JP2014052192A - Current detection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current detection circuit which is capable of easily and highly accurately detecting a current flowing in a main switching element Qm by excluding an influence of current noise.SOLUTION: The current detection circuit includes: a plurality of sub-switching elements Qs1 and Qs2 which are provided in parallel with the main switching element Qm for large power which is driven to be turned on/off by application thereto of a control signal, and are driven to be turned on/off by application thereto of the control signal and are smaller than that of the main switching element and are mutually different in size; a plurality of current detection resistances R1 and R2 connected in series to the sub-switching elements respectively; and a differential amplifier Amp which detects a current flowing in the main switching element in accordance with a difference between voltages generated in respective current detection resistances.

Description

  The present invention relates to a current detection circuit that can detect a current flowing in a switching element such as an IGBT with high accuracy.

  In a drive circuit for a switching element for high power such as an IGBT used for an ignition device of an internal combustion engine or a switching power supply, when an overcurrent exceeding a rating flows in the switching element, not only the switching element but also the switching element It often incorporates a current limiting function to protect the circuit and load connected to Therefore, it is important to accurately detect the current flowing through the switching element.

  Therefore, conventionally, for example, as shown in FIG. 5, the element area (size) of the main switching element (IGBT) Qm in parallel with the main switching element (IGBT) Qm for switching a large current is [1 / M] and a small sub-switching element (IGBT) Qs for current detection. And it is proposed to detect the current flowing through the sub-switching element Qs via a current detection resistor (sensing resistor) R connected in series to the emitter of the sub-switching element Qs (see, for example, Patent Documents 1 and 2). reference). In the figure, RL is a load of the main switching element Qm.

  Incidentally, the ratio of the current flowing through the main switching element Qm and the current flowing through the sub switching element Qs is determined by the size ratio (element area ratio) between the main switching element Qm and the sub switching element Qs. In general, in order to suppress power loss and heat generation in the current detection resistor R, and to minimize the area demerit for providing the auxiliary switching element Qs, the M value for determining the size ratio is [M >> 1], specifically, about several hundred to several thousand.

JP 2006-271098 A JP 2001-345686 A

  However, the above-described method does not directly detect the current flowing through the main switching element Qm, but indirectly detects the current through the sub-switching element Qs. Moreover, as described above, the sub-switching element Qs is realized as a size of [1 / M] of the main switching element Qm. Therefore, the sub-switching element Qs is more susceptible to current noise due to electromagnetic interference or radiation by peripheral devices than the main switching element Qm, and accurately detects (estimates) the current flowing through the main switching element Qm. ) Will leave challenges.

  The present invention has been made in consideration of such circumstances, and its purpose is to provide a current that can easily and accurately detect the current flowing through the main switching element Qm without the influence of current noise. It is to provide a detection circuit.

In order to achieve the above-described object, the current detection circuit according to the present invention is suitable for detecting a current flowing in a main switching element for high power that is turned on / off by applying a control signal,
A plurality of sub-switching elements that are provided in parallel with the main switching element and are turned on / off by being applied with the control signal, and are smaller than the main switching element and different in size;
A plurality of current detection resistors connected in series to each of these sub-switching elements,
And a differential amplifier for detecting a current flowing through the main switching element from a difference in voltage generated in each of the current detection resistors.

  Preferably, the main switching element and the plurality of sub switching elements are made of, for example, IGBT or MOSFET, and are formed on the same semiconductor substrate. The plurality of current detection resistors preferably have the same resistance value.

  The main switching element is turned on / off by applying the control signal to the control terminal via an input resistor, and the control signal is directly applied to the control terminal of the plurality of sub-switching elements. It is preferable to configure such that the on / off driving is performed.

  According to the current detection circuit configured as described above, the current flowing through the main switching element can be detected in parallel as the current flowing through each of the current detection resistors via the plurality of sub switching elements. The difference between the current detection signals (voltages) detected through each of these current detection resistors is obtained, and the influence of in-phase current noise entering each of the plurality of sub-switching elements can be removed or reduced. it can. Therefore, it is possible to provide a current detection circuit having excellent noise resistance.

The figure which shows schematic structure of the current detection circuit which concerns on one Embodiment of this invention. The figure which shows schematic structure of the current detection circuit which concerns on another embodiment of this invention. The figure which shows the structural example of the ignition device for internal combustion engines using the electric current detection circuit which concerns on this invention. The figure which shows schematic structure of the current detection circuit which concerns on another embodiment of this invention. The figure which shows the structural example of the conventional electric current detection circuit.

