Isolated, Loop-Powered Voltage-to-Current Converter

The 1B21 is an isolated voltage-to-current converter that incorporates a unique circuit design utilizing transformer-based isolation and automated surface-mount manufacturing technology. It provides an unbeatable combination of versatility and performance in a compact plastic package. Designed for industrial applications, it is especially suited for harsh environments with extremely high common-mode interference.

Functionally, the V/I converter consists of four basic sections: input conditioning, modulator, demodulator and current source (see Figure 1). The input is a resistor-programmable gain stage that accepts a 0 V to 1 V up to 0 V to 10 V voltage input. This maps into a 0 mA to 20 mA output or can be offset by 20% using the internal reference for 4 mA to 20 mA operation. The high level signal is modulated and passed across the barrier which provides complete input to output galvanic isolation of 1500 V rms continuous by the use of transformer-coupling techniques. Nonlinearity is an excellent ±0.05% maximum.

Designed for multichannel applications, the 1B21 requires an external loop supply and can accept up to 30 V maximum. This provides a loop supply compliance of 27V, which is sufficient to drive a 1.35 kΩ load resistance.

The 1B21 is fully specified over −25°C to +85°C and operates over the industrial (−40°C to +85°C) temperature range.

APPLICATIONS

* Multichannel Process Control

* D/A Converter - Current Loop Interface

* Analog Transmitters and Controllers

* Remote Data Acquisition System

* Wide Input Range: 0-1V to 0-10V

* High CMV Isolation: 1500V rms

* Programmable Output Ranges: 4mA to 20mA 0 to 20mA

* Load Resistance Range: 0 to 1.35kΩ max

* Meets IEEE std. 472: Transient Protection (SWC)