JP4213459B2 - Constant current generating circuit and constant current setting method of the constant current generating circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a constant current generation circuit with low temperature dependency, and more particularly to a constant current generation circuit capable of improving accuracy with respect to a target current value by trimming and a constant current setting method for the constant current generation circuit.
[0002]
[Prior art]
The performance required for the constant current generating circuit is high in accuracy with respect to the target current value, is not affected by fluctuations in temperature and power supply voltage, and it is also important that all the circuits are easily integrated on one chip. The desired constant current can be created by applying the threshold voltage of a constant current diode or FET. However, when obtaining a certain level of performance, the output voltage of the constant voltage circuit is converted into a voltage-current converter. Generally, it is converted into current by a circuit.
For example, by converting a threshold voltage difference between two transistors with a resistor, and then converting the obtained current into a current-voltage with the same type of resistor, a threshold having a small temperature dependency is obtained. There is a circuit that obtains a reference voltage by amplifying a value voltage difference (see, for example, Patent Document 1).
[0003]
On the other hand, in recent years, as a constant voltage circuit, a band gap regulator having a small temperature dependency and suitable for an integrated circuit is often used. For example, by monitoring the forward voltage with a band gap type reference voltage that uses the forward voltage of the resistor and the pn junction, the magnification applied to the thermal voltage is adjusted by trimming the resistor, and the temperature characteristics of the reference voltage are adjusted. There was a reference voltage circuit to be corrected (see, for example, Patent Document 2).
[0004]
FIG. 2 is a circuit diagram showing an example of a conventional constant current generation circuit using such a constant voltage circuit and a voltage-current conversion circuit.
The constant current generation circuit 100 in FIG. 2 converts the output voltage Vo of the band gap regulator 101, for example, about 1.25 V into a constant current by the voltage-current conversion circuit 102, and outputs the constant current. The band gap regulator 101 is well known, and the description of its operation is omitted here.
[0005]
In the voltage-current conversion circuit 102, the voltage across the resistor 123 is controlled to be the same value as the output voltage Vo of the constant voltage circuit 101 by the operational amplifier 121 and the NMOS transistor 122. Therefore, a current (Vo / R123) obtained by dividing the output voltage Vo of the constant voltage circuit 101 by the resistance value R123 of the resistor 123 flows through the resistor 123. The current becomes the drain current of the NMOS transistor 122 and is output from the drain of the PMOS transistor 125 via the PMOS transistors 124 and 125 constituting the current mirror circuit.
[0006]
As described above, since the output current Io from the voltage-current conversion circuit 102 is determined by the output voltage Vo of the constant voltage circuit 101 and the resistance value of the resistor 123, in order to set the constant current Io to a target value. It can be seen that the output voltage Vo of the constant voltage circuit 101 may be adjusted or the resistance value of the resistor 123 may be adjusted. However, since the output voltage Vo of the constant voltage circuit 101 is a physically determined value, the resistance value of the resistor 123 is usually set by trimming.
[0007]
As the trimming method for the resistor 123, the output current Io is measured and the trimming amount is determined from the deviation from the target value, and the resistor 123 is trimmed while the output current Io is measured. There was a so-called function trimming that ended trimming when the value was reached.
[0008]
[Patent Document 1]
JP 7-44255 A [Patent Document 2]
Japanese Patent Laid-Open No. 2002-91589
[Problems to be solved by the invention]
However, the former trimming method described above can be performed in a short time, but if the amount of deviation between the output current Io and the target value is large, the trimming accuracy deteriorates. Therefore, when the deviation amount is large, the output current Io can be set to a desired target value by repeating the same trimming twice or three times with a little trimming amount in order to improve accuracy. There is a problem that the time required for trimming becomes long.
[0010]
The latter trimming method described above has a problem that the adjustment accuracy of the output current Io is high, but it takes time for trimming, and a dedicated trimming device is required for function trimming. Furthermore, even if the resistor 123 is trimmed and the resistance value is adjusted to the optimum value, the resistance value of the resistor 123 changes depending on the temperature, so that there is a problem that the output current Io changes. In addition, when the constant voltage circuit 101 and the voltage-current conversion circuit 102 are integrated in an IC, the resistor 123 formed in the integrated circuit usually has temperature dependence, and therefore the constant voltage circuit 101 has a small temperature dependence band. Even if the gap regulator is used, the output current Io has temperature dependency, and there is a problem that an accurate constant current output cannot be obtained.
