nor an overvoltage state, the transistor 8 is on and the control terminal IN is at the H level when the control terminal IN that controls the transistor 8 is at the L level (MOSFET 4 is on, MOSFET 5 is off). In this case (MOSFET 4 is off, MOSFET 5 is on), transistor 8 is turned off.
[0004]
The protection current function of the circuit shown in FIG. It is assumed that some problem occurs in the load 7 with the transistor 8 turned on, for example, a short circuit between the collector terminal of the transistor 8 and the power supply 2, and an excessive current flows through the transistor 8. In this case, a current Ices according to the mirror ratio flows through the mirror transistor 9 which is a mirror element for the transistor 8. Accordingly, since the current Ices flows also through the resistor 10 connected to the emitter terminal of the mirror transistor 9, a voltage corresponding to the magnitude of the current Ices is generated at both ends of the resistor 10. The differential amplifier 11 amplifies the voltage applied to both ends of the resistor 10 and inputs the output S 1 to the level conversion circuit 12.
[0005]
The voltage level in the overcurrent state is set in advance in the level conversion circuit 12, and when the input voltage level of S1 exceeds the voltage level in the overcurrent state, an H level signal S2 is output. When the signal S2 output from the level conversion circuit 12 becomes H level, as shown in the truth table of FIG. 4B, the output of the OR gate 3 also becomes H level, so that the MOSFET 5 is turned on and the MOSFET 4 Is turned off. That is, even if the output of the control terminal IN is an on command (L level), the transistor 8 is forcibly turned off. Thereby, it is possible to prevent an overcurrent from continuing to flow through the transistor 8.
[0006]
Next, the overvoltage protection function will be described. A technique relating to this overvoltage protection function is disclosed in JP-A-11-55937. It is assumed that a high voltage equal to or higher than the breakdown voltage of the transistor 8 is applied to the collector terminal of the transistor 8 with the transistor 8 turned off. When the Zener voltage of the Zener diode 6 is set in advance to be equal to or lower than the breakdown voltage of the transistor 8 (referred to as a clamp voltage VceC), a voltage higher than the clamp voltage VceC + the base-emitter voltage Vbe is applied to the collector terminal of the transistor 8. The current Id flows through the Zener diode 6 in the direction shown in FIG. Accordingly, when the current Id flows through the base terminal of the transistor 8, the transistor 8 is turned on, and a current flows between the collector and the emitter. Thereby, the energy of the overvoltage applied to the collector terminal can be consumed, so that the overvoltage can be prevented from continuing to be applied to the transistor 8.
[0007]
[Problems to be solved by the invention]
However, when the above-described conventional technology is applied to a power transistor having a very large current capacity, a large current flows through the Zener diode 6 in order to realize the overvoltage protection function, and thus the heat generation of the Zener diode 6 increases. There is a problem. Further, it is very difficult to realize a Zener voltage as high as 400 V, for example, from the viewpoints of heat dissipation, cost, reliability, and the like.
[0008]
An object of the present invention is to provide a circuit for a current-driven semiconductor switching element that realizes overvoltage protection and overcurrent protection without using a Zener diode.
[0009]
[Means for Solving the Problems]
A circuit for a current control type semiconductor switching element according to the present invention includes a current control type semiconductor switching element, a mirror element of the current control type semiconductor switching element, a control means for performing on / off control of the current control type semiconductor switching element, and a mirror. Overvoltage detection means for detecting an overvoltage applied to the current control type semiconductor switching element based on a leak current flowing through the element, and an overcurrent for detecting an overcurrent flowing through the current control type semiconductor switching element based on a current flowing through the mirror element Detecting means, and when the overvoltage state of the current control type semiconductor switching element is detected by the overvoltage detection means, the control means turns on the current control type semiconductor switching element, and the current control type semiconductor switching element is detected by the overcurrent detection means. When an overcurrent condition is detected, the current controlled semiconductor By turning off the switching element, to achieve the above object.