Hereinafter, a current detection circuit according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a schematic configuration of a current detection circuit according to an embodiment of the present invention. Qm is a main switching element for high power made of, for example, IGBT, and RL is connected to a collector of the main switching element Qm. Load. The main switching element Qm receives a gate control signal from a drive circuit (not shown) at its gate and is turned on / off to supply predetermined power to the load RL.

  In contrast to such a main switching element Qm, in this embodiment, a first sub-switching element Qs1 having a size of [1 / M] of the main switching element Qm and a second having a size of [1 / N] are used. Sub-switching elements Qs2 are provided in parallel with each other. These first and second sub-switching elements Qs1 and Qs2 are made of IGBTs formed on the same semiconductor substrate (not shown) as the main switching element Qm, and their gates and collectors are mutually connected in common. Are provided in parallel.

  Current detection resistors R1 and R2 are connected in series to the emitters of the first and second sub-switching elements Qs1 and Qs2, respectively, and current detection signals (voltages) generated in the current detection resistors R1 and R2, respectively. ) Is input to the differential amplifier Amp. The differential amplifier Amp removes or reduces in-phase current noise mixed in each of the sub-switching elements Qs1 and Qs2 by obtaining a difference between the current detection signals (voltages), thereby reducing the main switching element Qm. It plays a role of obtaining a current detection signal corresponding to the current flowing through the.

  The first and second sub-switching elements Qs1 and Qs2 are preferably close to each other on the semiconductor substrate so that the effects of current noise caused by electromagnetic interference and radiation by peripheral devices are as common as possible. It is desirable to provide in the position. The resistance values of the current detection resistors R1 and R2 are desirably as small as possible, preferably the same value, as will be described later.

Here, when the current flowing through the main switching element Qm is I, a current of [I / M] flows through the first sub-switching element Qs1 having a size of [1 / M], and the current of [1 / N] A current of [I / N] flows through the second sub-switching element Qs2 having the size. Further, if the current fluctuation amount due to the current noise mixed in each of the current detection resistors R1 and R2 is ΔIn, and the resistance values of the current detection resistors R1 and R2 are r1 and r2, the current detection resistors R1 and R2 In R2, V1 = (I / M) × r1 + ΔIn × r1
V2 = (I / N) × r2 + ΔIn × r2
Each produces a voltage.

Here, the current flowing through the main switching element Qm due to the decrease in the gate-emitter voltage of the first and second sub-switching elements Qs1, Qs2 due to the voltage drop generated in the current detection resistors R1, R2. It is assumed that there is no change in the shunt ratio of I. The M and N values indicating the size are [1 / M> 1 / N], and the resistance value is [r1 ≧ r2]. Then, if the gain of the differential amplifier Amp is G, the output of the differential amplifier Amp is Vsense = G (V1-V2)
= G {(r1 / M-r2 / N) I + (r1-r2) ΔIn}
A current detection signal Vsense is obtained.

Therefore, the current I flowing from the current detection signal Vsense to the main switching element Qm is
I = {MN / (N · r1−M · r2)}
X {(Vsense / G)-(r1-r2) ΔIn}
Can be obtained as As shown in this equation, the term of the current fluctuation amount ΔIn due to the current noise becomes smaller as the difference between the resistance values r1 and r2 of the current detection resistors R1 and R2 becomes smaller, and particularly when the values are equal. It can be virtually ignored.

  Therefore, according to the current detection circuit configured as described above, the current I flowing through the main switching element Qm can be accurately detected by removing or reducing the influence of current noise caused by electromagnetic interference and radiation by peripheral devices. Can do. In addition, by using the first and second sub-switching elements Qs1 and Qs2 having different sizes, the currents flowing through the sub-switching elements Qs1 and Qs2 are made to flow into the current detection resistors R1 and R2, respectively. Since the operation is performed so that the amounts of current noise are equalized and these current noises are canceled out, the effects of being able to easily and accurately detect the current I flowing through the main switching element Qm are exhibited.

  Incidentally, as shown in FIG. 2, three sub-switching elements Qs1, Qs2, and Qs3 having different sizes may be connected in parallel to the main switching element Qm to detect the current I flowing through the main switching element Qm. . In this case, the sizes of the three sub-switching elements Qs1, Qs2, and Qs3 are made different as [1 / M], [1 / N], and [1 / L], and the sub-switching elements Qs1, Qs2, and Qs3 What is necessary is just to comprise so that the difference of the voltage which generate | occur | produced in current detection resistance R1, R2, R3 connected in series with each emitter may be calculated | required.

