JP2003202355A - Current detection circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a current detection circuit by which a drain current flowing in a power MOS transistor can be detected satisfactorily. <P>SOLUTION: A drain terminal D and a gate terminal G of a shunt MOS transistor 12 are installed sharing those of the power MOS transistor 11. One end of a shunt detecting resistance 13 having a comparatively large resistance value is connected to a source terminal 12S of the transistor 12. The other end of the resistance 13 is connected to a collector terminal C of an npn transistor 14, and an emitter terminal E of the npn transistor 14 is connected to a negative-voltage power supply 15 used to generate a negative voltage (-VDD). A potential of the source terminal 12S of the transistor 12 is held at the same potential as a source terminal 11S of the transistor 11 by a function of a potential holding circuit 18. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current detection circuit for detecting a drain current flowing in a power MOS transistor.

[0002]

2. Description of the Related Art For example, in an electric power steering apparatus, an electric motor is used as a source of a steering assist force to be given to a steering mechanism of a vehicle, and a motor drive circuit for supplying a drive current to the electric motor. Adopts an inverter circuit having a configuration in which a series circuit of two power MOS transistors is connected in parallel by the same number as the number of phases of the electric motor. Then, a target current value is set according to the steering torque applied to the steering wheel and the vehicle speed, and the motor drive circuit (electric motor) is feedback-controlled based on the set target current value.

In order to realize the feedback control of the motor drive circuit, it is essential to detect the drive current supplied from the motor drive circuit to the electric motor. The drive current can be detected, for example, by detecting the current flowing through each power MOS transistor that constitutes the motor drive circuit. FIG. 4 is a diagram showing a circuit configuration for detecting a current flowing through the power MOS transistor. A large current flows through the power MOS transistor 91 forming the motor drive circuit, and it is difficult to directly detect the large current. Therefore, the circuit for detecting the current flowing through the power MOS transistor 91 is a power MOS transistor. The current (main current) flowing in 91 is detected at a predetermined current division ratio (for example, 1/100).

That is, in this current detection circuit, in order to divide the main current flowing through the power MOS transistor 91, the drain terminal D and the gate terminal G are connected to the power MO.
A shunt MOS transistor 92 shared with the S transistor 91 is provided. Power MOS transistor 91
The source terminal 91S of is connected to the ground 93,
The source terminal 92S of the shunt MOS transistor 92 is connected to the ground 93 via the shunt current detection resistor 94.

With this configuration, when a gate voltage higher than the threshold voltage of the power MOS transistor 91 is applied to the common gate terminal G of the power MOS transistor 91 and the shunt MOS transistor 92, the power MOS transistor 91
The transistor 91 and the shunt MOS transistor 92 are turned on, the main current (drain current) flows through the power MOS transistor 91, and the main current is supplied at a shunt ratio substantially equal to the on resistance ratio of the power MOS transistor 91 and the shunt MOS transistor 92. A proportional shunt current flows through the shunt MOS transistor 92. This shunt current is a potential difference (shunt M) between both ends of the shunt current detection resistor 94.
It can be calculated by detecting the potential of the source terminal 92S of the OS transistor 92 by a voltage detection circuit and dividing the detected potential difference by the resistance value (for example, 100Ω) of the shunt current detection resistor 94. Then, by dividing the calculated shunt current by the shunt ratio, the power MOS
The main current flowing through the transistor 91 can be calculated.

[0006]

The power MOS transistor 91 is designed to have a small on-resistance in order to suppress the amount of heat generated when a large current flows, and the power MOS transistor 91 has a small ON resistance.
The source-drain voltage of the transistor 91 in the ON state is about several hundred mV even when the maximum current that can be supplied to the power MOS transistor 91 is supplied. Further, in the above circuit configuration, the potential difference between both ends of the shunt current detection resistor 94 does not become larger than the source-drain voltage when the power MOS transistor 91 is in the ON state. Therefore, when the main current flowing through the power MOS transistor 91 is weak, the potential difference between both ends of the shunt current detection resistor 94 becomes very small, and the very small potential difference cannot be detected well by the voltage detection circuit. The current detection accuracy (resolution) was not good.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned technical problems and to provide a current detection circuit capable of satisfactorily detecting a current flowing through a power MOS transistor.

