JPS62293326A - Constant current source circuit - Google Patents

Abstract

PURPOSE:To supply the constant current at a fixed level to plural loads by providing a start circuit, a current negative feedback circuit which corrects the error between two reference voltage levels, and a feedback value reducing circuit which prevents the abnormal oscillation in order to cope with the variance of the power supply voltage. CONSTITUTION:A start circuit consists of a current mirror circuit containing the NPN transistors TR 2 and 3, the PNP TR 7 and 8, the NPN TR 10 and 11 and a PNP TR 9 of a constant current circuit. The base of an NPN TR 5 for detection of current error is connected to the collector of the TR 10. While a current negative feedback circuit is formed with a current mirror circuit consisting of the TR 7, 8 and 9. Furthermore a circuit is connected to the TR 9 via a PNP TR 13 to reduce the current feedback value caused by the NPN TR 14 and 15. Thus it is possible to prevent the circuit abnormal oscillation to cope with the variance of the power supply voltage and to supply the constant current at a fixed level to plural loads.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention Field of Industrial Application The present invention relates to a constant current source circuit used in an integrated circuit.

BACKGROUND OF THE INVENTION FIG. 3 shows a low-voltage constant current circuit conventionally used in integrated circuits. In FIG. 3, the base and collector of the NPNI transistor 25 are connected to the base of the 3/NPN transistor 24 to form a current mirror circuit, and the base and collector of the NPN transistor 26 are connected to the base of the PNP transistor 23. The collector of the transistor 24 is connected to the collector (NPN).
The PNP transistors 22 and 23, which are connected to the base and collector of the P transistor 22 and the base of the PNP transistor 23, also constitute a current mirror circuit. Further, the resistor 18 is connected between the base and collector of the NPN transistor 190 and the base of the NPN transistor 2o and the power supply. A resistor 21 is connected, and the collector of the NPN transistor 20 is connected to the base and collector of a PNP transistor 22.

The operation of the constant current source circuit configured as above will be described below.

First, when the power supply voltage is turned on, the diode-connected NPN)
Current flows through the transistor 19, and at the same time it forms a current mirror circuit with the NPN transistor 19)
Current flows through the emitter and collector of transistor 2o,
A current is generated in the diode-connected PNP transistor 22. By selecting large values for the resistors 18 and 21, a small current can be passed through the PNP transistor 22.

When a small current flows through the PNP transistor 22, the NPN
The base-emitter contact voltage of the transistor 26 is NPN.
If it is lower than the base-collector contact voltage of the transistor 24, the sum of the base-emitter contact voltage of the NPN transistor 25 and the voltage drop across the resistor 26 due to the emitter current of the NPN transistor 25 is the base-emitter contact voltage of the NPN transistor 2o. The circuit is in equilibrium when the voltage is equal to the voltage. In other words, equilibrium is reached at point F in FIG.

Here, the curve G is the characteristic of the transistor 24 side in FIG. 3, and the curve H is the characteristic of the series circuit of the transistor 25 and the resistor 26. Also, the voltage between the 0' point and ground in Figure 3,
2 is the emitter current of transistors 24 and 25. The current is taken out as a collector current of -127 to the PNP transistor 5 whose base and collector are common to the PNP transistor 23. This current is NPN
) Ratio of emitter areas of transistors 24 and 25, resistance 2
It can be adjusted by a value of 6.

Problems to be Solved by the Invention Incidentally, in the conventional circuit, there is a problem in that the current changes due to the Early effect. In FIG. 3, when the voltage at point E increases, the collector current of transistor 23 increases due to the Early effect of transistor 23, and the current flowing through transistor 25 and resistor 26 also increases. On the other hand, the collector current and emitter current of the transistor 24 also increase due to the Early effect. Since the base voltages of the transistors 24 and 26 are equal, in FIG. 4, the transistor 24 side is balanced at 11 points and the transistor 25 is at the F2 point, and the emitter current decreases by (I-I,). The collector current of transistor 27 also causes a current decrease of (I-I2). If the potential at point E decreases, the opposite will occur, and the equilibrium point will move to F3 and F4,
The current increases by (I, -1).

