Robin Barton

Resistor Circuits

Resistors are commonly combined in one of the following configurations: Series, Parallel or Bridge. These circuits are discussed below.

Series Resistors

If the resistors are connected in series, the total resistance is equal to the sum of the individual resistances i.e.:

R_Total = R₁ + R₂ + ... + R_n

Series resistors are often used as voltage dividers to provide a reference voltage of a fixed percentage of the supply voltage. Below is an interactive example.

⚠ The application of these circuits requires careful consideration as the load can affect the effective resistance of the part of the divider that it is connected across - see parallel resistors.

Parallel Resistors

If resistors are connected in parallel, the total resistance is equal to the inverse of the sum of the inverse of the individual resistances i.e.:

⅟R_Total = ⅟R₁ + ⅟R₂ + ... + ⅟R_n

Parallel resistors are often used to obtain non-preffered resistance values i.e. where a value is required that cannot be bought off the shelf or as current dividers (shunts). Parallel resistance calculations also come into play when you introduce a load across part of a voltage divider. Below is an interactive example.

Resistor Bridge

Resistor Bridges are generally used for measurement circuits for example Wheatstone Bridge circuits. Normally one of the resistors would be replaced with a device such as a thermistor or light dependant resistor. They combine series and parallel resistances.

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