JPH0615113U - Constant current circuit - Google Patents

Abstract

(57) [Summary] [Purpose] The present invention relates to a constant current circuit for supplying a bias current to a comparator or the like, and an object thereof is to obtain a constant current from a low voltage to a high voltage. [Configuration] NPN transistor Q ₁₁ and NPN transistor Q ₁₁ whose base and collector are connected via a resistor R _13.
Current amplifying circuit 11a and current amplifying circuit 11a composed of an NPN transistor Q ₁₂ whose collector and base are connected together.
Whose NPN transistor Q ₁₂ has its base connected to the collector and whose collector is connected via a resistor R _16.
Via the P transistor Q ₁₃ and the PNP transistor Q ₁₃ of the collector and the base is further a PNP transistor Q ₁₄ which is connected a current amplifier circuit 11b and a current mirror circuit 11c after amplifying the current by generating an output current.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a constant current circuit, and more particularly to a constant current circuit that supplies a bias current to a comparator or the like.

[0002]

[Prior art]

FIG. 4 shows a circuit configuration diagram of the comparator. The NPN transistors Q ₁ and Q ₂ are comparison transistors, and the collectors of the NPN transistors Q ₁ and Q ₂ are connected to the collectors of PNP transistors Q ₃ and Q ₄ forming a current mirror circuit. The voltage Vcc is applied to the emitters of the PNP transistors Q ₃ and Q ₄ . The emitters of the NPN transistors Q ₁ and Q ₂ are both connected to the constant current circuit 1 composed of NPN transistors Q ₅ and Q ₆ , and the base of the NPN transistor Q ₁ is of resistors R ₁ and R ₂ for dividing the voltage Vcc. The base of the NPN transistor Q ₂ is connected to the connection point, and is connected to the connection point between the resistor R ₃ forming the reference voltage source 2 and the Zener diode Dz. Comparison of the base voltage bets transistor Q _1, Q ₂ in accordance with the ratio of currents flowing through the transistor Q _1, the transistor Q ₂ is performed, PNP transistor Q ₇ is operated as an output preparative transistor according to the comparison result .

Here, the constant current circuit 1 uses the constant voltage V _BE between the base and emitter of the transistor Q ₅ to turn on the transistor Q ₆ , keeps the current I ₁ constant, and causes the transistor Q ₆ to supply the current I _01. A constant current I ₂ obtained by multiplying by n ₀ was obtained.

As a conventional constant current circuit for supplying a bias current used in this type of comparator, a circuit as shown in FIG. 5 has been used.

In the circuit shown in FIG. 5A, a resistor R ₄ corresponding to the resistors R ₁ and R ₂ described above is provided, and resistors R ₅ and R ₆ that determine the current amplification factor are provided to the emitters of the transistors Q ₅ and Q _6. However, since the current amplification factor cannot be large, it has a voltage-current characteristic with a slow rise as shown by the broken line in FIG.

Further, in the circuit shown in FIG. 5B, resistors R ₇ , R ₈ and an NPN transistor Q ₈ whose base is connected to the connection points of the resistors R ₇ and R ₈ are connected in series to generate a voltage. Since the collector of the NPN transistor Q _{8 and} the base of the NPN transistor Q ₉ to which the voltage V cc is applied are connected between the collector of the NPN transistor Q _{8 and} the base of the NPN transistor Q ₉ , a relatively large current amplification factor can be obtained. As shown by the alternate long and short dash line, the rise of the voltage Vcc can make the rise of the current slightly faster than that of the circuit shown in FIG. However, the current tended to decrease when the voltage Vcc increased.

[0007]

[Problems to be solved by the device]

 However, since the conventional constant current circuit cannot obtain a large current amplification factor, there is a problem that the voltage-dependent characteristic rises slowly and a constant current cannot be supplied at low voltage as shown by the broken line in FIG. It was

Further, if an attempt is made to improve the rise of the voltage-dependent characteristic, there is a problem that a constant current cannot be secured because the current decreases at a high voltage as shown by the alternate long and short dash line in FIG.

The present invention has been made in view of the above points, and an object thereof is to provide a constant current circuit that can obtain a constant current from a low voltage to a high voltage.

[0010]

[Means for Solving the Problems]

 The present invention has a plurality of current amplification circuits each including a control transistor whose base and collector are connected via a resistor and an output transistor whose base is connected to the collector of the control transistor. Connect the connection point of the control transistor base of the next stage current amplification circuit and the resistor to the collector of the output transistor, and apply power and voltage to the connection point of the control transistor base of the first stage current amplification circuit and the resistor. Then, a constant current is output from the collector of the output transistor of the final stage current amplifier circuit.