[0008]

Means for Solving the Problems and Effects of the Invention The invention according to claim 1 for achieving the above object is a power M.
In order to detect the drain current flowing in the OS transistor (11), the power MOS transistor and the shunt MOS transistor in which the drain terminal (D) and the gate terminal (G) are common.
A circuit for detecting a shunt current flowing through a transistor (12), which is an auxiliary power supply (15) for generating a voltage lower than a source voltage of the power MOS transistor by a predetermined amount, and one end of the auxiliary power supply. A shunt current detecting resistor (13; 1) connected to the other end of which is connected to the source terminal (12S) of the shunt MOS transistor.
31) and the potential of the source terminal of the shunt MOS transistor, the source terminal (1
1S) potential holding circuit for holding the same potential (14,
181; 141, 142, 191) are included in the current detection circuit.

The alphanumeric characters in parentheses represent corresponding components in the embodiments described later. The same applies in this section below. According to the present invention, since the shunt current detecting resistor is connected to the auxiliary power supply, the shunt current detecting resistor allows a maximum voltage drop corresponding to the voltage generated by the auxiliary power supply. Therefore, since a resistor having a large resistance value can be used as the shunt current detecting resistor, even if the drain current flowing through the power MOS transistor is small and the shunt current flowing through the shunt current detecting resistor is small, the small shunt current will be used. The current causes a large potential difference across the shunt current detection resistor. Therefore, even if the drain current flowing through the power MOS transistor is small, the small drain current can be satisfactorily detected.

When the source terminals of a plurality of power MOS transistors are at the same potential and all of these power MOS transistors are turned on at different timings, the other end of the shunt current detecting resistor is connected to each power MOS transistor. MOS
If the source terminals of the shunt MOS transistors provided corresponding to the transistors are connected, these shunt MOSs can be connected.
Shunt current flowing through a transistor (a plurality of power MOS
The drain current flowing through the transistor 11) can be detected by the common current detection circuit. If you do this
As described in claim 3, a current detection circuit is connected in parallel to the other end of the shunt current detection resistor, and a plurality of interference prevention resistors (each connected to the source terminals of different shunt MOS transistors) 22) is preferably further included.

According to a second aspect of the present invention, the power MOS is provided.
The power MOS is interposed between the source terminal of the transistor and the source terminal of the shunt MOS transistor.
2. The current detection circuit according to claim 1, further comprising a diode (21) which passes a current only in a direction from the source terminal of the transistor to the source terminal of the shunt MOS transistor. According to the present invention, the potential of the source terminal of the shunt MOS transistor can be more reliably maintained at the same potential as the source terminal of the power MOS transistor.

According to a fourth aspect of the present invention, the shunt current detection resistor has a resistance value different from that of the shunt current detection resistor, one end of which is connected to the auxiliary power supply, and the other end of which is connected to the source terminal of the shunt MOS transistor. A second shunt current detecting resistor (132) connected in parallel with the current detecting resistor, and a shunt current for switching the shunt current to the shunt current detecting resistor (131) or the second shunt current detecting resistor. Switching means (19
2, 193, 195) is further included in the current detection circuit according to any one of claims 1 to 3.

According to the present invention, the second shunt current detecting resistor has a resistance value different from that of the first shunt current detecting resistor. Therefore, normally, a shunt current is made to flow through the shunt current detection resistor with the smaller resistance value, and the drain current is detected based on the potential difference across the shunt current detection resistor. If the shunt current is made to flow through the shunt current detection resistor having the larger resistance value and the main current is calculated based on the potential difference across the shunt current detection resistor, the power MOS transistor The drain current can be satisfactorily detected in a wide range.

[0014]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a circuit diagram showing a configuration of a current detection circuit according to an embodiment of the present invention. The current detection circuit is, for example, a circuit for detecting a current (main current) flowing in a power MOS transistor 11 included in a motor drive circuit for driving an electric motor.
A shunt MOS transistor 12 is provided for shunting a relatively small current (shunt current) from the current flowing through the first transistor. The threshold voltage of the shunt MOS transistor 12 is set lower than the threshold voltage of the power MOS transistor 11.

The shunt MOS transistor 12 has a power M
The drain terminal D and the gate terminal G are shared with the OS transistor 11. The source terminal 12S of the shunt MOS transistor 12 is connected to one end of a shunt current detection resistor 13 having a relatively large resistance value (for example, 100Ω). The other end of the shunt current detection resistor 13 is
It is connected to the collector terminal C of the npn transistor 14, and the emitter terminal E of this npn transistor 14 is connected.
Is connected to a negative voltage power supply 15 (auxiliary power supply) that generates a negative voltage (-V _DD ). The source terminal 11S of the power MOS transistor is connected to the ground 16.