[0010]
【The invention's effect】
According to the current control type semiconductor switching element circuit of the present invention, the overvoltage state and the overcurrent state are detected based on the current flowing through the mirror element of the current control type semiconductor switching element, and the current control is performed when the overvoltage state is detected. Since the current control type semiconductor switching element is turned off when the overcurrent state is detected by turning on the type semiconductor switching element, the overvoltage protection function and the overcurrent protection function can be realized without using a Zener diode.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
First Embodiment FIG. 1A is a diagram showing a configuration of a first embodiment of a circuit for a current driven semiconductor switching element according to the present invention. The circuit shown in FIG. 1A includes a control terminal IN, an XOR gate 13, a transistor driving power source 1, a P-type MOSFET 4, N-type MOSFETs 5, 17, a load 7, and a load 7 for driving the load 7. The power supply 2 includes a bipolar transistor (main power transistor) 8, a mirror transistor 9, resistors 15 and 16, a differential amplifier 11, a level conversion circuit 12, and an INV gate 14.
[0012]
In a normal operation that is neither an overcurrent state nor an overvoltage state, when the control terminal IN that controls the transistor 8 is at L level, the MOSFET 4 is turned on and the MOSFET 5 is turned off, so that the transistor 8 is turned on. On the other hand, when the control terminal IN is at the H level, the MOSFET 4 is turned off and the MOSFET 5 is turned on, so that the transistor 8 is turned off. The mirror transistor 9 corresponding to the transistor 8 has the same device structure as the transistor 8 and has the same on / off characteristics as the transistor 8. A current corresponding to the mirror ratio flows through the transistor 9. For example, when the mirror ratio is 100: 1, when a current of 100 A flows through the transistor 8, a current of 1 A flows through the mirror transistor 9.
[0013]
FIG. 2 is a diagram showing a leakage current characteristic that flows from the collector terminal of the mirror transistor 9 to the emitter terminal with respect to the collector-emitter voltage Vce of the transistor 8 when the mirror transistor 9 is off. As shown in FIG. 2, the leakage current increases as the voltage Vce increases, and when the voltage Vce reaches the breakdown voltage of the transistor 8, a so-called breakdown state occurs and a large amount of current flows.
[0014]
The resistance values of the resistor 15 and the resistor 16 connected in parallel to the differential amplifier 11 and having one end connected to the emitter terminal of the mirror transistor 9 and the other end connected to the emitter terminal of the transistor 8 are expressed by the following equation (1) ) Is established.
Resistance value of resistor 16 >> Resistance value of resistor 15 (1)
Therefore, when the N-type MOSFET 17 connected in series between the resistor 15 and the emitter terminal of the transistor 8 is on, the current flowing through the mirror transistor 9 flows through the resistor 15 having a small resistance value. On the other hand, when the N-type MOSFET 17 is off, all the current flowing through the mirror transistor 9 flows through the resistor 16. The emitter terminal of the transistor 8 is grounded.
[0015]
As will be described later, when the overvoltage state is detected, the voltage applied to both ends of the resistor 16 as a result of the leakage current Ices flowing through the resistor 16 is detected by the differential amplifier 11, so that a sufficient voltage can be input even with the leakage current. Thus, the resistance value of the resistor 16 needs to be large. As will be described later, the resistor 15 is used when detecting an excessive current state. However, it is necessary to use a resistance value having an appropriate magnitude so that an appropriate voltage is input to the differential amplifier 11. . That is, the resistance values of the resistors 15 and 16 need to be set to appropriate values in consideration of the breakdown voltage of the transistor 8 and the like.
[0016]
A signal obtained by inverting the signal level of the control terminal IN at the INV gate 14 is input to the gate of the N-type MOSFET 17. Accordingly, when the control terminal IN is at the L level, the N-type MOSFET 17 is turned on, and when the control terminal IN is at the H level, the N-type MOSFET 17 is turned off.