[0011]

[Action]

 By providing a plurality of current amplification circuits, a large current amplification factor can be obtained, so that the degree of current at the time of rising of the applied voltage can be sharpened, and thus a constant current can be secured even at a low voltage. Further, when the applied voltage rises, the fluctuation of the output current can be made small with respect to the applied voltage by the plural stages of current amplifier circuits.

[0012]

【Example】

 FIG. 1 shows a circuit configuration diagram of an embodiment of the present invention. In the present embodiment, will the constant current circuit contained in the comparator and generating the bias current be explained? In the figure, 11 indicates a constant current circuit section. The constant current circuit unit 11 includes current amplifier circuits 11a and 11b and a current mirror circuit 11c.

The current amplification circuit 11a includes an NPN transistor Q ₁₁ that serves as a control transistor, an NPN transistor Q ₁₂ that serves as an output transistor, and resistors R ₁₃ , R ₁₄ , and R ₁₅ . The base of the NPN transistor Q ₁₁ is applied with the power supply voltage Vcc through the resistors R ₁₁ and R ₁₂ and is connected to the collector through the resistor R ₁₃ . The emitter of NPN transistor Q ₁₁ is grounded via resistor R ₁₄ .

The connection point between the resistor R ₁₃ and the collector of the NPN transistor Q ₁₁ is connected to the base of the NPN transistor Q ₁₂ . The emitter of the NPN transistor Q ₁₂ is grounded via the resistor R ₁₅ , and the collector is connected to the current amplifier circuit 11b.

The current amplifier circuit 11b includes a PNP transistor Q ₁₃ that serves as a control transistor, a PNP transistor Q ₁₄ that serves as an output transistor, and resistors R ₁₆ , R ₁₇ , and R ₁₈ . The power supply voltage Vcc is applied to the emitter of the PNP transistor Q ₁₃ through the resistor R ₁₇ , the collector is connected to the base through the resistor R _16, and the collector of the transistor Q ₁₂ that becomes the output of the current amplification circuit 11a at the previous stage. Connected with. The connection point between the collector of the PNP transistor Q ₁₃ and the resistor R ₁₆ is connected to the base of the PNP transistor Q ₁₄ . The power supply voltage Vcc is applied to the emitter of the PNP transistor Q ₁₄ via the resistor R ₁₈ , and the collector is connected to the current mirror circuit 11c.

The current mirror circuit 11c is an NPN transistor Q.₁₅, Q₁₆, Resistance R₁₉, R₂₀ Consists of. NPN transistor Q₁₅Is the PNP transistor Q that becomes the output of the current amplification circuit 11b.₁₄Is connected to the collector of PNP transistor Q ₁₅ And PNP transistor Q₁₆The base of is connected. PNP transistor Q₁₆ The emitter is a resistor R₂₀Grounded through. In addition, PNP transistor Q₁₆This collector serves as a constant current output terminal and is connected to the comparison circuit section 12.

The comparison circuit unit 12 includes a PNP transistor Q that forms a current mirror circuit.₁₇, Q ₁₈ , The NPN transistor Q which constitutes the comparison section₁₉, Q₂₀Consists of. PNP Transistor Q₁₉The base is resistance R₁₁And resistance R₁₂Connected to the connection point of PNP Transistor Q₂₀The base of is connected to the reference voltage generation circuit 13. The reference voltage generation circuit 13 has a resistor R_{twenty one}And Zener diode D₁And resistance R_{twenty one}And Zener diode D₁Are connected in series between the power supply voltage Vcc and the ground, and the reference voltage is output from the connection point, and the transistor Q₂₀Applied to the base of. NPN transistor Q₁₉, Q ₂₀ The collectors of the PNP transistors Q respectively constitute a Karen mirror circuit.₁₇, Q₁₈ Connected to the collector of PNP transistor Q₁₇, Q₁₈The power supply voltage Vcc is applied to the emitter of the.

The emitters of the NPN transistors Q ₁₉ and Q ₂₀ are both connected to the collector of the NPN transistor Q ₁₆ which constitutes the current mirror circuit 11c.

