JP2002196832A - Reference voltage generating circuit and regulated current circuit using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the precision of a regulated current circuit. SOLUTION: This reference voltage generation circuit 10 is provided with zapping diodes D1 and D2 in parallel with resistors R4 and R5 for deciding an output reference voltage VR. The both edge of the resistors R4 and R5 are short-circuited by the zapping of the zapping diodes so that a reference voltage VR can be adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reference voltage generating circuit for generating a constant reference voltage and a constant current circuit using the same.

[0002]

2. Description of the Related Art Conventionally, semiconductor integrated circuits (IC, LS
I etc.), various constant current circuits are used. For example, a constant current circuit is also used in a charger used for charging a battery. The constant current circuit obtains a constant current by, for example, passing a reference voltage from a normal reference voltage generating circuit through a reference resistor, and extracts the constant current with a current mirror to obtain a constant current output.

[0003]

Here, a constant current circuit used for a charger is required to have a performance of ± 2.5% or less as a variation accuracy of an output constant current. On the other hand, in the above-described conventional constant current circuit, the variation width of the voltage source is about ±
3.0%, the variation width of the mirror circuit is about 2.5%,
There is a problem that the variation of the output constant current is about ± 5%.

The present invention has been made in view of the above problems, and provides a reference voltage generating circuit capable of generating a more accurate reference voltage and a constant current circuit capable of generating a highly accurate constant current using the same. The purpose is to do.

[0005]

According to the present invention, there is provided a reference voltage generating circuit for generating a constant reference voltage, comprising a resistor for determining an output reference voltage, wherein the reference resistor includes at least two resistors connected in series. A zapping diode connected in parallel with at least one of the reference resistors, and a pad for applying a voltage to the zapping diode,
By zapping the zapping diode by applying a voltage from a pad, the resistance value of the reference resistor can be changed to change the output voltage value. As described above, by zapping the zapping diode, the output reference voltage can be arbitrarily adjusted.

Preferably, at least three of both ends and an intermediate portion of the reference resistor are connected to independent pads, and a desired zapping can be performed by adjusting a voltage between the pads. .

Further, the present invention is characterized in that the present invention is a constant current circuit for generating a constant current using a reference voltage from the reference voltage generating circuit. Since the accuracy of the reference voltage is high, the accuracy of the output constant current can be improved.

The reference voltage is input to a control terminal of an input transistor via a positive input terminal of an operational amplifier, and a connection point between the input transistor and a reference resistor through which a current of the input transistor flows is negatively fed back to the operational amplifier. It is preferable that the potential at the connection point between the input transistor and the reference resistor be kept at the reference voltage so that a constant current flows through the reference resistor according to the reference voltage, and the constant current is output via a current mirror.

Preferably, the transistors used for the input transistor and the current mirror are larger in size than the transistors used for the operational amplifier. The accuracy of the current mirror can be improved by increasing the size of the transistor forming the current mirror. Thus, the constant current can be output with an accuracy of 2.5% or less in total variation, together with the improvement of the accuracy of the reference voltage.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a constant current circuit according to the present embodiment. The reference voltage from the reference voltage generation circuit 10 is input to the positive input terminal of the operational amplifier OP. The output of the operational amplifier OP is an NPN-type input transistor QE.
Connected to the base. The emitter of the input transistor QE is connected to ground via a reference resistor RA. Further, the emitter of the input transistor QE is negatively fed back to the negative input terminal of the operational amplifier OP.

Therefore, the operational amplifier OP operates so that the emitter of the input transistor QE always becomes the reference voltage, and a constant current obtained by dividing the reference voltage by the resistance value of the reference resistor RA always flows through the reference resistor RA and the input transistor QE. Become.

The collector of the input transistor QE is connected to a power supply VCC via two PNP transistors QA and QC.
It is connected to the. That is, the emitter of the transistor QA is connected to the power supply VCC, and the collector of the transistor QA is connected to the emitter of the transistor QC. The collector of the transistor QC is connected to the collector of the transistor QE.

The base of the transistor QA is PN
The base of the transistor QC is connected to the base of the P-type transistor QB, and the base of the transistor QC is connected to the base of the PNP-type transistor QD. The transistor QB has an emitter connected to the power supply VCC, and a collector connected to the emitter of the transistor QD. The collector-base of the transistor QB and the collector-base of the transistor QC are short-circuited. Therefore, the transistors QA and QB and the transistors QC and QD
Each constitutes a current mirror. That is, the current flowing through the transistor QE is
, And the same current flows through the transistors QD and QB.

