0-5V to 4-20mA Converter Schematic
Introduction
In industrial automation, 4-20mA current loops are widely used for signal transmission due to their advantages such as high noise immunity, long-distance transmission capability, and ease of implementation. However, many sensors and devices output a 0-5V analog signal, which needs to be converted to 4-20mA for compatibility with industrial equipment. This article provides a 0-5V to 4-20mA converter schematic to facilitate this conversion.
Circuit Description
The converter circuit consists of a voltage-to-current converter and a voltage reference circuit. The voltage-to-current converter is based on the LM334 voltage-controlled current source, which provides a high degree of linearity and stability. The voltage reference circuit uses the TLV703 low-dropout voltage regulator to generate a stable 5V supply for the converter.
Schematic Diagram
Here is the schematic diagram of the 0-5V to 4-20mA converter:
+---------------+
| Vin |
| (0-5V analog) |
+---------------+
|
|
v
+---------------+ +---------------+
| R1 | | R2 |
| (1kΩ) | | (2kΩ) |
+---------------+ +---------------+
| |
| |
v v
+---------------+ +---------------+
| U1 | | U2 |
| (LM334) | | (TLV703) |
+---------------+ +---------------+
| |
| |
v v
+---------------+ +---------------+
| R3 | | R4 |
| (250Ω) | | (1kΩ) |
+---------------+ +---------------+
| |
| |
v v
+---------------+ +---------------+
| Iout | | Vref |
| (4-20mA) | | (5V) |
+---------------+ +---------------+
Component List
- R1: 1kΩ resistor
- R2: 2kΩ resistor
- R3: 250Ω resistor
- R4: 1kΩ resistor
- U1: LM334 voltage-controlled current source
- U2: TLV703 low-dropout voltage regulator
- Vin: 0-5V analog input signal
- Iout: 4-20mA output signal
- Vref: 5V voltage reference output
How it Works
The circuit operates as follows:
- The 0-5V analog input signal is applied to the non-inverting input of the LM334.
- The LM334 converts the input voltage to a current output, which is proportional to the input voltage.
- The current output is sensed by resistor R3, which provides a 250Ω load to the current source.
- The voltage reference circuit, consisting of the TLV703 and resistors R1 and R2, generates a stable 5V supply for the converter.
- The output current, Iout, is proportional to the input voltage and ranges from 4mA to 20mA.
Conclusion
The 0-5V to 4-20mA converter schematic presented in this article provides a simple and reliable solution for converting analog voltage signals to current signals compatible with industrial automation equipment. The circuit is easy to implement and requires minimal components, making it a cost-effective solution for industrial applications.