[0011]
The present invention has been made in order to solve the above-described problems. By canceling the change in the constant current output due to the temperature dependence of the resistance built in the integrated circuit, the present invention has a constant temperature dependence. An object is to obtain a current generation circuit and a constant current setting method for the constant current generation circuit.
[0012]
[Means for Solving the Problems]
A constant current generation circuit according to the present invention generates a constant voltage from a power supply voltage of a DC power source and outputs the constant voltage circuit section formed by a band gap reference, and a constant voltage output from the constant voltage circuit section. In a constant current generation circuit including a voltage-current conversion circuit unit that converts a voltage into a current and outputs a predetermined constant current,
The constant voltage circuit unit is:
A first operational amplifier for outputting the predetermined constant voltage;
A first resistor circuit that generates a combined resistor with a plurality of resistors and that receives the output voltage of the first operational amplifier at one end;
A first resistor and a first diode connected between the other end of the first resistor circuit and the negative power supply voltage of the DC power supply are connected in series, and the first resistor and the first diode A second series circuit connected between the first series circuit connected to one input terminal of the first operational amplifier and the other end of the first resistor circuit and the negative power supply voltage of the DC power supply; A second series circuit in which a resistor, a third resistor, and a second diode are connected in series, and a connection portion of the second resistor and the third resistor is connected to the other input terminal of the first operational amplifier;
With
The voltage-current conversion circuit unit is
A current supply circuit that outputs a constant voltage output from the constant voltage circuit unit and outputs a current corresponding to the constant voltage;
A second resistor circuit configured to generate a combined resistor by a plurality of resistors, to which a constant voltage output from the constant voltage circuit unit is applied and a current corresponding to the constant voltage is supplied by the current supply circuit;
An output circuit for outputting a current corresponding to the current flowing through the second resistance circuit;
With
The second resistance circuit includes the plurality of resistors and a plurality of fuses, and a current corresponding to a constant voltage from the constant voltage circuit unit is set so that an output current from the output circuit has a desired value. Each fuse is selectively cut so as to flow through the combined resistance of the second resistance circuit.
[0013]
Specifically, the first resistance circuit includes the plurality of resistors and the plurality of fuses, and each fuse is selectively configured to have a temperature characteristic that cancels the temperature characteristic of the voltage-current conversion circuit unit. I was cut off.
[0014]
The second resistor circuit may include a switch circuit that performs switching according to a control signal input from the outside and changes a combined resistance of the second resistor circuit.
[0015]
On the other hand, the current supply circuit is
A second operational amplifier in which a constant voltage from the constant voltage circuit unit is input to one input terminal;
A control signal input terminal connected to the output terminal of the second operational amplifier, and a transistor for supplying a current from a DC power source to the second resistor circuit;
With
The other input terminal of the second operational amplifier is connected to the input terminal of the second resistance circuit to which the current from the transistor is input.
[0016]
Further, the constant current setting method according to the present invention includes a plurality of resistors and a plurality of fuses, and the output voltage changes according to the combined resistance of the first resistor circuit set by selectively cutting the fuses. A constant voltage circuit section formed by a band gap reference that generates and outputs a predetermined constant voltage from a power supply voltage of a DC power supply, and has a plurality of resistors and a plurality of fuses, and is set by selectively cutting the fuses The constant voltage output from the constant voltage circuit unit is converted into a current by outputting a constant current corresponding to the current flowing through the combined resistor of the second resistance circuit to which the output voltage from the constant voltage circuit unit is applied. A voltage-current conversion circuit unit that outputs a predetermined constant current, and the voltage-current conversion circuit unit performs switching in accordance with an externally input control signal to synthesize the second resistance circuit. In the constant current method of setting the constant current generating circuit having a switching circuit for changing anti a,
Switching the switch circuit;
Measure the output current of the voltage-current conversion circuit unit for each combined resistance of the second resistance circuit according to the switching,
From the output current value of the voltage-current conversion circuit unit measured for each combined resistance value of the second resistance circuit, an approximate calculation is performed to obtain a characteristic indicating the relationship between the combined resistance and the output current. ,
From the obtained characteristics, a combined resistance value of the second resistance circuit with respect to a desired output current value is obtained.
