SU1515116A1 - Voltage-to-current converter - Google Patents

Abstract

The invention relates to electrical measuring equipment and can be used in output stages of digital-to-analog converters. The purpose of the invention is to improve the accuracy of the conversion. The converter contains an operational amplifier 1, a transistor 2, a resistor 3. The introduction of optocouplers 5 and 6 and new connections ensures the elimination of the error associated with the base current of transistor 2. On a large signal, the base current of transistor 2 is closed to the load 4 through the photodetector 9, on a small the signal is transmitted by the optocoupler 6. 1 Il.

Description

ate

1515116

This invention relates to electrical measuring technology.

The purpose of the invention is to improve the accuracy of the conversion,

The drawing shows a functional diagram of the device.

The device contains an operational amplifier 1, the non-inverting input of which is connected to the input of the device, the inverting input - with the emitter of the transistor 2 and through resistor 3rd common bus device. The collector of the transistor 2 is connected to the load 4 through the power source E The first and second optocouplers 5, 6 consist of emitters 7, 8 and photodetectors 9, 10, respectively. Emitters 7, 8 are connected in parallel and opposite to each other between the output of amplifier 1 and the common bus. The receiver 9 is connected between the base and the collector of transistor 2, and the photodetector 10 is connected between the base and emitter of transistor 2.

The device works as follows.

The non-inverting input of opamp 1 is converted voltage U, with f g. b 0 If, where IT is the dark current of the photodetector 9; B is the current gain of transistor 2, and R is the resistance of resistor 3, due to the negative feedback that is connected to amplifier 1, the voltage at its output will be positive, while the emitter 7 of the optocoupler 5 is turned on. Transistor 2 is in active mode , moreover, its base is galvanically developed using optocouplers 5 and 6 from the output circuit of the operational amplifier 1.

The current flowing in the load 4,

 (one)

 Color

 - R,

0

five

0

five

five

0

0

With Ugj, due to the effect of negative feedback, encompassing operational amplifier 1, the voltage at the output of the latter becomes negative. In this case, the emitter 8 of the optocoupler 6 is turned on, the photodetector 10 of this optocoupler shunts the emitter junction of the transistor 2, and skips part of the dark current of the photoreceiver 9.

Since, in this case, the negative feedback is valid, then equation (1) is also valid in this range of input voltages of the converter.

Claims (1)

Ig does not enter the device conversion equation; therefore, the error associated with it in the described device is eliminated, and the conversion accuracy is improved. . Claims of the invention. A voltage-to-current converter containing an operational amplifier, the non-inverting input of which is connected to the input of the device, and the inverting input to the emitter of the transistor and through a resistor to the common bus of the device, the collector of the transistor is connected to the output of the device through a power source that differs in THAT, in order to improve the accuracy, two optocouplers were introduced into Him, the emitters of which are connected in parallel and opposite to each other between the output of the operational amplifier and the common bus of the device, The first optocoupler coupler is connected between the base and collector of the transistor, and the photodetector of the second optocoupler is connected between the base and the emitter of the transistor.