JPH0219909A - Constant current circuit - Google Patents

Abstract

PURPOSE:To realize the reduction of the parts cost and the control manhour and at the same time to attain the control with high accuracy for a constant current circuit by providing a means which divides the reference voltage. CONSTITUTION:A voltage dividing circuit D consists of the resistances R1-R4 having different resistance values, and the switches 12-14. The switches 12-14 are turned on and off by the set inputs 9-11. For instance, the reference voltage serves directly as the plus input voltage of an OP amplifier 2 when the switches 12-14 are kept off. At the same time, the output current is equal to a constant current of about (voltage of reference voltage source 1)/(value of resistance 10). Then the switch 12 is turned on when the input 9 is turned on, and the reference voltage is divided by the resistances R1 and R2 and applied to the plus input of the amplifier 2. Thus it is possible to attain the reduction of the parts cost and the control manhour and also to perform the control with high accuracy for a constant current circuit.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to constant current circuits.

[Prior Art] Devices that require constant operation, such as camera shutters, are often driven by constant voltage and/or constant current circuits, regardless of the power supply voltage, especially those that require precision. As shown in FIG. 5, the one shown in FIG. 5 is conventionally known.

In the figure, reference numeral 1 indicates a reference voltage, which is applied to the positive terminal of an OP amplifier 2 serving as comparison means. A switch 4 is connected between the base of a transistor 5 serving as a control means and the output terminal of the OP amplifier 2, and is controlled to be 0N10FF by a control signal 3. The transistor 5 has a collector connected to a power source 8 via a load 7, an emitter connected to ground via a variable resistor 6, and also connected to a negative terminal of the OP amplifier 2.

The output of the OP amplifier 2 is enabled by an external control signal 3, and at this time the transistor 5 sinks current from the power supply 8 through the load 7.

The current and the minute base current flow into the ground through the resistor 6, and the voltage drop across the resistor 6 at this time is OP
Applied to the negative input of amplifier 2.

The current flowing through the load 7 is adjusted by a variable resistor 6 for adjustment.

[Problems to be Solved by the Invention] The conventional constant current circuit uses a variable resistor 6 to adjust the current, which has the problems of requiring a lot of man-hours for adjustment and increasing the cost of parts. there were.

As a solution to these problems, E”FRO
Cameras that use M to adjust the system are known, but such adjustments are so-called "getta-like"
The so-called "
The problem is that the control is limited to "electronic" control, and it is not possible to make high-precision adjustments to analog values such as drive, flow, etc.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a constant current circuit that can reduce component costs, reduce the number of adjustment steps, and perform highly accurate adjustment.

[Means for Solving the Problems] In order to achieve such an object, the present invention provides a power source that allows current to flow through a constant resistor via a load, a voltage across the constant resistor, and a base voltage of $1.
Comparing means for comparing voltages, control means for controlling current according to the error voltage output from the comparing means, and voltage dividing means for dividing the reference voltage by combining resistors according to an external signal. It is characterized by

Further, the present invention provides a power supply that flows a current through a load, a comparison means that effectively compares the voltage across the load and a reference voltage, a control means that controls the current according to an error voltage output from the comparison means, #l Features include voltage dividing means for dividing the reference voltage by combining resistors in accordance with an external signal.

[Function] In the present invention, a reference voltage is divided by combining resistors according to external No. 42, a current is caused to flow through a constant resistor via a load by a power supply, and the voltage across the constant resistor is divided by a voltage dividing means. The comparison means compares the voltage obtained by dividing the reference voltage, and the control means controls the current according to the error voltage output from the comparison means.

Furthermore, in the present invention, the reference voltage is divided by combining resistors according to an external signal, and a current is passed through the load by a current source.
The comparison means compares the voltage across the load with the voltage obtained by dividing the reference voltage by the voltage dividing means, and the control means controls the current according to the error voltage output from the comparison means.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a first embodiment of the invention.

In comparison with the conventional example, this embodiment is different in the resistor connected between the emitter of the transistor 5 and the ground and the voltage applied to the positive terminal of the OP amplifier 2. That is, the resistor connected between the emitter of the transistor 5 and the ground is a variable resistor 6 in the conventional example, but a fixed resistor 10 is used in this embodiment. In addition, the voltage applied to the positive terminal of the OP amplifier 2 is the voltage of the reference voltage power supply 1 in the conventional example, but in this embodiment, it is obtained by dividing the voltage of the reference voltage power supply 1 using a voltage dividing circuit. It is voltage.

Next, the voltage dividing circuit will be explained.

In the voltage divider circuit, the resistance value is 1, the resistance R1 is Ω, and the resistance value is 10
The resistor R2 has a resistance value of 20.OMEGA., a resistor R3 has a resistance value of 20.OMEGA., a resistor R4 has a resistance value of 40.OMEGA., and switches 12, 13.14. A resistor R1 is connected between the positive terminal of the OP amplifier 2 and the reference voltage power supply 1.

