JPH0752370B2 - Current detection circuit for semiconductor devices - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a current detection circuit in a switching circuit using a semiconductor element such as a transistor, and particularly to a current detection circuit suitable for a switching circuit for an ignition device of an internal combustion engine. Regarding the circuit.

[Prior Art] In an internal combustion engine ignition device, a high voltage for ignition is generated at a predetermined timing by controlling the energization of an ignition coil. In recent years, such an ignition device has been energized. Using a semiconductor switching element for control,
So-called electronic ignition devices have become widely adopted.

By the way, in such an electronic ignition device, in order to control the ignition energy and protect the semiconductor switching element, the current flowing through the semiconductor switching element is detected, and the current is controlled to a predetermined value according to the detection result. As a result, which requires a current detection function.

Therefore, in the early days, a resistor for detection was connected in series to the current path of the semiconductor switching element for current control,
The voltage drop due to this was taken in.

However, in this method, the loss in the resistance for detection becomes considerably large, which causes problems of heat generation and power loss.

Therefore, the specification of U.S. Pat.
According to the specification of No. 84, another semiconductor element (this is a sub-element) having a predetermined relationship with a semiconductor element (which is a main element) to be subjected to current detection is provided. We have proposed a current detection circuit that estimates the current of the original semiconductor element by detecting the current of the element. Hereinafter, the proposed current detection circuit will be described. , The current detection of the semiconductor switching circuit by MOSFET (MOS field effect transistor), when the area of the source part of the main element is set to 1, the sub-element having the source area of 1 / N (N >> 1) is provided. The current flowing through the sub-element is detected, and the current of the main element is detected by calculation from this detection result and the above N. As shown in FIG. 2, the sub-element 2 is connected to the main element 1 composed of a MOSFET. Provided,
A resistor 31 for current detection is connected in series with the sub-element 2, and the voltage drop generated in the resistor 31 is measured to detect the current flowing in the main element 1 from the above relationship. That is, if the relationship between the source areas of the main element 1 and the sub-element 2 is set as in the above equation, an ON signal is applied to the control terminal A to bring both elements 1 and 2 into conduction, and the load current I _L When the current flows, the load current I _L is shunted to both elements, but the shunt ratio at this time is proportional to the source area, and the current I _{SN that} is 1 / N of the current of the main element 1 flows to the sub element 2. And this sub-element 2
If the current value is detected by the voltage drop of the resistor 31, the current of the main element 1 can be calculated and detected from the detected value and the numerical value N.

According to this method, the current flowing through the resistor 31 for current detection is only about 1 / N of the load current I _L. Therefore, the loss at the resistor 31 is set from the above setting (N >> 1). The problem of heat generation can be eliminated.

[Problems to be Solved by the Invention] The above-mentioned conventional technology has a problem in that there is a limit to the accuracy of current detection because no consideration is given to the influence of voltage drop due to the resistance for current detection. That is, the voltage drop due to the resistance for current detection described above causes a difference in control voltage between the main element and the sub element, so that the above-described shunt ratio is strictly limited to the source area. Because it will not depend on it.

An object of the present invention is to provide a current detection circuit for a semiconductor device, which eliminates the above-mentioned influence of the voltage drop and can obtain sufficient detection accuracy even when the current is detected by the sub-device.

[Means for Solving the Problems] The above object is to provide a voltage source that generates a voltage equal to a voltage drop appearing in a resistor for current detection, and
This is achieved by superimposing the control signal of the main semiconductor element with the opposite polarity or superimposing the control signal of the sub semiconductor element with the same polarity.

[Operation] The voltage drop due to the current detection resistor affects only the control voltage of the sub semiconductor element, and does not affect the control voltage of the main semiconductor element.

Therefore, by providing a voltage source that generates the same voltage as the voltage drop that appears in the current detecting resistor and superposing this voltage on the control signal of the main semiconductor element in the opposite polarity, or in the sub semiconductor element, If they are superimposed on the control signal with the same polarity, it is possible to cancel the influence of the voltage drop due to the resistance for current detection, suppress a decrease in detection accuracy, and obtain high accuracy.

This will be described in more detail with reference to the principle diagram of FIG. 3. In the present invention, as shown in FIG. 3, the voltage drop of the resistor 31 is detected, and the signal conversion circuit 10 converts the signal to a floating potential state. Produce the voltage of. That is, since the voltage generated in the resistor 31 is the ground potential (common point potential), the condition is not good as it is, and the signal conversion circuit 10 shifts the level. The voltage generated in this way is used by the voltage source 12
Alternatively, it is applied to 13 to create an equivalent voltage, which is inserted in series in the signal path to the gate of MOSFET 1 or 2. At this time,
The output impedance of the signal conversion circuit 10 is made sufficiently low so that the influence of the insertion of the voltage sources 12 and 13 does not appear as much as possible.

