JP2003232816A - Current detection circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a current detection circuit capable of setting a detection current more accurately by suppressing an influence caused by the voltage difference between gate sources of an output transistor and a sense transistor. <P>SOLUTION: The source terminal 130 of an NMOS sense transistor 11 is connected to the inverting input terminal of an operational amplifier 13, and a resistance 12 for detecting a current is interposed between the inverting input terminal and the output terminal of the operational amplifier 13, and the noninverting terminal of the operational amplifier 13 is connected to a GND terminal 121, and the source terminals of the NMOS output transistor and the NMOS sense transistor are adjusted to have the same potential, to thereby prevent the voltage difference between the gate sources of both transistors caused by the voltage VSENSE applied to the resistance RSENSE. <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 semiconductor device that detects a current.

[0002]

2. Description of the Related Art The structure of a conventional current detection circuit is shown in FIG. The drain voltage supply terminal 100 supplies a high voltage to the drain terminals of both transistors. The gate voltage supply terminal 110 supplies an arbitrary voltage to the gate terminals of both transistors. The source terminal of the NMOS output transistor 10 is connected to the GND terminal 120. NM
The source terminal 130 of the OS sense transistor 11 is connected to the positive terminal of the resistor 12. The negative terminal of the resistor 12 is connected to the GND terminal 121. The sense transistor source terminal 130 also serves as a detection voltage output.

The current detection circuit is composed of an NMOS output transistor 10, an NMOS sense transistor 11 and a resistor 12. NMOS output transistor 10 and NMO
When the S sense transistors 11 are both operating in the same state, the NMOS sense transistor 11 has an NMO.
A current proportional to the current flowing through the S output transistor 10 flows, and the ratio thereof is substantially the transistor size ratio of both. The current flowing through the NMOS output transistor 10 is IO
UT, if the current flowing in the NMOS sense transistor 11 is ISENCE, the size of the NMOS output transistor 10 is K1, and the size of the NMOS sense transistor 11 is K2, then ISENSE = K2 / K1 * IOUT-- it can.

Further, the voltage drop across the resistor 12 is
If NSE and the resistance value of the resistor 12 are RSENSE, then VSENSE = RSENSE * ISENSE ----

[0005]

In the circuit shown in FIG.
Due to the voltage drop VSENSE across the resistor 12, NMO
The gate-source voltage of the S sense transistor 11 is N
The voltage becomes lower than the gate-source voltage of the MOS output transistor 10. Then, the gates of the NMOS output transistor 10 and the NMOS sense transistor 11
Since the source-to-source voltage is different, the current ratio between them is different from the transistor size ratio between them. As the voltage drop VSENSE applied to the resistor 12 increases, the current ISENSE flowing through the NMOS sense transistor 11 becomes smaller than the current value obtained from the equation.

[0006]

In the present invention, the NM
The source terminal 130 of the OS sense transistor 11 is connected to the inverting input terminal of the operational amplifier 13, and the non-inverting input terminal of the operational amplifier 13 is connected to the GND terminal 1 via the resistor 12 for detecting the current between the inverting input terminal and the output terminal of the operational amplifier 13.
By connecting the source terminals of the NMOS output transistor and the NMOS sense transistor to the same potential, the difference between the gate-source voltage of both transistors due to the voltage VSENSE applied to the resistor RSENSE is prevented.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In a current detection circuit according to an embodiment of the present invention, an output transistor and a sense transistor of the same conductivity type as that of the output transistor are in the same operating state, and a current flowing through the sense transistor is detected. To do.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of the current detection circuit of the present invention. The current detection circuit shown in FIG. 1 has the same configuration as the current detection circuit shown in FIG.
An operational amplifier 13 with negative feedback is added to the source terminal 130 of the MOS sense transistor. The source terminal 130 of the NMOS sense transistor 11 has a resistor 12
Of the operational amplifier 13 is connected to the inverting input terminal of the operational amplifier 13, and the output of the operational amplifier 13 is connected to the negative terminal of the resistor 12 and the detection voltage output terminal 140. The non-inverting input terminal of the operational amplifier 13 has a GND terminal 1
21 is connected. Positive and negative power supplies are connected to the operational amplifier 13. In the positive power source, the input terminal 150 supplies a positive voltage. If there is no negative power supply, a separate negative voltage generator 1
It is necessary to generate a negative voltage at 4 and supply it to the operational amplifier 13. Examples of the negative voltage generator include an inverting charge pump and an inverting switching regulator.

