Loads of accuracy from miniature current sources

Datel has made two additions to its growing family of miniature electronic loads.

Datel has made two additions to its growing family of miniature electronic loads.

Designed for use in the cost-effective implementation of computer controlled, power-supply and power-component test and burn-in equipment, the DTL3A and DTL4A are digitally controlled (serial input, 12bit, TTL compatible), near ideal current sources.

The DTL3A features an output/load current of 0-2A, over an operating voltage range of 2.5-200V, giving it a resolution of 500uA per LSB (least significant bit).

The DTL4A features an output/load current of 0-10A, over an operating voltage range of 2.5-150V, giving it a resolution of 2.5mA per LSB.

Each is rated to a maximum output/load power of 100W.

The DTL3A and DTL4A exploit 12bit D/A convertors to achieve their high-resolution current control.

The 12bit digital input word (typically supplied by any standard digital I/O card) is buffered, optically isolated (500V DC isolation guaranteed) and latched before being presented to the onboard DAC.

The DAC output drives a near-ideal (10Mohm minimum output impedance), voltage-controlled current source.

In the case of DTL3A, the output current source can tolerate load voltages up to 200V.

For the DTL4A, the load voltage can be as high as 150V.

The DTL3A/4A's current control derives from the fact that 1LSB of digital output data equates to 0.0244% (1/4096) of output current range.

As noted, this correlates to 500uA for the DTL3A and 205mA for the DTL4A.

The testing/burn-in of power supplies (AC/DC and DC/DC), power components (transistors, diodes, mosfets etc), and all manner of other power devices (batteries, current and voltage sources, capacitors, etc) normally requires putting those devices under load.

Historically, electronic loads have been implemented as expensive "boxes" with assorted dial, knobs, displays, and unnecessarily high power ratings.

By default, power resistors (fixed values, expensive, bulky, inaccurate) have become the technique of choice for implementing load in both the evaluation/characterisation and production environments.

Needless to say, neither of those older options offers the precise current control of the DTL3A and DTL4A.

A single DATEL DTL3A/4A, under the control of a PC, simulates with high precision all desired static/dynamic load conditions.

The low cost, small size and total programmability of DTLs enable the construction of a multipurpose, multiproduct, test/burn-in systems that reduce development costs, minimise factory-floor requirements, and improve end-product reliability.

Despite their high voltage ratings, the DTL3A and 4A can operate all the way down to output/load voltages as low as 2.5V.

Below this point, the devices' output stage may become improperly biased, and unpredictable operation (including shut down) may occur.

To avoid such situations, Datel installed an output "fault line" that activates and warns users whenever the voltage gets dangerously low.

The DTL3A and DTL4A both guarantee +0.1% maximum gain error, +0.5/3mA (respectively) maximum offset error and +1% overall accuracy (under all conditions of load current/voltage, temperature and +Vcc).

Their fast setting DACs and proprietary, mosfet-based output stages provide quick updates (to 20kHz) and fast setting times (100us).

Additionally, all DTLs feature miniature 51 x 51 x 13mm six-side-shielded, metal packages that are heatsink friendly.

(This was Electronicstalk's Top Story on 28 January 2002).

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