JP5698055B2 - Constant current circuit - Google Patents

Description

  The present invention relates to a constant current circuit, and more particularly to a constant current circuit having a trimming resistor for adjusting an output current value.

  FIG. 5 is a circuit diagram of a constant current circuit having a conventional trimming resistor. This constant current circuit includes a trimming resistor TR1, transistors Q1, Q2, and Q3, and resistors R1 and R2, and an output current Iout is output from the collector of the transistor Q3. Here, the transistors Q1, Q2, and Q3 are NPN type transistors. The output current Iout is controlled by the base voltage of the transistor Q3. A voltage obtained by subtracting the voltage drop of the trimming resistor TR1 and the base-emitter voltage of the transistor Q2 from the high potential power supply voltage VDD is applied to the base of the transistor Q3. Is given. For this reason, when the resistance value of the trimming resistor TR1 is decreased by trimming, the voltage drop of the trimming resistor TR1 is reduced and the base voltage of the transistor Q3 is increased, so that the collector current (= output current Iout) of the transistor Q3 increases. . Conversely, when the resistance value of the trimming resistor TR1 is increased by trimming, the voltage drop of the trimming resistor TR1 increases and the base voltage of the transistor Q3 decreases, so that the collector current (= output current Iout) of the transistor Q3 decreases.

  At this time, the trimming resistor used in the integrated circuit can only be selected to adjust the resistance value in an increasing direction or to decrease in a decreasing direction by trimming. For this reason, the output current of the constant current circuit can only be selected to either increase or decrease the output current Iout by trimming.

  Therefore, as shown in FIG. 4, a circuit configuration in which the trimming resistor TR2 is connected between the base of the transistor Q2 and the low potential power supply GND has been proposed (see, for example, Patent Document 1). As a result, the base voltage of the transistor Q2 is determined by the resistance ratio between the trimming resistor TR1 and the trimming resistor TR2. Accordingly, the output current Iout can be increased or decreased by increasing (or decreasing) the resistance value of either the trimming resistor TR1 or the trimming resistor TR2.

Japanese Patent Laid-Open No. 62-219117

  However, the method of adjusting the output current Iout using the two trimming resistors TR1 and TR2 as described in Patent Document 1 has a problem that the trimming process becomes complicated and the adjustment time increases. .

  An object of the present invention is to provide a constant current circuit which can be trimmed by one trimming resistor and can adjust the increase and decrease of the output current.

In order to solve the above-mentioned problem, the invention according to claim 1 is characterized in that one end of a series resistor of a trimming resistor and a resistive element is connected to a common connection between a base and a collector of a first transistor, A constant current circuit for outputting a current from a collector of a second transistor having a base connected to a common connection of the collector; a third transistor having a base connected to a common connection of the base and the collector of the first transistor; A resistor having one end connected to a collector of the third transistor, a fourth transistor having a base connected to a connection point of the trimming resistor and the resistive element, and a connection point of the resistor and the third transistor And a fourth transistor having the same polarity as the fourth transistor and having a common emitter connected to the fourth transistor, A current source connected to a common emitter of the transistor and the fifth transistor; a sixth transistor connected to the collector of the fifth transistor; and a base and a collector commonly connected; and a base and a collector of the sixth transistor And a seventh transistor having a collector connected to a connection point of the resistive element and the first transistor, and a resistance value of the trimming resistor is set to the fourth value by trimming. The base voltage of the first transistor and the base voltage of the fifth transistor are set over a range of switching. The invention according to claim 2 is characterized in that, in claim 1, each of the transistors is replaced with a field effect transistor, the base is replaced with a gate, the emitter is replaced with a source, and the collector is replaced with a drain.

  According to the present invention, the increase / decrease in the output current of the constant current circuit can be adjusted by one trimming resistor.

1 is a circuit diagram of a constant current circuit according to a first exemplary embodiment of the present invention. It is a figure which shows the relationship between the resistance value of trimming resistance TR11 based on 1st Example of this invention, and the electric current value of output current Iout. It is a circuit diagram of the constant current circuit of the 2nd Example of this invention. It is a circuit diagram which shows the constant current circuit which can adjust the conventional output current to both the increase direction and the decrease direction. It is a circuit diagram which shows the constant current circuit which can adjust the conventional output current to either the increase direction or the reduction | decrease direction.