Specifically, for example, a difference between voltages generated in the current detection resistors R1 and R2 is obtained by the first differential amplifier Amp1, and further, the second differential amplifier Amp2 determines the first differential amplifier Amp1. The difference between the output voltage and the voltage generated in the current detection resistor R3 may be obtained. That is, in this case, the current detection resistors R1, R2, and R3 have V1 = (I / M) × r1 + ΔIn × r1.
V2 = (I / N) × r2 + ΔIn × r2
V3 = (I / L) × r3 + ΔIn × r3
Each produces a voltage.

Therefore, for example, if the gain of the first differential amplifier Amp1 is set to [1], the output of the first differential amplifier Amp1 is Vamp = (V1-V2)
= (R1 / M-r2 / N) I + (r1-r2) ΔIn
Is obtained.

If the difference between the output voltage Vamp of the first differential amplifier Amp1 and the voltage V3 generated in the current detection resistor R3 is obtained by the second differential amplifier Amp2, the output of the second differential amplifier Amp2 is obtained. As Vsense = G (Vamp−V3)
= G (V1-V2-V3)
= G (r1 / M-r2 / N-r3 / L) I + G (r1-r2-r3) ΔIn
A current detection signal Vsense is obtained.

  Therefore, if the resistance values r2 and r3 of the current detection resistors R2 and R3 are set to [1/2] of the resistance value r1 of the current detection resistor R1, for example, current noise is reduced as in the previous embodiment. The current I flowing through the main switching element Qm can be detected with high accuracy by removing or reducing the influence. However, in this case, it cannot be denied that the configuration is more complicated than the case where the two sub-switching elements Qs1 and Qs2 described above are used, and the influence of current noise is more likely to occur. Therefore, the embodiment described above is preferable in practical use.

  FIG. 3 is a schematic configuration diagram of a main part of an internal combustion engine ignition device configured using the above-described current detection circuit. In this internal combustion engine ignition device, the main switching element Qm controls the current flowing through the primary coil 11 of the ignition coil 10 in a pulsed manner, and the ignition plug 13 connected to the secondary coil 12 of the ignition coil 10 is ignited. It is something to control. Specifically, a gate drive circuit 21 for inputting an ignition control signal from an in-vehicle control unit (ECU) 20 applies a gate drive signal to the gate of the main switching element Qm via a gate resistor 22, thereby The spark plug 13 is configured to ignite.

  The current detection circuit for detecting the current I flowing through the main switching element Qm functioning as described above includes two sub-switching elements Qs1 and Qs2 provided in parallel to the main switching element Qm as described above. Voltages proportional to the current I are detected via current detection resistors R1 and R2 connected to the emitters of the sub-switching elements Qs1 and Qs2, respectively.

  The voltage generated in each of the current detection resistors R1 and R2 is detected via the differential amplifier Amp, and the current detection signal Vsense which is the output of the differential amplifier Amp is input to the overcurrent detection circuit 23 to detect the overcurrent. Detect outbreaks. Specifically, in the overcurrent detection circuit 23, the current detection signal Vsense is compared with a preset reference voltage Vref, and when the current detection signal Vsense exceeds the reference voltage Vref, this is detected as the main switching element. It is detected that an overcurrent flows in Qm. The operation of the gate drive circuit 21 is controlled by the output of the overcurrent detection circuit 23, and the current I flowing through the main switching element Qm is reduced by, for example, reducing the gate drive voltage for the main switching element Qm. As a result, not only the main switching element Qm but also the ignition coil 10 and the spark plug 13 are protected from overcurrent.

  Incidentally, when the reduction control of the current I flowing through the main switching element Qm by the reduction of the gate drive voltage, that is, the feedback control of the current is executed, the size of the main switching element Qm and the two sub-switching elements Qs1 and Qs2 described above. Due to the difference, the main switching element Qm tends to have a response delay with respect to a change in its gate control signal. Then, when the current flowing through the main switching element Qm is kept constant by the feedback control described above, there is a concern that the main switching element Qm cannot follow the change in the gate control signal and induce oscillation.

