JP3119781B2 - Current generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current generator which operates at a low current voltage and can set the output to zero.

[0002]

2. Description of the Related Art FIG. 3 shows a configuration of a conventional current generating device, in which a current generating circuit is constituted by a monolithic IC.
The output current can be set by a current setting resistor. In FIG. 3, reference numeral 101 denotes Japanese Patent Application Laid-Open No. 60-191.
No. 508 discloses a current generating circuit,
02 is a starting circuit of the current generating circuit 101, and 60 is a current setting terminal for setting an output current of the current generating circuit 101. The current generation circuit 101 receives a transistor 16 having a base and a collector connected as inputs, and
A current mirror circuit 40 having the collectors of 3, 14, 31 as outputs, transistors 11, 12, 15 and a resistor 19;
And a capacitor 20 for phase compensation.
1 is the output I ₀ of the current generating circuit 101, and the current setting terminal 60 is connected to the voltage source 30 having the voltage value Vcc via the current setting resistor 17. The transistor 11 is configured by connecting N same transistors in parallel. The starting circuit 102 includes transistors 41 and 42, a resistor 43, and a current source 44.

Next, the operation of the above conventional example will be described.
You. Now, the base voltages of the transistors 11 and 12 are set to V₁
Then V₁And the collector voltage of transistors 11 and 12
Style Ic ₁₁, Ic₁₂Is expressed by the following equations (1) and (2).
It is. V₁= Vt × 1n (Ic₁₁/ N / Is) + Ic₁₁× R₁ ... (1) V₁= Vt × 1n (Ic₁₂/ Is) (2) where Vt = kT / q k: Boltzmann constant T: absolute temperature q: charge of electrons Is: reverse saturation current R of npn transistor₁: Resistance value of the resistor 17 Here, the current amplification factor hfe of the transistor is sufficiently large.
In other words, the collector current Ic of the transistors 11 and 12
₁₁, Ic₁₂Is the output current I of the current mirror circuit 40
c₁₃, Ic₁₄And Ic₁₃, Ic₁₄Is the same current
Ic₁₁And Ic ₁₂Is also equal. That is, Ic₁₁= Ic₁₂ (3) Therefore, from the equations (1), (2) and (3), Ic₁₁= Vt / R₁× In (N) (4), and the emitter voltage Vt × 1n of the transistor 11
(N) is the resistance value R of the current setting resistor 17₁Current value divided by
become.

[0004] In this case, the value of V ₁ to V ₁ '. Now
The transistors 13 and 1 of the output of the current mirror circuit 40
Assuming that the collector currents Ic ₁₃ , Ic ₁₄ and Ic _{31 of} the transistors 4 and ₃₁ slightly increase, the base voltage V ₁ of the transistors 11 and 12 slightly increases than V ₁ ′. Then I
c ₁₁ <Ic _{12 and} the base current Ib of the transistor 15
₁₅ and the collector current Ic ₁₅ is also reduced. Therefore, the input current of the current mirror circuit 40 is reduced, the output current is also reduced, and V ₁ is reduced. When the collector current Ic _13, Ic _14, Ic ₃₁ of the transistors 13,14,31 of the output of the current mirror circuit 40 conversely to the decreases, the base voltage V ₁ of the transistor 11 and 12 is V ₁ '
More slightly reduced. Then, Ic ₁₁ > Ic ₁₂ and the base current Ib ₁₅ of the transistor ₁₅ is increased.
The collector current Ic _{15 is} also increased. Therefore, the input current of the current mirror circuit 40 is increased, the output current is also increased, and V ₁ is increased. By performing the negative feedback operation as described above, it becomes stable at the intersection of the curves of the above equations (1) and (2). That is, the current becomes stable at a current value obtained by dividing the emitter voltage Vt × 1n (N) of the transistor 11 expressed by the equation (4) by the resistance value R ₁ of the resistor 17. In addition, there is another stable point, which is the point where Ic ₁₁ = Ic ₁₂ = 0 from the equations (1) and (2). Therefore, the voltage source 30
The starting circuit 102 is provided so as to ensure the stability at the stable point represented by the equation (4) when the first time is added. In Japanese Patent Application No. 60-191508, the starting circuit 102 includes a resistor 1 connected between the collector of the transistor 16 and the ground.
8 and had been, but since the current flowing through the resistor 18 depends on the supply voltage, a current source 44 and transistors 41 and 42 to be independent of the power supply voltage a resistor 43, a current mirror collector Ic ₄₁ of the transistor 41 A small current flows through the collector of the transistor 11 via the circuit 40 and is biased so that Ic ₁₁ = Ic ₁₂ = 0, thereby eliminating this stable point.