<First embodiment>
FIG. 1 is a circuit diagram of a constant current circuit having a trimming resistor according to the present invention. The trimming resistor TR11 has one end connected to the high potential power supply VDD and the other end connected to the source of a junction field effect transistor J11 (corresponding to a resistive element) whose gate is connected to the high potential power supply VDD. The drain of the junction field effect transistor J11 is connected to a common connection point between the base and collector of the transistor Q11. The base of the transistor Q11 is commonly connected to the transistors Q12, Q13, and Q18, and a current proportional to the size ratio of each transistor is supplied from the transistors Q12, Q13, and Q18. The resistor R11 has one end connected to the high potential power supply VDD and the other end connected to the collector of the transistor Q12 to supply current. Transistors Q14 and Q15 have their emitters connected in common and are connected to the collector of current source transistor Q13. The base of one transistor Q14 of the differential pair is connected to the connection point between the trimming resistor TR11 and the source of the junction field effect transistor J11, and the base of the other transistor Q15 is connected to the connection point between the resistor R11 and the collector of the transistor Q12. Connected. The collector of the transistor Q15 is connected to the transistor Q16 that commonly connects the base and the collector, and a current proportional to the transistor size ratio of the current flowing through the transistor Q16 is folded by the transistor Q17 that commonly connects the transistor Q16 and the base. The collector of the transistor Q17 is connected to a common connection point between the drain of the junction field effect transistor J11 and the base and collector of the transistor Q11. The transistor Q18 has a base connected in common with the transistor Q11, and outputs a current Iout proportional to the size ratio of the transistor from the collector of the transistor Q18. Transistors Q11 to Q15, transistor Q18 are NPN type, transistors Q16 and Q17 are PNP type, and junction field effect transistor J11 is P channel.

  The operation of this embodiment will be described below with reference to FIG. The junction field effect transistor J11 whose gate is connected to a high potential power supply operates as a resistive element and serves to limit the maximum current flowing through the trimming resistor TR11. The bases of the transistor Q11 and the transistor Q12 are connected in common, and a current that is proportional to the size ratio of each transistor flows through the resistor 11 through the transistor Q11. The differential pair of transistors Q14 and Q15 compares the voltage drop across the trimming resistor TR11 and the resistor R11. First, when the voltage drop of the trimming resistor TR11 is smaller than the voltage drop of the resistor R11, the transistor Q14 is turned on and the transistor 15 is turned off, so that no current flows through the transistors Q16 and Q17. Therefore, the current I2 becomes substantially 0, and only the current I1 is supplied to the transistor Q11. Next, when the voltage drop of the trimming resistor TR11 is larger than the voltage drop of the resistor R11, the transistor Q15 is turned on. As a result, a current I2 in which the current flowing through the transistor Q16 is proportional to the size ratio of the transistors Q16 and Q17 flows. Therefore, current I1 + current I2 flows through transistor Q11.

  FIG. 2 shows the relationship between the resistance value of the trimming resistor TR11 and the output current Iout when the resistor R11 is 4 kΩ and the size ratio of the transistors Q11 and Q12 is 1: 1 in the constant current circuit of FIG. It is shown. When the resistance value of the trimming resistor TR11 is 1 kΩ, the output current Iout is 135 μA (point A). As the resistance value of the trimming resistor increases, the output current Iout decreases. When the resistance value of the trimming resistor TR11 is 4 kΩ, the output current Iout becomes 90 μA (point B). When the resistance value of the trimming resistor further increases, the output current Iout increases, and when the trimming resistor TR11 is 20 kΩ, the value of the output current Iout is 160 μA (point C).

