JPH0429027B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a current detection circuit.

[Prior art] Conventionally, a current detection circuit has been proposed that applies the voltage across a current detection resistor between the base and emitter of a transistor and uses the voltage (threshold voltage) V _BE between the base and emitter of the transistor. has been done.

[Problems to be Solved by the Invention] Such a current detection circuit has a drawback in that the detected current changes due to temperature changes due to the temperature dependence of the transistor base-emitter voltage V _BE . Furthermore, since a detection signal cannot be obtained unless the voltage drop across the current detection resistor reaches approximately 0.7 volts, there is a drawback that the voltage loss is large and it cannot be used in low voltage circuits.

An object of the present invention is to provide a current detection circuit that improves detection current accuracy and reduces voltage loss.

[Means for Solving the Problems] According to the basic feature of the present invention, a resistor is provided between the base and the emitter of the current detection transistor, and between the base and the collector. A voltage equal to the voltage across the resistor is applied, and the emitter current densities of both transistors are set equal.

[Examples] Hereinafter, the present invention will be described in detail along with Examples.

FIG. 1 is a basic circuit diagram showing one embodiment of the present invention.

A current - between the current path T ₁ and T ₂ of the current I to be detected
A resistor R ₁₀₁ is provided for voltage conversion. A resistor is connected between the base and collector of a transistor _Q15 whose emitter is connected to one terminal _T2 of this resistor _R101 .
_R18 is provided. A bias constant current circuit _I2 is provided at the connection point between the resistor _R18 and the base of the transistor _Q15 .

On the other hand, the other terminal T ₁ of the resistor R ₁₀₁ is connected to the emitter of the transistor Q ₁₆ . The base of this transistor Q ₁₆ is connected to the connection point between the collector of transistor Q ₁₅ and resistor R ₁₈ . As a result, a voltage equal to the sum of the voltage at the resistor _R101 and the voltage between the emitter and collector of the transistor _Q15 is applied between _the emitter and the base of the transistor Q16.

In other words, the emitter-collector voltage of the transistor Q ₁₅ is a constant voltage obtained by subtracting the voltage drop (R ₁₈ ×I ₂ ) in the resistor R ₁₈ from the base-emitter voltage V _BEQ15 of the transistor Q ₁₅ .

Further, a constant current circuit _I1 is provided at the collector of the transistor _Q16 , and the current difference between the collector current of the transistor _Q16 and the constant current I1 is output as an output signal OUT.
is output as

The transistors Q ₁₅ and Q ₁₆ are arranged so that the emitter current densities of the transistors Q ₁₅ and Q 16 are approximately equal.
For the emitter area of Q ₁₆ , the above constant currents I ₁ and I ₂
The current value is set. For example, transistor
When the emitter areas of Q ₁₅ and Q ₁₆ are the same,
Currents I ₁ and I ₂ are set equal.

The conditions for turning on the transistor _Q16 are determined by the following equation (1).

V _BEQ16 IR ₁₀₁ +V _BEQ15 −I ₂ R ₁₈ …(1) Here, since the emitter current densities of transistors Q ₁₆ and Q ₁₅ are set equal, the currents I ₁ and I ₂ are also set equal. Due to this, when transistor _Q16 is on,
Since V _BEQ16 and V _BEQ15 are equal, from equation (1) above,
V _BEQ16 and V _BEQ15 can be completely removed and transformed as shown in the following equation (2).

IR18/R101...(2) That is, under I<R18/R101I2, the transistor _Q16 is turned off and no collector current flows, so that a constant current _I1 is obtained at the output OUT.

On the other hand, under IR18/R101I2, when the transistor _Q16 turns on and its collector current becomes equal to the constant current _I1 , the current at the output terminal OUT becomes zero, and the current higher than IR18/R101I2 flows through the current path T. ₁ and _T2 can be detected.

As is clear from the above conditional expression, the transistor
As a result of the voltages between the bases and emitters of Q ₁₆ and Q ₁₅ being canceled out, the current value to be detected will not vary due to the influence of the temperature dependence of the transistors, and therefore temperature compensation will be achieved. Furthermore, by forming the transistors Q ₁₅ and Q ₁₆ on the same silicon chip, the current value to be detected is not affected by manufacturing variations in the base-emitter voltage V _BE . This allows highly accurate current detection.

Also, the minimum required voltage drop across resistor R ₁₀₁ can be set by voltage drop R ₁₈ × I ₂ across resistor R ₁₈ , and the voltage between the base and emitter of transistor Q ₁₆
This is a small voltage value below V _BEQ16 . Therefore,
Voltage loss in the current path can also be reduced, and its uses can be expanded.

FIG. 2 is a circuit diagram of an embodiment in which the present invention is applied to a motor drive circuit.

