Voltage and current measurement circuit design based on high linear optocoupler HCNR201 - News - Global IC Trade Starts Here Free Join

Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

Photocoupler

The accuracy and stability of the analog signal value acquisition determine the operational reliability of the entire project. However, the site environment is harsh and the interference is severe. In order to linearly convert the analog signal without introducing various noise interferences in the field to the control system, A good linear separation between the measured analog signal and the control system must be performed. In general, DC isolation measures can be implemented by using a dedicated isolation operational amplifier (ISO124 series) plus a high-precision isolated DC power supply to achieve linear isolation of the measured analog signal from the control system through electrical coupling, but this method is costly. And the temperature drift is large. In this paper, the linear optocoupler HCNR201 is used to achieve linear isolation between the measured analog signal and the control system. The isolation principle of linear optocouplers is not much different from that of ordinary optocouplers, except that it will change the single-shot single-receive mode of ordinary optocouplers, add a photodiode for feedback and increase the linear region. Both photodiodes are non-linear, but their nonlinear characteristics are the same, so the nonlinearity of the through path can be offset by the nonlinearity of the feedback path, thus achieving linear transmission of the signal.

How does HCNR201 work?
HCNR201 is a high-linearity optocoupler device introduced by Avago. It can realize the photoelectric isolation conversion circuit of AC and DC current and voltage by externally connecting different discrete devices. The internal structure is shown in Figure 1. The HCNR201 is composed of a high-performance AlGaAs type light emitting diode and two photodiodes PD1 and PD2 having a strict proportional relationship. When the current IF flows through the LED, the light emitted by the PD1, PD2 in the photodiode induces photocurrents IPD1 and IPD2 proportional to the luminous intensity of the LED, where IF, IPD1, and IPD2 satisfy the following relationship: