currentlimiters

Current limiters are devices or circuits designed to restrict electrical current to a safe maximum in a circuit. They protect components, control power delivery, and mitigate surge currents during startup or fault conditions. Current limiting can be achieved passively through impedance changes or actively via feedback-controlled regulation.

Common approaches

- Passive resistive limiters: a simple series resistor provides a fixed limit but causes a voltage drop and heat, making it inefficient for wide loads.

- Inrush current limiters (NTC thermistors): high resistance when cold to curb startup surges; resistance falls as the device heats, allowing normal operation.

- PTC thermistors: exhibit increasing resistance as temperature rises, providing resetting overcurrent protection and, in some cases, constant protection against sustained faults.

- Fuses: one-time or self-resetting devices that interrupt current when a threshold is exceeded.

- Inductive limiters: series inductors or saturable reactors that slow rapid current changes, useful in power electronics and motor drives.

- Active current limiters: circuits using sense resistors, comparators, and switches (transistors or MOSFETs) to clamp or regulate current precisely over a range of conditions.

- Constant-current sources: powered regulators designed to maintain a set current regardless of load voltage within specified limits; widely used for charging batteries and driving LEDs.

- LED current regulation: dedicated current-limiting devices or drivers ensure stable LED brightness and prevent damage.

Applications and considerations

Current limiters appear in power supplies, battery charging, LED lighting, motor control, telecommunications, and safety devices. Trade-offs include voltage drop, heat dissipation, response time, and protection versus efficiency. Selecting a limiter involves matching the desired protection level, response characteristics, and acceptable voltage or power loss for the application.