As a result, the true gate-source voltages V _GS1 and V _GS2 of the main element 1 for current control and the sub-element 2 for current detection can be made equal, and the linearity of the ratio of the source currents between these elements can be made. Can be greatly improved.

[Embodiment] A semiconductor element current detection circuit according to the present invention will be described in detail below with reference to the illustrated embodiment.

FIG. 1 shows an embodiment of the present invention in which MOSFETs are used as a main element for current control and a sub element for current detection, as in the prior art described in FIG. The present invention is
Needless to say, the semiconductor element used is not limited to the MOSFET, and it can be implemented by using, for example, a bipolar transistor.

In FIG. 1, 11 is an operational amplifier and 21 is an amplifying element.
NPN bipolar transistors 32 and 33 are resistors having the same resistance value R as the current detection resistor 31. It should be noted that MOSFETs (hereinafter referred to as MOS) 1 and 2 to be the main element and the sub element
The current detecting resistor 31 is the same as that of the conventional technique shown in FIG.

First, as described above, the gate-source voltages of MOS1 and V2 are set to V _GS1 and V _GS2 , respectively, and the gate voltage of MOS2,
That is, the voltage at the control input terminal is V _G. The resistance value of the resistors 31, 32, 33 is R as described above.

Now, it is assumed that a predetermined control signal is input and, as a result, a certain detection current I _SN flows.

Then, a voltage drop of V ₃₁ = R · I _SN appears in the current detection resistor 31, and the voltage V _{31 of} this appears in the operational amplifier 1
It will be input to the positive input terminal of 1.

By the way, the output of this operational amplifier 11 is a transistor 21
Is connected to the base of the operational amplifier 11, and the emitter of the transistor 21 is connected to the negative input terminal of the operational amplifier 11. Further, this negative input terminal is connected to the supply potential point via the resistor 32.

As a result, the operational amplifier 11 works so that its two input terminals have the same potential, and a current having a value equal to the current I _SN flowing through the detection resistor 31 flows through the resistor 32.

Here, if the emitter current of the transistor 21 is I _E and the collector current is I _C , there is a relation of I _E ≈I _C between them, so that a relation of I _C ≈I _SN is eventually given. Will be there.

The collector current I _C of this transistor 21 is
Since it flows through the resistor 33 which is inserted in series with the gate signal line of, the voltage drop of V ₃₃ = R · I _C = V ₃₁ appears in the resistor 33, and this voltage is the signal voltage with the polarity shown in the figure. It will be superimposed on V _G and applied to the gate of MOS1.

By the way, the gate potential of MOS2 (voltage to terminal C) is
V _G , and the voltage obtained by subtracting the voltage V ₃₁ from this is this MOS
Since the gate-source voltage V _GS2 is ₂ , V _GS2 = V _G −V ₃₁ = V _G −R · I _SN .

On the other hand, regarding the gate-source voltage V _GS1 of the MOS1, as is clear from the figure, this is the voltage V _{G at the} terminal A minus the voltage drop due to the resistor 33.
That is, V _GS1 = V _G −V ₃₃ = V _G −R · I _C.

Then, as described above, since I _C ≉I _SN ∴V ₃₃ = R · I _C = V ₃₁ , eventually, according to this embodiment, it is possible to set V _GS1 = V _GS2 and MOS1 MOS2 means that it operates under the same gate-source voltage, and is not affected by the current detection resistor 31 at all, and is the main element MOS1.
Can be detected with sufficient accuracy by calculation with the ratio N of these source areas by the current flowing in the subelement MOS2.

By the way, in the embodiment of FIG. 1, the operational amplifier 11 is shown by a symbol.
It is a figure.

The sources of the MOSs 40 and 41 are made common, connected to the ground terminal 43 via the resistor 42, and the drains thereof are connected to the power supply terminal 46 via the resistor 44 and the resistor 45, respectively. Further, the operational amplifier 11 can be realized by connecting the gate of MOS2 to the minus input terminal 47, the drain to the output terminal 48, and the gate of MOS1 to the plus input terminal 49.

Since the circuit configuration of the embodiment shown in FIG. 1 is simple, it can be easily integrated into an IC.

FIG. 5 shows another embodiment of the present invention.

The MOS1, 2 and the detecting resistor 31 and the resistor 33 are the same as those in the embodiment of FIG. 1, but are characterized in that the bypass current sources 51, 52 constituted by bipolar transistors are provided.