  The gate resistor 22 described above forms a low-pass filter with the input parasitic capacitance (not shown) of the main switching element Qm, and plays a role of changing the gate control signal only slowly with respect to the main switching element Qm. . In other words, the gate control signal is directly applied to the gates of the two sub-switching elements Qs1 and Qs2, thereby ensuring high-speed response. As a result, the feedback control of the gate control signal is promptly executed, and the protection operation against the overcurrent is reliably executed.

  Further, according to the above-described configuration, the main switching element Qm and the current detection circuit are often mounted in the vicinity of a site where an engine (internal combustion engine) that is a noise generation source in the vehicle and various motors are provided. Therefore, the improvement in noise resistance described above has a great practical effect.

  By the way, for example, when three sub-switching elements Qs1, Qs2, and Qs3 having different sizes are used as described above, they are generated in the current detection resistors R1 and R2 in the first differential amplifier Amp1 as shown in FIG. The difference between the voltages is obtained, and the difference between the voltages generated in the current detection resistors R3 and R1 is obtained by the second differential amplifier Amp2. Then, the difference between the output voltages of the differential amplifiers Amp1 and Amp2 may be obtained by the third differential amplifier Amp3.

In this case, if each gain of the differential amplifiers Amp1 and Amp2 is set to [1], the output of the first differential amplifier Amp1 is Vamp1 = (V1−V2)
= (R1 / M-r2 / N) I + (r1-r2) ΔIn
Is obtained.

Further, as the output of the second differential amplifier Amp2, Vamp2 = (V3-V1)
= (R3 / L-r1 / M) I + (r3-r1) ΔIn
Is obtained.

If the gain of the differential amplifier Amp3 is set to [G], the output of the third differential amplifier Amp3 is Vsense = G (Vamp1-Vamp2)
= G {(V1-V2- (V3-V1))
= G (2.V1-V3-V2)
= G (2 · r1 / M−r2 / N−r3 / L) I
+ G (2 · r1-r2-r3) ΔIn
A current detection signal Vsense is obtained.

  Therefore, for example, if the resistance values r2 and r3 of the current detection resistors R2 and R3 are set to be equal to the resistance value r1 of the current detection resistor R1, respectively, the current noise is reduced as in the previous embodiments. The current I flowing through the main switching element Qm can be detected with high accuracy by removing or reducing the influence. In addition, with such a configuration, after removing in-phase components of the currents flowing through the second and third sub-switching elements Qs2 and Qs3 from the current flowing through the first sub-switching element Qs1, the third difference Since the detection error can be canceled in the dynamic amplifier Amp3, the detection accuracy of the current I flowing through the main switching element Qm can be further increased.

  The present invention is not limited to the embodiment described above. For example, the values M and N of the sizes [1 / M] and [1 / N] of the sub-switching elements Qs1 and Qs2 may be set to about several hundred to several thousand as described above. Needless to say, it should be determined in accordance with. It is sufficient to determine the gain G of the differential amplifier Amp according to the control specifications. Furthermore, the switching elements Qm, Qs1, and Qs2 are not limited to the IGBTs described above, but may be MOSFETs or bipolar transistors. In addition, the present invention can be variously modified and implemented without departing from the scope of the invention.

Qm Main switching element Qs1, Qs2 Sub switching element R1, R2 Current detection resistor Amp Differential amplifier RL Load 10 Ignition coil 13 Spark plug 20 On-vehicle control unit (ECU)
21 Gate drive circuit 22 Gate resistance 23 Overcurrent detection circuit

Claims (5)

A current detection circuit for detecting a current flowing in a main switching element that is driven on and off by applying a control signal;
A plurality of sub-switching elements that are provided in parallel with the main switching element and are turned on / off by being applied with the control signal, and are smaller than the main switching element and different in size;
A plurality of current detection resistors connected in series to each of these sub-switching elements,
A current detection circuit comprising: a differential amplifier that detects a current flowing through the main switching element from a difference in voltage generated in each of the current detection resistors.   The current detection circuit according to claim 1, wherein the main switching element and the plurality of sub switching elements are formed on the same semiconductor substrate.   The current detection circuit according to claim 1, wherein the plurality of current detection resistors have the same resistance value.   The main switching element is turned on / off by applying the control signal to the control terminal via an input resistor, and the plurality of sub switching elements are turned on by directly applying the control signal to the control terminal. The current detection circuit according to claim 1, which is driven off.   The current detection circuit according to claim 1, wherein the main switching element and the plurality of sub switching elements are each formed of an IGBT or a MOSFET.

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