- The job of a Resistor is to limit the current flowing through an electrical circuit.
- Resistance is measured in Ohm’s and is given the symbol Ω
- Carbon, Film and Wirewound are all types of resistors.
- Resistor colour codes are used to identify the resistance and tolerance rating of small resistors.
- The BS1852 Standard uses letters and is used to identify large size resistors.
- Tolerance is the percentage measure of the accuracy of a resistor from its preferred value with the E6 (20%), E12 (10%), E24 (5%) and E96 (1%) series of tolerance values available.
Series Resistor Tutorial
- Resistors that are daisy chained together in a single line are said to be connected in SERIES.
- Series connected resistors have a common Current flowing through them.
Itotal = I1 = I2 = I3 …. etc
- The total circuit resistance of series resistors is equal to:
Rtotal = R1 + R2 + R3 + ….. Rn etc.
- Total circuit voltage is equal to the sum of all the individual voltage drops.
Vtotal = V1 + V2 + V3 …. etc
- The total resistance of a series connected circuit will always be greater than the highest value resistor.
Parallel Resistor Tutorial
- Resistors that have both of their respective terminals connected to each terminal of another resistor or resistors are said to be connected in PARALLEL.
- Parallel resistors have a common Voltage across them.
VS = V1 = V2 = V3 …. etc
- Total resistance of a parallel circuit is equal to:
- Total circuit current flow is equal to the sum of all the individual branch currents added together.
Itotal = I1 + I2 + I3 …. etc
- The total resistance of a parallel circuit will always be less than the value of the smallest resistor.
Resistor Power Rating
- The larger the power rating, the greater the physical size of the resistor to dissipate the heat.
- All resistors have a maximum power rating and if exceeded will result in the resistor overheating and becoming damaged.
- Standard resistor power rating sizes are 1/8 W, 1/4 W, 1/2 W, 1 W, and 2 W.
- Low ohmic value power resistors are generally used for current sensing or power supply applications.
- The power rating of resistors can be calculated using the formula:
- In AC Circuits the voltage and current flowing in a pure resistor are always “in-phase” producing 0o phase shift.
- When used in AC Circuits the AC impedance of a resistor is equal to its DC Resistance.
- The AC circuit impedance for resistors is given the symbol Z.