With this structure, when a gate voltage higher than the threshold voltage of the power MOS transistor 11 is applied to the common gate terminal of the power MOS transistor 11 and the shunt MOS transistor 12, the power MOS transistor 11 is applied.
When the transistor 11 and the shunt MOS transistor 12 are turned on, the main current (drain current) flows through the power MOS transistor 11, and the npn transistor 14 is turned on, the shunt MOS transistor 1
2. A shunt current flows in the series circuit of the shunt current detection resistor 13 and the npn transistor 14. Therefore, if the voltage detection circuit 17 detects the potential difference between both ends of the shunt current detecting resistor 13 at this time, the shunt current flowing through the shunt current detecting resistor 13 can be calculated based on the detected potential difference. .

Ratio of shunt current to main current (shunt ratio)
Is the source terminal 11S of the power MOS transistor 11.
And the source terminal 12S of the shunt MOS transistor 12 have the same potential, the ratio is equal to the ratio (for example, 1/100) of the number of minute transistors forming the power MOS transistor 11 and the shunt MOS transistor 12, respectively. Therefore, the power MOS transistor 11
When the source terminal 11S and the source terminal 12S of the shunt MOS transistor 12 have the same potential, the main current flowing through the power MOS transistor 11 is divided by dividing the shunt current flowing through the shunt current detecting resistor 13 by the shunt ratio. Can be calculated.

Therefore, in this current detection circuit, the shunt MO
A potential holding for holding the potential of the source terminal 12S of the S-transistor 12 so as to match the potential of the source terminal 11S of the power MOS transistor 11 (zero in this embodiment because the source terminal 11S is connected to the ground 16). A circuit 18 is provided. Potential holding circuit 18
Is the source terminal 11S of the power MOS transistor 11.
Potential and source terminal 12 of shunt MOS transistor 12
Operational amplifier 181 that amplifies and outputs the difference from the potential of S
And the output terminal of the operational amplifier 181 and the negative voltage power supply 15
And two resistors 182 and 183 that are connected in series between and. The source terminal 11S of the power MOS transistor 11 is connected to the positive side input terminal of the operational amplifier 181, and the source terminal 12S of the shunt MOS transistor 12 is connected to the negative side input terminal of the operational amplifier 181. Then, the operational amplifier 181 and the resistor 1
The series circuit of 82 and 183 has two resistors 182 and 183.
Is connected to the base terminal B of the npn transistor 14.

With this configuration, when the potential of the source terminal 12S of the shunt MOS transistor 12 becomes lower than the potential of the source terminal 11S of the power MOS transistor 11,
By the operation of the operational amplifier 181, the npn transistor 1
The base voltage of 4 is raised. As a result, the collector current flowing through the npn transistor 14 increases, the voltage applied across the shunt current detecting resistor 13 increases, and the potential of the source terminal 12S of the shunt MOS transistor 12 rises. On the other hand, the potential of the source terminal 12S of the shunt MOS transistor 12 is the power MOS transistor 11
When it becomes higher than the potential of the source terminal 11S, the base voltage of the npn transistor 14 is lowered by the operation of the operational amplifier 181. As a result, the npn transistor 1
The collector current flowing in 4 decreases, the voltage applied to the shunt current detecting resistor 13 decreases, and the potential of the source terminal 12S of the shunt MOS transistor 12 decreases. Thus, the source terminal 12S of the shunt MOS transistor 12
Is maintained at the same potential as the potential of the source terminal 11S of the power MOS transistor 11.

Therefore, based on the potential difference between both ends of the shunt current detecting resistor 13 detected by the voltage detecting circuit 17,
The main current flowing through the power MOS transistor 11 can be calculated by calculating the shunt current flowing through the shunt current detection resistor 13 and gradually reducing the calculated shunt current by the shunt ratio. Further, in this current detection circuit, the shunt current detection resistor 13 is connected to the negative voltage power supply 15 via the npn transistor 14, so that the shunt current detection resistor 1
In 3, the maximum voltage drop corresponding to the generated voltage of the negative voltage power supply 15 is allowed. Therefore, since a resistor having a large resistance value can be used as the shunt current detecting resistor 13, even if the main current flowing through the power MOS transistor 11 is small and the shunt current flowing through the shunt current detecting resistor 13 is small, The voltage detection circuit 17 can satisfactorily detect the potential difference generated between both ends of the shunt current detection resistor 13 due to the small shunt current. Therefore, in this current detection circuit, even if the main current flowing through the power MOS transistor 11 is small, the small main current can be satisfactorily detected.