  The operation of the circuit of FIG. 1 will be described below with reference to FIG. When the value of the trimming resistor TR11 is point A, the voltage drop of the trimming resistor TR11 is smaller than the voltage drop of the resistor R11. At this time, since the base voltage of the transistor Q14 constituting the differential pair is higher than the base voltage of the transistor Q15, most of the tail current of the transistor Q13 flows to the transistor Q14. Therefore, no current flows through the transistor Q15, and no current flows through the transistor Q16 that commonly connects the collector and the base. Therefore, no current flows through the transistor Q17 that commonly connects the transistor Q16 and the base. Therefore, the current I2 becomes substantially 0, and only the current I1 flows through the transistor Q11. Thus, the output current Iout becomes a current proportional to the size ratio of the transistors Q11 and Q18 of the current I1.

  When the resistance value of the trimming resistor TR11 is increased from the point A, the current I1 is decreased and the current I2 is substantially 0, so that the output current Iout is decreased (points A to B).

  When the resistance value of the trimming resistor TR11 further increases and the difference between the base voltage of the transistor Q14 and the base voltage of the transistor Q15 is within 3 × Vt (Vt is a thermal voltage) that is necessary for switching the differential pair, Part of the tail current begins to flow through transistor Q15. Further, when the resistance value of the trimming resistor TR11 increases and the base voltage of the transistor Q15 becomes higher than the base voltage of the transistor Q14, more tail current flows to the transistor Q15. The current flowing through the transistor Q15 flows through the transistor Q16 having the base and the collector connected in common, and a current I2 proportional to the size ratio of the transistors Q16 and Q17 flows through the collector of the transistor Q17. When the decrease in current I1 due to the increase in the resistance value of trimming resistor TR11 becomes equal to the increase in current I2, an inflection point at point B is formed. Further, as the resistance value of the trimming resistor TR11 increases, the increase in the current I2 becomes dominant, so that the current flowing through the transistor Q11 increases and the output current Iout also increases (points B to C).

  As described above, in the present invention, it is possible to adjust the output current Iout in both the increasing direction and the decreasing direction with one trimming resistor.

  Although the first embodiment has been described above, the present invention is not limited to the circuit diagram of FIG. 1, and it goes without saying that various modifications can be made without departing from the scope of the invention. For example, the current source composed of the transistors Q11, Q12, Q13, and Q18 can be configured by a Wilson current mirror to increase the current accuracy. It is also possible to adjust the increase / decrease of the output current Iout by inserting a resistor between the emitters of the transistors Q16 and Q17 and the high power supply voltage VDD. It is also possible to replace the junction field effect transistor J11 with a high resistance having an appropriate value.

<Second embodiment>
FIG. 3 is a circuit diagram of a constant current circuit having a trimming resistor of the present invention. In this embodiment, the NPN transistor of the first embodiment is changed to an N-channel MOS transistor, and the PNP transistor is changed to a P-channel MOS transistor.

J11: P-channel junction field effect transistor TR11: Trimming resistor R11: Resistors Q11, Q12, Q13, Q14, Q15, Q18: NPN transistor Q16, Q17: PNP transistors M11, M12, M13, M14, M15, M18: N-channel MOS transistors M16 and M17: P-channel MOS transistors

Claims (2)

One end of the series resistor of the trimming resistor and the resistive element is connected to the common connection of the base and the collector of the first transistor, and the second transistor is connected to the common connection of the base and the collector of the first transistor. In the constant current circuit that outputs current from the collector,
A third transistor having a base connected to a common connection of the base and collector of the first transistor;
A resistor having one end connected to the collector of the third transistor;
A fourth transistor having a base connected to a connection point between the trimming resistor and the resistive element;
A fifth transistor having a base connected to a connection point between the resistor and the third transistor, having the same polarity as the fourth transistor, and commonly connecting an emitter;
A current source connected to a common emitter of the fourth transistor and the fifth transistor;
A sixth transistor connected to the collector of the fifth transistor and commonly connecting a base and a collector;
A base connected to a common connection between the base and collector of the sixth transistor, and a collector connected to the connection point of the resistive element and the first transistor;
The constant current circuit is characterized in that the resistance value of the trimming resistor is set over a range where the level relationship between the base voltage of the fourth transistor and the base voltage of the fifth transistor is switched by trimming.   2. The constant current circuit according to claim 1, wherein each transistor is replaced with a field effect transistor, the base is replaced with a gate, the emitter is replaced with a source, and the collector is replaced with a drain.

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