Editing Resistor (section)

== Common usage patterns ==

There are several common usage patterns that resistors are commonly configured in.<ref>{{cite book |title=Electronics for Beginners |chapter=Basic Resistor Circuit Patterns |date=2020 |chapter-url=https://link.springer.com/chapter/10.1007/978-1-4842-5979-5_9 |doi=10.1007/978-1-4842-5979-5_9 |last1=Bartlett |first1=Jonathan |pages=129–144 |isbn=978-1-4842-5978-8 |s2cid=226539488 }}</ref>

=== Current limiting ===

Resistors are commonly used to limit the amount of current flowing through a circuit.  Many circuit components (such as LEDs) require the current flowing through them to be limited, but do not themselves limit the amount of current.  Therefore, oftentimes resistors will be added to prevent overcurrent situations.  Additionally, oftentimes circuits do not need the amount of current that would be otherwise flowing through them, so resistors can be added to limit the power consumption of such circuits.

=== Voltage divider ===
{{main|Voltage divider}}

Oftentimes circuits need to provide various reference voltages for other circuits (such as voltage comparators). A fixed voltage can be obtained by taking two resistors in series between two other fixed voltages (such as the source voltage and ground). The terminal between the two resistors will be at a voltage that is between the two voltages, at a linear distance based on the relative resistances of the two resistors. For instance, if a 200&nbsp;ohm resistor and a 400&nbsp;ohm resistor are placed in series between 6&nbsp;V and 0&nbsp;V, the terminal between them will be at 4&nbsp;V.

=== Pull-down and pull-up resistors ===
{{main|Pull-up resistor}}

When a circuit is not connected to power, the voltage of that circuit is not zero but undefined (it can be influenced by previous voltages or the environment).  A pull-up or pull-down resistor provides a voltage for a circuit when it is otherwise disconnected (such as when a button is not pushed down or a transistor is not active).  A pull-up resistor connects the circuit to a high positive voltage (if the circuit requires a high positive default voltage) and a pull-down resistor connects the circuit to a low voltage or ground (if the circuit requires a low default voltage).  The resistor value must be high enough so that, when the circuit is active, the voltage source it is attached to does not over influence the function of the circuit, but low enough so that it "pulls" quickly enough when the circuit is deactivated, and does not significantly alter the voltage from the source value.