Also, Ic₁₃Is Ic₁₁And Ib₁₁And Ib₁₂When
Divided into Ic₁₄Is Ic₁₂And Ib ₁₅Divided into
But Ib₁₅And Ib₁₁+ Ib₁₂Ic so that₁₆
If you set₁₆By Ib₁₅Is adjusted,
Ic₁₁And Ic₁₂Are controlled to be the same, and Ic₁₁When
Ic₁₂Is less affected by hfe.

The collector-emitter voltages of transistors 11 and 12 and the collector-emitter voltages of transistors 13 and 14
The emitter voltages have the same value, and the effect of the power supply voltage is small.

In order to stabilize the system of the negative feedback operation, a capacitor 20 for phase compensation and a transistor 1
5 is provided with a resistor 19 for reducing the transconductance.

As described above, the output of the above-described conventional current generator is
The force current is the emitter voltage Vt × 1n of the transistor 11.
(N) is the resistance value R of the current setting resistor 17₁Current value divided by
And the resistance value R of the current setting resistor 17₁By current
Output current Ic of raw circuit 101 ₃₁Can be set freely
it can.

[0009]

However, when the output current is to be reduced to zero, the output current can be reduced to zero by setting the current setting resistor 17 to infinity, that is, by opening the emitter terminal of the transistor 11. Although it seems to be possible, since the starting current Ic ₄₁ of the starting circuit 102 is input to the current mirror circuit 40, even if the terminal of the emitter of the transistor 11 is opened, a current equal to Ic ₄₁ is output. In addition, the output current of the current generation circuit 101 cannot be reduced to zero.

Further, even in a configuration in which the output current of the starting circuit 102 flows only when the current generating circuit 101 is not started, the starting circuit 102 generates the output current because the current generating circuit 101 is not started. Since it is impossible to distinguish between zero and zero by opening the resistor 17,
The starting circuit 102 operates. Therefore, even with this configuration, the output current of the current generation circuit 101 cannot be reduced to zero by opening the current setting terminal. Therefore, in order to make the output current of the current generator 101 zero, in addition to the current setting terminal, the starting circuit 102
However, there is a problem that a terminal is required to make the output current zero.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide a current generating device which can set the output current of a current generating circuit to zero with one terminal and can set a set current. I do.

[0012]

According to the present invention, in order to achieve the above object, a current mirror circuit, a first output of the current mirror circuit is connected to a collector and a base, and an emitter is connected via a first resistor. And a second transistor having a collector connected to the first output of the current mirror circuit, a second output of the current mirror circuit connected to the collector, an emitter grounded, and a base connected to the base of the first transistor, and a current mirror circuit. A third transistor having a collector connected to the input of the second transistor, a base connected to the collector of the second transistor, a second resistor connected between the emitter of the third transistor and ground, and a current mirror circuit. The collector of the transistor is connected to the input of the fourth transistor, the emitter is grounded via the third resistor, and the emitter is the emitter of the fourth transistor. Is connected to the jitter, the base is that a fifth transistor connected to the emitter of the first transistor. A diode may be used instead of the fifth transistor.

[0013]

According to the present invention, since the fourth transistor can be cut off by the base voltage of the fifth transistor, the output current of the current generator can be set to zero and the set current at one terminal. can do.

(Embodiment 1) FIG. 1 shows the configuration of a first embodiment of the present invention. 1, the same elements as those of the conventional example shown in FIG. 3 are denoted by the same reference numerals, and a transistor 50 and a switch 51 are added to the configuration of the conventional example. That is, 101 is disclosed in JP-A-60-1915.
08 is a current generating circuit disclosed in
Reference numeral 2 denotes a starting circuit of the current generating circuit 101, and reference numeral 60 denotes a current setting terminal for setting an output current of the current generating circuit 101. The current generation circuit 101 receives a transistor 16 having a base and a collector connected as inputs,
A current mirror circuit 40 that outputs the collectors of the transistors 14 and 31;
And a transistor 12, which is a second transistor, a transistor 15, which is a third transistor, and a resistor 19, which is a second resistor. The collector of the transistor 31 is an output of the current generating circuit 101. The transistor 11 is formed by connecting N transistors having the same characteristics in parallel. The starting circuit 102 includes a transistor 41 as a fourth transistor, a transistor 42, a resistor 43, and a current source 44. Reference numeral 20 denotes a phase compensation capacitor, and reference numeral 30 denotes a voltage source having a voltage value Vcc.
The transistor 50 as the fifth transistor has a collector connected to the power supply voltage Vcc, an emitter connected to the resistor 43 as the third resistor, and a base connected to the transistor 11.
Are connected to the current setting terminal 60 of the emitter. The switch 51 has a fixed terminal connected to the current setting terminal 60 and a movable terminal a connected to the current setting resistor 17 which is the first resistor.
Is connected to the negative side of the voltage source 30, and the movable-side terminal b is connected to the positive side of the voltage source 30.