Assuming that the detected current I _SN is flowing now, the current sources 51 and 52 operate due to the voltage drop across the resistor 31 and generate the current I _SN proportional to the voltage drop.

As a result, the gate voltage of the MOS2 is increased by the current source 52, but the current of the current source 52 is absorbed by the current source 51, so that the gate voltage of the MOS1 is not changed.

Therefore, according to this embodiment as well, V _GS1 and V _GS2 of the MOS1 and MOS2 can be set to be substantially equal to each other, so that the current detection accuracy can be improved.

FIGS. 6 and 7 show examples of the current sources 51 and 52. First, when the current source 52 is composed of elements, it becomes as shown in FIG.

The emitter of the bipolar transistor 61 is connected to the power supply terminal 63 via the resistor 62, the base to the resistors 64 and 65, and the collector to the constant current terminal 66.

The resistors 64 and 65 are provided to divide the voltage between the bipolar transistor 67 and the power supply terminal 63 and supply it to the base of the bipolar transistor 61.

The base of the bipolar transistor 67 is connected to the input terminal 68, and the emitter is connected to the ground terminal 69.

The current source 52 can be realized by the above circuit configuration.

Next, FIG. 7 shows an embodiment of the current source 51 in which the emitter of the transistor 71 is connected to the power supply terminal 72, the base is connected to the resistors 73 and 74, and the collector is connected to the resistor 75.

The resistors 73 and 74 function to divide the voltage between the transistor 75 and the power supply terminal 72 and supply it to the base of the transistor 71.

The collector of the transistor 76 is connected to the constant current terminal 77, the emitter is connected to the ground terminal 78, and the base is connected to the resistors 79 and 80. The resistors 79 and 80 function to divide the voltage between the transistor 71 and the ground terminal 78 and input it to the base of the transistor 76.

The collector of the transistor 75 is connected to the resistor 74, the base is connected to the input terminal 81, and the emitter is connected to the ground terminal 78.

With the above, the current source 51 can be obtained.

According to the embodiment shown in FIG. 5, the current supplied from the current source 52 to the resistor 33 is absorbed by the current source 51, so that the effect that the input terminal A side is not affected can be obtained.

FIG. 8 shows still another embodiment of the present invention, in which the MOS1, 2, the operational amplifier 11 and the resistors 31, 32 are the same, but the gate of the MOS1 is the photoconductive element 85 and the output terminal of the operational amplifier 11 is the light emitting diode. 86 is provided.

Assuming that the detected current I _SN is flowing, a current I _SN also flows through the resistor 31 as in the case of FIG. 1, the light emitting diode 86
Emits light. Then, the photoconductive element 85 receives the light from the light emitting diode 86 and generates a voltage. Since this photoconductive element 85 generates a voltage proportional to light, the voltage generated in the photoconductive element 85 can be controlled according to the detected current I _SN .

As a result, the gate-source voltages of the MOS1 and MOS2 can be set equal, so that the current detection accuracy can be improved.

The photoconductive element 85 shown in FIG. 8 can be realized by CdSe (cadmium selenium) or the like.

The present embodiment has the effect of electrically insulating the current detection side and the gate side.

FIG. 9 shows another embodiment of the present invention.

The embodiment shown in FIG. 9 is obtained by adding a current limiting circuit to the embodiment shown in FIG. 1, and MOS1,2, operational amplifier 11, transistor 21, resistors 31,32,33 are the same as those in the embodiment shown in FIG. Is.

The MOS3 controls the gate-drain voltage of the MOS2 together with the resistor 34 in accordance with the voltage drop of the resistor 32, thereby performing the current limiting action. Therefore, according to this embodiment, even if the current limiting function is provided, the current I _SN always flows through the resistors 31, 32 and 33, so that the current detection accuracy does not deteriorate.

By the way, in the above embodiments, the MOSFET is used as the semiconductor element which is the main element and the sub element.
Needless to say, it is not limited to MOSFETs. FIG. 10 shows an embodiment using a bipolar transistor, and FIG. 11 shows an embodiment using an insulated gate bipolar transistor (IGBT).

First, in FIG. 10, 201 is a bipolar transistor which is a main element for current control, 202 is a bipolar transistor which is a sub element for current detection, 203 is a bipolar transistor for current limiting, and others are shown in FIG. Same as the embodiment.

Next, in FIG. 11, 101 is an IGBT which is a main element for current control, 102 is an IGBT which is a sub element for current detection, and 1
Reference numeral 03 is an IGBT for limiting current, and the other components are the same as those in the embodiment shown in FIG.