Therefore, the same constant current I0 as the current flowing from transistor QD to the transistor QE flows from the collector of transistor QD.
Is output.

As described above, in this embodiment, a two-stage current mirror is used to output the same current as the current flowing through the input transistor QE. As a result, the accuracy of the current mirror is increased and the accuracy of the output current (constant current I0) can be increased as compared with the case of one stage.

Further, in this embodiment, the transistor Q
The sizes of A to QE are increased. That is,
The size of these transistors QA to QE is eight times as large as the size of transistors normally used inside the IC. As a result, the accuracy of the current mirror circuit is improved, and even when the voltage of the power supply VCC changes by about 8 to 15 V, the variation of the output constant current can be suppressed to about ± 0.5%.

Next, FIG. 2 shows the configuration of the reference voltage generating circuit 10 in the present embodiment. The startup circuit 20 outputs a voltage that rises to a predetermined potential when the power supply voltage rises, and then returns to the ground. The output of this starting circuit is
It is connected to the base of NPN transistor Q1. A transistor Q2 is connected in parallel to the transistor Q1. That is, the collectors and the emitters of the transistors Q1 and Q2 are commonly connected. The emitters of the transistors Q1 and Q2 are connected to a resistor R1.
And the collector is connected to the collector of the PNP transistor Q3.

Therefore, when the power supply rises, the transistor Q1 turns on, a current flows through the transistor Q3, and thereafter the transistor Q2 keeps turning on, so that the current determined by the resistor R1 is changed by the transistors Q3, Q3.
Flow to 4.

The emitter of the transistor Q3 has a power supply VCC.
And the collector and base are short-circuited. The emitter of the transistor Q3 also has a power supply VC.
The base of a PNP transistor Q4 connected to C is connected, and the transistors Q3 and Q4 form a current mirror.

The collector of the transistor Q4 is connected to the collector of an NPN transistor Q5 whose collector and base are short-circuited. The emitter of the transistor Q5 is connected to the emitter of a PNP transistor Q6 whose collector is connected to ground. Have been. Therefore, the current flowing through the transistor Q4 flows through the transistors Q5 and Q6.

The base of transistor Q6 is connected to the collector of PNP transistor Q7, and the emitter of transistor Q7 is connected to the base of transistor Q2. The base of the transistor Q7 has an emitter connected to the base of the transistor Q2 and the base of a PNP transistor Q8 whose collector and emitter are short-circuited. Therefore, transistors Q7 and Q8 constitute a current mirror.

The collector of the transistor Q7 and the base of the transistor Q6 are connected to the collector of an NPN transistor Q9. The emitter of the transistor Q9 is connected to the ground via the resistor R3. The collector of the transistor Q8 is connected to the collector of the NPN transistor Q10. The emitter of the transistor Q10 is connected to the emitter of the transistor Q9 via the resistor R2. The base of the transistor Q9 is connected to the base of the transistor Q10.

The base of the transistor Q5 has N
The base of the PN transistor Q11 is connected, the collector of the transistor Q11 is connected to the power supply VCC, and the emitter is connected to the ground via the resistor r7. Further, the emitter of the transistor Q11 is connected to the base of the transistor Q2 and serves as the output reference voltage VR.

The output reference voltage VR, which is the emitter of the transistor Q11, is connected to ground via a series connection of resistors R4, R5, R6. The connection point between the resistors R5 and R6 is connected to the bases of the transistors Q9 and Q10. Furthermore, zapping diodes D1 and D2 are connected in parallel to the resistors R4 and R5, respectively, so as to block current to the ground.

The zapping diodes D1 and D2
The pad A is connected to the connection point of the resistors R4 and R5, the pad B is connected to the bases of the transistors Q9 and Q10 which are the anode terminals of the zapping diode D2, and the output reference which is the cathode terminal of the zapping diode D1. The pad C is connected to the voltage VR. Therefore, by applying a desired voltage to the pads A, B, and C, a desired voltage can be separately applied to the zapping diodes D1 and D2, and the desired zapping diodes D1 and D2 can be zapped.

In such a circuit, the transistor Q
9 and a current corresponding to the difference between VBEs of Q10 flows through the resistor R2, and this current flows through the transistors Q8, Q7 and Q9,
As a result, the base potential V of the transistors Q9 and Q10
0 is determined. Then, for this voltage V0, the resistance R
The voltage determined by the resistance division of R4, R5, and R6 becomes the output reference voltage VR.