Next, the operation of the first embodiment will be described.
I will tell. First, the switch 51 is moved to the terminal a side,
Emitter of transistor 11 and base of transistor 50
Is connected to the resistor 17. Now, Current Mira
-The output of the circuit 40, the transistors 13, 14, 31
Lector current Ic₁₃, Ic₁₄, Ic₃₁Increased slightly
Then, the base voltage V of the transistors 11 and 12₁Is
V₁'Slightly increased. Then Ic₁₁<Ic₁₂
And the base current Ib of the transistor 15₁₅Also reduced
Let Therefore, the input current of the current mirror circuit 40 is reduced.
Output current. That is, this system is negative
Forming feedback and stabilizing this system is based on (1),
Attempts to stabilize at the stable point obtained from equations (2) and (3)
You. Further, the base potential Vb of the transistor 50₅₀Is a tiger
Vt × 1n (N) of the emitter voltage of the transistor 11
Vt × 1n (N) cuts off transistor 50
N is set to 2 × 10
⁸By setting as follows, the emitter voltage of the transistor 50
Is not lower than the ground potential, the transistor 50
Base-emitter voltage Vbe₅₀Is less than 0.5V
And the transistor 50 is cut off. Yo
Since the collector current of the transistor 50 does not flow,
The starting circuit 102 is in a state where the transistor 50 is not connected.
The collector current Ic of the transistor 41
₄₁Flows slightly. Therefore, the current generation circuit 101
Ic₁₁= Ic₁₂= 0 is not stable,
The emitter voltage Vt of the transistor 11 determined by the equation (4)
× 1n (N) is the resistance value R of the current setting resistor 17 ₁Divided by
The current value becomes stable and the output current Ic₃₁Is resistor 1
7 can be freely changed by the resistance value.

On the other hand, when the switch 51 is turned to the terminal b and the emitter of the transistor 11 and the base of the transistor 50 are connected to the plus side of the power supply voltage Vcc, the base-emitter voltage Vbe of the transistor 11
₁₁ is reverse biased and transistor 11 is cut off. Since the base of the transistor 50 is connected to the power supply voltage Vcc, the transistor 50 is turned on. If the resistance value of the resistor 43 is R ₂ , the voltage drop VR ₂ will be between the power supply voltage Vcc and the base-emitter of the transistor 50. becomes a voltage obtained by subtracting the voltage Vbe _50, it becomes as represented by the following equation (5). VR ₂ = Vcc-Vbe ₅₀ (5) Here, since the power supply voltage Vcc is applied with a voltage of about 0.9 V or more at which the current generation circuit 101 operates, the resistance 43
The collector current Ic ₅₀ of the voltage drop VR ₂ and the transistor 50, when the Vbe ₅₀ ≒ 0.7 V, the following (6) and (7). VR ₂ = (Vcc−Vbe ₅₀ )> 0.2 V (6) Ic ₅₀ = (Vcc−Vbe ₅₀ ) / R ₂ (7) The base of the transistor 41 is the transistor 42.
, The base-emitter voltage Vbe ₄₁ of the transistor ₄₁ is expressed by the equation (8). Vbe ₄₁ = Vbe ₄₂ −VR ₂ (8) From this, the base-emitter voltage V of the transistor 42 is obtained.
Assuming that be ₄₂ is 0.7 V, V be ₄₁ becomes a voltage value smaller than 0.5 V from the equation (7), and the transistor 41 can be cut off. Thus, the input current of the current mirror circuit 40, the transistor 11 and the transistor 41 is cut off, it is possible to make the input current zero, the output current Ic ₃₁ of the current generator circuit 101 can also be zero.

[0017] In this case, because it depends on the power supply voltage Vcc from the collector current Ic ₅₀ of the transistor 50 is (7), the power supply voltage Vcc becomes a problem that current consumption increases higher. The following second embodiment solves this problem.

(Embodiment 2) FIG. 2 shows the configuration of a second embodiment of the present invention. In FIG. 2, the same elements as those in the first embodiment shown in FIG. 1 are denoted by the same reference numerals, and those different from the first embodiment are that the transistor 50 is diode-connected and The terminal b is connected to the positive side of the current source 30 via the resistor 70.