[0017]
The differential amplifier 11 amplifies the voltage applied to both ends of the resistor 15 or 16 and outputs the amplified voltage to the level conversion circuit 12. When the N-type MOSFET 17 is off, a voltage applied to the resistor 16 is input to the differential amplifier 11. When the N-type MOSFET 17 is on, a voltage applied to both ends of the resistor 15 is input to the differential amplifier 11. The level conversion circuit 12 outputs an H level signal when the input voltage signal exceeds a preset clamp voltage VceC level.
[0018]
FIG. 1B is a truth table of the XOR gate 13. The XOR gate 13 receives the signal from the control terminal IN and the output signal S2 from the level conversion circuit 12, and outputs a logical sum S3. During normal operation that is neither an overcurrent state nor an overvoltage state, the output signal S2 of the level conversion circuit 12 is at the L level. Therefore, as shown in FIG. 1B, when the control terminal IN is at L level, the output S3 of the XOR gate 13 is at L level and the transistor 8 is turned on. When the control terminal IN is at H level, the XOR gate is turned on. 13 output S3 becomes H level, and the transistor 8 is turned off. Therefore, during normal operation, the transistor 8 is turned on / off according to the signal level of the control terminal IN.
[0019]
On the other hand, in the overcurrent state or the overvoltage state, the output signal S2 of the level conversion circuit 12 is at the H level as will be described later. Therefore, when the control terminal IN is at the L level, the output S3 of the XOR gate is at the H level, so that the transistor 8 is turned off. When the control terminal IN is at the H level, the output S3 of the XOR gate 13 is at the L level, so that the transistor 8 is turned on.
[0020]
-Overvoltage protection function-
An overvoltage protection function when the transistor 8 is off in the circuit shown in FIG. It is assumed that a high voltage higher than the breakdown voltage of the transistor 8 is applied to the collector terminal of the transistor 8 in a state where the control terminal IN is at the H level and the transistor 8 is turned off. In this case, since the gate of the N-type MOSFET 17 is at L level, the MOSFET 17 is off. A leak current Ices according to the collector-emitter voltage of the transistor 8 flows between the collector and emitter of the mirror transistor 9, but since the MOSFET 17 is off, all the leak current Ices flows through the resistor 16. Note that the magnitude of the leakage current Ices depends on the mirror ratio.
[0021]
The differential amplifier 11 amplifies the voltage applied to both ends of the resistor 16 and outputs the differential amplifier output S1 to the level conversion circuit 12. The level conversion circuit 12 outputs an H-level signal S2 when the input signal S1 exceeds a preset breakdown voltage of the transistor 8, that is, the clamp voltage VceC level. Therefore, when a voltage higher than the withstand voltage is applied to the collector terminal of the transistor 8, the output signal S2 of the level conversion circuit 12 becomes H level.
[0022]
Since the H level signal of the control terminal IN and the H level signal of the level conversion circuit 12 are input to the XOR gate 13, the gate output S3 is L level from the truth table shown in FIG. It becomes. Accordingly, the P-type MOSFET 4 is turned on, the N-type MOSFET 5 is turned off, and the base current flows through the transistor 8, whereby a current flows between the collector and the emitter. As a result, the transistor 8 is turned on regardless of the control terminal IN being at the H level (transistor 8 off command), so that overvoltage energy applied to the collector terminal of the transistor 8 can be consumed, and an overvoltage is applied to the transistor 8. You can prevent it from continuing.
[0023]
-Overcurrent protection function-
Next, an overcurrent protection function when the transistor 8 is on will be described. In a state where the control terminal IN is at L level and the transistor 8 is turned on, some problem occurs in the load 7, for example, a short circuit occurs between the collector terminal of the transistor 8 and the power supply 2, and it does not flow during normal operation. It is assumed that an excessive current flows through the transistor 8. In this case, since the gate of the N-type MOSFET 17 is at the H level, the MOSFET 17 is on.