Since the output of the operational amplifier 13 is negatively fed back to the inverting input terminal of the operational amplifier 13 via the resistor 12, the NMOS sense transistor source terminal 130 is provided.
And the potential of the GND terminal 121 are the same. NM
The potential of the OS sense transistor source terminal 130 is GN
The same potential as the D potential means that the potential of the NMOS sense transistor source terminal 130 is the GND terminal 120.
It is the same as becoming the same potential as.

Therefore, the source potentials of the NMOS output transistor 10 and the NMOS sense transistor 11 are the same. As described above, since the gate terminal of the NMOS output transistor 10 and the gate terminal of the NMOS sense transistor 11 are short-circuited, the NMOS output transistor 1
0 and the gate-source voltage of the NMOS sense transistor 11 are equal. Also, the NMOS output transistor 10
, And the drain terminal of the NMOS sense transistor 11 are short-circuited, the drain-source voltages of the NMOS output transistor 10 and the NMOS sense transistor 11 are also equal.

As described above, the NMOS output transistor 1
0 and the NMOS sense transistor 11 have the same gate-source voltage and the same drain-source voltage. Therefore, regardless of the potential difference between the drain voltage supply terminal 100 and the GND terminals 120 and 121 and the gate voltage. , The operating states of both are the same. Ie NMO
The current ratio between the S output transistor 10 and the NMOS sense transistor 11 is the transistor size ratio between them. Of course, since the drain-source voltages of both are the same, the influence of the channel length modulation does not occur.

A specific description will be given. First, when an arbitrary voltage drop is applied to the resistor 12, since the NMOS sense transistor source terminal 130 is at the GND potential as described above, the gate-source voltage and the drain-source voltage of both transistors do not differ. Therefore, since the operating states of both transistors are the same as described above, the problem that the current ratio of both transistors becomes inaccurate does not occur.

From the above, it is clear that the same effect can be obtained even when both the NMOS output transistor 10 and the NMOS sense transistor 11 are p-channel type.

[0014]

According to the present invention, the output current can be detected more accurately by making the operating states of the NMOS output transistor and the NMOS sense transistor the same so that the ratio of the currents flowing through them becomes the transistor size ratio. There is an effect called.

[Brief description of drawings]

FIG. 1 is an example of a current detection circuit of the present invention.

FIG. 2 is an example of a conventional current detection circuit.

[Explanation of symbols]

10 NMOS output transistor 11 NMOS sense transistor 12 resistance 13 Op-amp 14 Negative voltage generator 100 Drain voltage supply terminal 110 gate voltage supply terminal 120, 121 GND terminal 130 NMOS sense transistor source terminal 140 Detection voltage output terminal 150 input voltage supply terminal

Claims (3)

[Claims] 1. A current detection circuit, wherein the output transistor and a sense transistor of the same conductivity type as that of the output transistor are in the same operating state, and a current flowing through the sense transistor is detected. 2. The output transistor and the sense transistor are p-channel type transistors, the gate terminal of the output transistor and the gate terminal of the sense transistor are made common, and the drain terminal of the output transistor and the drain of the sense transistor The common terminal is used, the inverting input terminal of the operational amplifier is connected to the source terminal of the sense transistor, and a resistance element for detecting a current is provided between the inverting input terminal of the operational amplifier and the output terminal. The current detection circuit according to claim 1, wherein an input power supply is connected to the non-inverting input terminal. 3. The output transistor and the sense transistor are n-channel transistors, the gate terminal of the output transistor and the gate terminal of the sense transistor are made common, and the drain terminal of the output transistor and the drain terminal of the sense transistor. Common to each other, the inverting input terminal of the operational amplifier is connected to the source terminal of the sense transistor, and a resistance element for detecting a current is provided between the inverting input terminal and the output terminal of the operational amplifier, The current detection circuit according to claim 1, wherein the inverting input terminal is connected to GND.