Although this motor drive circuit is not particularly limited,
Used in cassette tape recorders.

In FIG. 2, circuit elements surrounded by dotted lines are formed on one silicon chip by a well-known semiconductor manufacturing method. Furthermore, the numbers surrounded by circles are terminal numbers.

This embodiment circuit is broadly divided into an emitter follower current amplifying circuit as a voltage follower circuit, a surge protection circuit, a bias circuit, and a current limiting circuit using the current detection circuit according to the present invention.

The emitter follower circuit includes a Darlington type drive transistor Q ₁₁ , an output transistor Q ₁₂ ,
It is constituted by a bias circuit provided between the base of transistor _Q11 and the emitter of transistor _Q12 , which are input and output. This bias circuit is composed of the following elements. In other words, the voltage between the base and the collector of the transistor Q ₁₃ , which has a resistor R ₁₄ between the base and the emitter and a diode (including a diode-type transistor) Q ₁₄ between the base and the collector, is used as a bias voltage. ₇ , Q ₈ base,
Through the emitters, the above transistors Q ₁₁ , Q ₁₂
The voltage is applied between the base and emitter. A bias current for forming the above bias voltage is supplied to the collector of the transistor _Q13 from a constant current transistor _Q6 .

In addition, this emitter follower circuit functions as a current extraction circuit for the load, in other words,
Transistor cascaded to output transistor Q ₁₂ for low output impedance
Q ₁₀ will be established. At the base of this transistor _Q10 is a transistor that constitutes a bias circuit.
The collector current of the inverting transistor _Q9 , which is driven by the collector voltage division current of _Q8 , is input. This allows transistor _Q10 to operate complementary to output transistor _Q12 .

On the other hand, transistor Q ₁ has a constant current formed by resistor R ₃ and Zener diode ZD applied to its base, and a power supply voltage V _CC divided by resistors R ₁ and R ₂ applied to its emitter. It is a transistor. A resistor _R4 is provided at the collector of this transistor _Q1 , and the on operation of the surge protection transistors _Q17 and _Q19 controlled by the surge detection voltage forces the drive transistor _Q11 and the output transistor _Q12 to turn off. I am made to do so.

Furthermore, the transistor _Q2 of the constant current source circuit that forms the bias current of the current limiting circuit, which will be described next, is also forcibly turned off by the on operation of the surge protection transistor _Q18 , which is similarly limited by the surge detection voltage.

The collector of the output transistor _Q12 is connected to the No. 4 terminal. Then, terminal 4 and power supply voltage V _CC
Connect a current detection resistor between the 5th terminal and the
R ₁₀₁ is connected as an external component.

Transistors Q ₁₅ and Q ₁₆ configuring the current detection circuit as described above are connected to the 4th and 5th terminals.
and a resistor _R18 . Transistor Q ₂₀
A constant current _I2 is formed to flow a bias current to the transistor _Q15 . Also, transistor _Q3 is
It forms the constant current _I1 .

These constant currents I ₁ and I ₂ are formed based on the constant voltage formed by the Zener diode ZD. That is, a resistor R ₅ is connected to the emitter of the transistor Q ₂₂ to which the Zener constant voltage is applied to the base.
A constant voltage is formed by a diode-type transistor Q ₂ and an emitter resistor R ₆ , and is applied to the bases of the constant current transistors Q ₃ and Q ₂₀ . The constant current I ₁ obtained from the collector of the constant current transistor Q ₂ is also used as a base drive current to the drive transistor Q ₁₁ via transistors Q ₄ and Q ₅ forming a current mirror circuit. In addition, along with the above transistor _Q4 ,
Constant current transistor _Q6 also constitutes a current mirror circuit, forming a constant current to the bias circuit.

In addition, in the current detection circuit in this embodiment, a resistor R ₂₀ and a capacitor C ₂ constituting a low-pass filter are provided at the base of the transistor Q ₁₆ to prevent oscillation during current limiting operation, which will be described later. There is. Inserting resistor _R20 only at the base of transistor _Q16 will affect the current detection operation, so inserting resistor _R19 with a similar resistance value into the transistor
It is inserted into the base of Q ₁₆ to equalize the voltage drop in the base current between both transistors Q ₁₅ and Q ₁₆ .

The operation of this example circuit will be understood in the following description.

The input voltage V _IN applied from the second terminal is transmitted to the base of the drive transistor Q ₁₁ through the emitter and base of the transistor Q ₇ . Therefore, the output voltage V _OUT obtained from the No. 1 terminal connected to the emitter of the output transistor Q ₁₂ is V _IN −
The voltage becomes V _BEQ12 and drives the DC motor that is the load. The rotational speed of this motor is converted into a voltage and fed back to the input side to obtain a predetermined rotational speed, and the voltage V _IN
is formed (not shown).