[0017]
Further, the temperature characteristic of the combined resistance of the second resistance circuit with respect to the desired output current value is obtained,
Determining a combined resistance of the first resistance circuit that cancels the obtained temperature characteristic;
Selectively disconnecting the fuse of the first resistance circuit so as to obtain the resultant combined resistance;
Switching the switch circuit;
Measure the output current of the voltage-current conversion circuit unit for each combined resistance of the second resistance circuit according to the switching,
From the output current value of the voltage-current conversion circuit unit measured for each combined resistance value of the second resistance circuit, an approximate calculation is performed to obtain a characteristic indicating the relationship between the combined resistance and the output current. ,
From the obtained characteristics, a combined resistance value of the second resistance circuit with respect to a desired output current value is obtained,
The fuse of the second resistor circuit is selectively cut so that the combined resistance of the second resistor circuit becomes the obtained combined resistance value.
[0018]
Specifically, the output current of the voltage-current conversion circuit unit is measured for each of the three types of combined resistors of the second resistor circuit according to the switching of the switch circuit, and the three types of combined of the second resistor circuit are measured. From the output current value of the voltage-current conversion circuit unit measured for each resistance value, an approximate calculation may be performed to obtain a characteristic that forms a quadratic curve indicating the relationship between the combined resistance and the output current. Good.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Next, the present invention will be described in detail based on the embodiments shown in the drawings.
First embodiment.
FIG. 1 is a circuit diagram showing an example of a constant current generating circuit according to the first embodiment of the present invention.
In FIG. 1, a constant current generating circuit 1 includes a constant voltage circuit 2 constituting a band gap reference, a voltage-current conversion circuit 3 that converts a constant voltage Vo1 output from the constant voltage circuit 2 into a current, and outputs the current. It consists of The constant voltage circuit 2 forms a constant voltage circuit unit, and the voltage-current conversion circuit 3 forms a voltage-current conversion circuit unit. The constant voltage circuit 2 and the voltage-current conversion circuit 3 are operated by the power source supplied from the DC power source 5, and the current output from the voltage-current conversion circuit 3 becomes the output current Io 1 of the constant current generation circuit 1.
[0020]
The constant voltage circuit 2 includes an operational amplifier 11, pnp transistors 12 and 13, resistors A1 to Am (m is an integer of m> 1), 14 to 16, and fuses FA1 to FAm. The operational amplifier 11 is the first operational amplifier, the resistors A1 to Am and the fuses FA1 to FAm are the first resistor circuit, the pnp transistor 12 and the resistor 14 are the first series circuit, and the pnp transistor 13 and the resistors 15 and 16 are the resistors. Each of the second series circuits is formed. The pnp transistor 12 forms a first diode, and the pnp transistor 13 forms a second diode.
[0021]
Between the output terminal of the operational amplifier 11 and the negative power supply voltage GND of the DC power supply 5, there are a series circuit in which resistors A1 to Am are connected in series, and a series circuit in which the resistor 14 and the pnp transistor 12 are connected in series. Connected in series. Corresponding fuses FA1 to FAm are connected in parallel to the resistors A1 to Am, respectively, and a series circuit of the resistors 15 and 16 and the pnp transistor 13 is connected in parallel to the series circuit of the resistor 14 and the pnp transistor 12.
[0022]
The connection b between the resistor 14 and the pnp transistor 12 is connected to the non-inverting input terminal of the operational amplifier 11, and the connection c between the resistors 15 and 16 is connected to the inverting input terminal of the operational amplifier 11. A connection portion of the resistor Am, the fuse FAm, and the resistors 14 and 15 is defined as a connection portion a. In the pnp transistor 12, the base is connected to the collector, and in the pnp transistor 13, the base is connected to the collector, and the pnp transistors 12 and 13 each form a diode. The voltage output from the output terminal of the operational amplifier 11 forms the output voltage Vo1 of the constant voltage circuit 2.
[0023]
Next, the voltage-current conversion circuit 3 includes an operational amplifier 21, NMOS transistors 22 to 24, PMOS transistors 25 and 26, resistors B1 to Bn (n is an integer of n> 1), 27 to 29, and fuses FB1 to FBn. It consists of The operational amplifier 21 and the NMOS transistor 24 constitute a current supply circuit, the PMOS transistors 25 and 26 constitute an output circuit, the NMOS transistors 22 and 23, the resistors B1 to Bn and the fuses FB1 to FBn constitute a second resistor circuit, respectively. Transistors 22 and 23 form a switch circuit.