The switch 12 has its terminal connected to the positive terminal of the op amplifier 2 via the resistor R2, and its contact piece connected to the ground, and is set to 0N10FF by the setting manual 9. The switch 13 has a terminal connected to the positive terminal of the op amplifier 2 via a resistor R3, and a contact piece connected to the ground, and is set to 0N10FF by the setting manual 10. The switch 14 has its terminal connected to the positive terminal of the OP amplifier 2 via the resistor R4, and its contact piece connected to the ground, and is set to 0N10FF by the setting manual 11.

When switches 12, 13, and 14 are OFF, the reference voltage becomes the positive input terminal of OP amplifier 2, and the output current is approximately (voltage of reference voltage power supply 1)/(value of resistor 1o)
It becomes a constant current. When setting manual 9 is turned on, switch I
2 is turned on, the reference voltage is divided by resistor R1 and resistor R2 and applied to the positive power of OP amplifier 2, and 1
To 0/(1 to +10k) 490%--approx. minus 1
It becomes 0 zero. Further, when the setting human power 10 is ON, it is about -5 foxes, and when the setting human power 10 is ON, it is about -2.5 zero.

In this way, approximately 2.
Approximately minus 17.59 from 100 zero in steps of 5°6
Eight current values can be set up to 6 (f12.59L,).

Further, the manual setting 9.10.11 can be easily controlled by the CPU or the like, and the setting value can be stored in the E2PflOM or the like, so the current can be easily set.

FIG. 2 shows a second embodiment of the invention.

This is an example of a voltage dividing circuit integrated into an IC. The same or corresponding parts as in FIG. 1 are given the same reference numerals.

In comparison with the first example, the unimplemented example has setting inputs 9,
10.11, the switch that is turned ON and 10FF is different from the switch that is turned ON and 10FF according to the control signal 3. In other words, 0N10F due to setting manual power 9, 10.11
The switch that is turned on is a 12° 13.14 switch in the first embodiment, but a 24° 25.26 transistor in this embodiment. Also, control signal 3 allows 0N10F
The switch that is turned on is the switch 4 in the first embodiment, but it is the transistor 27 in this embodiment.

In this embodiment, the setting inputs 9, 10, and 11 are colored blue by logically operating a control signal input to the terminal 18, a clock input to the terminal 19, and data input to the terminal 20 using a logic circuit. The logic circuit includes an inverter 23, a Nandgate 21, an Anthode 22, and a D-flip-flop 15.
, 16.17, when the terminal 18 is set high and a clock is sent to the terminal 19, and data is sent from the terminal 2o, the D-flip-flops 15, 16. Setting inputs 9, 10.11 which are outputs
is set.

Terminal 2o, which was a data line at the time of setting, is connected to inverter 23.
, the control signal 3 is controlled by an I gate 22, and the output is controlled as shown in part B of FIG. In this embodiment, the number of IC bins is reduced, and since the terminal 19 is enabled by the terminal 18, it can be shared by time sharing with other 19 PINs, such as signals to other ICs, such as this IC.

FIG. 4 shows a third embodiment of the invention.

This embodiment is different from the first embodiment in the feedback circuit. That is, in the first embodiment, the voltage across the resistor lO was fed back to the negative terminal of the OP amplifier 2, but in this embodiment, the voltage across the load 7 was fed back to the negative terminal of the OP amplifier 2. .

[Effects of the Invention] As explained above, according to the present invention, since it is configured as described above, it is possible to reduce the cost of parts, reduce the number of adjustment steps, and perform highly accurate adjustment.

1...Reference voltage power supply, 2...OP amplifier, 5...transistor, R1 to R4, 6...resistance, 7...Load, +2.13.14...Switch.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention, FIG. 2 is a circuit diagram showing a second embodiment of the present invention, and FIG. 3 is a diagram showing the timing of signals of each part shown in FIG. FIG. 4 is a circuit diagram showing a third embodiment of the present invention, and FIG. 5 is a diagram showing a conventional constant current circuit. Yijun Tablet Piezoelectric Thickness OP A) F. Su, matter, child Figure 1

Claims (1)

[Scope of Claims] 1) A power supply that causes current to flow through a constant resistor through a load, a comparison means for comparing a voltage across the constant resistor with a reference voltage, and A constant current circuit comprising: a control means for controlling a current; and a voltage dividing means for dividing the reference voltage by using a combination of resistors in accordance with an external signal. 2) a power source that causes current to flow through the load; a comparison device that effectively compares the voltage across the load with a reference voltage; and a control device that controls the current according to the error voltage output from the comparator; A constant current circuit comprising voltage dividing means for dividing the reference voltage by combining resistors in accordance with an external signal.