Application note
AN0001External Economizer Design Guidelines
Why external PWM coil drivers are used instead of internal economizers, and how to design one for REC35 contactors.
Summary
External economizer circuits control the power delivered to a high-voltage contactor coil by supplying high inrush current during the roughly 100 ms pull-in phase and then reducing to a lower hold current, which minimizes coil heating while keeping the contacts reliably closed. This application note explains the operating principles of external PWM economizers and why some designs use an external coil driver instead of an internal economizer, such as when engineers need to tailor pull-in timing, hold current, and diagnostic monitoring to a specific application. It provides design guidelines for implementing external economizer control with Rincon Power REC35 contactors, including the customer-supplied PWM coil driver and fast-dropout TVS circuit these versions require.
