Current Sense Resistor in Motor Control PCB Applications

A large manufacturer of motorised garage door controllers had a pcb based micro controller circuit which required determination of several important parameters to protect the motor.


  • Determination of Current flow through the garage door drive motor
  • Determination of overload of the drive motor. In instances where the garage door jammed or failed to move for some reason, indicating a fault. The micro controller then needed to receive this signal and then via a p.c.b. mounted relay, cut off the drive motor, avoiding damage to the motor and possible damage to the drive chain of the door opener.
Being a pcb mount design, the engineer wanted an elegant ‘on board’ solution for a suitable current sense resistor that was flame proof and had a rating of around 4 watts. The Current Sense Resistor Application - Motor ControlFSR series of resistor met the requirements for this application. The FSR-05 (pictured, right), has a 5 watt power rating at 85C and is designed for p.c.b. mounting. Importantly the construction of the resistor lends itself to high reliability applications due to the welded leads which ensure both electrical and mechanical integrity. For ease of checking voltage drop across the resistor in field testing and fault finding a test point is available, making voltage measurement easy and safe.
The flat strip construction of this current sensing resistor makes it economical yet very versatile in its application. Typical inductance is less than 10 Nanohenries and it is available from 0.005 ohms to 0.05 ohms.