# Op-Amp: Current to Voltage Converter

Hey friends, Welcome to the Kohiki web ALL ABOUT ELECTRONICS. So, in the previous article, we have seen that how to design the voltage to current converter using the op-amp.

So, now in this article, let’s understand how to design the current to voltage converter using the op-amp.

## Why Current to Voltage Conversion is required in the circuits

Now, these types of current to voltage converter circuits are useful in many applications. For example, let’s say, you have one sensor or the circuit component which gives the output in terms of the current. For example, let’s say you have a photodiode.

which gives the output in terms of the current. And let’s say, you want to log the data of this photodiode for the entire day. And let’s assume that for that you are using the data acquisition system.

Now, most of the time this type of system used to accept the data in terms of the voltage. So, you need to convert this current into voltage. And for this, I to V or the current to voltage converters are useful.

Now, this current to voltage converter is also an example of a current-controlled voltage source, because if you observe over here, the input to this circuit is in terms of the current.

While the output of this circuit is in terms of the voltage. So, just by controlling the input current, we can control the output voltage.

• How do you convert the voltage to current: As we know, if we apply a voltage VIN across a resistor R, then a proportional current starts flowing through the circuit IOUT = VIN / R. We can say that this is a voltage-cause-current formulation of Ohm’s law: I = V / R. In this voltage-supplied circuit, resistor R determines the current flowing through it.
• What device converts current to voltage: We usually say that the resistor converts the current IIN into a proportional voltage VOUT or that it acts as a simple current-to-voltage converter – with a transfer ratio k = VOUT / IIN [V / mA] A linear circuit. A bare resistor can convert current to voltage.
• Which application uses voltage to current converter: Voltage can be used for current converter in low voltage DC and AC Voltmeter, diode matching finder, light-emitting diode, and Zener diode Examiner.

## Passive Current to Voltage Converter circuit and its limitations

So, now let’s understand, how we can design this current to voltage converter. Now, before we see the op-amp-based current to voltage converter, first of all, let’s see how we can design this converter using the passive circuit components.

And what are the limitations of this passive converter? So, just by connecting the resistor across this current source, we can convert this current into voltage. And the voltage that is developed across this resistor can be given by this simple expression.

So, now suppose if we connect the load across this resistor R, then ideally the same voltage should also appear across the load.

But whenever we connect the load to this resistor, then some current will also flow through this resistor RL. And because of that, the voltage which appears across this resistor RL can be given by this expression.

That is the input current, multiplied by the parallel combination of this R and RL. So, as you can see over here, in the case of this current to voltage converter, the voltage which appears across the load will also depend upon this load resistance.

Now, ideally in this current to voltage converter, the converted voltage should be independent of this load resistance. So, unless the value of this load is much greater than this resistor R, the actual voltage which appears across this load will be less than the voltage that is getting converted by this converter.

• What is the need for current to voltage converter: The voltage-current is proportional to the given current. This circuit is required when your measuring instrument is only capable of measuring voltage and you need to measure the current output.
• How an op-amp can be used as current to voltage converter: A current-amp e based current outputs the output when the voltage is turned on when the current is applied to its inverting terminal, According to the virtual short concept, the voltage at the inverting input terminal of the op-amp will be equal to the voltage at its non-inverting input terminal.

## Active Current to Voltage Converter using the op-amp

So, this problem can be avoided by using this active converter. So, here this input current is connected at the inverting terminal of this op-amp. And the feedback resistor R is connected between the output terminal and the inverting input terminal.

And here the non-inverting terminal is at ground potential. So, because of the virtual ground concept, this node will be also at zero voltage. Now here, we are assuming that the op-amp is an ideal op-amp.

So, the current is flowing into the op-amp terminals. So, if we apply the KCL at this node A, then we can say that this input current Iin should be equal to the current which is flowing through this resistor R.

And that will be equal to 0 minus Vout divided by this resistor R. So, we can say that the output voltage vout will be equal to minus input current times the value of this resistor R.

So, as you can see over here the output voltage Vout is proportional to the input current. So, in this way, we can convert this input current into the output voltage.

Now, in this circuit even if you connect the load at the output terminal, then also the output voltage will remain as it is. So, basically, it is independent of the load resistance.

Now, this type of current to voltage converter is also known as the trans-impedance amplifier. Because here the current is applied as an input and the output of this amplifier is in terms of the voltage.

So, here the ratio of this output voltage divided by this input current has a unit of impedance. And that’s why this type of amplifier is known as the trans-impedance amplifier. So, now let’s see some of the applications of this current to voltage converter.