[0024]
A current Ices according to the mirror ratio flows between the collector and the emitter of the mirror transistor 9. As described above, since the resistance value of the resistor 16 is larger than the resistance value of the resistor 15, the current Ices flows through the resistor 15 when the MOSFET 17 is on. The differential amplifier 11 amplifies the voltage applied to both ends of the resistor 15 and outputs the differential amplifier output S1 to the level conversion circuit 12. The level conversion circuit 12 outputs an H-level signal S2 when the input signal S1 exceeds a preset clamp voltage VceC level. That is, when an excessive current flows through the transistor 8, the output signal S2 of the level conversion circuit 12 becomes H level.
[0025]
Since the XOR gate 13 receives the L level signal from the control terminal IN and the H level signal from the level conversion circuit 12, the gate output S3 is at the H level from the truth table shown in FIG. It becomes. Accordingly, since the P-type MOSFET 4 is turned off and the N-type MOSFET 5 is turned on, the transistor 8 is forcibly turned off regardless of whether the control terminal IN is at L level (an on command for the transistor 8). Thereby, it is possible to prevent excessive current from continuing to flow through the transistor 8.
[0026]
According to the current-driven semiconductor switching element circuit in the first embodiment, the overcurrent flowing through the transistor 8 is detected based on the current Ices flowing through the mirror transistor 9 and flows into the mirror transistor 9 when the transistor 8 is turned off. Since the overvoltage is detected based on the leakage current Ices, it is possible to share circuit elements for detecting the overvoltage state and the overcurrent state. That is, since the mirror transistor 9, the differential amplifier 11, and the level conversion circuit 12 can be shared in order to realize the overvoltage protection function and the overvoltage protection function of the circuit, the cost can be reduced. Further, when an overvoltage state or an overcurrent state is detected, the transistor 8 is turned on / off regardless of the signal level of the control terminal IN, so that the transistor 8 can be protected from the overvoltage state and the overcurrent state.
[0027]
Since the value of the current flowing through the mirror transistor 9 differs greatly between the overcurrent state and the overvoltage state, two types of resistors having different resistance values were used as the resistors used when detecting the overcurrent and overvoltage. Thereby, an overvoltage state and an overcurrent state can be reliably detected. The overvoltage state and the overcurrent state are detected by comparing a voltage obtained by amplifying a voltage applied to both ends of the resistor 15 or the resistor 16 with a predetermined voltage. The predetermined voltage is a clamp voltage which is a withstand voltage of the transistor 8. Therefore, the transistor 8 can be reliably protected from overvoltage and overcurrent.
[0028]
Further, since the Zener diode 6 as described in the prior art is unnecessary, the problem of heat generation in the Zener diode 6 does not occur. Further, when the Zener diode 6 is used, there is a problem that the voltage range of the circuit that can be used is limited as described above. In this embodiment, the clamp voltage setting range is set to the resistance of the resistor 16. Since this can be dealt with by setting values, the applicable voltage range of the circuit is widened.
[0029]
Second Embodiment FIG. 3 is a diagram showing a configuration of a second embodiment of a circuit for a current driven semiconductor switching element according to the present invention. The same components as those in the circuit according to the first embodiment are denoted by the same reference numerals and description thereof is omitted. In the circuit according to the second embodiment, leakage current and overcurrent are detected using a single resistor 20, and an amplification gain (amplification degree) of a detection voltage is switched by a gain variable differential amplifier 21.
[0030]
The variable gain differential amplifier 21 includes amplifiers 21a and 21b having different gains from the differential amplifier 11, and a switch 21c. The switch 21c switches the amplifiers 21a and 21b to be used according to the output signal S4 from the INV gate 14, that is, the signal level of the control terminal IN. The gain of the amplifier 21a is n, and the gain of the amplifier 21b is m (>> n). When the transistor 8 is on during normal operation, that is, when the control terminal IN is at L level, the amplifier 21a is selected to detect an overcurrent state. On the other hand, when the transistor 8 is off during normal operation, that is, when the control terminal IN is at the H level, the amplifier 21b is selected to detect an overvoltage state. That is, in the overcurrent state, the current flowing through the resistor 20 increases. Therefore, the amplifier 21a having a small gain value is selected, and when the leak current flows through the resistor 20 in the overvoltage state, the gain value is large. The amplifier 21b is selected.
