JPH071471B2 - Constant current circuit - Google Patents

Description

The present invention relates to a so-called bandgap type constant current circuit.

<Prior Art> One of the circuits conventionally used as a constant current source is
There is a circuit shown in FIG. In this circuit, current is passed through the collectors of the transistors Q12, 11 via the transistors Q14, 15 that operate as a constant current source equal to the current value flowing in the transistor Q16, so that both transistors Q12, 11 Have the same collector current. However, the size of the emitter of the transistor Q12 is formed larger than that of the transistor Q11, and if the ratio of the size of the emitter of the transistor Q12 to that of Q11 is M (M> 1), the transistor Q12
The difference between the voltage between the base-emitter of Q12 and that of Q11 is (KT / q) × ln M (K is the Boltzmann constant, T is the absolute temperature, q is the electron charge). .

As a result, the collector currents of the transistors Q14 and Q15 are
If the value of the resistor R1 is 1 and the value of the resistor R1 is r11, the current flowing through the collector of the transistor Q13 is controlled so that the relationship of (KT / q) × ln M = I11 × r11 is established. Therefore, the transistor Q17 operates so that its collector output serves as a constant current source that outputs a current value I11 that satisfies the above relationship.

<Problems to be Solved by the Invention> Since the constant current values that are the outputs of the above circuits are constants K, T, and q, the ratio M of the sizes of the emitters of the transistors Q11 and Q12 and the value r11 of the resistor R11. It is uniquely determined by, but if you examine the current flowing through the resistor R11 in detail,
The value is a value obtained by subtracting the current flowing through the base of the transistor Q11 from the current flowing through the transistor Q14.

That is, the value of the output current of the transistor Q17 (this value is equal to the current value I11 flowing in the transistor Q14) is KT / q
Is a value that satisfies the relationship of A × ln M = (I11−IB11) × r11 (IB11 represents the base current flowing in the transistor Q11). Let this formula be a formula.

On the other hand, the value of the base current IB11 is shown as I11 / hfe9 ... When the current amplification factor of the transistor Q11 is hfe9 (collector current and Q of the transistor Q14).
15 collector currents are equal).

Substituting the equation into the above equation, the equation is shown as A × ln M = I11 (1-1 / hfe9) × r11. That is, I11 =, A × ln M / ((1-1 / hfe9) × r11) (the above formula is used as a formula).

On the other hand, at the time of manufacturing the IC, it is possible to control the ratio of the sizes of the emitters of the two transistors and the resistance value extremely accurately, but the control of the current amplification factor should be performed insufficiently. I can't. Therefore, the value of the current amplification factor hfe9 of the transistor Q11 is, for example, 100 to 200.
When the output current value of the transistor Q17 varies depending on the formula, the value of the output current value of the transistor Q17 varies in the order close to percent, which is a problem.

The present invention was created to solve the above problems, and an object thereof is to provide a constant current circuit that can reduce the influence of variations in the current amplification factor of transistors on the value of the output current.

<Means for Solving the Problems> A constant current circuit according to the present invention includes an NPN type first transistor whose emitter is grounded, an emitter size n times that of the first transistor, and a collector and a base. A first current mirror consisting of an NPN type second transistor whose emitter is grounded via a reference resistor while being connected to the base of the first transistor, and an emitter which is grounded via a resistor, First base
And a circuit for generating a current equal to the collector current of the fifth transistor and supplying it to the collectors and loads of the first and second transistors, respectively. , A base is connected to the collector and the collector of the fifth transistor, and a PNP-type sixth transistor is connected to the base of the sixth transistor, and a collector is connected to the collector of the first transistor A PNP-type seventh transistor, a base of which is connected to the base of a sixth transistor, and a collector of which is connected to a collector of the second transistor, and a PNP-type eighth transistor whose base is sixth transistor A second PNP-type transistor which is connected to the base of the It is assumed that the constant current circuit is composed of a current mirror and, and instead of connecting the collector of the second transistor in the first current mirror to the base and the base of the first transistor, the emitter has first and second emitters. The NPN type fourth transistor whose collector is connected to the base and the collectors of the second and eighth transistors, and the emitter is connected to the bases of the first and second transistors. , And a third current mirror having a base connected to the base of the fourth transistor and a collector connected to the positive power source side and an NPN-type third transistor.

<Operation> Since the third current mirror is composed of the third and fourth transistors, the emitter currents of the third and fourth transistors are equal to each other. The sum of this emitter current becomes each base current of the first and second transistors,
These base currents operate the first current mirror.