## Application : Current to Voltage Converter in photodiode circuits

So, this type of converter is particularly useful in photodiode circuits. So, as you can see over here the photodiode is connected at the inverting input terminal of this op-amp.

And the non-inverting terminal is at ground potential. So, by applying the concept of virtual ground we can say that this inverting terminal is also at ground potential.

Now, depending upon the light which is falling on this photodiode, the photocurrent will flow through this photodiode.

And if we apply the KCL at this node, then we can say that this photocurrent Iph will be equal to the current IR which is flowing through this resistor R. And that will be equal to Vout divided by this resistor R.

So, from this, we can say that the output voltage Vout will be equal to this photocurrent Iph times this resistor R.

So, in this way, we convert this photocurrent into the output voltage. So, similarly this current to voltage converter can also be used along with this photoresistor. So, in the case of this photoresistor, the value of the resistance will change according to the light that is falling on it.

## Application: Current to Voltage Converter in Digital to Analog Converter (DAC)

so, apart from these applications, this current to voltage converter is also used in digital to analog converters. So, here we have a four-bit of digital to analog converter. And to this converter, the four bits of digital data has been applied.

So, according to the applied digital bits, we will get the analog output voltage at the output terminal. Now, in this converter circuit, the logical one treated as 5V, and the logical 0 is treated as 0V.

And here, this D3 is the most significant bit of the applied input and D0 is the least significant bit of the applied input. So, let’s say these four bits are applied to this DAC.

So, here this D0 is the logical 1. So, here it is connected to the 5V. And accordingly, some current I will flowthrough this resistor R. And that current I will be equal to 5V divided by this 10 Kilo-Ohm resistor. That is equal to 0.5 mA current.

So, because of this D0 bit, 0.5 mA of current will flow through this resistor R. Now, similarly, if we consider this D1 bit, it is a logical 0. So, it is connected to the ground. So, no current will flow through this 5 Kilo-Ohm resistor. Or we can say that the current I2 will be equal to 0 mA.

Similarly, if we consider this D2 bit, then it is also connected to the ground potential. So, the current I3 will also equal 0 mA. And now if we consider this most significant bit, that is D3, it represents the logical 1.

So, it is connected to the 5V and because of that, the current I4 will be equal to 5 V divided by 1.25 Kilo-Ohm resistor. So, that will be equal to 4mA.

So, now the summation of these individual four currents will flow through this resistor Rf. Because here we are assuming that the op-amp is an ideal op-amp. So, the current is flowing into the op-amp terminals.

So, whenever we apply 1001 as an input, then the total current IT, will be equal to 0.5 mA plus 4mA. That is equal to 4.5 mA. Now, this current will flow through this resistor. And because of that, we will get the output voltage V out as minus IT times this feedback resistor Rf.

So, the output voltage Vout will be equal to (-4.5 mA) times this 1Kilo-Ohm resistor. And that is equal to – 4.5 V. So, this will be the output voltage whenever we apply this 1001 as the input sequence.

So, in this way, by using this current to voltage converter circuit, we can convert the digital data into the analog output voltage.

And depending upon the applied input sequence, the output of this digital to analog converter will change. So, these are some of the applications of this current to voltage converter.

## FAQ

### How do you convert current signal to voltage?

“A resistance is placed across the input terminals of the controller.” A 250Ω resistance during a 4-20mA DC current loop can turn out a 1-5VDC signal, as indicated in Ohm’s law: E = I · R, wherever E is voltage, in volts; I is current, in amps; and R is resistance, in ohms.

### How can op amp be used to convert voltage to current?

To analyse the present to voltage device by scrutiny, if we have a tendency to apply KCL to the node at V- (the inverting input) and let the input current to the inverting input be I-, then Vout−V−Rf=Ip+I− since the output is connected to V- through Rf, the opamp is during a feedback configuration. therefore V−=V+=0.

### What is VI converter application?

Photoconductive devices turn out a current that’s proportional to a happening energy or lightweight (i.e). It will be accustomed sight the sunshine. Photocells, photodiodes, electrical phenomenon cells offer associate output current that depends on the intensity of sunshine and freelance of the load.

### What is an op amp and what does it do?

An operational electronic equipment is AN microcircuit which will amplify weak electrical signals. AN operational electronic equipment has 2 input pins and one output pin. Its basic role is to amplify and output the voltage distinction between the 2 input pins.

### Why do we convert voltage to current?

So generally it’s essential to make current that is corresponding or proportional to an explicit voltage. For this purpose Voltage to Current Converters (also referred to as V to I converters) area unit used. It will merely amendment the carrier of electrical information from voltage to current.