[0031]
-Overvoltage protection function-
The overvoltage protection function of the circuit shown in FIG. 3 will be briefly described. It is assumed that a high voltage higher than the breakdown voltage of the transistor 8 is applied to the collector terminal of the transistor 8 in a state where the control terminal IN is at the H level and the transistor 8 is turned off. In this case, a leak current Ices corresponding to the mirror ratio flows between the collector and the emitter of the mirror transistor 9, so that a voltage corresponding to the magnitude of the leak current Ices is applied to both ends of the resistor 20.
[0032]
As described above, when the control terminal IN is at the H level, the amplifier 21b is selected. Therefore, the voltage applied to both ends of the resistor 20 is amplified by the differential amplifier 11, is multiplied by m by the amplifier 21 b, and is output to the level conversion circuit 12. Similar to the first embodiment, the level conversion circuit 12 outputs an H level signal S2 when the voltage level of the input signal S1 exceeds a preset clamp voltage VceC level. As a result, the output S3 of the XOR gate 13 becomes L level, and the base current flows through the transistor 8. Therefore, the current flows between the collector and the emitter, and the overvoltage energy applied to the collector terminal of the transistor 8 can be consumed. .
[0033]
-Overcurrent protection function-
The overcurrent protection function of the circuit shown in FIG. 3 will be briefly described. It is assumed that in the state where the control terminal IN is at L level and the transistor 8 is on, some problem occurs in the load 7 and an excessive current that does not flow during normal operation flows through the transistor 8. A leak current Ices corresponding to the mirror ratio flows between the collector and the emitter of the mirror transistor 9. As described above, when the control terminal IN is at the L level, the amplifier 21a is selected, so that the voltage applied to both ends of the resistor 20 is amplified by the differential amplifier 11 and then multiplied by n by the amplifier 21a. Is output to the level conversion circuit 12.
[0034]
The level conversion circuit 12 outputs an H-level signal S2 when the input signal S1 exceeds a preset clamp voltage VceC level. As a result, the gate output S3 of the XOR gate 13 becomes the H level, the P-type MOSFET 4 is turned off, and the N-type MOSFET 5 is turned on. 8 is forcibly turned off. Thereby, it is possible to prevent excessive current from continuing to flow through the transistor 8.
[0035]
According to the current-driven semiconductor switching element circuit in the second embodiment, as in the first embodiment, there is an effect that it is not necessary to use a Zener diode, and the amplifiers 21a and 21b having different gains are provided. By using it, an overvoltage protection function and an overcurrent protection function can be realized by using one resistor 20. Since the overvoltage and overcurrent states differ depending on the signal level (H / L) of the control terminal IN, the overvoltage state and the overcurrent state are reliably detected by switching the gain according to the signal level of the control terminal IN. be able to. Further, since the voltage applied to the resistor 20 is small when detecting the overvoltage state, the amplifier 21b having a large gain (amplification degree) is selected, so that the overvoltage state can be reliably detected.
[0036]
The present invention is not limited to the embodiment described above. For example, although the case where the bipolar transistor 8 is used as the current control type semiconductor switching element has been described, other switching elements can also be used. In addition, the current control type semiconductor switching element is not limited to the configuration of the low-side switch, and may be used as a high-side switch or applied to various circuit configurations such as a half-bridge configuration, an H-bridge configuration, and an inverter configuration. can do.
[0037]
The correspondence between the constituent elements of the claims and the constituent elements of the embodiment is as follows. That is, the bipolar transistor 8 is a current control type semiconductor switching element, the mirror transistor 9 is a mirror element, the control terminal IN, MOSFETs 4 and 5, the level conversion circuit 12 and the XOR gate 13 are control means, a resistor 16, and a differential amplifier 11 The level conversion circuit 12 is an overvoltage detection means, the resistor 15, the differential amplifier 11 and the level conversion circuit 12 are overcurrent detection means, the resistor 16 is a first resistance, the resistance 15 is a second resistance, and the gain is variable. The differential amplifier 21 constitutes voltage amplification means. In addition, unless the characteristic function of this invention is impaired, each component is not limited to the said structure.
