DC contactors come in various forms, styles, and technologies. Depending on your application, a specific type of relay might be the only suitable option, while in other cases, multiple types might be appropriate. By understanding the pros and cons of different relays, you should be able to choose the one best suited for your task.

Although many conclusions in this document apply to all DC contactor applications, it specifically discusses factors to consider when using different types of relays for switch modules intended for Automatic Test Equipment (ATE) applications. The comparisons made here are between relays with similar voltage, current, and power ratings that can be found in typical switch modules.

Common relay types in ATE applications include:

• Electromechanical Relays

• Reed Relays

• Solid-State Relays

• Field-Effect Transistor (FET) Switches

FET switches are commonly used in multiplexer configurations for high-speed, low-voltage applications. DC contactors are widely used in today's ATE applications. They consist of a coil, armature mechanism, and electrical contacts. When the coil is energized, the induced magnetic field moves the armature, opening or closing the contacts.

FET switches, like SSRs, are not mechanical devices. FET switches use a series of CMOS transistors to achieve switching. Unlike SSRs, the control circuit directly drives the gate of the transistor rather than driving an LED. Direct driving of the transistor gate results in faster switching speeds because the LED's turn-off time is not a factor. Typically, FET switches are fast switches discussed here. Additionally, because there are no mechanical parts or LEDs in the package, FET switches can be very small. However, a major drawback of FET switches is their lack of physical isolation, so they can only be used with low-voltage signals.

DC contactors often have larger and more robust contacts compared to some other relay types. The larger contacts allow them to handle unexpected surge currents caused by parasitic capacitance in circuits and cables. Unfortunately, the larger contacts require a larger package size, so they cannot be densely packed in switch modules.