The output voltage Vo 1 of the constant voltage circuit 2 is input to the non-inverting input terminal of the operational amplifier 21, and the output terminal of the operational amplifier 21 is connected to the gate of the NMOS transistor 24.
[0024]
The PMOS transistors 25 and 26 form a current mirror circuit, each gate is connected and connected to the drain of the PMOS transistor 25, and each source of the PMOS transistors 25 and 26 is respectively a positive power supply voltage of the DC power supply 5. Vbat is applied. An NMOS transistor 24 and resistors B1 to Bn and 27 to 29 are connected in series between the drain of the PMOS transistor 25 and the negative power supply voltage GND of the DC power supply 5, and corresponding to the resistors B1 to Bn. The fuses FB1 to FBn are connected in parallel.
[0025]
An NMOS transistor 22 is connected in parallel to the series circuit of the resistor 28 and the resistor 29, and an NMOS transistor 23 is connected in parallel to the resistor 29. An external control signal S 1 is input to the gate of the NMOS transistor 22, and an external control signal S 2 is input to the gate of the NMOS transistor 23. The current output from the drain of the PMOS transistor 26 forms the output current Io1.
[0026]
In such a configuration, the voltage-current conversion circuit 3 will be described.
The resistors B1 to Bn are trimming resistors, and trimming fuses FB1 to FBn are connected in parallel to each resistor.
The NMOS transistor 22 constituting the switch circuit is turned on when a high level signal is inputted to the gate, the connection part of the resistor 27 and the resistor 28 is connected to the negative power supply voltage GND, and the source and the negative side of the NMOS transistor 24 are connected. The combined resistance value α with the power supply voltage GND can be reduced. Similarly, the NMOS transistor 23 forming the switch circuit is connected between a connection portion between the resistor 28 and the resistor 29 and the negative power supply voltage GND, and is turned on when a high level signal is input to the gate. And the resistance 29 can be connected to the negative power supply voltage GND to reduce the combined resistance value α.
[0027]
By the operational amplifier 21 and the NMOS transistor 24, the source voltage of the NMOS transistor 24 is controlled to be the same as the output voltage Vo1 of the constant voltage circuit 2. Therefore, a current (Vo1 / α) obtained by dividing the output voltage Vo1 of the constant voltage circuit 2 by the combined resistance value α flows through the resistance group of the resistors B1 to Bn and 27 to 29 of the voltage-current conversion circuit 3. The current becomes a drain current of the NMOS transistor 24 and is output from the drain of the PMOS transistor 26 via the PMOS transistors 25 and 26.
[0028]
Here, when the resistance values of the resistors B1 to Bn are RB1 to RBn and the resistance values of the resistors 27 to 29 are R27 to R29, the combined resistance value α before trimming is (R27 + R28 + R29). Now, the output current Io1 when the NMOS transistors 22 and 23 are both off is expressed by the following equation (1).
Io1 = Vo1 / (R27 + R28 + R29) (1)
[0029]
Next, the output current Io1 when the NMOS transistor 22 is off and the NMOS transistor 23 is on is expressed by the following equation (2).
Io1 = Vo1 / (R27 + R28) ............ (2)
The output current Io1 when the NMOS transistor 22 is turned on is expressed by the following equation (3).
Io1 = Vo1 / (R27) ………… (3)
[0030]
Approximate the combined resistance value α for obtaining the target output current Io1 from each output current Io1 of the above formulas (1) to (3) and the combined resistance value α at that time, and turn on / off the NMOS transistors 22 and 23. And the fuses FB1 to FBn to be cut by trimming are determined.
Thus, using the two NMOS transistors 22 and 23, the respective output currents Io1 for the three types of combined resistance value α are measured, and a quadratic curve showing the relationship between the combined resistance value α and the output current Io1 is obtained. Obtainable. Therefore, the non-linear portion of the NMOS transistor 24 can be compensated, and the combined resistance value α for obtaining the desired output current Io1 can be obtained from the quadratic curve.