When the current to the DC motor is within the allowable value, the transistor Q ₁₆ is off, so the constant current I ₁ is supplied to the collector of the drive transistor Q ₁₁ and the transistor Q ₁₂ of the bias circuit. has been done.

When an excessive current flows to the DC motor through the output transistor Q ₁₂ , the transistor Q ₁₆ turns on and supplies current to the transistor Q ₃ which forms a constant current I ₁ . The current to drive transistor Q ₁₁ and the bias circuit can be reduced to limit the current flowing to transistor Q ₁₂ . This can prevent damage to the output transistor _Q12 and the motor.

As in this embodiment, the transistors Q ₁₅ , Q ₁₆ and the resistor R ₁₈ and the constant current I ₁ , which constitute the current detection circuit,
When the circuit forming I ₂ is formed on the same silicon chip, not only can transistors Q ₁₅ and Q ₁₆ with the same characteristics be formed, but also the voltage drop across resistor R ₁₈ can be reduced by resistor R ₅ which can be formed with high precision. ，
Since it is determined by the resistance ratios of R ₆ , R _L , R ₁₁ and R ₁₈ , highly accurate current detection can be performed without being affected by variations in elements.

That is, the voltage at which the transistor _Q16 turns on is when the voltage drops across the resistor _R18 and the resistor _R101 become equal.

FIG. 3 shows a circuit diagram showing another embodiment of the present invention.

In this embodiment, a current detection resistor _R101 is provided on the emitter side of the emitter follower output transistor _Q12 . Therefore, transistors Q ₁₅ ′ and Q ₁₆ ′ forming the current detection circuit are different from those in the previous embodiment.
An npn transistor is used, and the bias current I ₁ ′,
I ₂ ′ is also replaced by a constant pushing current.

In addition, a current detection transistor _Q16 ' is inserted between the base and emitter of the output transistor _Q12 ,
It is supposed to directly limit the base current of the output transistor _Q12 . And the transistor
Q ₁₆ ′ is a resistor to prevent oscillation when it is on.
R ₂₀ , capacitor C ₂ and compensation resistor R ₁₉ are provided as before.

Furthermore, a voltage amplification signal is applied to the base of the output transistor Q ₁₂ , which is composed of an amplification transistor Q ₂₁ and a constant current load provided at its collector and also serving as the bias current source I ₁ '.

The operation of this circuit is such that when the emitter current of transistor _Q12 exceeds a predetermined current value, the transistor
By turning on Q ₁₆ ' and limiting the base current to transistor Q ₁₂ , the same protection operation as described above is performed.

By adding an output transistor connected in cascade to the output transistor _Q12 and switched by the output midpoint voltage to the output transistor _Q12 , this embodiment circuit can be transformed into a class B push-pull output circuit.

The present invention can be widely used as a current detection circuit in various current limiting circuits and the like.

[Brief explanation of drawings]

FIG. 1 is a basic circuit diagram showing one embodiment of the invention, and FIGS. 2 and 3 are specific circuit diagrams showing one embodiment of the invention.

Claims (1)

[Claims] 1. A first resistor provided in the path of the current to be detected.
R ₁₀₁ and the second transistor Q ₁₅ , which is provided between the base and collector of the first transistor Q ₁₅ whose emitter is connected to one terminal serving as a reference in the first resistor R ₁₀₁ , through which the collector current flows.
A voltage which is the sum of the voltage between the emitter and collector of the resistor _R18 , the emitter and collector of the first transistor _Q15 , and the voltage generated at the first resistor _R101 is applied between the emitter and the base of the second transistor _Q16 , and the voltage generated by the first resistor R101. The first constant current circuit connected to the collector of two transistors _Q16
I ₁ and a second constant current circuit I ₂ connected to the base of the first transistor Q ₁₅ , the emitter current density of the first transistor Q ₁₅ and the second transistor Q ₁₆ are made substantially equal to each other. 1. Set the current values of the second constant current circuits I1 and I2, and obtain a detection signal from the collector of the second transistor _Q16 ,
The first and second transistors Q ₁₅ , Q ₁₆ and the first transistor,
A current detection circuit characterized in that the second constant current circuits I ₁ and I ₂ are formed on the same silicon chip. 2. A patent characterized in that the emitter sizes of the first transistor Q ₁₅ and the second transistor Q ₁₆ are made equal, and the current values of the first constant current circuit I ₁ and the first constant current circuit I ₂ are made equal. A current detection circuit according to claim 1. 3. The current to be detected is the current flowing through the power output transistor, and the detection signal limits the input current of the power output transistor.
Current detection circuit described in section.