Voltage and current transmission integrated circuit AM462 principle and application - Power Circuit - Circuit Diagram

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

MOS power IC full range

1.5PF SOT23-6 Low Capacitance 5V Breakdown Voltage 6V SRV05

One-piece inductor

The analog circuit interface industry generally employs either voltage signals ranging from 0-5(10)V or current signals ranging from 0(4)-20mA as the primary methods for analog signal transmission. These are also commonly utilized techniques in programmable control machines. While both methods serve similar purposes, they differ significantly in terms of application scenarios and performance. Below is a brief overview of their distinctions and appropriate usage.

Voltage signal transmission such as 0-5(10)V: When transmitting an analog voltage signal from the source to the receiver via a long cable, the signal may become distorted due to various factors. The voltage signal encounters the output impedance of the transmitting circuit, along with the resistance of the cable and contact resistance, leading to voltage drops and subsequent transmission errors. These errors are essentially the sum of the input bias current of the receiving circuit multiplied by the aforementioned resistances. For minimal transmission error, the receiving circuit must have a high input impedance. However, achieving this without increasing costs and maintaining negligible resistance requires careful consideration. High-impedance circuits, especially those at the input of amplifiers, are prone to electromagnetic interference, potentially causing significant inaccuracies. Thus, with voltage signal transmission, a balance must be struck between minimizing transmission errors and mitigating electromagnetic interference.

Conclusion of voltage signal transmission: If electromagnetic interference is low or the transmission cable is short, a suitable receiving circuit can effectively transmit the voltage signal 0-5(10)V.

Current signal transmission such as 0(4)-20mA: In environments with strong electromagnetic interference and when requiring longer transmission distances, people have long preferred using standardized current signals for transmitting data. Unlike voltage signals, a current source ensures that the provided current remains consistent regardless of the cable resistance or contact resistance. This means the transmission of current signals is unaffected by the hardware configuration. Conversely, voltage signals suffer from the impact of electromagnetic interference due to the low input impedance of the receiving circuit and the grounding of the current source. This makes current signal transmission more robust against external noise.

Conclusion of current signal transmission: If electromagnetic interference, such as from electric welding equipment, is a concern and the transmission distance is long, the method of current signal transmission is ideal for such cases (analog signal transmission). In practice, current transmission methods are frequently employed in two-wire and three-wire configurations. Given the significance of the two-wire system, the two-wire method, also known as the current loop method, will be the focus here.

Comprehensive characteristics of the current loop: The current loop offers several advantages. It is simple to use: If the operating current of the signal transmitting circuit and other connected circuits remains constant, both the operating current and signal current can be transmitted through the same cable. A load sampling resistor is needed, and the voltage drop across the load resistor serves as the useful signal. It's crucial to ensure the operating voltage is sufficiently high to meet the voltage drop requirements in the current loop. Additionally, compared to digital signal transmission, which requires an AD conversion, the current loop method only necessitates one cable, one load resistor, and a measuring voltmeter, making it more cost-effective. Its error diagnostic capabilities are another strong point: The 4-20mA current signal transmission provides automatic error information, enabling long transmission distances and strong interference resistance. If the calibrated system outputs a zero signal (4mA output), receiving a signal greater than zero but less than 4mA indicates a fault in the system. A zero current signal suggests a broken cable or issues with the signal reception. Exceeding 20mA implies signal overload or problems with the input signal reception. Furthermore, the current loop supports long-distance transmission, with the distance depending on the driving capability of the transmitting signal terminal, the resistance of the cable, and the measuring resistance (load resistance) at the receiving end. Including a measuring instrument in the signal transmission cable means considering the input impedance of the measuring instrument and the monitoring recording instrument. These instruments are often connected in the current loop and powered directly from the 4mA operating power supply, eliminating the need for an external power supply. Hence, the load capacity of the current source loop should be taken into account during circuit design.

The simplest case of two-wire current signal transmission involves an adjustable current source and resistor composed of the current signal sender and receiver (receiving signals from the load resistor), as illustrated in Figure 1.

In Figure 1, the sender assumes it produces the desired signal current IOUT = 4-20mA corresponding to the measured value. The resistor RL acts as the receiver and can measure the voltage drop VA above it or directly measure the ammeter in series with the circuit to obtain IOUT. In reality, the sender often comprises numerous functional circuits. In the sensor field, the sender is frequently used as a signal measurement converter, which includes a sensor, a working power supply for the sensor, and a current source (Figure 2). Apart from the measurement signal, the current source loop can also function as an isolation amplifier for the output stage of PWM-modulated pulse-width signals or simply as a voltage-output signal source.

Figure 2: Complete Current Signal Transmitter Circuit. Typically, the sensor signal or PWM-modulated pulse-width signal varies from zero to a full-scale value (FS), meaning the voltage-controlled current source must generate a zero-point current of 4mA and a full-scale current of 20mA (a difference of 16mA). In industrial control, the control device (control room) is often located far from the measurement signal transmission circuit. If the power line is also used as a signal transmission line, the signal can be sent with just two wires, reducing costs and simplifying the circuit. This is known as the two-wire current transmission method.

Figure 3: Two-wire Application Circuit. As shown in Figure 3, one provides a working power supply from the control device (control room) that can simultaneously power multiple transmission circuits.

If you have any questions about the above content, please feel free to reach out for further clarification.