[0031]
For example, when the output current Io1 is used in a switching frequency generation circuit of a DC-DC converter, the switching frequency is measured for each combination of on / off of the NMOS transistors 22 and 23, and the switching frequency and the combined resistance value α are calculated. By performing the approximate calculation, it is possible to compensate for the non-linearity generated in the portion where the switching frequency is generated from the output current Io1. Needless to say, when sufficient accuracy can be obtained by linear approximation, one of the NMOS transistors 22 and 23 is deleted to make two types of measurement points of the combined resistance value α and the output current Io1, and the approximation calculation is simplified. May be.
[0032]
On the other hand, when the voltage-current conversion circuit 3 is integrated in an IC, each of the resistance elements constituting the resistors B1 to Bn and 27 to 29 has temperature dependence, and the output current Io1 is targeted by the above method. Even if the fuses FB1 to FBn are trimmed so as to have a current value, they may deviate from the target current value due to a temperature change. When P-type polysilicon resistors are used for the resistors RB1 to RBn and 27 to 29, the temperature coefficient is about 600 ppm / ° C. That is, when the P-type polysilicon resistor is used, the output current Io1 varies by 0.6% every time the temperature changes by 1 ° C. For example, when used in a portable device, the temperature change must be 60 ° C. or more because it must correspond to a temperature range exceeding 40 ° C. from below freezing point. If the temperature change is 60 ° C., the fluctuation of the output current Io1 is 3.6%, which deviates from the target current value depending on the application.
[0033]
Therefore, the output voltage Vo1 of the constant voltage circuit 2 input to the voltage-current conversion circuit 3 is made temperature dependent so as to cancel the temperature coefficients of the resistors B1 to Bn and 27 to 29 of the voltage-current conversion circuit 3. You can do it.
Here, the output voltage Vo1 of the operational amplifier 11 is derived.
The base-emitter voltage of the pnp transistor 12 is set to VBE1, the base-emitter voltage of the pnp transistor 13 is set to VBE2, and the resistance values of the resistors 14 and 15 are made the same.
[0034]
The connection part b and the connection part c in FIG. 1 are connected to the two input terminals of the operational amplifier 11 and thus have the same voltage. Further, since the resistor 14 and the resistor 15 are commonly connected at the connection part a, the voltages at both ends of the resistor 14 and the resistor 15 are equal. That is, the collector currents Ic of the pnp transistors 12 and 13 are equal to each other, and the collector currents Ic are expressed by the following equation (4).
Ic = Is * exp {q / (k * T)} * VBE1
= N * Is * exp {q / (k * T)} * VBE2 (4)
In the equation (4), N is the emitter area ratio between the pnp transistor 12 and the pnp transistor 13, Is is the saturation current of the pnp transistor 12 and the pnp transistor 13, k is the Boltzmann constant, and q is the charge of the electrons. The quantity, T, is absolute temperature.
[0035]
From the equation (4), the base-emitter voltages VBE1 and VBE2 can be expressed by the following equations (5) and (6).
VBE1 = (k × T) / q × ln (Ic / Is) (5)
VBE2 = (k × T) / q × ln {Ic / (N × Is)} (6)
[0036]
Also, assuming that the resistance values of the resistors 14 to 16 are R14 to R16, VBE1 = Ic × R16 + VBE2.
(k × T) / q × ln (Ic / Is) = Ic × R16 + (k × T) / q × ln (Ic / N × Is) (7)
When Ic is obtained from the equation (7), the following equation (8) is obtained.
Ic = (k × T) / q × ln (N) / R16 (8)
[0037]
From the above results, assuming that the combined resistance value between the output terminal of the operational amplifier 11 and the connection part a is β, the output voltage Vo1 of the operational amplifier 11 is expressed by the following equation (9).
Vo1 = VBE1 + Ic × R14 + 2 × Ic × β
= VBE1 + Ic × (R14 + 2 × β)
= VBE1 + (R14 + 2 × β) × (k × T) / q × ln (N) / R16 (9)
[0038]
The resistors A1 to Am and 14 to 16 are made of high resistance polysilicon and have a temperature coefficient of about −2300 ppm / ° C., and the equation (9) is VBG / (1−KT × T). By setting the resistors A1 to Am and 14 to 16 so as to satisfy the above, the temperature dependence of the voltage-current conversion circuit 3 can be canceled. VBG is a voltage corresponding to the energy band gap, and KT is a temperature coefficient of the combined resistance value α.