Furthermore, in conventional circuits, when the current amplification factor decreases due to variations in the current amplification factor of the transistors, the effect of the base current of the transistor that supplies current to the circuit, such as the PNP transistor 27 in Fig. 3, becomes noticeable. There is also the problem that the equilibrium state of the constant current circuit changes, and the current value of the current source changes.

This has a greater impact as the number of transistors supplying current to the circuit increases. In order to improve this problem, there is a circuit shown in FIG. 6 as a circuit for reducing the base current dependence of the output transistor in a balanced state. In this circuit, transistors 32 and 33 are connected by a PNP transistor 34.

Since the base current of transistor 38 is supplied, the transistor 32.
The effect of the base current of 33.38 is reduced to 1/(current amplification factor of PNP transistor 34).

However, with this circuit, voltage reduction operation can only be guaranteed up to about 1.4 μ.

The present invention provides a constant current source circuit that can improve current stability due to variations in current amplification factors of transistors without deteriorating characteristics.

Means for Solving the Problems In order to solve the above problems, the constant current source circuit of the present invention has the following features:
A current mirror using a series connection of a diode and a resistor and a transistor having a base-emitter contact voltage higher than that of the diode, a current negative feedback circuit for detecting a current error of the Karen mirror, and a feedback amount of the current negative feedback circuit. The device is equipped with a circuit for reducing the noise, and a starting circuit that generates a minute current in the current mirror when the power is turned on.

The present invention is capable of supplying a stable constant current output down to a low potential by detecting current errors due to the Early effect and variations in current amplification factors of transistors and applying negative feedback. .

Embodiment Hereinafter, a constant current source circuit according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention.

In FIG. 1, the base and collector of an NPN transistor 11 are connected to the base of an NPN transistor 1° whose base-ever contact voltage is higher than that of the transistor 11, forming a current mirror circuit configuration.
) A resistor 12 is connected to the emitter of the transistor 11. NPNI - The collector of transistor 11 is NPN.
The collector of the PNP transistor 9 that supplies current to the transistor 11 is connected to the collector of the NPN transistor 10, and the collector of the PNP transistor 8 that supplies current to the NPN transistor 1o is connected. PNP) transistors 8 and 90 each have a common base and emitter. The collector of the NPN transistor 10 is further connected to the base of the NPN transistor 6 for current error detection, and the collector of the NPN transistor is connected to the base and collector of the PNP transistor 7.
By being connected to the bases of NP transistors 8 and 90, PNP transistor 7 and PNP transistor 8
and 9 constitute a current mirror circuit configuration, and constitute a current negative feedback circuit. Also, the bases and emitters of PNP transistors 8 and 9 are
The base and emitter of transistor 13 are connected, and PN
P) The collector of transistor 13 is NPN transistor 1
4 base and collector, plus NPN) transistor 1
6 and connected to the bases of NPN transistors 14 and 1
6 has a current mirror circuit configuration. By connecting the collector of the NPN transistor 16 to the collector of the NPN transistor 5, a circuit is configured to reduce the amount of current feedback. Also, the power supply voltage and the NPN transistor 2
A resistor 1 is connected between the collector and base of the NPN transistor and the base of the NPN transistor, and the NPNI transistors 2 and 3 have a current mirror circuit configuration.

The collector of NPN transistor 3 is connected to the base and collector of PNP transistor 3.

The operation of the constant current source circuit configured as above will be described below with reference to FIGS. 1 and 2.

First, when the power supply voltage is turned on, the diode is connected to 10'-
・ Current flows through NPNl and transistor 2, and at the same time NPN
N constitutes a current mirror circuit with transistor 2
PN) A current flows through the emitter and collector of the transistor 3, and current flows through the PNP transistor 7.

By choosing large values for resistors 1 and 6,
A minute current can flow through the PNP transistor 7.