Therefore, according to the embodiment shown in FIGS. 10 and 11,
Since the base-emitter voltage or the gate-emitter voltage of each transistor can be made equal as in the embodiment of FIG. 9, high-precision current detection can be easily obtained, and in the embodiment of FIG. Since all semiconductor devices are bipolar transistors, all circuits in the bipolar process
There is an effect that the IC can be realized and the yield can be easily improved. On the other hand, according to the embodiment of FIG. 11, there is an effect that it is easy to apply to a control circuit for a large current. is there.

FIG. 12 is a further embodiment of the present invention, which is characterized in that a conduction resistance of a bipolar transistor is used in place of the current detection resistance connected in series with the sub-element. In the figure, 205 is a transistor for this purpose.

Then, the current I _SN is detected by this transistor 205, the same current I _S is made to flow in the collector of the transistor 206, and this current is used as the detection current.

The voltage drop between the collector and the emitter of the transistor 205 is
Since it is always equal to the voltage drop across resistor 32, resistors 32 and 33
By setting the resistance value of the transistor 33 to the same value, a voltage equal to the collector-emitter voltage drop of the transistor 205 can be generated across the resistor 33.
By eliminating the difference between the base and emitter voltages of 1 and 202, it is possible to easily obtain highly accurate current detection.

Further, according to this embodiment, since it is not necessary to use a resistor for current detection, the temperature characteristic is improved and the accuracy can be further improved.

EFFECTS OF THE INVENTION According to the present invention, the operating conditions of the main semiconductor element for current control and the sub-semiconductor element for current detection can be made sufficiently equal, so that highly accurate current detection can be easily obtained. be able to.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing one embodiment of a semiconductor element current detection circuit according to the present invention, FIG. 2 is a circuit diagram showing a conventional example, and FIG.
FIG. 4 is a circuit diagram for explaining the principle of the present invention, FIG. 4 is a circuit diagram showing an example of an operational amplifier, FIG. 5 is a circuit diagram showing another embodiment of the present invention, and FIGS. 6 and 7 are respectively. FIG. 8 is a circuit diagram showing an embodiment of a current source, FIG. 8 is a circuit diagram showing an embodiment of the present invention using an optical coupling element, and FIG. 9 is an embodiment of the present invention to which a current limiting function is added. Circuit diagram, FIG. 10 is a circuit diagram showing an embodiment of the present invention using a bipolar transistor, FIG. 11 is a circuit diagram showing an embodiment of the present invention using an insulated gate bipolar transistor, and FIG. 12 is a current detection circuit. It is a circuit diagram which shows one Example of this invention which used ON resistance of a transistor as resistance. 1 ... Main semiconductor element for current control composed of MOSFET, 2 ...
… Sub-semiconductor element consisting of MOSFET for current detection, 11 …… operational amplifier, 21 …… NPN transistor serving as amplification element, 31
...... Current detection resistors, 32,33 ...... Resistors.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masayoshi Suzuki 2520 Takaba, Katsuta City, Ibaraki Prefecture Sawa Factory, Hitachi, Ltd. (56) References JP 58-18715 (JP, A) -132635 (JP, U)

Claims (3)

[Claims] 1. A current detecting resistor in which a current flowing through a current controlling semiconductor element is connected in parallel to this semiconductor element and is connected in series to a current detecting semiconductor element to which a control signal is supplied from the same control signal input terminal. In the voltage detection circuit of the method of detecting by the voltage drop of the voltage detector, a variable voltage source that generates a voltage equal to the voltage drop of the current detection resistor is provided, and the voltage generated by the variable voltage source is A current detecting circuit for a semiconductor element, wherein the current detecting circuit is configured to be superimposed on a control signal of the current controlling semiconductor element with an opposite polarity. 2. A current detecting resistor in which a current flowing through a current controlling semiconductor element is connected in parallel to this semiconductor element and is connected in series to a current detecting semiconductor element to which a control signal is supplied from the same control signal input terminal. In the voltage detection circuit of the method of detecting by the voltage drop of the voltage detector, a variable voltage source that generates a voltage equal to the voltage drop of the current detection resistor is provided, and the voltage generated by the variable voltage source is A current detecting circuit for a semiconductor element, wherein the current detecting circuit is configured to be superimposed on the control signal of the current detecting semiconductor element with the same polarity. 3. The invention according to claim 1 or 2, wherein the variable voltage source is connected in series to one control signal path of the current control semiconductor element or the current detection semiconductor element, A current detection circuit for a semiconductor device, comprising: an operational amplifier circuit for connecting a current flowing through the resistor according to a voltage drop of the current detection resistor.