KR920004323Y1 - Stable curret circuit - Google Patents

Abstract

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Description

Constant current circuit

1 is a conventional constant current circuit diagram.

2 is a constant current circuit diagram of the present invention.

3 is a detailed view of a constant current circuit of the present invention.

4 is a graph showing the current-temperature characteristics of the constant current circuit of the present invention.

* Explanation of symbols for main parts of the drawings

TR ₁₁ , TR ₁₂ : Transistor OP ₁₁ : Operational Amplifier

R ₁₁ -R ₁₄ : resistance

The present invention relates to a constant current circuit used in an integrated circuit such as a digital / analog converter and a constant voltage regulator, and more particularly, to a constant current circuit allowing a constant current to flow regardless of ambient temperature changes.

A conventional constant current circuit is connected to the base of the power supply terminal (Vcc) is a collector, and the transistor (TR _1, TR ₂₎ of the transistor (TR ₁₎ via a resistor (R _1), as shown in FIG. 1, transistor There is the emitter resistance (R ₂₎ is connected to the (TR ₂₎ it consisted of a constant current to flow in the collector of the transistor (TR _2).

In the conventional constant current circuit configured as described above, the voltage V _R2 between both ends of the resistor R ₂ is as follows.

Here, I ₂ is a collector current of transistor TR ₂ , V _BE1 and V _BE2 are voltages between the base and emitter of transistors TR _{1 and} TR ₂ , and V _T is a temperature equivalent voltage.

Therefore, the collector current I ₂ , that is, the current I ₂ flowing in the load of the transistor TR ₂ is as follows.

As can be seen from Equation (1) above, the current I ₂ flowing in the load is proportional to the temperature equivalent voltage V _{T which} varies with temperature, so that the digital / analog converter and the constant voltage operate regardless of the temperature change. There was a defect that it was difficult to produce integrated gray scale such as a regulator.

The present invention has been made in view of the above conventional defects, and devised a constant current circuit allowing a constant current to flow regardless of the change in temperature, which will be described in detail with reference to the accompanying drawings 2 to 4 as follows.

2 and 3, the power supply terminal Vcc is connected to the base of the transistors TR ₁₁ and TR ₁₂ through the resistors R ₁₁ and R ₁₂ , and the connection point is connected to the transistor ( to the base of a) (connected to +) and an output terminal of the operational amplifier (OP _11), a transistor _{(TR 11, TR 12) -} TR 13 -TR 19) of the operational amplifier (OP ₁₁₎ inverting and non-inverting input terminal (in junction box as well as to be configured to connect to the emitter and the load of the emitter, the transistor (TR ₁₂₎ of the transistor (TR ₁₁₎ over the post via a resistor (R ₁₃₎ to the connection point, a resistance (R _14), in the The values of the resistors R ₁₁ and R ₁₂ are the same, and the area of the emitter of the transistor TR ₁₁ is made larger than that of the emitter of the transistor TR ₁₂ .

According to the present invention configured as described above, when power is applied to the power supply terminal Vcc, the current I ₁₁ (I ₁₂ ) flowing through the transistors TR ₁₁ and TR ₁₂ by the resistors R ₁₁ and R ₁₂ and the operational amplifier OP ₁₁ . ₂₀ ) becomes the same, and the currents I ₁₁ and I ₁₂ are as follows.

I = I ₁₁ = I ₁₂ = i ₀ exp (qV _BE / KT). (11)

i ₀ = C T ^N exp (−q V _go / K T). (12)

Where q is the charge amount, V _BE is the voltage between the emitter and base of the transistors TR ₁ , TR ₁₂ , K is the Boltzmann constant, T is the temperature, Vgo is the bandgap voltage of silicon, and C is This is a constant depending on the type of transistor used.

Substituting equation (12) into equation (11),

If V _BE is obtained from equation (13),

Differentiating equation (14) with respect to temperature (T),

In equation (13),

Substituting equation (16) into equation (15),

here, ego, Therefore, equation (17) is

The voltage V _BE12 between the base and emitter of the transistor TR ₁₂ is as follows.

V _BE = I ₁₃ R ₁₃ . (19)

Differentiating equation (19) with respect to temperature (T),

Substituting equation (18) into equation (20),

Substituting equation (19) into equation (21),

In addition, the voltage between both ends of the resistor R ₁₄ is as follows.

Since I ₁₁ = I ₁₂ = I, equation (23) is

_{I 11 · R 14 = V T} · 1nN

Differentiating equation (24) with respect to temperature (T),

In equation (24),

Therefore, equation (25) is as follows.

The constant current I ₁₄ flowing to the load is as follows.

I = I ₁₁ + I ₁₂ + I ₁₃

= 2I ₁₁ + I ₁₃ ... (27)

Differentiating equation (27) with respect to temperature T,

Substituting equation (22) and equation (26) into equation (28),

As can be seen from Equation (29), when the power of the resistors R ₁₃ and R ₁₄ and the power supply terminal Vcc is adjusted such that 2I ₁₁ = I ₁₃ , a constant current I ₁₄ regardless of temperature flows. do.

As described in detail above, the present invention allows a constant current to flow to a load regardless of a change in temperature, thereby producing an integrated circuit such as an analog / digital converter and a constant voltage regulator that operate stably even when the temperature changes.

Claims (1)

The power supply terminal Vcc is connected to the collector of the transistors TR ₁₁ (TR1 ₂ ) through the resistors R ₁₁ and R ₁₂ , and the connection points thereof are inverted and non-inverting input terminals of the operational amplifier OP ₁₁ ( + And-terminals, and the output terminal of the operational amplifier OP ₁₁ is connected to the base of the transistors TR _{11 and} TR ₁₂ , and the connection point is made through the resistor R ₁₃ , and then the resistor R ₁₄ . And an emitter of the transistor (TR ₁₁ ), an emitter of the transistor (TR ₁₂ ) and a load through the constant current circuit.