FIG. 2 is a circuit diagram showing the configuration of a current detection circuit according to another embodiment of the present invention. 2, parts corresponding to the respective parts shown in FIG. 1 are designated by the same reference numerals as in FIG. In the current detection circuit according to this embodiment, the source terminal 12S of the shunt MOS transistor 12 has a predetermined resistance value (for example, 1Ω).
And one end of the first shunt current detecting resistor 131, and the second shunt current detecting resistor 1 having a resistance value (for example, 100Ω) larger than that of the first shunt current detecting resistor 131.
One end of 32 is connected. The other end of the first shunt current detection resistor 131 is connected to the collector terminal of the npn transistor 141.
The emitter terminal of No. 1 is connected to a negative voltage power supply 15 that generates a negative voltage (-V _DD ). The other end of the second shunt current detection resistor 132 is connected to the collector terminal of the npn transistor 142, and the emitter terminal of the npn transistor 142 has a negative voltage power supply 15 that generates a negative voltage (-V _DD ). It is connected to the. That is, the shunt MO
Source terminal 12S of S transistor 12 and negative voltage power supply 1
5, the first shunt current detection resistor 131 and np
A series circuit of the n-transistor 141 and a series circuit of the second shunt current detection resistor 132 and the npn transistor 142 are provided in parallel.

Further, this current detection circuit has a power MO.
The potential of the source terminal 11S of the S transistor 11 and the shunt M
An operational amplifier 191 that amplifies and outputs the difference from the potential of the source terminal 12S of the OS transistor 12 is provided. The source terminal 11S of the power MOS transistor 11 is connected to the positive input terminal of the operational amplifier 191, and the source terminal 12S of the shunt MOS transistor 12 is connected to the negative input terminal of the operational amplifier 191.

The output of the operational amplifier 191 is applied to one input terminal of the first AND circuit 192 and one input terminal of the second AND circuit 193. To the other input terminal of the first AND circuit 192, for example, a measurement range switching signal output from a microcomputer (not shown) is applied.
The output signal of 2 is amplified by the transistor 194,
It is adapted to be applied to the base terminal of the pn transistor 141. Further, the measurement range switching signal is inverted and given to the other input terminal of the second AND circuit 193 by the inverting circuit 195, and the output signal of the second AND circuit 193 is amplified by the transistor 196. And is applied to the base terminal of the npn transistor 142.

With this configuration, when the measurement range switching signal is at a high level, the first AND circuit 192 outputs a signal corresponding to the output of the operational amplifier 191, the npn transistor 141 is turned on, and the shunt MOS transistor 1 is turned on.
2. A shunt current that is proportional to the main current flowing through the power MOS transistor 11 at a predetermined shunt ratio flows in the series circuit of the first shunt current detection resistor 131 and the npn transistor 141. Therefore, the first shunt current detection resistor 131
The shunt current can be calculated by detecting the potential difference between both ends of the voltage detection circuit 17 (see FIG. 1). Further, the main current flowing through the power MOS transistor 11 is calculated based on the calculated shunt current. can do. At this time, a low level signal obtained by inverting the measurement range switching signal is given to the second AND circuit 193, and
Since no signal is output from the AND circuit 193, np
The n-transistor 142 is kept off, and no shunt current flows in the series circuit of the second shunt-current detecting resistor 132 and the npn transistor 142.

On the other hand, when the measurement range switching signal is low level, the second AND circuit 193 outputs a signal corresponding to the output of the operational amplifier 191, and the npn transistor 142.
Is turned on, the shunt MOS transistor 12, the second shunt current detecting resistor 132 and the npn transistor 14 are turned on.
A shunt current, which is proportional to the main current flowing through the power MOS transistor 11 at a predetermined shunt ratio, flows through the two series circuits.
Therefore, if the voltage detection circuit 17 detects the potential difference across the second shunt current detecting resistor 132, the shunt current can be calculated, and the power MOS transistor 11 can be calculated based on the calculated shunt current. The main current flowing can be calculated. At this time, since the low level measurement range switching signal is given to the first AND circuit 193 and no signal is output from the first AND circuit 193, the npn transistor 141 is kept off, and the first shunt current detecting circuit is used. Resistor 131 and npn transistor 14
No shunt current flows in the series circuit of 1.

The second shunt current detecting resistor 132 has a resistance value larger than that of the first shunt current detecting resistor 131. Therefore, even if the shunt current is weak such that a potential difference is hardly generated between both ends of the first shunt current detecting resistor 131 when flowing through the series circuit of the first shunt current detecting resistor 131 and the npn transistor 141, Second shunt current detection resistor 132 and npn transistor 142
The second shunt current detecting resistor 1
A potential difference is generated between both ends of 32.

