Driving loads such as electric motors, relay coils, and solenoids requires a relatively large initial pull-in or start-up current from a driver in order to initiate operation of the load. To maintain continuous operation, the hold or running operating current required for a load may be 20% or less of the initial pull-in or startup current. The problem is that a standard driver circuit acting as a switch continues to provide the same current throughout operation, wasting energy, and must be large enough to provide the large current continuously.

A new driver provides a smaller, less costly method of reducing energy to drive the load. It uses a transformerless direct-coupled pulse width modulation (PWM) switching driver to control the current to the load. Circuit area is reduced by directly coupling the driver circuitry to the load, thus eliminating the transformer, diodes, and output capacitors. This invention does not provide the electrical isolation of the transformer-coupled topology or as wide an input voltage operational range. However, many applications do not require isolation or the wide operating input voltage range of the transformer-coupled method. Therefore, they can benefit from the reduced energy consumption and circuit area of the direct-coupled topology described here.

This innovation uses electronic components that are assembled and interconnected on a printed wiring board to isolate the conhigh and low side of a dual bus input. The driver circuit uses a PWM control topology with a series switching element. The PWM provides control of the output current by modulating the switching duty-cycle. The current may thus be controlled to any level desired using any number of potential algorithms. For example, the current feedback to the PWM control circuitry may be fed through a delay element that inhibits the current limiting for a period of time required for proper pull-in or start-up of the load. This provides two distinct levels of load current: a large initial pull-in or startup current followed by the lower hold or running operating current. This could also be accomplished by simply timing the turnon and switching between one or more control points as desired.

This driver can maintain a consistent level of isolation between independent power inputs. No single failure within the avionics electronics will cause independent power buses to lose electrical isolation, and a simple diode O-ring cannot be used. These requirements apply to both supply and return lines.

The innovation also addresses a high-reliability problem of load control via electronic circuit breaker (ECB). ECB dynamic control can be implemented via simple FPGA (field programmable gate array) means.

This work was done by Nathan Moyer, Thomas Bingel, Deanne Tran-Vo, George Cebry, Paul Santrach, and Charles McCracken III of Honeywell for Johnson Space Center. For further information, contact the JSC Innovation Partnerships Office at (281) 483-3809.

Title to this invention has been waived under the provisions of the National Aeronautics and Space Act {42 U.S.C. 2457(f)} to Honeywell. Inquiries concerning licenses for its commercial development should be addressed to:

Honeywell
P.O. Box 52199
Phoenix, AZ 85072-2199

NASA Tech Briefs Magazine

This article first appeared in the February, 2014 issue of NASA Tech Briefs Magazine.

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Refer to MSC-24766-1/7-1/76-1/82-1.