Next, the operation of the second embodiment of the present invention will be described. Now, when the switch 51 is turned to the terminal a side and the emitter of the transistor 11 and the base of the transistor 50 are connected to the resistor 17, the transistor 50 can be cut off by the same principle as in the first embodiment. , the output current Ic ₃₁ of the current generation circuit 101 becomes a current value set in (4) below.

On the other hand, the switch 51 is moved to the terminal b side to
The emitter of the transistor 11 and the transistor
Source and collector are connected to power supply voltage Vcc via resistor 70.
Then, the base-emitter voltage of the transistor 11
Vbe₁₁Becomes a reverse bias, and the transistor 11
Cut off. Also, the voltage drop VR at the resistor 43 _Two
Is the collector current Ic of the transistor 41₄₁Can be ignored
As described above, the voltage drop of the resistor 43 becomes about 0.2 V or more.
The resistance value R of the resistor 70_ThreeAs shown in the following equation (10).
Set. VR₁= (Vcc-Vbe₅₀) × R_Two/ (R_Two+ R_Three) = 0.2V (9) R_Three= (Vcc-Vbe₅₀) × R_Two/ VR₁-R_Two (10) Then, similarly to the first embodiment, the transistor 41 is closed.
Can be turned off, the input current of the current mirror 11 is
It becomes zero, and the output current can also be made zero. this
In this case, the collector current Ic of the transistor 50₅₀Is (1
1) is obtained by the equation. Ic₅₀= (Vcc-Vbe₅₀) / (R_Two+ R_Three・ ・ ・ ・ ・ ・ (11)

As described above, according to the second embodiment,
Transistor collector current Ic ₅₀ of 50 may be set by the resistance value R ₃ of the resistor 70, it can be set small current consumption.

Although the resistor 70 can be eliminated,
In this case, the same current as in the first embodiment is applied to the transistor 50.
Will flow to

In the first and second embodiments,
The terminal b of the switch 51 is not limited to the power supply voltage Vcc, and may be connected to a voltage source at which the transistors 11 and 41 are cut off.

Although the transistor 50 is a bipolar transistor, a diode or other element may be used as long as the transistor operates in the same manner.

Further, the starting circuit 102 may use another method as long as it has a similar drop.

[0026]

According to the present invention, as is apparent from the above embodiment, the output current of the current generator can be set by connecting a resistor between the current setting terminal and the ground. By setting the potential to be equal to or higher than the forward voltage between the base and the emitter of the transistor, the output current can be made zero. Therefore, a zero current and a set current can be obtained from one terminal.

[Brief description of the drawings]

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

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

FIG. 3 is a circuit diagram showing a configuration of a conventional current generator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 1st transistor 12 2nd transistor 15 3rd transistor 17 1st resistance 19 2nd resistance 30 Voltage source 40 Current mirror circuit 41 4th transistor 43 3rd resistance 44 Current source 50 5th transistor 60 Current setting terminal 101 Power generation circuit 102 Start circuit

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-303050 (JP, A) JP-A-6-139794 (JP, A) JP-A-4-112307 (JP, A) 29218 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03F 1/30-1/40 H03F 1/42-1/56 H03F 3/20-3/36 H03F 3/42 -3/44 H03F 3/50-3/52 G05F 3/26 G05F 1/56

Claims (3)

(57) [Claims] 1. A current mirror circuit, and a first output of the current mirror circuit is connected to a collector and a base,
A first transistor having an emitter grounded through a first resistor; a second output of the current mirror circuit connected to a collector; an emitter grounded; and a base connected to a base of the first transistor. A second transistor having a collector connected to an input of the current mirror circuit and a base connected to a collector of the second transistor; and a third transistor having an emitter and a ground connected to the emitter of the third transistor. And a fourth transistor whose collector is connected to the input of the current mirror circuit, whose emitter is grounded via a third resistor, and whose emitter is connected to the emitter of the fourth transistor. And a fifth transistor having a base connected to the emitter of the first transistor. 2. A current mirror circuit, and a first output of the current mirror circuit is connected to a collector and a base,
A first transistor having an emitter grounded through a first resistor; a second output of the current mirror circuit connected to a collector; an emitter grounded; and a base connected to a base of the first transistor. A second transistor having a collector connected to an input of the current mirror circuit and a base connected to a collector of the second transistor; and a third transistor having an emitter and a ground connected to the emitter of the third transistor. And a fourth transistor having a collector connected to the input of the current mirror circuit, an emitter grounded via a third resistor, and one end connected to the emitter of the fourth transistor. And a diode connected at the other end to the emitter of the first transistor. 3. The current generator according to claim 1, wherein the base current of the third transistor is set so that the collector current of the first transistor is equal to the collector current of the second transistor.