Several circuits of current-to-voltage

The realization method of several kinds of voltage transformation of electric transferTime: 2011-08-19-14:28 Author: Race Micro editor Source: Network

This paper introduces several implementation methods of I/v transform:

　　Voltage Divider Method

Use the voltage divider shown in Figure 1 to pass the current into the resistor. The voltage signal is sampled on the resistor. In this case, the output voltage can be adjusted using a potentiometer. This is the simplest approach, but the choice of power and magnification needs to be considered.

　　

　Hall Sensor Method

Using the Hall effect, the voltage is output by passing current I at both ends of the element and applying the magnetic field of magnetic induction B in the vertical direction of the element. The linear relationship is obtained by the following formula.

　　

Wherein, the RH is the hall constant, I is the input current, B is the magnetic induction, D is the hall element thickness.

This method is more used to measure the current, although the conversion can also be achieved, but the precision is limited.

　　Integral Circuit Method

The voltage can be regarded as the integral of the current, using the diagram circuit as follows:

　　

　　

In order to ensure the accuracy, select the OP amp as far as possible to find the input impedance large. The circuit is commonly used in PID adjustment, the integral circuit is mature and the magnification and precision is good. However, it is important to note that the output voltage of this circuit is opposite to the phase of the input current.

　　method of direct lap of op Amp (transimpedance amplifiers)

Make full use of the concept of "virtual short" and "Virtual break" to convert the current into a voltage signal, such as the diagram circuit

　　

The current is passed through the resistor, which creates a voltage drop on the resistor and establishes the relationship between the current and the

This method avoids the integral error caused by the influence of the OP amp input offset voltage and input bias current and offset current. It also avoids the error caused by the leakage current of the capacitance. However, the accuracy of resistance and op amp is higher than that of stable and high precision amplification.

Transistor Method

Transistors also have amplification capability, but they are used more in op amp. Circuit as shown in figure

　　

The following is a practical example of the entire implementation process.

Attempt to convert a 0~5a signal to a 0~5v signal. The simplest is to add a 1 ohms resistor, but the heat power is too large, so a current transformer needs to be used to make the original current smaller. According to the general transformer indicator is the input 0~10a signal, the ratio is 200:1, that is, the 0~5a signal becomes 0~25ma. The conversion is realized by the method of direct lap of op-amp. Considering the phase problem, the circuit is improved. Using the 50 ohm resistor at the positive end of the voltage generated by the same conditions as the negative end, and using the amplifier function of op amp to achieve the final requirements. As shown in figure. In addition, the integrated op amp OP27 is used to achieve higher computational accuracy; 50 ohms is a front-end transformer with load requirements.