When the output reference voltage VR rises, the base potential of the transistor Q9 rises, the collector potential of the transistor Q9 falls, and accordingly, the base and emitter potentials of the transistor Q6 fall. And
The base potential of the transistor Q5 decreases, the base potential of the transistor Q11 decreases, and the output reference voltage VR decreases, and is kept constant. On the other hand, when the output reference voltage VR decreases, the transistor Q
9, the base potential of the transistor Q9 rises, and the base potential of the transistor Q6 and the emitter potential of the transistor Q6 rise accordingly. Then, the base battery of the transistor Q5 rises, the base potential of the transistor Q11 rises, and the output reference voltage VR rises and is kept constant.

Here, the output reference voltage VR of this circuit is determined by the ratio of the resistors R4, R5 and R6. That is, it is determined by the output reference voltage VR = V0 (R4 + R5 + R6) / R6. On the other hand, the zapping diodes D1 and D2 are diodes that are zapped and short-circuited by applying a predetermined + potential to the cathode and a predetermined − potential to the anode. Therefore, by controlling the potentials of the pads A, B and C arbitrarily, the zapping diode D
1, D2 can be arbitrarily brought into a short state.

Therefore, the zapping diodes D1, D2
, One or both of the resistors R4 and R5 can be short-circuited. Therefore, (i) both ends of the resistor R4 are short-circuited, (ii) both ends of the resistor R5 are short-circuited, (i)
v) The four states of both ends of the resistors R4 and R5 can be formed by zapping.

Therefore, the voltage of the output reference voltage VR can be adjusted in four stages by zapping, and the output reference voltage VR can be controlled to a desired level.

Thus, in the case without zapping,
Variation range of about 3%, variation range ± 1%
Within.

As described above, by increasing the transistor size of the mirror circuit constituting the hand current output to about eight times the normal case, the variation of the constant current circuit can be reduced to within ± 1.5%, and It can be smaller than about ± 2%. Thus, the variation of the entire constant current circuit including the reference voltage generating circuit can be kept within ± 2.5%.

When such a circuit of the present embodiment is used for a current detection circuit of a secondary circuit of a charger, the detection accuracy is dramatically improved, and the performance as a set of the charger is improved. Can be. Further, conventionally, as a means for obtaining a high-precision constant current, a power supply IC and a discrete transistor circuit have been used. However, according to the circuit of the present embodiment, the IC can be integrated into one chip, and the reliability of the set can be improved. Improvement, cost reduction, and downsizing can be achieved.

[0035]

As described above, by zapping the zapping diode, the output reference voltage can be adjusted arbitrarily. Further, by using this reference voltage generation circuit, the accuracy of the output constant current can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a constant current circuit.

FIG. 2 is a diagram illustrating a configuration of a reference voltage generation circuit.

[Explanation of symbols]

10 reference voltage generating circuit, 20 starting circuit, QA to Q
E, Q1 to 11 transistors, RA, R1 to R7 resistors.

Claims (5)

[Claims] 1. A reference voltage generating circuit for generating a constant reference voltage, comprising: a resistor for determining an output reference voltage, wherein at least two resistors are connected in series; A zapping diode connected in parallel; and a pad for applying a voltage to the zapping diode. The zapping of the zapping diode by applying a voltage from the pad changes the resistance value of the reference resistor to output voltage value. A reference voltage generation circuit that can be changed. 2. The circuit according to claim 1, wherein at least three of both ends and an intermediate portion of the reference resistor are connected to independent pads, and a desired zapping is performed by adjusting a voltage between the pads. Reference voltage generation circuit that can perform 3. A constant current circuit for generating a constant current using a reference voltage from the reference voltage generation circuit according to claim 1. 4. The circuit according to claim 3, wherein the reference voltage is input to a control terminal of an input transistor through a positive input terminal of an operational amplifier, and a connection point between the input transistor and a reference resistor through which a current of the input transistor flows. Is fed back to the operational amplifier, and a constant current is applied to the reference resistor according to the reference voltage by maintaining a potential at a connection point between the input transistor and the reference resistor at a reference voltage, and the constant current is output via a current mirror. Constant current circuit. 5. The constant current circuit according to claim 4, wherein the transistors used for the input transistor and the current mirror are larger in size than the transistors used for the operational amplifier.