As a result, the emitter current of the second transistor, in other words, the current flowing through the reference resistor and the collector current of the first transistor become substantially equal to each other, regardless of the variations in the current amplification factors of the first and second transistors.

<Embodiment> FIG. 1 is a circuit diagram showing an electrical configuration of an embodiment of the present invention.

A current mirror (corresponding to a first current mirror) is configured by a first transistor Q1 whose emitter is grounded and a second transistor Q2 whose emitter is grounded via a resistor R1 (reference resistor).

A fifth transistor Q5 whose emitter is grounded is connected to the output side of this current mirror via a resistor R2.

On the other hand, transistors Q23 (sixth transistor), Q21
A current mirror (corresponding to a second current mirror) is constituted by (seventh transistor), Q22 (eighth transistor), and Q24 (ninth transistor). This current mirror generates a current equal to the collector current of the fifth transistor Q5, and the collectors of the first and second transistors Q1 and Q2 and a load not shown (connected to the collector side of the transistor Q24). To supply each.

The third transistor Q3 and the fourth transistor Q4 form a current mirror (corresponding to a third current mirror). The present invention is characterized in that the current mirror is provided. The details will be described below.

In the figure, four PNP transistors Q21 to Q2 having the same configuration are shown.
4 has its emitters connected to each other and to the positive power supply P, whose base is
Similarly, they are connected to each other and also to the collector of the transistor Q23. The collector of the transistor Q23 is connected to the collector of the fifth transistor Q5 whose emitter is grounded via the resistor R2.

The collector of the transistor Q21 is led to the collector of the first transistor Q1 whose emitter is grounded and the base of the fifth transistor Q5.

The collector of the transistor Q22 is connected via a resistor R1 to the collector of the second transistor Q2 whose emitter is grounded and the collector of the fourth transistor Q4. The base of the fourth transistor Q4 is connected to its own collector and to the base of the third transistor Q3, and the emitters of the third and fourth transistors Q3 and Q4 are both the first and the second. Second
Are led to the bases of transistors Q1 and Q2. Therefore, the first transistor Q1 and the second transistor Q2 are
The bases are connected to each other. The collector of the third transistor Q3 is connected to the positive power source P.

Regarding the configuration of the first transistor Q1 and the second transistor Q2, the second transistor Q2 has a configuration in which ten transistors having the same size as the emitter size of the first transistor Q1 are connected in parallel. Therefore, the size of the emitter of the second transistor Q2 is 10 times the size of the emitter of the first transistor Q1.

Further, as shown in the figure, NPN transistors are used for the first to fifth five transistors Q1 to Q5.

The operation of one embodiment of the present invention having the above configuration will be described below.

FIG. 2 is an explanatory diagram showing a current flowing through a main part. In the following, the description will proceed with reference to FIG. 2 as necessary.

Since the transistors Q21 and Q22 operate as a current mirror for the transistor Q23, the currents I1 and I2 flowing out from the respective collectors have the same value.

The current I2 from the transistor Q22 is the current I14 flowing through the collector of the second transistor Q2, the current I16 flowing through the collector of the fourth transistor Q4, and the current flowing through the bases of the third and fourth transistors Q3 and Q4. Its value is equal to the sum of I13.

On the other hand, since the third transistor Q3 and the fourth transistor Q4 form a current mirror, I11 = I16. Also, ignoring the difference in current amplification factor between the third transistor Q3 and the fourth transistor Q4, their respective emitters are connected to each other and to the bases of the first and second transistors Q1 and Q2. Therefore, the currents I18 and I19 flowing in each emitter are I18 = I19. Also, the emitter current I1 of the third transistor Q3
9 is I19 = I11 + I17, and the current I18 flowing through the emitter of the fourth transistor Q4 is I18 = I16 + I13−I17.

If the current amplification factor of the first transistor Q1 is hfe1, then hfe1 × I19 = I21. In addition, the current amplification factor of the third transistor Q3 is set to hfe3
Then I17 × hfe3 = I19. That is, the current I17 flowing through the base of the third transistor Q3 is I17 = I21 / (hef1 × hfe3). Therefore, the current I15 flowing through the emitter of the second transistor Q2 becomes I15 = I2-I17 = I2-I21 / (hef1 * hfe3).

On the other hand, the current flowing through the emitter of the first transistor Q1
I22 is I22 = I1−I20 + I19, but I1 = 15 is always established, so I19 = I20 is obtained, ignoring the difference in current amplification factor between the first transistor Q1 and the fifth transistor Q5. Therefore, I22 = I1.

