Power-to-frequency
converters replace
mechanical watt-hour meters

A family of power-to-frequency converters promises to replace the traditional electromechanical power meters currently used in residential and industrial applications.

The AD7750 power-to-frequency converter from Analog Devices (Norwood, MA) can be configured either for power measurement, voltage-to-frequency conversion, or to convert the product of two voltages to frequency. This first member of the company's AD775x power-to-frequency converter family may be used either to create a fully electronic watt-hour meter or simply to implement a lower-cost mechanical meter.

The AD7750 is the first member of a power-to-frequency
converter family designed to replace electromechanical
watt-hour meters in residential and industrial applications.

As part of an electronic meter, the converter paves the way for many advanced metering functions such as theft protection and remote meter reading. Future members of the family will promote such functionality with anti-pilfering enhancements, digital calibration, and a microprocessor interface.

The AD7750 contains two A/D converters, a multiplier, an offset compensator, a digital-to-frequency converter, and a reference, as well as other conditioning circuitry. Both channels are driven by differential gain amplifiers. Channel 1 provides selectable gains of 1 and 16, while channel 2 has a gain of 2. A high-pass filter can be switched into the signal path of one channel to remove the effects of offset.

Operating from a 5-V supply, the converter accepts analog inputs of ±1 V. Nonlinearity for either input is 0.05% max. The device also features two sets of frequency outputs that consist of fixed-width pulse streams whose frequencies are pin selectable. The device produces a broad range of outputs, from low-frequency outputs for driving stepping motors to higher-frequency pulse streams appropriate for calibration and test.

In the signed mode, outputs can be configured to represent the result of four-quadrant multiplication, while in the unsigned mode, results have only a positive magnitude. A reverse-power function indicates when negative power is detected in the unsigned mode.

The AD7750 is currently available in 20-pin SOPs and DIPs and is priced at $2.50 each in quantities of 100,000. For more information about the AD775x power-to-frequency converter family, call Analog Devices at 781-937-1428, fax 781-821-4273.