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History of Solenoids

Current Control Driver for a 24 V DC Solenoid TIDA-00289

Solenoids, a term coined back in 1827, are among the oldest electrical devices. They were first introduced when electricity was little more than a parlor trick.

Pioneers realized that the magnetic field created by current in a coil could be used to perform useful work. This led to solenoids being used to convert electricity into linear motion.

Soon, manufacturers began to produce solenoids, relays and motors, in quantity. Currently, valves, relays, and contactors all use electromechanical solenoids for their operation.

Though the technology is old, there is always room for improvements. For instance, current control drivers for solenoids from Texas Instruments (TI) feature improvements to: reliability, miniaturization, precision, and energy conservation.

Current Control Drivers for Solenoids

The TI TIDA-00289 is a current controlled driver for 24-volt DC solenoids while the TIDA-00284 serves the same function for 230-volt AC applications. These current control designs can detect plunger movement into the solenoid coil,. The plunger movement causes change in the magnetic field created by the solenoid.This movement is detected using Hall Effect sensors that provide output voltages proportional to the magnetic flux density. TIDA-00289 has an additional option to detect the plunger movement by sensing the current profile of the solenoid.

The TI TIDA-00289 and TIDA-00284 solenoids can reduce power consumption, simplify usage and enhance monitoring capabilities. Solenoid coils need more current only during actuation and they need approximately 30% of their nominal current in steady state. Continuing to use this nominal current consistently, however, dissipates more power and raises the temperature. Therefore, the current control driver reference designs regulate the solenoid current and monitor the proper operation of the plunger. This in turn optimizes energy use.

Traditionally, a solenoid coil is controlled with the general-purpose I/Os (GPIOs) of a micro-controller (MCU) through an external BJT or MOSFET. TI’s driving system, however, employs PWM to control the current waveform which simplifies the analog-to-digital interface for many applications. The duty cycle of the PWM determines the average current through the coil and hence can regulate the current with a well-controlled waveform to reduce power dissipation.

TIDA-00284 Schematic Diagram

The overall schematic for the TIDA-00284 is nearly identical to the TIDA-00289 with exception to the voltage. Other features that are common to both current control drivers include:

· Optimized power consumption

· An automatic switch from peak to hold the current at the end of plunger excursion

· An alarm signal in the event of faulty plunger movement.

· Compliance with EN55011-Class A conducted emission limits.

Implementing Current Control Drivers for Solenoids

The support TI provides to design engineers is noteworthy. For instance, reference documents called ‘TI Designs’ give a discussion of current control driver theory, methodology and testing. This offers the designer an understanding of both the technology and the product. In addition, TI offers a library of design/application documents, factory support, the TI Wiki, and a sponsored engineer-to-engineer online community.

An example of the generous test data provided – in this case, a four-channel plot of source current, fault indicator and amplified solenoid current – appears below.

Four-channel plot of source, fault indicator and output current

With components such as those created by TI, it isn’t necessary to choose among characteristics that may seem contradictory (such as precision, reliability, and energy efficiency). Furthermore, the design attributes and support can help to reduce the time-to-market.

Texas Instruments has sponsored this post. They have no editorial input to this post - all opinions are mine. Arnie Peskin