[0039]
Next, a trimming procedure for the fuses FA1 to FAm of the constant voltage circuit 2 and the fuses FB1 to FBn of the voltage-current conversion circuit 3 will be described.
First, before trimming the fuses FB1 to FBn, the NMOS transistors 22 and 23 of the voltage-current conversion circuit 3 are alternately turned on / off, and an approximate calculation is performed to perform the combined resistance value α and the output current Io1. And a combined resistance value α for the desired output current Io1 is obtained from the obtained quadratic curve. From the obtained combined resistance value α, a fuse to be cut is selected from the fuses FB1 to FBn. Of the fuses FA1 to FAm, the fuse to be cut is selected and trimmed so as to cancel the temperature coefficient of the combined resistance value α of the resistor to which the selected fuse is connected and the resistors 27 to 29.
[0040]
When the selected fuse of the fuses FA1 to FAm is cut, the output voltage Vo1 of the constant voltage circuit 2 slightly changes, so that the NMOS transistors 22 and 23 of the voltage-current conversion circuit 3 are alternately turned on / off again, An approximate calculation is performed to obtain a quadratic curve indicating the relationship between the combined resistance value α and the output current Io1, and the combined resistance value α for the desired output current Io1 is obtained from the obtained quadratic curve. From the obtained combined resistance value α, a fuse to be cut is selected from the fuses FB1 to FBn and trimmed to cut. The constant current generating circuit according to the first embodiment can obtain a highly accurate constant current generating circuit with low temperature dependence by trimming the fuses FA1 to FAm and FB1 to FBn in such a procedure. it can.
[0041]
【The invention's effect】
As is clear from the above description, according to the constant current generation circuit of the present invention, the temperature characteristic of the voltage-current conversion circuit unit can be offset by providing the first resistance circuit of the constant voltage circuit unit with the temperature characteristic. Therefore, even when the IC is used and a resistor having a small temperature coefficient cannot be used in the voltage-current conversion circuit unit, a highly accurate and stable constant current can be generated and output.
[0042]
According to the constant current setting method of the present invention, the approximate calculation is performed from the output current value of the voltage-current conversion circuit unit for each combined resistance value of the second resistance circuit obtained by switching the switch circuit. Thus, the characteristic indicating the relationship between the combined resistance of the second resistance circuit and the output current is obtained, and the combined resistance value of the second resistance circuit with respect to the desired output current value is obtained from the obtained characteristics. Therefore, before trimming and cutting the desired fuse, the combined resistance value of the second resistor circuit can be obtained, the fuse to be cut can be selected, and high-precision constant current setting can be performed in a short time. It can be carried out.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an example of a constant current generating circuit according to a first embodiment of the present invention.
FIG. 2 is a circuit diagram showing an example of a conventional constant current generating circuit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Constant current generation circuit 2 Constant voltage circuit 3 Voltage-current conversion circuit 5 DC power supply 11, 21 Operational amplifier 12, 13 pnp transistors 22-24 NMOS transistors 25, 26 PMOS transistors A1-Am, B1-Bn, 14-16, 27 to 29 Resistors FA1 to FAm, FB1 to FBn Fuse

Claims (7)

A constant voltage circuit unit formed by a band gap reference that generates and outputs a predetermined constant voltage from a power supply voltage of a DC power supply, and the constant voltage output from the constant voltage circuit unit is converted into a current and converted into a predetermined constant voltage. In a constant current generation circuit including a voltage-current conversion circuit unit that outputs current,
The constant voltage circuit unit is:
A first operational amplifier for outputting the predetermined constant voltage;
A first resistor circuit that generates a combined resistor with a plurality of resistors and that receives the output voltage of the first operational amplifier at one end;
A first resistor and a first diode connected between the other end of the first resistor circuit and the negative power supply voltage of the DC power supply are connected in series, and the first resistor and the first diode A first series circuit having a connection portion connected to one input terminal of the first operational amplifier;
A second resistor, a third resistor and a second diode connected between the other end of the first resistor circuit and the negative power supply voltage of the DC power supply are connected in series, and the second resistor and the second resistor A second series circuit in which a connection with three resistors is connected to the other input terminal of the first operational amplifier;
With
The voltage-current conversion circuit unit is
A current supply circuit that outputs a constant voltage output from the constant voltage circuit unit and outputs a current corresponding to the constant voltage;