PNP) When a minute current flows through Langistafu, the PNP transistor 7 and a current mirror circuit are configured.
A minute current also flows through transistors 8 and 9. Here PN
If the electrical characteristics of P transistors 8 and 9 are the same, P
NP) Since the base-emitter voltages of transistors 8 and 9 are equal, the collector currents of PNP transistors 8 and 9 are also equal. Since the base-collector contact voltage of the NPN) transistor 11 is lower than the base-collector contact voltage of the NPN) transistor 10, the NPN) run raster 11
0 base-collector contact voltage and NPN) transistor 1
The sum of voltage drops across resistor 12 at emitter current of 1 is N
When applied between the base and emitter of the NPN) transistor 1o, the current flowing through the NPN) transistor 11 is 11 t\-.If the current is a minute current, the emitter current of the NPN transistor is smaller than the emitter current of the NPN) transistor 11, so the NPN ) Emitter current of transistor 11 and NPN
The difference in emitter current of transistor 1o flows as an error current to the base of NPN) transistor 5, and the collector current of NPN transistor 7 increases, increasing the current flowing to PNP) transistor 5 and increasing the current of PNP) transistors 8 and 9. Increase the NPN transistor 10
When the emitter currents of and 11 become equal, an equilibrium state is reached. In other words, an equilibrium state is reached at point D in FIG. In FIG. 2, curve B is the characteristic on the transistor 1o side of FIG. 1, and curve C is the characteristic on the transistor 11 side. Also, VB is the first
0 point in the figure, voltage between ground, 1 is transistor 24
and 26 emitter currents. The current is taken out as a collector current of a PNP transistor 17 whose base and emitter are common to PNP transistors 8 and 9 and whose electrical characteristics are the same as PNP transistors 8 and 9. The current value in the equilibrium state can be adjusted by the emitter area ratio of the transistors 10 and 11 and the resistor 12.

For example, if the area of the emitter of the transistor 11 is n times that of the transistor 1o (where n>1), and if the resistance value of the resistor 12 is R, then the current value is given by the following equation. k: *)>t, v7 constant T ■--qlnn//R However, q: Electron charge T: Absolute temperature Now, the potential at point A in Figure 1 increases, and due to the Early effect, PNP) transistor 8 and Assuming that the collector current of NPN) transistors 1o and 1 increases.
The collector current and emitter current of transistor 10 increase, the potential at point 0 in FIG. 1 changes from VB to VB, and the emitter current of transistor 1o changes to 11 in FIG.
The emitter current of transistor 11 becomes I. ■1 and ■
2, the base current of NPN) transistor is N
PN) flows to the collector of transistor 10, the collector current of NPN transistor 5 decreases, which reduces the current flowing to PNP) transistor 10, reduces the collector current of PNP) transistor 13-8 and 9, and reduces the collector current of transistor 8 and 9.
It returns to equilibrium at the point. When the voltage at point A in FIG. 1 increases, the opposite operation occurs and an equilibrium state is reached at point D in FIG. First, even if the potential at point A in FIG. 2 rises, the equilibrium point remains unchanged, and the current supplied by the collector of the PNP transistor 17 is not affected by the Early effect.

Next, when a plurality of PNP transistors 17 (same as PNP transistors 27 in Fig. 3) for supplying load circuit current in Fig. 1 are used, their base currents change the equilibrium state in the conventional circuit. , the output current value changed, but
The NPN transistor 6 in the circuit diagram of this example in FIG.
and PNP) It is not affected by the base current because it passes through a current negative feedback circuit composed of Langisthu.

The closed circuit gain of the current negative feedback circuit configured as described above is extremely high, and abnormal oscillation is likely to occur.

In order to prevent abnormal oscillation, a capacitor can be connected between the base of the NPN transistor and the power supply line A, or the collector of the PNP transistor 9.
The capacitance of the capacitor is limited within the range. Also, in order to reduce the closed circuit gain, there is a method of connecting a resistor 6 between the emitter of the NPN transistor 6 in Figure 1 and the ground, but if the value of the resistor 6 is set to a large value, the voltage will be reduced due to the potential difference between both ends of the resistor 60. The characteristics deteriorate, and the collector potential of the PNP transistor 8 becomes higher than the collector potential of the PNP transistor 9, causing a difference in the Early effects of the PNP transistors 8 and 9, resulting in a current error. Therefore, the first
The amount of current feedback is adjusted by a PNP transistor 13 and NPN transistors 14 and 16 in the figure.