Therefore, normally, the measurement range switching signal is set to a high level, and a shunt current is caused to flow in the series circuit of the first shunt current detecting resistor 131 and the npn transistor 141, so that the first shunt current detecting resistor 131 is connected. The main current is calculated based on the potential difference between both ends, and when the potential difference between both ends of the first shunt current detection resistor 131 is equal to or less than a predetermined value, the measurement range switching signal is switched to a low level, If a shunt current is caused to flow in the series circuit of the second shunt current detection resistor 132 and the npn transistor 142, and the main current is calculated based on the potential difference between both ends of the second shunt current detection resistor 132, the main current ( The shunt current) can be satisfactorily detected in a wide range.

Although the two embodiments of the present invention have been described above, the present invention can be implemented in other forms. For example, as shown by a broken line in FIG. 1, the source terminal 11S of the power MOS transistor 11 and the shunt MO are connected.
The source terminal 12S of the shunt MOS transistor 12 is connected to the source terminal 12S of the S-transistor 12 via a diode 21 such as a Zener diode.
S may be more surely held at the same potential as the source terminal 11S of the power MOS transistor 11.

Further, as shown in FIG. 3, the source terminals 11S of a plurality (three in FIG. 3) of power MOS transistors 11 are connected to the ground 16, and these power MOS transistors 11 are all at different timings. When turned on, the source terminal 12S of the shunting MOS transistor 12 provided at one end of the shunting current detection resistor 13 in association with each power MOS transistor 11.
May be connected, and the shunt current flowing through these shunt MOS transistors 12 (main current flowing through the plurality of power MOS transistors 11) may be detected by a common current detection circuit.

In this case, each shunt MOS transistor 12
It is preferable to connect the source terminals 12S of the above to the shunt current detecting resistor 13 via the interference preventing resistor 22, respectively. By doing so, for example, the influence of the sneak current when a reverse potential is applied to the source terminal 12S of each shunt MOS transistor 12 can be reduced. In addition, various design changes can be made within the scope of the matters described in the claims.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a current detection circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a current detection circuit according to another embodiment of the present invention.

FIG. 3 is a circuit diagram showing a configuration in which currents flowing through a plurality of power MOS transistors are detected by a common current detection circuit.

FIG. 4 is a diagram showing a conventional circuit configuration for detecting a current flowing through a power element.

[Explanation of symbols]

11 Power MOS transistor 11S source terminal 12 shunt MOS transistor 12S source terminal 13 Shunt current detection resistor 14 transistors 15 Negative voltage power supply 18 Potential holding circuit 181 operational amplifier 21 diode 22 Resistance to prevent interference 141 transistor 142 transistor 191 operational amplifier 192 AND circuit 193 AND circuit 195 Inversion circuit D drain terminal G gate terminal

Continued front page    F term (reference) 2G035 AA01 AB02 AC01 AD02 AD03                       AD08 AD10 AD20 AD27 AD28                 5H410 BB05 CC02 DD02 DD03 EA11                       EB37 EB39 FF05                 5H550 AA16 CC01 EE08 GG05 GG10                       HB03 KK01 LL14 LL22 LL53                       MM02 MM09

Claims (4)

[Claims] 1. A shunt MOS having a common power MOS transistor, drain terminal, and gate terminal for detecting a drain current flowing through the power MOS transistor.
A circuit for detecting a shunt current flowing through a transistor, an auxiliary power supply generating a voltage lower than the source voltage of the power MOS transistor by a predetermined amount, and one end of which is connected to the auxiliary power supply, A shunt current detecting resistor whose end is connected to the source terminal of the shunt MOS transistor, and a potential holding circuit for holding the potential of the source terminal of the shunt MOS transistor at the same potential as the source terminal of the power MOS transistor. A current detection circuit comprising: 2. The current is interposed between the source terminal of the power MOS transistor and the source terminal of the shunt MOS transistor, and the current flows only in the direction from the source terminal of the power MOS transistor to the source terminal of the shunt MOS transistor. The current detection circuit according to claim 1, further comprising a diode that passes through. 3. A plurality of interference-preventing resistors, which are connected in parallel to the other end of the shunt current detecting resistor and are connected to the source terminals of different shunt MOS transistors, respectively. The current detection circuit described in 1 or 2. 4. A resistor having a resistance value different from that of the shunt current detecting resistor, one end of which is connected to the auxiliary power source, and the other end of which is connected to the source terminal of the shunt MOS transistor in parallel with the shunt current detecting resistor. A second shunt current detecting resistor connected to the second shunt current, and switching means for switching the shunt current to the shunt current detecting resistor or the second shunt current detecting resistor. Item 5. The current detection circuit according to any one of Items 1 to 3.