A second resistor circuit configured to generate a combined resistor by a plurality of resistors, to which a constant voltage output from the constant voltage circuit unit is applied and a current corresponding to the constant voltage is supplied by the current supply circuit;
An output circuit for outputting a current corresponding to the current flowing through the second resistance circuit;
With
The second resistance circuit includes the plurality of resistors and a plurality of fuses, and a current corresponding to a constant voltage from the constant voltage circuit unit is set so that an output current from the output circuit has a desired value. A constant current generating circuit, wherein each fuse is selectively cut so as to flow through a combined resistor of a second resistor circuit. The first resistance circuit includes a plurality of resistors and a plurality of fuses, and each fuse is selectively cut so as to have a temperature characteristic that cancels a temperature characteristic of the voltage-current conversion circuit unit. The constant current generating circuit according to claim 1. 3. The constant current generation circuit according to claim 2, wherein the second resistance circuit includes a switch circuit that performs switching according to a control signal input from the outside and changes a combined resistance of the second resistance circuit. The current supply circuit includes:
A second operational amplifier in which a constant voltage from the constant voltage circuit unit is input to one input terminal;
A control signal input terminal connected to the output terminal of the second operational amplifier, and a transistor for supplying a current from a DC power source to the second resistor circuit;
With
4. The constant current generation circuit according to claim 2, wherein the other input terminal of the second operational amplifier is connected to an input terminal of the second resistance circuit to which a current from the transistor is input. A predetermined constant voltage is generated from the power supply voltage of the DC power supply, which is composed of a plurality of resistors and a plurality of fuses, and the output voltage changes according to the combined resistance of the first resistor circuit set by selectively cutting the fuses A constant voltage circuit unit formed by a bandgap reference to be output and a plurality of resistors and a plurality of fuses, and the output voltage from the constant voltage circuit unit is set by selectively cutting the fuses A voltage-current conversion circuit that outputs a constant current according to the current flowing through the combined resistance of the second resistance circuit, converts the constant voltage output from the constant voltage circuit section into a current, and outputs a predetermined constant current And the voltage-current conversion circuit unit has a switching circuit that switches according to a control signal input from the outside and changes a combined resistance of the second resistance circuit. In the constant current setting method of generating circuit,
Switching the switch circuit;
Measure the output current of the voltage-current conversion circuit unit for each combined resistance of the second resistance circuit according to the switching,
From the output current value of the voltage-current conversion circuit unit measured for each combined resistance value of the second resistance circuit, an approximate calculation is performed to obtain a characteristic indicating the relationship between the combined resistance and the output current. ,
A constant current setting method characterized in that a combined resistance value of the second resistance circuit with respect to a desired output current value is obtained from the obtained characteristics. Obtaining a temperature characteristic of the combined resistance of the second resistance circuit with respect to the desired output current value;
Determining a combined resistance of the first resistance circuit that cancels the obtained temperature characteristic;
Selectively disconnecting the fuse of the first resistance circuit so as to obtain the resultant combined resistance;
Switching the switch circuit;
Measure the output current of the voltage-current conversion circuit unit for each combined resistance of the second resistance circuit according to the switching,
From the output current value of the voltage-current conversion circuit unit measured for each combined resistance value of the second resistance circuit, an approximate calculation is performed to obtain a characteristic indicating the relationship between the combined resistance and the output current. ,
From the obtained characteristics, a combined resistance value of the second resistance circuit with respect to a desired output current value is obtained,
6. The constant current setting method according to claim 5, wherein the fuse of the second resistance circuit is selectively cut so that the combined resistance of the second resistance circuit becomes the obtained combined resistance value. The output current of the voltage-current conversion circuit unit for each of the three types of combined resistors of the second resistor circuit corresponding to the switching of the switch circuit is measured, and the three types of combined resistance values of the second resistor circuit are measured. 6. The characteristic of forming a quadratic curve indicating the relationship between the combined resistance and the output current is obtained by performing an approximate calculation from the output current value of the voltage-current conversion circuit unit measured respectively. 6. The constant current setting method according to 6.

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