A current having the above-described value flows through the emitter of the second transistor Q2 and the emitter of the first transistor Q1.

On the other hand, due to the physical properties of the transistor, the current flowing through the collector is IC, the reverse saturation collector current is IO, the Boltzmann constant is K, the absolute temperature is T, and the value of the charge is q, which occurs between the base and the emitter. When the voltage is VBE, the relationship of VBE = (K + T / q) × ln (IC / IO) is established.

Therefore, between the voltage generated between the base-emitter of the first transistor Q1 and the base-emitter of the second transistor Q2 having the emitter formed 10 times as large as the emitter of the first transistor Q1. A difference of (K × T / q) × ln10 occurs with the generated voltage.

The current flowing through the second transistor Q2 changes so that the voltage of this difference becomes equal to the voltage generated across the resistor R1, but the first transistor Q1 and the second transistor Q2
Since the transistors Q21 and Q22 are configured so that the same current flows, the change in the current flowing in the second transistor Q2 changes the current flowing in the first transistor Q1 and the base of the fifth transistor Q5. Change the current flowing through.

As a result, the collector current flowing through the fifth transistor Q5 changes, and the first, second, and fifth transistors Q1, Q
2. Balance when the currents flowing in Q5 become equal.

In other words, the value of the current flowing in the transistors Q21 and Q22 is
The configuration is determined by the voltage generated across R1. Therefore, the current value of the output of the transistor Q24, which performs the same current mirror operation as the transistors Q21 and Q22, is also determined by the voltage across the resistor R1.

As described above, considering the current flowing through the resistor R1 that determines the output current value of the transistor Q24 that serves as the constant current source, the current I15 is I2-I21 / (hfe1 × hfe3) and I21 / (hfe1 × hfe3) is a very small current value, and each of the current amplification factors hfe1 and hfe3 is from 100 to 2
When it varies between 00, the amount of change in the current flowing through the resistor R1 is the same as I2 and I21, so I2 × (1-1 / 10000) is changed to I2 × (1-1 / 000). 40,000) and the variation is less than 0.1%.

The present invention is not limited to the above embodiment, and the ratio of the sizes of the emitters of the first transistor Q1 and the second transistor Q2 is not limited to 10 times, and other magnifications such as 20 times are possible. The ratio can be set to

<Effects of the Invention> As described above, in the case of the constant current circuit according to the present invention, the first and second
Since the emitter current of the second transistor, in other words, the current flowing through the reference resistor and the collector current of the first transistor are substantially equal to each other regardless of the variation in the current amplification factor of the transistor, First,
The influence of the variation in the current amplification factor of the second transistor on the value of the output current can be reduced. In addition, since the currents flowing through the first and second transistors have the same value, the constant current operation is more stable.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an electrical configuration of an embodiment of the present invention,
FIG. 2 is an explanatory diagram showing a current flowing through a main part, and FIG. 3 is a circuit diagram showing an electrical connection of a conventional technique. Q1 ...... First transistor Q2 ...... Second transistor Q3 ...... Third transistor Q4 ...... Fourth transistor Q5 ...... Fifth transistor R1 ...... Resistance P ...... Positive power supply.

Claims (1)

[Claims] 1. An NPN-type first transistor having a grounded emitter and an n-type emitter of the first transistor.
And a collector connected to the base and the base of the first transistor while the emitter is connected to the base of the first transistor and an NPN-type second transistor grounded via a reference resistor.
The current mirror and the emitter are grounded via a resistor, and the base is the first
And a circuit for generating a current equal to the collector current of the fifth transistor and supplying it to the collectors and loads of the first and second transistors, respectively. , A base is connected to the collector and the collector of the fifth transistor, and a PNP-type sixth transistor is connected to the base of the sixth transistor, and a collector is connected to the collector of the first transistor A PNP-type seventh transistor, a base of which is connected to the base of a sixth transistor, and a collector of which is connected to a collector of the second transistor, and a PNP-type eighth transistor whose base is sixth transistor A second PNP-type transistor connected to the load while being connected to the base of In a constant current circuit composed of a current mirror and, instead of connecting the collector of the second transistor in the first current mirror to the base and the base of the first transistor, the emitter has a first and a second transistor. The NPN-type fourth transistor whose collector is connected to the base and the collectors of the second and eighth transistors while being connected to the base, and the emitter of which is connected to the bases of the first and second transistors A constant current circuit comprising a third current mirror, which is connected to the base of the fourth transistor and has a collector connected to the positive power source side and an NPN-type third transistor.