Here, the collector current of NPN) transistor 15 is . ,
5PNP) If the current flowing through Langistav is I7, then
When the collector of the NPN transistor 15 is connected to the NPN transistor 6, the amount of current feedback is 1-Ic16/I7) times as much as when it is not connected. in this case(
1-I. 16/I7) ) If it is set as o, no current will flow through the NPN transistor 5 and no feedback will be applied, resulting in a latch amplifier, so the collector current of the NPN transistor 16 will be lower than the current flowing through the PNP transistor 7. It has to be reduced.

- For example, in FIG. 1, a resistor 16 is inserted between the emitter of an NPN transistor 16 and the ground to change the mirror ratio.

As described above, according to this embodiment, by providing a startup circuit, two reference voltages, a current negative feedback circuit, and a current feedback adjustment circuit, it is possible to stably supply a constant current down to a low voltage, and the driving circuit The current change when there is a plurality of circuits can also be suppressed to an extremely low level compared to conventional circuits.

In addition, in FIG. 1, a resistor 16 is connected between the emitter of the NPN transistor 15 and the ground.
Although the collector current of the NPN transistor 14 is adjusted, the base-emitter contact voltage of the NPN transistor 14 may be lower than the base-emitter contact voltage of the NPN transistor 16.

Effects of the Invention As described above, the present invention includes a starting circuit, a current negative feedback circuit that compares two reference voltages, detects and corrects the error,
By providing a feedback amount reduction circuit to prevent abnormal oscillation, a constant constant current can be supplied even if the power supply voltage fluctuates up to about 0.9V or a plurality of loads are connected.

[Brief explanation of the drawing]

Fig. 1 is an electrical connection diagram of a constant current source circuit according to an embodiment of the present invention, Fig. 2 is a characteristic diagram of the current reference section in the circuit of Fig. 1, and Figs. 3 and 6 are conventional constant current source circuits. The electrical connection diagram of the source circuit, FIG. 4, is a characteristic diagram of the current reference section in the circuits of FIGS. 3 and 6. 1.4,6,12,16...resistance, 7,8,9
゜13.17... PNP transistor, 2, 3, 5゜1o, 11, 14.15--NPN door 7 transistor. Name of agent: Patent attorney Toshio Nakao and one other person Figure 1 r, 4. c, i2-(E-JfE42.3.5.
i05ヅf1me4. t5- NPN h laser resistor q
#, q, i3.17-PNp = Fig. 2 VB y8 VB jq, 20, 24, Z5
3.27-・P/JP = Figure 4

Claims (1)

[Claims] first and second transistors having a common base; third and fourth transistors having different polarities from the first and second transistors; and a plurality of diodes connected in parallel or a base emitter of the third transistor. a fifth element comprising a diode having a contact voltage lower than a contact voltage between the first transistor and a sixth element comprising a diode or a diode-connected transistor, the collector of the first transistor being connected to the third transistor; and a base of the fourth transistor, a collector of the second transistor is connected to one of the fifth elements, and a first transistor is connected to the other of the fifth element and the emitter of the third transistor. a current negative feedback circuit which connects a resistor of the fourth transistor to the bases of the first and second transistors and one of the sixth element; a starting circuit that causes current to flow to operate the current negative feedback circuit;
and a seventh transistor having the same polarity as the second transistor and whose bases are connected in common, and an eighth element consisting of a diode or a diode-connected transistor;
the collector of the seventh transistor is connected to one of the eighth elements and the base of the ninth transistor, and the collector of the ninth transistor is connected to the collector of the ninth transistor. 4. A constant current source circuit comprising: a current feedback reduction circuit connected to the collector of the transistor No. 4;