In addition, the NPN transistor Q₁₉Is a PNP transistor Q that becomes an output transistor._{twenty one}Connected to the base of PNP transistor Q_{twenty one}A power supply voltage Vcc is applied to the emitter of and the collector is connected to the drive stage as an output terminal. Next, the operation of the circuit will be described. When the power supply voltage Vcc begins to rise above 0 (V), the current I₁₁Flows, transistor Q₁₁, Q₁₂Turns on and the current I₁₂Flows. Current I₁₂ Transistor Q₁₃, Q₁₄Turns on and the current I₁₃Flows. Current I₁₃Is flowing, transistor Q₁₄, Q₁₅Is turned on and becomes the bias current of the comparison unit 12, the current I _Four Flows.

At this time, the current I ₁ is amplified by the transistor Q ₁₂ to the current I ₂ multiplied by n ₁ , and the current I ₂ is multiplied by the current I ₂ by n ₁₃ / n ₁₂ by the transistors Q ₁₃ and Q _14. The current I ₃ is amplified. Therefore, as shown by the solid line in FIG. 2, the current I ₄ can be raised in quick response to the rise of the power supply voltage Vcc. Therefore, a constant voltage can be supplied even when the voltage Vcc is low.

By thus performing current amplification by the two-stage current amplification circuits 11a and 11b, a constant current can be supplied to the comparison unit 12 even at a low voltage, and the operation of the comparison unit 12 is stabilized even at a low voltage. be able to.

Further, since the output current is output through the current amplifier circuits 11a and 11b when the voltage rises, it is less affected by the voltage Vcc, and a constant current can be continuously supplied as shown by the solid line in FIG. .

FIG. 3 shows a circuit diagram of another embodiment of the present invention. In the figure, the same components are designated by the same reference numerals and the description thereof will be omitted. This embodiment is obtained by realizing the transistor of FIG. 1 in reverse polarity preparative transistors, resistors R _11, in correspondence to the R _12, resistors R _21, R ₂₂ and setting only the current amplifying circuit 21a of the current amplifier circuit 11a NPN transistors Q ₁₁ , Q ₁₂ and resistors R ₁₃ , R ₁₄ , R ₁₅ correspond to NPN transistors Q ₃₁ , Q ₃₂ , resistors R ₃₃ , R ₃₄ , R ₃₅ , and current amplifier circuit 21b is a current amplifier circuit. PNP Trang register Q _13, Q ₁₄ of 11b, the resistor R _16, so as to correspond to R _17, R _18, composed of NPN transistors Q _33, Q _34, resistors _{R 36, R 37, R 38} , current mirror circuit 21c is NPN transistors Q _15, Q ₁₆ of the current mirror circuit 11c, the resistor R _19, so as to correspond to R _20, composed of a PNP transistor Q _35, Q _36, resistors R _39, R _40, comparing section 22 PNP comparison section 12 Transistor _17, Q _18, to correspond to NPN transistors Q _19, Q _20, NPN transistors Q _37, Q _38, constituted by a PNP transistor Q _39, Q _40, PNP transistor capacitor Q to correspond to NPN transistors Q ₂₁ serving as an output transistor ₄₁ is provided.

The current characteristic of this embodiment is substantially the same as that shown by the solid line in FIG. 2, and has the same effect as that of the embodiment in FIG.

[0025]

[Effect of device]

 As described above, according to the present invention, the current amplification degree can be increased by the current amplification by the multiple-stage current amplification circuit, so that the rise of the current at the low voltage can be speeded up and the constant current can be maintained even at the low voltage. In addition to being able to secure a constant current, the current fluctuation can be reduced even when the voltage rises, a constant current can be obtained from a low voltage to a high voltage, and constant current characteristics are improved.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of an embodiment of the present invention.

FIG. 2 is a voltage-current characteristic diagram of an embodiment of the present invention.

FIG. 3 is a circuit configuration diagram of another embodiment of the present invention.

FIG. 4 is a circuit configuration diagram of a conventional example.

FIG. 5 is a configuration diagram of a main part of a conventional example.

[Explanation of symbols]

 11 constant current circuit section 11a, 11b current amplification circuit 11c current mirror circuit 12 comparison circuit section

Claims (1)

[Scope of utility model registration request] 1. A current amplification circuit of a preceding stage, comprising a plurality of current amplification circuits each including a control transistor having a base and a collector connected via a resistor, and an output transistor having a base connected to the collector of the control transistor. Connect the connection point of the control transistor base of the next stage current amplification circuit and the resistor to the collector of the output transistor of, and apply the power supply voltage to the connection point of the control transistor base of the first stage current amplification circuit and the resistor. , A constant current circuit configured to output a constant current from the collector of the output transistor of the final stage current amplification circuit.