[Brief description of the drawings]
FIG. 1A is a diagram showing a configuration of a first embodiment of a circuit for a current control type semiconductor switching element according to the present invention, and FIG. 1B is a truth table of an XOR gate; Indicates.
FIG. 2 is a diagram showing a relationship between a voltage between an emitter and a collector of a transistor 8 and a leakage current flowing in the mirror transistor 9. FIG. 3 is a circuit diagram of a second circuit for a current-controlled semiconductor switching element according to the present invention. FIG. 4A is a diagram showing a circuit configuration of the prior art, and FIG. 4B is a truth table of an OR gate used in the circuit of the prior art. .
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Transistor drive power supply, 2 ... Load drive power supply, 3 ... OR gate, 4 ... P-type MOSFET, 5, 17 ... N-type MOSFET, 6 ... Zener diode, 7 ... Load, 8 ... Bipolar transistor, 9 ... Mirror Transistors 10, 15, 16, 20 ... resistors, 11 ... differential amplifier, 12 ... level conversion circuit, 13 ... XOR gate, 14 ... INV gate, 21 ... variable gain differential amplifier, 21a, 21b ... amplifier, 21c ... switch

Claims (7)

A current-controlled semiconductor switching element;
A mirror element of the current control type semiconductor switching element;
Control means for performing on / off control of the current control type semiconductor switching element;
Overvoltage detection means for detecting an overvoltage applied to the current-controlled semiconductor switching element based on a leak current flowing in the mirror element;
Overcurrent detection means for detecting an overcurrent flowing through the current control type semiconductor switching element based on a current flowing through the mirror element;
The control means turns on the current control type semiconductor switching element when the overvoltage state of the current control type semiconductor switching element is detected by the overvoltage detection means, and the current control type semiconductor switching element is turned on by the overcurrent detection means. When the overcurrent state is detected, the current-controlled semiconductor switching element is turned off. The current control type semiconductor switching element circuit according to claim 1,
The overvoltage detection means includes a first resistor connected to the mirror element, and an overvoltage state of the current control type semiconductor switching element is based on a voltage applied to both ends of the first resistor and a predetermined voltage. Detect
The overcurrent detection unit has a second resistor connected to the mirror element in parallel with the first resistor, and is based on a voltage applied to both ends of the second resistor and the predetermined voltage. A circuit for a current control type semiconductor switching element, wherein an overcurrent state of the current control type semiconductor switching element is detected. In the circuit for current control type semiconductor switching elements according to claim 2,
The circuit for a current control type semiconductor switching element, wherein a resistance value of the first resistor is larger than a resistance value of the second resistor. The current control type semiconductor switching element circuit according to claim 1,
A resistor connected to the mirror element;
Voltage amplifying means for amplifying the voltage applied to both ends of the resistor,
The overvoltage detection means detects the overvoltage state by comparing a voltage applied at both ends of the resistor by the voltage amplification means with a voltage amplified at a first amplification degree and a predetermined voltage,
The overcurrent detection means detects the overcurrent state by comparing the voltage applied at both ends of the resistor by the voltage amplification means with a voltage amplified by a second amplification degree and the predetermined voltage. A circuit for a current-controlled semiconductor switching element. In the circuit for current control type semiconductor switching elements according to claim 4,
The voltage amplification means switches between the first amplification degree and the second amplification degree based on an on / off command of the current control type semiconductor switching element. circuit. In the circuit for current controlled semiconductor switching elements according to claim 4 or 5,
The circuit for a current control type semiconductor switching element, wherein the first amplification degree is larger than the second amplification degree. In the circuit for current controlled semiconductor switching elements according to any one of claims 2 to 6,
The circuit for a current control type semiconductor switching element, wherein the predetermined voltage is determined based on a clamp voltage of the current control type semiconductor switching element.

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